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THIS  BOOK  IS  DUE  ON  THE  DATE 
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POSTED  AT  THE  CIRCULATION 
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THE  ANATOMY 


OF  THE 


DOMESTIC  ANIMALS 


SEPTIMUS  SISSON,  S.B.,  V.S. 

PROFESSOR   OF   COMPARATIVE    ANATOMY  IN  THE   OHIO  STATE   UNIVERSITY,    COLUMBUS,   OHIO 

MEMBER   OF   THE    AMERICAN    ASSOCIATION    OF    ANATOMISTS 

FELLOW   OF   THE    AMERICAN    ASSOCIATION    FOR    THE    ADVANCEMENT   OF    SCIENCE 


WITH  725  ILLUSTRATIONS 
MANY  IN  COLORS 


SECOND  EDITION,  ENTIRELY  RESET 


PHILADELPHIA  AND  LONDON 

W.  B.  SAUNDERS  COMPANY 


Copyright,  1910,  by  W.  B.  Saunders  Company 


Reprinted  June,  1911 


Revised,  Entirely  Reset,  Reprinted 

AND  ReCOPYRIGHTED  SEPTEMBER,  1914 


Copyright.  1914,  by  W.  B.  Saunders  Company 


Reprinted  September,  1917 


Reprinted  March,  1921 


Reprinted  October,  1927 


Reprinted  September,  1930 


PRESS  OF 

W.    B.    SAUNDERS   COMPANY 

PHILADELPHIA 


TO 
MY  WIFE 

KATHERINE  OLDHAM  SISSON 

IN  GRATEFUL  RECOGNITION  OF  CONSTANT  INSPIRATION 
AND  ENCOURAGEMENT 


PREFACE 

This  book  supersedes  the  author's  Text-book  of  Veterinary  Anatomy.  A 
comparison  of  the  two  will  show  the  new  title  to  be  justified  by  the  extent  and 
character  of  the  changes  which  have  been  made. 

The  number  of  illustrations  has  been  increased  from  588  to  725.  More  than 
three  hundred  new  and  original  figures  have  been  prepared.  Nearly  all  of  these 
are  reproductions  of  photographs,  most  of  which  were  taken  by  the  author.  The 
preparation  of  the  prints  for  reproduction  has  been  executed  by  Mr.  W.  J.  Norris 
with  unusual  care  and  skill. 

Continued  observations  of  well-hardened  material  and  frozen  sections  have  led 
to  a  considerable  number  of  modifications  of  statement.  It  is  scarcely  necessary 
to  say  that  the  recent  literature,  so  far  as  available,  has  been  utilized. 

Many  changes  in  nomenclature  have  been  made.  Most  of  the  synonyms  have 
been  dropped  or  relegated  to  foot-notes.  Exceedingly  few  new  names  have  been 
introduced.  Nearly  all  eponyms  have  been  eliminated,  on  the  ground  that  they 
are  not  designative  and  are  usually  incorrect  historically.  The  changes  made  in 
this  respect  are  in  conformity  with  the  report  of  the  Committee  on  Revision  of 
Anatomical  Nomenclature  which  was  adopted  by  the  American  Veterinary  Med- 
ical Association  two  years  ago.  Progress  in  the  direction  of  a  simplified  and  uni- 
form nomenclature  is  much  impeded  by  the  archaic  terminology  which  persists  to 
a  large  extent  in  clinical  literature  and  instruction. 

The  author  is  under  special  obligation  to  Professors  EUenberger,  Baum,  and 
Schmaltz,  and  to  their  publishers,  for  permission  to  use  or  to  copy  figures  from 
their  excellent  works.  Their  generosity  in  this  matter  has  been  of  great  value  to 
those  who  are  unable  to  use  the  German  literature.  A  few  illustrations  have  been 
taken  from  other  sources  and  credit  has  been  given  in  each  case. 

For  helpful  suggestions  and  for  assistance  in  the  reading  of  the  proof-sheets 
the  author  is  much  indebted  to  his  colleague,  Dr.  F.  A.  Lambert. 

Great  credit  is  due  the  publishers  for  their  determination  to  spare  neither 
pains  nor  expense  in  attaining  a  high  degree  of  typographical  excellence. 

Septimus  Sisson 
The  Ohio  State  University,  Columbus,  Ohio. 


PREFACE  TO  THE  FIRST  EDITION 

The  lack  of  a  modern  and  well-illustrated  book  on  the  structure  of  the  princi- 
pal domestic  animals  has  been  acutely  felt  for  a  long  time  by  teachers,  students, 
and  practitioners  of  veterinary  medicine.  The  work  here  offered  is  the  expression 
of  a  desire  to  close  this  gap  in  our  literature. 

The  study  of  frozen  sections  and  of  material  which  has  been  hardened  by  intra- 
vascular injection  of  formalin  has  profoundly  modified  our  views  concerning  the 
natural  shape  of  many  of  the  viscera  and  has  rendered  possible  much  greater  pre- 
cision in  topographic  statements.  The  experience  of  the  author  during  the  last 
ten  years,  in  which  almost  all  of  the  material  used  for  dissection  and  for  frozen 
sections  in  the  anatomical  laboratory  of  this  University  has  been  hardened  with 
formalin,  has  demonstrated  that  many  of  the  current  descriptions  of  the  organs  in 
animals  contain  the  same  sort  of  errors  as  those  which  prevailed  in  regard  to  similar 
structures  in  man  previous  to  the  adoption  of  modern  methods  of  preparation. 

While  the  method  of  treatment  of  the  subject  is  essentially  systematic,  topog- 
raphy is  not  by  any  means  neglected  either  in  text  or  illustrations;  it  is  hoped  that 
this  will  render  the  book  of  value  to  the  student  in  his  chnical  courses  and  to 
the  practitioner.  Embryological  and  histological  data  have  been  almost  entirely 
excluded,  since  it  was  desired  to  offer  a  text-book  of  convenient  size  for  the  student 
and  a  work  of  ready  reference  for  the  practitioner.  It  is  believed  that  the  use  of 
black  type  for  the  names  of  important  structures  and  of  small  print  for  certain 
details  or  matter  of  secondary  importance  will  prove  useful  in  this  respect. 

Veterinary  anatomical  nomenclature  is  at  present  quite  chaotic  in  EngUsh- 
speaking  countries.  In  this  work  an  attempt  is  made  to  eliminate  some  terms 
which  do  not  appear  to  the  author  to  fulfil  any  useful  purpose,  and  others  which  are 
clearly  erroneous  or  otherwise  undesirable.  In  many  cases  the  terms  agreed  upon 
by  the  Congresses  at  Baden  and  Stuttgart  are  adopted  either  in  the  original  Latin 
or  in  anglicized  form;  otherwise  these  terms  are  added  in  parenthesis.  The 
author  favors  the  substantial  adoption  of  this  terminology,  but  considered  it 
desirable  to  offer  a  sort  of  transitional  stage  at  present. 

The  original  illustrations  are  chiefly  reproductions  of  photographs,  many  of 
which  were  taken  by  Mr.  F.  H.  Haskett.  The  preparation  of  the  pictures  for 
reproduction  was  carried  out  by  Messrs.  J.  V.  Alteneder  and  W.  J.  Norris.  The 
author  takes  pleasure  in  expressing  his  appreciation  of  the  care  and  skill  exercised 
by  these  gentlemen  in  this  often  difficult  task. 

The  author  is  under  great  obligation  to  Professors  Ellenberger  and  Baum  in 
Dresden,  to  Professor  Schmaltz  in  Berlin,  and  to  their  pubUshers  for  permission  to 
use  or  to  copy  figures  from  their  most  excellent  works.  Their  generosity  in  this 
matter  has  made  it  possible  to  supply  this  text  with  a  larger  number  of  high-class 
illustrations  than  is  to  be  found  in  any  other.  A  few  figures  have  been  taken  from 
other  sources,  and  proper  credit  has  been  given  in  each  case. 

For  checking  over  certain  data  and  for  assistance  in  the  correction  of  the  proofs 
the  author  is  much  indebted  to  his  associate,  Dr.  F.  B.  Hadley. 

The  author  desires  to  express  his  high  appreciation  of  the  determination  and 
constant  effort  of  the  publishers  to  do  all  in  their  power  to  render  the  book  worthy 
of  favorable  reception  by  the  profession  for  whom  it  is  intended. 

Ohio  State  University,  Columbus,  Ohio  Septimus  Sisson. 


CONTENTS 


INTRODUCTION 

OSTEOLOGY  p^ob 

The  Skeleton 20 

Structure  of  Bones 21 

Development  and  Growth  of  Bone 23 

Composition  and  Physical  Properties  of  Bone 24 

Descriptive  Terms 25 

The  Vertebral  Column 25 

The  Ribs  and  Costal  Cartilages 27 

Costal  Cartilages 27 

The  Sterjium 28 

The  Thorax 28 

The  Skull 28 

Bones  of  the  Thoracic  Limb 29 

Bones  of  the  Pelvic  Limb 30 

Skeleton  of  the  Horse 32 

Vertebral  Column 33 

Ribs 45 

Sternum 48 

Bones  of  the  Skull 49 

Cranium 49 

Face 63 

The  Skull  as  a  Whole 73 

The  Cranial  Cavity 81 

The  Nasal  Cavity 82 

The  Paranasal  Sinuses 84 

Bones  of  the  Thoracic  Limb 86 

Bones  of  the  Pelvic  Limb 105 

Skeleton  of  the  Ox 125 

Vertebral  Column 125 

Ribs 130 

Sternum 131 

Bones  of  the  Skull 131 

The  Skull  as  a  Whole 140 

Bones  of  the  Thoracic  Limb 145 

Bones  of  the  Pelvic  Limb 151 

Skeleton  of  the  Sheep 156 

Vertebral  Column 156 

Ribs 156 

Sternum 157 

Skull 157 

Bones  of  the  Thoracic  Limb 160 

Bones  of  the  Pelvic  Limb 160 

Skeleton  of  the  Pig 161 

Vertebral  Column 161 

Ribs 165 

Sternum 166 

Bones  of  the  Skull 166 

The  Skull  as  a  Whole 173 

11 


12  CONTENTS 

PAGE 

Bones  of  the  Thoracic  Limb 176 

Bones  of  the  Pelvic  Limb 180 

Skeleton  of  the  Dog 184 

Vertebral  Column 184 

Ribs 188 

Sternum 188 

Bones  of  the  Skull 188 

The  Skull  as  a  Whole 195 

Bones  of  the  Thoracic  Limb 197 

Bones  of  the  Pelvic  Limb 202 

ARTHROLOGY 
Synarthroses 207 

DiARTHROSES 208 

Amphiarthroses 210 

Articulations  of  the  Horse 211 

Joints  and  Ligaments  of  the  Vertebrae 211 

Atlanto-occipital  Articulation 214 

Costo-vertebral  Articulations 215 

Costo-chondral  Articulations 216 

Chondro-sternal  Ailiculations 216 

Sternal  Joints  and  Ligaments 217 

Articulations  of  the  Skull 217 

Articulations  of  the  Thoracic  Limb 218 

Articulations  of  the  Pelvic  Limb 229 

Articulations  of  the  Ox,  Pig,  and  Dog 244 

MYOLOGY 

The  Muscles  and  Accessory  Structures 252 

Fascl«  and  Muscles  of  the  Horse 254 

Fasciae  and  Muscles  of  the  Head 255 

Fascia?  and  Muscles  of  the  Neck 266 

Fascite  and  Muscles  of  the  Back  and  Loins 276 

Fasciae  and  Muscles  of  the  Tail 279 

Muscles  of  the  Thorax 281 

Abdominal  Fasciae  and  Muscles 287 

Muscles  of  the  Thoracic  Limb 293 

Fasciae  and  Muscles  of  the  Pelvic  Limb 317 

Muscles  of  the  Ox 343 

Muscles  of  the  Pig 359 

Muscles  of  the  Dog 368 

SPLANCHNOLOGY 

Digestive  System  of  the  Horse 385 

The  Mouth 385 

The  Tongue 390 

The  Teeth 394 

The  SaHvary  Glands 404 

The  Pharynx 405 

The  CEsophagus 409 

The  Abdominal  Cavity 410 

The  Peritoneum 411 

The  Pelvic  Cavity 412 

The  Stomach 415 

The  Small  Intestine 419 

The  Large  Intestine 422 

The  Pancreas 432 

The  Liver 434 


CONTENTS  13 

PAGE 

The  Spleen 439 

The  Peritoneum 441 

Digestive  System  of  the  Ox 444 

Digestive  System  of  the  Sheep 470 

Digestive  System  of  the  Pig 477 

Digestive  System  of  the  Dog 491 

THE   RESPIRATORY   SYSTEM 

Respiratory  System  of  the  Horse 508 

The  Nasal  Cavity 508 

The  Larynx 514 

The  Trachea 523 

The  Bronchi 525 

The  Thoracic  Cavity 525 

The  Pleuraj 526 

The  Lungs 530 

The  Thyroid  Gland  of  the  IIorse 535 

The  Thymus  of  the  Horse 536 

Respiratory  System  of  the  Ox 537 

Respiratory  System  of  the  Pig 545 

Respiratory  System  of  the  Dog 548 

THE  UROGENITAL   SYSTEM 

Urinary  Organs  of  the  Horse 554 

The  Kidneys 554 

The  Ureters 561 

The  Urinary  Bladder 561 

The  Adrenal  Bodies 563 

LTrinary  Organs  of  the  Ox 564 

Urinary  Organs  of  the  Pig 567 

Urinary  Organs  of  the  Dog 569 

THE   MALE   GENITAL  ORGANS 

Genital  Organs  of  the  Stallion 571 

The  Testicles 571 

The  Scrotum 574 

The  Ductus  Deferens 575 

The  Spermatic  Cord 575 

The  Tunica  VaginaUs 576 

Descent  of  the  Testicles 577 

The  Vesiculse  Seminales 578 

The  Prostate 578 

The  Uterus  MascuUnus 579 

The  Bulbo-urethral  Glands 579 

The  Penis 580 

The  Prepuce 582 

Genital  Organs  of  the  Bull 586 

Genital  Organs  of  the  Boar 591 

Genital  Organs  of  the  Dog 593 

THE  FEMALE  GENITAL  ORGANS 

Genital  Organs  of  the  Mare 596 

The  Ovaries 596 

The  Uterine  or  Fallopian  Tubes 599 

The  Uterus 599 

The  Vagina 602 


14  CONTENTS 

PAGB 

The  Vulva 603 

The  Urethra 604 

The  Mammary  Glands 604 

Genital  Organs  of  the  Cow 605 

Genital  Organs  of  the  Ewe 609 

Genital  Organs  of  the  Sow 610 

Genital  Organs  of  the  Bitch 612 

ANGIOLOGY 

General  Considerations 614 

The  Organs  of  Circulation 614 

Blood-vasct'lar  System  of  the  Horse 617 

The  Pericardium 617 

The  Heart 617 

The  Pulmonary  Artery 629 

The  Systemic  Ai-teries 629 

The  Coronary  Arteries 630 

Common  Brachiocephalic  Trunk 631 

Arteries  of  the  Thoracic  Limb 650 

Branches  of  the  Thoracic  Aorta 660 

Branches  of  the  Abdominal  Aorta 661 

Arteries  of  the  Pelvic  Limb 673 

The  Veins 681 

The  Pulmonary  Veins 681 

Cardiac  Veins 681 

The  Anterior  Vena  Cava  and  its  Tributaries 682 

The  Posterior  Vena  Cava  and  its  Tributaries 692 

The  Lymphatic  System 697 

The  Thoracic  Duct 697 

The  Right  Lymphatic  Duct 698 

The  Lymph  Glands  and  Vessels  of  the  Head  and  Neck 698 

The  Lymph  Glands  and  Vessels  of  the  Thorax 700 

The  Lymph  Glands  and  Vessels  of  the  Abdomen  and  Pelvis 701 

The  Lymph  Glands  and  Vessels  of  the  Thoracic  Limb 703 

The  Lymph  Glands  and  Vessels  of  the  Pelvic  Limb 703 

The  P'cetal  Circulation 704 

Blood-vascular  System  op  the  Ox 705 

The  Pericardium  and  Heart 705 

The  Arteries 706 

The  Veins 719 

Lymphatic  System  of  the  Ox  and  Sheep 722 

Circulatory  System  of  the  Pig 734 

The  Pericardium  and  Heart 734 

The  Arteries 736 

The  Veins 740 

Lymphatic  System 740 

Circulatory  System  of  the  Dog 742 

The  Pericardium  and  Heart 742 

The  Arteries 744 

The  Veins 754 

Lymphatic  System 756 

NEUROLOGY.— THE   NERVOUS   SYSTEM 

General  Considerations 760 

Nervous  System  of  the  Horse 764 

The  Spinal  Cord 764 

The  Brain 768 


CONTENTS  15 

PAGE 

The  Cranial  Nerves 793 

The  Spinal  Nerves 810 

Sympathetic  Nervous  System  of  the  Horse 829 

Nervous  System  of  the  Ox 834 

Nervous  System  of  the  Pig 843 

Nervous  System  of  the  Dog 847 

^STHESIOLOGY 

The  Sense  Organs  and  Common  Integument  of  the  Horse 857 

The  Eye 857 

The  Ear 870 

The  Common  Integument 884 

The  Ergot  and  Chestnut 895 

The  OKactory  and  Gustatory  Apparatus 895 

The  Sense  Organs  and  Common  Integument  of  the  Ox 896 

The  Sense  Organs  and  Common  Integument  of  the  Pig 900 

The  Sense  Organs  and  Common  Integument  of  the  Dog 902 


Index 907 


THE  ANATOMY  OF  THE  DOMESTIC  ANIMALS 


INTRODUCTION 

Anatomy  is  the  branch  of  biological  science  which  deals  with  the  form  and 
structure  of  organisms,  both  animal  and  vegetal.  It  is  therefore  in  close  correlation 
with  physiology,  which  treats  of  the  functions  of  the  body. 

Etymologically  the  word  "anatomy"  signifies  the  cutting  apart  or  disassociat- 
ing of  parts  of  the  body.  In  the  earlier  phases  of  its  development  anatomy  was 
necessarily  a  purely  descriptive  science,  based  on  such  observations  as  were  possible 
with  the  unaided  eye  and  simple  dissecting  instruments — the  scalpel,  forceps,  and 
the  like.  At  this  time,  therefore,  the  term  adequately  expressed  the  nature  of  the 
subject.  But  as  the  scope  of  the  science  extended  and  the  body  of  anatomical 
knowledge  grew,  subdivisions  became  necessary  and  new  terms  were  introduced  to 
designate  special  fields  and  methods  of  work.  With  the  introduction  of  the  mi- 
croscope and  its  accessories  it  became  possible  to  study  the  finer  details  of  structure 
and  minute  organisms  hitherto  unknown,  and  this  field  of  inquiry  rapidly  developed 
into  the  science  of  microscopic  anatomy  or  histology  as  conventionally  distinguished 
from  macroscopic  or  gross  anatomy.  In  the  same  way  the  study  of  the  changes 
which  organisms  undergo  during  their  development  soon  attained  sufficient  im- 
portance to  be  regarded  on  practical  grounds  as  a  separate  branch  known  as 
embryology.^ 

Comparative  anatomy  is  the  description  and  comparison  of  the  structure  of 
animals,  and  forms  the  basis  for  their  classification.  By  this  means — including 
extinct  forms  in  the  scope  of  inquiry — it  has  been  possible  to  show  the  genetic 
relationship  of  various  groups  of  animals  and  to  elucidate  the  significance  of  many 
facts  of  structure  which  are  otherwise  quite  obscure.  The  deductions  concerning 
the  general  laws  of  form  and  structure  derived  from  comparative  anatomical 
studies  constitute  the  science  of  morphology  or  philosophical  anatomy.  The 
morphologist,  however,  deals  only  with  such  anatomical  data  as  are  necessary  to 
form  a  basis  for  his  generalizations.  The  anatomical  knowledge  required  in  the 
practice  of  medicine  and  surgery  is  evidently  of  a  different  character  and  must 
include  many  details  which  are  of  no  particular  interest  to  the  morphologist. 

Special  anatomy  is  the  description  of  the  structure  of  a  single  type  or  species, 
e.  g.,  anthropotomy,  hippotomy. 

Veterinary  anatomy  is  the  branch  which  deals  with  the  form  and  structure  of 
the  principal  domesticated  animals.  It  is  usually  pursued  with  regard  to  pro- 
fessional requirements,  and  is  therefore  largely  descriptive  in  character.  As  a 
matter  of  convenience,  the  horse  is  generally  selected  as  the  type  to  be  studied  in 
detail  and  to  form  a  basis  for  comparison  of  the  more  essential  differential  characters 
in  the  other  animals. 

Two  chief  methods  of  study  are  employed — the  systematic  and  the  topo- 
graphic.    In  the  former  the  body  is  regarded  as  consisting  of  systems  of  organs  or 

1  Tliis  term  is  usually  limited  in  its  application  to  the  earlier  phases  of  development  during 
which  the  tissues  and  organs  are  formed.     The  term   ontogeny  is  used  to  designate  the  entire 
development  of  the  individual.     The  ancestral  history  or  phylogeny  of  the  species  is  constituted 
by  the  evolutionary  changes  which  it  has  undergone  as  disclosed  by  the  geological  record. 
2  17 


X8  INTRODUCTION 

apparatus  which  are  similar  in  origin  and  structure  and  are  associated  in  the  per- 
formance of  certain  functions.     The  divisions  of  systematic  anatomy  are : 

1.  Osteology,  the  description  of  the  Skeleton. 

2.  Arthrology,  the  description  of  the  Joints. 

3.  Myology,  the  description  of  the  Muscles  and  accessory  structures. 

4.  Splanchnology,  the  description  of  the  Viscera.  This  includes  the  following 
subdivisions : 

(1)  Digestive  System 

(2)  Respiratory  System 

(3)  Urogenital  System 

(a)  Urinary  Organs 
(h)  Genital  Organs 

5.  Angiology,  the  description  of  the  Organs  of  Circulation 

6.  Neurology,  the  description  of  the  Nervous  System 

7.  ^sthesiology,  the  description  of  the  Sense  Organs  and  Common  Integu- 

ment 

The  term  topographic  anatomy  designates  the  methods  by  which  the  relative 
positions  of  the  various  parts  of  the  body  are  accurately  determined.  It  presup- 
poses a  fair  working  knowledge  of  systematic  anatomy. 

Descriptive  Terms. — In  order  to  indicate  precisely  the  position  and  direction 
of  parts  of  the  body,  certain  descriptive  terms  are  employed,  and  must  be  under- 
stood at  the  outset.  In  the  explanation  of  these  terms  it  is  assumed  here  that 
they  apply  to  a  quadruped  such  as  the  horse  in  the  ordinary  standing  position. 
The  surface  directed  toward  the  plane  of  support  (the  ground)  is  termed  ventral 
(or  inferior),  and  the  opposite  surface  is  dorsal  (or  superior) ;  the  relations  of  parts  in 
this  direction  are  named  accordingly.  The  longitudinal  median  plane  divides  the 
body  into  similar  halves.  A  structure  or  surface  which  is  nearer  than  another  to  the 
meclian  plane  is  medial  (or  internal)  to  it,  and  an  object  or  surface  which  is  further 
than  another  from  the  median  plane  is  lateral  (or  external)  to  it.  Planes  parallel 
to  the  median  plane  are  sagittal.  Transverse  or  segmental  planes  cut  the  long  axis 
of  the  body  perpendicular  to  the  median  plane,  or  an  organ  or  limb  at  right  angles 
to  its  long  axis.  A  frontal  plane  is  perpendicular  to  the  median  and  transverse 
planes.  The  term  is  also  used  with  reference  to  parts  of  the  limbs  or  various  organs 
in  a  similar  sense.  The  head  end  of  the  body  is  termed  anterior  or  cranial;  and  the 
tail  end  posterior  or  caudal ;  relations  of  structures  with  regard  to  the  longitudinal 
axis  of  the  body  are  designated  accordingly.  With  respect  to  parts  of  the  head, 
the  corresponding  terms  are  oral  and  aboral.  Certain  terms  are  used  in  a  special 
sense  as  applied  to  the  limbs.  Proximal  and  distal  express  relative  distances  of 
parts  from  the  long  axis  of  the  body.  The  anterior  face  of  the  thoracic  limb  from 
the  elbow  downward  is  termed  dorsal,  and  the  opposite  face  volar.  In  the  corre- 
sponding part  of  the  pelvic  limb  the  terms  are  dorsal  and  plantar  respectively.  In 
the  same  regions  radial  and  ulnar  (thoracic  limb),  tibial  and  fibular  (pelvic  limb), 
may  be  used  to  designate  that  side  of  the  extremity  on  which  the  corresponding 
bone  is  situated;  they  are  therefore  equivalent  respectively  to  medial  and  lateral 
in  the  animals  with  which  we  are  concerned.  The  terras  superficial  (superficialis) 
and  deep  (profundus)  are  useful  to  indicate  relative  distances  of  i);irts  from  the 
surface  of  the  body. 

It  is  evidently  advantageous  to  employ  terms  which  are  as  far  as  possible  independent  of 
the  position  of  the  body  in  space  and  capable  of  general  application,  e.  g.,  dorsal,  ventral,  proximal, 
etc.  It  is  also  desirable  that  the  terms  internal  and  external  be  reserved  to  indicate  relations  of 
depth  in  cavities  or  organs,  and  medial  and  lateral  to  designate  relations  to  the  median  plane. 
Such  terms  are  coming  into  more  extensive  use  in  human  and  veterinary  anatomy,  but  the  older 
nomenclature  is  very  firmly  established  and  cannot  well  be  discarded  at  once  and  entirely.  To 
facilitate  the  transition,  a  table  of  the  older  and  more  recent  terms  is  given  below;  the  recent 
terms  are  in  the  first  column  and  the  older  equivalents  in  the  second. 


INTRODUCTION 

A.  Relating  to  Head,  Neck,  and  Trunk: 

Dorsalis Superior 

Ventralis Inferior 

MediaUs I?tf™^\ 

LateraUs External 

Cranialis  1  Anterior 

Oralis        / 

Caudalis    1  Posterior 

Aboralis    J 

B.  Relating  to  Limbs: 

Proximalis Superior 

Distalis Mf"?^ 

DorsaUs Anterior 

Volaris       \  ,  .  Posterior 

Plantaris   f 

Radialis    ]  Internal 

Tibialis      f    

Ulnaris      \  External 

Fibularis   f 


19 


OSTEOLOGY 

THE  SKELETON 
The  term  skeleton  is  applied  to  the  framework  of  hard  structures  which  sup- 
ports and  protects  the  soft  tissues  of  animals.     In  the  descriptive  anatomy  of  the 
higher  animals  it  is  usually  restricted  to  the  bones  and  cartilages,  although  the 
ligaments  Avhich  bind  these  together  might  well  be  included. 

In  zoology  the  term  is  used  in  a  much  more  comprehensive  sense,  and  includes  all  the  harder 
supporting  and  protecting  structures.  When  the  latter  are  situated  externally,  they  form  an 
exoskeleton,  derived  from  the  ectoderm.  Examples  of  this  are  the  shells  and  cliitinous  coverings 
of  many  invertebrates,  the  scales  of  fishes,  the  shields  of  turtles,  and  the  feathers,  hair,  and  hoofs 
of  the  higher  vertebrates.  The  endoskeleton  (with  which  we  have  to  deal  at  present)  is  embedded 
in  the  soft  tissues.  It  is  derived  from  the  mesoderm,  but  includes  the  notochord  or  primitive 
axial  skeleton,  which  is  of  entodermal  origin. 

The  skeleton  may  be  divided  primarily  into  three  parts:  (1)  axial;  (2)  appen- 
dicular; (3)  splanchnic. 

The  axial  skeleton  comprises  the  vertebral  column,  ribs,  sternum,  and  skull. 

The  appendicular  skeleton  includes  the  bones  of  the  limbs. 

The  splanchnic  or  visceral  skeleton  consists  of  certain  bones  developed  in  the 
substance  of  some  of  the  viscera  or  soft  organs,  e.  g.,  the  os  penis  of  the  dog  and  the 
OS  cordis  of  the  ox. 

The  number  of  the  bones  of  the  skeleton  of  an  animal  varies  with  age,  owing 
to  the  fusion  during  growth  of  skeletal  elements  which  are  separate  in  the  fostus 
or  the  young  subject.  Even  in  adults  of  the  same  species  numerical  variations 
occur,  e.  g.,  the  tarsus  of  the  horse  may  consist  of  six  or  seven  bones,  and  the  carpus 
of  seven  or  eight;  in  all  the  domestic  mammals  the  number  of  coccygeal  vertebrae 
varies  considerably. 

The  bones  are  commonly  divided  into  four  classes  according  to  their  shape 
and  function.^ 

(1)  Long  bones  (Ossa  longa)  are  typically  of  elongated  cylindrical  form  with 
enlarged  extremities.  They  occur  in  the  limbs,  where  they  act  as  supporting 
columns  and  as  levers.  The  cylindrical  part,  termed  the  shaft  or  body  (Corpus), 
is  tubular,  and  incloses  the  medullary  cavity,  which  contains  the  medulla  or  marrow. 

(2)  Flat  bones  (Ossa  plana)  are  expanded  in  two  directions.  They  furnish 
sufficient  area  for  the  attachment  of  muscles  and  afford  protection  to  the  organs 
which  they  cover. 

(3)  Short  bones  (Ossa  brevia),  such  as  those  of  the  carpus  and  tarsus,  present 
somewhat  similar  dimensions  in  length,  breadth,  and  thickness.  Their  chief  func- 
tion appears  to  be  that  of  diffusing  concussion.  Sesamoid  bones,  which  are  de- 
veloped in  the  capsules  of  some  joints  or  in  tendons,  may  be  included  in  this  group. 
They  diminish  friction  or  change  the  direction  of  tendons. 

(4)  Irregular  bones  (Ossa  irregularia) .  This  group  would  include  bones  of 
irregular  shape,  such  as  the  vertebrae  and  the  bones  of  the  cranial  base;  they  are 
median  and  unpaired.  Their  functions  are  various  and  not  so  clearly  specialized 
as  those  of  the  preceding  classes. 

^  This  classification  is  not  entirely  satisfactory;  some  bones,  e.  g.,  the  ribs,  are  not  clearly 
provided  for,  and  others  might  be  variously  placed. 

20 


STRUCTURE    OF   BONES 


21 


STRUCTURE  OF  BONES  i 
Bones  consist  chiefly  of  bone  tissue,  but  considered  as  organs  they  present 
also  an  enveloping  membrane,  termed  the  periosteum,  the  marrow,  vessels,  and 
nerves. 

The  architecture  of  bone  can  be  studied  best  by  means  of  longitudinal  and 
transverse  sections  of  specimens  which  have  been  macerated  so  as  to  remove  most 
of  the  organic  matter.  These  show  that  the  bone 
consists  of  an  external  shell  of  dense  compact  sub- 
stance, within  which  is  the  more  loosely  arranged 
spongy  substance.  In  tyjDical  long  bones  the  shaft 
is  hollowed  to  form  the  medullary  cavity  (Cavum 
medullare) . 

The  compact  substance  (Substantia  compacta) 
differs  greatly  in  thickness  in  various  situations,  in 
conformity  with  the  stresses  and  strains  to  which 
the  bone  is  subjected.  In  the  long  bones  it  is 
thickest  in  or  near  the  middle  part  of  the  shaft  and 
thins  out  toward  the  extremities.  On  the  latter  the 
layer  is  very  thin,  and  is  especially  dense  and  smooth 
on  joint  surfaces. 

The  spongy  substance  (Substantia  spongiosa) 
consists  of  delicate  bony  plates  and  spicules  which 
run  in  various  directions  and  intercross.  These  are 
definitely  arranged  with  regard  to  mechanical  re- 
quirements, so  that  systems  of  pressure  and  tension 
plates  can  be  recognized,  in  conformity  with  the 
lines  of  pressure  and  the  pull  of  tendons  and  liga- 
ments respectively.  The  intervals  between  the 
plates  are  occupied  by  marrow,  and  are  termed 
marrow  spaces  (Cellulse  meduUares).  The  spongy 
substance  forms  the  bulk  of  short  bones  and  of  the 
extremities  of  long  bones;  in  the  latter  it  is  not  con- 
fined to  the  ends,  but  extends  a  variable  distance 
along  the  shaft  also.  Some  bones  contain  air-spaces 
within  the  compact  substance  instead  of  spongy 
bone  and  marrow,  and  hence  are  called  pneimiatic 
bones  (Ossa  pneumatica) .  These  cavities  are  termed 
sinuses,  and  are  lined  with  mucous  membrane; 
they  communicate  indirectly  with  the  external  air. 
In  certain  situations  the  two  compact  layers  of  flat 
bones  are  not  separated  by  spongy  bone,  but  fuse 
with  each  other;  in  some  cases  of  this  kind  the  bone 
is  so  thin  as  to  be  translucent,  or  may  undergo 
absorption,  producing  an  actual  deficiency. 

The  flat  bones  of  the  cranial  vault  and  sides 
are  composed  of  an  outer  layer  of  orchnary  compact 
substance,  the  lamina   externa,   an   inner   layer   of 
very  dense  bone,  the  lamina  interna  or  tabula  vitrea,  and  between  these  a  variable 
amount  of  spongy  bone,  here  termed  diploe. 

The  periostetun  is  the  membrane  which  invests  the  outer  surface  of  bone, 
except  where  it  is  covered  with  cartilage.     It  consists  of  an  outer  protective  fibrous 

1  Only  the  gross  structure  is  discussed  here.     For  the  microscopic  structure  reference  is  to 
be  made  to  histological  works. 


Fig.  1. — Sagittal  Section  op  Large 
Metatarsal  Bone  of  Horse 
(Right). 

S.c,  Compact  substance;  S.s., 
spongy  substance;  Cm.,  medullary 
cavity;  F.n.,  nutrient  foramen.  Note 
the  greater  thickness  of  the  compact 
substance  of  the  anterior  part  of  the 
shaft. 


22 


OSTEOLOGY 


layer,  and  an  inner  cellular  osteogenic  layer.  During  active  gro^vth  the  osteogenic 
layer  is  well  developed,  but  later  it  becomes  much  reduced.  The  fibrous  layer 
varies  much  in  thickness,  being  in  general  thickest  in  exposed  situations.  The 
adhesion  of  the  periosteum  to  the  bone  also  differs  greatly  in  various  places;  it 
is  usually  very  thin  and  easily  detached  where  it  is  thickly  covered  with  muscular 
tissue  which  has  little  or  no  attachment.  The  degree  of  vascularity  conforms  to 
the  activit}^  of  the  periosteum. 

The  endosteum  is  a  thin  fibrous  membrane  which  lines  the  medullary  cavity 
and  the  larger  Haversian  canals. 

The  marrow  (Medulla  ossium)  occupies  the  interstices  of  the  spongj^  bone  and 
the  medullary  cavity  of  the  long  bones.  There  are  two  varieties  in  the  adult — 
red  and  yellow.  In  the  young  subject  there  is  only  red  marrow  (Medulla  ossium 
mbra),  but  later  this  is  replaced  in  the  medullary  cavity  by  yellow  marrow  (Medulla 
ossium  flava).  The  red  marrow  contains  several  types  of  characteristic  cells  and 
is  a  blood-forming  suV)stance,  Avhile  the  yellow  is  practically  ordinary  adipose  tissue.^ 

Vessels  and  Nerves. — It  is  customary  to  recognize  two  sets  of  arteries — the 
periosteal  and  the  medullary.     The  former  ramify  in  the  periosteum  and  give  off 


Fig.  2. — Cross-section  of  Proximal  Third  of  Shaft 
OF  Right  Humerus  of  Horse. 


Fig. 


Cross-section  of  Distal  Third  of  Shaft  op 
Left  Humerus  of  Horse. 
Section  passes  through  nutrient  foramen  and  canal. 


innumerable  small  branches  which  enter  minute  openings  (Volkmann's  canals)  on 
the  surface  and  reach  the  Haversian  canals  of  the  compact  substance.  Other 
branches  enter  the  extremities  of  the  long  l^ones  and  supply  the  spongy  bone  and 
marrow  in  them.  In  the  case  of  the  larger  bones — and  especially  the  long  bones — 
the  large  nutrient  or  medullary  artery  (Arteria  nutricia)  enters  at  the  so-called  nu- 
trient foramen  (Foramen  nutricium),  passes  in  a  canal  (Canalis  nutricius)  through 
the  compact  substance,  and  ramifies  in  the  marrow;  its  branches  anastomose  -with 
the  central  branches  of  the  periosteal  set.  The  larger  veins  of  the  spongy  bone  do 
not,  as  a  rule,  accompany  the  arteries,  but  emerge  chiefly  near  the  articular  surfaces. 
Within  the  bone  thej^  are  destitute  of  valves.  The  l5anph-vessels  exist  as  peri- 
vascular channels  in  the  periosteum  and  the  Haversian  canals  of  the  compact  sub- 
stance. They  also  form  a  fine  subperiosteal  network,  froxn  which  the  larger  vessels 
proceed,  usually  in  company  with  veins.  Lymph-spaces  exist  at  the  periphery  of 
the  marrow. 

The  nerves  appear  to  be  distributed  chiefly  to  the  blood-vessels.     Special  nerve- 

1  Since  yellow  marrow  is  formed  by  regressive  changes  in  red  marrow,  including  fatty  infiltra- 
tion and  degeneration  of  the  characteristic  cells,  we  find  transitional  forms  or  stages  in  the  process. 
In  aged  or  badly  nourished  subjects  the  marrow  may  undergo  gelatinous  degeneration,  resulting 
in  the  formation  of  gelatinous  marrow. 


DEVELOPMENT  AND  GROWTH  OF  BONE 


23 


endings  (Vater-Pacini  corpuscles)  in  the  periosteum  are  to  be  regarded  as  sensory, 
and  probably  are  concerned  in  mediating  the  muscle  sense  (kinesthesia) 


DEVELOPMENT  AND  GROWTH  OF  BONEi 

The  primitive  embryonal  skeleton  consists  of  cartilage  and  fibrous  tissue,  in 
which  the  bones  develop.  The  process  is  termed  ossification  or  osteogenesis,  and 
is  effected  essentially  by  bone-producing  cells,  called  osteoblasts.  It  is  customary, 
therefore,  to  designate  as  membrane  bones  those  which  are  developed  in  fibrous 
tissue,  and  as  cartilage  bones  those  which  are  preformed  in  cartilage.  The  princi- 
pal membrane  bones  are  those  of  the  roof  and  sides  of  the  cranium  and  most  of  the 
bones  of  the  face.  The  cartilage  bones  comprise, 
therefore,  most  of  the  skeleton.  Correspondingly 
we  distinguish  intramembranous  and  endochondral 
ossification. 

In  intramembranous  ossification  the  process 
begins  at  a  definite  center  of  ossification  (Punctum 
ossificationis) ,  where  the  osteoblasts  surround  them- 
selves with  a  deposit  of  bone.  The  process  extends 
from  this  center  to  the  periphery  of  the  future  bone, 
thus  producing  a  network  of  bony  trabeculae.  The 
trabeculae  rapidly  thicken  and  coalesce,  forming  a 
bony  plate  which  is  separated  from  the  adjacent 
bones  by  persistent  fibrous  tissue.  The  superficial 
part  of  the  original  tissue  becomes  periosteum,  and 
on  the  deep  face  of  this  successive  layers  of  perios- 
teal bone  are  formed  by  osteoblasts  until  the  bone 
attains  its  definitive  thickness.  Increase  in  circum- 
ference takes  place  by  ossification  of  the  surround- 
ing fibrous  tissue,  which  continues  to  grow  until 
the  bone  has  reached  its  definitive  size. 

In  endochondral  ossification  the  process  is 
fundamentally  the  same,  but  not  quite  so  simple. 
Osteoblasts  emigrate  from  the  deep  face  of  the  peri- 
chondrium or  primitive  periosteum  into  the  cartilage 
and  cause  calcification  of  the  matrix  or  ground- 
substance  of  the  latter.  Vessels  extend  into  the  cal- 
cifying area,  the  cartilage  cells  shrink  and  disappear, 
forming  primary  marrow  cavities  which  are  occupied 
by  processes  of  the  osteogenic  tissue.  There  is  thus 
formed  a  sort  of  scaffolding  of  calcareous  trabeculae 
on  which  the  bone  is  constructed  by  the  osteoblasts. 
At  the  same  time  perichondral  bone  is  formed  by 

the  osteoblasts  of  the  primitive  periosteum.  The  calcified  cartilage  is  broken  down 
and  absorbed  through  the  agency  of  large  cells  called  osteoclasts,  and  is  replaced 
by  bone  deposited  by  the  osteoblasts.  The  osteoclasts  also  cause  absorption  of  the 
primitive  bone,  producing  the  marrow  cavities;  thus  in  the  case  of  the  long  bones 
the  primitive  central  spongy  bone  is  largely  absorbed  to  form  the  medullary  cavity 
of  the  shaft,  and  persists  chiefly  in  the  extremities.  Destruction  of  the  central 
part  and  formation  of  subperiosteal  bone  continue  until  the  shaft  of  the  bone  has 
completed  its  growth. 

A  typical  long  bone  is  developed  from  three  primary  centers  of  ossification, 

1  Only  a  brief  general  statement  of  osteogenesis  can  be  made  here;   details  must  be  sought 
in  embryological  literature. 


Fig.  4. — Left  Femur  of  Young  Piq, 
Lateral    View,    to     Show    Di- 
VI8IOX    OF   A    Long    Bone    into 
Shaft  (s)  and  Extremities. 
Proximal     extremity     consists    of 
two   parts,    head    (h)    and    trochanter 
major     (t.m.),     which     have     separate 
centers  of  ossification.     Distal  extrem- 
ity consists  of  trochlea  (0  and  condyles 
(c);     e.L,    epiphyseal    cartilages;      s.f., 
supracondyloid  fossa. 


24  OSTEOLOGY 

one,  which  appears  first,  for  the  diaphysis  or  shaft  and  one  for  each  epiphysis  oi 
extremity.  Many  bones  have  secondary  centers  from  which  processes  or  apophyses 
develop. 

The  foregoing  outhne  accounts  for  the  gro^Hh  of  bones  except  in  regard  to 
length.  Increase  in  length  may  be  explained  briefly  as  follows :  Provision  for  con- 
tinued ossification  at  either  end  of  the  diaphysis  is  made  by  a  layer  of  actively 
groAving  cartilage — the  epiphyseal  cartilage — which  intervenes  between  the  diaph- 
ysis and  the  epiphysis.  It  is  evident  that  so  long  as  this  cartilage  persists  and 
grows,  new  bone  may  continue  to  be  formed  at  its  expense,  and  increase  of  length 
is  possible.  When  the  epiphyseal  cartilage  ceases  to  grow,  it  undergoes  ossification, 
the  bone  is  consolidated,  and  no  further  increase  in  length  is  possible.  This  fusion 
takes  place  at  fairly  definite  periods  in  the  various  bones,  and  it  is  of  value  to  know 
the  usual  times  at  which  it  occurs  in  the  larger  bones  of  the  limbs  at  least.  In  the 
case  of  membrane  bones,  increase  in  circumference  is  provided  for  by  the  ossification 
and  new  formation  of  the  surrounding  fibrous  tissue. 

After  the  bones  have  reached  their  full  size,  the  periosteum  becomes  relatively  reduced  and 
inactive  so  far  as  its  osteogenic  layer  is  concerned;  the  bone-forming  function  may  be  stimulated 
by  various  causes,  as  is  well  seen  in  the  heaUng  of  fractures  and  the  occurrence  of  bony  enlarge- 
ments. 

Profound  changes  occur  in  the  skeleton  after  birth,  and  during  the  period  of  growth  the  bones 
are  much  more  plastic  than  might  be  supposed.  In  the  new-])orn  foal,  for  example,  it  is  evident 
that  the  rnetacarpal  and  metatarsal  bones  are  relatively  long  and  the  scapula  and  humerus  short; 
also  that  in  general  the  shafts  of  the  long  bones  are  slender  in  comparison  with  the  extremities. 
The  various  prominences  are  much  less  pronounced  than  in  the  adult,  and  most  of  the  minor 
surface  markings  are  absent,  so  that  the  bones  have  a  relatively  smooth  appearance.  The  period 
of  gro^v-th  may  be  regarded  as  terminating  with  the  union  of  the  extremities  and  shafts  of  the  long 
bones  and  the  fusion  of  the  parts  of  other  bones.  During  adult  life  the  skeletal  changes  proceed 
more  slowly;  they  comprise  accentuation  of  the  larger  prominences  and  depressions  and  the  ap- 
pearance of  smaller  ones.  These  secondary  markings  are  chiefly  correlated  with  the  attachments 
of  muscles,  tendons,  and  hgaments,  or  are  produced  by  pressure  exerted  by  various  structures  on 
the  bones.  Later  in  hfe  ossification  invades  more  or  less  extensively  the  cartilages  and  the  at- 
tachments of  tendons  and  ligaments.  Senile  changes  in  the  bones,  consisting  of  decrease  of  the 
organic  matter  and  rarefaction  of  the  bone  tissue,  render  them  brittle  and  liable  to  fracture. 


CHEMICAL  COMPOSITION  OF  BONE 
Dried  bone  consists  of  organic  and  inorganic  matter  in  the  ratio  of  1  :  2  ap- 
proximately. The  animal  matter  gives  toughness  and  elasticity,  the  mineral 
matter  hardness,  to  the  bone  tissue.  Removal  of  the  organic  matter  by  heat  does 
not  change  the  general  form  of  a  bone,  but  reduces  the  weight  by  about  one-third, 
and  makes  it  very  fragile.  Conversely,  decalcification,  while  not  affecting  the  form 
and  size  of  the  bone,  renders  it  soft  and  pliable.  The  organic  matter  (ossein)  when 
boiled  yields  gelatin.  The  following  table  represents  the  composition  in  100  parts 
of  ox  bone  of  average  quality : 

Gelatin 33.30 

Phosphate  of  Ume 57.35 

Carbonate  of  lime 3.85 

Phosphate  of  magnesia 2.05 

Carbonate  and  chlorid  of  sodium 3.45 

100.00 
PHYSICAL  PROPERTIES  OF  BONE 
Fresh  dead  bone  has  a  yellowish-white  color;  when  macerated  or  boiled  and 
bleached,  it  is  white.  The  specific  gravity  of  fresh  compact  bone  is  a  little  over 
1.93.  It  is  very  hard  and  resistant  to  pressure;  a  5-millimeter  cube  of  compact 
bone  of  the  ox  will  resist  pressure  up  to  852  pounds,  if  the  pressure  be  applied  in 
the  line  of  the  lamellae  (Rauber).  Its  tensile  strength  is  estimated  to  be  nearly 
twice  that  of  oak. 


THE    VERTEBRAL    COLUMN  25 


DESCRIPTIVE  TERMS 

The  surfaces  of  the  bones  present  a  great  variety  of  eminences  and  depressions, 
as  well  as  perforations.  The  prominences  and  cavities  may  be  articular,  or  non- 
articular,  furnishing  attachment  to  muscles,  tendons,  ligaments,  or  fascia.  A 
number  of  descriptive  terms  are  used  to  designate  these  features,  and  the  following 
are  some  of  those  in  general  use: 

Process  (Processus)  is  a  general  term  for  a  prominence. 

A  tuberosity  (Tuber,  Tuberositas)  is  a  large,  rounded  projection;  a  tubercle 
(Tuberculum)  is  a  smaller  one. 

The  term  trochanter  is  applied  to  a  few  prominences,  e.  g.,  the  trochanters  of 
the  femur. 

A  spine  (Spina)  or  spinous  process  (Processus  spinosus)  is  a  pointed  projection. 

A  crest  (Crista)  is  a  sharp  ridge. 

A  line  (Linea)  is  a  very  small  ridge. 

A  head  (Caput)  is  a  rounded  articular  enlargement  at  the  end  of  a  bone;  it 
may  be  joined  to  the  shaft  by  a  constricted  part,  the  neck  (Collum). 

A  condyle  (Condylus)  is  an  articular  eminence  which  is  somewhat  cylindrical; 
a  non-articular  projection  in  connection  with  a  condyle  may  be  termed  an  epi- 
condyle  (Epicondylus). 

A  trochlea  is  a  pulley-like  articular  mass. 

A  glenoid  cavity  (Cavitas  glenoidalis)  is  a  shallow  articular  depression,  and  a 
cotyloid  cavity  or  acetabulum  is  a  deeper  one. 

The  term  facet  is  commonly  applied  to  articular  surfaces  of  small  extent, 
especially  when  they  are  not  strongly  concave  or  convex. 

The  terms  fossa,  fovea,  groove  or  sulcus,  and  impression  are  applied  to  various 
forms  of  depressions. 

A  foramen  is  a  perforation  for  the  transmission  of  vessels,  nerves,  etc. 

A  sinus  is  an  air-cavity  within  a  bone  or  bones;  it  is  lined  with  mucous  mem- 
brane and  communicates  with  the  exterior. 

Other  terms,  such  as  canal,  fissure,  notch,  etc.,  require  no  explanation.^ 


THE  VERTEBRAL  COLUMN 

The  vertebral  coliram  (Columna  vertebralis)  is  the  fundamental  part  of  the 
skeleton.  It  consists  of  a  chain  of  median,  unpaired,  irregular  bones  which 
extends  from  the  skull  to  the  end  of  the  tail.  In  the  adult  certain  vertebrae  have 
become  fused  to  form  a  single  bony  mass  with  which  the  pelvic  girdle  articulates. 
Vertebrae  so  fused  are  termed  fixed  (or  ''false")  vertebrae  (Vertebrae  immobiles),  as 
distinguished  from  the  movable  (or  'Hrue")  vertebrae  (Vertebrae  mobiles). 

The  column  is  subdivided  for  description  into  five  regions,  which  are  named 
according  to  the  part  of  the  body  in  which  the  vertebrae  are  situated.  Thus  the 
vertebrae  are  designated  as  cervical,  thoracic,  lumbar,  sacral,  coccygeal  (Vertebrae 
cervicales,  thoracales,  lumbales,  sacrales,  coccygeae).  The  number  of  vertebrae  in 
a  given  species  is  fairly  constant  in  each  region  except  the  last,  so  that  the  verte- 
bral formula  may  be  expressed  (for  the  horse,  for  example)  as  follows: 

C7Ti8L6S5Cyi5.21. 

The  vertebrae  in  a  given  region  have  characters  by  which  they  may  be  dis- 
tinguished from  those  of  other  regions,  and  individual  vertebrae  have  special 
characters  which  are  more  or  less  clearly  recognizable.     All  typical  vertebrae  have 

1  As  might  be  expected  from  the  history  of  anatomy,  a  good  many  of  these  terms  are  more  or 
less  interchangeable;  furthermore,  a  given  skeletal  feature  may  differ  greatly  in  various  species. 


26 


OSTEOLOGY 


a  common  plan  of  structure,  which  must  first  be  understood.     The  parts  of  which 
a  vertebra  consists  are  the  body,  the  arch,  and  the  processes. 

The  body  (Corpus  vertebrae)  is  the  more  or  less  cylindrical  mass  on  which  the 
other  parts  are  constructed.  The  anterior  and  posterior  extremities  of  the  body 
are  attached  to  the  adjacent  vertebrse  by  intervertebral  fibro-cartilages,  and  are 
usually  convex  and  concave  respectively.  The  dorsal  surface  is  flattened  and  enters 
into  the  formation  of  the  vertebral  canal,  while  the  ventral  aspect  is  rounded  later- 
ally, and  is  in  relation  to  various  muscles  and  viscera.  In  the  thoracic  region  the 
body  presents  two  pairs  of  facets  (Foveae  costales)  at  the  extremities  for  articula- 
tion with  part  of  the  heads  of  two  pairs  of  ribs. 

The  arch  (Arcus  vertebrae)  is  constructed  on  the  dorsal  aspect  of  the  body. 
It  consists  originally  of  two  lateral  halves,  each  of  which  is  considered  to  consist 
of  a  pedicle  and  a  lamina.  The  pedicle  (Radix  arcus  vertebrge)  forms  the  lateral 
part  of  the  arch,  and  is  cut  into  in  front  and  behind  by  the  vertebral  notches  (In- 
cisura  vertebralis  cranialis,  caudalis).  The  notches  of  two  adjacent  vertebrae  form 
intervertebral  foramina  (Foramina  intervertebralia)  for  the  passage  of  the  spinal 

nerves  and  vessels;  in  some  vertebrae,  how- 
ever, there  are  complete  foramina  instead 
of  notches.  The  laminae  are  plates  which 
complete  the  arch  dorsally,  uniting  with  each 
other  medially  at  the  root  of  the  spinous 
process. 

The  body  and  the  arch  form  a  bony 
ring  which  incloses  the  vertebral  foramen 
(Foramen  vertebrale);  the  series  of  verte- 
bral rings,  together  with  the  ligaments  which 
unite  them,  inclose  the  vertebral  canal 
(Canalis  vertebralis),  Avhich  contains  the 
spinal  cord  and  its  coverings  and  vessels. 

The  articular  processes,   two  anterior 
and    two   posterior    (Processus    articulares 
craniales,   caudales),   project  from  the  bor- 
ders  of  the   arch.     They  present   articular 
surfaces  adapted  to  those  of  adjacent  verte- 
brae, and  the  remaining  surface  is  roughened 
for  muscular  and  ligamentous  attachment. 
The  spinous  process  or  spine  (Processus 
spinosus)  is  single,  and  projects  dorsally  from  the  middle  of  the  arch.     It  varies 
greatly  in  form,  size,  and  direction  in  different  vertebrae.     It  furnishes  attachment 
to  muscles  and  ligaments. 

The  transverse  processes  (Processus  transversi)  are  two  in  number  and  project 
laterally  from  the  sides  of  the  arch  or  from  the  junction  of  the  arch  and  body. 
In  the  thoracic  region  each  has  a  facet  for  articulation  with  the  tubercle  of  a  rib 
(Fovea  costalis  transversalis) .  They  also  give  attachment  to  muscles  and  liga- 
ments. 

Some  vertebrae  have  also  a  ventral  spine  or  a  haemal  arch. 
Mammillary  processes  (Processus  mamillares)  are  found  in  most  animals  on 
the  last  thoracic  and  anterior  lumbar  vertebrse,  between  the  transverse  and  an- 
terior articular  processes  or  on  the  latter. 

Accessory  processes  (Processus  accessorii),  when  present,  are  situated  between 
the  transverse  and  posterior  articular  processes. 

Development. — The  vertebrae  are  developed  by  ossification  in  the  cartilage 
Avhich  surrounds  the  notochord  and  forms  the  sides  of  the  neural  canal.  There  are 
three  primary  centers  of  ossification,  one  for  the  body  and  one  for  each  side  of  the 


Cosraijkcef 


Fig.  5. — First  Thoracic  Vertebra  of  Horse. 
To  illustrate  plan  of  structure  of  vertebrae. 


THE    COSTAL    CARTILAGES  27 

arch.  Secondary  centers  appear  later  for  the  summit  of  the  spinous  process 
(except  in  the  cervical  region),  the  extremities  of  the  transverse  processes,  and  the 
thin  epiphyseal  plates  at  the  extremities  of  the  body. 

Sometimes  there  are  at  first  two  centers  for  the  body,  which  soon  fuse.  The  process  of  ossifi- 
cation extends  from  the  lateral  centers  to  form,  not  only  the  corresponding  part  of  the  arch,  but 
also  the  processes  and  a  part  of  the  body  next  to  the  root  of  the  arch  (Radix  arcus) .  In  the  horse 
and  ox  the  body  and  arch  are  fused  at  birth  or  unite  very  soon  after,  but  the  epiphyses  do  not 
fuse  till  growth  is  complete.  In  the  pig,  sheep,  and  dog  the  body  and  arch  are  united  at  l)irth 
by  cartilage  (neurocentral  synchondrosis),  but  fuse  in  the  first  few  months. 

THE  RIBS 

The  ribs  (Costae)  are  elongated  curved  bones  which  form  the  skeleton  of  the 
lateral  thoracic  walls.  They  are  arranged  serially  in  pairs  which  correspond  in 
number  to  the  thoracic  vertebrae.  Each  articulates  dorsally  with  two  vertebrae 
and  is  continued  ventrally  by  a  costal  cartilage.  Those  which  articulate  with  the 
sternum  by  means  of  their  cartilages  are  termed  sternal  ribs  (Costae  sternales); 
the  remainder  are  asternal  ribs  (Costae  asternales).  Ribs  at  the  end  of  the  series 
which  have  their  ventral  ends  free  in  the  abdominal  wall  are  named  floating  ribs 
(Costae  fiuctuantes).  The  intervals  between  the  ribs  are  termed  intercostal  spaces 
(Spatia  intercostalia) . 

A  typical  rib^  consists  of  a  shaft  and  two  extremities.  The  shaft  (Corpus 
costae)  is  band-like  and  varies  much  in  length,  breadth,  and  curvature  in  different 
ribs.  In  the  case  of  some  ribs  the  curvature  is  not  uniform,  but  is  accentuated  at  a 
certain  point,  termed  the  angle  of  the  rib  (Angulus  costae) ;  this  occurs  at  a  variable 
distance  from  the  vertebral  end,  and  is  usually  marked  by  a  rough  ridge.  The 
direction  also  varies;  the  first  rib  is  usually  almost  vertical,  while  the  remainder 
slope  backward  in  increasing  degree.  The  lateral  surface  (Facies  lateralis)  is  con- 
vex, and  the  medial  surface  (Facies  medialis)  flattened  from  edge  to  edge;  on  the 
latter,  close  to  the  posterior  border,  is  the  costal  groove  (Sulcus  costae),  which  fades 
out  ventrally.  It  contains  the  intercostal  vein.  The  anterior  and  posterior 
borders  (Margo  cranialis,  caudalis)  are  thin  and  sharp  on  some  ribs,  rounded  on 
others. 

The  vertebral  extremity  (Extremitas  vertebralis)  consists  of  the  head,  neck, 
and  tubercle.  The  head  (Capitulum  costae)  is  the  actual  end  of  the  rib,  and  is 
rounded  and  somewhat  enlarged.  It  presents  two  facets  (Facies  articularis  capituli 
costae)  for  articulation  with  the  bodies  of  two  adjacent  thoracic  vertebrae;  these 
surfaces  are  separated  by  a  groove  in  which  the  conjugal  ligament  is  attached. 
The  neck  (CoUum  costae)  joins  the  head  to  the  shaft.  It  varies  in  length  and 
diameter.  Its  lateral  surface  is  rough,  its  medial  smooth.  The  tubercle  (Tuber- 
culum  costae)  projects  backward  at  the  junction  of  the  neck  and  shaft.  It  has  a 
facet  (Facies  articularis  tuberculi  costae)  for  articulation  with  the  transverse  process 
of  the  posterior  vertebra  of  the  two  with  which  the  head  articulates.  The  tubercle 
gradually  approaches  the  head  in  the  posterior  ribs,  and  eventually  fuses  with  it. 

The  sternal  extremity  (Extremitas  sternalis)  is  commonly  slightly  enlarged, 
and  is  roughened  at  the  junction  with  the  costal  cartilage. 

Development. — The  ribs  are  ossified  in  cartilage  from  three  centers — one  each 
for  the  shaft  (and  sternal  end),  head,  and  tubercle;  the  third  center  is  absent  in 
some  ribs  at  the  terminal  part  of  the  series. 

THE  COSTAL  CARTILAGES 

These  (Cartilagines  costales)  are  bars  of  hyaline  cartilage  which  continue  the 
ribs.     Those  of  the  sternal  ribs  articulate  with  the  sternum,  while  those  of   the 

1  The  term  is  employed  here,  as  is  usual  in  descriptive  anatomy,  to  designate  only  the  bony 
part  of  the  rib  (Os  costale) ;  morphologically  it  includes  the  cartilaginous  part  also. 


28  OSTEOLOGY 

asternal  ribs  overlap  and  are  attached  to  each  other  to  form  the  costal  arch  (Arcus 
costalis).     The  cartilages  of  floating  ribs  are  not  attached  to  those  adjacent. 


THE  STERNUM 

The  stemxun  (or  breast-bone)  is  a  median  segmental  bone  -which  completes  the 
skeleton  of  the  thorax  ventrally,  and  articulates  Avith  the  cartilages  of  the  sternal 
ribs  laterally.  It  consists  of  six  to  eight  bony  segments  (Sternebra^)  connected  by 
intervening  cartilage  in  the  yoimg  subject.  Its  form  varies  with  that  of  the  thorax 
in  general  anil  with  the  development  of  the  clavicles  in  animals  in  which  these  bones 
are  present.  Its  anterior  extremity,  the  manubrium  stemi  or  presternum,  is 
specially  affected  by  the  latter  factor,  being  broad  and  strong  when  the  clavicles 
are  well  ileveloped  and  articulate  with  it  (as  in  man),  relatively  small  and  laterally 
compressed  Avhen  they  are  absent  (as  in  the  horse)  or  rudimentary  (as  in  the  dog). 
The  cartilages  of  the  first  pair  of  ribs  articulate  with  it.  The  body  or  mesostemimi 
(Corpus  sterni)  presents  laterally,  at  the  junction  of  the  segments,  concave  facets 
(Incisura^  costales)  for  articulation  Avith  the  cartilages  of  the  sternal  ribs.  The 
posterior  extremity  or  metastemiun  presents  the  xiphoid  cartilage  (Processus 
xiphoideus) ;  this  is  thin  and  wide,  as  in  the  horse  and  ox,  or  narroAv  and  short,  as 
in  the  dog. 

Development. — The  cartilaginous  sternmn  is  formed  by  the  fusion  medially 
of  two  lateral  bars  which  unite  the  ventral  ends  of  the  first  eight  or  nine  costal 
cartilages,  and  is  primitively  imsegmented.  The  manubrium  ossifies  from  a  single 
center,  but  the  centers  for  the  other  segments  appear  to  be  primitively  paired. 
The  sternum  never  becomes  completely  ossified;  details  in  regard  to  persisting 
cartilage  will  be  given  in  the  special  descriptions.  The  layer  of  compact  tissue  is 
for  the  greater  part  very  thin  and  the  spongy  substance  is  open-meshed  and  ver^' 
vascular. 

THE  THORAX 

The  skeleton  of  the  thorax  comprises  the  thoracic  vertebnp  dorsally.  the  ribs 
and  costal  cartilages  laterally',  and  the  sternmn  ventrally.  The  thoracic  cavity 
(CaAinn  thoracis)  resembles  in  shape  an  irregular  truncated  cone;  it  is  compressed 
laterally,  especially  in  front,  and  the  dorsal  wall  or  roof  is  much  longer  than  the 
ventral  wall  or  floor.  The  anterior  apertvire  or  inlet  (Apertura  thoracis  cranialis)  is 
bc^unded  by  the  first  thoracic  vertebra  dorsally,  the  first  pair  of  ribs  and  costal 
cartilages  laterally,  and  the  manubrium  sterni  ventrally.  The  posterior  aperture 
(Apertura  thoracis  caudalis)  is  bounded  by  the  last  thoracic  vertebra,  the  last 
pair  of  ribs,  the  costal  arches,  and  the  anterior  part  of  the  xiphoid  cartilage. 

It  may  be  noted  here  that  the  diaphragm  (which  forms  the  partition  hetween  the  thoracic 
and  abdominal  caA-ities)  does  not  follow  the  costal  arches  in  its  posterior  attachment,  so  that  the 
posterior  ribs  enter  also  into  the  formation  of  the  abdominal  wall. 


THE  SKULL 

The  term  skull  is  usually  imderstood  to  include  all  of  the  bones  of  the  head. 
The  head  consists  of  the  cranium  and  the  face,  and  it  is  therefore  convenient  to 
diAnde  the  bones  into  cranial  antl  facial  groups. 

The  cranial  bones  (Ossa  cranii)  inclose  the  brain  AA-ith  its  membranes  and 
vessels  and  the  essential  organs  of  hearing.  They  concur  with  the  facial  bones  in 
forming  the  orbital  and  nasal  caA'ities,  in  AA-hich  the  peripheral  organs  of  sight  ami 
of  smell  are  situated. 

The  facial  bones  (Ossa  faciei)  form  the  skeleton  of  the  oral  and  nasal  caA'ities, 
and  also  support  the  pharA'nx,  the  larynx,  and  the  root  of  the  tongue. 


THE  BONES  OF  THE  THORACIC  LIMB  29 

Most  of  the  bones  of  the  skull  are  flat  bones,  developed  in  membrane;  those 
of  the  cranial  base  may  be  classed  as  irregular,  and  are  developed  in  cartilage.  Only 
two  form  permanent  movable  joints  with  other  parts  of  the  skull.  The  mandible 
(or  lower  jaw-Vjone)  forms  diarthrodial  joints  with  the  temporal  bones,  and  the 
hyoid  bone  is  attached  to  the  latter  Vjy  bars  of  cartilage.  The  other  bones  form 
immovable  joints,  most  of  which  disappear  with  age. 

In  order  to  study  the  separate  bones,  skulls  of  young  subjects  are  necessary,  since  later  most 
of  the  hnes  of  demarcation  become  effaced.  The  relations  of  each  bone  to  its  surroundings  should 
be  specially  noted,  since  the  final  object  is  to  understand  the  skull  as  a  whole.  In  the  descriptions 
which  follow  the  skull  is  considered  with  its  long  axis  horizontal,  and  that  of  the  horse  will  serve 
as  a  type. 

THE  BONES  OF  THE  THORACIC  LIMB 

The  thoracic  limb  (Extremitas  thoracalis)  consists  of  four  chief  segments,  viz., 
the  shoulder  girdle,  the  arm,  the  forearm,  and  the  manus. 

The  shoulder  girdle  (Cingulum  extremitatis  thoracalis) ,  when  fully  developed, 
consists  of  three  bones — the  scapula  (or  shoulder-blade),  the  coracoid,  and  the 
clavicle  (or  collar-bone).  In  the  domesticated  mammals  only  the  scapula,  a  large, 
flat  bone,  is  well  developed,  and  the  small  coracoid  element  has  fused  with  it,  while 
the  clavicle  is  either  absent  or  is  a  small  rudiment  embedded  in  the  brachiocephali- 
cus  muscle.  There  is  therefore  no  articulation  of  the  shoulder  with  the  axial 
skeleton. 

The  shoulder  girdle  is  fully  developed  in  birds  and  the  lower  mammals  (monotremata) .  In 
the  higher  manmials  the  coracoid  is  reduced  to  the  coracoid  process  of  the  scapula,  and  the  develop- 
ment of  the  clavicle  is  in  conformity  with  the  function  of  the  hmb.  Thus  in  typical  quadrupeds, 
such  as  the  horse  and  ox,  in  which  the  foreUmbs  are  used  only  for  support  and  locomotion,  the 
clavicle  is  absent.  Other  animals  which  use  these  hmbs  for  grasping,  burrowing,  chmbing,  etc. 
(e.  g.,  man,  apes,  moles),  have  well-developed  cla\'icles  which  connect  the  scapula  with  the  stemiun. 

The  arm  (Brachium)  contains  a  single  long  bone,  the  humerus  (or  arm  bone). 

In  the  forearm  (Antibrachium)  are  two  bones,  the  radius  and  ulna.  These 
vary  in  relative  size  and  mobility.  In  the  horse  and  ox  the  two  bones  are  fu.sed, 
and  the  distal  part  of  the  limb  is  fixed  in  the  position  of  pronation.  The  radius  is 
placed  in  front  and  supports  the  weight.  The  ulna  is  well  developed  only  in  its 
proximal  part,  which  forms  a  lever  for  the  extensor  muscles  of  the  elbow.  In  the 
pig  the  ulna  is  the  larger  and  longer  of  the  two  bones,  but  is  closely  attached  to 
the  back  of  the  radius.  In  the  dog  the  ulna  is  also  well  developed  and  a  small 
amount  of  movement  is  possible  between  the  two  bones. 

The  manus,!  the  homologue  of  the  hand  in  man,  consists  of  three  subdivi- 
sions, viz.,  the  carpus,  metacarpus,  and  digit  or  digits. 

The  carpus,  popularly  termed  the  "knee"  in  animals,  and  homologous  with 
the  wrist  of  man,  contains  a  group  of  short  bones,  the  ossa  carpi.^  These  are  typic- 
ally eight  in  number  and  are  arranged  in  two  transverse  rows — a  proximal  or  anti- 
brachial,  and  a  distal  or  metacarpal.  The  bones  of  the  proximal  row,  named  from 
the  radial  to  the  ulnar  side  {i.  e.,  from  within  outward),  are  the  radial,  intermediate, 
ulnar,  and  accessory  carpal  bones.  The  bones  of  the  distal  row  are  designated 
numerically,  in  the  same  direction,  as  first,  second,  third,  and  fourth  carpal  bones. 

This  nomenclature,  introduced  by  Gegenbaur,  and  now  used  largely  by  comparative  anat- 
omists, seems  decidedly  preferable  to  the  ^'ariety  of  terms  borrowed  from  human  anatomy  and 
based  on  the  form  of  the  bones  in  man.  The  follo^vang  table  of  synonyms  in  cornmon  use  is  ap- 
pended for  comparison.     The  Latin  terms  and  abbreviated  notations  are  given  in  parentheses. 

1  It  is  unfortunate  that  there  is  no  popular  name  for  this  part  of  the  limb.  The  term  "fore- 
foot" is  sometimes  appUed  to  it,  but  this  leads  to  confusion,  since  the  word  "foot"  has  long  been 
used  in  a  different  sense. 

2  The  term  "knee"  as  applied  to  this  region  is  unfortunate,  but  the  usage  is  very  firmly 
established  and  there  is  no  other  popular  name. 


30  OSTEOLOGY 

The  central  carpal  bone  (Os  carpi  centrale)  is  omitted,  since  it  is  not  a  separate  element  in  the 
animals  under  consideration  here. 

Radial  (Os  carpi  radiale,  Cr) Scaphoid 

Intermediate  (Os  carpi  intermedium,  Ci) Semilunar 

Ulnar  (Os  carpi  ulnare,  Cu) Cuneiform 

Accessory  (Os  carpi  accessorium,  Ca) Pisiform 

First  carpal  (Os  carpale  primum,  CI) Trapezium 

Second  carpal  (Os  carpale  secundum,  C2j Trapezoid 

Third  carpal  (Os  carpale  tertium,  C3) Os  magnum 

Fourth  carpal  (Os  carpale  quartum,  C4) Unciform 

The  metacarpus  contains  typically  five  metacarpal  bones  (Ossa  metacarpalia 
I-V),  one  for  each  digit;  they  are  long  bones  and  are  designated  numerically  from 
the  radial  to  the  ulnar  side  (i.  e.,  from  within  outward).  This  arrangement  occurs 
in  the  dog,  although  the  first  metacarpal  is  much  smaller  than  the  others,  and  the 
second  and  fifth  are  somewhat  reduced.  Further  reduction  has  taken  place  in  the 
other  animals,  resulting  in  the  perissodactyl  and  artiodactyl  forms.  In  the  horse 
the  first  and  fifth  metacarpals  are  absent,  the  third  is  the  large  supporting  meta- 
carpal bone  and  carries  the  single  digit,  while  the  second  and  fourth  are  much  re- 
duced. In  artiodactyls  (e.  g.,  ox,  sheep,  pig)  the  third  and  fourth  are  the  chief 
metacarpals  and  carry  the  well  developed  digits;  they  are  fused  in  the  ox  and  sheep. 
The  others  are  variously  reduced  or  absent,  as  noted  in  the  special  descriptions  to 
follow. 

The  fossil  remains  of  the  ancestors  of  the  existing  Equidse  illustrate  in  a  most  complete  man- 
ner the  reduction  which  has  occurred  in  this  respect.  The  earliest  known  ancestor  of  the  horse, 
Eohippus  of  the  Lower  Eocene,  had  four  well  developed  metacarpal  bones,  each  of  which  carried 
a  digit;  the  first  metacarpal  bone  was  small.  Intermediate  forms  show  the  gradual  evolution  of 
the  race  from  this  primitive  animal,  which  was  about  the  size  of  the  domestic  cat.  There  is  reason 
to  believe  that  earlier  forms  had  five  digits. 

The  digits  (Digiti  manus)  are  homologous  with  the  fingers  of  man,  and  are 
typically  five  in  number.  They  are  designated  numerically  from  the  radial  to 
the  ulnar  side,  in  correspondence  with  the  metacarpus.  The  full  number  is  present 
in  the  dog.  In  the  ox  and  pig  the  third  and  fourth  are  well  developed  and  support 
the  weight,  while  the  second  and  fifth  are  reduced.  The  existing  horse  has  a  single 
digit,  the  third  of  his  pentadactyl  ancestors.  The  skeleton  of  each  fully  developed 
digit  consists  of  three  phalanges  and  certain  sesamoid  bones.  The  first  phalanx 
(Phalanx  prima)  articulates  with  the  corresponding  metacarpal  bone  above  and 
with  the  second  phalanx  (Phalanx  secunda)  below.  The  third  phalanx  (Phalanx 
tertia)  is  inclosed  in  the  hoof  or  claw,  and  is  modified  to  conform  to  the  latter.  The 
sesamoid  bones  (Ossa  sesamoidea)  are  developed  along  the  course  of  tendons  or  in 
the  joint  capsules  at  points  where  there  is  increased  pressure.  Two  proximal 
sesamoids  (Ossa  sesamoidea  phalangis  primse)  occur  at  the  flexor  side  of  the  meta- 
carpo-phalangeal  joint  and  form  a  pulley  for  the  flexor  tendon.  The  distal  sesa- 
moid (Os  sesamoideum  phalangis  tertise)  is  similarly  placed  between  the  deep 
flexor  tendon  and  the  joint  between  the  second  and  third  phalanx;  it  is  absent  in 
the  dog,  which  has  a  small  sesamoid  on  the  extensor  side  of  the  metacarpo-phalan- 
geal  joint,  and  often  at  the  proximal  interphalangeal  joint  also. 

Numerous  cases  are  recorded  of  the  occurrence  of  supernumerary  digits  (hyperdactylism) 
in  the  horse  and  other  animals.  In  some  pigs,  on  the  other  hand,  the  two  chief  digits  are  fused,, 
and  the  condition  (syndactylism)  appears  to  be  inherited. 


THE  BONES  OF  THE  PELVIC  LIMB 

The  pelvic  limb  (Extremitas  pelvina),  like  the  thoracic,  consists  of  four  seg- 
ments, viz.,  the  pelvic  girdle,  thigh,  leg,  and  the  pes;  the  last  is  subdivided  into 
tarsus,  metatarsus,  and  digits. 

The  pelvic  girdle  (Cingulum  extremitatis  pelvinse)  consists  of  the  os  coxae  (or 


THE    BONES    OF   THE    PELVIC    LIMB  31 

hip  bone),  which  joins  its  fellow  of  the  opposite  side  ventrally  at  the  symphysis 
pelvis,  and  articulates  very  finnlj^  with  the  sacrum  dorsally.  The  two  coxal  bones, 
together  with  the  sacrum  and  the  first  three  or  more  coccygeal  vertebrae,  constitute 
the  bony  pelvis.  The  os  coxae  consists  originally  of  three  flat  bones,  the  ilium, 
ischium,  and  pubis,  which  meet  at  the  acetabulum,  a  large  cotyloid  cavity  with 
which  the  head  of  the  femur  articulates.  These  three  parts  are  fused  before  growth 
is  complete,  but  are  considered  separately  for  convenience  of  description.  The 
iliimi  (Os  ilium)  is  situated  in  the  lateral  wall  of  the  pelvis,  the  pubis  (Os  pubis)  in 
the  anterior  part,  and  the  ischium  (Os  ischii)  in  the  posterior  part  of  the  ventral 
wall. 

The  thigh  (Femur),  like  the  arm,  contains  a  single  long  bone,  the  femur  (or 
thigh  bone)  (Os  femoris).  This  articulates  with  the  acetabulum  above  and  the 
tibia  and  patella  below. 

The  skeleton  of  the  leg  (Crus)  comprises  three  bones  (Ossa  cruris),  viz.,  the 
tibia,  fibula,  and  patella.  The  tibia  is  a  large,  prismatic  long  bone  which  supports 
the  weight,  and  articulates  distally  with  the  tibial  tarsal  bone.  The  fibula  is 
situated  along  the  lateral  border  of  the  tibia,  from  which  it  is  separated  by  the 
interosseous  space  of  the  leg.  It  is  much  more  slender  than  the  tibia  and  does  not 
articulate  with  the  femur.  In  the  pig  and  dog  it  has  a  complete  shaft  and  two 
extremities,  but  in  the  horse  and  ox  it  is  much  reduced  and  otherwise  modified. 
The  patella  (or  "knee-cap")  is  a  short  bone  which  articulates  with  the  trochlea  of 
the  distal  end  of  the  femur;  it  is  to  be  regarded  as  a  large  sesamoid  bone  intercalated 
in  the  tendon  of  the  quadriceps  femoris  muscle. 

The  tarsus  (or  "hock")  consists  of  a  group  of  short  bones,  the  ossa  tarsi, 
numbering  five  to  seven  in  the  different  animals.  The  proximal  or  crural  row  con- 
sists of  two  bones,  the  tibial  and  fibular  tarsals ;  the  former  is  situated  at  the  tibial 
side,  and  has  a  trochlea  for  articulation  with  the  distal  end  of  the  tibia;  the  latter, 
situated  at  the  fibular  side,  has  a  process,  the  tuber  calcis,  which  projects  upward 
and  backward  and  constitutes  a  lever  for  the  muscles  which  extend  the  hock  joint. 
The  distal  or  metatarsal  row  consists  of  four  bones  when  seven  tarsal  elements  are 
present,  as  in  the  pig  and  dog.  They  are  best  designated  numerically  as  first  tarsal, 
second  tarsal,  etc.     The  central  tarsal  is  interposed  between  the  rows. 

The  preceding  terms  are  anglicized  abbreviations  of  those  introduced  by  Gegenbaur  into 
comparative  anatomy.     The  Latin  names  and  synonyms  are  given  in  the  following  table: 

Tibial  (Os  tarsi  tibiale,  Tt.) Astragalus  or  Talus 

Fibular  (Os  tarsi  fibulare,  Tf.) Calcaneus  or  Os  calcis 

Central  (Os  tarsi  centrale,  Tc.) Scaphoid  or  Navicular 

First  Tarsal  (Os  tarsale  primum,  Tl) First  or  internal  cuneiform 

Second  Tarsal  (Os  tarsale  secundum,  T2) Second  or  middle  cuneiform 

Third  Tarsal  (Os  tarsale  tertium,  T3) Third  or  external  cuneiform 

Fourth  Tarsal  (Os  tarsale  quartum,  T4) Cuboid 

The  metatarsal  and  digital  bones  resemble  in  general  those  of  the  corresponding 
regions  of  the  thoracic  limb;  the  differential  features  will  be  noted  in  the  special 
descriptions. 


32 


THE    SKELETON    OF   THE    HORSE 


THE  SKELETON  OF  THE  HORSE 

The  skeleton  of  the  horse  consists  of  205  bones,  as  shown  in  the  following  table: 

Vertebral  column 54 

Ribs 36 

Sternum 1 

Skull  (including  auditory  ossicles) 34 

Thoracic  limbs 40 

Pelvic  limbs 40 

205 

In  this  enumeration  the  average  number  of  coccygeal  vertebrae  is  taken  to  be  18,  the  tem- 
poral and  OS  coxae  are  not  divided  into  parts,  the  usual  number  of  carpal  and  tarsal  elements  is 
taken,  and  the  sesamoids  are  included. 

t 


Fig.  6. — Skeleton  of  Horse,  with  Outune  of  Contour  of  Body. 
I.H.,  Atlas;  7.H.,  seventh  cervical  vertebra;  I.R.,  first  thoracic  vertebra;  17. R.,  seventeenth  thoracic  vertebra; 
I.L.,  first  lumbar  vertebra;  O.L.,  sixth  lumbar  vertebra;  K,  sacrum;  I.S.,  first  coccygeal  vertebra;  16.S.,  sixteenth 
coccygeal  vertebra;  ^.i?.,  sixth  rib;  e. A'.,  costal  cartilage;  18. R.,  lust  rih;  1,  scapula;  1',  cartilage  of  scapula;  2,  spine 
of  scapula;  4,  humerus;  4'  lateral  epicondyle  of  humerus;  5,  lateral  tuberosity  of  humerus;  6,  deltoid  tuberosity; 
7,  shaft  of  ulna;  8,  olecranon;  9,  radius;  10,  carpus;  11,  accessory  carpal  bone;  12,  metacarpus;  13,  digit;  14,  sternum, 
14",  xiphoid  cartilage;  15,  ilium;  16,  16',  angles  of  ilium;  17,  ischium;  18,  femur  (shaft) ;  19,  trochanter  major;  20, 
patella;  21,  tibia  (shaft);  21',  lateral  condyle  of  tibia;  2.3,  fibula;  22,  tarsus;  24,  tuber  calcis;  25,  metatarsus; 
26,  digit;  27,  trochanter  minor  of  femur;  28,  trochanter  tertius  of  femur.  (After  EUenberger-Baum,  Anat.  fiir 
Kiinstler.) 


THE   VERTEBRAL    COLUMN 


33 


The  Vertebral  Column 

The  vertebral  formula  of  the  horse  is  C7Ti8L6S5Cyi5-2i. 


Anterior  artic- 
ular process 
of  axis 
Spinous  proc- 
ess of  axis 


Transverse 
process  of  axis 


Fig.  7. — Cervical  Vertebrae  of  Horse;  Dorsal  View. 
a,  Articular  processes;  b,  transverse  processes;  1, 
dorsal  arch  of  atlas;  2,  w-ing  of  atlas;  3,  intervertebral 
foramen  of  atlas;  4,  alar  foramen  of  atlas;  6,  foramen 
transversarium  of  atlas;  6,  dens  of  axis;  7,  intervertebral 
foramen  of  axis;  8,  foramen  transversarium  of  axis;  9, 
spinous  processes. 

3 


Fig.    8. — Cervical    Vertebr.e     of    Horse;    Ventral 
View. 
a.  Transverse  processes;    1,  ventral  tubercle  of  atlas; 

3,  anterior  articular  cavities  of  atlas;    S,  fossa  atlantis; 

4,  alar  foramen;  6,  foramen  transversarium;  6,  ventral 


34 


THE    SKELETON    OF   THE    HORSE 


Head 

Fig.  9. — Sixth  Cervical  Vertebra  of  Horse;  Anterior  View. 


THE  CERVICAL  VERTEBRA 

The  cervical  vertebrae  (Vertebrae  cervicales)  are  seven  in  number. 
The  first  and  second  cervical  vertebrae  are  highly  modified  in  conformity  with 

the  special  functions  of  support 
and  movements  of  the  head. 
The  sixth  and  seventh  present 
special  characters,  but  do  not 
differ  greatly  from  the  tj'pe. 
With  the  exception  of  the  first, 
they  are  quadrangular,  mass- 
ive, and  longer  than  the  ver- 
tebrae of  other  regions;  they 
decrease  in  length  from  the 
second  to  the  last.  The  third, 
fourth,  and  fifth  have  the  fol- 
lowing characters: 

1.  The  body  is  long  as 
compared  with  those  of  other 
vertebrae.  The  ventral  surface 
presents  a  median  ventral 
spine,  which  becomes  more 
prominent  as  it  is  traced  back- 
ward, and  is  tuberculate  at  its 
posterior  end ;  it  separates  two 
concave  areas.  The  dorsal  sur- 
face has  a  flat  central  area  which  is  narrow  in  the  middle  of  the  vertebrae,  and  ^\^de 
at  either  end ;  it  gives  attachment  to  the  dorsal  longitudinal  ligament.  On  either 
side  of  this  area  there  is  a  groove  which  lodges  the  longitudinal  spinal  vein.  These 
lateral  grooves  are  connected  about  the  middle  of  the  surface  by  a  transverse  furrow, 
in  which  there  are  several  for- 
amina through  which  veins 
emerge  from  the  spongy  sub- 
stance of  the  body.  The  an- 
terior extremity  or  head  (Ca- 
put vertebrae)  has  an  oval 
articular  surface  which  faces 
forward  and  downward;  it  is 
strongly  convex,  and  wider 
above  than  below.  The  pos- 
terior extremity  is  larger  and 
has  a  nearly  circular  cotyloid 
cavity  (Fossa  vertebrae). 

2.  The  arch  is  large  and 
strong.  It  is  perforated  on 
either  side  by  a  foramen  which 
communicates  with  the  for- 
amen trans  versarium.  The 
vertebral  notches  are  large. 

3.  The  articular  processes 
are  large.     Their  articular  sur- 
faces are  extensive,  oval  in  outline,  and  slightl}^  concave;   the  anterior  ones  are 
directed  dorso-medially;  the  posterior,  ventro-laterally.     The  remaining  surface  is 
mainly  roughened  for  ligamentous  and  muscular  attachment.     A  crest  connects 


—    Spinous  process 

Vertebral 

foramen  Articular 

I  process 


PlBff^             — '           f 

jii  iri, 

fW>-— -^     A 

/  1      m    \ 

L|^jL^ 

^-'  Trans- 
H^      perse 

process 

^^^^^^^ 

Ventral  spine 
Seventh  Cervical  Vertebra  of  Horse; 

Anterior  View 

THE    ATLAS 


35 


the  articular  processes  of  the  same  side  on  the  fourth  and  fifth;  on  the  third  it  does 
not  reach  the  anterior  process. 

4.  The  transverse  processes  are  large  and  plate-like.  Each  arises  by  two 
roots,  one  from  the  arch  and  one  from  the  body;  between  these  is  the  foramen 
transversariiun,  through  which  the  vertebral  vessels  and  a  nerve  pass.  The  aggre- 
gate of  these  foramina  constitutes  the  canalis  transversarius.  The  process  divides 
laterally  into  anterior  and  posterior  branches,  which  are  thickened  and  rough  for 
muscular  attachment. 

5.  The  spinous  process  has  the  form  of  a  low  crest  (Crista  spinosa),  which 
widens  behind,  and  is  connected  by  ridges  with  the  posterior  articular  processes. 

The  sixth  cervical  vertebra  has  the  following  distinctive  features:  It  is  shorter 
and  wider  than  the  fifth.  The  arch  is  large,  especially  posteriorly.  The  posterior 
articular  processes  are  shorter,  thicker,  and  further  apart;  each  is  connected  with 
the  corresponding  anterior  one  by  a  thick  ridge.  The  spinous  process  is  less  rudi- 
mentary; it  is  half  an  inch  or  more  (ca.  1.5  cm.)  in  height.  The  transverse  proc- 
esses have  three  branches;  the  third  part  is  a  thick,  almost  sagittal  plate,  which 
forms  with  its  fellow  and  the  body  a  wide  ventral  groove;  the  other  branches 
correspond  to  those  of  the  typical  vertebrae,  but  are  short  and  thicker.^  The  fora- 
men transversarium  is  large;  below  its  posterior  end  there  is  a  fossa.  The 
ventral  spine  is  small  and  is  less  prominent  posteriorly. 

The  seventh  cervical  vertebra  is  readily  distinguished  by  the  following  charac- 
ters :  It  is  shorter  and  wider  than  the  others.  The  body  is  flattened  dorso-ventrally 
and  wide,  especially  behind;  here  it  has  a  facet  on  each  side  for  articulation  with 
part  of  the  head  of  the  first  rib.  The  arch  and  its  notches  are  large.  The  anterior 
articular  processes  are  wider  and  longer  than  the  posterior  pair.  The  spinous 
process  is  an  inch  or  more  (ca.  3  cm.) 
in  height.  The  transverse  process  is 
undivided,  and  has  no  foramen  trans- 
versarium.2  The  ventral  crest  is  re- 
placed by  a  pair  of  tubercles. 


The  Atlas 

This  vertebra  is  decidedly  atypi- 
cal in  form  and  structure.  The  body 
and  spinous  process  are  absent.  It 
has  the  form  of  a  strong  ring,  from 
which  two  curved  plates,  the  wings, 
project  laterally.  The  ring  incloses  a 
very  large  vertebral  foramen,  and  con- 
sists of  two  lateral  masses  connected 
by  dorsal  and  ventral  arches. 

The  lateral  masses  (Massse  later- 
ales)  present  two  deep  oval  anterior 
articular  cavities  (Foveas  articulares 

craniales)  which  receive  the  occipital  condyles;  they  are  separated  by  a  wide  notch 
above  and  a  narrow  one  below.  The  lateral  margin  is  also  notched,  and  a  trian- 
gular non-articular  depression  cuts  into  the  medial  part  of  each  cavity.  The  pos- 
terior articular  surfaces  (Facies  articulares  caudales)  are  somewhat  saddle-shaped; 
they  are  confluent  on  the  ventral  arch,  but  are  widely  separated  dorsally,  and  do 
not  conform  in  shape  to  the  corresponding  surfaces  of  the  axis. 

1  The  third  branch  of  the  transverse  process  and  the  fossa  are  sometimes  absent  or  reduced 
on  one  side. 

2  In  some  specimens  a  large  foramen  transversarium  is  present  on  one  side  or  (rarely)  on 
both  sides. 


Fig. 


Atlas  of  Horse,  Dorsal,  View  after  Removal 
OF  Dorsal  Arch. 
1,  Anterior  articular  cavities;  2,  2',  posterior  articular 
surfaces;    3,  articular  surface  of    ventral    arch    for  dens  of 
axis;  4,  transverse  ridge;   5,  5',  alar  foramina;    6,  6',  foram- 
ina transversaria. 


'36  THE    SKELETON   OF   THE   HORSE 

The  dorsal  arch  (Arcus  dorsalis)  presents  a  median  dorsal  tubercle  (Tuber- 
culum  dorsale)  and  is  concave  ventrally.  It  is  perforated  on  either  side  near  its 
anterior  margin  by  the  intervertebral  foramen  (Foramen  invertebrate).  The  an- 
terior border  is  deeply  notched,  and  the  posterior  is  thin  and  concave. 

The  ventral  arch  (Arcus  ventrahs)  is  thicker,  narrower,  and  less  curved  than 
the  dorsal.  On  its  lower  surface  is  the  ventral  tubercle  (Tuberculum  ventrale), 
into  which  the  terminal  tendon  of  the  longus  colli  muscle  is  inserted.  The  upper 
face  has  posteriorly  a  transversely  concave  articular  surface,  the  fovea  dentis,  on 
which  the  dens  or  odontoid  process  of  the  axis  rests.  In  front  of  this  is  a  transverse 
rough  excavation  and  a  ridge  for  the  attachment  of  the  ligamentum  dentis. 

The  wings  or  alae  are  modified  transverse  processes.  They  are  extensive 
curved  plates  which  project  ventro-laterally  and  backward  from  the  lateral  masses. 
The  dorsal  surface  is  concave.  Between  the  ventral  aspect  of  the  wing  and  the 
lateral  mass  is  a  cavity,  the  fossa  atlantis;  in  this  there  is  a  foramen  which  opens 
into  the  vertebral  canal.  The  border  is  thick  and  rough;  its  position  can  be  recog- 
nized in  the  living  animal.  Two  foramina  perforate  each  Aving.  The  anterior  one, 
the  foramen  alare,  is  connected  with  the  intervertebral  foramen  by  a  short  groove. 
The  posterior  one  is  the  foramen  transversariimi. 

Development. — The  atlas  ossifies  from  four  centers,  two  for  the  ventral  arch, 
and  one  on  either  side  for  each  lateral  mass,  wing,  and  half  of  the  dorsal  arch.  At 
birth  the  bone  consists  of  three  pieces — the  ventral  arch  and  two  lateral  parts, 
which  are  separated  by  a  layer  of  cartilage  in  the  dorsal  median  line  and  by  two 
ventro-lateral  layers.     These  parts  are  usually  fused  at  about  six  months. 

The  Axis 

The  axis  (Axis  s.  Epistropheus)  is  the  longest  of  the  vertebrae,  and  is  character- 
ized by  the  presence  of  the  dens  or  odontoid  process,  which  projects  from  the  an- 
terior part  of  the  body. 

The  anterior  extremity  of  the  body  presents  centrally  the  dens  or  odontoid 


Spinous  process 


Dens 


Anterior  articular  process 


Posterior  articular  process 

\ 

Trajisverse  process 


Body 

Fig.  12. — Axis  of  Horse,  Left  View. 
1,  Arch;    2,  intervertebral  foramen;    3,  notch;    4.  foramen  transversarium. 

process  (Dens  axis) ;  this  has  a  convex  articular  surface  ventrally  for  articulation 
with  the  ventral  arch  of  the  atlas,  and  two  rough  depressions  for  the  attachment  of 
the  ligamentum  dentis  dorsally.  Flanking  this  on  either  side  are  the  modified 
anterioi  articular  processes,  which  have  saddle-shaped  articular  surfaces  confluent 


THE    THORACIC    VERTEBRA 


37 


ventrally  with  that  of  the  dens.  The  posterior  extremity  has  the  usual  cavity. 
The  ventral  spine  resembles  that  of  the  typical  vertebrae. 

The  arch  presents  in  the  young  subject  a  notch  on  each  side  of  its  anterior 
border;  this  is  converted  into  a  foramen  by  a  ligament  which  ossifies  later.  The 
posterior  border  has  the  usual  notches. 

The  posterior  articular  processes  are  typical. 

The  transverse  processes  are  small,  single,  and  project  backward.  The 
foramen  transversariiun  is  small. 

The  spinous  process  is  very  large  and  strong.  Its  free  border  is  rough,  thickens 
posteriorly,  and  is  continued  to  the  articular  processes  by  two  ridges.  The  lateral 
surfaces  are  concave  and  rough  for  muscular  attachment. 

Development. — The  axis  has  six  or  seven  centers  of  ossification.  In  addition 
to  the  usual  five,  one  or  two  appear  for  the  dens,  which  is  regarded  as  the  displaced 
body  of  the  atlas.  A  nucleus  behind  the  dens,  which  remains  distinct  to  three  or 
four  years  of  age,  is  considered  to  be  the  head  of  the  axis. 


Spinous 
process 


THE  THORACIC  VERTEBRA 
The  thoracic  vertebrae  (Vertebrae  thoracales)  are  usually  eighteen  in  number  in 
the  horse,  but  there  are  sometimes  nineteen,  rarely  seventeen.     As  regional  char- 
acters we  note  the  surfaces  for  articulation  with  the  ribs  and  the  length  and  form  of 
the  spinous  processes.     Those  in  the 
middle    of    the   series   are   the    most 
typical  and  present  the  following  fea- 
tures: 

1.  The  bodies  are  short  and  con- 
stricted in  the  middle.  The  ends  are 
expanded  and  have  articular  surfaces 
which  are  not  strongly  curved;  the  an- 
terior surface  is  convex,  the  posterior 
concave.  On  the  upper  part  of  each 
side  are  anterior  and  posterior  costal 
facets  (Fovea  costalis  cranialis,  cau- 
dalis),  which,  with  those  of  adjacent 
vertebrae  and  the  intervening  fibro-car- 
tilages,  form  sockets  for  the  heads  of 
the  ribs. 

2.  The  arches  are  small.  Their 
posterior  notches  are  relatively  large 
and  are  often  converted  into  foram- 
ina. 

3.  The  articular  processes  are 
small.  The  anterior  processes  are  in 
fact  represented  only  by  two  oval  facets 
on  the  anterior  part  of  the  arch  which 
face  almost  directly  upward.  The  pos- 
terior processes  spring  from  the  base  of  the  spinous  process;  their  facets  face 
almost  directly  downward. 

4.  The  transverse  processes  are  short,  thick,  and  tuberous  at  the  free  end. 
Each  has  a  facet  (Fovea  transversaria)  for  articulation  with  the  tubercle  of  the 
rib  which  has  the  same  serial  number. 

5.  The  spinous  process  is  large,  narrow,  and  slopes  upward  and  backward. 
The  anterior  border  is  thin,  the  posterior  wider  and  furrowed.  The  summit  is 
expanded  and  rough. 


Facet  for  tubercle 
of  rib 

Facet  for 
head 
of  rib 


Body 


Fig.  13. — Seventh  Thoracic  Vertebra  of  Horse,  An- 
terior View. 


38 


THE    SKELETON    OF   THE    HORSE 


The  first  thoracic  vertebra  has  the  following  specific  characters:   The  body  is 
wide  and  flattened  dorso-ventrally.     In  front  it  has  a  head  like  the  cervical  verte- 


Spinnus  process 
Articular  processes 

Arch 


Facet  for  tubercle  of  first  rib       A^  ~-^__^      Transverse  process 

Facet  for  head  of  second  rib         ""'^fl^'^         Body 
Fig.  14. — First  Thoracic  Vertebra  of  Horse,  Posterior  View. 


brae,  and  behind  a  cavity  somewhat  deeper  than  any  other  thoracic  vertebra.     Two 
large  costal  facets  are  found  on  either  side,  and  a  well-marked  spine  ventrallj". 


Fir.,  l.'i. — T,\sT  Three  THORArir  ^■ERTEBR.E  of  Horse,  [.eft  \'iew. 

1,  Body;  2,  2,  facets  for  head  of  rib;   S,  facet  for  tubercle  of  rib;   4,  J/ ,  articular  processes;   5,  intervertebral  foramen; 

6,  mammillary  process;    7,  spinous  process. 

The  arch  is  large  and  strong,  and  has  large  notches.  The  articular  processes  are 
much  larger  than  those  of  other  thoracic  vertebrae,  and  resemble  a  good  deal  those 
of  the  seventh  cervical.     The  transverse  processes  are  short  and  thick,  and  each 


THE    LUMBAR   VERTEBRA  39 

has  on  its  ventral  aspect  a  large  concave  facet  for  articulation  with  the  tubercle  of 
the  first  rib.  The  spinous  process  is  curved  backward  and  tapers  to  a  point.  Its 
length  is  usually  about  three  or  four  inches  (ca.  8  to  10  cm.).  This  vertebra  may  be 
mistaken  at  first  glance  for  the  last  cervical,  but  is  promptly  identified  by  the  three 
costal  facets  on  each  side  and  the  length  of  the  spine. 

The  last  thoracic  vertebra  is  distinguished  by  the  absence  of  the  posterior  pair 
of  costal  facets,  and  the  confluence  of  the  anterior  pair  with  those  on  the  transverse 
processes. 

The  serial  position  of  others  may  be  determined  at  least  approximately  by  the 
following  data:  (1)  The  bodies  graduallj^  diminish  in  length  and  width  to  the 
middle  of  the  region  and  then  increase  slightly.  Their  costal  facets  become  smaller 
and  less  concave  from  first  to  last.  The  ventral  crest  is  distinct  on  three  or  four 
vertebrae  at  either  end  of  the  region.  (2)  The  transverse  processes  diminish  in 
size  and  are  placed  lower  down  as  they  are  traced  backward.  Their  costal  facets 
become  smaller  and  lower  in  position;  on  the  last  (and  sometimes  on  its  predecessor 
also)  it  fuses  with  the  costal  facet  of  the  body.  The  upper  non-articular  part  of 
the  process  gradually  becomes  more  sharply  defined,  and  in  the  last  four  or  five 
forms  a  distinct  mammillary  process.  (3)  The  spinous  processes  increase  in  length 
to  the  third  and  fourth,  and  then  gradually  diminish  to  the  fifteenth,  beyond  which 
they  have  about  the  same  length.  The  backward  inclination  is  most  pronounced 
in  the  second,  the  sixteenth  is  vertical,  and  the  last  two  are  directed  a  little  forward. 
The  longest  spines  {i.  e.,  those  of  the  withers)  are  the  thickest  and  have  expanded 
summits  which  remain  more  or  less  cartilaginous;  the  others  are  more  plate-like, 
and  are  surmounted  by  a  thick  lip.  The  second  spine  is  more  than  twice  as  large 
as  the  first.  The  summits  of  the  fourth  and  fifth  usually  form  the  highest  point 
of  the  withers. 

Development. — There  are  six  or  seven  centers  of  ossification,  three  for  the 
body,  two  for  the  arch,  and  one  for  the  spinous  process;  some  of  the  latter  have  an 
additional  center  for  the  summit. 


THE  LUMBAR  VERTEBRJE 

The  lumbar  vertebrae  (Vertebrae  lumbales)  are  usually  six  in  number  in  the 
horse.     They  are  characterized  by  the  size  and  form  of  their  transverse  processes. 

The  bodies  of  the  first  three  are  semi-elliptical  on  cross-section,  and  present  a 
distinct  ventral  crest.  From  the  fourth  backward  they  become  wider  and  flatter 
and  the  ventral  crest  subsides. 

The  arches  of  the  first  three  are  about  equal  in  size  and  similar  to  that  of  the 
last  thoracic;  behind  this  they  increase  in  breadth  and  height.  The  posterior 
notches  are  much  deeper  than  the  anterior  ones. 

The  anterior  articular  processes  are  fused  with  the  mammillary  processes,  and 
present  dorsally  concave  surfaces  for  articulation  with  the  posterior  pair  of  the 
preceding  vertebra.  The  posterior  articular  processes  project  distinctly  from  the 
arch  at  the  base  of  the  spinous  process,  and  have  ventrally  convex  articular  surfaces, 
which  fit  into  the  concave  surfaces  of  the  anterior  pair  of  the  next  vertebra. 

The  transverse  processes  are  elongated  plates,  flattened  dorso- ventrally,  which 
project  outward  and  usually  curve  slightly  downward;  their  length  increases  to 
the  third  or  fourth,  and  then  diminishes  to  the  last,  which  is  the  shortest.  The 
first  one  or  two  usually  curve  somewhat  backward,  the  last  two  decidedly  forward. 
Those  of  the  fifth  have  an  oval  concave  facet  on  the  medial  part  of  the  posterior 
border  for  articulation  with  the  sixth  process;  the  latter  has  a  corresponding  con- 
vex facet  on  the  anterior  border,  and  a  larger  concave  surface  on  the  posterior  border 
for  articulation  with  the  wing  of  the  sacrum.  Sometimes  the  fifth  process  has  a 
small  surface  for  articulation  with  the  fourth.     The  medial  part  of  the  sixth  process 


40 


THE    SKELETON    OF   THE    HORSE 


is  tliick,  the  lateral  part  thinner,  narrower,  and  curved  forward.  The  medial  part 
of  the  fifth  is  also  somewhat  thickened.  Medial  to  the  articular  surfaces  the  edges 
of  the  transverse  processes  are  cut  into  by  notches,  which  form  foramina  by  apposi- 
tion with  each  other  and  the  sacrum. 

The  spinous  processes   resemble  those  of  the  last  two   thoracic   vertebrae. 


Spinous  process 

Mammilhinj  process 
Articular  process 


\r  f  ■}  ■   Transverse  process 


Ventral  spine 
Fig.  16. — Second  Lumbar  Vektebra  of  Horse;  Posterior  View. 


They  are  usually  about  equal  in  height,  but  minor  differences  are  common,  and  the 
width  diminishes  in  the  last  three. 

Development. — This  is  similar  to  that  of  the  thoracic  vertebrae.  The  extremi- 
ties of  the  transverse  processes  remain  cartilaginous  for  some  time  after  ossification 
is  otherwise  complete. 

The  transverse  processes  of  this  region  are  considered  equivalent  to  the  proper  transverse 
process  +  the  costal  element,  and  hence  the  distinctive  term  processus  lateralis  (s.  costarius) 


Spinous  process 

Vertebral  foramen 
>  Articular  processes 


Transverse  process 


Notch 


Body 


Articular  surface  for 
wing  of  sacrum 
-Last  Lumbar  Vertebra  op  Horse;  Posterior  View. 


has  been  proposed.  The  occurrence  of  a  rib  in  connection  with  the  transverse  process  of  the  first 
lumbar  vertebra  is  common.  Reduction  of  the  number  to  five  has  been  observed  frequently,  and 
may  or  may  not  be  compensated  by  an  additional  thoracic  vertebra.  Very  few  cases  are  recorded 
of  seven  lumbar  vertebra^ — especially  with  the  normal  thoracic  number.  An  anomalous  vertebra 
with  mixed  thoracic  and  lumbar  characters  sometimes  occurs  at  the  junction  of  the  two  regions. 


THE    SACRUM 


41 


THE  SACRUM 

The  sacrum  (Os  sacrum)  is  formed  by  the  fusion  of  five  vertebrae,  and  is  con- 
veniently described  as  a  single  bone.  It  is  triangular  in  form  and  is  wedged  in 
between  the  ilia,  with  which  it  articulates  very  firmly  on  each  side.  Its  long  axis 
is  gently  curved  and  slightly  oblique,  so  that  the  posterior  end  is  a  little  higher 
than  the  anterior.     It  presents  two  surfaces,  two  borders,  a  base,  and  an  apex. 

The  dorsal  surface  (Facies  dorsalis)  presents  centrally  the  five  sacral  spines 
(Processus  spinosi),  which  are  directed  upward  and  backward,  and  have  (with  the 
exception  of  the  first)  tuberous  summits  which  are  sometimes  bifid. 


Wing 


Transverse  process 


Fig.  18. — Sacrum  of  Horse;  Dorso-lateral  View. 
I-V,  Spinous  processes;  I-4,  dorsal  sacral  foramina;  5,  0',  articular  processes;  6,  surfaces  of  wings  for  articulation 
with    transverse    processes    of    last    lumbar  vertebra;    7,  body  of  first  sacral  vertebra.     Arrows  point  into  sacral 
canal. 


The  first  spine  is  relatively  thin  and  narrow,  and  is  not  so  high  as  the  sacral  angle  of  the 
ilium.  The  second  is  the  longest  and  highest,  and  the  length  and  height  diminish  to  the  last. 
The  bases  of  the  spines  are  often  fused  in  old  subjects. 

On  either  side  of  the  spines  there  is  a  groove,  in  which  are  the  four  dorsal  sacral 
foramina  (Foramina  sacralia  dorsalia);  the  dorsal  branches  of  the  sacral  nerves 
emerge  through  them. 

The  pelvic  surface  (Facies  pelvina)  is  concave  in  its  length,  wide  in  front, 
narrow  behind.  The  curvature  is  variable  and  is  more  pronounced  in  the  mare 
than  in  the  stallion.  It  is  marked  by  four  more  or  less  distinct  transverse  lines 
(Lineae  transversse) ,  which  indicate  the  demarcation  of  the  bodies  of  the  vertebrae. 
At  the  ends  of  these  lines  are  the  ventral  sacral  foramuia  (Foramina  sacralia  ven- 


42 


THE    SKELETON    OF   THE   HORSE 


tralia),  which  are  larger  than  the  dorsal  series  and  diminish  in  size  from  first  to 
last;  they  transmit  the  ventral  divisions  of  the  sacral  nerves. 

The  dorsal  and  ventral  foramina  communicate  with  the  sacral  canal  and  are 
together  equivalent  to  the  usual  intervertebral  foramina. 

The  lateral  borders  are  rough,  thick  in  front,  thin  behind. 

The  base  (Basis  ossis  sacri)  is  directed  forward,  and  is  relatively  very  wide. 
It  presents  centrally  the  body  of  the  first  sacral  segment,  which  is  wide  transversely, 
flattened  dorso-ventrally,  and  has  a  rounded  surface  which  articulates  with  the 
last  lumbar  vertebra  through  the  medium  of  an  intervertebral  fibro-cartilage. 
The  ventral  margin  projects  slightly,  forming  the  promontory  (Promontorium) .     On 


Fig.  19. — Sacrum  of  Horse;  Ventral  View. 
J- F,  Bodies  of  original  five  vertebrse,  marked  off    by  transverse  lines;   /-4,  ventral  sacral  foramina;  5,  articular 
surface  of  body  of  first  vertebra;  6,  6,  notches;   7,  7,  surfaces  of  wings  for  articulation  with  transverse  processes  of  last 
lumbar  vertebra;   S,  S,  wings;    9,  auricular  surface;   10,  lateral  border;   11,  transverse  process;    12,  posterior  orifice 
of  sacral  canal;   13,  last  spinous  process. 


either  side  of  the  body  there  is  a  smooth  notch,  which,  with  one  on  the  last  lumbar 
vertebra,  forms  a  large  foramen  for  the  passage  of  the  ventral  branch  of  the  last 
lumbar  nerve.  Above  the  body  is  the  entrance  to  the  sacral  canal,  flanked  by  a 
pair  of  articular  processes,  which  project  upward  and  forward  from  the  arch,  and 
have  concave  surfaces  medially  for  articulation  with  those  of  the  last  Imnbar 
vertebra.  Lateral  to  each  of  these  is  a  smooth  notch  which  is  converted  into  a 
foramen  by  apposition  with  the  last  lumbar  vertebra.  The  lateral  parts  of  the  base, 
the  alae  or  wings  (Alae  sacrales),  are  strong  prismatic  masses  with  pointed  ends. 
Each  has  in  front  a  large,  oval,  slightly  convex  surface  for  articulation  with  the 
transverse  process  of  the  last  lumbar  vertebra.  Posteriorly  there  is  an  elongated 
oval  area  which  faces  dorso-laterally;  this  is  the  auricular  surface  (Facies  auricu- 


THE  COCCYGEAL  VERTEBRA  43 

laris),  which  articulates  with  the  ihum;  it  is  slightly  concave  in  its  length,  and 
somewhat  rough  and  irregular.  The  rest  of  the  dorsal  surface  of  the  wing  is  rough- 
ened for  ligamentous  attachment,  while  the  ventral  surface  is  smooth. 

The  apex  (Apex  ossis  sacri)  is  the  posterior  aspect  of  the  last  sacral  vertebra 
and  is  quite  small.  It  presents  the  elliptical  flattened  surface  of  the  body,  above 
which  is  the  triangular  posterior  opening  of  the  sacral  canal,  surmounted  by  the 
last  sacral  spine.  There  is  a  pair  of  narrow  notches  between  the  arch  and  body, 
above  which  rudiments  of  articular  processes  may  occur. 

The  name  sacral  canal  (Canalis  sacralis)  is  applied  to  that  part  of  the  vertebral 
canal  which  traverses  the  sacrum.  Its  anterior  part  is  large  and  has  the  form  of 
a  triangle  with  the  angles  rounded  off;  its  width  is  nearly  tAvice  its  height.  Traced 
backward  it  is  seen  to  diminish  in  size  rapidly,  and  the  posterior  opening  is  small 
and  triangular. 

The  term  lateral  part  (Pars  lateralis)  designates  the  portion  lateral  to  the 
foramina,  which  results  from  the  fusion  of  the  transverse  processes. 

Development. — The  several  sacral  vertebrae  ossify  in  the  typical  manner. 
Separate  centers  for  costal  elements  in  the  lateral  parts  have  not  yet  been  found  in 
the  domesticated  animals.  Fusion  begins  in  front,  and  is  usually  not  complete 
till  adult  age.i  The  lateral  parts  unite  before  the  bodies.  It  is  rather  curious 
that  the  epiphyseal  plates  of  adjacent  segments  unite  with  each  other  before  they 
fuse  with  the  main  portion  of  the  bodies. 


THE  COCCYGEAL  VERTEBRA 

The  coccygeal  vertebrae  (Vertebrae  coccygeae)  vary  considerably  in  number,  but 
eighteen  may  be  taken  as  an  average.  From  first  to  last  they  become  reduced 
in  size  and,  with  the  exception  of  a  few  at  the  beginning  of  the  series,  consist  of 


] 'crtebral  foramen  Vertebral  foramen 

Arch 
A  rch 

Transverse  process 


Spinous  process  Spinous  process 

Vertebra 

Transverse  proc- 


Groove 
Body  Body 

Fig.    20. — First   CoccygEAL   Vertebra  of    Horse;  Fig.  21. — Second  Coccygeal  Vertebra  of    Horse; 

View.  Posterior  View. 


Leader  to  arch  points  to  rudimentary  articular 

bodies  only.  The  first  three  have  bodies  which  are  somewhat  flattened  dorso- 
ventrally,  constricted  in  the  middle,  and  have  at  the  ends  convex,  elliptical,  artic- 
ular surfaces.  The  ventral  surface  has  a  median  groove  (Sulcus  vasculosus)  for 
the  coccygeal  artery.  The  arch  is  small  and  triangular;  it  is  formed  of  two  flat 
plates  which  are  prolonged  to  form  a  short  spinous  process  with  a  thickened  and 
often  double  summit.  The  anterior  notches  are  absent.  Functional  articular 
processes  are  not  present,  but  small  rudiments  of  the  anterior  pair  commonly  occur. 
The  transverse  processes  are  relatively  large  plates  which  project  horizontally 
outward.  Further  back  the  arch  becomes  incomplete  dorsally,  and  soon  disap- 
pears; the  transverse  processes  gradually  fade  out,  and  the  vertebrae  are  reduced 
to  cylindrical  rods  of  diminishing  size.     The  last  one  has  a  pointed  end. 

^  It  is  not  rare  to  find  fusion  of  some  of  the  bodies  incomplete  even  in  adult  subjects. 


44 


THE    SKELETON    OF   THE    HORSE 


Variations. — The  number  is  said  by  good  observers  to  vary  between  fourteen  and  twenty- 
one.  In  old  age  the  first  is  often  fused  with  the  sacrum,  and  sometimes  with  the  second.  The 
arch  of  the  third  may  be  open. 


THE  VERTEBRAL  COLUMN  AS  A  WHOLE 

In  the  mid-dorsal  line  is  the  series  of  spinous  processes,  which  are  low  ridges 
in  the  cervical  region  with  the  exception  of  the  second  and  seventh,  reach  their 
maximum  height  at  the  fourth  and  fifth  thoracic  vertebrae,  and  diminish  to  the 
fifteenth  or  sixteenth  thoracic.  Behind  this  they  are  about  equal  in  height  as  far 
as  the  last  lumbar  and  first  sacral,  which  are  somewhat  lower.  The  second  sacral 
spine  is  about  as  high  as  the  middle  luml^ar;  behind  this  they  diminish  rather 
rapidly  in  height  and  fade  out  about  the  third  coccygeal.  Their  inclination  back- 
ward is  most  decided  at  the  second  thoracic  and  diminishes  from  the  sixth  or  seventh 
to  the  sixteenth  thoracic,  which  is  vertical  and  is  termed  the  anticlinal  or  dia- 
phragmatic vertebra.  Behind  this  they  are  inclined  a  little  forward  until  the 
sacrum  is  reached;  here  there  is  an  abrupt  change  to  the  backward  inclination,  so 
that  a  considerable  interspinous  angle  is  formed. 

On  either  side  of  the  spinous  processes  is  a  vertebral  groove  which  contains  the 
deep  muscles  of  the  spine.  The  floor  of  the  groove  is  formed  by  the  arches  and 
articular  processes.     It  is  wide  in  the  neck  and  narrows  progressively  in  the  back. 

Viewed  from  the  side,  the  column  presents  a  series  of  curves.  When  the  head 
and  neck  are  in  the  ordinary  neutral  position,  the  anterior  part  of  the  cervical  spine 
forms  a  gentle  curve,  concave  ventrally.  The  posterior  cervical  and  first  thoracic 
vertebrae  form  a  more  pronounced  curve  in  the  opposite  direction.  At  the  junction 
of  the  cervical  and  thoracic  regions  there  is  a  marked  change  of  direction,  forming  a 
ventral  projection  or  angle.  At  the  second  thoracic  vertebra  a  gentle  curve,  con- 
cave ventrally,  begins.  This  is  continued  to  the  lumbo-sacral  junction,  where 
there  is  a  change  of  direction,  and  hence  a  promontory.  The  sacrum  has  a  variable, 
but  never  very  pronounced,  ventral  concave  curvature,  which  is  continued  in  a 
much  accentuated  form  in  the  coccygeal  region.  It  should  be  noted  that  a  line 
through  the  summits  of  the  spines  does  not  correspond  to  these  curves  formed  by 
the  bodies. 

The  vertebral  canal  corresponds  in  its  curvature  to  that  of  the  bodies.  Its 
caliber  varies  greatly  at  different  points.  The  greatest  diameter  is  in  the  atlas, 
where  it  contains  the  dens  of  the  axis  in  addition  to  the  spinal  cord,  and  provision 
must  be  made  for  extensive  movement.  It  is  very  much  smaller  in  the  axis.  It 
widens  considerably  at  the  junction  of  the  cervical  and  thoracic  regions  to  accom- 
modate the  cervical  enlargement  of  the  spinal  cord.  Beyond  this  it  diminishes, 
and  is  smaller  in  the  middle  of  the  back  than  at  any  preceding  point ;  this  is  corre- 
lated with  the  small  size  of  the  spinal  cord  and  the  very  limited  movement  of  the 
spine  here.  Beyond  the  middle  of  the  lumbar  region  it  again  enlarges  considerably 
to  contain  the  lumbar  enlargement  of  the  spinal  cord.  The  caliber  diminishes  very 
rapidly  from  the  second  sacral  segment  backward,  and  the  canal  ceases  to  be  com- 
plete at  the  fourth  coccygeal  vertebra. 

The  transverse  and  vertical  diameters  of  the  vertebral  canal  at  various  points  are  given 
in  the  annexed  table.  The  measurements  were  made  on  a  horse  of  medium  size;  they  represent 
the  maximum  width  and  height  in  the  middle  of  the  vertebra  and  are  expressed  in  centimeters. 


Vertebra 

CI 

C2 

C4 

C7 

TIO 

L3 

L6 

SI 

So 

5.2 
4.2 

2.6 
2.5 

2.6 
2.1 

3.5 
2.5 

2.3 
1.7 

2.4 
l.S 

4.0 
2.5 

4.0 
2.1 

1.8 

Vertical 

1.5 

The  articular  processes  are  very  large  and  wide  apart  in  the  neck,  greatly 


THE   RIBS  45 

reduced  and  much  closer  together  in  the  back,  larger  and  interlocking  in  the  lumbar 
region. 

The  transverse  processes  are  large  and  outstanding  in  the  neck,  where  they 
form  the  lateral  boundary  of  a  ventral  groove  occupied  by  the  longus  colli  muscle. 
In  the  back  they  are  short  and  stout,  and  are  characterized  by  the  facets  for  the 
tubercles  of  the  ribs.  On  the  first  thoracic  vertebra  this  facet  is  large,  deeply  con- 
cave, and  situated  almost  directly  outward  from  the  cavity  for  the  head  of  the  rib; 
traced  backward  it  becomes  smaller  and  flatter,  and  gradually  comes  to  lie  behind 
the  cavity  for  the  head  of  the  rib,  with  which  it  is  fused  on  the  last  and  often  also  on 
the  next  to  the  last  thoracic  vertebra.  The  processes  in  the  lumbar  region  have  a 
characteristic  elongated  plate-like  form.  In  the  sacral  region  they  are  fused  to 
form  the  wings  and  lateral  parts  of  the  sacrum.  In  the  coccygeal  region  they  are 
at  first  of  considerable  size  relatively,  but  undergo  rapid  reduction,  and  disappear 
at  the  fifth  or  sixth  vertebra. 

The  cavities  for  the  heads  of  the  ribs  diminish  progressively  in  size  and  depth 
from  first  to  last. 

The  mammillary  processes  are  usually  distinct  on  the  fourteenth  to  the  seven- 
teenth thoracic  vertebrae.  In  front  of  these  they  blend  with  the  transverse,  behind 
with  the  anterior  articular,  processes. 

The  length  of  the  vertebral  column  (including  the  intervertebral  fibro-cartilages)  in  a  horse 
of  medium  size  is  about  nine  feet  (ca.  2.7  meters).  The  relative  lengths  of  the  various  regions  ap- 
pear to  vary  most  in  the  neck  and  back.  The  following  average  lengths  of  the  several  regions 
were  obtained  by  measurement  of  several  subjects:  Cervical,  70  cm.;  thoracic,  86  cm.;  lumbar, 
34  cm.;  sacral,  20  cm.;  coccygeal,  60  cm.  The  percentage  values  are  approximately  26,  32,  12.5 
7.5,  22. 


The  Ribs 

There  are  usually  eighteen  pairs  of  ribs  in  the  horse,  but  a  nineteenth  rib  on 
one  side  or  both  is  not  at  all  rare.  Eight  are  sternal  ribs,  the  remainder  asternal. 
Ribs  from  different  parts  of  the  series  vary  much  in  length,  curvature,  and  other 
characters.  We  will  therefore  consider  as  a  type  a  rib  from  the  middle  of  the  series 
first,  and  afterward  note  the  chief  serial  differences;  such  a  rib  has  the  following 
characters : 

The  shaft  or  body  (Corpus  costae)  is  elongated,  relatively  very  narrow,  and 
strongly  curved;  the  curvature  is  most  pronounced  in  the  dorsal  third,  and  the 
ventral  part  is  twisted  and  inclined  inward,  so  that  when  a  rib  is  laid  with  its  lateral 
surface  on  the  table,  the  sternal  end  is  raised.  The  lateral  surface  is  convex  in 
its  length  and  also  transversely;  its  anterior  part  is,  however,  grooved  longitudin- 
ally. A  distinct  angle,  i.  e.,  a  point  at  which  the  curve  of  the  rib  changes  rather 
suddenly,  as  in  man,  can  scarcely  be  said  to  exist  in  the  horse.  The  term  is  some- 
times applied,  however,  to  a  corresponding  rough  elevation  which  gives  attachment 
to  the  longissimus  muscle.  The  medial  surface  is  smooth,  concave  in  its  length, 
and  rounded  from  side  to  side;  the  costal  groove  (Sulcus  costse),  situated  posteriorly, 
is  very  distinct  above  and  fades  out  about  the  middle;  it  contains  the  intercostal 
vein.     The  anterior  border  is  concave,  the  posterior  convex. 

The  vertebral  extremity  (Extremitas  vertebralis)  consists  of  the  head,  neck, 
and  tubercle.  The  head  (Capitulum  costse)  has  an  articular  surface  (Facies 
articularis  capituli  costse)  which  is  composed  of  two  convex  facets,  anterior  and 
posterior,  separated  by  a  groove  (Sulcus  capituli)  for  the  attachment  of  the  con- 
jugal ligament.  It  articulates  with  the  cavity  formed  by  facets  on  the  bodies  of 
two  adjacent  thoracic  vertebrae  and  the  intervertebral  fibro-cartilage.  The  neck 
(Collum  costse)  is  roughened  above  and  in  front.  The  tubercle  (Tuberculum  costse) 
is  placed  above  and  behind  the  junction  of  neck  and  shaft;   it  has  an  oval  surface 


46 


THE    SKELETON    OF   THE    HORSE 


(Facies  articularis  tuberculi  costae)  for  articulation  with  the  transverse  process  of 
the  corresponding  thoracic  vertebra. 

The  sternal  extremity  (Extremitas  sternalis)  is  slightly  enlarged,  and  is  united 
with  the  costal  cartilage. 

The  first  rib  is  easily  distinguished.  It  is  shortest  and  the  shaft  widens  greatly 
toward  the  sternal  end.     At  the  lower  part  of  the  anterior  border  there  is  a  smooth. 


Tubercle 


^    Costal  groove 


Head    Neck    Tubercle 


Groove 


Head 


Anterior  border 


Anterior  border - 


Sternal  extremity 
Fig.  22. — Left  Eighth  Rib  of  Horse;  Lat- 


Costo- 
chondral 
junction 


Sternal  extremity  of  costal  cartilage 

Fig.    23. — Right    Eighth   Rib  and   Costal  Cartilage  of 
Horse;  Medial  View. 


impression  where  the  brachial  vein  curves  around  it;  above  this  there  is  commonly 
a  small  tubercle  (Tuberculum  scaleni)  which  indicates  the  lower  limit  of  the  in- 
sertion of  the  scalenus  muscle.  The  costal  groove  is  absent.  The  head  is  large  and 
has  two  facets  of  unecjual  extent,  which  meet  at  an  acute  angle  in  front ;  the  smaller 
one  faces  forward  antl  articulates  with  the  last  cervical  vertebra;  the  larger  one  is 
directed  medially  and  articulates  with  the  first  thoracic  vertebra.  The  neck  is 
thick  and  very  short.     The  tubercle  is  larger  than  that  of  any  other  rib  and  has  an 


THE    COSTAL   CARTILAGES 


47 


Tubercle 


extensive  articular  surface  which  is  convex  in  its  length.     The  sternal  end  is  larger 
than  that  of  any  other  rib;  it  is  thick  and  very  wide,  and  is  turned  a  little  forward. 

The  last  rib  is  the  most  slender  and  regularly  curved.  It  is  usually  but  little 
longer  than  the  second.  The  facet  on  the  tubercle  is  confluent  with  that  of  the  head. 
(This  feature,  however,  is  common  on  the  seventeenth  also,  and  may  occur  on  the 
sixteenth.) 

The  serial  position  of  the  other  ribs  may  be  determined  approximately  by  the  fol- 
lowing considerations :  The  length  increases  from  the  first  to  the  tenth  and  eleventh 
and  then  diminishes.  The  width  increases  somewhat  to  the  sixth  and  then  diminishes. 
The  anterior  border  is  thin  and  sharp  from  the 
second  to  the  eighth,  and  behind  this  becomes  thick 
and  rounded.  The  groove  of  the  lateral  surface  is 
distinct  on  the  fourth  to  the  eighth  inclusive.  The 
curvature  increases  in  degree  rapidly  from  the  second 
to  the  seventh,  remains  a])Out  the  same  to  the  six- 
teenth, and  then  decreases  very  noticeably.  In  re- 
gard to  dorso-ventral  direction,  the  first  rib  inclines 
a  little  forward,  the  second  is  about  vertical,  while 
behind  this  they  slope  l)ackward  in  increasing  de- 
gree, so  that  a  transverse  plane  tangent  to  the  ventral 
ends  of  the  last  pair  cuts  the  third  lumbar  vertebra. 
The  head  and  tubercle  diminish  in  size  from  first  to 
last.  Their  relative  positions  change,  in  that  the 
tubercle  of  the  first  rib  is  almost  directly  lateral  to 
the  head,  while  further  back  it  gradually  comes  to 
lie  behind  it.  The  neck  is  longest  on  the  longest 
ribs,  and  is  absent  on  the  last  two  or  three.  A 
costo-transverse  foramen  (Foramen  costo-transver- 
sarium)  is  formed  between  the  neck  and  the  trans- 
verse process. 

Development. — The  ribs  ossify  in  cartilage  from 
three  centers,  one  each  for  the  shaft,  head,  and 
tul)ercle;  the  third  center  is  absent  in  some  of  the 
posterior  ribs. 


Cartilage 


-Left  First  Rib  of  Horse; 
Medial  View. 


Variations. — A  nineteenth  rib  on  one  side  or  both  is  not 
at  all  rare.     It  is  usually  imperfectly  developed  and  quite  vari-       j-j^   24. 
able.     In  many  cases  it  is  a  mere  strip  of  cartilage  connected 
by  ligament  with  the  first  lumbar  transverse  process;  in  other 
cases  it  is  well  developed,  and  may  be  fused  with  the  process; 

in  others  again  it  is  connected  with  a  vertebra  which  may  be  thoracic  or  lumbar  or  ambiguous 
in  character.  It  is  commonly  floating,  but  may  be  attached  to  the  eighteenth  costal  cartilage. 
Reduction  in  number  is  uncommon.  In  rare  cases  the  first  rib  is  imperfectly  developed  and  does 
not  reach  to  the  sternum.     Partial  fusion  of  adjacent  ribs  and  other  anomalies  occur. 


THE  COSTAL  CARTILAGES 

The  first  costal  cartilage  is  an  inch  or  more  (2.5  to  3  cm.)  in  length.  The 
dorsal  end  is  very  wide  and  thick.  The  sternal  end  is  small.  The  two  articulate 
with  each  other  as  well  as  with  the  sternum.  The  cartilages  of  the  other  sternal 
ribs  increase  progressively  in  length  and  become  more  rounded.  The  sternal  end 
is  enlarged  and  has  an  elliptical  convex  facet  for  articulation  with  the  sternum. 
The  cartilages  of  the  asternal  ribs  are  long,  slender,  and  pointed.  The  ninth  is 
very  firmly  attached  to  the  eighth;  it  and  the  next  two  are  the  longest  and  behind 
this  they  diminish  progressively  in  size.  The  cartilages  of  the  asternal  ribs  overlap 
and  are  attached  to  each  other  by  elastic  tissue,  forming  the  costal  arch  (Arcus 


48 


THE    SKELETON    OF   THE    HORSE 


costarum).  Except  in  the  case  of  the  first,  the  cartilage  does  not  continue  the 
direction  of  the  rib,  but  forms  with  the  latter  an  angle  which  is  open  in  front,  and 
increases  from  second  to  last.  More  or  less  extensive  ossification  is  to  be  regarded 
as  a  normal  occurrence,  especially  in  the  cartilages  of  the  sternal  ribs. 


Costal 
carlilages"^^^^ 


Cariniform 
cartilage 


Ribs 


The  Sternum 

The  sternum  of  the  horse  is  shaped  somewhat  like  a  canoe;   it  is  compressed 

laterally,  except  in  its  posterior  part,  which  is  flattened  dorso-ventrally.     It  is 

inclined  obliquely  so  that  the  posterior  end 
is  about  six  to  eight  inches  (15  to  20  cm.) 
lower  than  the  anterior. 

The  dorsal  surface  (Facies  dorsalis)  has 
the  form  of  a  very  narrow  isosceles  triangle 
with  the  apex  in  front.  It  is  concave  longi- 
tudinally, flattened  transversely. 

The  lateral  surfaces  (Facies  laterales) 
are  convex  above,  slightly  concave  below,  and 
diminish  in  extent  behind.  Each  presents  on 
its  upper  part  seven  costal  cavities  (Foveas 
costales),  with  which  the  sternal  ends  of  the 
second  to  the  eighth  costal  cartilages  inclu- 
sive articulate.  These  cavities  are  situated 
in  series  at  the  intersternebral  junctions. 
The  first  four  are  elliptical  in  outline  with 
the  long  diameter  vertical,  and  are  sepa- 
rated by  considerable  regular  intervals. 
The  others  are  progressively  smaller,  more 
circular,    and   closer   together.      The   area 

below  these  cavities  gives  attachment  to  the  pectoral  muscles. 

The  dorso-lateral  borders  separate  the  dorsal  and  lateral  surfaces.     They  give 

attachment  to  the  lateral  branches  of  the  sternal  ligament. 

The  ventral  border  forms  the  prominent  keel-like  crest  of  the  sternum  (Crista 

sterni)  which  may  be  felt  in  the  living  animal;   it  fades  out  behind. 


Xiphoid  cartilage 


Fig.  25. — Sternum  and  Costal  Cartilages  of 
Horse;  Ventral  View.  (After  Ellenberger- 
Baum,  Anat.  f.  Kiinstler.) 


yi/rarinJfor"l 


r    a.   I 

Fig.  26. — Sternum  of  Horse;  Lateral  View. 
The  sternebrae  are  designated  by  Roman  numerals  and  the  costal  facets  by  ordinary  figu 


The  anterior  extremity  or  manubrium  sterni^  can  be  distinctly  felt  in  the 
central  furrow  of  the  breast.  It  consists  largely  of  a  lal;erally  compressed  cartil- 
aginous prolongation,  commonly  called  the  cariniform  cartilage.  Its  lateral  sur- 
faces are  flat  and  furnish  attachment  to  muscles  of  the  breast  and  neck.     The 

^  The  manubrium  sterni  of  man  is  equivalent,  strictly  speaking,  to  the  cariniform  cartilage 
-h  the  first  osseous  segment  of  the  horse. 


THE  THORAX — THE  OCCIPITAL  BONE 


49 


ventral  border  is  rounded,  and  is  continued  backward  on  the  body  of  the  bone. 
The  dorsal  border  is  concave  and  has  an  articular  cavity  for  the  first  pair  of  costal 
cartilages. 

The  posterior  extremity  is  formed  by  the  xiphoid  cartilage  (Processus  xiphoideus). 
This  is  a  thin  plate,  connected  in  front  with  the  last  bony  segment  by  a  relatively 
thick,  narrow  neck,  and  expanding  in  nearly  circular  form  behind  and  laterally. 
Its  dorsal  surface  is  concave,  and  gives  attachment  to  the  diaphragm.  The  ventral 
surface  is  convex  and  furnishes  attachment  to  the  transversus  abdominis  and  the 
linea  alba.     The  free  margin  is  very  thin. 

Development. — At  birth  the  sternum  of  the  horse  consists  of  seven  bony  seg- 
ments termed  sternebrse,  which  are  united  by  in- 
tersternebral  cartilages.  The  last  two  sternebra} 
fuse  in  the  second  month,  but  the  others  do  not 
usually  unite  completely  even  in  old  age.  The 
sternebrse  consist  of  very  vascular  spongy  bone 
covered  by  a  very  thin  layer  of  compact  sub- 
stance. The  adult  sternum  thus  consists  to  a  /v-^IP^  Jil^  ^- First 
very  considerable  extent  of  persisting  cartilage,  w  .,«  ^^"'^fc.^vl      thoracic 

viz.,  the  intersternebral  cartilages,  the  ventral 
keel,  and  the  extremities;  in  old  age  these  under- 
go partial  ossification. 


THE  THORAX 


The  bony  thorax  of  the  horse  is  remarkably 
compressed  laterally  in  its  anterior  part,  but 
widens  greatly  behind.  The  anterior  aperture 
(Apertura  thoracis  cranialis)  is  oval  and  very 
narrow  below;  in  a  horse  of  medium  size  its 
greatest  width  is  about  4  inches  (10  cm.),  and  its 
height  7  to  8  inches  (ca.  18-20  cm.).  The  ventral 
wall  or  floor  is  about  16  inches  (40  cm.)  long,  and 
the  dorsal  wall  or  roof  about  38  to  40  inches 
(95-100  cm.)  long.  The  height  from  the  last  seg- 
ment of  the  sternum  to  the  seventh  or  eighth 
thoracic  vertebra  is  about  twice  that  of  the  anterior 
aperture;  this  is  due  to  the  obliquity  and  diver- 
gence of  the  roof  and  floor.  The  greatest  width  of 
the  posterior  aperture  is  about  20  to  24  inches 

(50-60  cm.).  The  intercostal  spaces  (Spatia  intercostalia)  increase  in  width  from 
the  first  to  the  seventh  or  eighth,  and  then  diminish.  Their  average  width  is 
about  I'j/i  to  13^  inches  (3-3.5  cm.). 


vertebra 


First  rib 


Cariniform 
cartilage  of 
sternum 


Fig.  27. — Anterior  Aperture  of  Tho- 
rax OF  Horse.  (After  Schmaltz,  Atlas 
d.  Anat.  d.  Pferdes.) 


The  Skull 

(A)  BONES  OF  THE  CRANroM 
The  bones  of  the  cranium  (Ossa  cranii)  are  the  occipital,  sphenoid,  ethmoid, 
interparietal,  parietal,  frontal,  and  temporal.     The  first  three  are  single,  the  others 
paired. 

The  Occipital  Bone 

The  occipital  bone  (Os  occipitale)  is  situated  at  the  posterior  part  of  the  era- 
oium,  of  which  it  forms  the  posterior  wall  and  part  of  the  ventral  wall  or  base.^ 
1  The  long  axis  of  the  skull  is  considered  to  be  horizontal  in  these  descriptions. 


50 


THE    SKELETON    OF   THE    HORSE 


Its  lower  part  is  perforated  centrally  by  a  large,  almost  circular  opening,  the 
foramen  magnum  (Foramen  occipitale  magnum),  at  which  the  cranial  cavity  and 
vertebral  canal  join.  The  foramen  is  bounded  laterally  and  dorsally  by  the  lateral 
parts  of  the  bone,  and  ventrally  by  the  basilar  part.  Above  the  lateral  parts — 
but  not  entering  into  the  formation  of  the  foramen  magnum — is  the  squamous' part. 

The  lateral  parts  (Partes  laterales)^  bear  the  occipital  condyles  (C'ondyli  oc- 
cipitales),  which  articulate  with  the  atlas.  The  condyles  are  obliquely  placed, 
wide  apart  dorsally,  and  separated  ventrally  by  a  small  interval  (Incisura  inter- 
condyloidea).     The  articular  surface  is  curvecl  so  sharply  in  the  dorso- ventral 

Occipital     Parietal     Squamous  temporal 


Fig.  2S. — Skull  of  Horse,  Right  View. 
1,  Occipital  condyle;  2,  paramastoid  process;  3,  mastoid  process;  4>  posterior  process  of  squamous  temporal  bone; 
6,  external  acoustic  process;  6,  zygomatic  process  of  temporal  bone;  7,  postglenoid  process;  8,  glenoid  cavity  of  squamous 
temporal  bone;  9,  condyle  of  same;  10,  supraorbital  process  of  frontal  bone;  11,  temporal  part  of  frontal  bone;  12, 
orbital  part  of  frontal  bone;  /5,  fossa  sacci  lacrimalis;  74,  orbital  surface  of  lacrimal  bone;  75,  lacrimal  tubercle;  16, 
zygomatic  process  of  malar  bone;  77,  maxillary  tuberosity;  ZS,  facial  crest;  79,  infraorbital  foramen;  ^0,  naso-maxil- 
lary  notch;  21,  body  of  premaxilla;  21',  nasal  process  of  same;  22,  body  of  mandible;  23,  mental  foramen;  24,  25^ 
horizontal  and  vertical  parts  of  ramus  of  mandible;  26,  condyle  of  mandible;  27,  coronoid  process  of  mandible;  2S, 
angle  of  mandible;  29,  vascular  impression;  30,  interalveolar  margin;  31,  incisor  teeth;  32,  canine  teeth;  33,  hyoid 
bone  (great  cornu) . 


direction  as  to  form  a  blunt  ridge.  The  cranial  surface  is  concave  and  smooth. 
Lateral  to  the  condyle  is  the  paramastoid  process  (Processus  paramastoideus),^  a 
strong  plate  of  bone  which  projects  downward  and  backward;  its  lateral  surface  is 
convex  and  roughened  for  muscular  attachment ;  its  medial  surface  is  concave  from 
end  to  end.  Between  the  root  of  this  process  and  the  condyle  is  a  smooth  depres- 
sion, the  condyloid  fossa  (Fossa  condyloidea  ventralis) ;  in  this  is  the  h3rpoglossal 
foramen  (Foramen  hypoglossi),  which  transmits  the  nerve  of  like  name. 

The  basilar  part  (Pars  basilaris)^  is  a  strong,  somewhat  prismatic  bar,  which 

1  Also  known  as  the  exoccipitals.  ^  Also  known  as  the  styloid  or  jugular  process. 

'  Also  termed  the  basi-occipital  or  basilar  process. 


THE    OCCIPITAL    BONE 


51 


extends  forward  from  the  ventral  margin  of  the  foramen  magnum.  It  is  wide  and 
flattened  behind,  narrower  and  thicker  in  front.  The  ventral  surface  is  rounded. 
The  cranial  surface  is  concave  and  smooth ;  its  posterior  part  supports  the  medulla 
oblongata,  and  its  anterior  part  has  a  shallow  cavity  on  which  the  pons  rests.  The 
lateral  borders  are  thin  and  sharp,  and  form  the  medial  margin  of  the  foramen 
lacerum.  The  anterior  end  has,  in  the  young  subject,  a  semicircular,  flat,  pitted 
surface  which  is  attached  to  the  body  of  the  sphenoid  bone  by  a  layer  of  cartilage ; 
in  the  adult  there  is  complete  fusion.  On  the  ventral  aspect  of  the  junction  are  the 
basilar  tubercles  (Tubercula  basilaria)  for  the  attachment  of  the  ventral  straight 
muscles  of  the  head. 

The  squamous  part  (Squama  occipitalis)^  is  the  somewhat  quadrilateral  mass 


Fig.  20. — Occipital  Bone  of  Colt;  Front  View. 
1,  Depression  of  squamous  part  for  cort'bclluin;   2,  foramen  magnum;   3,  paramastoid  process;   4,  condyloid  fossa; 
a,  squamous  part;   6,  lateral  part;   c,  basilar  part;   rf,  junction  with  interparietal  bone;   e,  junction  with  parietal  bone; 
/,  junction  with  petro-mastoid  part  of  temporal  bone. 


situated  dorsal  to  the  lateral  parts,  from  which  it  remains  distinct  till  the  second 
year.  The  external  surface  is  crossed  by  a  very  prominent  ridge,  the  nuchal  crest 
(Crista  nuchalis) ;  the  middle  part  of  this  is  thick,  transverse  in  direction,  and  forms 
the  highest  point  of  the  skull  when  the  head  is  in  the  ordinary  position;  laterally  it 
becomes  thinner  and  runs  downward  and  forward  to  join  the  temporal  crest.-  The 
crest  divides  the  surface  into  two  very  unequal  parts;  the  small  dorsal  area  (Planum 
parietale)  presents  a  median  ridge  which  is  the  posterior  part  of  the  external  parietal 
crest  (Crista  sagittahs  externa) ;  the  large  area  ventral  to  the  crest  (Planum  nu- 
chale)  has  a  central  eminence,  the  external  occipital  protuberance,  on  which  the  funic- 
ular part  of  the  ligamentum  nuchte  is  attached.     The  internal  surface  is  concave 

^  Also  known  as  the  supraoccipital. 

^  The  nuchal  crest  of  this  description  is  equivalent  to  the  external  occipital  protuberance 
and  superior  nuchal  line  of  man;  it  has  been  commonly  termed  the  occipital  crest,  but  is  not  the 
equivalent  of  that  feature  of  the  human  skull.  A  curved  line  a  httle  lower  down,  which  is  con- 
tinued on  the  paramastoid  process,  represents  the  inferior  nuchal  line  of  man. 


52  THE  SKELETON  OF  THE  HORSE 

and  presents  a  deep  central  depression  and  two  shallower  lateral  ones  which  adapt 
it  to  the  surface  of  the  cerebellum. 

The  parietal  border  (INIargo  parietalis)  is  united  by  suture  with  the  parietal 
and  interparietal.  The  mastoid  border  (Margo  mastoideus)  joins  the  petro- 
mastoid  part  of  the  temporal  bone.  The  basilar  part  is  connected  by  cartilage  (in 
the  young  subject)  with  the  body  of  the  sphenoid.  The  condyles  articulate  with 
the  atlas. 

Development. — The  occipital  bone  ossifies  in  cartilage  from  four  centers,  and 
consists  at  birth  of  four  pieces  as  described  above.     The  lateral  parts  unite  with  the 


11  10 

Fig.  30. — Cranium  of  New-born  Fo.\l;  Posterior  View. 
A,  B,  C,  Squamous,  lateral,  and  basilar  parts  sf  occipital  bone;  D,  interparietal  bone;  E,  parietal  bone;  F,  squa- 
mous temporal  bone;  6',  petro-mastoid  part  of  temporal  bone;  1,  external  occipital  protuberance;  2,  2,  depressfons  in 
which  complexus  tendons  are  attached;  3,  sutural  (preinterparietal?)  bone;  4,  supraorbital  process;  5,  zygomatic 
process  of  temporal  bone;  6,  postglenoid  process;  7,  posterior  process  of  squamous  temporal  bone;  8,  mastoid  process; 
9,  paramastoid  process;    10,  occipital  condyle;   11,  arrow  in  foramen  magnum. 

basilar  part  at  three  to  four  months,  and  with  the  squama  in  the  second  year,  when 
the  bone  is  consolidated. 

The  parieto-occipital  suture  and  the  spheno-occipital  synchondrosis  are  ob- 
literated about  the  fifth  year  usually.  The  occipito-mastoid  suture  partially  ossifies 
in  old  subjects. 

The  Sphenoid  Bone 

The  sphenoid  bone  (Os  sphenoidale)  is  situated  in  the  base  of  the  cranium,  its 
central  part  lying  in  front  of  the  basilar  part  of  the  occipital.  It  consists  of  the 
body,  two  pairs  of  wings,  and  two  pterygoid  processes. 

The  body  (Corpus)  is  situated  medially;  it  is  cylindrical,  but  flattened  dorso- 
ventrall}',  and  wider  in  front  than  behind.  Its  ventral  surface  (Facies  externa)  is 
convex  in  the  transverse  direction,  and  its  anterior  part  is  concealed  to  a  large  extent 
by  the  vomer  and  pterygoid  bones.  The  cerebral  surface  (Facies  cerebralis) 
presents  the  following  features:  (1)  In  front  there  is  a  raised,  flattened  part  (Jugum 
sphenoidale)  which  is  partially  subdivided  by  a  median  elevation  into  two  slightly 
concave  lateral  areas;   this  part  has  a  posterior,  thin,  free  margin  (Limbus  sphe- 


THE    SPHENOID    BONE 


53 


noidalis),  which  overhes  the  entrance  to  the  optic  foramina.  The  median  ridge  is 
termed  the  ethmoidal  spine,  since  it  fits  into  a  notch  of  the  cribriform  plate  of  the 
ethmoid  bone  and  joins  the  crista  galh.  (2)  Just  behind  this  and  at  a  lower  level 
is  a  smooth  transverse  depression,  the  optic  groove  (Sulcus  chiasmatis),  on  which 
the  optic  chiasma  rests.  (3)  From  each  end  of  this  groove  the  optic  foramen 
(Foramen  opticum)  passes  forward  and  outward  to  terminate  in  the  posterior  part 
of  the  orbital  fossa. ^  (4)  Near  the  posterior  end  is  a  central  depression,  the  hypo- 
physeal or  pituitary  fossa  (Fossa  hypophyseos) ,  which  lodges  the  hypophysis  cerebri 
or  pituitary  body.  On  each  side  of  this  is  a  shallow  groove  for  the  internal  carotid 
artery  and  the  cavernous  sinus.  The  anterior  end  is  expanded,  and  joins  the  eth- 
moid and  palatine  bones;  it  is  excavated  to  form  the  sphenoidal  sinuses.  These 
cavities  extend  back  as  far  as  the  optic 
groove,  and  are  usually  continuous  in  front 
with  the  cavities  in  the  vertical  parts  of  the 
palate  bones;-  they  are  separated  by  a  com- 
plete septum  which  is  not  always  median. 
The  posterior  end  is  flat  and  is  joined  to 
the  basilar  part  of  the  occipital ;  at  the  line 
of  junction  there  is  dorsally  a  slight  trans- 
verse elevation,  the  spheno-occipital  crest 
(Crista  spheno-occipitalis). 

The  orbital  wings  (Alse  orbitales)  curve 
dorso-laterally  from  the  sides  of  the  body  of 
the  presphenoid.  Their  cerebral  surface  is 
concave,  and  is  marked  by  digital  impres- 
sions (Impressiones  digitatse)  for  the  gyri 
of  the  cerebrum.  The  lateral  surface  is  con- 
vex and  is  largely  concealed  by  the  overlap- 
ping temporal  wing  and  the  squamous  tem- 
poral and  frontal  bones ;  a  narrow  part  of  it 
(Facies  orbitalis)  is  uncovered  on  the  medial 
wall  of  the  orbital  cavity  at  the  sphenoidal 
notch  of  the  frontal  bone.  The  dorsal  bor- 
der unites  with  the  frontal  bone  at  the 
spheno-frontal  suture.  The  anterior  border 
joins  the  ethmoid  at  the  spheno-ethmoidal 
suture ;  at  its  lower  part  it  concurs  with  the 
ethmoid  and  frontal  in  the  formation  of  the 
ethmoidal  foramen  (Foramen  ethmoidale).^ 
The  posterior  border  is  overlapped  by  the 
temporal  wing  and  the  squamous  temporal. 
The  root  of  the  wing  is  perforated  by  the 
optic  foramen  (Foramen  opticum) .  Immedi- 
ately below  and  behind  the  latter  (i.  e.,  beneath  the  root)  is  the  foramen  orbitale. 
Below  this,  and  separated  from  it  usually  by  a  thin  and  often  incomplete  plate,  is  a 
larger  opening,  the  foramen  rotundum,  which  is  bounded  externally  by  the  root  of 
the  pterygoid  process. 

The  temporal  wings  (Alse  temporales)  extend  outward  and  somewhat  upward 
from  the  body  of  the  postsphenoid;    they  are  smaller  than  the  orbital  wings  and 


Fig.  31. — Sphenoid  Bone  and  Basilar  Part  of 
Occipital  Bone  of  New-born  Foal;  Dorsal 
View. 

C,  Body  of  presphenoid;  C,  body  of  postsphe- 
noid; B.O.,  basilar  part  of  occipital  bone;  A.o.,  orbital 
wing  of  sphenoid  bone;  A.t.,  temporal  wing  of  sphe- 
noid bone;  1,  1,  optic  foramina;  2,  optic  groove;  3, 
hypophyseal  fossa;  4,  5,  grooves;  6,  ethmoidal 
notch;  7,  ethmoidal  spine;  8,  junction  with  crib- 
riform plate  of  ethmoid  bone;  9,  junction  with 
frontal  bone;  10,  junction  with  squamous  temporal 
bone;  11,  margin  of  foramen  lacerum  anterius;  12, 
spheno-occipital  crest;  13,  junction  of  basilar  part 
of  occipital  bone  with  lateral  part. 


1  This  foramen  might  well  be  called  a  canal,  since  it  is  an  inch  or  more  in  length. 

2  The  cavity  so  formed  may  be  termed  the  sphenopalatine  sinus.  The  sphenoidal  sinus  may 
be  a  separate  cavdty  which  communicates  only  with  the  ventral  ethmoidal  meatuses;  this  arrange- 
ment exists  in  about  a  third  of  the  cases  according  to  Paulh. 

'  Also  called  the  internal  orbital  foramen. 


54  THE  SKELETON  OF  THE  HORSE 

are  irregularly  quadrilateral  in  outline.  The  temporal  surface  (Facies  temporalis) 
enters  into  the  formation  of  the  infratemporal  fossa,  and  bears  the  pterygoid  process 
on  its  anterior  part;  at  the  junction  with  the  body  there  is  a  small  groove  which 
leads  forward  to  the  pterygoid  canal.  The  cerebral  surface  (Facies  cerebralis) 
presents,  at  the  junction  with  the  body,  two  longitudinal  grooves  (Sulci  nervorum). 
The  lateral  groove  is  the  larger,  and  leads  forward  to  the  foramen  rotundum;  it 
contains  the  maxillary  nerve.  The  medial  groove  conducts  to  the  foramen  orbitale, 
and  contains  the  cavernous  sinus  of  the  dura  mater.  The  outer  groove  is  bounded 
laterally  by  a  thin  overhanging  crest,  on  which  is  a  small  groove  for  the  fourth  nerve. 
The  remainder  of  the  surface  is  concave  and  supports  the  pyriform  lobe  of  the  brain. 
The  dorsal  border  joins  the  squamous  temporal  at  the  spheno-squamous  suture. 
The  anterior  border  joins  the  orbital  A\dng  above;  below  this  it  is  free  and  forms  the 
pterygoid  crest  (Crista  pterygoidea) .  The  crest  is  continued  on  the  pterygoid 
process;  on  or  under  its  upper  part  there  is  usually  a  small  opening,  the  trochlear 
foramen  (Foramen  trochleare).  Just  behind  the  crest  is  the  foramen  alare  parvimi,^ 
through  which  the  anterior  deep  temporal  artery  emerges  from  the  alar  canal  of 
the  pterygoid  process.  The  posterior  border  forms  the  anterior  boundarj?-  of  the 
foramen  lacerum;  it  presents  three  notches,  which  are,  from  within  outward,  the 
carotid,  oval,  and  spinous  (Incisura  carotica,  ovalis,  spinosa).  The  angle  of  junc- 
tion of  the  dorsal  and  posterior  borders  articulates  with  the  parietal  bone. 

The  pterygoid  processes  (Processus  pterygoidei)  arise  from  the  temporal  wings 
and  the  body.  They  project  downward  and  forward,  and  curve  outward  at  the 
lower  part.  The  root  is  perforated  by  the  alar  canal  (Canalis  alaris),-  which  trans- 
mits the  internal  maxillary  artery.  From  this  canal  a  branch  leads  upward  and 
forward  to  open  at  the  foramen  alare  parvum.  The  lateral  surface  is  concave,  and 
is  marked  by  lines  for  muscular  attachment.  The  medial  surface  is  convex;  it  is 
largely  concealed  by  the  overlapping  palate  and  pterygoid  bones. 

The  pterygoid  canal  (Canalis  pterygoideus)^  continues  the  groove  noted  on  the 
ventral  surface  of  the  temporal  wing  at  its  junction  with  the  body.  It  extends  for- 
ward and  upward  between  the  root  of  the  pterygoid  process,  the  presphenoid,  and 
the  pterygoid  bone,  and  opens  in  the  posterior  part  of  the  pterygo-palatine  fossa. 
It  transmits  the  nerve  of  the  pterygoid  canal. 

Development. — The  sphenoid  is  ossified  in  cartilage,  and  consists  in  early  life 
of  two  distinct  parts,  the  presphenoid  and  postsphenoid.  The  former  develops 
from  two  centers,  one  in  each  wing;  the  latter  has  three  centers,  one  for  the  body 
and  one  for  each  wing.  The  pterygoid  processes  ossify  from  the  centers  of  the 
temporal  wings. 

In  the  new-born  foal  the  unossified  dorsal  part  of  the  orbital  wing  fits  into  a  hiatus  of  the 
frontal  bone;  in  some  cases  it  comes  to  the  surface  through  a  defect  in  the  frontal  bone  at  the  place 
where  the  horn  process  is  situated  in  animals  which  have  frontal  horns. 

The  Ethmoid  Bone 

The  ethmoid  bone  (Os  ethmoidale)  lies  in  front  of  the  body  and  orbital  wings 
of  the  sphenoid.  It  projects  forward  between  the  orbital  parts  of  the  frontal  bones 
and  enters  into  the  formation  of  the  cranial,  nasal,  and  paranasal  cavities.^  It 
consists  of  four  parts — the  cribriform  plate,  two  lateral  masses,  and  the  perpen- 
dicular plate. 

The  cribriform  plate  (Lamina  cribrosa)  is  a  sieve-like  partition  between  the 

^  Also  termed  the  temporal  foramen. 

^  This  is  also  called  the  subsphenoidal  canal  or  pterygoid  foramen. 

^  Also  known  as  the  Vidian  canal. 

^  On  account  of  its  deep  situation  and  the  fact  that  it  cannot  be  separated  from  its  surround- 
ings, the  ethmoid  must  be  studied  by  means  of  appropriate  sagittal  and  transverse  sections  of  the 
ekuU. 


THE    ETHMOID    BONE 


55 


cranial  and  nasal  cavities.  Its  margin  joins  the  orbital  wings  of  the  sphenoid 
laterally,  the  body  of  the  sphenoid  ventrally,  and  the  cranial  plate  of  the  frontal 
bones  dorsally.  Its  cerebral  surface  is  divided  into  two  parts  by  a  median  ridge, 
the  crista  galli,  which  may  be  regarded  as  the  intracranial  projection  of  the  perpen- 
dicular plate.  Each  half  forms  a  deep  oval  cavity,  the  ethmoidal  fossa,  which 
lodges  the  olfactory  bulb.  The  plate  is  perforated  by  numerous  small  foramina  for 
the  passage  of  the  olfactory  nerve  filaments,  and  on  either  side  is  the  much  larger 
ethmoidal  foramen.  The  nasal  surface  is  convex,  and  has  the  lateral  masses 
attached  to  it. 

Each  lateral  mass  or  labyrinth  (Labyrinthus  ethmoidalis)  is  conical  in  shape  and 
its  base  is  attached  to  the  cril)riform  plate.     It  projects  forward  into  the  posterior 


Vomer 

Fig.  .32. — Cross-section  of  Cranium  of  Horse.     The  Section  Passes  Through  the  Middle  of  the  Orbits  and 

IS  Viewed  from  In  Front. 
1,  Lateral  mass  of  ethmoid  bone;    2,  perpendicular  plate  of  same;    3,  common  nasal  meatus;    4,  sphenopalatine 
sinu=i;    .■>,  perpendicular  part  of  palatine  bone;    6,  zygomatic  process  of  temporal  bone;    7,  zygomatic  arch;    8,  orbital 
part  of  frontal  bone. 


part  of  the  nasal  cavity.  The  medial  surface  is  separated  by  a  narrow  space  from  the 
perpendicular  plate.  The  lateral  surface  is  convex  and  faces  chiefly  into  the  frontal 
and  maxillary  sinuses,  but  is  attached  behind  to  the  inner  wall  of  the  orbital  cavity; 
it  is  covered  by  a  very  thin  layer  of  bone,  the  lamina  lateraUs.  The  mass  consists 
of  a  large  number  of  delicate,  scroll-like  plates  of  bone,  termed  ethmo-turbinates.^ 
These  are  attached  to  the  lamina  lateralis,  and  are  separated  by  narrow  intervals 
termed  ethmoidal  meatuses,  which  communicate  with  the  nasal  cavity.  In  the 
fresh  state  the  ethmo-turbinates  are  covered  with  mucous  membrane. 

The  lateral  mass  is  a  very  complex  structure,  the  arrangement  of  which  may  be  understood 
by  examination  of  cross-sections.    Each  mass  consists  of  six  turbinates  which  extend  almost  to  the 

'  The  term  "ethmoid  cell,"  borrowed  from  human  anatomy,  should  not  be  retained,  since 
it  connotes  an  entirely  erroneous  conception  of  these  structures  in  macrosmatic  animals,  such  as 
those  under  consideration. 


56 


THE   SKELETON    OF   THE    HORSE 


perpendicular  plate  and  are  termed  endoturbinates.  These  diminish  in  size  from  above  down- 
ward; the  largest  is  attached  to  the  nasal  bone,  and  is  hence  usually  called  the  dorsal  or  nasal 
turbinate;  the  second  is  much  smaller,  and  is  very  commonly  termed  the  great  ethmoid  cell. 
The  cavaty  enclosed  by  this  communicates  laterally  with  the  maxillary  sinus,  but  not  directly 
with  the  nasal  cavity.  Between  the  endoturbinates  are  twenty-one  small  ectoturbinates,  and 
all  are  beset  ^\-ith  secondary  and  tertiary  coiled  lamellae. 

The  perpendicular  plate  (Lamina  perpendicularis)  is  median,  and  forms  the 
posterior  part  of  the  septum  nasi.  Its  lateral  surfaces  are  nearly  plane,  but  are 
marked  below  by  some  grooves  and  ridges;  they  are  covered  by  the  nasal  mucous 
membrane.  The  anterior  border  is  irregular  and  is  continuous  with  the  septal 
cartilage.     The  posterior  border  projects  into  the  cranial  cavity  as  a  ridge,  the 

Posterior  end        Siipraorbital 
of  frontal  sinus      process 

{sawn  off) 


Frontal  bone  {temporal  pari) 
Orbital  icing  of  sphenoid 


Foramen  orbitale 
—  Foramen  rotundum 
Alar  canal 


Body  of  sphenoid        Pterygoid  process 


Fig  33. — Cross-section  of  Cranium  of  Horse.     The  Section  is  Cut  Just  in  Front  of  the  Temporal  Condyle 

AND  Is  Viewed  from  Behind. 

1,  Internal  plate  of  frontal  bone;   2,  crista   galli;    3,  cribriform  plate;   4,  ethmoidal   foramen;   5,   ethmoidal    spine    of 

sphenoid  bone;  6,  optic  foramina. 


crista  galli.     The  dorsal  border  joins  the  frontal  l^ones  at  their  line  of  junction. 
The  ventral  border  is  received  into  the  groove  of  the  vomer. 

Development. — The  ethmoid  develops  in  cartilage  from  five  centers,  two  for 
each  lateral  mass,  and  one  for  the  perpendicular  plate;  from  the  latter  ossification 
extends  into  the  cribriform  plate.  At  birth  the  perpendicular  and  cribriform  plates 
are  cartilaginous.  By  the  time  ossification  is  complete  the  ethmoid  has  united 
with  surrounding  bones  to  such  an  extent  that  it  cannot  be  separated  intact  for 
study. 

The  Interparietal  Bone 

This  bone  (Os  interparietale)  is  centrally  placed  between  the  squamous  part 
of  the  occipital  and  the  parietal  bones.  It  is  usually  described  as  a  single  bone, 
although  it  ossifies  from  two  chief  lateral  centers,  and  is  often  distinctly  paired  in 
skulls  of  young  foals. 


THE    PARIETAL    BONES 


57 


The  external,  parietal  surface  (Facies  parietalis)  is  quadrilateral  and  is  flat  and 
smooth  in  the  very  young  foal;   later  it  presents  the  parietal  crest. 

The  internal,  cerebral  surface  (Facies  cerebralis)  presents  the  internal  occipital 
protuberance,  a  three-sided  process  which  projects  downward  and  forward  into  the 
cranial  cavity  between  the  cerebral  hemispheres  and  the  cerebellum;  it  has  three 
concave  surfaces,  and  three  sharp  borders  which  form  part  of  the  tentorium  osseum. 
Behind  the  base  of  the  protuberance  there  is  a  transverse  groove  for  the  sinus  com- 
municans  of  the  dura  mater. 

The  posterior  border  is  thick;    it  joins  the  squamous  part  of  the  occipital 
bone.     The  lateral  and  anterior  borders  are 
united  with  the  parietal  bones.  Squaytwus  part  of 

Development.— The  interparietal  ossi-  occipital  bone 

fies  in  membrane  from  two  chief  lateral  cen- 
ters.^ It  fuses  first  with  the  parietals,  some- 
what later  with  the  occipital,  but  the  period 
at  which  this  union  takes  place  is  quite 
variable. 

The  Parietal  Bones 

The  two  parietal  bones  (Ossa  parie- 
talia)  form  the  greater  part  of  the  roof  of 
the  cranium;  they  unite  in  the  median  line, 
forming  the  parietal  suture.  Each  is  quadri- 
lateral in  outline  and  has  two  surfaces  and 
four  borders. 

The  external,  parietal  surface  (Facies 
parietalis)  is  convex,  and  is  marked  by  a 
more  or  less  prominent  curved  line,  the  ex- 
ternal parietal  crest;  this  is  median  in  its 
posterior  part,  and  is  continuous  with  the 
crest  of  like  name  on  the  interparietal  and 
occipital;  in  front  it  curves  outward  and  is 
continuous  with  the  frontal  crest.  The  sur- 
face lateral  to  the  crest  (Planum  temporale) 
enters  into  the  formation  of  the  temporal 
fossa,  and  is  roughened  for  the  attachment 
of  the  temporal  muscle. 

The  internal,  cerebral  surface  (Facies 
cerebralis)  is  concave.  It  presents  numerous 
digital  impressions  (Impressiones  digitatae) 

which  correspond  to  the  gyri,  and  ridges  (Juga  cerebralia)  which  correspond  to  the 
sulci,  of  the  cerebrum.  There  are  also  furrows  (Sulci  vasculosi)  for  the  meningeal 
arteries.  Along  the  medial  border  there  is  a  sagittal  groove  (Sulcus  sagittalis)  for 
the  superior  longitudinal  sinus. 

The  anterior  border  joins  the  frontal  bone  at  the  parieto-frontal  suture  (Sutura 
parieto-f  rontalis) . 

The  posterior  border  meets  the  occipital  bone  at  the  parieto-occipital  suture. 
Below  this  junction  it  curves  inward  and  concurs  with  the  temporal  bone  in  the 
formation  of  the  temporal  canal  (Meatus  temporalis) .  A  transverse  groove  (Sulcus 
transversus)  connects  this  canal  with  the  sagittal  sulcus. 

The  medial  border  is  thick  and  serrated.  It  joins  its  fellow  in  great  part  at  the 
parietal  suture,  but  (in  the  young  subject)  meets  the  interparietal  at  its  posterior 

^  According  to  Martin,  there  are  originally  four  centers,  two  anterior  and  two  posterior 
(smaller)  ones,  which  fuse  in  a  variable  manner. 


Fig.  34. — Interparietal  and  Squamous  Part  or 
Occipital  Bone  of  New-born  Foal;  Ven- 
tral View. 

1,  Junction  of  interparietal  with  squamous 
part  of  occipital  bone;  2,  interparietal  suture;  3, 
internal  occipital  protuberance;  4,  transverse  groove 
for  sinus;  5,  depression  for  vermis  cerebelli;  6,  de- 
pression for  hemisphere  of  cerebellum;  7,  junction 
of  squamous  part  with  lateral  part  of  occipital 
bone;  8,  junction  of  occipital  with  petro-mastoid; 
9,  9,  junction  of  interparietal  with  parietal. 


58 


THE    SKELETON    OF   THE    HORSE 


part.     The  line  of  junction  of  the  two  parietal  bones  is  marked  internally  by  the 
internal  parietal  crest  (Crista  parietalis  interna). 

The  lateral  border  is  })eveled  and  is  overlapped  by  the  squamous  temporal 


Fig.  .35.— Right  Parietal  Bone  of  New-born  Foal;   Dorso-lateral  View. 

1,  Junction  with  opposite  bone;  2,  junction  with  interparietal;  3,  junction  with  occipital;  4,  junction  with  squamoua 

temporal;  .5,  junction  with  frontal, 

bone,  forming  the  squamous  suture  (Sutura  squamosa).  The  angle  of  junction  of 
the  lateral  and  posterior  liorders  articulates  with  the  posterior  angle  of  the  temporal 
wing  of  the  sphenoid. 

Development. — Each  parietal  bone  ossifies  in  membrane  from  a  single  center. 


Fig.  36. — Right  Parietal  Bone  of  New-born  Foal,  Cerebral  Surface. 

1,  Junction  with  opposite  bone;  2,  junction  with  interparietal;  3,  junction  with  occipital;  4,  junction  with  squamous 

temporal;   5,  junction  with  frontal;   6,  edge  which  concurs  with  temporal  bone  in  formation  of  temporal  canal. 


In  the  young  foal  the  central  part  of  the  bone  is  more  convex  than  in  the  adult  and 
forms  a  prominence  similar  to  the  pronounce  1  tuber  parietale  of  the  young  child; 
the  external  parietal  crest  is  not  present,  and  the  external  surface  is  smooth.     The 


THE    FRONTAL    BONES 


59 


parietal  suture  is  usually  closed  at  four  years,  the  parieto-occipital  at  five  years,  and 
the  squamous  at  twelve  to  fifteen  years. 

The  Frontal  Bones 

The  frontal  bones  (Ossa  frontalia)  are  situated  on  the  limits  of  the  cranium 
and  face,  between  the  parietals  behind  and  the  nasal  bones  in  front.  Each  is 
irregularly  quadrilateral,  and  consists  of  naso-frontal,  orbital,  and  temporal  parts. 

The  naso-frontal  part  (Pars  naso-frontalis)  forms  the  basis  of  the  forehead. 
Its  external  or  frontal  surface  (Fades  frontalis)  is  nearly  flat,  and  is  smooth  and 
subcutaneous ;  it  is  separated  from  the  temporal  part  by  the  external  frontal  crest 
(Crista  frontalis  externa).  At  the  junction  with  the  orbital  part  the  supraorbital 
or  zygomatic  process  (Proc.  zygomaticus)  curves  outward  and  downward  to  join 
the  zygomatic  arch.  The  process  partially  separates  the  orbit  from  the  temporal 
fossa;  its  root  is  perforated  by  the  supraorbital  foramen  (Foramen  supraorbitale), 
or  presents  instead  a  notch  on  its  anterior  l)order;  its  upper  surface  is  convex,  while 
the  orbital  surface  is  concave  and  smooth,  forming  a  shallow  fossa  for  the  lacrimal 


Fir,.  37. — Left  Frontal  Bone  of  New-born  Fo.\l;    Ventro-medi.\l  View. 
.4,  Cerebral  surface;    B,  B,  vorbital  part;    C,  temporal  part;   D,  nasal  surface;    1,  surface  of  junction  with  opposite 
bone;   2,  frontal  sinus;  3,  ridge  to  which  cribriform  plate  of  ethmoid  bone  is  attached;  5,  fissure  into  which  orbital  wing 
of  .sphenoid  bone  fits;  6,  sphenoidal  notch;   7,  supraorbital  process;   8,  junction  with  nasal  bone;   9,  junction  with  pari- 
etal bone;    10,  junction  with  squamous  temporal  bone. 


gland  (Fossa  glandulae  lacrimalis).  The  internal  surface  enters  into  the  formation 
of  the  cranial  and  nasal  cavities.  The  two  plates  of  the  bone  separate  and  diverge 
in  front,  and  thus  inclose  a  large  air-space  which  is  part  of  the  frontal  sinus.  The 
internal  plate  curves  downward  and  forward  and  joins  the  cribriform  plate  of  the 
ethmoid.  Beyond  this  it  inclines  upward  and  joins  the  external  plate  at  the  naso- 
frontal suture.  The  cerebral  surface  presents  digital  impressions  for  the  cerebral 
gyri.  The  nasal  surface  is  longitudinally  grooved.  The  external  plate  extends 
forward  and  joins  the  nasal  and  lacrimal  bones. 

The  orbital  part  (Pars  orbitalis)  forms  the  major  part  of  the  medial  wall  of  the 
orbital  cavity.  It  is  separated  from  the  naso-frontal  part  by  a  prominent  ridge 
which  is  part  of  the  orbital  margin.  Its  orbital  surface  (Facies  orbitalis)  is  concave 
and  smooth,  and  presents  superiorly  a  small  depression  (Fovea  trochlearis),  which 
is  bridged  by  a  small  bar  of  cartilage,  around  which  the  superior  oblique  muscle  of 
the  eye  is  reflected.  The  lower  border  concurs  with  the  orbital  wing  of  the  sphenoid 
in  the  formation  of  the  ethmoidal  foramen.  The  nasal  surface  faces  into  the 
frontal  sinus  and  is  to  a  small  extent  united  with  the  lateral  mass  of  the  ethmoid. 

The  temporal  part  (Pars  temporalis)  is  separated  from  the  orbital  part  by  the 


60  THE  SKELETON  OF  THE  HORSE 

deep  sphenoidal  notch  (Incisura  sphenoidalis),  which  is  closed  by  the  orbital  wing 
of  the  sphenoid.  Its  lateral  svurface  forms  part  of  the  inner  wall  of  the  temporal 
fossa.  The  medial  surface  is  largely  covered  by  the  orbital  wing  of  the  sphenoid 
in  the  young  subject,  but  later  forms  part  of  the  wall  of  the  frontal  sinus. 

The  principal  connections  of  the  frontal  bone  are  as  follows:  (1)  The  medial 
border  joins  its  fellow  at  the  frontal  suture.  (2)  The  anterior  border  meets  the 
nasal  and  lacrimal  at  the  naso-frontal  and  fronto-lacrimal  sutures.  (3)  Laterally 
it  forms  the  spheno-frontal  suture  with  the  orljital  wing  of  the  sphenoid,  and  also 
joins  the  palatine  bone  and  maxilla  at  the  fronto-palatine  and  fronto-maxillary 
sutures.  (4)  Posteriorly  it  meets  the  parietal  at  the  parieto-frontal  suture,  and 
articulates  below  this  with  the  squamous  temporal  at  the  squamous  suture. 
(5)  The  extremity  of  the  supraorbital  process  unites  with  the  zygomatic  process 
of  the  temporal  bone. 

Development. — Each  ossifies  in  membrane  from  one  center  which  appears  in 
the  root  of  the  supraorbital  process.  In  the  new-born  foal  there  is  a  slit  between 
the  cranial  plate  and  the  orbital  and  temporal  plates  which  receives  the  unossified 
dorsal  part  of  the  orbital  wing  of  the  sphenoid. 

The  Temporal  Bones 

The  temporal  bone  (Os  temporale)  forms  the  greater  part  of  the  lateral  wall 
of  the  cranium.  It  is  situated  between  the  occipital  behind,  the  parietal  dorsally, 
the  frontal  in  front,  and  the  sphenoid  ventrally.  It  consists  in  the  horse  of  two 
distinct  parts,  squamous  and  petrous. 

1.  The  squamous  temporal  bone  (Squama  temporalis)  is  a  shell-like  plate 
which  has  two  surfaces  and  four  borders. 

The  cerebral  surface  (Facies  cerebralis)  is  concave  and  is  largely  overlapped 
by  the  surrounding  bones,  but  its  central  part  is  free  and  presents  digital  impres- 
sions and  vascular  grooves. 

The  temporal  surface  (Facies  temporalis)  is  convex,  and  enters  into  the  forma- 
tion of  the  temporal  fossa.  From  its  ventral  part  there  springs  the  zygomatic 
process  (Processus  zygomaticus) ,  which  forms  the  lateral  boundary  of  the  tem- 
poral fossa.  The  process  is  at  first  directed  outward,  and  is  wide  and  flattened 
dorso-ventrally.  It  then  turns  forward,  becomes  narrower,  and  is  twisted  so  that 
its  surfaces  are  medial  and  lateral.  Its  anterior  end  is  pointed  and  joins  the  zygo- 
matic process  of  the  malar  bone,  wdth  which  it  forms  the  zygomatic  arch  (Arcus 
zygomaticus) .  The  narrow  anterior  part  has  a  convex  lateral  surface  and  a  concave 
medial  one.  Its  dorsal  border  has  a  rough  area  for  articulation  with  the  supra- 
orbital process  of  the  frontal.  Its  ventral  border  is  wide  and  rough.  The  wide 
posterior  part  presents  on  its  ventral  face  a  surface  for  articulation  with  the  condyle 
of  the  mandible.  This  surface  consists  of  a  transversely  elongated  condyle  (Condy- 
lus  temporalis) ,  behind  which  is  the  glenoid  cavity.  The  fossa  is  limited  behind  by 
the  postglenoid  process  (Processus  postglenoidalis),  the  anterior  surface  of  which 
is  articular.  Behind  this  process  there  is  a  fossa,  in  which  is  the  postglenoid  fora- 
men (F.  postglenoidale),  the  external  opening  of  the  temporal  canal.  The  dorsal 
surface  is  concave  and  forms  the  lateral  boundary  of  the  temporal  fossa.  The 
dorsal  border  is  sinuous  and  is  continuous  behind  with  the  temporal  crest. 

The  posterior  process  (Processus  aboralis)  springs  from  the  posterior  part  of 
the  squama.  Its  lateral  surface  bears  the  temporal  crest,  which  forms  here  the 
lateral  limit  of  the  temporal  fossa.  The  medial  surface  forms  the  outer  boundary 
of  the  temporal  canal,  and  is  elsewhere  applied  to  the  petrous  portion.  It  divides 
into  two  branches,  upper  and  lower;  the  upper  branch  unites  with  the  occipital 
bone,  while  the  lower  one  curves  downward  behind  the  external  acoustic  process 
and  overlaps  the  mastoid  process. 

The  dorsal  border  of  the  squamous  temporal  articulates  with  the  parietal, 


THE   TEMPORAL   BONES 


61 


forming  the  squamous  suture.  The  ventral  border  joins  the  temporal  wing  of  the 
sphenoid  at  the  spheno-squamous  suture.  The  anterior  border  unites  with  the 
frontal  bone  at  the  squamo-frontal  suture,  and  the  posterior  with  the  occipital 
and  petrous  temporal  bones. 

2.  The  petrous  temporal  bone  (Os  petrosum)  is  placed  between  the  occipital 


Fig.  38. — Right  Squamous  Temporal  Bone  of  New-born  Foal;    Lateral  View. 
1,  Zygomatic  process;    2,  glenoid  cavity;     3,  condyle;    4,  postglenoid  process;    5,  notch;    6,  posterior  process;   7, 
temporal  crest;  8,  junction  with  parietal;  9,  junction  with  frontal;    10,  junction  with  supraorbital  process;   11,  junction 
with  zygomatic  process  of  malar;    12,  junction  with  sphenoid;    13,  junction  with  petro-mastoid-     14,  junction  with  oc- 
cipital. 


behind  and  the  parietal  in  front,  and  is  largely  overlapped  by  the  squamous  tem- 
poral.    It  has  the  form  of  a  four-sided  pyramid,  the  base  of  which  is  ventral. 

The  lateral  surface  is  mainly  concealed  by  the  squamous  temporal,  but  two 
features  are  visible.  A  short  tube  of  bone,  the  external  acoustic  process  (Processus 
acusticus  externus) ,  protrudes  from  the  lowest  part  through  the  notch  of  the  squa- 
mous temporal.     The  process  is  directed  outward,  upward,  and  a  little  forward. 


Fig.  39. — Right  Squamous  Temporal  Bone  op  New-born  Foal;    Medial  View. 
F.C.,  Cerebral  surface;    1,  zygomatic  process;    2,  junction  with  parietal;    3,  junction  with  temporal  wing  of  sphenoid; 
4,  posterior  process   (overlaps  petro-mastoid). 


It  gives  attachment  to  the  annular  cartilage  of  the  ear.  Its  lumen,  the  external 
acoustic  meatus  (Meatus  acusticus  externus),  conducts  to  the  cavity  of  the  middle 
ear  (tympanum)  in  the  dry  skull,  but  is  separated  from  it  by  the  tympanic  mem- 
brane in  the  natural  state.  The  mastoid  process  (Processus  mastoideus)  projects 
ventrally  in  the  interval  between  the  posterior  process  of  the  squamous  temporal 


62 


THE    SKELETON    OF    THE    HORSE 


and  the  root  of  the  paramastoid  process  of  the  occipital  bone.  It  is  crossed  by  a 
groove  which  leads  to  the  mastoid  foramen  (Foramen  mastoideum),  from  which  a 
canal  extends  forward  to  the  temporal  canal. 

The  medial  surface  faces  into  the  cerebellar  fossa  of  the  cranium.  It  is  con- 
cave and  smooth.  l)ut  irregular.  In  its  ventral  part  is  the  entrance  to  a  short  canal, 
the  internal  acoustic  meatus  (Meatus  acusticus  internus),  which  transmits  the 
seventh  and  eighth  cranial  nerves. 

The  entrance  to  the  meatus  is  termed  tlie  porus  acusticus  internus.  The  fundus  of  the 
meatus  is  divided  by  a  crest  into  two  fossae.  In  the  superior  one  is  the  origin  of  the  facial  canal, 
which  curves  through  the  bone  and  opens  externally  at  the  stylo-mastoid  foramen;  it  transmits 
the  facial  (seventh  cranial)  nerve.  The  inferior  fossa  presents  small  foramina  for  the  passage  of 
fibers  of  the  acoustic  (eighth  cranial)  nerve. 

Behind  the  meatus  and  near  the  posterior  margin  of  the  surface  is  the  slit-like 
external  opening  of  the  aquseductus  vestibuli  (Apertura  externa  aquseductus  ves- 


FlG. 


40. — Left    Petrous    Temporal 
Lateral  View. 


OF   Horse: 


1,  External  acoustic  meatus;  2,  mastoid  process;  3, 
hyoid  process;  4,  muscular  process;  5,  petrosal  crest;  6, 
groove  which  concurs  in  formation  of  temporal  canal; 
7,  groove  for  posterior  meningeal  artery. 


Fig.  41. — Left  Petrots  Temporal  Bone  of  Horse; 
postero-medial  view. 
1,  Mastoid  process;  2,  notch  which  concurs  with 
occipital  bone  in  formation  of  mastoid  foramen;  3,  apex; 
4,  opening  of  aquseductus  vestibuli;  5,  medial  surface; 
6,  petrosal  crest;  7,  internal  acoustic  meatus;  8,  mus- 
cular process;  9,  bullaossea;  10,  stylo-mastoid  foramen; 
A.c,  opening  of  aquseductus  cochleae. 


tibuli),  covered  by  a  scale  of  bone.  Below  this  there  is  a  narrow  fissure,  the 
orifice  of  the  aquseductus  cochleae  (Apertura  externa  aquseductus  cochlese). 

The  anterior  surface  looks  upward  and  forward.  The  greater  part  articulates 
with  the  parietal  bone,  but  a  small  medial  part  faces  into  the  cerebral  fossa  of  the 
cranium.  A  sharp  border,  the  petrosal  crest  (Crista  petrosa),  separates  this  sur- 
face from  the  medial  one. 

The  posterior  surface  is  slightly  concave  and  is  attached  to  the  lateral  part  of 
the  occipital  bone. 

The  base  forms  the  lateral  boundary  of  the  foramen  lacerum.  It  is  very 
irregular  and  presents  a  number  of  important  features.  The  hyoid  process  (Pro- 
cessus hyoideus)  is  a  short  rod  which  projects  doAvnward  and  forward  below  the 
base  of  the  external  acoustic  process,  inclosed  in  a  bony  tube;  it  is  connected  by  a 
bar  of  cartilage  with  the  hyoid  bone.  The  stylo-mastoid  foramen  (F.  stylo- 
mastoideum)  is  situated  between  the  hyoid  process  and  the  mastoid  process;   it  is 


BONES    OF   THE    FACE— THE   MAXILLAE  63 

the  external  opening  of  the  facial  canal,  through  which  the  facial  nerve  emerges.  The 
bulla  ossea  is  a  considerable  eminence  situated  centrally;  it  is  thin  walled  and 
incloses  a  cavity  which  is  part  of  the  tympanum.  The  muscular  process  (Processus 
muscularis)^  is  a  sharp  spine  which  projects  downward  and  forward  from  the  an- 
terior part  of  the  base;  it  gives  origin  to  the  tensor  and  levator  palati  muscles. 
Lateral  to  the  root  of  the  preceding  is  the  small  petrotympanic  fissure  (Fissura 
petrotympanica)  for  the  passage  of  the  chorda  tympani  nerve.  The  osseous 
auditory  or  Eustachian  tube  (Tuba  auditiva  ossea)  is  a  semicanal  at  the  medial 
side  of  the  root  of  the  muscular  process;  it  leads  to  the  tympanum.  At  the  medial 
side  of  the  preceding  is  the  slit-like  orifice  of  the  petrosal  canal,  which  communi- 
cates Avith  the  facial  canal. 

The  apex  projects  upward  and  backward  between  the  squamous  temporal  and 
the  occipital  bone. 

Development. — The  squamous  temporal  develops  in  membrane.  The  pe- 
trous temporal  may  be  regarded  as  consisting  of  petro-mastoid  and  tympanic  parts. 
The  latter  includes  the  external  acoustic  process,  the  bulla  ossea,  and  the  muscu- 
lar process;  it  is  developed  in  membrane.  The  petro-mastoid  is  developed  in  the 
cartilaginous  ear  capsule.  Its  petrous  part  consists  of  very  dense  bone  which  con- 
tains the  labyrinth  or  internal  ear  and  forms  the  medial  wall  of  the  tympanum. 

The  auditory  ossicles  and  the  interior  of  the  petrous  temporal  bone  are  described  in  the 
section  on  the  organ  of  hearing. 

The  temporal  canal  (Meatus  temporalis)-  is  a  continuation  of  the  transverse 
groove  which  extends  laterally  from  the  base  of  the  tentorium  osseum.  It  is 
directed  downward,  forward,  and  somewhat  outward,  and  opens  externally  in  front 
of  the  root  of  the  acoustic  process.  It  is  bounded  by  the  squamous  temporal 
laterally,  the  petrous  behind,  and  the  parietal  in  front  and  medially.  Several 
foramina  open  from  it  into  the  temporal  fossa.  It  contains  a  large  vein  (Vena 
cerebralis  dorsalis),  the  continuation  of  the  transverse  sinus  of  the  dura  mater. 

The  foramen  lacerum  (basis  cranii)  is  a  large,  irregular  opening  in  the  cranial 
base,  bounded  medially  by*  the  basilar  part  of  the  occipital  bone,  laterally  by  the 
petrous  temporal,  and  in  front  by  the  temporal  wing  of  the  sphenoid.  It  consists 
of  a  large  anterior  part  (Foramen  lacerum  anterius),  and  a  narrow  posterior  part 
(Foramen  lacerum  posterius) .  It  transmits  the  internal  carotid  artery,  the  middle 
meningeal  artery,  the  mandibular,  ninth,  tenth,  and  eleventh  cranial  nerves,  and 
the  ventral  cerebral  vein. 

In  the  fresh  state  the  foramen  is  occupied  by  a  dense  fibrous  membrane  which  is  perforated 
by  apertures  for  the  various  structures  transmitted.  Thus  there  are  three  openings  in  front  for 
the  internal  carotid  artery,  the  mandibular  nerve,  and  the  middle  meningeal  artery;  these  are 
named  (from  within  outward)  the  foramen  caroticum,  ovale,  spinosum. 


(B)  BONES  OF  THE  FACE 
The  bones  of  the  face  (Ossa  faciei)   are  the  maxilla,  premaxilla,  palatine, 
pterygoid,  nasal,  lacrimal,  malar,  dorsal  turbinate,  ventral  turbinate,  vomer,  mandi- 
ble, and  hyoid.     The  last  three  are  single,  the  others  paired. 

The  MAXILL.E 
The  maxillae  are  the  principal  bones  of  the  upper  jaw  and  carry  the  upper 
cheek  teeth.     They  are  situated  on  the  lateral  aspect  of  the  face,  and  articulate 
Avith  almost  all  of  the  facial  bones  and  the  frontal  and  temporal  also.     For  descrip- 
tion each  may  be  divided  into  a  body  and  two  processes. 

1  This  has  been  termed  the  styloid  process.     It  is  not  the  homologue  of  the  styloid  proc- 
ess of  man. 

*  This  is  also  known  as  the  parieto-temporal  canal. 


64 


THE   SKELETON    OF   THE    HORSE 


The  body  (Corpus  maxillae)  presents  two  surfaces,  two  borders,  and  two  ex- 
tremities. The  lateral  surface  (Facies  lateralis)  is  somewhat  concave  in  front  and 
convex  behind.^  On  its  posterior  part  there  is  a  horizontal  ridge,  the  facial  crest 
(Crista  facialis) ;  in  a  skull  of  medium  size  its  anterior  end  is  about  an  inch  and  a 
half  (3  to  4  cm.)  above  the  third  or  fourth  cheek  tooth,  and  it  is  continued  behind 
on  the  malar  bone.  About  two  inches  (5  cm.)  above  and  a  little  in  front  of  the 
anterior  end  of  the  crest  is  the  infraorbital  foramen  (Foramen  infraorbitale) ;  this 
is  the  external  opening  of  the  infraorbital  canal. 

The  medial  or  nasal  surface  (Facies  nasalis)  is  concave  dorso-ventrally;  it 
forms  the  greater  part  of  the  lateral  wall  of  the  nasal  cavity.  Its  upper  part  is 
crossed  obliquely  forward  and  downward  by  the  shallow  lacrimal  groove  (Sulcus 
lacrimalis),  which  contains  the  naso-lacrimal  duct;  in  the  adult  the  posterior  part 
of  the  groove  is  converted  into  a  canal,  which  is  continuous  Avith  that  on  the  inner 
surface  of  the  lacrimal  bone.  Below  the  groove  is  the  ventral  turbinate  crest 
(Crista  turbinata  ventralis),  to  which  the  ventral  turbinate  Ijone  is  attached. 
Lower  down  and  parallel  with  the  turbinate  crest  is  the  palatine  process,  which 


Fig.  42. — Right  Maxilia  of  New-born  Foal;  Medial  View. 
1,  Lacrimal  groove;    2,  ventral  turbinate  crest;   3,  palatine  process;   4,  maxillary  sinus;    5,  5,  area  of  articulation 
with  palatine  bone;    0,  groove  which  concurs  with  one  on  the  palatine  bone  to  form  the  palatine  canal;    7,  zygomatic 
process;    8,  maxillary  tuberosity;    9,  junction  with  nasal  bone;    10,  junction  with  nasal  process  of  premaxilla. 


projects  horizontally  like  a  shelf.  Behind  this  the  surface  is  rough  for  articulation 
with  the  palatine  bone;  this  area  is  crossed  b,y  a  groove  which  concurs  with  one  on 
the  palatine  bone  in  the  formation  of  the  palatine  canal  (Canalis  palatinus).  The 
posterior  part  of  the  bone  is  excavated  to  form  part  of  the  maxillary  sinus. 

The  dorsal  border  is  irregular  and  scaly.  Its  anterior  part  is  grooved  and 
its  posterior  part  beveled  for  articulation  with  the  nasal  process  of  the  premaxilla 
and  the  nasal  and  lacrimal  bones. 

The  ventral  or  alveolar  border  (Processus  alveolaris)  is  in  its  greater  part  thick, 
and  presents  six  large  cavities,  the  dental  alveoli,  for  the  cheek  teeth.  The  alveoli 
are  separated  by  transverse  interalveolar  septa.  There  is  often  a  small  alveolus 
for  the  first  premolar  ("wolf  tooth")  close  to  the  first  large  one.  At  the  bottom 
of  the  alveoli  there  are  small  openings  (Foramina  alveolaria)  for  the  passage  of 
vessels  and  nerves.  Further  forward  the  border  is  narrow  and  forms  part  of  the 
interalveolar  or  interdental  space  (Margo  interalveolaris).  Behind  the  last  alve- 
olus is  a  rough  area,  the  alveolar  tuberosity  (Tuber  alveolare). 

The  anterior  extremity  is  pointed.  It  joins  the  premaxilla,  and  forms  with  it 
the  alveolus  for  the  canine  tooth. 

-  In  the  young  horse  the  anterior  part  of  the  surface  is  convex  over  the  embedded  parts  of  the 
teeth.  As  the  hitter  are  extruded  the  surface  flattens  and  becomes  concave  in  old  subjects. 
The  form  of  the  underlying  teeth  may  be  indicated  by  ridges  (Juga  alveolaria),  and  sometimes  in 
young  horses  there  may  be  defects  in  the  bone  over  the  teeth. 


THE    PREMAXILL^  65 

The  posterior  extremity  forms  a  rounded  prominence,  the  maxillary  tuberosity 
(Tuber  maxillare).  Medial  to  the  tuberosity  is  a  deep  recess  (Recessus  maxillaris), 
in  which  are  three  foramina.  The  upper  one,  the  maxillary  foramen  (Foramen 
maxillare) ,  leads  into  the  infraorbital  canal.  The  lower  one,  the  posterior  palatine 
foramen  (Foramen  palatinum  aborale),  is  the  entrance  to  the  palatine  canal.  The 
sphenopalatine  foramen  (Foramen  sphenopalatinum)  perforates  the  medial  wall 
of  the  recess  and  opens  into  the  nasal  cavity. 

The  zygomatic  process  (Processus  zygomaticus)  projects  backward,  dorso- 
lateral to  the  tuberosity;  it  is  overlapped  by  the  corresponding  part  of  the  malar 
and  also  articulates  with  the  zygomatic  process  of  the  temporal.  A  small  curved 
plate  (Processus  temporalis)  extends  medially  from  it  and  joins  the  frontal  and 
palatine  bones,  forming  part  of  the  floor  of  the  orbit. 

The  palatine  process  (Processus  palatinus)  is  a  horizontal  plate  which  projects 
from  the  lower  part  of  the  medial  surface  of  the  body.  It  forms  the  greater 
part  of  the  basis  of  the  hard  palate.  Its  nasal  surface  is  smooth  and  is  con- 
cave transversely;  on  its  anterior  part,  close  to  the  medial  border,  there  is  a 
shallow  groove  in  which  the  vomero-nasal  organ  (of  Jacobson)  is  situated.  The 
palatine  surface  is  slightly  concave  from  side  to  side,  and  presents  along  its  lateral 
part  the  palatine  groove  (Sulcus  palatinus);  this  is  continuous  at  the  anterior 
palatine  foramen  (Foramen  palatinum  orale)  with  the  palatine  canal,  and  con- 
tains the  palatine  vessels  and  nerve.  The  medial  border  unites  with  its  fellow  to 
form  the  median  palatine  suture;  its  nasal  aspect  bears  the  nasal  crest  (Crista 
nasalis),  which  forms,  with  that  of  the  opposite  process,  a  groove  for  the  vomer. 
The  posterior  border  unites  with  the  horizontal  part  of  the  palatine  bone  at  the 
transverse  palatine  suture.  Variable  accessory  palatine  foramina  perforate  the 
process. 

The  infraorbital  canal  (Canalis  infraorbitalis)i  extends  almost  horizontally 
from  the  maxillary  foramen  to  the  infraorbital  foramen.  It  is  placed  at  the  upper 
edge  of  the  inner  plate  of  the  maxilla,  and  traverses  the  maxillary  sinus.  Near  the 
infraorbital  foramen  it  gives  off  a  small  canal  (Canalis  alveolaris  incisivus)  which 
lies  above  the  roots  of  the  premolars  and  extends  also  into  the  premaxilla,  carrying 
vessels  and  nerves  to  the  teeth  there. 

Development. — The  maxilla  ossifies  in  membrane  ventral  and  lateral  to  the 
cartilaginous  nasal  capsule.  It  has  one  chief  center  and  a  supplementary  one  in 
the  region  of  the  deciduous  canine  tooth  (Martin). 

The  Premaxilla 

The  premaxillae  (Ossa  incisiva)  form  the  anterior  part  of  the  upper  jaw  and 
carry  the  incisor  teeth.  Each  consists  of  a  body,  a  nasal  process,  and  a  palatine 
process. 

The  body  (Corpus)  is  the  thick  anterior  part  which  carries  the  incisor  teeth. 
Its  labial  surface  (Facies  labialis)  is  convex  and  smooth,  and  is  related  to  the  upper 
lip.  The  palatine  surface  (Facies  palatina)  is  concave  and  often  presents  a  foramen 
a  little  behind  its  middle.-  The  medial  surface  (Facialis  medialis)  is  rough,  and 
joins  the  opposite  bone;  it  is  marked  by  a  curved  groove,  which  forms,  with  that  on 
the  opposed  surface,  the  foramen  incisivum.  The  alveolar  border  (Limbus  alveo- 
laris) separates  the  palatine  and  labial  surfaces ;  it  is  curved  and  thick,  and  presents 
three  deep  alveoli  for  the  incisor  teeth;  behind  the  third  alveolus  it  is  free,  forming 
part  of  the  interalveolar  space. 

The  nasal  process  (Processus  nasalis)  projects  backward  and  upward  from  the 
body,  forming  here  the  lateral  wall  of  the  nasal  cavity.     The  two  surfaces,  facial 

^  This  is  also  known  as  the  superior  dental  canal. 

"^  This  foramen  is  somewhat  variable  in  position,  but  is  commonly  opposite  the  corner  in- 
cisor.    Smaller  inconstant  foramina  are  often  present. 
5 


66 


THE    SKELETON    OF   THE    HORSE 


and  nasal,  are  smooth  and  rounded.  The  dorsal  border  is  free,  thick,  and  smooth; 
it  concurs  with  the  free  margin  of  the  nasal  bone  in  forming  the  naso-maxillary 
notch  (Incisura  nasomaxillaris).  The  ventral  border  is  dentated  and  joins  the 
maxilla;  at  its  anterior  end  it  forms  with  the  latter  the  alveolus  for  the  permanent 

canine  tooth. ^  The  posterior  ex- 
tremity fits  into  the  interval  be- 
tween the  nasal  bone  and  the 
maxilla. 

The  palatine  process  (Pro- 
cessus palatinus)  is  a  thin  plate 
which  forms  the  anterior  part  of 
the  basis  of  the  hard  palate.  Its 
nasal  surface  (Facies  nasalis)  has 
a  longitudinal  ridge  which  forms 
with  that  of  the  other  side  a  groove 
for  the  septal  cartilage;  lateral  to 
the  ridge  there  is  a  groove  for  the 
vomero-nasal  organ.  The  palatine 
surface  (Facies  palatina)  is  flat. 
The  medial  border  is  serrated  and 
meets  its  fellow  at  the  median  pala- 
tine suture.  The  lateral  border  is 
separated  from  the  maxilla  and  the 
nasal  process  by  the  palatine  fis- 
sure (Fissura  palatina).  The  pos- 
terior extremity  fits  into  the  inter- 
val between  the  vomer  and  the 
palatine  process  of  the  maxilla. 

Development. — The  premax- 
illa  ossifies  from  a  single  center. 
Fusion  of  the  two  bones  is  com- 
plete at  the  end  of  the  third  or 
the  beginning  of  the  fourth  year. 

The  Palatine  Bones 

The  palatine  bones  (Ossa  pala- 
tina) are  situated  on  either  side  of 
the  choanse  or  posterior  nares,  and 
form  the  posterior  margin  of  the 
hard  palate.  Each  is  twisted  so  as 
to  form  a  horizontal  and  a  perpen- 
dicular part. 

The  horizontal  part  (Pars  hori- 
zontalis)  is  a  narrow^  plate  which 
forms  the  posterior  part  of  the 
hard  palate.  It  presents  smooth 
nasal  and  palatine  surfaces  (Facies 
nasalis,  palatina).  The  medial  border  meets  its  fellow  at  the  median  palatine 
suture,  on  the  nasal  aspect  of  which  is  the  nasal  crest.  The  anterior  border  joins 
the  palatine  process  of  the  maxilla  at  the  transverse  palatine  suture,  and  forms  with 
it  the  anterior  palatine  foramen  (Foramen  palatinum  anterius).  The  posterior 
border  is  concave  and  free ;  it  gives  attachment  to  the  aponeurosis  of  the  soft  palate. 


Fia.  43. — Upper  .Jaw  of  Horse  About  Four  and  a  Half 
Years  Old;  Ventral  View. 
1,  1,  Choanse  or  posterior  nares;  2,  vomer;  3,  horizontal 
part  of  palatine  bone;  4,  anterior  palatine  foramen;  5,  palatine 
groove;  6,  transverse  palatine  suture;  7,  median  palatine  suture; 
8,  palatine  process  of  maxilla;  9,  palatine  process  of  premaxilla; 
10,  foramen  incisivum;  11,  malar  bone;  12,  maxilla;  13,  anterior 
end  of  facial  crest;  14,  interalveolar  space;  /.  1-3,  incisor  teeth; 
C,  canine  tooth;  P.l,  first  premolar  or  "wolf"  tooth.  The 
opening  lateral  to  9  is  the  palatine  fissure. 


The  alveolus  for  the  temporary  canine  is  commonly  formed  in  the  maxilla  alone. 


THE    PTERYGOID    BONES THE    NASAL    BONES  67 

The  perpendicular  part  (Pars  perpendicularis)  is  more  extensive  and  forms 
most  of  the  lateral  wall  of  the  choanse  or  posterior  nares.  The  nasal  surface  (Facies 
nasalis)  is  in  the  greater  part  of  its  extent  concave  and  smooth,  but  presents  a 
narrow  rough  area  to  which  the  pterygoid  bone  is  attached.  Below  this  the  bone 
curves  outward,  forming  the  pterygoid  process.  The  maxillary  surface  (Facies 
maxillaris)  presents  three  areas  for  consideration.  The  largest  articulates  with  the 
maxilla;  it  is  rough  and  is  crossed  by  a  groove  which  concurs  with  one  on  the  max- 
illa in  the  formation  of  the  palatine  canal.  Behind  this  is  a  smooth  part  which 
assists  in  forming  the  pterygo-palatine  fossa  (Fossa  pterygopalatina).  The  rough 
area  below  this  is  overlapped  by  the  pterygoid  process  of  the  sphenoid  bone.  The 
dorsal  border  is  perforated  by  the  sphenopalatine  foramen.  Behind  the  foramen 
the  two  plates  of  the  bone  separate  to  inclose  part  of  the  sphenopalatine  sinus. 
The  inner  plate  curves  medially  to  articulate  with  the  vomer.  The  outer  plate 
joins  the  maxilla  and  frontal  and  the  orbital  wing  of  the  sphenoid;  it  may  join  the 
lacrimal  bone  also. 

Development. — The  palatine  bone  ossifies  in  membrane  from  a  single  center. 

The  Pterygoid  Bones 

The  pterygoid  bones  (Ossa  pterygoidea)  are  narrow,  thin,  bent  plates,  situated 
on  either  side  of  the  posterior  nares.  Each  has  two  surfaces  and  two  extremities. 
The  medial  surface  is  smooth,  and  forms  part  of  the  wall  of  the  posterior  nares. 
The  lateral  surface  articulates  with  the  palatine,  vomer,  and  sphenoid,  concurring 
with  the  last  in  the  formation  of  the  pterygoid  canal.  The  ventral  extremity  is 
free,  turned  slightly  outward,  and  forms  the  hamulus  pterygoideus ;  this  is  grooved 
externally  and  forms  a  pulley  around  which  the  tendon  of  the  tensor  palati  muscle 
is  reflected. 

Development. — The  pterygoid  ossifies  in  membrane  from  a  single  center. 

The  Nasal  Bones 

The  nasal  bones  (Ossa  nasalia)  are  situated  in  front  of  the  frontal  bones  and 
form  the  greater  part  of  the  roof  of  the  nasal  cavity.  They  have  an  elongated 
triangular  outline,  wide  behind,  pointed  in  front.  Each  presents  two  surfaces,  two 
borders,  and  two  extremities. 

The  facial  surface  is  smooth  and  is  convex  transversely;  the  profile  contour  is 
usually  slightly  wavy,  with  a  depression  about  its  middle  and  a  variably  prominent 
area  in  front. 

The  nasal  surface  is  smooth  and  concave  from  side  to  side.  About  in  its 
middle  it  presents  the  dorsal  turbinate  crest  (Crista  turbinata  dorsalis),  which  is 
parallel  with  the  medial  border,  and  has  the  dorsal  turbinate  bone  attached  to  it. 
Most  of  this  surface  faces  into  the  nasal  cavity,  but  its  posterior  part,  lateral  to 
the  turbinate  crest,  enters  into  the  formation  of  the  frontal  sinus;  the  latter  area  is 
marked  off  by  an  oblique  ridge  which  corresponds  to  the  septum  between  the  an- 
terior and  posterior  parts  of  the  dorsal  turbinate  bone. 

The  medial  border  is  straight,  and  meets  the  opposite  bone  at  the  nasal  suture. 

The  lateral  border  is  irregular.  Its  anterior  third  is  free  and  concurs  with 
the  nasal  process  of  the  premaxilla  in  forming  the  naso-maxillary  notch  (Incisura 
naso-maxillaris) .  Behind  this  it  joins  the  end  of  the  nasal  process,  the  maxilla, 
and  the  lacrimal,  forming  the  naso-maxillary  and  naso-lacrimal  sutures. 

The  greater  part  of  the  edge  is  beveled  and  fits  into  a  groove  on  the  upper  border  of  the 
nasal  process,  the  maxilla,  and  the  lacrimal  bone. 

The  posterior  extremity  or  base  is  beveled  and  overlaps  the  frontal  bone, 
forming  the  naso-frontal  suture. 

The  anterior  extremity  or  apex  is  pointed  and  thin. 


68  THE  SKELETON  OF  THE  HORSE 

Development. — Each  nasal  bone  ossifies  in  membrane  from  a  single  center. 
The  nasal  suture  does  not  close  completely  even  in  old  age.  In  some  cases  the  two 
plates  separate  to  inclose  a  small  air-space  (nasal  sinus)  in  the  posterior  part. 

The  Lacrimal  Bones 

The  lacrimal  bones  (Ossa  lacrimalia)  are  situated  at  the  anterior  part  of  the 
orbit,  and  extend  forward  on  the  face  to  the  posterior  border  of  the  maxilla.  Each 
presents  three  surfaces  and  a  circumference. 

The  lateral  face  is  clearly  divided  into  orbital  and  facial  parts  by  the  orbital 
margin.  The  orbital  surface  (Facies  orbitalis)  is  triangular  in  outline,  smooth  and 
concave ;  it  forms  part  of  the  medial  and  front  wall  of  the  orbit.  Near  the  orbital 
margin  it  presents  a  funnel-like  fossa  (Fossa  sacci  lacrimalis),  which  is  the  entrance 
to  the  lacrimal  canal;  the  fossa  is  occupied  by  the  lacrimal  sac,  which  is  the  dilated 
origin  of  the  naso-lacrimal  duct.  Behind  this  is  a  depression  in  which  the  inferior 
oblique  muscle  of  the  eye  takes  origin.  The  facial  surface  (Facies  facialis)  is  more 
extensive,  and  has  the  form  of  an  irregular  pentagon.  It  is  slightly  convex  and 
smooth  in  the  foal,  flattened  in  the  adult.  It  usually  bears  the  small  lacrimal 
tubercle,  which  is  situated  nearly  an  inch  (ca.  2  cm.)  from  the  orbital  margin. 
The  orbital  margin  (Margo  orbitalis)  is  concave,  rough  above,  smooth  below. 

The  nasal  surface  (Facies  nasalis)  faces  into  the  frontal  and  maxillary  sinuses. 
It  is  concave  and  very  irregular,  and  is  crossed  almost  horizontally  by  the  osseous 
lacrimal  canal  (Canalis  lacrimalis  osseus). 

The  circumference  articulates  dorsally  with  the  frontal  and  nasal  bones, 
ventrally  with  the  malar  and  maxilla,  in  front  with  the  maxilla,  and  behind  with 
the  frontal.  The  various  sutures  so  formed  are  designated  by  combinations  of  the 
names  of  the  bones. 

Development. — Each  ossifies  in  membrane  from  a  single  center. 

The  Malar  Bones 

The  malar  or  zygomatic  bones  (Ossa  zygomatica)  are  placed  between  the  lac- 
rimal above  and  the  maxilla  below  and  in  front.  Each  is  irregularly  triangular  in 
outline  and  presents  three  surfaces,  three  borders,  and  a  process. 

The  facial  surface  (Facies  facialis)  is  smooth,  slightly  convex,  wide  in  front, 
and  narrow  behind.  At  its  lower  part  it  presents  the  facial  crest,  which  is  continu- 
ous in  front  with  the  similar  ridge  on  the  maxilla  and  behind  with  the  zygomatic 
process  of  the  temporal;  the  crest  is  rough  below,  where  the  masseter  muscle  is 
attached  to  it. 

The  orbital  surface  is  much  smaller  than  the  facial  surface,  from  which  it  is 
separated  by  the  concave  orbital  margin  (Margo  orbitalis).  It  is  concave  and 
smooth,  and  forms  part  of  the  lower  and  front  wall  of  the  orbit. 

The  nasal  surface  is  concave  and  faces  into  the  maxillary  sinus.  In  the  young 
foal  a  consideraljle  part  of  it  articulates  with  the  maxilla. 

The  dorsal  border  articulates  with  the  lacrimal  chiefly,  but  to  a  small  extent 
behind  with  the  maxilla  also. 

The  ventral  and  anterior  borders  articulate  with  the  maxilla. 

The  posterior  extremity  is  formed  by  the  zygomatic  process,  which  is  beveled 
above  and  is  overlapped  by  the  zygomatic  process  of  the  temporal  bone. 

Development. — Each  ossifies  in  membrane  from  one  or  two  centers. 

The  Turbinate  Bones 
These  (Ossa  turbinata)  are  delicate,  scroll-like  bones,  four  in  number,  which 
are  attached  to  the  lateral  walls  of  the  nasal  cavity.     They  project  into  the  cavity 
and  greatly  diminish  its  extent.     Each  is  composed  of  a  very  thin  lamina,  cribri- 


THE    TURBINATE    BONES 


69 


form  in  many  places,  and  covered  on  both  sides  witli  mucous  membrane  in  the  fresh 
state.     They  are  arranged  in  two  pairs,  dorsal  and  ventral. 

The  dorsal  turbinate  bone  (Os  turbinatum  dorsale)^  is  somewhat  cylindrical  in 
form,  but  is  flattened  from  side  to  side  and  tapers  at  each  end.  It  is  attached  to 
the  turbinate  crest  of  the  nasal  bone  and  the  nasal  plate  of  the  frontal  bone.  The 
anterior  part  is  rolled  like  a  scroll  one  and  a  half  times,  thus  inclosing  a  cavity  which 
communicates  with  the  middle  meatus  nasi.  The  arrangement  is  best  seen  on  a 
cross-section  (Fig.  55).  The  posterior  part  is  not  rolled,  but  its  ventral  border  is 
attached  to  the  lateral  nasal  wall,  thus  helping  to  inclose  a  large  space  which  is  part 
of  the  frontal  sinus.  This  cavity  is  separated  from  that  of  the  scroll-like  part  by  a 
transverse  septum.  The  medial  surface  is  flattened,  and  is  separated  from  the  sep- 
tum nasi  by  a  narrow  interval,  the  common  meatus  (Meatus  nasi  communis). 
Another  narrow  passage,  the  dorsal  meatus  (Meatus  nasi  dorsalis),  separates  the 
dorsal  surface  from  the  roof  of  the  nasal  cavity.  The  space  between  the  ventral 
surface  and  the  ventral  turbinate  is  the  middle  meatus  (Meatus  nasi  medius).    The 


A^asal  Frontal 

sinus  sinus 


Nasal 
bone 


at  nasal 


13       Sphenoidal 
sinus 

Hamulus  of 
pterygoid  bone 

Fig.  44. — Part  of  Sagittal  Section  of  Skull  op  Horse. 
1,  Perpendicular  plate  of  ethmoid  bone;    2,  great  ethmo-turbinate;    3,  dorsal  turbinate;    4,  ventral  turbinate;    5, 
vomer;   6,  middle  nasal  meatus;   7,  ventral  nasal  meatus;   8,  perpendicular  part  of  palatine  bone;   9,  palatine  process  of 
maxilla;   10,  body  of  premaxilla;  11,  nasal  process  of  premaxilla;  12,  palatine  process  of  premaxilla;   13,  pterygoid  proc- 
ess of  palatine  bone.    Dotted  lines  indicate  septa. 


anterior  extremity  is  prolonged  toward  the  nostril  by  two  small  bars  of  cartilage. 
The  posterior  extremity  is  small,  and  joins  the  cribriform  plate  and  lateral  mass  of 
the  ethmoid. 

The  ventral  turbinate  bone  (Os  turbinatum  ventrale)^  is  shorter  and  smaller 
than  the  upper  one.  It  is  attached  to  the  ventral  turbinate  crest,  and  consists', 
like  the  upper  one,  of  an  anterior  coiled  and  a  posterior  uncoiled  portion. 

To  express  briefly  the  mode  of  coiling  of  the  two  bones  of  the  same  side  we  may  say  that 
they  are  rolled  toward  the  septum  and  each  other. 

The  ventral  and  posterior  borders  of  the  posterior  part  are  attached  to  the 
maxilla,  thus  helping  to  inclose  a  cavity  which  is  part  of  the  maxillary  sinus.  The 
lower  surface  is  separated  from  the  floor  of  the  nasal  cavity  by  the  ventral  meatus 
(Meatus  nasi  ventralis),  which  is  much  larger  than  the  other  nasal  passages.  The 
anterior  extremity  is  prolonged  toward  the  nostril  by  a  curved  bar  of  cartilage. 

Development. — Each  ossifies  in  cartilage  from  a  single  center. 

1  This  bone  is  also  termed  the  naso-turbinal ;  it  is  really  a  greatly  developed  first  ethmor 
turbinate. 

^  This  is  also  called  the  maxillo-turbinal. 


70  THE  SKELETON  OF  THE  HORSE 


The  Vomer 

The  vomer  is  a  median  bone,  which  assists  in  forming  the  ventral  part  of  the 
septum  nasi.  It  is  composed  of  a  thin  lamina  which  is  bent  (except  in  its  posterior 
part)  so  as  to  form  a  narrow  groove  (Sulcus  vomeris) ,  in  which  the  lower  part  of  the 
perpendicular  plate  of  the  ethmoid  bone  and  the  septal  cartilage  are  received.  The 
lateral  surfaces,  right  and  left,  are  highest  near  the  posterior  end  and  diminish 
gradually  to  the  anterior  end;  they  are  slightly  convex  dorso-ventrally,  and  are 
covered  by  the  nasal  mucous  membrane  during  life.  The  ventral  border  is  thin 
and  free  in  its  posterior  third,  and  divides  the  choanae  or  posterior  nares  medi- 
ally; in  the  remainder  of  its  extent  it  is  wider  and  is  attached  to  the  nasal  crest. 
The  anterior  extremity  lies  above  the  ends  of  the  palatine  processes  of  the  premax- 
illae.  The  posterior  extremity  consists  of  two  wings  (Alae  vomeris)  which  extend 
outward  below  the  body  of  the  presphenoid;  posteriorly  they  form  a  notch  (In- 
cisura  vomeris),  and  laterally  join  the  palatine  and  pterygoid  bones. 

Development. — The  vomer  is  primitively  double,  and  ossifies  from  a  center  on 
cither  side  in  the  membrane  covering  the  cartilaginous  septum  nasi;  the  two 
laminse  then  fuse  below  and  form  a  groove. 

The  Mandible 

The  mandible  (Mandibula),^  or  lower  jaw  bone,  is  the  largest  bone  of  the 
face.  The  two  halves  of  which  it  consists  at  birth  unite  during  the  second  or  third 
month,  and  it  is  usually  described  as  a  single  bone.  It  carries  the  lower  teeth,  and 
articulates  l^y  its  condyles  with  the  squamous  temporal  on  either  side.  It  consists 
of  a  body  and  two  rami.^ 

The  body  (Corpus  mandibulse)  is  the  thick  anterior  part  which  bears  the  incisor 
teeth.  It  presents  two  surfaces  and  a  border.  The  lingual  surface  (Facies  lin- 
gualis)  is  smooth  and  slightly  concave;  during  life  it  is  covered  by  mucous  mem- 
brane, and  the  tip  of  the  tongue  overlies  it.  The  mental  surface  (Facies  mentalis) 
is  convex  and  is  related  to  the  lower  lip.  It  is  marked  by  a  median  furrow  which 
indicates  the  position  of  the  primitive  symphysis  mandibulse.  The  curved  alveolar 
border  (Limbus  alveolaris)  presents  six  alveoli  for  the  incisor  teeth,  and  a  little 
further  back  two  alveoli  for  the  canine  teeth  in  the  male;  in  the  mare  the  latter  are 
usually  absent  or  small. 

The  rami  (Rami  mandibulse)  extend  backward  from  the  body  and  diverge  to 
inclose  the  mandibular  (or  submaxillary)  space  (Spatium  mandibulare).  Each 
ramus  is  bent  so  as  to  consist  of  a  horizontal  part  (Pars  molaris)  which  bears  the 
lower  cheek  teeth,  and  a  vertical  part  (Ramus  mandibulse  [S.  N.  A.])  which  is  ex- 
panded and  furnishes  attachment  to  powerful  muscles;  the  term  angle  is  applied 
to  the  most  prominent  part  of  the  curve.  The  ramus  presents  two  surfaces,  two 
borders,  and  two  extremities.  The  lateral  surface  is  smooth  and  slightly  convex 
from  edge  to  edge  on  the  horizontal  part;  at  the  junction  with  the  body  it  presents 
the  mental  foramen  (Foramen  mentale),  which  is  the  external  opening  of  the  man- 
dibular canal.  On  the  vertical  part  it  is  somewhat  concave  and  presents  a  number 
of  rough  lines  for  the  attachment  of  the  masseter  muscle.  The  medial  surface  of 
the  horizontal  part  is  smooth,  and  presents  a  shallow  longitudinal  depression  in  its 
middle;  above  this  there  is  often  a  faint  mylo-hyoid  line  (Linea  mylohyoidea)  for 
the  attachment  of  the  muscle  of  like  name.  At  the  lower  part  of  the  junction  with 
the  body  there  is  a  small  fossa  for  the  attachment  of  the  genio-hyoid  and  genio- 

^  This  bone  is  also  commonly  called  the  inferior  maxilla. 

^  In  the  Stuttgart  Anatomical  Nomenclatm-e  (S.  N.  A.)  the  body  (Corpus)  is  the  part  which 
bears  the  teeth,  and  is  divided  into  a  pars  incisiva  and  a  pars  molaris.  The  ramus  is  the  rest  of 
the  bone.  This  mode  of  description  is  copied  from  the  Basel  Nomina  Anatomica.  It  does  not 
seem  to  the  author  to  be  well  adapted  to  comparative  purposes. 


THE    MANDIBLE  71 

glossus  muscles.  On  the  vertical  part  the  surface  is  concave,  and  is  marked  in  its 
lower  and  posterior  part  by  rough  lines  for  the  attachment  of  the  medial  pterygoid 
n^.uscle.  In  front  of  its  middle  is  the  mandibular  foramen  (Foramen  mandibulare)/ 
which  is  the  posterior  orifice  of  the  mandibular  canal  (Canalis  mandibulae).-  The 
canal  curves  downward  and  passes  forward  below  the  cheek  teeth,  opening  exter- 
nally at  the  mental  foramen;  it  is  continued  into  the  body  of  the  bone  as  a  small 
canal  (CanaUs  alveolaris  incisivus),  which  carries  the  vessels  and  nerves  to  the 
incisor  teeth.  The  dorsal  or  alveolar  border  (Limbus  alveolaris)  forms  anteriorly 
part  of  the  interalveolar  space;  here  it  is  thin.  Behind  this  it  is  thick  and  is  ex- 
cavated by  six  alveoli  for  the  lower  cheek  teeth.  Behind  the  last  alveolus  it  curves 
sharply  upward  and  is  narrow  and  rough.  In  the  young  foal  there  is  commonly  a 
small  alveolus  for  the  vestige  of  the  first  premolar  ("wolf  tooth")  close  to  the  first 
large  one.  The  ventral  border  of  the  horizontal  part  is  nearly  straight;  it  is  thick 
and  rounded  in  the  young  horse,  becoming  narrower  and  sharp  in  old  subjects.     At 


6 

Fig.  45. — Left  Half  of  Mandible  of  Hor.se;   Medial  View. 
1,  Body  of  mandible  (median  section);  2,  2',  horizontal  and  vertical  parts  of  ramus;  3,  interalveolar  border;  4, 
depression  for  attachment  of  genio-hyoideus  muscle;    o,  mandibular  foramen;    6,  vascular  impression;    7,  angle;    8, 
condyle;   9,  coronoid  process;    10,  mandibular  notch;    11,  incisor  teeth;    12,  canine  tooth;    13,  cheek  teeth. 

its  posterior  part  there  is  a  smooth  impression  (Incisura  vasorum)  where  the  facial 
vessels  and  parotid  duct  turn  round  the  bone.  Behind  this  point  the  border  curves 
sharply  upward,  forming  the  angle  of  the  mandible  (Angulus  mandibulse) ;  this  part 
is  thick  and  has  two  roughened  lips,  separated  by  a  considerable  intermediate  space; 
near  the  condyle  it  becomes  narrower.  The  anterior  extremity  joins  the  body. 
The  articular  extremity  comprises  the  coronoid  process  in  front  and  the  condyle 
behind,  the  two  being  separated  by  the  mandibular  notch  (Incisura  mandibulae), 
through  which  the  nerve  to  the  masseter  muscle  passes.  The  coronoid  process 
(Processus  coronoideus)  is  thin  transversely  and  curved  slightly  medially  and 
backward.  It  projects  upward  in  the  temporal  fossa  and  furnishes  insertion  to 
the  temporal  muscle.  The  condyle  of  the  mandible  (Condylus  mandibulae)  lies  at 
a  much  lower  level  than  the  end  of  the  coronoid  process.  It  is  elongated  trans- 
versely and  articulates  with  the  squamous  temporal  through  the  medium  of  an 

^  This  is  also  commonly  called  the  inferior  maxillary  foramen. 
^  This  is  also  termed  the  inferior  dental  canal. 


72 


THE   SKELETON    OF   THE    HORSE 


articular  disc.  The  part  below  the  condyle  is  usually  termed  the  neck  of  the 
mandible  (CoUum  mandibulse) ;  on  its  antero-medial  part  is  a  depression,  the  fovea 
pterygoidea,  in  which  the  lateral  pterygoid  muscle  is  attached.  The  middle  of  the 
vertical  part  of  the  ramus  consists  to  a  large  extent  of  a  single  plate  of  compact 
substance  which  may  be  so  thin  in  places  as  to  be  translucent. 

Development. — The  mandible  develops  from  two  chief  centers  in  the  connec- 
tive tissue  which  overlies  the  paired  Meckel's  cartilages.  At  birth  it  consists  of 
two  symmetrical  halves  which  meet  at  the  median  symphysis  mandibulae.  Fusion 
usually  occurs  in  the  second  or  third  month. 

Age  Changes. — These  are  associated  largely  with  the  growth,  and  later  with  the  reduction, 
of  the  teeth.  In  the  young  horse,  in  which  the  teeth  are  long  and  are  in  great  part  embedded 
in  the  bone,  the  body  is  thick  and  strongly  curved,  and  the  horizontal  part  of  the  ramus  is  also 
thick.  Later,  as  the  teeth  are  extruded  from  the  bone,  the  body  becomes  flattened  and  narrower, 
and  the  horizontal  part  of  the  ramus  is  thinner,  especially  in  its  lower  part.  In  the  old  subject 
the  angle,  the  vascular  impression  in  front  of  it,  and  the  lines  for  the  attachment  of  tendinous 
layers  of  the  masseter  and  pterygoid  muscles  are  more  pronounced. 


The  Hygid  Bone 

The  hyoid  bone  (Os  hyoideum)  is  situated  chiefly  between  the  vertical  parts 
of  the  rami  of  the  mandible,  but  its  upper  part  extends  somewhat  further  back. 
It  is  attached  to  the  petrous  temporal  bones  by  rods  of  cartilage,  and  supports  the 

root  of  the  tongue,  the  pharynx,  and  the 
larynx.  It  consists  of  a  body,  a  lingual 
process,  and  three  pairs  of  cornua. 

The  body  or  basihyoid  (Corpus  ossis 
hyoidei)  is  a  short  transverse  bar,  com- 
pressed dorso-ventrally.  The  dorsal  sur- 
face is  concave  and  smooth  in  its  middle, 
and  presents  at  each  end  a  convex  facet 
or  tubercle  for  articulation  with  the  small 
cornu.  The  ventral  surface  is  flattened 
and  is  slightly  roughened  for  muscular 
attachment.  The  anterior  border  carries 
medially  the  lingual  process.  The  pos- 
terior border  is  concave  and  smooth  in  its 
middle,  and  carries  on  either  side  the  thy- 
roid cornu.  The  body,  the  lingual  proc- 
ess, and  the  thyroid  cornua  are  fused 
and  may  be  compared  to  a  spur  or  a  fork 
with  a  very  short  handle. 

The  lingual  process  (Processus  lingu- 

alis)  projects  forward  medially  from  the 

body,  and  is  embetlded  in  the  root  of  the 

tongue  during  life.     It  is  compressed  laterally  and  has  a  blunt-pointed  free  end. 

The  lateral  surfaces  are  slightly  concave.     The  dorsal  border  is  thin  and  irregular, 

and  the  ventral  border  is  thick  and  rough. 

The  thyroid  cornua  or  thyrohyoids  (Cornua  thyreoidea)i  extend  backward  and 
upward  from  the  lateral  parts  of  the  body.  They  are  compressed  laterally  (except 
at  their  junction  with  the  body),  and  the  posterior  end  has  a  short  cartilaginous 
prolongation  which  is  connected  with  the  anterior  cornu  of  the  thyroid  cartilage 
of  the  larynx. 

The  small  cornua  or  keratohyoids  (Cornua  minora)  are  short  rods  which  are 
directed  upward  and  forward  from  either  end  of  the  body.     Each  is  somewhat 
constricted  in  its  middle  part  and  has  slightly  enlarged  ends.     The  ventral  end  has 
'  These  correspond  to  the  great  cornua  of  man. 


Fia.  46. — Hyoid  Bone  or  Horse,  Viewed  from  the 
Side  and  Somewhat  from  in  Front. 
o.  Body;  6,  lingual  process;  c,  thyroid  cornu;  c', 
cartilage  of  c;  d,  small  cornu;  e,  middle  cornu;  /.great 
cornu;  /',  muscular  angle  of  great  cornu;  g,  cartilage 
of  great  cornu.  (EUenberger-Baum,  Anat.  d.  Haus- 
tiere.) 


THE    SKULL   AS    A    WHOLE  73 

a  small  concave  facet  which  articulates  with  the  body.  The  dorsal  end  articulates 
with  the  great  cornu,  or  with  the  middle  cornu  when  present. 

The  great  comua  or  stylohyoids  are  much  the  largest  parts  of  the  bone.  They 
are  directed  dorsallj"  and  backward,  and  are  connected  above  with  the  base  of  the 
petrous  temporal  bones.  Each  is  a  thin  plate,  seven  or  eight  inches  (ca.  18  to  20 
cm.)  long,  which  is  slightly  curved  in  its  length,  so  that  the  lateral  surface  is  con- 
cave and  the  medial  surface  is  convex;  both  are  smooth.  The  borders  are  thin. 
The  dorsal  extremity  is  large  and  forms  two  angles;  the  articular  angle  is  connected 
by  a  rod  of  cartilage  with  the  hyoid  process  of  the  petrous  temporal  bone;  the 
muscular  angle  is  somewhat  thickened  and  rough  for  muscular  attachment.  The 
ventral  extremity  is  small,  and  articulates  with  the  small  or  the  middle  cornu. 

The  middle  comua  or  epihyoids  are  small,  wedge-shaped  pieces  or  nodules 
interposed  between  the  small  and  great  cornua.  They  are  usually  transitory,  and 
unite  with  the  great  cornua  in  the  adult. 

Development. — The  hyoid  ossifies  in  the  cartilages  of  the  second  and  third 
visceral  arches.  Each  part  has  a  separate  center,  except  the  lingual  process,  which 
ossifies  by  extension  from  the  body.  In  the  foal  there  is  a  separate  nucleus  at  each 
end  of  the  body  which  intervenes  between  the  latter  and  the  thyroid  cornu;  it 
articulates  with  the  small  cornu.  The  anterior  part  of  the  lingual  process  may  be 
a  separate  piece. 


THE  SKULL  AS  A  WHOLE 

The  skull  of  the  horse  has,  as  a  whole,  the  form  of  a  long,  four-sided  pyramid, 
the  base  of  which  is  posterior.  It  is  convenient,  however,  to  exclude  the  mandible 
and  hyoid  from  present  consideration.  The  division  between  the  cranium  (Cra- 
nium cerebrale)  and  the  face  (Cranium  viscerale)  may  be  indicated  approxi- 
mately by  a  transverse  plane  through  the  anterior  margins  of  the  orbits. 

The  dorsal  or  frontal  surface  (Norma  frontalis)  is  formed  by  the  squamous 
part  of  the  occipital,  interparietal,  parietal,  frontal,  nasal,  and  premaxil- 
lary  bones.  It  may  be  divided  into  parietal,  frontal,  nasal,  and  premaxillary 
regions.  The  parietal  region  extends  from  the  nuchal  crest  to  the  parieto-frontal 
suture.  It  is  marked  medially  by  the  external  parietal  crest,  which  bifurcates  in 
front,  the  branches  becoming  continuous  with  the  frontal  crests.  The  latter  curve 
outward  on  either  side  to  the  root  of  the  supraorbital  process.  The  frontal  region 
is  the  widest  part  of  the  surface,  and  is  smooth  and  almost  flat.  It  is  bounded  in 
front  by  the  naso-frontal  suture.  On  either  side  of  it  is  the  root  of  the  supraorbital 
process,  pierced  by  the  supraorbital  foramen.  The  nasal  region  is  convex  from 
side  to  side,  wide  behind,  narrow  in  front.  Its  profile  is  in  some  cases  nearly 
straight;  in  others  it  is  undulating,  with  a  variably  marked  depression  about  its 
middle  and  at  the  anterior  end.  The  premaxillary  region  presents  the  osseous 
nasal  aperture  (Apertura  nasalis  ossea)  and  the  foramen  incisivum. 

The  lateral  surface  (Norma  lateralis)  (Fig.  28)  may  be  divided  into  cranial, 
orbital,  and  preorl)ital  or  maxillary  regions. 

The  cranial  region  presents  the  temporal  fossa,  the  zygomatic  arch,  and  the 
outer  part  of  the  petrous  temporal  bone.  The  temporal  fossa  is  bound  medially 
by  the  parietal  and  frontal  crests,  laterally  by  the  temporal  crest  and  the  zygomatic 
arch,  and  behind  by  the  nuchal  crest.  Its  upper  and  middle  parts  are  rough  for 
the  attachment  of  the  temporal  muscle.  In  its  lower  posterior  part  are  several 
foramina  which  communicate  with  the  temporal  canal.  The  fossa  is  continuous 
in  front  with  the  orbital  cavity.  The  zygomatic  arch  is  formed  by  the  zygomatic 
processes  of  the  temporal,  malar,  and  maxilla.  Its  ventral  face  presents  the  con- 
dyle and  glenoid  cavity  for  articulation  with  the  lower  jaw,  through  the  medium 
of  the  articular  disc.     Behind  the  glenoid  cavity  is  the  postglenoid  process.     The 


74 


THE    SKELETON    OF   THE    HORSE 


external  acoustic  process  projects  outward  through  a  deep  notch  in  the  ventral 
margin  of  the  squamous  temporal  below  the  temporal  crest.  A  little  further  back 
is  the  mastoid  process,  crossed  in  its  upper  part  by  a  groove  for  the  posterior 
meningeal  artery. 

The  orbital  region  comprises  the  orbit  and  the  pterygo-palatine  fossa.     The 


Nuchal  crest 


Occipital 
Interparietal  - 

Parietal  ^//  / 


Squamous  temporal 


Frontal 


Parietal  crest 

Temporal  fossa 
Temporal  crest 


Coronoid  process 
Zygomatic  arch 

Supraorbital  process 
S  upraorbital  foramen 

Orbit 
Facial  crest 


I >ifra orbital  foramen 


Nasal  process  of  premaxilla 


Body  of  premaxilla 


Foramen,  incisivum 


Fig.  47. — Skull  of  Horse;  Dorsal  View. 
1,  Parieto-ocoipital  suture;    2,  squamous  suture;    3,  parietal  suture;    4,  parieto-frontal  suture;    5,  frontal  suture; 
•6,  naso-frontal  suture;    7,  naso-lacrimal  suture;    8,  lacrimo-malar  suture;    9,  lacrimo-maxillary  suture;    10,  maxillo- 
■malar  suture;    11,  naso-maxillary  suture;    12,  nasal  suture. 


orbit  is  a  cavity  which  incloses  the  eyeball,  with  the  muscles,  vessels,  and  nerves 
associated  with  it.  It  is  not  separated  in  the  skeleton  from  the  temporal  fossa. 
The  axis  of  the  orbit  (Axis  orbitse),  taken  from  the  optic  foramen  to  the  middle  of 
the  inlet,  is  directed  forward,  outward,  and  slightly  upward.  The  medial  wall 
(Paries  medialis)  is  complete  and  extensive.  It  is  concave  and  smooth,  and  is 
formed  by  the  frontal  and  lacrimal  and  the  orbital  wing  of  the  sphenoid.     In  its 


THE    SKULL   AS    A    WHOLE 


75 


extreme  anterior  part  is  the  fossa  for  the  lacrimal  sac.  Behind  this  there  is  a  small 
depression  in  which  the  inferior  oblique  muscle  of  the  eye  arises;  here  the  plate 
which  separates  the  orbit  from  the  maxillary  sinus  is  very  thin.  The  dorsal  wall 
(Paries  dorsalis)  is  formed  by  the  frontal  and  to  a  small  extent  by  the  lacrimal  bone. 
It  presents  the  supraorbital  foramen,  which  perforates  the  root  of  the  supraorbital 
process.  The  ventral  wall  (Paries  ventralis)  is  very  incomplete,  and  is  formed  by 
the  malar,  the  zygomatic  process  of  the  temporal,  and  to  a  small  extent  by  the  max- 
illa. The  lateral  wall  (Paries  lateralis)  is  the  supraorbital  process.  At  the  extreme 
posterior  part  is  the  orbital  group  of  foramina.  Four  are  situated  in  front  of  the 
pterygoid  crest.     Of  these,  the  uppermost  is  the  ethmoidal  foramen,  which  trans- 


FlG.  48. — Cranial  and  Orbital  Regions  of  Skull  of  Horse;  Lateral  View.  The  Zygomatic  Arch  and  Supra- 
orbital Process  Have  Been  Sawn  Off. 
5. 0.,  Squamous  part  of  occipital;  P,  parietal;  S,  squamous  temporal;  B.o.,  basilar  part  of  occipital;  B.s.,  body  of 
sphenoid;  A. «.,  temporal  wing  of  sphenoid;  A. o.,  orbital  wing  of  sphenoid;  P<. p.,  pterygoid  process  of  sphenoid;  P.p., 
perpendicular  part  of  palate  bone;  F,  F',  facial  and  orbital  parts  of  frontal  bone;  L,  L' ,  orbital  and  facial  parts  of  lacri- 
mal bone;  M,  facial  part  of  malar  bone;  M.x.,  maxilla;  a,  parieto-occipital  suture;  b,  squamous  suture;  c,  d,  spheno- 
squamous suture;  e,  fronto-palatine  suture;  /,  fronto-lacrimal  suture.  1,  Occipital  condyle;  2,  condyloid  fossa;  3, 
paramastoid  process;  4,  nuchal  crest;  5,  external  occipital  protuberance;  6,  external  acoustic  meatus;  7,  mastoid 
process;  8,  hyoid  process;  9,  stylomastoid  foramen;  10,  muscular  process;  11,  foramen  lacerum;  12,  postglenoid 
process;  13,  glenoid  cavity;  14,  temporal  condyle;  15,  pterygoid  groove;  16,  alar  canal  of  pterygoid  process  indicated 
by  arrow;  17,  alar  foramen;  18,  ethmoidal  foramen;  19,  optic  foramen;  20,  foramen  orbitale;  21,  maxillary  fora- 
men; 22,  sphenopalatine  foramen;  23,  posterior  palatine  foramen;  24,  supraorbital  foramen  (opened) ;  25,  fossa  for 
lacrimal  sac;  26,  depression  for  origin  of  obliquus  oculi  inferior;  27,  facial  crest;  28,  maxillary  tuberosity;  29,  alveolar 
tuberosity ;   30,  hamulus  of  pterygoid  bone. 


mits  the  ethmoidal  vessels  and  nerve.  The  optic  foramen  is  situated  a  little  lower 
and  further  back;  it  transmits  the  optic  nerve.  Immediately  below  the  optic  is 
the  foramen  orbitale,  which  transmits  the  ophthalmic,  third,  sixth,  and  sometimes 
the  fourth  nerve;  commonly  there  is  a  very  small  trochlear  foramen  in  the  crest 
for  the  last-named  nerve.  The  foramen  rotundum  is  below  the  foramen  orbitale, 
from  which  it  is  separated  by  a  thin  plate;  it  transmits  the  maxillary  nerve.  The 
alar  canal  opens  in  common  with  the  foramen  rotundum,  and  the  anterior  opening 
of  the  pterygoid  canal  is  also  found  here.  The  foramen  alare  parvum  is  just  be- 
hind the  pterygoid  crest  and  on  a  level  with  the  foramen  orbitale.  It  is  the  upper 
opening  of  a  canal  which  leads  from  the  alar  canal,  and  through  it  the  anterior  deep 


76 


THE   SKELETON    OF   THE   HORSE 


temporal  artery  emerges.  The  inlet  of  the  orbital  cavity  (Aditus  orbitae)  is  cir- 
cumscribed by  a  complete  bony  ring,  which  is  nearly  circular.  Its  infraorbital 
margin  (Margo  infraorbitalis)  is  smooth  and  rounded;  the  supraorbital  margin 
(Margo  supraorbitalis)  is  rough  and  irregularly  notched.  During  life  the  cavity  is 
completed  by  the  periorbita,  a  conical  fibrous  membrane,  the  apex  of  which  is  at- 
tached around  the  optic  foramen.  Ventral  to  the  orbital  cavity  is  the  pterygo- 
palatine fossa.  Its  wall  is  formed  by  the  pterygoid  process,  the  perpendicular 
part  of  the  palate  bone,  and  the  tuber  maxillare.  Its  deep  anterior  recess  contains 
three  foramina.     The  upper  one,  the  maxillary  foramen,  is  the  entrance  to  the  in- 


Nuchal  ere  at 

Dorsal  border  of 

for.  magnum 

Foramen  magnum 

Hypoglossal  foramen 

For.  lacenim  posterms 

Stylomastoid  foramen 

Hyoid  process 

Muscular  process 
For.  lacerum  anterius 
Basilar  tubercles 

Alar  canal 

Pterygoid  process 
of  sphenoid 
Pterygoid  hone 

Vomer  {alee) 
Pterygoid  process  of 

palatine  bone 
Palatine  bone  {per- 
pendicular part) 
Alveolar  tuberosity 

Posterior  nares 
Last  molar  tooth 


External  occipital  pro- 
tuberance 

Occipital  condyle 

Paramastoid  process 

Condyloid  fossa 

Mastoid  process 

Bulla  ossea 


process 


Glenoid  cavity 

Temporal  condyle 
Zygomatic  process 
Infratemporal  fossa 
Zygomatic  process  of 
malar 


Pterygo-palatine  fossa 
Maxillary  recess 
Maxillary  tuberosity 
Facial  crest 
Hatnulus  of  pterygoid 
Vomer 

Palatine  bone  {hori- 
zontal part) 
Ant.  palatine  foramen 

Palatine  groove 

Palatine  process  of 
maxilla 

Fig.  49. — Line  Drawing  of  Posterior  Half  of  Base  of  Skull  of  Horse,  Without  Mandible.     (Key  to  Fig.  50.) 
A,  Basilar  part  of  occipital;    B,  body  of  sphenoid;    C,  temporal  wing  of  sphenoid;    D,  squamous  temporal  bone; 


£,  petrous  temporal  bone;  F,  orbital  part  of  frontal  bone,  i,  Incisura  carotica;  ; 
4,  external  orifice  of  temporal  canal;  5,  osseous  auditory  or  Eustachian  tube;  6 
acoustic  process;  S,  hyoid  process ;  S,  pterygoid  groove ;  iO,  supraorbital  process. 


ovalis;  3,  incisuraspinosa; 
petro-tympanic  fissure;    7,  external 


fraorbital  canal,  which  transmits  the  infraorbital  nerve  and  vessels.  The  spheno- 
palatine foramen  perforates  the  medial  wall  of  the  recess  and  transmits  vessels  and 
nerves  of  like  name  to  the  nasal  cavity.  The  lower  foramen,  the  posterior  palatine, 
transmits  the  palatine  artery  and  nerve  to  the  palatine  canal.  The  upper  part  of 
the  fossa  is  smooth,  and  is  crossed  by  the  internal  maxillary  artery  and  the  maxillary 
nerve.  The  lower  part  is  chiefly  roughened  for  the  attachment  of  the  lateral 
pterygoid  muscle,  but  is  crossed  in  front  by  a  smooth  groove  in  which  the  palatine 
vein  lies.  In  its  extreme  posterior  part  is  the  small  opening  of  the  pterygoid 
canal. 

The  preorbital  or  maxillary  region  is  formed  chiefly  by  the  maxilla,  but  also  by 


THE    SKULL   AS    A   WHOLE 


77 


the  premaxilla,  and  the  facial  parts  of  the  lacrimal  and  malar  bones.  Its  contour 
is  approximately  triangular,  the  base  being  posterior.  It  offers  two  principal 
features.  The  facial  crest  extends  forward  from  the  ventral  margin  of  the  orbit, 
and  ends  abruptly  at  a  point  about  an  inch  and  a  quarter  (ca.  3  to  3.5  cm.)  above  the 


Fig.   50. — Ventral  Surface  op  Skull  of  Hohse,  Posterior  Half  Without  Mandible. 
The  skull  is  inclined  slightly.     (Notation  on  key  Fig.  49.) 


third  or  fourth  cheek  tooth  ;i  its  ventral  aspect  is  rough  for  the  attachment  of  the 
masseter  muscle.  The  infraorbital  foramen  is  situated  in  a  transverse  plane  about 
an  inch  (ca.  2  to  3  cm.)  in  front  of  the  end  of  the  crest  and  about  two  inches  (5  cm.) 

1  This  relation  varies  with  age.  In  the  new-born  foal  the  posterior  part  of  the  second  tooth, 
in  the  young  horse  the  posterior  part  of  the  third  tooth,  in  the  older  subject  the  fourth,  lies  below 
the  end  of  the  crest. 


78  THE  SKELETON  OF  THE  HORSE 

above  it.  The  foramen  opens  forward,  and  through  it  the  infraorbital  artery  and 
nerve  emerge.  The  surface  over  the  premolar  teeth  varies  greatly  with  age,  in 
conformity  "s^dth  the  size  of  the  embedded  parts  of  the  teeth.  In  the  young  horse 
the  surface  here  is  strongly  convex,  the  outer  plate  of  bone  is  thin  and  even  defective 
sometimes  in  places,  and  the  form  of  the  teeth  is  indicated  by  eminences  (Juga 
alveolaria).  In  the  old  animal  the  surface  is  concave  on  account  of  the  extrusion 
of  the  teeth  from  the  bone.  The  downward  curve  of  the  premaxilla  is  pronounced 
in  the  young  subject,  very  slight  in  the  aged. 

In  some  skulls  there  is  a  distinct  depression  a  short  distance  in  front  of  the  orbit;  here  the 
levator  labii  superioris  proprius  arises. 

The  ventral  or  basal  surface  (Norma  basalis),  exclusive  of  the  mandible, 
consists  of  cranial,  choanal,  and  palatine  regions. 

The  cranial  region  (Basis  cranii  externa)  extends  forward  to  the  vomer  and 
pter3'goid  processes  (Fig.  50).  x\t  its  posterior  end  is  the  foramen  magnum,  flanked 
by  the  occipital  condyles.  Lateral  to  these  is  the  condyloid  fossa,  in  which  is  the 
hypoglossal  foramen,  which  transmits  the  hypoglossal  nerve  and  the  condyloid 
vein.  Further  outward  are  the  paramastoid  processes  (Processus  jugulares) 
of  the  occipital  bone.  Extending  forward  centrally  is  a  prismatic  bar,  formed 
by  the  basilar  part  of  the  occipital  and  the  body  of  the  sphenoid  bone;  at  the 
junction  of  these  parts  are  tubercles  for  the  attachment  of  the  ventral  straight 
muscles  of  the  head.  On  either  side  of  the  basilar  part  of  the  occipital  bone  is  the 
foramen  lacerum  (basis  cranii),  bounded  laterally  by  the  base  of  the  petrous  tem- 
poral bone.  In  front  of  these  the  region  becomes  very  wide  on  account  of  the  lateral 
extension  of  the  zygomatic  processes,  which  present  ventrally  the  condyle  and 
glenoid  cavity  for  articulation  with  the  mandible.  Beyond  this  the  process  turns 
forward  and  joins  the  zygomatic  process  of  the  malar,  completing  the  zygomatic 
arch  and  the  surface  for  the  attachment  of  the  masseter  muscle.  On  either  side  of 
the  body  of  the  sphenoid  is  the  infratemporal  fossa,  formed  by  the  temporal  wing 
and  the  root  of  the  pterygoid  process  of  the  sphenoid  bone.  It  is  bounded  in  front 
by  the  pterygoid  crest,  which  separates  it  from  the  orbit  and  the  pterygo-palatine 
fossa.  In  it  is  the  alar  canal,  which  transmits  the  internal  maxillary  artery.  A 
little  lower  is  the  entrance  to  the  pterygoid  canal. 

The  choanal  region  presents  the  pharyngeal  orifice  of  the  nasal  cavity.  This 
is  elliptical  and  is  divided  in  its  depth  medially  b}^  the  vomer  into  two  choanae  or 
posterior  nares.  It  is  bounded  in  front  and  laterally  by  the  palate  and  pterygoid 
bones,  behind  by  the  vomer.  It  is  flanked  by  the  hamular  process  of  the  pterygoid 
bone.  The  plane  of  the  opening  is  nearly  horizontal,  and  the  length  is  about 
twice  the  width. 

The  palatine  region  comprises  a  little  more  than  half  of  the  entire  length 
of  the  base  of  the  skull  (Fig.  43).  The  hard  palate  (Palatum  durum)  is  concave 
from  side  to  side,  and  in  its  length  also  in  the  anterior  part.  It  is  formed  by  the 
palatine  processes  of  the  premaxillae  and  maxillse,  and  the  horizontal  parts  of  the 
palatine  bones.  It  is  circumscribed  in  front  and  laterally  by  the  alveolar  parts  of 
the  maxilla  and  premaxilla.  The  interalveolar  space  (]\Iargo  interalveolaris)  is  that 
part  of  the  arch  in  which  alveoli  are  not  present.  Behind  the  last  alveolus  is  the 
alveolar  tuberosity,  and  medial  to  this  is  a  groove  for  the  palatine  vein.  In  the 
middle  line  is  the  median  palatine  suture  (Sutura  palatina  mediana).  In  the  line 
of  the  suture,  a  little  behind  the  central  incisors,  is  the  foramen  incisivum,  through 
which  the  palato-labial  artery  passes.  On  either  side,  parallel  with  the  alveolar 
part  of  the  maxilla,  is  the  palatine  groove  (Sulcus  palatinus),  which  contains  the 
palatine  vessels  and  nerve.  It  is  continuous  at  the  anterior  palatine  foramen  with 
the  palatine  canal,  which  is  situated  between  the  maxilla  and  the  palatine  bone. 
The  palatine  fissure  is  the  narrow  interval  along  the  lateral  margin  of  the  palatine 


THE    SKULL    AS    A   WHOLE 


79 


process  of  the  premaxilla;  it  is  closed  in  the  fresh  state  by  a  process  of  the  cartilage 
of  the  septum  nasi.  Scattered  along  each  side  of  the  palate  are  several  accessory 
foramina.  The  transverse  palatine  suture  (Sutura  palatina  transversa)  is  about 
half  an  inch  from  the  posterior  border.  The  latter  is  opposite  to  the  fifth  cheek 
tooth  in  the  adult,  and  is  concave  and  free. 

The  nuchal  or  occipital  surface  (Norma  occipitalis)  is  formed  by  the  occipital 


Zygomatic  arch 
Glenoid  cavity 

Condyle  of 
mandible 

Neck  of  mandible 


Angle  of  mandible 

Fig.  51. — Skull  of  Horse;  PosTp:nioR  View 


The  Hyoii)  F,( 


is  Been  Removed. 

1,  External  occipital  protuberance;  2,  curved  line;  3,  foramen  magnum;  4,  occipital  condyle;  5,  paramastoid 
process;  6,  basilar  part  of  occipital;  7,  mastoid  foramen;  8,  mastoid  process;  9,  postglenoid  process;  10,  muscular 
process  of  petrous  temporal;  11,  alar  canal;  12,  pterygoid  process  of  sphenoid;  13,  body  of  sphenoid;  14,  vomer;  15, 
15',  perpendicular  and  horizontal  parts  of  palatine  bone;  16,  16,  posterior  nares  or  choanae;  17,  hamulus  of  pterygoid 
bone;  18,  maxillary  tuberosity;  19,  palatine  process  of  maxilla;  20,  palatine  process  of  premaxilla;  21,  palatine  fissure; 
22,  accessory  palatine  foramina;   23,  bodj'  of  mandible;  24,  mandibular  foramen. 


bone.  It  is  trapezoidal  in  outline,  wider  below  than  above,  concave  dorso-ventrally, 
convex  transversely.  It  is  separated  from  the  dorsal  surface  by  the  nuchal  crest. 
Below  the  crest  are  two  rough  areas  for  that  attachment  of  the  complexus  muscles. 
A  little  lower  is  a  central  eminence,  the  external  occipital  protuberance,  on  which  the 
ligamentum  nuchse  is  attached.  At  the  lowest  part  centrally  is  the  foramen  mag- 
nmn.  This  is  bounded  laterally  by  the  occipital  condyle,  lateral  to  which  is  the 
paramastoid  process. 


80 


THE    SKELETON    OF   THE    HORSE 


i 


.a  g 

li 


i  g'^ 


"    ft  « 

o     ^"    I 


-2    O    m 
a.  .S   « 


THE    CRANIAL    CAVITY 


81 


The  apex  of  the  skull  is  formed  by  the  bodies  of  the  premaxillae  and  mandible, 
carrying  the  incisor  teeth. 

THE  CRANIAL  CAVITY 

This  cavity  (Cavum  cranii)  incloses  the  brain,  with  its  membranes  and  vessels. 
It  is  relatively  small  and  is  ovoid  in  shape. 

The  dorsal  wall  or  roof  (Calvaria)  (Fig.  52)  is  formed  by  the  supraoccipital, 
interparietal,  parietal,  and  frontal  bones.  In  the  middle  line  is  the  internal  parietal 
crest,  which  joins  the  crista  galli  in  front,  and  furnishes  attachment  to  the  falx 
cerebri.     Posteriorly  the  crest  is  continued  by  the  sharp  anterior  margin  of  the 


Occipital  bone 
{squamous  part) 


Parietal  bone 


Frontal  bone 


Paramasioid      Occipital  hone     Sphenoid  bone 
process  {basilar  part)  {body) 


^^gg^^. 


Fig.  54. — Sagittal  Section  of  Cranium  or  Horse. 
1,  Lateral  wall  of  foramen  magnum;  2,  hypoglossal  foramen;  3,  foramen  lacerum  posterius;  4,  5,  6,  carotid,  oval, 
and  spinous  notches;  7,  floccular  fossa;  8,  internal  acoustic  meatus;  9,  petrosal  crest;  10,  hypophyseal  or  pituitary 
pons  (Fossa  pontis)  depression  below  12  is  the  hjijophyseal  fossa;  11,  groove  for  maxillary  nerve;  12,  groove  for  cav- 
ernous sinus;  13,  optic  foramen;  14,  14,  sphenoidal  sinus;  15,  crista  galli;  16,  perpendicular  plate  of  ethmoid  bone; 
17,  vomer;  18,  septum  between  frontal  sinuses;  19,  orbital  wing  of  sphenoid;  20,  temporal  wing  of  sphenoid;  21,  in- 
ternal occipital  protuberance;  22,  canalis  transversus;  23,  depression  for  vermis  cerebelli. 


tentorium  osseum,  which  projects  downward  and  forward  into  the  cavity,  and  gives 
attachment  to  the  tentorium  cerebelli  by  its  sharp  lateral  edges.  Behind  this  the 
roof  is  grooved  centrally  for  the  middle  lobe  or  vermis  of  the  cerebellum.  Trans- 
verse grooves  pass  from  the  base  of  the  tentorium  osseum  to  the  temporal  canals. 
The  anterior  part  of  the  roof  is  hollowed  by  the  frontaj  sinus.  The  occipital  part 
is  very  thick  and  strong. 

The  lateral  wall  (Fig.  54)  is  formed  chiefly  by  the  temporal  and  frontal  bones 
and  the  orbital  wing  of  the  sphenoid.  It  is  crossed  obliquely  by  the  petrosal  crest, 
which  concurs  with  the  margin  of  the  parietal  bone  and  the  internal  occipital  pro- 
tuberance in  dividing  the  cavity  into  cerebral  and  cerebellar  compartments.  Behind 


32  THE  SKELETON  OF  THE  HORSE 

the  crest  is  a  depression  for  the  hemisphere  of  the  cerebellum.  Behind  this  are  the 
internal  acoustic  meatus  and  the  openings  of  the  aquseductus  vestibuli  and  aquse- 
ductus  cochlese. 

The  roof  and  lateral  walls  are  marked  by  digital  impressions  and  vascular 
grooves. 

The  ventral  wall  or  floor  (Basis  cranii  interna)  (Fig.  53)  may  l)e  regarded  as 
forming  three  fossae.  The  anterior  fossa  (Fossa  cranii  oralis)  supports  the  frontal 
and  olfactory  parts  of  the  cerebrum.  It  is  formed  chiefly  by  the  presphenoid,  and 
lies  at  a  higher  level  than  the  middle  fossa.  In  front  the  fossa  is  divided  medially 
by  the  crista  galli,  lateral  to  which  are  the  deep  ethmoidal  fossae  for  the  olfactory 
bulbs.  The  ethmoidal  foramen  perforates  the  cranial  wall  at  the  outer  side  of  these 
fossae.  Further  back  the  central  part  of  the  surface  is  slightly  elevated,  and  is 
flanked  by  shallow  depressions  which  support  the  olfactory  tracts.  Posteriorly 
is  a  bony  shelf  which  covers  the  entrance  to  the  optic  foramina;  the  edge  of  this 
shelf  and  the  posterior  borders  of  the  orbital  wings  of  the  sphenoid  may  be  taken  as 
the  line  of  demarcation  between  the  anterior  and  middle  fossae.  The  middle  fossa 
(Fossa  cranii  media)  is  the  widest  part  of  the  cavity.  It  extends  backward  to  the 
spheno-occipital  and  petrosal  crests,  thus  corresponding  to  the  postsphenoid.  In  its 
middle  is  the  hypophyseal  fossa  in  which  the  hypophysis  cerebri  lies.  On  either  side 
are  two  grooves:  the  medial  one  transmits  the  cavernous  sinus  and  the  ophthalmic, 
third,  and  sixth  nerves  to  the  foramen  orbitale;  the  lateral  one  leads  to  the  foramen 
rotundum,  and  lodges  the  maxillary  nerve.  Lateral  to  the  grooves  is  a  depression 
for  the  piriform  lobe  of  the  cerebrum.  The  posterior  fossa  (Fossa  cranii  posterior) 
corresponds  to  the  basilar  part  of  the  occipital  bone.  It  contains  the  medulla 
oblongata,  pons,  and  cerebellum.  In  front  is  a  median  depression  (Fossa  pontis) 
for  the  pons.  The  surface  behind  this  (Fossa  meduUae  oblongatae)  is  concave  trans- 
versely and  slopes  gently  downward  to  the  foramen  magnum;  it  supports  the 
medulla  oblongata.  On  either  side  are  the  foramen  lacenmi  and  the  h3rpoglossal 
foramen. 

The  anterior  or  nasal  wall  (Fig.  33)  is  formed  by  the  cribriform  plate  of  the 
ethmoid,  which  separates  the  cranium  from  the  nasal  cavity.  It  is  perforated  by 
numerous  foramina  for  the  passage  of  the  olfactory  nerve-bundles. 


THE  NASAL  CAVITY 

The  nasal  cavity  (Cavum  nasi)  is  a  longitudinal  passage  which  extends  through 
the  upper  part  of  the  face.  It  is  divided  into  right  and  left  halves  by  a  median 
septum  nasi.  The  lateral  walls  are  formed  by  the  maxilla,  premaxilla,  the  per- 
pendicular part  of  the  palatine,  and  the  turbinate  and  ethmoid  bones  in  part.  This 
wall  is  crossed  obliquely  by  the  lacrimal  canal  and  groove  for  the  naso-lacrimal 
duct,  and  its  posterior  part  is  perforated  by  the  sphenopalatine  foramen.  The 
dorsal  wall  or  roof  is  formed  by  the  frontal  and  nasal  bones,  which  form  a  median 
prominence  at  their  junction.  It  is  concave  from  side  to  side,  and  nearly  straight 
longitudinally,  except  in  the  posterior  part,  where  it  curves  downward.  The  ven- 
tral wall  or  floor  is  formed  by  the  palatine  processes  of  the  premaxillae  and  max- 
illae, and  the  horizontal  parts  of  the  palate  bones.  It  is  wider  but  considerably 
shorter  than  the  roof.  It  is  concave  transversely,  and  nearly  horizontal  from 
before  backward,  except  in  the  posterior  third,  where  there  is  a  slight  declivity. 
The  anterior  part  presents  a  median  groove  for  the  cartilage  of  the  septum,  and  a 
furrow  for  the  vomero-nasal  organ  (of  Jacobson)  on  either  side.  Posteriorly  there 
is  a  median  elevation,  the  nasal  crest,  to  which  the  vomer  is  attached.  Lateral  to 
the  palatine  process  of  the  premaxilla  is  the  palatine  fissure. 

The  septum  nasi  osseum  is  formed  by  the  perpendicular  plate  of  the  ethmoid 


THE    NASAL    CAVITY 


83 


behind,  and  the  vomer  below.     In  the  fresh  state  it  is  completed  by  che  cartilage 
of  the  septum  nasi  (Cartilago  septi  nasi). 


Fig.  55. — Cross-section  of  Nasal  Region  op  Skull 
OF  Horse;    the  Section  Passes  Through  the 
Anterior  End  of  the  Facial  Crest,  and  Be- 
tween the  Third  and  Fourth  Cheek  Teeth. 
a,  Dorsal,  6,  ventral,  turbinate  bone;    c,  d,  cavities 
of  a  and  6;   e,  common  meatus;  /,  g,  h,  dorsal,  middle, 
ventral  meatus;    i,  k,  passages  to  cavities  of  turbinate 
bones;    I,  naso-lacrimal  duct;    m,  infraorbital  canal;   n, 
anterior  end   of   maxillary  sinus;     o,   septal   cartilage. 
(After  EUenberger,  in  Leisering's  Atlas.) 


Fig.  56. — Cross-section  of  Nasal  Region  of  Skull 
OF  Horse;    the  Section  is  Cut  About  Half- 
way  between   the    Orbit   and    the   Anterior 
End    op   the    Facial   Crest,    and    Passes    be- 
tween the  Fifth  and  Sixth  Cheek  Teeth. 
o.  Dorsal,  b,  ventral,  turbinate  bone;  c,  d,  cavities 
of  a  and  b;   e,  common  meatus;  /,  dorsal,  g,  middle,  h, 
ventral  meatus;  i,  placed  over  ridge  in  maxillary  sinus; 
k,  communication  between  outer  and  inner  (turbinate) 
part  of  maxillary  sinus;    I,  naso-maxillary  opening;    m, 
naso-lacrimal    canal;      n,    infraorbital    canal.       (After 
EUenberger,  in  Leisering's  Atlas.) 


The  turbinate  bones  divide  each  half  of  the  nasal  cavity  into  three  meatus 
nasi. 

The  dorsal  meatus  (Meatus  nasi  dorsalis)  is  a  narrow  passage  between  the 
roof  and  the  dorsal  turbinate  bone.     It  ends  at  the  cribriform  plate  of  the  ethmoid. 


Fig.  57. — Skull  of  Young  Horse;  Lateral  View,  with  Sinuses  Opened  Up. 
A',  A,  Anterior  and  posterior  compartments  of  maxillary  sinus;  B,  B' ,  frontal  and  turbinate  parts  of  frontal  siiiu.i, 
C,  orbit;  1,  septum  between  compartments  of  maxillary  sinus;  2,  2,  infraorbital  canal;  3,  turbinate  part  of  maxillary 
Binus;  4,  5,  6,  last  three  cheek  teeth  (covered  by  thin  plate  of  bone) ;  7,  anterior  limit  of  maxillary  sinus  in  older  subject; 
8,  infraorbital  foramen;  9,  anterior  end  of  facial  crest;  10,  course  of  naso-lacrimal  duct;  11,  fossa  for  lacrimal  sac;  12, 
dorsal  turbinate  bone;    13,  fronto-maxillary  opening. 


The  middle  meatus  (Meatus  nasi  medius)  is  the  space  between  the  two  turbinate 
bones.  In  its  posterior  part  is  the  very  narrow  opening  into  the  maxillary  sinus. 
The  ventral  meatus  (Meatus  nasi  ventralis)  is  the  channel  along  the  floor  which  is 


84 


THE    SKELETON    OF   THE    HORSE 


overhung  by  the  ventral  turbinate  bone;   it  is  much  the  largest  and  is  the  direct 
path  between  the  nostrils  and  posterior  nares. 

The  osseous  nasal  aperture  (Apertura  nasi 
ossea)  is  bounded  by  the  nasal  bones  and  the 
premaxillse. 

The  posterior  extremity  or  fundus  is  separ- 
ated from  the  cranial  cavity  by  the  cribriform 
plate  of  the  ethmoid,  and  is  largely  occupied  by 
the  lateral  masses  of  that  bone. 


THE  PARANASAL  SINUSES 

Connected  directly  or  indirectly  with  the 
nasal  cavity,  of  which  they  are  diverticula,  are 
four  pairs  of  air-sinuses  (Sinus  paranasales), 
viz.,  maxillary,  frontal,  sphenopalatine,  and 
ethmoidal. 

The  maxillary  sinus  (Sinus  maxillaris)  is  the 
largest.  Its  lateral  wall  is  formed  by  the  maxilla, 
the  lacrimal,  and  the  malar.  It  is  bounded  medi- 
ally by  the  maxilla,  the  ventral  turbinate,  and  the 
lateral  mass  of  the  ethmoid  bone.  It  extends 
backward  to  a  transverse  plane  in  front  of  the 
root  of  the  supraorbital  process,  and  its  anterior 
limit  is  indicated  approximately  by  a  line  drawn 
from  the  anterior  end  of  the  facial  crest  to  the 
infraorbital  foramen.  Its  dorsal  boundary  cor- 
responds to  a  line  drawn  backward  from  the  in- 
fraorbital foramen  parallel  to  the  facial  crest. 
The  ventral  wall  or  floor  is  formed  by  the  alve- 
olar part  of  the  maxilla;  it  is  very  irregular  and 
is  crossed  by  bony  plates  running  in  various 
directions.  The  last  three  cheek  teeth  project 
up  into  the  cavity  to  an  extent  which  varies 
with  age;  they  are  covered  by  a  thin  plate  of 
bone.  The  cavity  is  divided  into  anterior  and 
posterior  parts  by  an  oblique  septum  (Septum 
sinus  maxillaris) .  The  lateral  margin  of  the  sep- 
tum is  commonly  about  two  inches  (ca.  5  cm.) 
from  the  anterior  end  of  the  facial  crest;  from 
here  it  is  directed  inward,  backward,  and  up- 
ward. The  upper  part  of  the  septum  (formed 
by  the  posterior  end  of  the  ventral  turbinate 
bone)  is  very  delicate  and  usually  cribriform. 


Fig.  58. — Skull  of  Young  Horse;  Dorsal 
View,  with  Sinuses  Opened  Up. 
1,  2,  Ends  of  frontal  sinus;  3,  fronto- 
maxillary  opening:  4,  dorsal  turbinate  bone; 
5,  lateral  mass  of  ethmoid  bone;  6,  6',  two 
compartments  of  maxillary  sinus;  7,  septum 
between  6  and  G';  8,  orbit;  9,  anterior  end 
of  facial  crest;  A,  frontal  bone;  B,  nasal 
bone;  C,  lacrimal  bone;  D,  maxilla.  Note 
difference  in  position  and  form  of  septum  in 
maxillary  sinus  as  compared  with  preceding 
figure. 


The  position  and  shape  of  the  septum  are  very 
variable.  It  is  often  further  forward — in  some  cases 
even  as  far  forward  as  the  anterior  end  of  the  facial  crest.  Exceptionally  it  is  much  nearer  the 
orbit  than  is  stated  above.  In  the  recent  state,  i.  e.,  when  covered  by  the  mucous  membrane  on 
both  surfaces,  it  is  nearly  always  complete,  but  in  very  exceptional  cases  there  is  an  opening  of 
variable  size  in  the  upper  part. 

The  anterior  compartment,  often  called  the  inferior  maxillary  sinus,  is  partially 
divided  by  the  infraorl)ital  canal  into  a  lateral  maxillary  part  and  a  medial  smaller 
turbinate  part.  The  latter  communicates  with  the  middle  meatus  by  a  very  narrow 
slit  situated  at  its  highest  part.     The  posterior  compartment,  often  called  the 


THE    PARANASAL    SINUSES 


85 


superior  maxillary  sinus,  is  also  crossed  by  the  infraorbital  canal,  over  which  it 
opens  freely  into  the  sphenopalatine  sinus.  It  communicates  dorsally  with  the 
frontal  sinus  through  the  large  oval  fronto-maxillary  opening,  situated  at  the  level 
of  the  osseous  lacrimal  canal  and  the  corresponding  part  of  the  medial  wall  of  the 
orbit;  the  orifice  is  commonly  about  one  and  a  half  to  two  inches  (ca.  4  to  5  cm.) 
long  and  an  inch  or  more  (2  to  3  cm.)  wide.  Just  in  front  of  this,  and  covered  by  a 
thin  plate,  is  the  narrow  naso-maxillary  fissure  (Aditus  naso-maxillaris),  by  which 
the  sinus  opens  into  the  posterior  part  of  the  middle  meatus. 

The  foregoing  statements  refer  to  the  arrangement  in  the  average  adult  aniinal.  In  the 
foal  the  cavity  (with  the  exception  of  its  turbinate  part)  is  largely  occupied  by  the  developing 
teeth.  In  horses  five  to  six  years  of  age  the  maxillary  part  of  the  sinus  is  filled  up  to  a  large  degree 
by  the  embedded  parts  of  the  teeth.  As  the  teeth  are  extruded  to  compensate  the  wear,  more 
and  more  of  the  cavity  becomes  free,  until  in  old  age  only  the  short  roots  project  up  in  the  floor, 
covered  by  a  layer  of  bone.  Other  facts  in  this  connection  will  be  given  in  the  description  of  the 
teeth.  In  exceptional  cases  the  posterior  part  of  the  ventral  turbinate  is  smaller  than  usual  and 
leaves  a  considerable  interval,  through  which  the  maxillary  sinus  communicates  with  the  nasal 
cavity.     The  fronto-maxillary  opening  is  very  variable  in  size. 


Squamous 
Squamous    Parietal    temporal 
part  of  occip-       bone       bone  Frontal 


ital  bone 


bone 


Lacrimal   Max- 


Nasal  bone 


Premaxilla 


Lateral 

part  of 

occipital 

bone 


Basilar  part  of 
occipital  bone 


Mandible  Incisor  teeth 

(first  and  second) 

Fig.  59. — Skull  of  Foal  About  Two  Months  Old. 
This  figure  illustrates  differential  features  of  skull  of  young  foal  as  compared  with  that  of  adult  animal  shown  in 
Fig.  28.  1,  Occipital  condyle;  2,  paramastoid  process;  3,  mastoid  process;  4,  external  acoustic  meatus;  5,  zygomatic 
process  of  temporal  bone;  6,  supraorbital  process  of  frontal  bone;  7,  zygomatic  process  of  malar  bone;  8,  facial  crest; 
9,  infraorbital  foramen;  10,  mental  foramen;  11,  angle  of 'mandible;  12,  condyle  of  mandible;  13,  coronoid  process 
of  mandible. 


The  frontal  or  frbnto-turbinate  sinus  (Sinus  frontalis)  consists  of  frontal  and 
turbinate  parts.  The  frontal  part  is  bounded  chiefly  by  the  two  plates  of  the 
frontal  bone,  but  its  floor  is  formed  in  part  by  the  lateral  mass  of  the  ethmoid.  It 
extends  forward  to  a  plane  through  the  anterior  margins  of  the  orbits,  backward  to 
one  through  the  temporal  condyles,  and  outward  into  the  root  of  the  supraorbital 
process.  It  is  separated  from  the  sinus  of  the  opposite  side  by  a  complete  septum 
(Septum  sinuum  frontalium).  It  is  partially  subdivided  by  a  number  of  bony 
plates.  The  turbinate  part  is  situated  in  the  posterior  part  of  the  dorsal  turbinate 
bone,  roofed  in  by  the  nasal  and  lacrimal  bones.  It  extends  forward  to  a  transverse 
plane  about  half-way  between  the  anterior  margin  of  the  orbit  and  the  end  of  the 
facial  crest.  It  is  in  free  communication  behind  with  the  frontal  part  over  the 
lateral  mass  of  the  ethmoid.     It  is  separated  from  the  nasal  cavity  by  the  thin 


80  THE  SKELETON  OF  THE  HORSE 

turbinate  plate.     The  frontal  and  maxillary  sinuses  communicate  through  the 
large  opening  described  above. 

The  sphenopalatine  sinus  (Sinus  sphenopalatinus)  consists  of  two  parts  which 
communicate  under  the  lateral  mass  of  the  ethmoid.  The  sphenoidal  (posterior) 
part  is  excavated  in  the  body  of  the  presphenoid.  The  palatine  (anterior)  part  is 
between  the  two  plates  of  the  perpendicular  part  of  the  palatine  bone,  under  the 
lateral  mass  of  the  ethmoid;  it  communicates  freely  with  the  maxillary  sinus.  The 
septum  between  the  right  and  left  sinuses  is  not  usually  median  in  the  sphenoidal 
part. 

In  about  one-third  of  the  cases  (according  to  PauUi)  the  sphenoidal  and  palatine  parts  are 
separated  by  a  transverse  septum,  and  the  sphenoidal  part  then  communicates  only  with  the  ven- 
tral ethmoidal  meatuses. 

The  term  ethmoidal  sinus  is  often  applied  to  the  cavity  of  the  largest  ethmo- 
turbinate.  It  communicates  with  the  maxillary  sinus  through  an  opening  in  the 
lateral  lamina. 


The  Bones  of  the  Thoracic  Limb 
the  scapula 

The  scapula  is  a  flat  bone  which  is  situated  on  the  anterior  part  of  the  lateral 
wall  of  the  thorax;  its  long  axis  extends  obliquely  from  the  fourth  thoracic  spine 
to  the  sternal  end  of  the  first  rib.  It  is  curved  slightly  and  slopes  outward  in 
adaptation  to  the  form  of  the  thoracic  wall.  It  is  triangular  in  outline,  and  has 
two  surfaces,  three  borders,  and  three  angles. 

The  lateral  surface  (Facies  lateralis)  is  divided  into  two  fossae  by  the  spine  of 
the  scapula  (Spina  scapulae),  which  extends  from  the  vertebral  border  to  the  neck 
of  the  bone,  where  it  subsides.  The  free  edge  of  the  spine  is  thick,  rough,  and  in 
great  part  subcutaneous.  A  little  above  its  middle  there  is  a  variable  prominence, 
the  tuber  spinas,  to  which  the  trapezius  muscle  is  attached.  The  supraspinous 
fossa  (Fossa  supraspinata)  is  situated  in  front  of  the  spine,  and  the  infraspinous 
fossa  (Fossa  infraspinata)  behind  it.  The  former  is  much  the  smaller  of  the  two; 
it  is  smooth  and  is  occupied  by  the  supraspinatus  muscle.  The  infraspinous  fossa 
lodges  the  infraspinatus  muscle;  it  is  wide  and  smooth  in  its  upper  part,  narrower 
below,  where  it  is  marked  by  several  rough  lines  for  muscular  attachment;  near 
the  neck  is  the  nutrient  foramen,  and  a  little  lower  is  a  vascular  groove. 

The  costal  surface  (Facies  costalis)  is  hollowed  in  its  length  by  the  subscapular 
fossa  (Fossa  subscapularis) ;  this  occupies  nearly  the  whole  of  the  lower  part  of  the 
surface,  but  is  pointed  above  and  separates  two  rough  triangular  areas  (Facies 
serrata),  to  which  the  serratus  ventralis  is  attached.  In  the  lower  third  there  is  a 
vascular  groove  with  several  branches. 

The  anterior  border  (Margo  cranialis)  is  convex  and  rough  above,  concave  and 
smooth  below. 

The  posterior  border  (Margo  caudalis)  is  slightly  concave.  It  is  thick  and 
rough  in  its  upper  third,  thin  in  its  middle,  and  thickens  again  below. 

The  vertebral  border  (Margo  vertebralis)  carries  the  scapular  cartilage  (Car- 
tilago  scapulae).  In  the  young  subject  this  edge  of  the  bone  is  thick,  and  is  pitted 
by  impressions  into  which  the  cartilage  fits.  The  cartilage  is  the  unossified  part 
of  the  foetal  scapula.  Its  lower  edge  fits  the  depressions  and  elevations  of  the  bone. 
It  thins  out  toward  the  free  edge,  which  is  convex  and  lies  alongside  of  the  vertebral 
spines.  In  front  it  continues  the  line  of  the  bone,  but  behind  it  forms  a  rounded 
projection.  The  lower  part  of  the  cartilage  undergoes  more  or  less  ossification,  so 
that  the  vertebral  border  of  the  bone  in  old  subjects  is  thin,  irregular,  and  porous. 

The  anterior  or  cervical  angle  (Angulus  cranialis)  is  at  the  junction  of  the 


THE    SCAPULA 


87 


/ 


■APULA  OF  Horse;  Lateral  Surface, 
1,  Spine;  2,  tuber  spinse;  3,  cartilage;  4,  anterior 
angh';  5,  posterior  angle;  6,  supraspinous  fossa;  7,  in- 
fraspinous  fossa;  8,  anterior  border;  9,  posterior  bor- 
der; 10,  muscular  lines;  11,  nutrient  foramen;  12, 
vascular  groove ;  13,  neck;  14,  tuber  scapulse;  15,  glen- 
oid cavity. 


Fig.  61. — Right  Scapula  of  Horse;  Costal  Surface. 
1,  Anterior  angle;  2,  posterior  angle;  3,  anterior  border; 
4,  posterior  border;  5,  neck;  6,  vascular  groove;  7,  glenoid 
cavity;    8,  coracoid  process;    9,  tuber  scapulas. 


anterior  and  vertebral  borders  and  lies  opposite  to  the  second  thoracic  spine.     It  is 
relatively  thin  and  is  about  a  right  angle. 

The  posterior  or  dorsal  angle  (Angulus  caudalis)  is  thick  and  rough;    it  is 
opposite  to  the  vertebral  end  of  the  seventh  rib,  and 
its  position  can  be  determined  readily  in  the  living 
animal. 

The  glenoid  or  articular  angle  (Angulus  glenoid- 
alis)  is  joined  to  the  body  of  the  bone  by  the  neck 
of  the  scapula  (Collum  scapulae).  It  is  enlarged, 
especially  in  the  sagittal  direction.  It  bears  the 
glenoid  cavity  (Cavitas  glenoidalis)  for  articulation 
with  the  head  of  the  humerus.  The  cavity  is  oval 
in  outline,  and  its  margin  is  cut  into  in  front  by  the 
glenoid  notch  (Incisura  glenoidalis),  and  is  rounded 
off  laterally;  just  above  its  postero-lateral  part  is  a 
tubercle  to  which  a  tendon  of  the  teres  minor  is  at- 
tached. The  tuber  scapulae^  is  the  large  rough 
prominence  in  front,  to  w^hich  the  tendon  of  origin 

»  Formerly  termed  the  bicipital  tuberosity. 


Glenoid 
cavity 


Fig.  62. — Distal  Extremity  of  Left 
Scapula    of   Horse;   End    View. 


88  THE  SKELETON  OF  THE  HORSE 

of  the  biceps  brachii  is  attached;  projecting  from  its  medial  side  is  the  small  coracoid 
process  (Processus  coracoideus),  from  which  the  coraco-brachiahs  muscle  arises. 

Development. — The  scapula  has  four  centers  of  ossification,  viz.,  one  each  for 
the  body  of  the  bone,  the  tuber  scapulae  and  coracoid  process,  the  anterior  part  of 
the  glenoid  cavity,  and  the  tuber  spinae.  The  last  ossifies  after  birth  and  fuses  with 
the  spine  about  the  third  year.  The  tuber  scapulae  and  coracoid  process  fuse  with 
the  body  of  the  bone  about  the  end  of  the  first  year. 

In  old  subjects  the  spongy  substance  disappears  at  the  middle  part  of  the  fossse,  so  that  the 
bone  consists  here  of  a  thin  layer  of  compact  substance.  Considerable  ossification  of  the  cartilage 
is  usual,  the  borders  become  much  rougher,  the  muscular  lines  are  more  pronounced,  and  a  medul- 
lary cavity  may  appear  in  the  neck.  Aluch  variation  occurs  in  dimensions  and  slope.  The  aver- 
age ratio  between  the  length  and  breadth  (scapular  index)  is  about  1  :  0..5,  but  in  many  cases  the 
base  is  relatively  wider.  The  inclination  on  a  horizontal  plane  varies  from  .50  to  6.5  degrees.  Ex- 
ceptionally the  coracoid  process  reaches  a  length  of  an  inch  or  more  (2}^  to  3  cm.),  and  the  chief 
nutrient  foramen  may  be  on  the  posterior  border  or  in  the  subscapular  fossa. 


THE  HUMERUS 

The  humerus  is  a  long  bone  which  extends  from  the  shoulder  above,  where  it 
articulates  with  the  scapula,  to  the  elbow  below  and  behind,  where  it  articulates 
with  the  radius  and  ulna.  It  is  directed  obliquely  downward  and  backward,  form- 
ing an  angle  of  about  55  degrees  with  a  horizontal  plane.  It  consists  of  a  shaft 
and  two  extremities. 

The  shaft  (Corpus  humeri)  is  irregularly  cylindrical  and  has  a  twisted  appear- 
ance. It  may  be  regarded  as  having  four  surfaces.  The  lateral  surface  (Facies 
lateralis)  is  smooth  and  is  spirally  curved,  forming  the  musculo-spiral  groove 
(Sulcus  musculi  brachialis),  which  contains  the  brachialis  muscle;  the  groove  is 
continuous  with  the  posterior  surface  above  and  winds  around  toward  the  front 
below.  The  medial  surface  (Facies  medialis)  is  nearly  straight  in  its  length, 
rounded  from  side  to  side,  and  blends  with  the  anterior  and  posterior  surfaces. 
Just  above  its  middle  is  the  teres  tuberosity  (Tuberositas  teres),  to  which  the 
tendon  of  the  latissimus  dorsi  and  teres  major  muscles  is  attached.  The  nutrient 
foramen  is  in  the  distal  third  of  this  surface.  The  anterior  surface  (Facies  crani- 
alis)  is  triangular,  wide  and  smooth  above,  narrow  and  roughened  below.  It  is 
separated  from  the  lateral  surface  by  a  distinct  border,  the  crest  of  the  humerus 
(Crista  humeri),  which  bears  above  its  middle  the  deltoid  tuberosity  (Tuberositas 
deltoidea).  From  the  latter  a  rough  line  curves  upward  and  backward  to  the 
lateral  surface  of  the  neck,  and  gives  origin  to  the  lateral  head  of  the  triceps  muscle. 
Below  the  tuberosity  the  border  inclines  forward,  becomes  less  salient,  and  ends  at 
the  coronoid  fossa.  The  posterior  surface  (Facies  caudalis)  is  rounded  from  side 
to  side  and  smooth. 

The  proximal  extremity  (Extremitas  proximalis)  consists  of  the  head,  neck, 
two  tuberosities,  and  the  intertuberal  groove.  The  head  (Caput  humeri)  presents 
an  almost  circular  convex  articular  surface,  which  is  about  twice  as  extensive  as  the 
glenoid  cavity  of  the  scapula,  with  which  it  articulates.  In  front  of  the  head  is  a 
fossa,  in  which  are  several  foramina.  The  neck  (Collum  humeri)  is  well  defined 
behind,  but  is  practically  absent  elsewhere.^  The  lateral  tuberosity  (Tuberositas 
lateralis)-  is  placed  antero-laterally,  and  consists  of  two  parts:  the  anterior  part 
forms  the  lateral  boundary  of  the  intertuberal  or  bicipital  groove  and  gives  attach- 
ment to  the  lateral  branch  of  the  supraspinatus  muscle;  the  posterior  part  gives 
attachment  to  the  short  insertion  of  the  infraspinatus,  while  its  outer  surface  is 
coated  with  cartilage,  over  which  the  chief  tendon  of  the  same  muscle  passes  to  be 

^  The  proper  "anatomical  neck"  (Collum  anatomicum)  is,  however,  indicated  by  the  shallow 
depression  which  separates  the  head  from  the  tuberosities,  and  gives  attachment  to  the  joint  capsule. 

"^  The  term  "tubercle"  as  used  in  human  anatomy  does  not  apply  well  to  the  domestic  ani- 
mals. 


THE    HUMERUS 


89 


inserted  into  a  triangular  rough  area  below  the  anterior  part.  The  medial  tuber- 
osity (Tuberositas  medialis)  is  less  salient,  and  consists  of  anterior  and  posterior 
parts;  the  anterior  part  forms  the  medial  boundary  of  the  intertuberal  groove, 
and  furnishes  insertion  to  the  medial  branch  of  the  supraspinatus  above,  and  the 
posterior  deep  pectoral  muscle  below;  the  posterior  part  gives  attachment  to  the 
subscapularis  muscle.  The  intertuberal  or  bicipital  groove  (Sulcus  intertuberalis)'^ 
is  situated  in  front;  it  is  bounded  by  the  anterior  parts  of  the  tuberosities,  and  is 
subdivided  by  an  intermediate  ridge.     The  groove  is  covered  in  the  fresh  state  by 


Intertuberal 
{or  bicipital)     Lateral 
groove         tuberosity 


crest 

Coronoid 

/- 

Medial 
condyle 


Lateral 
condyle 


Head 


Neck 


Lateral 
tuberosity 


Medial 
epicondyle 


Olecra- 
Lateral     non  fossa 
epicondyle 

Fig.  63. — Left  Humerus  of  Horse;  Lateral  View. 
1,  Rough  area  to  which  tendon  of  infraspinatus  is 
attached;    2,   crest;    3,  depression  for  attachment  of 
lateral  Ugament. 


Medial 
tuber- 


Medial 
condyle 


Fig.  64. — Right  Humerus  of  Horse;  Front  View, 

1,  Rough  area  for  attachment  of  extensor  carpi 

radialis  and  extensor  digitalis  communis;    2,  synovial 


cartilage,  and  lodges  the  tendon  of  origin  of  the  biceps  brachii  muscle.     Just  below 
the  intermediate  ridge  is  a  small  fossa  in  which  several  foramina  open. 

The  distal  extremity  has  an  oblique  surface  for  articulation  with  the  radius 
and  ulna,  which  consists  of  two  condyles  of  very  unequal  size,  separated  by  a  ridge. 
The  medial  condyle  (Condylus  medialis)  is  much  the  larger,  and  is  crossed  by  a 
sagittal  groove,  on  the  anterior  part  of  which  there  is  usually  a  synovial  fossa.  Pos- 
teriorly the  groove  extends  upward  considerably  above  the  rest  of  the  articular 
surface  and  reaches  the  olecranon  fossa,  and  this  part  articulates  with  the  semilunar 

^The  name  "intertuberal"  is  designative  of  the  position  of  the  groove,  while  the  term 
"bicipital"  has  reference  to  its  occupation  by  the  tendon  of  the  biceps  brachii.  The  term  "sulcus 
intertubercular's"  is  also  in  common  use. 


90 


THE    SKELETON    OF   THE    HORSE 


notch  of  the  ulna.  The  lateral  condyle  (Condylus  lateralis)  is  much  smaller  and 
is  placed  somewhat  lower  and  further  back,  giving  the  extremity  an  oblique  ap- 
pearance; it  is  marked  b}^  a  wide  shallow  groove.  The  coronoid  fossa  (Fossa  coro- 
noidea)  is  situated  in  front,  above  the  groove  on  the  medial  condjde;  it  furnishes 
origin  to  part  of  the  extensor  carpi,  and  lateral  to  it  is  a  rough  depression  from 
which  the  common  digital  extensor  arises.  Behind  and  above  the  condyles  are  two 
thick  ridges,  the  epicondyles.  The  medial  epicondyle  (Epicondylus  medialis) 
is  the  more  salient;  it  furnishes  origin  to  flexor  muscles  of  the  carpus  and  digit, 
and  bears  a  tul^ercle  for  the  attachment  of  the  medial  ligament  of  the  elbow  joint. 
The  lateral  epicondyle  (Epicondylus  lateralis)  bears  laterally  the  condyloid  crest 
(Crista  condyloidea),  which  forms  here  the  outer  boundary  of  the  musculo-spiral 
groove,  and  gives  origin  to  the  extensor  carpi  radialis.  Below  this  is  a  rough  excava- 
tion in  which  the  lateral  ligament  is  attached.  The  distal  border  of  the  epicondyle 
gives  attachment  to  the  ulnaris  lateralis.  Between  the  epicondyles  is  the  deep 
olecranon  fossa  (Fossa  olecrani),  into  which  the  processus  anconseus  projects. 


Fig.  Go. — Proximal  Extremity  of  Left  Humerus  of 
Horse;  End  View. 
1,  Intertuberal  (or  bicipital)  groove;  2,  3,  anterior 
parts  of  lateral  and  medial  tuberosities;  4,  fossa;  5,  6, 
posterior  parts  of  lateral  and  medial  tuberosities;  7, 
head. 


Fig.   60. — Dist.vl  Extremity  of  Left    Humerus  of 
Horse;    End  View. 
1,  Medial  condyle;    2,  lateral  condyle;    3,  part  of 
medial  epicondyle  to  which  medial  ligament  is  attached; 

4,  depression  in  which   lateral   ligament   is  attached; 

5,  6,  areas  of  attachment  of  flexor  and  extensor  muscles 
of  carpus  and  digit;   7,  olecranon  fossa. 


Development. — The  humerus  ossifies  from  six  centers,  viz.,  three  primary 
centers  for  the  shaft  and  extremities,  and  three  secondary  centers  for  the  lateral 
tuberosity,  the  deltoid  tuberosity,  and  the  medial  condyle  respectively.  The 
proximal  end  fuses  with  the  shaft  at  about  three  and  one-half  years,  the  distal  at 
about  one  and  a  half  years  of  age. 


THE  RADIUS 

The  radius  is  much  the  larger  of  the  two  bones  of  the  forearm  in  the  horse. 
It  extends  in  a  vertical  direction  from  the  elbow,  where  it  articulates  with  the  hum- 
erus, to  the  carpus.  It  is  gently  curved,  the  convexity  being  dorsal.  It  consists 
of  a  shaft  and  two  extremities. 

The  shaft  (Corpus  radii)  is  curved  in  its  length,  somewhat  flattened  from  before 
backward,  and  widened  at  its  ends.  It  presents  for  description  two  surfaces  and 
two  borders.  The  dorsal  surface  (Facies  dorsalis)  is  smooth,  slightly  convex  in 
its  length,  and  rounded  from  side  to  side.     The  volar  surface   (Facies  volaris) 


THE    RADIUS 


91 


is  correspondingly  concave  in  its  length  and  is  flattened  in  the  transverse  direction. 
At  its  proximal  part  there  is  a  smooth  shallow  groove,  which  concurs  with  the  ulna 
in  the  formation  of  the  interosseous  space  of  the  forearm  (Spatium  interosseum 
antibrachii) ;  the  nutrient  foramen  is  in  the  lower  part  of  this  groove  Below  this 
there  is  in  the  young  subject  a  narrow,  rough,  triangular  area  to  which  the  ulna  is 


Olecranon 


Processus  anconeus 

Semilunar  notch 
Humeral  articular 
surface  v 
Coronoid  — i«i:,r— '" 
process 
Radial  tu- 
berosity 


Olecranon 


Ridge 
2 


Fig.  07. — Left  R.\dius  and  VhN\  of  Hor.se;  L.\teral 
View. 
1,  Tuberosity  for  attachment  of  lateral  ligament  of 
elbow  joint,  and  common  and  lateral  extensor  muscles; 
2,  tuberosity  for  attachment  of  lateral  ligament  of 
carpal  joint;  3,  groove  for  common  extensor  tendon; 
4,  groove  for  lateral  extensor  tendon. 


Processus 

anconceus 
Semilunar  notch 

Glenoid  cavity 


Radial 
'-      'dM   tuberosity 


-Left  Radius  and  Ulna  of  Horse;  Medial 
View. 
1,  Tuberosity  for  attachment  of  short  part  of 
medial  ligament  of  elbow;  2,  prominence  for  long  part 
of  same;  3,  groove  for  end  of  brachialis  muscle;  4, 
tuberosity  for  attachment  of  medial  ligament  of  carpal 
joint;  5,  oblique  groove  for  tendon  of  extensor  carpi 
obUquus. 


attached  by  an  interosseous  ligament;  in  the  adult  the  two  bones  are  fused  here. 
A  variable  rough  elevation  distal  to  the  middle  and  close  to  the  medial  border  gives 
attachment  to  the  radial  check  ligament.  The  medial  border  (Margo  medialis) 
is  slightly  concave  in  its  length  and  is  largely  subcutaneous;  at  its  proximal  end 
there  is  a  smooth  area  on  which  the  tendon  of  insertion  of  the  brachialis  muscle  lies, 
and  a  small  rough  area  just  below  gives  attachment  to  that  muscle  and  the  long 


92  THE  SKELETON  OF  THE  HORSE 

medial  ligament  of  the  elbow-joint.  The  lateral  border  (Margo  lateralis)  is  more 
strongly  curved,  but  presents  no  special  features. 

The  proximal  extremity  or  head  ((Extremitas  proximalis  s.  capitulum  radii) 
is  flattened  from  before  backward  and  wide  transversely.  It  presents  the  humeral 
articular  surface  (Facies  articularis  humeralis)  which  corresponds  to  that  of  the 
distal  end  of  the  humerus;  it  is  crossed  by  a  sagittal  ridge,  which  has  a  synovial 
fossa  on  its  posterior  part,  and  ends  in  front  at  a  prominent  lip,  the  coronoid  proc- 
ess (Processus  coronoideus).  Just  below  the  posterior  border,  and  separated  by 
a  depression,  there  are  two  concave  facets  (Facies  articularis  ulnaris)  for  articula- 
tion with  the  ulna,  and  between  these  and  the  interosseous  space  is  a  quadrilateral 
rough  area  at  which  the  two  bones  are  united  by  an  interosseous  ligament.  At 
the  medial  side  of  the  dorsal  surface  is  the  radial  or  bicipital  tuberosity  (Tuberositas 
radii),  into  which  the  biceps  tendon  is  inserted.  The  medial  tuberosity  (Tuber- 
ositas proximalis  meclialis)  is  continuous  with  the  preceding  eminence,  and  fur- 
nishes attachment  to  the  short  part  of  the  medial  ligament.  The  lateral  tuberosity 
(Tuberositas  proximalis  lateralis)  is  more  salient;  it  gives  attachment  to  the  lateral 
ligament  and  to  the  common  and  lateral  extensor  muscles  of  the  digit. 

The  distal  extremity  is  also  compressed  from  before  backward.  It  presents 
the  carpal  articular  surface  (Facies  articularis  carpea),  which  consists  of  three  parts. 
The  medial  facet  is  the  largest,  is  quadrilateral,  concavo-convex  from  before  back- 
ward, and  articulates  with  the  radial  carpal  bone;  the  intermediate  one  is  some- 
what similar  in  form  but  smaller,  and  articulates  with  the  intermediate  carpal  bone; 
the  lateral  facet  is  smaller,  is  convex,  and  articulates  below  with  the  ulnar  carpal 
and  behind  with  the  accessory  carpal.  The  dorsal  surface  presents  three  grooves, 
separated  by  ridges.  The  middle  one  is  vertical  and  gives  passage  to  the  tendon 
of  the  extensor  carpi  radialis;  the  lateral  one  is  similar  and  contains  the  tendon  of 
the  common  digital  extensor;  the  medial  one  is  small  and  oblique  and  lodges  the 
tendon  of  the  extensor  carpi  obliquus.  The  volar  aspect  is  crossed  by  a  rough 
ridge,  below  which  are  three  depressions.  On  either  side  is  a  tuberosity  (Tuber- 
culum  ligament!)  to  which  the  collateral  ligament  is  attached.  The  lateral  one  is 
marked  by  a  small  vertical  groove  for  the  passage  of  the  lateral  extensor  tendon. 

Development.^ — The  radius  ossifies  from  four  centers,  viz.,  one  each  for  the 
shaft,  the  two  extremities,  and  the  lateral  part  of  the  distal  end;  the  last  is  morpho- 
logically the  distal  end  of  the  ulna  which  has  fused  with  the  radius,  and  the  line  of 
fusion  is  often  indicated  by  a  distinct  groove  on  the  carpal  articular  surface.  The 
proximal  extremity  unites  with  the  shaft  at  about  one  and  a  half  years,  the  distal 
end  at  about  three  and  a  half  years  usually. 


THE  ULNA 

The  ulna  of  the  horse  is  a  reduced  long  bone  situated  behind  the  radius,  with 
which  it  is  partially  fused  in  the  adult. 

The  shaft  (Corpus  ulnae)  is  three-sided  and  tapers  to  a  point  distally.  The 
dorsal  surface  (Facies  dorsalis)  is  applied  to  the  volar  surface  of  the  radius,  and  be- 
low the  interosseous  space  the  two  bones  are  fused  in  the  adult.  The  surface  which 
enters  into  the  formation  of  the  space  is  smooth  and  usually  presents  a  small  nu- 
trient foramen,  directed  upward.  Above  the  space  it  is  rough  and  is  attached  to 
the  radius  by  an  interosseous  ligament  which  is  usually  permanent.  The  medial 
surface  (Facies  medialis)  is  smooth  and  slightly  concave.  The  lateral  surface 
(Facies  lateralis)  is  flattened.  The  medial  and  lateral  borders  (Margo  medialis, 
lateralis)  are  thin  and  sharp,  except  at  the  interosseous  space.  The  volar  border 
(Margo  volaris)  is  slightly  concave  in  its  length  and  is  rounded.  The  distal  end  is 
pointed  and  is  usually  a  little  below  the  middle  of  the  radius.     It  is  commonly 


THE    CARPUS 


93 


continued  by  a  fibrous  cord  to  the  distal  tuberosity  of  the  radius,  but  this  band  may 
be  replaced  in  part  or  entirely  by  bone. 

The  proximal  extremity  (Extremitas  proximalis)  is  the  major  part  of  the  bone. 
It  projects  upward  and  somewhat  backward  behind  the  distal  end  of  the  humerus, 
and  forms  a  lever  arm  for  the  extensor  muscles  of  the  elbow.  The  medial  surface 
is  concave  and  smooth.  The  lateral  surface  is  convex  and  is  roughened  al)ove. 
The  dorsal  border  bears  on  its  middle  a  pointed  projection,  the  processus  anconaeus 
or  "beak,"  which  overhangs  the  semilunar  notch 

(Incisura  semilunaris).^     The  latter  is  triangular  '    " 

in  outline,  concave  from  above  downward,  convex 
transversely,  and  articulates  w4th  the  humerus;  in 
its  lower  part  there  is  an  extensive  synovial  fossa. 

Just  below  the  notch  are  two  convex  facets  which  *' 

articulate  with  those  on  the  volar  aspect  of  the 
proximal  end  of  the  radius.  The  volar  border  is 
nearly  straight,  and  is  thick  and  rounded.  The 
free  end  or  summit  is  a  rough  tuberosity,  the  ole- 
cranon, which  gives  attachment  to  the  triceps 
brachii  and  other  muscles. 

The  primitive  distal  extremity  has,  as  pre- 
viously stated,  fused  with  the  radius. 

Development. — The  ulna  ossifies  from  three 
centers,  of  which  one  is  for  the  main  part  of  the  .  .. — ^ 
bone,  one  for  the  olecranon,  and  one  for  the  distal 
end.  The  cartilaginous  embryonic  ulna  extends 
the  entire  length  of  the  forearm.  The  distal  part 
of  the  shaft  is  usually  reduced  to  a  small  fibrous 
band  or  may  disappear  entirely;  in  some  cases  a  ^v 
variable  remnant  of  it  ossifies.     The  distal  ex-  "»'  . 


-;i5,!'' 


Fig.  69. — Distal  End  of  Left  Radius  and  Ulna  of  Horse;  End 
View. 
1,  2,  3,  4,  Facets  which  articulate  with  radial,  intermediate,  ulnar, 
and  accessory  carpal  bones  respectively;  5,  groove  for  tendon  of  exten- 
sor carpi  radialis;  6,  groove  for  tendon  of  common  digital  extensor;  7, 
tuberosity  for  attachment  of  medial  ligament  of  carpal  joint. 


Fig.    70. — Sagittal    Section    of    Uppbb 

Part  of  Radius  and  Ulna  of  Horse. 

Cm,  Medullary  cavity  of  ulna. 


tremity  fuses  before  birth  with  the  radius.  The  olecranon  unites  with  the  rest 
of  the  bone  at  about  three  and  a  half  years.  A  medullary  cavity  appears  to  occur 
constantly  in  the  adult — contrary  to  the  statements  of  some  authors. 


THE  CARPUS 
The  carpus  of  the  horse  consists  of  seven  or  eight  carpal  bones  (Ossa  carpi) 


arranged  in  two  rows,  proximal  or  antibrachial  and  distal  or  metacarpal, 
1  Formerly  called  the  sigmoid  cavity. 


The 


94  THE  SKELETON  OF  THE  HORSE 

(abbreviated)  names  and  relative  positions  of  the  bones  of  the  left  carpus  are  in- 
dicated below: 

Proximal  Row: 
Radial        Intermediate        Ulnar        Accessory 


^. 


Distal  Row: 
First  Second  Third  Fourth 


The  Radial  Carpal  Bone 

The  radial  carpal  bone  (Os  carpi  radiale)4s  the  largest  bone  of  the  proximal  row; 
it  is  somewhat  compressed  transversely,  and  is  clearly  six-sided.  The  proximal 
surface  is  convex  in  front,  concave  behind,  and  articulates  with  the  medial  facet 
on  the  distal  end  of  the  radius.  The  distal  surface  is  also  convex  in  front  and  con- 
cave behind;  it  articulates  with  the  second  and  third  carpal  bones.  The  lateral 
surface  bears  upper  and  lower  facets  on  its  anterior  part  for  articulation  with  the 
intermediate;  between  and  behind  these  it  is  excavated  and  rough.  The  dorsal 
surface  is  rough  and  slightly  convex.  The  medial  surface  and  the  volar  surface 
are  rough  and  tuberculate. 

The  Intermediate  Carpal  Bone 

The  intermediate  carpal  bone  (Os  carpi  intermedium)-  is  somewhat  wedge- 
shaped,  wider  in  front  than  behind.  The  proximal  surface  is  saddle-shaped,  and 
articulates  with  the  middle  facet  on  the  distal  end  of  the  radius.  The  distal  sur- 
face is  smaller,  convex  in  front,  concave  behind,  and  articulates  with  the  third  and 
fourth  carpal  bones.  The  medial  surface  has  upper  and  lower  facets  for  articula- 
tion ^v^th  the  radial  carpal,  and  between  these  it  is  excavated  and  rough. 
The  lateral  surface  is  similar  to  the  preceding  and  articulates  with  the  ulnar  car- 
pal. The  dorsal  surface  is  rough  and  slightly  convex.  The  volar  siuiace  bears  a 
tuberosity  on  its  lower  part. 

The  Ulnar  Carpal  Bone 

The  ulnar  carpal  bone  (Os  carpi  ulnare)^  is  the  smallest  and  most  irregular 
bone  of  the  proximal  row.  The  proximal  surface  is  concave  and  fits  the  lower  part 
of  the  lateral  facet  on  the  distal  end  of  the  radius.  The  distal  surface  is  oblique 
and  undulating  for  articulation  with  the  fourth  carpal  bone.  The  medial  surface 
has  upper  and  lower  facets  for  articulation  with  the  intermediate.  The  dorsal  and 
lateral  surfaces  are  continuous,  convex,  and  rough.  The  volar  surface  is  oblique, 
and  bears  a  concave  facet  for  articulation  with  the  accessory  carpal  bone;  below 
this  is  a  tubercle. 

The  Accessory  Carpal  Bone 

The  accessory  carpal  bone  (Os  carpi  accessorium)*  is  situated  behind  the  ulnar 
carpal  bone  and  the  lateral  part  of  the  distal  end  of  the  radius.  It  is  discoid  and  pre- 
sents for  description  two  surfaces  and  a  circumference.  The  medial  surface  is  con- 
cave and  forms  the  lateral  wall  of  the  carpal  groove.  The  lateral  surface  is  con- 
vex and  rough;  a  smooth  groove  for  a  tendon  crosses  its  anterior  part  obliquely 
downward  and  slightly  forward.  The  dorsal  border  bears  two  facets;  the  proximal 
one  is  concave  and  articulates  with  the  back  of  the  lateral  facet  on  the  distal  end  of 
the  radius;  the  distal  one  is  convex  and  articulates  with  the  ulnar  carpal  bone. 
The  remainder  of  the  circumference  is  rounded  and  rough. 

1  Also  known  as  the  scaphoid.  ^  ^\^q  known  as  the  semilunar  or  lunar. 

^  Also  known  as  the  cuneiform. 

*  Also  known  as  the  pisiform  and  erroneously  as  the  trapezium. 


THE  FIRST  CARPAL  BONE THE  SECOND  CARPAL  BONE 


95 


The  accessory  does  not  directly  bear  weight,  and  may  be  regarded  as  a  sesamoid  bone 
interposed  in  the  course  of  the  tendons  of  the  middle  and  lateral  flexors  of  the  carpus,  which  it 
enables  to  act  at  a  mechanical  advantage.  The  posterior  border  furnishes  attachment  to  the 
transverse  carpal  ligament,  which  completes  the  carpal  canal  for  the  flexors  of  the  digit. 

The  First  Carpal  Bone 
The  first  carpal  bone  (Os  carpale  primum)i  is  a  small  inconstant  bone,  com- 
monly about  the  size  and  shape  of  a  pea,  which  is  situated  in  the  distal  part  of  the 
medial  ligament  of  the  carpus,  behind  the  second  carpal  bone. 

This  bone  appears  to  be  absent  on  both  sides  in  about  half  of  the  cases;  in  a  good  many 
subjects  it  is  present  on  one  side  only.  In  size  it  varies  from  a  minute  nodule  to  a  discoid  or  cylin- 
drical mass  12-15  mm.  in  length.  In  exceptional  cases  it  articulates  with  both  the  second  carpal 
and  the  second  metacarpal  bone;  in  other  cases  with  the  former  only,  but  in  the  majority  of  speci- 
mens no  articular  facet  is  present. 


Fig.  7L — Left  Corpus  of  Horse,  with  Parts  of  Adjacent  Bones;  L.^teral  View. 
a,  Intermediate  carpal;    Cu,  ulnar  carpal;    Ca,  accessory  carpal;    C3,  third  carpal;    C4,  fourth  carpal;    McIII, 
McIV,  metacarpal  bones;    1,  groove  for  common  extensor  tendon;    2,  groove  for  lateral  extensor  tendon;    3,  groove 
for  long  tendon  of  ulnaris   lateralis;   4,  metacarpal   tuberosity;  o,  original  distal  end  of  ulna,  which  is  fused  with  the 
radius  and  regarded  as  part  of  the  latter. 


The  Second  Carpal  Bone 

The  second  carpal  bone  (Os  carpale  secundum)-  is  the  smallest  constant  bone 

of  the  distal  row,  and  is  irregularly  hemispherical  in  shape.     The  proximal  surface 

is  a  convex  facet,  which  is  continued  upon  the  volar  surface  and  articulates  with  the 

radial  carpal.     The  lateral  surface  faces  obliquely  outward  and  forward,  and  bears 

1  Also  known  as  the  trapezium,  and  often  erroneously  called  the  pisiform. 
^  Also  known  as  the  trapezoid. 


96 


THE    SKELETON    OF   THE    HORSE 


three  facets  for  articulation  with  the  third  carpal  bone.  The  dorsal  and 
medial  surfaces  are  continuous  and  bear  a  tuberosity  to  which  the  collateral  liga- 
ment is  attached.  The  distal  surface  is  articular  and  consists  of  a  large  flattened 
facet  for  the  second  or  inner  metacarpal  bone,  and  a  small  one  for  the  third  or  large 
metacarpal  bone.  Some  specimens  have  a  small  facet  on  the  lower  part  of  the  volar 
surface  which  articulates  with  the  first  carpal  bone. 


Ca 


^ 


J 


\ 


The  Third  Carpal  Bone 

The  third  carpal  bone  (Os  carpale  tertium)^  is  much  the  largest  bone  of  the 

distal  row,  forming  more  than 
two-thirds  of  the  width  of  the 
latter.  It  is  flattened  from 
above  downward,  and  is  twice  as 
wide  in  front  as  behind.  The 
proximal  surface  consists  of  two 
facets  separated  by  an  antero-pos- 
terior  ridge;  the  medial  facet  is 
concave  and  articulates  with  the 
radial  carpal;  the  lateral  facet — 
for  the  intermediate  carpal — is 
concave  in  front  and  convex  be- 
hind, where  it  encroaches  on  the 
volar  surface.  The  distal  surface 
is  slightly  undulating,  and  articu- 
lates almost  entirely  with  the  third 
or  large  metacarpal  bone,  but  it 
usually  bears  a  small  oblique  facet 
at  its  medial  side  for  the  second 
metacarpal,  and  there  is  commonly 
a  non-articular  depression  later- 
ally. The  medial  surface  faces 
backward  and  inward,  and  bears 
three  facets  for  articulation  with 
the  second  carpal,  between  which 
it  is  excavated  and  rough.  The 
lateral  surface  has  two  facets  for 
articulation  with  the  fourth  car- 
pal, and  is  depressed  and  rough 
in  its  middle.  The  dorsal  sur- 
face is  convex  and  is  crossed 
by  a  rough  transverse  ridge.  The 
volar  surface  is  relatively  small, 
and   is   rounded;    its    upper   part 


MdU 


Pig.  72. — Left  Carpus  of  Horse,  with  Parts  of  Adjacent 
Bones;  Medial  View. 
Cr,  Radial  carpal;  Ca,  accessory  carpal;  Ct,  first  carpal; 
C2,  second  carpal;  McII,  McIII,  metacarpal  bones;  1,  tuber- 
osity of  radius  for  attachment  of  medial  ligament  of  carpus; 
2,  groove  for  tendon  of  extensor  carpi  obliquus;  3,  third  car- 
pal;  4,  metacarpal  tuberosity. 


is  encroached  upon  by  the  proximal  articular  surface,  below  which  it  is  rough. 


The  Fourth  Carpal  Bone 

The  fourth  carpal  bone  (Os  carpale  quartum)-  is  somewhat  wedge-shaped,  and 
is  readily  distinguished  from  the  second  by  its  greater  size  and  its  volar  tubercle. 
The  proximal  surface  articulates  with  the  intermediate  and  ulnar;  it  is  convex  and 
curves  outward,  backward,  and  downward,  encroaching  on  the  lateral  and  volar  sur- 
faces.    The  distal  surface  bears  two  medial  facets  for  the  third  or  large  metacarpal 

1  Also  known  as  the  os  magnum  or  capitatufti. 

2  Also  known  as  the  unciform  or  hamatum. 


THE  FOURTH  CARPAL  BONE 


97 


and  a  lateral  one  for  the  fourth  or  lateral  metacarpal  bone.  The  medial  surface 
has  two  or  three  facets  for  articulation  with  the  third  carpal,  between  which  it  is 
excavated  and  rough.     The  dorsal  surface  is  convex  and  rough.     The  lateral  sur- 


McIII 


Fig.  73. — Left  Carpus  of  Horse,  with  Pauts  )f  Adjacent  Bones;  Volar  View. 
The  accessory  and  first  carpal  bones  have  been  moved  out  of  their  natural  position  and  their  articular  connections 
indicated  by  arrows.  Cr,  Radial  carpal;  3,  intermediate  carpal;  Cu,  ulnar  carpal;  Co,  accessory  carpal;  CI,  first 
carpal;  C2,  second  carpal;  4,  third  carpal;  C4,  fourth  carpal;  1,  groove  for  lateral  extensor  tendon;  2,  tuberosity 
of  radius  for  medial  ligament  of  carpal  joint;  5,  volar  tubercle  of  fourth  carpal;  6,  rough  area  on  large  metacarpal 
bone  for  attachment  of  suspensory  ligament. 


Intermediate 


Third 


Radidl 


Fig.   74. — Proximal  Row  of  Left  Carpus   of    Horse; 

Proximal  View. 

1-4,  Articular  facets  corresponding  with  those  on  Fig.  69; 

5,  groove  for  tendon  of  ulnaris  lateralis. 

7 


Fourth 


Second 


First 

Fig.  7.5.— Distal  Row  of  Left  Carpus  of  Horse: 
Proximal  View. 
1,  Articulation  of  first  carpal  with  second;    2,  2, 
facets    for   radial;    3,   3',   facets  for  intermediate      4, 
facet  for  ulnar. 


THE    SKELETON    OF    THE    HORSE 


face  is  small,  being  encroached  upon  b}-  the  proximal  articular  surface. 
surface  bears  a  tubercle  on  its  distal  part.^ 


The  volar 


The  Carpus  as  a  Whole 
The  bones  of  the  carpus,  exclusive  of  the  accessory,  form  an  irregular  quadran- 
gular mass,  the  width  of  which  is  about  twice  the  height  or  the  dorso-volar  diameter. 
The  dorsal  surface  is  convex  from  side  to  side,  depressed  along  the  line  of  junction 
of  the  two  rows,  and  prominent  below.  The  volar  surface  is  in  general  slightly 
convex,  but  very  irregular.  It  forms  with  the  accessory 
carpal  the  carpal  groove  (Sulcus  carpi) ,  which  in  the  recent 
state  is  rendered  smooth  by  the  volar  ligament;  it  is  con- 
verted into  the  carpal  canal  (Canalis  carpi)  for  the  flexor 
tendons  by  the  transverse  carpal  ligament,  which  stretches 
across  from  the  accessory  bone  to  the  medial  side.  The 
proximal  surface  is  widest  medially  and  is  elevated  in  front, 
concave  behind ;  it  is  entirely  articular  and  adapted  to  the 
car])al  articular  surface  of  the  radius.  The  distal  surface 
is  also  articular  and  is  irregularly  faceted  in  adaptation  to 
the  surfaces  of  the  metacarpal  bones;  each  of  the  distal 
bones  usually  articulates  with  two  metacarpal  bones,  but 
sometimes  the  third  rests  on  the  third  metacarpal  only. 
The  medial  and  lateral  surfaces  are  both  irregular  and 
rough,  the  former  being  the  wider.  With  the  exception  of 
the  accessory,  ulnar,  and  second,  each  bone  articulates 
with  two  bones  of  the  other  row. 

Development. — Each  ossifies  from  a  single  center. 


McIV 


McIII 


Fig.  76. — Right  Metacarpal 
Bones  op  Horse;  Vol.\r 
View. 

1,  Nutrient  foramen  of 
large  (third)  metacarpal  bone; 
2,  3,  4,  proximal  extremities;  5, 
surface  for  attachment  of  sus- 
pensory ligament;  6,  sagittal 
ridge  of  distal  end  of  large  meta- 
carpal bone;  7,  7',  distal  ends  of 
small  (second  and  fourth)  meta- 
carpal bones. 


Fig. 


McII 
iRPAL  Bones  of  Horse;  End 


-Proximal  Extremities  of  Left  Metac. 
View. 
2,  2',  Facets  for  second  carpal  bone;  3,  3',  facets  for  third  carpal  bone;  4,  4',  facets 
for  fourth  carpal  bone;  5,  metacarpal  tuberosity. 


THE  METACARPUS 

Three   metacarpal   bones    (Ossa    metacarpalia)    are 
present  in  the  horse.     Of  these,  only  one,  the  third  or 
large  metacarpal  bone,  is  fully  developed  and  carries  a 
digit;  the  other  two,  the  second  and  fourth,  are  much 
reduced,  and  are  commonly  called  the  small  metacarpal  or  "splint"  bones. 

The  Third  or  Large  Metacarpal  Bone 
This  (Os  metacarpal  tertium)  is  a  very  strong  long  bone,  which  is  situated  ver- 
tically between  the  carpus  and  the  first  phalanx.     It  consists  of  a  shaft  and  two  ex- 
tremities. 

^  This  bone  is  probably  equivalent  to  the  fourth  and  fifth  carpals  of  forms  in  which  five 
carpal  elements  are  present  in  the  distal  row. 


THE  SMALL  METACARPAL  BONES  99 

The  shaft  (Corpus)  is  semicylindrical,  and  presents  two  surfaces  and  two 
borders.  The  dorsal  surface  is  smooth,  convex  from  side  to  side,  and  nearly 
straight  in  its  length.  The  volar  surface  is  somewhat  convex  from  side  to  side  and, 
with  the  small  bones,  forms  a  wide  groove  which  lodges  the  suspensory  ligament. 
On  either  side  of  its  proximal  two-thirds  it  is  roughened  for  the  attachment  of  the 
small  metacarpal  bones.  The  nutrient  foramen  occurs  at  the  junction  of  the 
proximal  and  middle  thirds.  The  distal  part  is  wider  and  flattened.  The  borders 
are  rounded. 

The  proximal  extremity  (Extremitas  proximalis  s.  basis)  bears  an  undulating 
articular  surface  adapted  to  the  distal  row  of  carpal  bones.  The  greater  part  sup- 
ports the  third  carpal  bone;  the  oblique  lateral  part,  separated  from  the  preceding 
by  a  ridge,  articulates  with  the  fourth,  and  a  small  facet  for  the  second  is  usually 
found  at  the  medio-volar  angle.  On  either  side  is  a  notch  separating  two  small 
facets  which  articulate  with  the  proximal  ends  of  the  small  metacarpal  bones. 
Toward  the  medial  side  of  the  dorsal  surface  is  the  metacarpal  tuberosity,  into 
which  the  extensor  carpi  radialis  is  inserted.  The  volar  surface  is  roughened  for 
the  attachment  of  the  suspensory  ligament. 

The  distal  extremity  (Extremitas  distalis  s.  capitulum)  presents  an  articular 
surface  for  the  first  phalanx  and  the  proximal  sesamoid  bones,  which  is  composed  of 
two  condyles,  separated  by  a  sagittal  ridge;  the  medial  condyle  is  slightly  the  larger. 
On  either  side  is  a  small  fossa,  surmounted  by  a  tubercle,  for  the  attachment  of  the 
collateral  ligaments  of  the  fetlock  joint. 

The  large  metacarpal  is  one  of  the  strongest  bones  in  the  skeleton.  The  compact  substance 
is  specially  thick  in  front  and  medially.  The  medullary  cavity  extends  further  toward  the  ends 
than  in  most  of  the  long  bones  of  the  horse  and  there  is  little  spongy  substance. 

The  Small  Metacarpal  Bones 

These,  numerically  the  second  and  fourth  metacarpal  bones  (Ossa  metacarpalia 
secundum  et  quartum) ,  are  situated  on  either  side  of  the  volar  surface  of  the  large 
metacarpal  bone,  and  form  the  sides  of  the  metacarpal  groove.  Each  consists  of  a 
shaft  and  two  extremities. 

The  shaft  (Corpus)  is  three-sided  and  tapers  to  the  distal  end.  It  is  variably 
curved,  convex  toward  the  middle  line  of  the  limb.  The  attached  surface  is  flat- 
tened and  is  rough,  except  in  its  lower  part;  it  is  attached  to  the  large  metacarpal 
bone  by  an  interosseous  ligament,  except  near  the  distal  end.  The  dorsal  or  ab- 
axial  surface  is  smooth  and  rounded  from  side  to  side  above,  grooved  below.  The 
volar  or  axial  surface  is  smooth  and  concave  from  edge  to  edge,  except  below, 
where  it  forms  a  rounded  edge. 

The  proximal  extremity  (Extremitas  proximalis  s.  basis)  is  relatively  large.  In 
the  case  of  the  medial  bone  it  usually  bears  two  facets  above  which  support  the  sec- 
ond and  third  carpal  bones,  while  the  lateral  bone  has  here  a  single  facet  for  articu- 
lation with  the  fourth  carpal  bone.  Each  has  also  two  facets  for  articulation  with 
the  large  metacarpal,  and  is  elsewhere  roughened  for  the  attachment  of  ligaments 
and  muscles.  The  medial  bone  may  present  a  small  facet  behind  for  the  first  carpal 
bone. 

The  distal  extremity  (Extremitas  distalis  s.  capitulum)  is  usually  a  small  nod- 
ule, which  projects  to  a  variable  extent  in  different  subjects,  and  is  easily  felt  in  the 
living  animal.     It  is  situated  two-thirds  to  three-fourths  of  the  way  down  the  region. 

The  small  metacarpal  bones  vary  much  in  length,  thickness,  and  curvature.  In  the  ma- 
jority of  cases  the  medial  bone  is  the  longer;  in  other  subjects  the  lateral  one  is  the  longer  or  there 
is  no  material  difference.  Sometimes  the  curvature  is  very  pronounced,  so  that  the  distal  end 
causes  a  decided  projection.  The  distal  end  is  very  variable  in  size  and  may  be  a  mere  point;  in 
other  cases,  especially  in  large  draft  horses,  it  may  present  a  prolongation  wliich  is  regarded  as  the 
vestige  of  the  digital  skeleton. 

Development. — The  large  metacarpal  bone  ossifies  from  three  centers.     The 


100 


THE    SKELETON    OF    THE    HORSE 


proximal  extremity  unites  with  the  shaft  before  birth,  the  distal  extremity  toward 
the  middle  of  the  second  year.  The  small  metacarpal  bones  ossify  from  two  cen- 
ters, one  of  which  is  for  the  proximal  extremity.  Their  distal  ends  are  cartilaginous 
at  birth.  Fusion  of  the  middle  part  of  the  shaft  with  the  large  metacarpal  bone  is 
common.  ■''■■:' 

THE  PHALANGES 
The  First  Phalanx 
The  first  phalanx  (Phalanx  prima)  ^  is  a  long  bone,  and  is  situated  between  the 
large  metacarpal  bone  and  the  second  phalanx.     It  is  directed  obliquely  downward 
and  forward,  forming  an  angle  of  50  to  55  degrees  with  the  horizontal  plane  in  well- 
formed  limbs.     It  consists  of  a  shaft  and  two  extremities. 


Distal  end  of  small  meta- 
carpal bone 


Proximal  sesamoid  hone 


Distal  end  of  first  phalanx 
Proximal  end  of  second  phalanx 


Distal  sesamoid  bone 


Distal  end  of  large  metacarpal  bone 
Proximal  end  of  first  phalanx 


Dorsal  groove  — 

Angle  _ .,    '-    ' 

DiMal  border  of  third  phalanx 
Fig.  78. — Skeleton  of  Digit  and  Distal  Part  of  Metacarpus  of  Horse;   Lateral  View. 
1-7,  Eminences  and  depression  for  attachment  of  ligaments.  Cartilage  of  third  phalanx  is  removed. 


The  shaft  (Corpus)  is  wider  and  much  thicker  above  than  below,  and  presents 
two  surfaces  and  two  borders.  The  dorsal  surface  is  convex  from  side  to  side  and 
smooth.  The  volar  surface  is  flattened,  and  bears  a  triangular  rough  area,  bounded 
by  ridges  which  begin  at  the  proximal  tuberosities  and  converge  distally;  this  area 
furnishes  attachment  to  the  distal  sesamoidean  ligaments.  The  borders,  medial 
and  lateral,  are  rounded  and  have  a  rough  area  or  a  tubercle  on  their  middle  parts. 

The  proximal  extremity  (Extremitas  proximalis  s.  basis)  is  relatively  large. 
It  bears  an  articular  surface  adapted  to  the  distal  end  of  the  large  metacarpal  bone, 
^  This  bone  is  also  called  the  large  pastern  bone  or  os  suffraginis. 


THE    FIRST    PHALANX 


101 


consisting  of  two  glenoid  cavities  separated  by  a  sagittal  groove;  the  medial  cavity- 
is  a  little  larger  than  the  lateral  one.  On  each  side  is  a  buttress-like  tuberosity  for 
ligamentous  attachment.  The  dorsal  surface  has  a  slight  elevation  for  the  attach- 
ment of  the  extensor  tendons. 

The  distal  extremity  (Extremitas  distalis)  is  smaller,  especially  in  its  dorso- 
volar  diameter.  It  presents  a  trochlea  for  articulation  with  the  second  phalanx, 
consisting  of  a  shallow  sagittal  groove  separating  two  condyles;    the  medial  con- 


I  Titer  mediate  groove 

Proximal  articular  surface 

Tuberosity 

Eminence  for  extensor  tendons 


Dorsal  surface  - 

Eminence  for  collateral  ligament    - 
Distal  articular  surface   ' 

Proximal  articular  surface  - 

Dorsal  surface   — 
Eminence  for  collateral  ligatncnt 
Distal  articular  surface 

Articular  surface 

Angle  .. 

Depression  for  collateral 
ligament 

Dorsal  groove 
Coronary  border  '''f"'\^ 
Articular  surface  -'*■'«.' 

Extensor  process  ■-' 

Dorsal  surface 


First  phalanx 


Second  phalanx 


Distal  sesamoid 


Third  phalanx 


Distal  border ■  '     '' 

Fig.  79. — Phalanges  and  Distal  Sesamoid  of  Horse;    Dorsal  Aspect. 


dyle  is  a  little  the  larger,  and  the  two  are  separated  posteriorly  by  a  notch.  On 
either  side,  just  above  the  margin  of  the  articular  surface,  is  a  depression  sur- 
mounted b}^  a  tubercle,  to  both  of  which  the  collateral  ligament  is  attached.  Be- 
hind the  tubercle  is  a  distinct  mark  to  which  the  superficial  flexor  tendon  is 
attached. 

Development. — The  first  phalanx  ossifies  from  three  centers.     The  distal  end 
unites  with  the  shaft  before  birth,  the  proximal  end  at  about  one  year  of  age. 

The  first  phalanx  contains  a  small  medullary  cavity  in  the  middle  of  the  shaft.     It  may  be 


JQ2  THE  SKELETON  OF  THE  HORSE 

remarked  that  the  bone  is  twisted  sUghtly;  when  placed  volar  surface  down  on  the  table,  it  touches 
the  latter  by  three  points  only,  the  proximal  tuberosities  and  the  medial  condyle. 

The  Second  Phalanx 
The  second  phalanx  (Phalanx  secunda)i  is  situated  between  the  first  and 
third  phalanges,  its  direction  corresponding  to  that  of  the  first  phalanx.     It  is 
flattened  from  before  l)ackward,  and  its  width  is  greater  than  its  height.     It  may 
be  described  as  possessing  four  surfaces. 

The  proximal  surface  presents  two  glenoid  cavities  separated  by  a  low  ridge, 

and  articulates  with  the  first  phalanx. 
The  middle  of  the  dorsal  border  is  ele- 
vated and  roughened  in  front  for  the 
attachment  of  the  common  extensor 
tendon.  The  volar  border  is  thick  and 
overhanging;  in  the  fresh  state  its  mid- 
dle part  is  covered  with  cartilage,  over 
which  the  deep  flexor  tendon  passes. 
On  either  side  there  is  an  eminence,  to 
which  the  collateral  ligament  and  the 
superficial  flexor  tendon  are  attached. 
The  distal  surface  is  trochlear, 
and  articulates  with  the  third  phalanx 
and  distal  sesamoid  bone.  It  resem- 
bles somewhat  the  trochlea  of  the  first 
phalanx,  but  is  more  extensive  and  en- 
croaches more  on  the  dorsal  and  volar 
surfaces. 

The  dorsal  surface  is  convex  from 
side  to  side  and  smooth  in  its  middle; 
on  each  side  of  its  distal  part  is  a  rough 
depression,  surmounted  by  a  tuber- 
osity, to  both  of  which  ligaments  are 
attached. 

The  volar  surface  is  smooth  and 
fiattened.  The  borders  which  separate 
the  dorsal  and  volar  surfaces  are  con- 
cave from  above  downward,  rounded 
from  before  backward. 

Development. — The  second  pha- 
laiLx  ossifies  like  the  first,  but  the  proxi- 
mal end  unites  with  the  shaft  two  or 
three  months  earlier. 


Tuberosity 


Ridges  for 

attachment 

of  middle 

distal  sesd- 

moid  ligament 

Imprint  for 

tendon  of 

superfici(d 

flexor 

Condyle 

Transverse 
prominence 


-Digital  Bones  of  Fore  Limb  of  Horse;  Volar 
Aspect. 


The  Third  Phalanx 
The  third  phalanx  (Phalanx  ter- 
tia)^  is  entirely  inclosed  by  the  hoof, 
It  presents  for  examination  three  sur- 


to  which  it  conforms  in  a  general  way. 
faces,  three  borders,  and  two  angles. 

The  articular  surface  (Facies  articularis)  faces  upward  and  backward,  and  is 
chiefly  adapted  to  the  distal  surface  of  the  second  phalanx,  but  a  narrow,  flattened 
area  along  the  volar  border  articulates  with  the  distal  sesamoid.  The  proximal  or 
coronary  border  bears  a  central  eminence,  the  extensor  process  (Processus  exten- 

1  This  bone  is  also  called  the  small  pastern  bone  or  os  coronse. 

2  This  bone  is  also  called  the  os  pedis  or  coffin  bone. 


THE   THIRD    PHALANX 


103 


sorius),  to  which  the  common  extensor  tendon  is  attached.     On  either  side  is  a  de- 
pression for  the  attachment  of  the  collateral  ligament. 

The  dorsal  or  wall  surface  (Facies  dorsalis)  slopes  downward  and  forward. 
The  angle  of  inclination  on  the  ground  plane  is  about  45  to  50  degrees  in  front. 


Cartilage 


h      Dorsal  Angle 

grooir 


)  Arlicular  surface 

Extensor  process 

Depression  for  collateral  ligament 
Dorsal  surface 


l)istal  border 


Fig.  si. — Third  Phalanx  of  Horse;  Lateral  View. 
a,  b.  Anterior  and  posterior  extremities  of  cartilage. 


Laterally  the  height  diminishes,  and  the  slope  becomes  steeper,  especially  on  the 
medial  side.  From  side  to  side  the  curvature  is  almost  semicircular.  The  surface 
is  rough  and  porous,  resembling  pumice  stone  somewhat.  It  is  perforated  by  nu- 
merous foramina  of  various  sizes;  a  series  of  larger  ones  is  situated  on  or  near  the 
distal  border.  On  either  side  the  dorsal  groove  (Sulcus  dorsalis)'^  passes  forward 
from  the  angle  and  ends  at  one  of  the 
larger  foramina.  In  the  fresh  state  this 
surface  is  covered  by  the  corium  of  the 
wall  of  the  hoof.  The  distal  border  is 
thin,  sharp,  and  irregularly  notched; 
there  is  commonly  a  wider  notch  in 
front. 

The  volar  surface  (Facies  volaris) 
is  arched,  and  divided  into  two  unequal 
parts  by  a  curved  rough  line,  the  semi- 
lunar crest  (Crista  semilunaris) .  The 
larger  area  in  front  of  the  crest  is  cres- 
cent-shaped, concave,  and  compara- 
tively smooth;  it  corresponds  to  the 
sole  of  the  hoof,  and  may  be  termed 
the  sole  surface.  The  part  behind  the 
crest  is  much  smaller,  and  is  semilunar; 
it  is  related  to  the  deep  flexor  tendon, 
and  is  hence  called  the  flexor  surface 
(Facies  flexoria) .  It  presents  a  central 
prominent  rough  area,  on  either  side  of 
which  is  the  volar  foramen  (Foramen 

volare),  to  which  the  volar  groove  (Sulcus  volaris)  conducts  from  the  angle.^ 
The  foramina  lead  into  the  semilimar  canal  (Canalis  semilunaris)  within  the 
bone,  from  which  small  canals  lead  to  some  of  the  foramina  of  the  dorsal  sur- 


FiG.  82. — Section  of  Third  Phalanx  of  Horse. 

Section  is  cut  approximately  parallel  with  volar  sur- 
face and  opens  up  the  semilunar  canal  (C.s.).  Volar  for- 
amina indicated  by  arrows. 


Formerly  termed  the  pyramidal  process. 
Formerly  termed  the  plantar  groove  and  foramen. 


Formerly  termed  the  preplantar  groove. 


104 


THE    SKELETON    OF   THE    HORSE 


face.     The  deep  flexor  tendon  is  inserted  into  the  semilunar  crest  and  the  central 

rough  area  behind  it. 

The  volar  grooves  and  foramina  transmit  the  terminations  of  the  digital  arteries  into  the 
semilunar  canal,  where  they  meet  and  form  a  terminal  arch,  from  which  branches  pass  through 
canals  in  the  bone  and  emerge  through  the  foramina  on  the  dorsal  surface. 

The  angles  or  wings  (Anguli)  are  prismatic  masses  which  project  l^ackward  on 
either  side;  the  medial  one  is  usually  the  shorter.  Each  is  divided  into  upper  and 
lower  parts  by  a  notch,  or  is  perforated  by  a  foramen  which  leads  to  the  dorsal 
groove.^     The  proximal  border  carries  the  cartilage. 

The  cartilages  of  the  third  phalanx  (Cartilagines  phalangis  tertise)-  are  rhom- 
boid curved  plates  which  surmount  the  angles  on  either  side.  They  are  relatively 
large  and  extend  above  the  margin  of  the  hoof  sufficiently  to  be  distinctly  palpable. 
The  abaxial  surface  is  convex,  the  axial,  concave.     The  proximal  border  is  sinuous 

and  thin ;  the  distal  is  thicker  and  is  in 
part  attached  to  the  wing.  The  anterior 
end  is  attached  by  ligament  to  the  side 
of  the  second  phalanx.  The  posterior 
end  curves  toward  its  fellow  at  the  heel, 
and  is  perforated  by  numerous  for- 
amina for  the  passage  of  veins. 

It  wll  be  noted  that  the  size  and  form 
of  the  angles  vary  much  in  difTerent  specimens. 
In  the  new-born  foal  the  angle  is  a  small, 
pointed  projection.  Later  the  process  of  ossi- 
fication invades  the  lower  part  of  the  car- 
tilage to  a  varying  extent.  In  some  cases  the 
greater  part  of  the  cartilage  is  ossified — a  con- 
dition commonly  termed  "  sidebone. "  In  the 
young  subject  the  cartilage  is  hyaline,  but  later 
it  changes  to  the  fibrous  type. 

Development. — The  ossification  of 
the  third  phalanx  is  peculiar.     While 
the  proximal  articular  part  is  still  car- 
tilaginous, a  perichondrial  cap  of  bone 
is  formed  in  relation  to  the  hoof.     Later 
the  process  extends  into  the  upper  part. 
Structure. — The    interior   of   this 
bone  is  channeled  by  numerous  canals 
for  vessels,  most  of  which  radiate  from 
the  semilunar  canal  to  the  dorsal  sur- 
face; these  are  not  canals  for  nutrient 
vessels    of    the    bone,     but    transmit 
arteries  to  the  corium  of  the  hoof.     Thick  layers  of  compact  substance  are  found 
at  the  articular  and  flexor  surfaces  and  the  extensor  process,  i.  e.,  at  the  points  of 
greatest  pressure  and  traction. 

The  Sesamoid  Bones 

The  two  proximal  sesamoids  (Ossa  sesamoidea  phalangis  primse)  are  situated 
behind  the  distal  end  of  the  large  metacarpal  bone,  and  are  closely  attached  to  the 
first  phalanx  by  strong  ligaments.  Each  has  the  form  of  a  three-sided  pyramid. 
The  articular  surface  (Facies  articularis)  conforms  to  the  corresponding  part  of  the 

^  The  upper  and  lower  divisions  of  the  angle  are  sometimes  termed  the  basilar  and  retrossal 
processes  respectively. 

^  These  are  usually  called  the  lateral  cartilages,  but  this  designation  could  not  be  retained. 
They  have  the  same  relation  to  the  third  phalanx  that  the  cartilage  of  the  scapula  has  to  the  latter 
bone,  and  are  here  named  in  similar  fashion. 


Fig.  8.3.  I  n  vi  >  ,..i  -  of 
New-born  1'o\l;  Dor- 
sal View. 

Cartilages  of  third  phalanx 
removed. 


Fig.  84. — Phalanges  and 
Distal  Sesamoid  of 
New-born  Foal;  Vo- 
lar View. 

Cartilages  of  third  phalanx 
removed. 


OS    COX^ THE    ILIUM  105 

distal  end  of  the  large  metacarpal  bone.  The  flexor  surface  (Facies  flexoria)  is 
flattened  and  oblique;  in  the  fresh  state  it  is  covered  by  a  layer  of  cartilage  which 
also  fills  the  interval  between  the  opposed  borders  of  the  two  bones,  and  forms  a 
smooth  groove  for  the  deep  flexor  tendon.  The  abaxial  surface  is  concave,  and 
gives  attachment  to  part  of  the  suspensory  ligament;  it  is  separated  from  the 
flexor  surface  by  a  rough  everted  border.  The  base  is  distal,  and  furnishes  attach- 
ment to  the  distal  sesamoidean  ligaments.     The  apex  is  proximal  and  is  rounded. 

The  distal  sesamoid  or  navicular  bone  (Os  sesamoideum  phalangis  tertise)  is 
shuttle-shaped,  and  is  situated  behind  the  junction  of  the  second  and  third  pha- 
langes. Its  long  axis  is  transverse,  and  it  possesses  two  surfaces,  two  borders,  and 
two  extremities.  The  articular  surface  (Facies  articularis)  faces  upward  and 
forward;  it  consists  of  a  central  eminence,  flanked  by  concave  areas,  and  articulates 
with  the  distal  end  of  the  second  phalanx.  The  flexor  or  tendon  surface  (Facies 
flexoria)  is  directed  downward  and  backward.  It  resembles  the  articular  surface 
in  form,  but  is  more  extensive  and  not  so  smooth.  In  the  fresh  state  it  is  coated 
with  cartilage  and  the  deep  flexor  tendon  plays  over  it.  The  proximal  border 
(Margo  proximalis)  is  wide  and  grooved  in  its  middle,  narrower  and  rounded  on 
either  side.  The  distal  border  (Margo  distalis)  bears  in  front  a  narrow  facet  for 
articulation  with  the  third  phalanx.  Behind  this  is  a  groove,  which  contains  a 
number  of  relatively  large  foramina,  and  is  bounded  behind  by  a  prominent  edge. 
The  extremities  are  blunt-pointed. 

Development. — Each  ossifies  from  a  single  center. 


The  Bones  of  the  Pelvic  Limb 

The  pelvic  girdle  (Cingulum  extremitatis  pelvinae)  consists  of  the  os  coxae, 
which  unites  ventrally  with  the  opposite  bone  at  the  symphysis  pelvis,  and  artic- 
ulates with  the  sacrum  dorsally. 

OS  COX^ 

The  OS  coxae  or  hip  bone^  is  the  largest  of  the  flat  bones.     It  consists  primarily 

of  three  parts,  the  ilium,  ischium,  and  pubis,  which  meet  to  form  the  acetabulum, 

a  large  cotyloid  cavity  for  articulation  with  the  head  of  the  femur.     These  parts 

are  fused  at  about  one  year  of  age,  but  it  is  convenient  to  describe  them  separately.^ 

The  Ilium 

The  ilium  (Os  ilium)  is  the  largest  of  the  three  parts.  It  is  irregularly  triangu- 
lar and  presents  two  surfaces,  three  borders,  and  three  angles. 

The  wide  part  of  the  bone  is  the  wing  (Ala  ossis  ilium).  Its  gluteal  surface 
(Facies  glutaa)  faces  dorso-laterally  and  backward.  It  is  wide  and  concave  in 
front,  narrower  and  convex  behind.  The  wide  part  is  crossed  by  the  curved 
gluteal  line  (Linea  glutaea),  which  extends  from  the  middle  of  the  medial  border 
toward  the  tuber  coxae.  This  surface  gives  attachment  to  the  middle  and  deep 
gluteal  muscles. 

The  pelvic  surface  (Facies  pelvina)  faces  in  the  opposite  direction;  it  is  convex, 
and  consists  of  two  distinct  parts.  The  medial  triangular  part  (Pars  articularis) 
is  roughened  for  ligamentous  attachment,  and  bears  an  irregular  facet,  the  auricu- 
lar surface  (Facies  auricularis) ,  for  articulation  with  the  sacrum.  The  lateral  quad- 
rilateral part  (Pars  iliaca)  is  in  general  smooth.  It  is  crossed  by  the  ilio-pectineal 
line  (Linea  iliopectinea),  which  begins  below  the  auricular  surface  and  is  continued 

1  Formerly  called  the  os  innominatum. 

2  The  proper  terms,  strictly  speaking,  for  these  bones  are  os  ilium,  os  ischii,  and  os  pubis,  but 
the  names  given  above  are  sanctioned  by  common  usage. 


106 


THE    SKELETON    OF   THE    HORSE 


on  the  shaft  of  the  bone  to  join  the  anterior  border  of  the  pubis.  The  hne  is  inter- 
rupted by  furrows  for  the  iliaco-femoral  vessels,  and  below  these  it  bears  the  psoas 
tubercle  (Tuberculum  psoadicum),  which  gives  attachment  to  the  psoas  minor  mus- 
cle.    The  iliacus  muscle  is  attached  to  the  surface  lateral  to  the  ilio-pectineal  line. 

The  anterior  border  or  crest  (Crista  iliaca)  is  concave,  thick,  and  rough. 

The  medial  border  (Margo  medialis)  is  deeply  concave.  Its  middle  part  forms 
the  greater  sciatic  notch  (Incisura  ischiadica  major)  and  it  is  continuous  behind 
with  the  ischiatic  spine. 

The  lateral  border  (Margo  lateralis)  is  concave  and  in  great  part  rough.  Its 
a,nterior  part  is  crossed  l)y  grooves  for  the  ilio-lumbar  vessels,  which  are  continued 


Sacral  spines 


Tuber  sacralf         Crest  of  ilium 


Apex  of  sacrum 


Tuber 
coxce 


Ac(  tabular  branch  of  pubis 


Ventral  ischiatic 
spine 

Fig.  85. — Right  Os  Cox-e  axd  Sacrum  op  Horse;  Right  Lateral  View. 
1,  Gluteal  line;    2,  impression  of  ilio-lumbar  artery;   3,  impression  of  iliaco-femoral  artery;    4,  depressions  for  at- 
tachments of  tendons  of  origin  ofj  rectus  femoris;   5,  crest  to  which   lateral  tendon  of  rectus  femoris  and  capsularis  are 
attached;  G,  6',  articular  surface  of  acetabulum  (facies  lunata) ;  7,  acetabular  fossa;    8,  obturator  foramen;   9,  line  for 
attachment  of  gemellus  muscle;   10,  lateral  border  of  sacrum;   11,  dorsal  sacral  foramina. 


Symphyseal  branch 
of  pubis 


on  the  pelvic  surface.  The  nutrient  foramen  is  usually  situated  on  or  near  the 
posterior  part  of  this  border. 

The  medial  angle  is  termed  the  tuber  sacrale;  it  curves  upward  and  a  little 
backward  opposite  to  the  first  sacral  spine,  and  forms  here  the  highest  point  of  the 
skeleton.     It  is  somewhat  thickened  and  rough. 

The  lateral  angle,  tuber  coxae,  forms  the  basis  of  the  point  of  the  hip.  It  is  a 
large  quadrangular  mass,  narrow  in  its  middle,  and  enlarged  at  either  end,  where 
it  bears  a  pair  of  tuberosities.     It  is  roughened  for  muscular  attachment. 

The  acetabular  angle  (Angulus  acetabularis)  meets  the  other  two  bones  at  the 
acetabulum,  of  which  it  forms  about  two-fifths.     Its  prominent  dorsal  border  forms 


THE   ISCHIUM 


107 


part  of  the  ischiatic  spine  (Spina  ischiadica),  which  is  roughened  laterally,  smooth 
medially.  Two  depressions  above  and  in  front  of  the  acetabulum  give  attachment 
to  the  tendons  of  origin  of  the  rectus  femoris  muscle.  This  angle  is  connected  with 
the  wing  or  wide  part  of  the  bone  by  a  constricted  part,  termed  the  shaft  (Corpus 
ossis  ilium).  The  latter  is  of  three-sided,  prismatic  form.  Its  lateral  surface  is 
convex  and  rough,  and  gives  attachment  to  the  deep  gluteus  muscle.  Its  pelvic 
surface  is  smooth  and  is  grooved  for  the  obturator  vessels  and  nerve.  Its  ventral 
surface  is  crossed  by  vascular  grooves,  below  which  there  is  a  rough  area,  which  is 
bounded  medially  by  the  psoas  tubercle. 


Tuber  sacrale 


Ischiatic  spine 


Tuber  ischii 


Ischial  arch 


Fig.  86. — Ossa  Cox.\rum  of  Horse;    Dorsal  View. 
A,  Wing;  A',  shaft  of  ilium;    B,  acetabular,  B',  symphyseal  branch  of  pubis;   C,  body,  C,  acetabular  branch  (or 
shaft),  C",  symphyseal  branch,  of  ischium;    1,  gluteal  line;    2,  grooves  for  obturator  nerve  and  vessels;    3,  symphysis 
pelvis;   4,  greater  sciatic  notch;  5,  ilio-pectineal  eminence;   6,  pubic  tubercle.     Dotted  hnes  indicate  primitive  separa- 
tion of  three  bones. 


The  Ischium 

The  ischium  (Os  ischii)  forms  the  posterior  part  of  the  ventral  wall  or  floor  of 
the  bony  pelvis.  It  slopes  a  little  downward  and  inward,  but  is  practically  hori- 
zontal in  the  longitudinal  direction.  The  body  of  the  ischium  (Corpus  ossis 
ischii)  is  irregularly  quadrilateral,  and  may  be  described  as  having  two  surfaces, 
four  borders,  and  four  angles. 

The  pelvic  surface  (Facies  pelvina)  is  smooth  and  slightly  concave  from  side 
to  side. 

The  ventral  surface  (Facies  ventralis)  is  nearly  flat,  and  is  in  great  part  rough- 
ened for  the  attachment  of  the  adductor  muscles. 

The  anterior  border  forms  the  posterior  margin  of  the  obturator  foramen. 


108 


THE    SKELETON    OF   THE    HORSE 


The  posterior  border  is  thick  and  rough.  It  slopes  medially  and  forward 
to  meet  the  border  of  the  other  side,  forming  with  it  the  ischial  arch  (Arcus 
ischiadicus). 

The  medial  border  meets  the  opposite  bone  at  the  symphysis  ischii. 

The  lateral  border  is  thick  and  rounded,  but  concave  in  its  length;  it  forms 
the  lesser  sciatic  notch  (Incisura  ischiadica  minor),  the  lower  boundary  of  the  lesser 
sciatic  foramen. 

The    antero-medial    angle    or    symphyseal    branch    (Ramus    symphyseos) 


C'nsl  of  ilium 


Grooves  for  ilio- 
lumbar vessels 
Grooves  for 
iliaco-femoral 


Depression  for 

medial  tendon 

of  rectus 

femoris 


Obturator  foramen 


Fig.  87. — O.ssa  Coxarum  of  Mare;  Ventral  View. 
A,  Wing,  A',  shaft  of  ilium;  B,  acetabular  branch,  B',  symphyseal  branch,  of  pubis;  C,  body,  C,  acetabular 
branch  (shaft),  C",  symphyseal  branch,  of  ischium;  1,  auricular  surface;  2,  ilio-pectineal  line;  2',  psoas  tubercle;  3, 
arcuate  hne;  4,  articular  part,  5,  iliac  part,  of  pelvic  surface  of  ihum;  6,  ilio-pectineal  eminence;  7,  pubic  tubercle;  8, 
acetabular  fossa;  9,  articular  surface  of  acetabulum  (facies  lunata) ;  10,  symphysis  pelvis;  11,  pubic  groove.  Dotted 
Unes  indicate  primitive  division  of  os  coxae. 


meets  the  pubis,  with  which  it  forms  the  medial  boundary  of  the  obturator 
foramen. 

The  antero-lateral  angle  or  acetabular  branch  (Ramus  acetabularis)  joins  the 
other  two  bones  at  the  acetabulum,  of  which  it  forms  more  than  half.  Dorsally 
it  bears  part  of  the  ischiatic  spine  (Spina  ischiadica),  and  medially  it  is  grooved  for 
the  obturator  vessels.  The  term  shaft  is  often  applied  to  the  constricted  part  of 
the  acetabular  branch. 

The  postero-medial  angle  joins  its  fellow  at  the  symp?iysis. 

The  posterolateral  angle  is  a  thick,  three-sided  mass,  the  tuber  ischii  (Tuber 
ischiadicum) ;  its  lower  border  is  the  ventral  ischiatic  spine,  to  which  the  biceps 
femoris  and  semitendinosus  muscles  are  attached. 


THE  PUBIS — THE  OBTURATOR  FORAMEN  109 


The  Pubis 


The  pubis  (Os  pubis)  is  the  smallest  of  the  three  parts  of  the  os  coxae.  It 
forms  the  anterior  part  of  the  pelvic  floor,  and  may  be  described  as  having  two 
surfaces,  three  borders,  and  three  angles. 

The  pelvic  surface  (Facies  pelvina)  is  convex  in  the  young  subject  and  the 
stallion,  concave  and  smooth  in  the  mare  and  usually  in  the  gelding  also.^ 

The  ventral  surface  (Facies  ventralis)  is  convex,  and  in  great  part  rough  for 
muscular  attachment.  Near  the  anterior  border  it  is  crossed  by  the  pubic  groove 
(Sulcus  pubis),  the  medial  part  of  which  is  occupied  by  a  large  vein,  the  lateral  part 
by  the  accessory  ligament;  the  groove  leads  to  the  acetabular  notch. 

The  anterior  border  is  thin  in  its  medial  part  (except  in  the  young  subject  and 
the  stallion),  forming  the  pecten  ossis  pubis.  Laterally  it  bears  the  rough  ilio- 
pectineal  eminence  (Eminentia  iliopectinea),  beyond  which  it  is  continuous  with 
the  ilio-pectineal  line.  Near  the  symphysis  is  a  variable  prominence,  the  tuber- 
culum  pubicum. 

The  medial  border  joins  the  opposite  bone  at  the  symphysis  pubis. 

The  posterior  border  forms  the  anterior  margin  of  the  obturator  foramen,  and 
is  marked  laterally  by  the  obturator  groove. 

The  medial  angle  meets  its  fellow  at  the  anterior  end  of  the  symphysis.  This 
part  is  very  thick  in  the  young  subject  and  the  stalHon,  but  in  the  mare,  and  usually 
in  the  gelding  also,  it  becomes  thin  with  advancing  age. 

The  acetabular  angle  joins  the  ilium  and  ischium  at  the  acetabulum. 

The  posterior  angle  joins  the  ischium,  with  which  it  forms  the  inner  boundary 
of  the  obturator  foramen. 

The  pubis  may  conveniently  be  regarded  as  consisting  of  a  body  (Corpus  ossis 
pubis)  and  two  l^ranches;  the  latter  are  termed  the  acetabular  branch  (Ramus 
acetabularis)  and  the  -symphyseal  branch  (Ramus  symphyseos) . 

The  Acetabulum 

The  acetabulum  is  a  cotyloid  cavity  which  lodges  the  head  of  the  femur.  It 
faces  ventro-laterally,  and  consists  of  an  articular  and  a  non-articular  part.  The 
articular  part  (Facies  lunata)  is  crescentic,  and  is  cut  into  internally  by  a  rough 
non-articular  depression,  the  acetabular  fossa  (Fossa  acetabuli).  The  medial 
part  of  the  rim  is  correspondingly  cut  into  by  the  acetabular  notch  (Incisura 
acetabuli),  which  is  converted  into  a  foramen  by  the  transverse  ligament  in  the 
fresh  state,  and  transmits  the  accessory  and  round  ligaments  to  the  head  of  the 
femur. 

The  Obturator  Foramen 

The  obturator  foramen  (Foramen  obturatum)  is  situated  between  the  pubis 
and  ischium.  It  is  oval  in  outline,  the  longer  axis  being  directed  forward  and 
outward.  Its  margin  is  grooved  antero-laterally  for  the  obturator  nerve  and  ves- 
sels. 

Development. — Each  division  of  the  os  coxse  ossifies  from  one  chief  center. 
The  center  for  the  ilium  first  appears  near  the  acetabulum,  followed  quickly  by  one 
for  the  ischium,  and  a  little  later  l\y  the  pubic  center.  Secondary  centers  appear 
for  the  crest  and  tuber  coxse  of  the  ilium,  the  tuber  and  posterior  border  of  the 
ischium,  and  the  acetabular  part  of  the  pubis.  The  symphyseal  branches  of  the 
pubis  and  ischium  are  usually  united  with  each  other  before  birth,  but  the  three 

1  The  pelvic  surface  of  the  pubis  is  quite  variable.  In  the  mare  and  in  geldings  which  have 
been  castrated  eariy  the  two  pubic  bones  form  a  central  depression  of  variable  depth  and  curvature. 
This  depression  is  bounded  posterioriy  by  two  obhque  convergent  hues  or  ridges,  to  which  the 
obturator  internus  muscle  is  attached.  Not  rarely  small  eminences  may  be  present  along  the 
symphysis. 


110 


THE    SKELETON    OF   THE   HORSE 


bones  are  not  fused  until  the  second  year.     The  epiphyseal  parts  fuse  with  the 
main  mass  at  four  and  a  half  to  five  years  of  age. 

The  acetabular  part  of  the  pubis  ossifies  from  a  separate  center.  It  is  most  distinct  in  the 
embryo  at  three  months,  and  is  often  called  the  os  acetabuli.  Martin  says  that  the  ilium  has  a 
center  for  the  acetabular  part,  one  for  the  shaft  and  wing,  and  a  third  for  the  crest.  He  also 
states  that  there  is  a  special  center  for  the  acetabular  part  of  the  ischium,  and  a  transitory  nucleus 
in  the  symphyseal  part  of  the  pubis. 

THE  PELVIS 
The  bony  pelvis  is  composed  of  the  ossa  coxarum,  the  sacrum,  and  the  first 
three  coccj^geal  vertebrae.     The  dorsal  wall  or  roof  is  formed  by  the  sacrum  and 
first  three  coccygeal  vertebrae,  and  the  ventral  wall  or  floor  by  the  pubic  and  ischial 


Crest  of  ilium 


Sacral       Tuber 
spines       sacrale 


Tuber  coxa 


Depressioji  in  which 
tendon  of  rectus 
femoris  is  attached 


I  Ho- pectineal  eminence 


Acetabidmn 


Tuber  ischii 


Ischium 
Pubic  tubercle 

Fig.  88. — Pelvic  Bones  op  Mare,  Viewed  from  in  Front  and  Somewhat  from  Below. 
1,  Body  of  first  sacral  segment;  2,  surface  on  wing  of  sacrum  for  articulation  with  like  surface  on  transverse  process 
of  last  lumbar  vertebra ;   3,  wing  of  sacrum;  4,  sacro-iliac  articulation ;   5,  sacral  canal;   6,  promontory;   7,  apex  of  sac- 
rum;  8,  ilio-pectineal  line;   9,  ischiaticspine;  10,  grooves  for  ilio-lumbar  vessels;   11,  grooves  for  iliaco-femoral  vessels. 


bones.  The  lateral  walls  are  formed  by  the  ilia  and  the  acetabular  part  of  the 
ischia.  The  defect  in  the  skeleton  here  is  supplied  in  the  fresh  state  by  the  sacro- 
sciatic  ligaments  and  semimembranosus  muscles. 

The  anterior  aperture  or  inlet  of  the  pelvis  (Apertura  pelvis  cranialis)  is  bounded 
by  the  terminal  line  (Linea  terminalis)  or  brim,  which  is  composed  of  the  base  of 
the  sacrum  dorsalh%  the  ilio-pectineal  lines  laterally,  and  the  pecten  pubis  ventrally. 
It  is  almost  circular  in  the  mare,  semi-elliptical  in  the  stallion,  and  faces  obliquely 
downward  and  forward.  It  has  two  principal  diameters.  Of  these,  the  con- 
jugate or  sacro-pubic  diameter  (Conjugata  anatomica)  is  measured  from  the  sacral 
promontory  to  the  anterior  end  of  the  symphysis.     The  transverse   diameter 


THE    PELVIS 


111 


(Diameter  transversa)  is  measured  at  the  greatest  width,  i.  e.,  just  above  the  psoas, 
tubercle. 

The  posterior  aperture  or  outlet  of  the  pelvis  (Apertura  pelvis  caudalis)  i& 
much  smaller  and  is  very  incomplete  in  the  skeleton.     It  is  bounded  dorsally  by  the 


Fig.  90. — Pelvic  Bones  op  Mare;    Front  View. 
C,  Conjugate,  D.t.,  transverse,  diameter  of  pelvic  inlet. 


third  coccygeal  vertebra  and  ventrally  by  the  ischial  arch;  in  the  fresh  state  it  is 
completed  laterally  by  the  sacro-sciatic  ligament  and  the  semimembranosus  muscle. 

The  axis  of  the  pelvis  is  an  imaginary  line  drawn  through  the  centers  of  the 
inlet,  cavity,  and  outlet. 

Sexual  Differences. — Marked  differences  exist  in  the  size  and  form  of  the  pel- 
vis in  the  two  sexes.     The  average  conjugate  diameter  is  about  93^  inches  (ca.  23  to 


112  THE  SKELETON  OF  THE  HORSE 

24  cm.)  in  the  mare,  73^  inches  (ca.  18.75  cm.)  in  the  stallion.  The  transverse 
diameter  of  the  inlet  is  about  the  same  as  the  conjugate  in  the  mare,  but  is  about 
8  inches  (ca.  20  cm.)  in  the  stallion.  The  obliquity  of  the  inlet  or  inclination  of  the 
pelvis  (Inclinatio  pelvis)  is  greater  in  the  female ;  the  difference  is  indicated  by  the 
fact  that  a  vertical  plane  from  the  pecten  cuts  the  fourth  sacral  segment  in  the  fe- 
male, the  second  in  the  male.  The  outlet  is  also  larger  in  the  mare,  the  ischial  arch 
being  about  one-third  wider  than  in  the  stallion.  The  cavity  is  much  more  roomy 
in  the  female;  the  transverse  diameter  between  the  middles  of  the  superior  ischiatic 
spines  is  about  8  inches  (20  cm.)  in  the  mare,  6  inches  (15  cm.)  in  the  stallion.  The 
pubic  part  of  the  floor  in  the  female  is  concave  and  lies  considerably  lower  than  the 
ischiatic  part,  which  is  wide  and  almost  flat.  In  the  stallion  the  pubis  is  very  thick 
medially,  and  this  part  of  the  floor  is  convex,  while  the  ischial  part  is  relatively  nar- 
row, and  is  concave  from  side  to  side.  The  obturator  foramina  are  correspondingly 
larger  in  the  female.  The  ilium  is  shorter,  especially  with  regard  to  its  shaft,  and 
the  greater  sciatic  notch  is  deeper  and  narrower  in  the  male.  The  pelvis  of  the  geld- 
ing, when  castration  has  been  performed  early,  resembles  that  of  the  mare;  other- 
wise the  male  characters  appear  to  be  retained  to  a  large  degree. 

THE  FEMUR 

The  femur  or  thigh  bone  (Os  femoris)  is  the  largest  and  most  massive  of  the 
long  bones.  It  extends  obliquely  downward  and  forward,  articulating  with  the 
acetabulum  above  and  the  tibia  and  patella  below.  It  presents  for  examination  a 
shaft  and  two  extremities. 

The  shaft  (Corpus  femoris)  is  in  general  cylindrical,  but  flattened  behind,  and 
larger  above  than  below.  The  anterior,  medial,  and  lateral  surfaces  are  continuous 
and  strongly  convex  from  side  to  side;  there  is  often  a  central  vertical  rough  line 
on  the  proximal  part,  but  otherwise  these  surfaces  are  smooth.  They  are  covered 
by  the  quadriceps  femoris  muscle.  The  posterior  surface  is  wide,  flat,  and  smooth 
in  its  proximal  fourth.  Distal  to  this  part  there  is  a  rough  elevation  laterally  for 
the  attachment  of  the  femoral  tendon  of  the  biceps  femoris,  and  a  rough  line  medi- 
ally to  which  the  quadratus  femoris  is  attached.  The  middle  third  is  narrower, 
and  is  rough  for  the  attachment  of  the  adductor  muscle.  Just  distal  to  this  area 
an  oblique  groove  crosses  the  surface,  indicating  the  position  of  the  femoral  vessels. 
The  medial  border  l^ears  on  its  proximal  part  the  trochanter  minor,  a  thick  rough 
ridge,  to  which  the  iho-psoas  muscle  is  attached.  From  this  a  rough  line  curves 
up  to  the  front  of  the  neck  and  indicates  the  posterior  limit  of  the  attachment  of 
the  vastus  medialis  muscle.  A  narrow  rough  area  about  the  middle  of  the  border 
gives  attachment  to  the  pectineus  muscle,  and  the  nutrient  foramen  is  usually 
found  just  in  front  of  this  mark.  The  medial  supracondyloid  crest  (Crista  supra- 
condyloidea  medialis)  is  situated  below  the  groove  for  the  femoral  vessels,  and  gives 
origin  to  the  medial  head  of  the  gastrocnemius.  The  lateral  border  is  prominent 
in  its  upper  part,  and  bears  at  the  junction  of  its  proximal  and  middle  thirds  the 
trochanter  tertius  ;^  this  process  is  curved  forward,  and  has  a  thick  edge  to  which 
the  tendon  of  the  superficial  gluteus  muscle  is  attached.  At  the  distal  part  is  the 
supracondyloid  fossa  (Fossa  supracondyloidea),^  in  which  the  superficial  digital 
flexor  arises;  it  is  bounded  laterally  by  a  thick,  rough  margin,  the  lateral  supra- 
condyloid crest  (Crista  supracondyloidea  lateralis),  to  which  the  lateral  head  of  the 
gastrocnemius  muscle  is  attached. 

The  proximal  extremity  (Extremitas  proximalis)  is  large  and  consists  of  the 
head,  neck,  and  trochanter  major.  The  head  (Caput  femoris)  is  placed  at  the 
medial  side  and  is  directed  inward,  upward,  and  somewhat  forward.  It  is  ap- 
proximately hemispherical  and  articulates  with  the  acetabulum.     It  is  cut  intc 

1  Also  termed  the  external  trochanter.  ^  ^|gQ  termed  the  fossa  plantaris. 


THE    FEMUR 


113 


medially  by  a  deep  notch,  the  fovea  capitis,  in  which  the  accessory  and  round  liga- 
ments are  attached.  The  articular  surface  is  surrounded  by  a  distinct  margin. 
The  neck  (Collum  femoris)  is  most  distinct  in  front  and  medially.  The  trochanter 
major  is  situated  laterally;  it  presents  three  features.  The  anterior  part  or  con- 
vexity is  situated  opposite  to  the  head  and  rises  little  above  the  level  of  the  latter; 
it  gives  attachment  to  the  deep  gluteus  muscle,  and  in  the  fresh  state  its  lateral 
surface  is  coated  with  cartilage,  over  which  a  tendon  of  the  middle  gluteus  passes, 
to  be  inserted  into,  the  crest,  which  is  placed  below  and  behind  the  convexity. 
The  posterior  part  or  summit  is  separated  from  the  anterior  part  by  a  notch;  it  is 
situated  behind  the  plane  of  the  head  and  rises  to  a  much  greater  height.     It 


Lateral 

epi- 

cundyle 


Medial 

epi- 

condyle 

Medial 
condyle 


Trochlea 
Fig.    91. — Right    Femur    of    Horse;    Froxt    View. 


Lateral 
condyle 

I  nterco  itdyloid  fossa 
-Right  Femur  of  Horse;  Posterior  View. 


furnishes  insertion  to  part  of  the  middle  gluteus  muscle.  Its  posterior  border  is 
continued  downward  as  the  trochanteric  ridge  (Crista  trochanterica),  which  forms 
the  lateral  wall  of  the  trochanteric  fossa  (Fossa  trochanterica).  A  number  of 
foramina  are  found  in  the  concave  area  medial  to  the  convexity. 

The  distal  extremity  (Extremitas  distalis)  is  large  in  both  directions  and  com- 
prises the  trochlea  in  front  and  two  condyles  behind.  The  trochlea  consists  of  two 
ridges  separated  by  a  groove,  and  forms  an  extensive  surface  (Facies  patellaris)  for 
articulation  with  the  patella.  It  is  very  unsymmetrical ;  the  medial  ridge  is  much 
wider,  more  prominent,  and  extends  up  higher  than  the  lateral  one,  and  the  two 
converge  below.     The  condyles,  medial  and  lateral  (Condylus  medialis,  lateralis), 


114 


THE   SKELETON    OF   THE    HORSE 


are  separated  by  the  deep  intercondyloid  fossa  (Fossa  intercondyloidea),  and 
articulate  with  the  condyles  of  the  tibia  and  the  menisci  of  the  stifle  joint.  A  ridge 
connects  each  condyle  with  the  lower  part  of  the  corresponding  ridge  of  the  trochlea. 
The  intercondyloid  fossa  lodges  the  spine  of  the  tibia  and  the  cruciate  ligaments  of 
the  stifle  joint,  which  are  attached  here. 

The  condyles  are  obliquely  placed  with  their  long  axes  directed  downward,  forward,  and 
inward.  The  articular  surface  of  the  lateral  condyle  is  more  strongly  convex  from  side  to  side 
than  that  of  the  medial  one,  and  the  ridge  which  connects  it  with  the  trochlea  is  much  narrower. 

The  medial  epicondyle  (Epicondylus  medialis)  is  a  rounded  prominence  on 
the  medial  surface  of  the  distal  extremity,  to  which  the  collateral  ligament  and  the 
adductor  muscle  are  attached.    The  corresponding  lateral  epicondyle  (Epicondylus 


Fig.  93. — Proximal  Extremity  of  Right  Femur  of 

Horse;   End  View. 

1,  Head;  2,  fovea  capitis;    3,  neck;  4,  5,  anterior  and 

posterior  parts  of  trochanter  major. 


Intercondyloid  fossa 

Fig.  94. — Distal  Extremity  of  Right  Femur  of 
Horse;  End  View. 
1,  1',  Medial  and  lateral  ridges  of  trochlea;  2,  2', 
medial  and  lateral  condyles;  3,  3',  medial  and  lateral 
epicondyles;  4,  extensor  fossa;  5,  depression  for  origin 
of  popliteus. 


lateralis)  is  less  distinct;  it  presents  a  mark  where  the  lateral  ligament  is  attached, 
below  and  behind  which  there  is  a  depression  (Fossa  musculi  poplitei)  in  which  the 
popliteus  muscle  arises.  Between  the  lateral  condyle  and  trochlea  is  the  extensor 
fossa  (Fossa  extensoria),  in  which  the  common  tendon  of  origin  of  the  extensor 
digitalis  longus  and  peroneus  tertius  is  attached. 

Development. — The  shaft  and  the  distal  end  each  ossify  from  one  center,  but 
the  proximal  end  has  two  centers,  one  of  which  is  for  the  head  and  the  other  for  the 
trochanter  major.  The  edge  of  the  trochanter  tertius  also  has  a  separate  center. 
The  proximal  end  fuses  with  the  shaft  at  three  to  three  and  a  half  years,  the  distal 
at  about  three  and  a  half  years. 


THE  TIBIA 

The  tibia  is  a  long  bone  which  extends  obliquely  downward  and  backward 
from  the  stifle  to  the  hock.  It  articulates  above  with  the  femur,  below  with  the 
tarsus,  and  laterally  with  the  fibula.     It  possesses  a  shaft  and  two  extremities. 

The  shaft  (Corpus  tibiae),  large  and  three-sided  above,  becomes  smaller  and 
flattened  in  the  sagittal  direction  below,  but  widens  at  the  distal  end.  It  presents 
for  notice  three  surfaces  and  three  borders.  The  medial  surface  (Facies  medialis) 
is  Inroad  above,  where  it  presents  rough  prominences  for  the  attachment  of  the 


THE   TIBIA 


115 


medial  ligament  and  the  sartorius  and  gracilis  muscles;  below  this  it  is  narrower, 
convex  from  edge  to  edge  and  subcutaneous.  The  lateral  surface  (Facies  lateralis) 
is  smooth  and  somewhat  spiral.     It  is  wide  and  concave  in  its  proximal  fourth, 


1— ■ 


95. — Right  Tibia  axd  Fibula  of  Horse 

ERAL  View. 
1,   Tuberosity;    2,   sulcus   muscularis;  3,  crest 


4, 
impres- 


spine;  5,  lateral  condyle;  6,  head  of  fibul 
sion  of  anterior  tibial  vessels;  8,  shaft  of  fibula;  9,  lat- 
eral border  of  tibia;  10,  lateral  malleolus;  11,  groove 
for  lateral  extensor  tendon. 


Fig.  96. — Right  Tibia  and  Fibula  of  Horse;  Poste- 
rior View. 
1,  Medial  condyle;  2,  lateral  condyle;  .3,  spine;  4, 
fossa  for  anterior  cruciate  ligament;  .5,  popliteal  notch; 
6,  tubercle  for  posterior  cruciate  ligament;  7,  head  of 
fibula;  8,  vascular  impression;  9,  interosseous  space; 
10,  shaft  of  fibula;  11,  muscular  lines;  12,  tubercle;  13, 
nutrient  foramen;  14,  medial  malleolus;  1.5,  groove  for 
tendon  of  flexor  digitalis  longus;    16,  lateral  malleolus. 


l)elow  which  it  becomes  narrower  and  convex,  and  winds  gradually  to  the  front  of 
the  bone;  near  the  distal  end  it  widens  a  little,  becomes  fiat,  and  faces  forward. 
The  posterior  surface  (Facies  caudalis)  is  flattened,  and  is  divided  into  two  parts 
by  the  rough  popliteal  line  (Linea  poplitea),  which  runs  obliquely  from  the  proxi- 


116 


THE    SKELETON    OF   THE    HORSE 


7  — 


mal  part  of  the  lateral  border  to  the  middle  of  the  medial  border.  The  triangular 
area  above  the  line  is  occupied  by  the  popliteus  muscle,  while  the  area  below  is 
marked  by  rough  lines  (Linese  musculares)  to  which  the  deep  flexor  muscle  of  the 

digit  is  attached;   the  lines  fade  out  distally, 
^  where  the  surface  is  smooth   and  flat.     The 

,t  nutrient  foramen  is  situated  on  or  near  the 

2  -.^  '  popliteal  line.     The  anterior  border   is  very 

prominent  in  its  proximal  third,  forming  the 
crest  of  the  tibia  (Crista  tibiae) ;  distally  it  is 
reduced  to  a  rough  line,  which  ends  at  a  small 
elevation  near  the  distal  end  of  the  bone.  The 
medial  surface  of  the  crest  presents  a  rough 
prominence  for  the  attachment  of  the  ten- 
don of  the  semitendinosus.  The  medial  border 
(Margo  medialis)  is  rounded  in  its  proximal 
half,  to  which  the  popliteus  muscle  is  attached, 
and  a  tubercle  is  found  on  this  part.  The  dis- 
tal part  is  a  rough  line  on  well-marked  bones. 
The  lateral  border  (Crista  interossea)  is  con- 
cave in  its  proximal  part  and  concurs  with  the 
fibula  in  the  formation  of  the  interosseous  space 
of  the  leg  (Spatium  interosseum  cruris);  a 
smooth  impression  indicates  the  course  of  the 
anterior  tibial  vessels  through  the  space  to  the 
front  of  the  leg.  About  the  middle  of  the  bone 
the  border  divides  and  incloses  a  narrow  trian- 
gular surface. 

The  proximal  extremity  (Extremitas  proxi- 
malis)  is  large  and  three-sided.  It  bears  two 
articular  eminences,  the  medial  and  lateral  con- 
dyles (Condylus  medialis,  lateralis) .  Each  pre- 
sents a  somewhat  saddle-shaped  surface  for  ar- 
ticulation with  the  corresponding  condyle  of  the 
femur  and  meniscus.  The  spine  or  intercondy- 
loid  eminence  (Eminentia  intercondyloidea)  is 
the  central  prominence,  upon  the  sides  of  which 
the  articular  surfaces  are  continued ;  it  consists 
of  a  high  medial  part  and  a  lower  lateral  part 
(Tuberculum  intercondyloideum  mediale,  lat- 
erale).  On,  l^efore,  and  l^ehind  the  spine  are 
the  intercondyloid  fossae,  in  which  the  anterior 
cruciate  ligament  and  the  menisci  are  attached. 
The  condyles  are  separated  behind  by  the  deep 
popliteal  notch  (Incisura  poplitea),  on  the 
medial  side  of  which  there  is  a  tubercle  for 
the  attachment  of  the  posterior  cruciate  liga- 
ment. The  lateral  condyle  has  an  overhang- 
ing outer  margin  (Margo  infraglenoidalis),  be- 
low which  there  is  a  facet  (Facies  articularis 
fibularis)  for  articulation  -v^dth  the  fibula.  The 
large  anterior  eminence  is  the  tuberosity  of  the 
tibia  (Tuberositas  tibiae).  It  is  marked  in  front  by  a  groove  (Sulcus  ligamenti), 
the  lower  part  of  which  gives  attachment  to  the  middle  patellar  ligament,  and 
the  groove  is  flanked  b}^  rough  areas  for  the  attachment  of  the  medial  and  lateral 


Fig.  97. — Right  Tibia  and  Fibula  of  Hor.se; 
Anterior  View. 
1,  Spine;  2,  tuberosity;  3,  groove  for 
toiddle  patellar  ligament;  4,  medial  condyle; 
5,  sulcus  muscularis;  6,  lateral  condyle;  7, 
head  of  fibula;  8,  interosseous  space;  9,  lateral 
surface  of  tibia;  10,  shaft  of  fibula;  11,  imprint 
for  attachment  of  gracilis;  12,  crest;  13,  promi- 
nence for  attachment  of  semitendinosus;  14, 
medial  surface  of  tibia;  15,  medial  malleolus; 
16,  lateral  malleolus. 


THE    FIBULA 


117 


patellar  ligaments.  A  semicircular  smooth  notch,  the  sulcus  muscularis,  separates 
the  tuberosity  from  the  lateral  condyle,  and  gives  passage  to  the  common  tendon 
of  origin  of  the  extensor  digitalis  longus  and  the  peroneus  tertius. 

The  distal  extremity  (Extremitas  distalis)  is  much  smaller  than  the  proximal 
one ;  it  is  quadrangular  in  form  and  larger  medially  than  laterally.  It  presents  an 
articular  surface  (Cochlea  tilDise),  which  is  adapted  to  the  trochlea  of  the  tibial 
tarsal  bone,  and  consists  of  two  grooves  separated  by  a  ridge.  The  ridge  and 
grooves  are  directed  ol^liquely  forward  and  laterally,  and  are  bounded  on  either 
side  by  the  malleoli,  to  which  the  collateral  ligaments  of  the  hock  joint  are  at- 
tached. A  shallow  synovial  fossa  is  usually  present  on  the  middle  of  the  articular 
ridge.  The  lateral  groove  is  wider  and  shallower  than  the  medial  one;  it  is  fre- 
quently marked  by  a  line  or  groove  which  indicates  the  former  demarcation  between 
the  tibia  and  fibula.  The  medial  malleolus  (Malleolus  medialis)  is  the  more  prom- 
inent of  the  two,  and  forms  the  anterior  Ijoundary  of  a  groove  for  the  tendon  of  the 
flexor  digitalis  longus.  The  lateral  malleolus  (Malleolus  lateralis)  is  broader,  and 
is  marked  by  a  vertical  groove  for  the  passage  of  the  lateral  extensor  tendon. 

Development. — The  tibia  has  the  usual  three  chief  centers  of  ossification  and 
supplementary  ones  for  the  tuberosity  and  the  lateral  malleolus.  The  latter  is 
really  the  distal  end  of  the  fibula;  it  is  a  separate  piece  at  birth,  and  the  line  of 
union  is  commonly  quite  evident  in  the  adult  in  the  articular  groove.  The  proxi- 
mal end  unites  with  the  shaft  at  about  three  and  a  half  years,  and  the  distal  end  at 
about  two  years  of  age. 


Fig.  98. — Proximal  Extremity  or  Right  Tibia  of 
Horse;  End  View. 
1,  Medial  condyle;  2,  lateral  condyle;  3,  groove 
on  2  for  popliteus  tendon ;  4,  popliteal  notch ;  5,  tuber- 
osity; 6,  groove  for  middle  patellar  ligament;  7,  tuber- 
cles of  spine;  8,  sulcus  mu.scularis;  l.c.a.,  l.c.p.,  depres- 
sions for  attachment  of  anterior  and  posterior  cruciate 
ligaments;     I,   m,   m,    depressions    for    attachment   of 


Fio.  99. — Distal  Extremity  of  Right  Tibia  (and 
Fibula)  of  Horse;  End  View. 
1,  1',  Articular  grooves;  2,  intormeliate  ridge  and 
synovial  fossa;  3,  line  of  fusion  of  primitive  distal  end 
of  fibula  with  tibia;  4,  medial  malleolus;  5,  5',  lateral 
malleolus;  6,  anterior  border. 


THE  FIBULA 

The  fibula  of  the  horse  is  a  much  reduced  long  bone,  situated  along  the  lateral 
border  of  the  tibia. 

The  shaft  (Corpus  fibula?)  is  a  slender  rod  which  forms  the  lateral  boundary  of 
the  interosseous  space  of  the  leg;  it  usually  terminates  below  in  a  pointed  end  about 
one-half  to  two-thirds  of  the  way  down  the  lateral  border  of  the  tibia. 

The  proximal  extremity  or  head  (Capitulum  fibula))  is  relatively  large,  and  is 
flattened  transversely.  Its  medial  surface  presents  a  narrow  area  (Facies  articu- 
laris  capituli)  along  the  upper  border  for  articulation  with  the  lateral  condyle  of 
tibia.  The  lateral  surface  is  rough  and  gives  attachment  to  the  lateral  ligament 
of  the  stifle  joint.     It  has  rounded  anterior  and  posterior  borders. 


118 


THE    SKELETON    OF   THE    HORSE 


The  distal  extremity  is  fused  with  the  til)ia,  constituting  the  lateral  malleolus. 

Development. — Tliis  resembles  that  of  the  ulna.  The  embryonic  cartilaginous 
fibula  extends  the  entire  length  of  the  leg,  but  does  not  articulate  with  the  femur. 
The  distal  part  of  the  shaft  is  usually  reduced  to  a  filjrous  band.  Three  centers  of 
ossification  appear,  one  each  for  the  shaft  and  the  extremities.  The  distal  end 
unites  early  with  the  tibia,  forming  the  lateral  malleolus. 

It  is  interesting  to  note  that  in  some  cases  the  entire  shaft  of  the  fibula  develops,  a  reversion 
to  the  condition  in  the  Miocene  ancestors  of  the  horse. 


THE  PATELLA 

The  patella  is  a  large  sesamoid  bone  which  articulates  with  the  trochlea  of  the 
femur.     It  presents  for  description  two  surfaces,  two  borders,  a  base,  and  an  apex. 

The  anterior,  free  surface  (Facies  libera)  is  quadrilateral,  convex,  and  rough 
for  muscular  and  ligamentous  attachment. 

The  articular  surface  (Facies  articularis)  is  also  quadrilateral,  ]:)ut  much  less 
extensive.     It  presents  a  vertical  rounded  ridge,  which  corresponds  to  the  groove 

Base 


Aj)ex 
Fig.  100. — Right  Patella  of  Horse;  Anterior  View. 
1,  Attachment  area  of  middle  patellar  ligament; 
2,   attachment   area  of   lateral   patellar   ligament  and 
biceps  femoris. 


Accessory  cartilage  Apex 

Fig.  101. — Right  Patella  of  Horse;  Posterior  View. 
1,  Medial  part,  2,  lateral  part,  of  articular  surface. 


on  the  trochlea  of  the  femur,  and  separates  two  concave  areas.  Of  the  latter,  the 
medial  one  is  much  the  larger,  and  is  not  very  well  adapted  to  the  corresponding 
ridge  of  the  trochlea;  in  the  fresh  state,  however,  it  is  completed  and  rendered  more 
congruent  b}^  the  curved  accessory  fibro-cartilage. 

The  borders,  medial  and  lateral,  converge  to  the  apex  below,  and  each  forms  an 
angle  at  the  base.  The  medial  border  is  concave.  The  lateral  border  is  rounded 
and  its  angle  is  less  prominent.  The  medial  angle  and  the  adjacent  part  of  the 
posterior  margin  of  the  base  give  attachment  to  the  fibro-cartilage  of  the  patella 
(Fibrocartilago  patellae) . 

The  base  (Basis  patellae)  faces  upward  and  backward,  and  is  convex  trans- 
versely, concave  from  before  backward. 

The  apex  (Apex  patellae)  forms  a  blunt  point  directed  distally. 

Development. — The  patella  develops  as  a  sesamoid  bone  from  a  single  center 
in  a  cartilaginous  deposit  in  the  te'ndon  of  the  quadriceps  femoris  muscle. 


THE  TARSUS 

The  tarsus  or  hock  of  the  horse  usually  comprises  six  short  bones  (Ossa  tarsi), 
but  exceptionally  seven  are  present. 


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120 


THE   SKELETON    OF   THE   HORSE 


The  Tibial  Tarsal  Bone 
The  tibial  tarsal  bone  (Os  tarsi  tibiale)  ^  is  the  medial  bone  of  the  proximal  row. 
It  is  extremely  irregular  in  form,  but  may  be  considered  as  offering  six  surfaces  for 
description. 

The  proximal  and  dorsal  surfaces  are  continuous,  and  form  a  trochlea  (Troch- 
lea tali)  for  articulation  with  the  distal  end  of  the  tibia.      The  trochlea  consists 
_  of  two  oblique  ridges  with  a  deep  groove 

between  them;  these  curve  spirally  for- 
ward, downward,  and  outward,  forming 
an  angle  of  12  to  15  degrees  with  a  sagittal 
plane.  There  is  usually  a  shallow  synovial 
fossa  in  the  groove.  The  distal  surface  is 
convex  from  before  backward,  and  most 
of  it  articulates  with  the  central  tarsal; 
laterally  it  has  an  oblique  facet  for  the 
fourth  tarsal,  and  a  non-articular  groove 
cuts  into  the  surface  to  its  middle.  The 
plantar  surface  (Facies  plantaris)  is  ob- 
lique and  extremely  irregular;  it  presents 
four  facets  for  articulation  with  the  fibular 
tarsal  bone;  the  facets  are  separated  by 

Trochlea 


Fig.  105. — Right  Tarsus  and  Proximal  Part  of 
Metatarsus  of  Horse;  Lateral  View. 
Tt,  Tibial  tarsal  (trochlea);  Tf,  fibular  tarsal 
(body);  Tc,  central  tarsal;  T3,  third  tarsal;  T4, 
fourth  tarsal;  1,  depression  for  attachment  of  lateral 
ligament;  2,  processus  cochlearis;  3,  prominence  for 
attachment  of  lateral  ligament;  4,  groove  for  great 
metatarsal  artery;  5,  tuber  calcis;  Mt.  Ill,  IV,  meta- 
tarsal bones.     Arrow  points  to  vascular  canal. 


Fig.  106. — Right  Tibial  Tarsal  Bone  of  Horse;  Plan- 
tar A'lEW. 
1-4,   Facets  for  articulation  with  fibular  tarsal;  5,   fossa; 
6,  distal  tuberosity;  7,  proximal  tuberosity. 


rough  excavated  areas,  and  the  largest 
fossa  (Sulcus  tali)  forms  with  a  corres- 
ponding one  on  the  fibular  tarsal  a  cavity 
termed  the  sinus  tarsi.  The  media4  surface  bears  on  its  distal  part  a  large  tuber- 
osity and  on  its  proximal  part  a  small  one  for  the  attachment  of  the  medial  liga- 
ment of  the  hock  joint.  The  lateral  surface  is  smaller  than  the  medial,  and  is 
marked  by  a  wide  rough  fossa  in  which  the  lateral  ligament  is  attached. 


The  Fibular  Tarsal  Bone 
The  fibular  tarsal  bone  (Os  tarsi  fibulare)^  is  the  largest  bone  of  the  hock.     It 
is  elongated,  flattened  from  side  to  side,  and  forms  a  lever  for  the  muscles  which 


Also  termed  the  astragalus  or  talus. 


2  Also  termed  the  calcaneum  or  os  calcis. 


THE   CENTRAL   TARSAL   BONE 


121 


extend  the  hock  joint.     It  consists  of  a  body  and  a  medial  process,  the  sustentacu- 
lum tali. 

The  body  (Corpus)  is  enlarged  at  its  proximal  end  to  form  the  tuber  calcis  or 
"point  of  the  hock";  the  posterior  part  of  this  eminence  gives  attachment  to  the 
tendon  of  the  gastrocnemius,  while  in  front  and  on  each  side  it  furnishes  insertion 
to  tendons  of  the  superficial  digital  flexor,  biceps,  and  semitendinosus  muscles. 
The  distal  extremity  bears  a  concave  facet  for  articulation  with  the  fourth  tarsal 
bone.  The  medial  surface  of  the  body  has  on  its  lower  part  a  strong  process,  the 
sustentaculum  tali,  which  projects  inward.  The  process  has  a  large,  oval,  slightly 
concave  facet  in  front  for  articulation  with  the  tibial  tarsal,  and  sometimes  a  small 
articular  surface  below  for  the  central  bone.  Its  plantar  surface  forms  with  the 
smooth  medial  surface  of  the  body  a  groove  for  the  deep  flexor  tendon  (Sulcus  tarsi) . 
Its  medial  surface  has  a  prominence  on  the  distal  part  for  the  attachment  of  the 
medial  ligament.  The  lateral  surface  of  the  body  is  flattened,  except  below,  where 
there  is  a  rough  prominence  for  the  attachment  of  the  lateral 
ligament.  The  dorsal  border  is  concave  in  its  length,  smooth 
and  rounded  in  its  upper  part.  About  its  middle  is  a  blunt- 
pointed  projection  (Processus  cochlearis)  which  bears  facets 
on  its  medial  and  lower  surfaces  for  articulation  with  the 
tibial  tarsal  bone,  and  is  roughened  laterally  for  ligamen- 
tous attachment.  Below  this  are  two  facets  for  the  tibial 
tarsal,  and  an  extensive  rough  fossa  which  concurs  in 
the  formation  of  the  sinus  tarsi.  The  plantar  border  is 
straight  and  broad,  and  widens  a  little  at  each  end;  it  is 
rough,  and  gives  attachment  to  the  long  plantar  ligament. 


Tuber 
calcis 


Fig.      107.  —  Right      Fibular  Fig.   108.— Right  Central  Tarsal  Bone  op  Horse;  Proximal  Surface. 

Tarsal  Bone  of   Horse;        i_  Articular  surface  for  tibial  tarsal;  2,  facet  for  fibular  tarsal;   3,   non-articular 

Dorsal  View.  depression. 

1-4,  Facets  for  articulation  with 
tibial  tarsal  bone;  5,  fossa. 


The  Central  Tarsal  Bone 
The  central  tarsal  bone  (Os  tarsi  centrale)^  is  irregularly  quadrilateral,  and  is 
situated  between  the  tibial  tarsal  and  the  third  tarsal.  It  is  flattened  from  above 
downward,  and  may  be  described  as  having  two  surfaces  and  four  borders.  The 
proximal  surface  is  concave  from  before  backward,  and  almost  all  of  it  articulates 
with  the  tibial  tarsal;  a  non-articular  depression  cuts  into  its  lateral  part,  and 
sometimes  there  is  a  facet  for  the  fibular  tarsal  bone  on  the  posterior  angle.  The 
distal  surface  is  convex,  and  is  crossed  by  a  non-articular  groove,  which  separates 
facets  for  articulation  with  the  third  and  the  first  and  second  (fused)  tarsals.  The 
dorsal  border  and  the  medial  border  are  continuous,  convex,  and  rough.  The 
plantar  border  bears  two  prominences,  separated  by  a  notch.  The  lateral  border 
is  oblique,  and  bears  anterior  and  posterior  facets  for  articulation  with  the  fourth 
tarsal,  between  which  it  is  excavated  and  rough. 

1  Also  termed  the  scaphoid  or  navicular  bone. 


122 


THE    SKELETON    OF   THE    HORSE 


First  and  Second  Tarsal  Bones 
The  first  and  second  tarsal  bones  (Os  tarsale  primum  et  secundum)  ^  are  usually- 
fused  in  the  horse,  forming  a  ])one  of  very  irregular  shape,  situated  in  the  medio- 
plantar  part  of  the  distal  row,  below  the  central  and  behind  the  third  tarsal.  It  is 
the  smallest  of  the  tarsal  bones,  and  may  he  described  as  having  four  surfaces  and 
two  extremities.  The  medial  surface  faces  backward  and  inward,  and  is  convex. 
Its  anterior  part  is  ridged,  and  gives  attachment  to  the  medial  ligament,  and  its 
posterior  part  l^ears  an  imprint  where  the  medial  tendon  of  the  tibialis  anterior  is 
inserted.  The  lateral  surface  is  marked  by  a  deep  notch  which  indicates  the  divi- 
sion between  the  first  and  second  tarsal  elements;  it  bears  on  its  anterior  part  a 
facet  for  the  third  tarsal.  The  proximal  surface  is  concave  and  has  two  facets  for 
articulation  with  the  central  tarsal;  it  is  separated  from  the  medial  surface  by  a 
prominent  border.     The  distal  surface  is  broad  in  front,  where  it  articulates  with 


Fig.  109. — Right  First  and  Sec- 
ond   (Fused)    Tarsal  Bones 
OF  Horse;  Lateral  Surface. 
Tl,  T2,  First  and  second  tarsal 
bones;   1,    1',   articular  surface    for 
central  tarsal;  2,  facet  for  third  tar- 
sal; 3,  facet  for  medial  small  meta- 
tarsal   bone.     Separation    between 
two  bones   (when  present)  is  indi- 
cated  so  far    as  visible    by  dotted 
line  between  1  and  1'. 


Fig.  110.— Right  Third  Tarsal 
Bone  of  Horse;  Proximal 
Surface. 

1,  2,  Facets  for  central  tarsal; 
3,  4,  facets  for  fourth  tarsal;  5,  non- 
articular  depression ;  6,  dorsal  ridge. 


Fig.  111. — Right  Fourth  Tarsal 
Bone  of  Horse;  Medial  Sur- 
face. 

1,  1',  Facets  for  central  tarsal; 
2,  2',  facets  for  third  tarsal;  3,  facet 
for  tibial  tarsal;  4,  4',  facets  for 
fibular  tarsal;  5,  facet  for  large 
metatarsal  bone;  6,  groove  which 
concurs  with  central  and  third  tar- 
sals in  formation  of  vascular  canal 
of  tarsus. 


the  large  and  medial  small  metatarsal  bones.     The  dorsal  extremity  bears  a  ridge 
or  tubercle.     The  plantar  extremity  is  a  blunt  point. 

In  some  cases  the  first  and  second  tarsal  Ijones  remain  separate — a  remarkable  reversion  to 
the  condition  in  the  early  ancestors  of  the  horse.  In  such  specimens  the  first  tarsal  is  a  discoid 
bone,  articulating  above  with  the  central,  below  with  the  small  metacarpal  bone.  The  second 
tarsal  is  quadrangular,  equivalent  to  the  thick  anterior  part  of  the  bone  as  described  above,  and 
overlapped  in  part  by  the  first  tarsal. 


The  Third  Tarsal  Bone 

The  third  tarsal  bone  (Os  tarsale  tertium)-  resembles  the  central,  but  is  smaller 
and  triangular  in  outline.  It  is  situated  between  the  central  above  and  the  large 
metatarsal  l)one  below.     It  possesses  two  surfaces  and  three  borders. 

The  proximal  surface  is  concave,  and  is  crossed  by  a  non-articular  depression 
which  divides  it  into  two  unequal  facets;  it  articulates  with  the  central  tarsal. 
The  distal  surface  is  slightly  convex,  and  rests  on  the  large  metatarsal  bone;  it 
has  an  extensive  central  rough  excavation.  The  dorsal  border  is  convex  and  bears 
a  rounded  ridge  on  its  medial  part.  The  medial  border  is  deeply  notched  and  has 
a  small  facet  for  the  second  tarsal  on  its  anterior  part.  The  lateral  border  is  also 
divided  by  a  notch  into  two  parts,  and  bears  two  diagonally  opposite  facets  for 


Also  termed  the  cuneiform  parvum. 


Also  termed  the  cuneiform  magnum  s.  tertium. 


THE   METATARSUS 


123 


articulation  with  the  fourth  tarsal.     In  some  cases  there  is  a  facet  for  the  medial 
small  metatarsal  bone. 

The  Fourth  Tarsal  Bone 
The  fourth  tarsal  bone  (Os  tarsale  quartum)i  jg  the  lateral  bone  of  the  distal 
row,  and  is  eriual  in  height  to  the  central  and  third  together.     It  is  cuboid  m  shape 
and  presents  six  sm-f aces.  ,.     ,  ,         n  •  a 

The  proximal  surface  is  convex  from  side  to  side,  and  articulates  chietly 
with  the  fibular  tarsal,  but  to  a  small  extent  with  the  tibial  tarsal  also. 
The  distal  surface  rests  on  the  large  and  lateral 
small  metatarsal  ])ones.  The  medial  surface  bears 
four  facets  for  articulation  with  the  central  and 
third  tarsal  bones.  It  is  crossed  from  before  back- 
ward by  a  smooth  groove,  which  l)y  apposition  with 
the  adjacent  bones  forms  the  canal  of  the  tarsus  (Can- 
alis  tarsi)  for  the  passage  of  the  perforating  tarsal 
vessels.  The  dorsal,  lateral,  and  plantar  surfaces  are 
continuous  and  rough.  A  tuberosity  behind  gives 
attachment  to  the  plantar  ligament. 

Development.— The  fibular  tarsal  bone  has  two 
centers  of  ossification,  one  for  the  main  mass  and  the 
other  for  the  tuber  calcis;  the  latter  fuses  with  the  rest 
of  the  bone  at  about  three  years  of  age.  The  first  and 
second  tarsals  have  separate  centers,  but  fusion  usu- 
ally occurs  before  birth.  Each  of  the  other  bones 
ossifies  from  a  single  center. 


THE  METATARSUS 
The  metatarsal  bones  (Ossa  metatarsalia) ,  three 
in  number,  have  the  same  general  arrangement  as 


/ 


Fig.  112. — Right  Metatarsal  Boxes 
OF  Horse;    Plantar  View. 
1,   Rough  area   for  attachment   of 
suspensory  ligament;  2,  nutrient  fora- 
men.    Compare  with  Fig.  76. 


Mt.n       Ml.  HI         ML  IV 


Fig.    113.— Proximal   Extremities    of  Right   Metatarsal    Bones  of 
Horse;    End  View. 
1,  Facet  for  first  tarsal;  2,  2',  facets  for  second  tarsal;  3,  3',  facets  for 
third  tarsal;  4,  4',  4",  facets  for  fourth  tarsal;  5,  non-articular  depr-- 
Compare  with  Fig.  77. 


the  metacarpal  bones,  but  present  some  important  differences.     Their  direction  is 
slightly  oblique,  downward,  and  a  little  forward.  ,     ,    ,.       .   ■      ,  ^„.  ^„p 

The  third  or  large  metatarsal  bone  (Os  metatarsal  tertium)  is  about  one- 
sixth  longer  than  the  corresponding  metacarpal;   in  an  animal  of  medium  size  the 
1  Also  termed  the  cuboid. 


124 


THE    SKELETON    OF   THE    HORSE 


difference  is  about  two  inches.  The  shaft  is  more  cyhndrical,  and  is  almost  cir- 
cular on  cross-section,  except  in  its  distal  part.  At  the  proximal  part  of  its  lateral 
surface  there  is  a  groove,  which  is  directed  obliquely  downward  and  backward,  and 
is  continued  by  the  furrow  formed  by  the  apposition  of  the  fourth  or  lateral  meta- 
tarsal bone;  it  indicates  the  course  of  the  great  metatarsal  artery.  A  shallow  im- 
pression in  a  similar  place  on  the  medial  side  marks  the  position  of  the  corresponding 

vein.  The  nutrient  foramen  is  rela- 
tively higher  than  on  the  metacar- 
pal bone.  The  proximal  extremity 
is  much  wider  from  before  back- 
ward than  that  of  the  metacarpal 
bone.  Its  articular  surface  is 
slightly  concave,  and  is  marked 
by  a  large  central  non-articular  de- 
pression, continued  outward  by  a 
deep  notch.  The  greater  part  of 
the  surface  articulates  with  the 
third  tarsal,  but  there  is  a  lateral 
facet  for  the  fourth,  and  usually  a 
small  facet  postero-medially  for  the 
second  tarsal  bone.  Posteriorly  there  are  two  pairs  of  facets  for  articulation  with 
the  small  metatarsal  bones.  The  front  is  crossed  by  a  rough  ridge  for  insertion, 
which  becomes  larger  and  turns  downward  on  the  lateral  side  behind  the  vascular 
groove.  The  distal  extremity  closely  resembles  that  of  the  corresponding  meta- 
carpal bone. 

In  some  cases  the  distal  part  of  the  shaft  is  bent  backward  somewhat.  The  distal  articular 
surface  extends  a  httle  higher  behind  than  in  the  case  of  the  metacarpal  bone.  The  large  meta- 
tarsal bone  is  even  more  strongly  constructed  than  the  metacarpal.  The  shell  of  compact  sub- 
stance is  very  thick  in  the  middle  of  the  shaft,  especially  in  front  and  medially. 


Fig.   114 
Figs.    114,    115. 


Fig.   115. 


OSS-SECTIONS     OF     LeFT      METACARPAL  ANI 

Metatarsal  Bones. 
Sections  are  cut  a  little  above  middle  of  bones. 


Fig.  110. — Third  Phalanx  of  Thoracic  Limb  of  Horse.        Fig.  117. — Third  Phalanx  of  Pelvic  Limb  of  Horse. 


The  small  metatarsal  bones  (Ossa  metatarsalia  secundum  et  quartum)  are  a 
little  longer  than  the  corresponding  metacarpals.  The  lateral  (fourth)  metatarsal 
bone  is  relatively  massive,  especially  in  its  upper  part.  The  head  is  large  and  out- 
standing, and  bears  one  or  two  facets  above  for  the  fourth  tarsal,  and  two  in  front 
and  medially  for  articulation  with  the  large  metatarsal ;  elsewhere  it  is  roughened 
for  attachment.  The  medial  (second)  metatarsal  bone  is  much  more  slender  than 
the  lateral  one,  especially  in  its  proximal  part.  The  head  bears  two  facets  above  for 
the  first  and  second  tarsals,  and  sometimes  one  for  the  third  tarsal. 


SKELETON    OF   THE    OX 


125 


THE  PHALANGES  AND  SESAMOID  BONES 

The  axis  of  the  phalanges  of  the  hind  Hmb  forms  with  the  ground  plane  an 
angle  which  is  about  five  degrees  greater  than  that  of  the  fore  limb,  and  the  chief 
differences  in  the  form  and  size  of  the  bones  are  as  follows : 

The  first  phalanx  is  a  little  shorter,  wider  above,  and  narrower  below. 

The  second  phalanx  is  narrower  and  slightly  longer. 

The  third  phalanx  is  narrower,  the  angle  of  inclination  of  the  dorsal  surface  is  a 
little  (ca.  5  degrees)  greater,  the  plantar  surface  is  more  concave,  and  the  angles 
are  less  prominent  and  closer  together.  The  term  plantar  is  to  be  substituted  for 
volar  in  the  designation  of  corresponding  features. 

The  proximal  sesamoids  are  a  little  smaller,  except  in  thickness.  The  distal 
sesamoid  is  narrower  and  shorter. 


SKELETON  OF  THE  OX 

VERTEBRAL  COLUMN 

The  usual  vertebral  formula  is  C7Ti3L6S5Cyi8-2o- 

The  cervical  vertebrae  are  much  shorter  than  those  of  the  horse  and  are  smaller 
in  their  other  dimensions.  The  articular  processes  are  smaller  than  in  the  horse, 
and  a  plate  of  bone  connects  each  two  of  the  same  side.  The  transverse  processes 
of  the  third,  fourth,  and  fifth  are  double;  the  upper  part  projects  backward,  and 
is  short  and  stout;  the  lower  part  is  directed 
downward  and  forward,  and  is  longer  and 
more  plate-like.  The  lower  part  of  the  sixth 
transverse  process  is  a  large,  thick,  quadri- 
lateral and  almost  sagittal  plate,  directed 
ventrally.  The  seventh  transverse  process  is 
single,  short,  and  thick,  and  presents  no  fora- 
men transversarium;  it  is  in  series  with  the 
upper  part  of  the  preceding  processes.  The 
spinous  processes  are  well  developed,  and  in- 
crease in  height  from  before  backward.  They 
are  directed  upward  and  forward,  with  the  ex- 
ception of  the  last,  which  is  nearly  vertical 
and  is  about  four  or  five  inches  (ca.  10  to  12 
cm.)  in  height.  The  summit  of  that  of  the 
third  vertebra  is  usually  bifid.  The  ventral 
spines  are  prominent  and  thick  in  their  pos- 
terior part ;  they  are  absent  on  the  last  two. 

The  atlas  has  a  large  rough  tuberosity 
on  its  dorsal  arch.  The  ventral  arch  is  very 
thick.     The  wings  are  less  curved  than  in  the 

horse,  and  the  foramen  transversarium  is  absent.  The  anterior  articular  cavities  for 
the  occipital  condyles  are  partially  divided  into  dorsal  and  ventral  parts  by  a  non- 
articular  area,  and  are  separated  by  a  narrow  interval  below.  The  posterior  artic- 
ular surfaces  are  flattened  behind  and  are  continued  into  the  vertebral  canal,  form- 
ing an  extensive  area  for  the  dens  of  the  axis. 

The  axis  is  short.  The  spine  projects  a  little  in  front,  and  increases  in  height 
and  thickness  behind;  its  posterior  border  descends  abruptly.  The  dens  is  wide, 
and  its  dorsal  surface  is  deeply  concave  from  side  to  side.     The  intervertebral 


Fig.  118. — Third  Cervical  Vertebra  of  Ox; 
Lateral  View. 
1,  Spinous  process;  2,  2',  anterior  and  pos- 
terior articular  processes;  .3,  3',  ends  of  body; 
4,  4',  transverse  process;  5,  foramen  transver- 
sarium;  6,  ventral  spine. 


126 


SKELETON    OF   THE   OX 


VERTEBRAL    COLUMN 


127 


foramen  is  circular  and  not  so  close  to  the  anterior  border  of  the  arch  as  in 
the  horse.  The  posterior  notches  are  not  so  deep.  The  transverse  processes  are 
stouter,  but  the  foramen  transversarium  is  small  and  sometimes  absent. 

The  thoracic  vertebrae,  thirteen  in  number,  are  larger  than  those  of  the  horse. 


Fig.  120. — Sixth  Cervical  Vertebra  of  Ox;  Pos- 
terior View. 
1,  Posterior  cavity  of  body;  2,  vertebral  foramen; 
3,  arch;  4,  4',  posterior  articular  processes;  5,  5,  an- 
terior articular  processes;  6,  6',  lateral  branches  of  trans- 
verse processes;  7,  7',  ventral  branches  of  transverse 
processes;   8,  foramen  transversarium;  9,  spinous  proc- 


/     9     >    #     \ 


Fig.  122. — Atlas  of  Ox;  Dorsal  View. 
1,  Dorsal  tubercle;   2,  intervertebral  foramen;   3,  alar 
foramen;  4,  wing;  5,  5,  posterior  articular  surfaces ;  6,  ven- 
tral arch  (surface  for  dens  of  asis). 


Fig.  121. — Seventh  Cervical  Vertebra  of  Ox;  Pos- 
terior View. 
1,  Posterior  cavity  of  body;   2,  2',  facets  for  head 
of  first  rib;   3,  vertebral  foramen;  4,  4',  arch;  5,  5',  ar- 
ticular processes;  6,  6',  transverse  processes;  7,  spinous 


Fig.   123.— Axis  of  Ox;  Lateral  View. 

1,  Body;  2,  ventral  spine;  3,  anterior  articular 
process;  4,  posterior  articular  process;  5,  dens;  6, 
arch;  7,  intervertebral  foramen;  8,  transverse  proc- 
ess; 9,  foramen  transversarium  and  canalis  trans- 
versarius  (dotted  line) ;   10,  spinous  process. 


128 


SKELETON    OF   THE    OX 


The  body  is  longer  and  is  distinctly  constricted  in  the  middle.  It  bears  a  thin- 
edged  ventral  crest.  The  arch — in  addition  to  the  usual  notches,  which  are 
shallow — is  perforated  in  the  posterior  part  by  a  foramen.     The  transverse  proc- 


FiG.  124. — Fourth  Lumbar  Vertebra  of  Ox;  Posterior  View. 
1,  Cavity  of  posterior  end  of  body;  2,  notch  of  arch;   3,  4,  articular  processes;   5,  spinous  process;   6,  transverse  process. 


ess  is  thick  and  strong,  and  bears  a  rounded  mammillary  process  (except  at  the 
posterior  end  of  the  series) ;  the  last  two,  although  prominent,  do  not  always  articu- 


late with  the  ribs.     The  spinous  process  is  long. 


Median  crest 


The  first  is  much  higher  than  in 
the  horse,  the  next  two  are  usu- 
ally the  most  prominent,  and  be- 
hind this  there  is  a  very  gradual 
diminution  in  height.  The  back- 
ward slope,  slight  at  first,  in- 
creases to  the  tenth;  the  last  is 
vertical  and  lumbar  in  charac- 
ter. The  summit  is  usually 
pointed  on  the  first,  and  the 
thickening  on  those  further  back 
is  less  than  in  the  horse.  The 
width  diminishes  from  the  fifth 
to  the  eleventh  usually.  Both 
borders  of  the  spines  are  in  gen- 
eral thin  and  sharp,  but  the  last 
three  or  four  sometimes  have 
thick  posterior  margins. 

The  lumbar  vertebrae,  six  in 
number,  are  much  longer  than  in 
the  horse.  The  body  is  much 
constricted  in  the  middle,  ex- 
panded at  either  end,  and  bears 
a  rudimentary  ventral  crest. 
The  fourth  and  fifth  are  usuall}^ 
the  longest.  The  intervertebral 
foramina  are  often  double  in 
the  anterior  part  of  the  series, 
and  are  very  large  further  back. 
The  articular  processes  are 
large,  and  their  facets  are  more 
strongly  curved  than  in  the 
horse.  The  transverse  proc- 
esses all  curve  forward.  They  are  separated  by  considerable  intervals,  and  form 
no  articulations  with  each  other  or  with  the  sacrum.     Their  borders  are  thin  and 


Fig.  125. — Sacrum  of  Ox;  Dorsal  View. 
1-4,  Dorsal  sacral  foramina;  5,  sacral  canal;  6,  6,  articular  processes; 
apex. 


auricular  surface; 


VERTEBRAL    COLUMN 


129 


irregular,  and  often  bear  projections  of  variable  size  and  form.  The  first  is  the 
shortest  and  the  length  increases  to  the  fifth,  the  last  being  considerably  shorter. 
The  spinous  processes  are  relatively  low  and  wide,  the  last  being  the  smallest; 
their  summits  are  moderately  thickened. 

The  sacrum  is  longer  than  that  of  the  horse.  It  consists  originally  of  five 
segments,  but  fusion  is  more  complete  and  involves  the  spinous  processes,  which 
are  united  to  form  a  median  sacral  crest  (Crista  sacralis  media),  with  a  convex 
thick  and  rough  margin.  A  lateral  sacral  crest  is  formed  by  the  fusion  of  the  ar- 
ticular processes.  The  pelvic  surface  is  concave  in  both  directions,  and  is  marked 
by  a  central  groove  (Sulcus  vasculosus),  which  indicates  the  course  of  the  middle 
sacral  artery.  The  ventral  sacral  foramina  are  large.  The  wings  curve  downward 
and  forward;  they  are  quad- 
rangular, short,  compressed 
from  before  backward,  and 
high  dorso-ventrally.  They 
have  an  extensive  anterior 
surface,  which  is  concave 
from  side  to  side  and  non- 
articular.  The  posterior  sur- 
face is  rough,  and  at  its  lower 
part  there  is  a  triangular  area 
for  articulation  with  the 
ilium.  The  body  of  the  first 
segment  is  very  wide,  and  the 
entrance  to  the  sacral  canal 
correspondingly  wide  and 
low.  The  anterior  articular 
processes  are  large  and 
widely  separated;  they  are 
concave  and  semicylindrical 
in  curvature  medially .  The 
lateral  borders  are  thin, 
sharp,  and  irregular.  The 
bone  does  not  become  nar- 
rower posteriorly,  so  that  the 
apex  is  usually  a  little  wider 
than  the  part  just  behind  the 
wings;  the  posterior  end  of 
the  median  crest  forms  a 
pointed  projection  over  the 
opening  of  the  sacral  canal. 

The  coccygeal  vertebrae 
are  longer  and  better  devel- 
oped than  in  the  horse.  The  first  five  or  six  have  complete  arches  and  spinous 
processes.  The  transverse  processes  are  relatively  large  in  the  anterior  part  of 
the  series,  in  which  there  are  also  anterior  articular  processes  (which  do  not  articu- 
late), and  a  pair  of  ventral  spines  which  form  a  groove  (Sulcus  vasculosus)  for  the 
middle  coccygeal  artery. 

Vertebral  Curves. — The  cervical  curve  is  very  slight  and  is  concave  dorsally. 
The  thoracic  and  lumbar  regions  form  a  gentle  curve,  concave  ventrally.  The 
promontory  is  more  pronounced  than  in  the  horse,  especially  in  subjects  in  which 
the  sacrum  is  inclined  upward  behind.  Another  prominence  occurs  at  the  junction 
of  the  sacrum  and  first  coccygeal  vertebrae. 

Length.— The    following    table   gives   the   lengths    (inclusive   of    the   inter- 


FiG.   126. — Sacrum  of  Ox;  Ventral  View. 
I-V,  Segments;  1-4,  ventral  sacral  foramina;  5,  anterior  end  of  body 
of  first  sacral  vertebra;    6,  vascular  groove;    7,  posterior  end  of  body  of 
last  sacral  vertebra. 


130 


SKELETON    OF   THE    OX 


vertebral    fibro-cartilages)    of    the    vertebral    regions   of    a   shorthorn    cow    of 
medium  size: 

Cervical 50  cm. 

Thoracic SO  cm. 

Lumbar 40  cm. 

Sacral 25  cm. 

Coccygeal 75  cm. 

270  cm. 

Variations. — Sometimes  fourteen  thoracic  vertebrae  and  fourteen  pairs  of  ribs  are  present; 

reduction   to   twelve   with   the   normal  number 
j^    ,        rryhcrcle  °^  lumbar  vertebrae  is  very  rare.     According  to 

^  Franck  there  are  sometimes  seven  lumbar  verte- 

brae with    the  normal    number  in  the    thoracic 

^^^^    region.     The  number  of  coccygeal  vertebrae  may 

Head  ^-J^^BIlt^SI^^  vary  from  sixteen  to  twenty-one. 


THE  RIBS 


Anterior  border- 


Thirteen  pairs  of  ribs  are  present 
normally,  of  which  eight  are  sternal  and 
five  asternal.  They  are  in  general  longer, 
wider,  flatter,  less  curved,  and  less  regular 
in  form  than  in  the  horse.  The  eighth, 
ninth,  and  tenth  are  the  longest  and 
widest.  The  width  of  most  of  the  ribs 
increases  considerably  in  the  middle,  and 


Tubercle 


Head 


Neck 


Anterior  border 


Sternal  end 
Fig.  127. — Right  Eighth  Rib  of  Ox;  Medial  View. 


/j 


t. 


Sternal  end 


Cartilage 


Fig.  12S.— First  Rib  of  Ox;  Medial  Vi 


the  breadth  of  the  intercostal  spaces  is  correspondingly  diminished ;  this  is  not  the 
case  in  the  posterior  part  of  the  series,  where  the  intercostal  spaces  are  very  wide. 


THE  STERNUM THE  THORAX THE  SKULL  131 

The  neck  is  long,  and  forms  (except  in  the  posterior  part  of  the  series)  a  smaller 
angle  with  the  shaft  than  in  the  horse.  The  articular  surface  of  the  tubercle  is 
concave  transversely,  except  on  the  last  two  or  three,  where  the  facet  is  small  and 
flat  or  absent.  The  ventral  ends  of  the  second  to  the  tenth  or  eleventh  inclusive 
form  diarthrodial  joints  with  the  costal  cartilages.  The  first  costal  cartilages  are 
very  short;  they  articulate  by  their  medial  surfaces  with  the  sternum,  but  not  with 
each  other. 

The  presence  of  a  fourteenth  rib  is  not  very  rare.  It  is  usually  floating  and  may  correspond 
to  an  additional  thoracic  vertebra  or  to  the  first  lumbar.  Reduction  of  the  thirteenth  is  more 
common.     The  eighth  cartilage  often  does  not  reach  the  sternum,  but  articulates  with  the  seventh. 


THE  STERNUM 
The  sternum  consists  of  seven  sternebrse,  most  of  which  are  developed  from 
two  lateral  centers.  It  is  wider,  flatter,  and  relatively  longer  than  in  the  horse, 
and  the  ventral  crest  or  "keel"  is  absent.  The  manubrium  is  somewhat  wedge- 
shaped  and  laterally  compressed.  Its  base  forms  a  diarthrodial  joint  with  the 
body  of  the  bone,  and  laterally  it  bears  extensive  facets  for  articulation  with  the 
first  pair  of  costal  cartilages.  The  body  widens  from  before  backward,  but  behind 
the  last  pair  of  costal  facets  it  becomes  much  narrower.  The  ventral  surface  is 
prominent  on  the  second  and  third  segments,  concave  further  back.  The  lateral 
borders  are  notched  for  the  passage  of  vessels.  The  cariniform  cartilage  is  absent. 
The  xiphoid  cartilage  is  like  that  of  the  horse  but  is  smaller. 


THE  THORAX 

The  bony  thorax  is  shorter  than  in  the  horse.  The  inlet  is  higher.  The  roof 
is  short,  and  the  floor  is  wider  and  relatively  longer.  The  transverse  diameter  is 
wider  in  the  posterior  part.  The  summits  of  the  spinous  processes  are  almost  in  a 
straight  line  from  the  second  thoracic  vertebra  to  the  middle  of  the  lumbar  region. 


The  Skull 

Bones  of  the  Cranium 
The  occipital  bone  forms  the  lower  part  only  of  the  posterior  surface  of  the 
skull,  and  is  separated  from  the  highest  part  (the  frontal  eminence)  by  the  parietal 
and  interparietal  bones.  The  supraoccipital,  interparietals,  and  parietals  fuse 
before  birth  or  soon  after,  and  the  mass  so  formed  is  separated  from  the  lateral 
parts  of  the  occipital  bone  by  a  transverse  suture  in  the  skull  of  the  calf.  Above 
this  suture  is  a  central  tuberosity,  the  external  occipital  protuberance,  to  which 
the  ligamentum  nuchse  is  attached,  and  the  surface  on  either  side  is  depressed  and 
rough  for  muscular  attachment.  There  is  commonly  a  median  occipital  crest 
which  extends  ventrally  from  the  protuberance.  Below  the  suture  the  bone  is 
much  wider  than  that  of  the  horse.  The  foramen  magnum  is  wide,  so  that  the 
condyles  are  further  apart,  except  below.  The  paramastoid  processes  are  short  and 
wide  and  are  bent  inward.  Usually  at  least  two  foramina  are  found  in  the  condy- 
loid fossa;  the  ventral  one  is  the  hypoglossal,  the  other  (often  double)  conducts  a 
vein  from  the  condyloid  canal.^  The  latter  passes  upward  from  a  foramen  on  the 
medial  side  of  the  condyle  and  opens  into  the  temporal  canal.     The  mastoid  for- 

^  The  number  of  foramina  here  is  variable.  In  exceptional  cases  the  foramen  which  opens 
into  the  condyloid  canal  is  very  small  or  absent;  much  oftener  there  are  two,  and  sometimes  three. 
In  some  cases  there  are  two  hypoglossal  foramina.  Thus  as  many  as  five  foramina  may  be  present 
here. 


132 


SKELETON    OF   THE    OX 


amen  is  situated  on  each  side,  at  the  junction  of  the  occipital  and  temporal  bones; 
it  communicates  with  the  temporal  and  condyloid  canals  at  their  junction.  The 
cerebral  surface  of  the  supraoccipital  presents  a  central  depression,  and  above  this 
is  a  variable  but  never  very  pronounced  eminence,  the  internal  occipital  protuber- 
ance. A  groove  on  either  side  leads  to  the  temporal  canal.  The  basilar  part  is  short 
and  wide ;  its  cerebral  surface  is  deeply  concave,  and  the  internal  spheno-occipital  crest 
is  prominent.     Two  large  tubercles  ventrally  mark  the  junction  with  the  sphenoid. 


Processus  corniis 


Nasal  bone 


Mental  foramen 


Mandible 


Angle  of  mandible 


Fig.  129. — Skull  of  Ox;   Lateral  View. 
separated  for  the  sake  of  clearness.     ^,  Parietal  bone;  B,  squamous  temporal  bone;   C,  occipital  bone; 

occipital 


The  jaws ; 
D,  perpendicular  part  of  palatine  bone;  E,  maxilla;  F,  malar  bone;  G,  lacrimal  bone;  H,  prema::illa; 
condyle;  2,  paramastoid  process;  3,  meatus  acusticus  externus;  4,  bulla  ossea;  5,  zygomatic  process  of  temporal  bone; 
6,  6',  zygomatic  and  temporal  processes  of  malar  bone;  7,  supraorbital  process;  8,  orbital  part  of  lacrimal  bone;  9, 
lacrimal  bulla;  10,  fossa  sacci  lacrimalis;  11,  facial  tuberosity;  12,  infraorbital  foramen;  13,  condyle  of  mandible;  14, 
coronoid  process  of  mandible. 


The  foramen  lacerum  is  short  and  very  narrow.     In  the  adult  animal  the  bone  is 
excavated  to  contain  an  air-cavity  which  is  regarded  as  a  part  of  the  frontal  sinus. 

The  sphenoid  bone  is  short.  The  cerebral  surface  of  the  body  presents  a  deep 
sella  turcica,  in  front  of  which  it  rises  abruptly.  The  high  anterior  part  bears  a 
central  ridge,  the  ethmoidal  spine,  which  joins  the  crista  galli  of  the  ethmoid. 
Two  foramina  occur  on  either  side.  Of  these,  the  large  anterior  one  is  equivalent 
to  the  foramen  rotundum,  orbitale,  and  trochleare  of  the  horse;   it  may  be  termed 


BONES   OF   THE    CRANIUM 


133 


Fig.  130. — Cross-section  of  Cranium  of  Ox. 

The  section  cuts  the  posterior  part  of  the  temporal  condyle  and  is  viewed  from  behind,     a,  Body  of  sphenoid;   b, 

bulla  ossea;    c,  temporal  condyle;    1,  dorsum  sellae;    2,  foramen  ovale;    .3,  hypophy.seal  or  pituitary  fossa;    4,  foramen 

orbito-rotundum;    .5,  optic  foramina;    6,  crista  galli;    7,  cribriform  plate  of  ethmoid;    8,  orbital  wing  of  sphenoid;    9, 

temporal  wing  of  sphenoid;    10,  internal  plate  of  frontal  bone;    11,  frontal  sinus;    12,  temporal  process  of  malar  bone. 


Fig.  131. — Cross-section  of  Cranium  of  Ox. 
The  section  cuts  the  posterior  part  of  the  temporal  condyle  and  is  viewed  from  in  front,  a.  Basilar  part  of  occipital 
bone;  6,  bulla  ossea;  c,  paramastoid  process;  d,  meatus  acusticus  externus;  e,  temporal  fossa;  1,  tympanic  cavity;  2, 
internal  opening  of  condyloid  canal;  3,  internal  opening  of  temporal  canal;  4,  depression  for  vermis  cerebelli;  5,  internal 
occipital  protuberance;  6,  internal  plate  of  parietal  bone;  7,  internal  plate  of  frontal  bone;  8,  frontal  sinus;  9,  petrous 
temporal  bone;   10,  postglenoid  process;   11,  hyoid  process. 


134 


SKELETON  OF  THE  OX 


the  foramen  orbito-rotundum.     The  posterior  one  is  the  foramen  ovale,  which 

transmits  the  mandibular  nerve.  The  orbital  wing  is  thick  and  is  overlapped  by 
the  frontal  in  such  manner  as  to  appear  externally  to  divide  into  two  branches; 
the  anterior  part  joins  the  ethmoid  at  the  sphenopalatine  foramen,  and  contains  a 
small  sinus  which  communicates  with  an  ethmoidal  meatus  The  temporal  wing  is 
small,  but  forms  a  prominent  thick  pterj'goid  crest.  The  pterygoid  process  is 
wide,  and  there  is  no  alar  canal.  The  sphenoidal  sinus  is  absent  in  the  calf  and 
small  in  the  adult ;  it  communicates  by  one  or  two  small  openings  with  an  ethmoidal 
meatus,  and  so  with  the  nasal  cavity. 


zs 


Fig.  132. — Cranial  and  Orbital  Regions  op  Skull  of  Ox. 
The  horn  core,  supraorbital  process,  and  greater  part  of  zygomatic  arch  have  been  sawn  off:  A,  Frontal  bone; 
A',  A",  temporal  and  orbital  parts  of  same;  B,  parietal  bone;  C,  squamous  temporal  bone;  D,  D',  orbital  and  facial 
parts  of  lacrimal  bone;  E,  malar  bone;  F,  maxilla;  G,  perpendicular  part  of  palatine  bone;  1,  occipital  condyle;  2, 
paramastoid  process;  3,  temporal  crest;  4,  temporal  condyle;  5,  postglenoid  process;  6,  external  opening  of  temporal 
canal;  7,  meatus  acusticus  externus;  S,  bulla  ossea;  9,  sty lo-mastoid  foramen;  10,  muscular  process  of  temporal  bone; 
11,  tip  of  basilar  tubercle;  12,  foramen  ovale;  13,  foramen  orbito-rotundum;  14,  optic  foramen;  lo,  ethmoidal  foramen; 
16,  orbital  opening  of  supraorbital  canal;  17,  pterygoid  crest;  18,  ridge  of  orbital  wing  of  sphenoid;  19,  pterygoid  proc- 
ess of  sphenoid;  20,  hamulus  of  pterygoid  bone;  21,  lacrimal  bulla;  22,  fossa  sacci  lacrimalis;  23,  root  of  supraorbital 
process;   24,  processus  cornus  (section) ;   25,  frontal  eminence. 


The  ethmoid  bone  has  an  extensive  perpendicular  plate.  The  lateral  mass 
consists  of  five  endoturbinates  and  eighteen  ectoturbinates  (Paulli).  The  largest 
ethmoturbinate  is  so  extensive  as  to  be  termed  a  third  or  middle  turbinate  bone ;  it 
projects  forward  between  the  dorsal  and  ventral  turbinates.  The  lamina  lateralis 
appears  to  a  small  extent  externally  in  the  pterygo-palatine  fossa,  forming  part 
of  the  dorsal  margin  of  the  sphenopalatine  foramen. 

The  interparietals  are  primitively  paired,  but  unite  before  birth.  As  already 
mentioned,  fusion  occurs  before  or  shortly  after  birth  with  the  parietals  and  supra- 
occipital.     The  bone  has  no  intracranial  projection. 

The  parietal  bones  do  not  enter  into  the  formation  of  the  roof  of  the  cranium. 


BONES    OF   THE    CRANIUM 


135 


They  constitute  the  upper  part  of  the  posterior  wall,  bend  sharply  forward  along 
the  lateral  wall,  and  enter  into  the  formation  of  the  temporal  fossa.  The  line  of 
inflection  is  marked  by  the  prominent  parietal  crest,  which  is  continuous  with  the 
temporal  crest  below  and  the  frontal  crest  anteriorly.  The  parietals  are  excavated 
to  form  part  of  the  frontal  sinuses  in  the  adult  animal. 


Frontal     Parietal 
eminence      bone 


Ti  mporal 
fossa 

Supraorbital  foramen 
Supraorbital  groove 


Nasal  bone 


Palatine  fissure 


Facial  tuberosity 


Nasal  process  of  premaxilla 


Palatine  process  of  premaxilla 


Daily  of  premaxilla 


Fig.   133. — Skull  of  Jersey  Cow;  Dorsal  View. 


The  condition  in  the  young  subject  is  as  follows:  The  two  parietals  are  united  with  each  other 
and  also  with  the  interparietal  and  supraoccipital.  The  resulting  mass  is  somewhat  horseshoe- 
shaped.  Its  occipital  part  (Planum  occipitale)  forms  the  greater  part  of  the  posterior  wall  of 
the  cranium  and  bears  about  its  center  the  tuberosity  for  the  attachment  of  the  Ugamentum 
nucha}.  From  either  side  of  this  a  line  curves  outward  and  divides  the  surface  mto  an  upper 
smooth  area  and  a  lower  area  which  is  rough  for  muscular  attachment.  The  upper  border  joms 
the  frontal  bone  and  concurs  in  the  formation  of  the  frontal  eminence.  The  temporal  parts 
(Plana  temporaha)  are  much  smaller  and  are  concave  externally;  they  join  the  frontal  above  and 
the  squamous  temporal  below.  A  median  occipital  crest  extends  ventrally  from  the  external 
occipital  protuberance. 

The  frontal  bones  are  very  extensive,  forming  about  one-half  of  the  entire 


136 


SKELETON    OF   THE    OX 


length  of  the  skull,  and  all  of  the  roof  of  the  cranium.  The  posterior  borders 
form  -with  the  parietals  a  large  central  frontal  eminence  (Torus  frontalis),  the 
highest  point  of  the  skull.  At  the  junction  of  the  posterior  and  the  lateral  border 
is  the  processus  comus  or  "horn  core,"  for  the  support  of  the  horn.     These  proc- 


FiG.  134. — Skull  OF  Ox,  without  Mandible;  Ventral  View. 
1,  Foramen  magnum;  2,  occipital  condyle;  3,  paramastoid  process;  4,  condyloid  foramen;  5,  foramen  lacerum; 
6,  basilar  part  of  occipital  bone;  7,  7',  basilar  tubercles;  8,  bulla  ossea;  9,  foramen  ovale  (concealed  by  muscular  proc- 
ess) ;  10,  meatus  acusticus  externus;  11,  zygomatic  process  of  temporal  bone,  12,  condyle  of  same;  13,  external  opening 
of  temporal  canal ;  14,  processus  cornus;  15,  muscular  process  of  temporal  bone;  16,  pterygoid  crest;  17,  orbital  open- 
ing of  supraorbital  canal;  18,  choanae  or  posterior  nares;  19,  hamulus  of  pterj'goid  bone;  20,  crest  formed  by  pterygoid 
processes  of  sphenoid  and  palatine  bones;  21,  horizontal  part  of  palatine  bone;  22,  anterior  palatine  foramen;  23, 
lacrimal  bulla;  24,  maxillary  tuberosity;  25,  palatine  process  of  maxilla;  26,  zygomatic  process  of  malar  bone;  27. 
facial  tuberosity:  28,  body  of  premaxilla;  29,  palatine  process  of  same;  30,  palatine  fissure;  31,  incisive  fissure;  32, 
premolars;   33,  molars. 


esses  are  of  elongated  conical  form,  and  vary  greatly  in  size,  length,  curvature, 
and  direction.  The  external  surface  is  rough  and  porous,  marked  by  numerous 
grooves  and  foramina;  in  the  fresh  state  it  is  covered  by  the  corium  of  the  horn. 
The  base  has  a  constriction,  the  neck.  The  interior  is  excavated  to  form  a  number 
of  irregular  spaces,  partially  divided  by  bony  septa,  and  communicating  with  the 


BONES   OF   THE   FACE  137 

frontal  sinus.  In  the  polled  breeds  these  processes  are  absent,  the  skull  is  narrower 
here,  and  the  frontal  eminence  more  pronounced  (Fig.  139).  The  supraorbital  proc- 
ess is  situated  about  half-way  between  the  anterior  and  posterior  margins;  it  is 
short  and  joins  the  frontal  process  of  the  malar  bone.  The  supraorbital  foramen 
(often  double)  is  situated  about  an  inch  medially  from  the  root  of  the  process;  it 
is  the  external  orifice  of  the  supraorbital  canal  (Canalis  supraorbitalis),  which  passes 
downward  and  forward  to  the  orbit.  The  foramen  is  in  the  course  of  the  supra- 
orbital groove  (Sulcus  supraorbitalis),  which  marks  the  course  of  the  frontal  vein. 
The  anterior  ends  of  the  naso-frontal  parts  form  a  notch  which  receives  the  nasal 
bones,  and  sutural  (or  Wormian)  bones  are  often  found  at  this  junction  (naso- 
frontal suture).  The  orbital  part  is  extensive;  it  is  perforated  behind  by  the  or- 
bital opening  of  the  supraorbital  canal,  and  below  by  the  ethmoidal  foramen.  It 
does  not  articulate  with  the  palatine  bone,  from  which  it  is  separated  by  the  or- 
bital wing  of  the  sphenoid.  The  temporal  part  is  also  more  extensive  than  in  the 
horse.  The  frontal  sinus  is  very  extensive,  being  continued  into  the  parietals  and 
occipital,  and  the  horn  processes  when  present. 

The  squamous  and  petrous  parts  of  the  temporal  bone  fuse  early — in  fact 
union  is  nearly  complete  at  birth.  The  squamous  part  is  relatively  small.  Its 
lateral  surface  is  divided  into  two  parts  by  the  prominent  temporal  crest,  which  is 
continuous  with  the  parietal  crest  above  and  turns  forward  below,  ending  at  a 
tubercle  above  the  external  acoustic  meatus.  The  part  behind  the  crest  faces 
backward,  and  is  partly  free,  partly  united  with  the  occipital.  The  area  in  front 
of  the  crest  is  concave  and  enters  into  the  formation  of  the  temporal  fossa;  it  is 
perforated  by  foramina  which  communicate  with  the  temporal  canal.  The  zygo- 
matic process  is  much  shorter  and  weaker  than  in  the  horse,  and  articulates  with  the 
malar  only.  The  condyle  is  convex  in  both  directions.  The  postglenoid  process 
is  less  prominent,  and  behind  it  is  the  chief  external  opening  of  the  temporal  canal. 
The  cerebral  surface  is  almost  completely  overlapped  by  the  parietal  and  sphenoid. 
The  petrous  part  is  small,  but  the  tympanic  part  is  extensive.  The  external 
acoustic  meatus  is  smaller  than  in  the  horse  and  is  directed  laterally.  From  it  a 
plate  projects  downward  and  helps  to  inclose  the  deep  depression  in  which  the  hyoid 
process  is  placed.  Behind  this  plate  is  the  stylo-mastoid  foramen.  The  muscular 
process  is  large  and  often  bifid  at  its  free  end.  The  bulla  ossea  is  large  and  later- 
ally compressed.  It  is  separated  from  th^  occipital  bone  by  a  narrow  opening 
which  is  equivalent  to  part  of  the  foramen  lacerum  of  the  horse.  The  temporal 
canal  is  formed  entirely  in  the  temporal  bone.  The  facial  canal,  on  the  other 
hand,  is  bounded  partly  by  the  occipital  bone. 

Bones  of  the  Face 
The  maxilla  is  shorter  but  broader  and  relatively  higher  than  in  the  horse. 
Its  lateral  surface  bears  the  rough  facial  tuberosity  (Tuber  faciale),  placed  above  the 
third  and  fourth  cheek  teeth;  a  rough  line  which  extends  backward  from  it  to  the 
upper  part  of  the  malar  bone  may  be  regarded  as  the  facial  crest.  The  infraorbital 
foramen — often  double — is  situated  above  the  first  cheek  tooth.  The  tuber  maxil- 
lare  is  small,  laterally  compressed,  and  usually  bears  a  small  pointed  process  (Pro- 
cessus pterygoideus) .  The  zygomatic  process  is  very  small.  The  interalveolar 
border  is  concave,  and  there  is  no  alveolus  for  a  canine  tooth.  The  palatine 
process  is  wider,  but  somewhat  shorter  than  in  the  horse.  It  incloses  a  large 
air-space,  which  is  continuous  behind  with  a  like  cavity  in  the  horizontal  part  of 
the  palate  bone,  forming  the  palatine  sinus  (Sinus  palatinus).  This  communi- 
cates laterally  (over  the  infraorbital  canal)  with  the  maxillary  sinus;  in  the 
macerated  skull  it  communicates  with  the  nasal  cavity  by  a  large  oval  opening, 
which  is  closed  by  mucous  membrane  in  the  fresh  state.     A  median  septum  sepa- 


138 


SKELETON    OF   THE    OX 


rates  the  two  palatine  sinuses.  The  alveoH  for  the  cheek  teeth  increase  in  size 
from  before  backward.  The  maxillary  sinus  proper  is  small  and  is  undivided. 
The  maxillary  foramen  is  a  narrow  fissure,  deeply  placed  at  the  medial  side  of  the 
lacrimal  bulla.  The  maxilla  takes  no  part  in  the  formation  of  the  palatine  canal. 
Sutural  (or  Wormian)  Iwnes  are  often  present  at  its  junction  with  the  lacrimal  and 
malar  bones. 

The  body  of  the  premaxilla  is  thin  and  flattened,  and  has  no  alveoli,  since 
the  canine  and  upper  incisor  teeth  are  absent.  A  deep  notch  takes  the  place  of 
the  foramen  incisivum.  The  nasal  process  is  short,  convex  laterally,  and  does  not 
reach  to  the  nasal  bone ;  the  space  between  the  two  processes  is  greater  than  in  the 
horse.  The  palatine  process  is  narrow  and  is  grooved  on  its  nasal  surface  for  the 
septal  cartilage  and  the  vomer.     The  palatine  fissure  is  very  wide. 

The  palatine  bone  is  very  extensive.     The  horizontal  part  forms  one-fourth  or 


Nasal  bone 


Fig.  135. — Sagittal  Section  of  Skull  of  Ox,  without  Mandible. 
A,  A',  Squamous  and  basilar  parts  of  occipital  bone;  B,  B',  postsphenoid,  presphenoid;  C,  lateral  mass  of  ethmoid 
bone;  Z),  internal  plate  of  frontal  bone;  jE,  parietal  bone;  F,  petrous  temporal  bone;  G,  pterygoid  bone;  //.perpendicu- 
lar part  of  palatine  bone;  I,  outline  of  vomer  (dotted  line) ;  J,  palatine  process  of  maxilla;  K,  nasal  process  of  premaxilla; 
L,  dorsal  turbinate  bone;  M,  ventral  turbinate  bone;  A'^,  middle  turbinate  bone  (great  ethmo-turbinate) ;  1,  occipital 
condyle;  2,  paramastoid  process;  3,  bulla  ossea;  4,  basilar  tubercle;  5,  muscular  process;  6,  hypoglossal  foramen;  7, 
openings  of  condyloid  canal;  8,  direction  of  condyloid  canal  (dotted  line);  9,  internal  opening  of  temporal  canal;  10, 
meatus  acusticus  internus;  11,  foramen  lacerum;  12,  sella  turcica;  13,  optic  foramen;  14,  sphenoidal  sinus;  15,  orbital 
wing  of  sphenoid  bone;  16,  frontal  sinus;  16',  anterior  limit  of  frontal  sinus  (dotted  line) ;  17,  dorsal  nasal  meatus;  18, 
middle  nasal  meatus;  18',  dorsal  branch  of  middle  meatus;  19,  ethmoidal  meatuses;  20,  maxilla;  21,  sphenopalatine 
foramen;  22,  opening  into  maxillary  sinus;  23,  opening  into  palatine  sinus,  and  arrow  indicating  communication  of 
latter  with  maxillary  sinus;  24,  palatine  sinus;  25,  cross  indicates  anterior  end  of  palatine  sinus;   26,  palatine  fissure. 


more  of  the  hard  palate.  The  anterior  palatine  foramen  opens  near  the  junction 
with  the  maxilla,  about  half  an  inch  from  the  median  palatine  suture  and  crest. 
Accessory  palatine  foramina  (Foramina  palatina  accessoria)  are  also  present.  The 
palatine  groove  is  usually  not  very  distinct.  The  palatine  canal  is  formed  entirely 
in  this  part,  and  there  is  no  articulation  with  the  vomer.  A  rounded  ridge  occurs 
on  the  nasal  side  of  the  median  suture.  The  interior  is  hollow,  forming  part  of  the 
palatine  sinus.  The  perpendicular  part  is  an  extensive,  quadrilateral,  thin  plate, 
which  forms  the  posterior  part  of  the  lateral  wall  of  the  nasal  cavity  and  in  part 
bounds  the  choanse  or  posterior  nares.  Its  nasal  surface  is  nearly  flat,  and  is  smooth 
and  free,  except  behind,  where  it  is  overlapped  by  the  pterygoid  bone.  The  lateral 
surface  is  attached  to  a  small  extent  to  the  pterygoid  process  behind,  and  is  free  else- 
where. The  sphenopalatine  foramen  is  a  long,  elliptical  opening,  formed  by  a  deep 
notch  in  the  upper  edge  of  the  palate  bone  and  completed  by  the  ethmoid  and  sphe- 


BONES    OF   THE    FACE  139 

noid.  The  edge  behind  this  foramen  articulates  with  the  orbital  wing  of  the  sphe- 
noid, not  the  frontal,  as  in  the  horse. 

The  pterygoid  bone  is  wider  than  in  the  horse,  and  forms  the  greater  part  of  the 
lateral  boundary  of  the  posterior  nares.  Its  lateral  surface  is  almost  entirely  united 
to  the  palatine  bone  and  the  pterygoid  process,  but  a  small  part  is  free  in  the  pterygo- 
palatine fossa.     The  hamulus  is  distinctly  hook-like,  thin,  and  sharp. 

The  nasal  bone  is  little  more  than  half  the  length  of  that  of  the  horse.  It  is 
straight  in  its  length,  but  strongly  curved  from  side  to  side.  It  does  not  fuse  later- 
ally with  the  adjacent  bones,  even  in  old  age.  The  posterior  extremity  is  pointed 
and  fits  into  the  notch  between  the  frontal  bones.  The  anterior  end  is  broader, 
and  is  divided  into  two  parts  by  a  deep  notch.  In  old  animals  there  is  a  small 
extension  of  the  frontal  sinus  into  this  bone. 

The  lacrimal  bone  is  very  large.  The  extensive  facial  part  is  concave  in  its 
length,  and  bears  no  lacrimal  tubercle.  The  orbital  margin  is  marked  by  several 
notches.  The  orbital  part  bears  ventrally  the  remarkable  lacrimal  bulla;  this  is  a 
large  and  very  thin-walled  protuberance,  which  bulges  backward  into  the  lower 
part  of  the  orbit,  and  contains  an  extension  of  the  maxillary  sinus.  The  fossa  for 
the  lacrimal  sac  is  small,  and  is  just  behind  the  orbital  margin. 

The  malar  bone  is  relatively  long.  The  facial  surface  is  extensive;  it  bears  a 
curved  crest  (Crista  facialis)  just  below  the  orbital  margin  which  is  continued  on 
the  maxilla,  and  below  this  it  is  concave  dorso-ventrally.  The  zygomatic  process 
divides  into  two  branches;  of  these,  the  frontal  branch  (Processus  frontalis)  turns 
upward  and  backward  and  joins  the  supraorbital  process  of  the  frontal  bone; 
the  temporal  branch  (Processus  temporalis)  continues  backward,  and  is  over- 
lapped by  the  zygomatic  process  of  the  temporal  bone,  completing  the  zygomatic 
arch. 

The  dorsal  turbinate  bone  is  less  cribriform  and  fragile  than  in  the  horse,  and 
is  widest  in  its  middle,  small  at  either  end.  It  is  attached  to  the  turbinate  crest 
of  the  nasal  bone,  and  curves  downward,  outward,  and  then  upward  to  be  applied 
outwardly  to  the  frontal  and  lacrimal  bones.  It  thus  incloses  a  cavity  which  com- 
municates with  the  middle  meatus  nasi.  (In  the  macerated  skull  it  opens  into  the 
frontal  sinus,  but  this  communication  is  closed  by  mucous  membrane  in  the  fresh 
state.) 

The  ventral  turbinate  bone  is  shorter  but  much  broader  than  in  the  horse.  It 
is  attached  to  the  maxilla  by  a  basal  lamella  about  an  inch  (ca.  2  to  3  cm.)  wide, 
which  slopes  ventro-medially.  At  the  inner  edge  of  this  it  splits  into  two  plates 
which  are  rolled  in  opposite  directions,  and  inclose  two  separate  cavities,  sub- 
divided by  several  septa.  The  dorsal  one  opens  into  the  middle  meatus,  the 
ventral  one  into  the  ventral  meatus  nasi. 

The  vomer  forms  a  wider  and  deeper  groove  than  in  the  horse.  Its  anterior 
end  rests  in  a  groove  formed  by  the  ends  of  the  palatine  processes  of  the  premaxillae. 
The  anterior  third  of  its  thin  ventral  edge  fits  into  the  nasal  crest  of  the  maxilla; 
behind  this  it  is  free  and  is  separated  by  a  considerable  interval  from  the  nasal  floor. 

The  two  halves  of  the  mandible  do  not  fuse  completely  even  in  advanced  age,  so 
that  a  symphysis  mandibulae  is  present.  The  symphyseal  surfaces  are  extremely 
rough  and  are  marked  by  reciprocal  projections  and  cavities.  The  body  is  shorter, 
wider,  and  flatter  than  in  the  horse,  and  has  eight  round  and  relatively  shallow 
alveoli  for  the  lower  incisors.  The  interalveolar  border  is  long,  curved,  thin,  and 
sharp.  There  are  no  alveoli  for  the  canine  teeth,  which  are  absent.  The  anterior 
part  of  the  ramus  is  narrow.  The  mental  foramen  is  further  forward  than  in  the 
horse,  and  is  in  the  posterior  end  of  a  fossa.  The  rami  diverge  more,  so  that  the 
mandibular  space  is  wilder  than  in  the  horse.  They  are  also  more  strongly  curved, 
and  the  angle  is  more  pronounced.  The  molar  part  is  not  so  high,  especially  in  its 
anterior  part.     Its  ventral  border  is  convex  in  its  length.     Its  alveolar  border  bears 


140 


SKELETON    OF   THE   OX 


six  alveoli  for  the  lower  cheek  teeth;  the  first  is  quite  small,  and  they  increase  in 
size  from  before  backward.  The  vertical  part  is  much  smaller  than  in  the  horse 
and  its  posterior  border  is  relatively  thin  below,  concave  and  wider  above.  The 
mandibular  foramen  is  about  in  the  middle  of  its  medial  surface,  and  a  groove  for 


Coronoid  process 


Condyle 


Angle 


Symphyseal  surface 


Fig.  136. — Right  Half  of  Mandible  of  Ox;  Medial  View. 
1,  Mandibular  foramen;  2,  groove  for  lingual  nerve. 


the  lingual  nerve  curves  downward  and  forward  from  it.  The  condyle  projects 
medially  further  than  in  the  horse,  and  is  concave  from  side  to  side.  The  coronoid 
process  is  extensive  and  curves  backward. 

The  hyoid  bone  has  a  short  tuberous  lingual  process.     The  middle  cornua 

are  almost  as  large  as  the  small  cornua. 
The  great  cornua  are  narrow,  except 
at  the  ends.  The  upper  end  divides 
into  two  branches,  which  correspond 
to  the  two  angles  of  that  of  the  horse. 
The  thyroid  cornua  do  not  fuse  with 
the  body  except  in  old  age. 


SKULL  OF  THE  OX  AS  A  WHOLE 

The  skull  of  the  ox  is  more  clearly 
pyramidal  than  that  of  the  horse,  and 
is  shorter  and  relatively  wider.  The 
cranium  is  quadrangular  and  larger 
externally  than  in  the  horse ;  its  large 
size  is  due  mainly  to  the  great  extent 
of  the  frontal  sinuses  and  does  not 
affect  the  cranial  cavity,  which  is 
smaller  than  in  the  horse. 

The  frontal  surface  (Fig.  133)  is 

formed  bj^  the  frontals,  nasals,  and 

premaxillae.       The    frontal    part    is 

quadrilateral   and   very  extensive,  the   greatest   width  being  at  the  orbits.     It 

presents  a  central  depression  on  its   anterior  part,  and  on  either  side   are  the 

supraorbital   grooves   and  foramina.     Behind  is  the   median  frontal   eminence, 


Fig.  137. — Hyoid  Bone  of  Ox. 
o,  Body;  b,  lingual  process;  c,  thyroid  cornu  and  cartil 
age,  c';  d,  small  cornu;  e,  middle  cornu;  /,  great  cornu;  g 
muscular  angle.     (Ellenberger-Baum,  Anat.  d.  Haustiere.) 


SKULL    OF   THE    OX   AS   A   WHOLE  141 

and  at  the  lateral  angles  the  "horn  cores"  project  in  horned  cattle.  The 
nasal  part  is  very  short.  The  osseous  nasal  aperture  is  wide.  The  premaxillae 
do  not  bend  downward  as  in  the  horse;  they  are  relatively  thin  and  weak, 
and  are  separated  by  an  interval  which  has  a  wide  anterior  part  in  place  of 
the  foramen  incisivum. 

The  lateral  surface  (Fig.  129)  is  more  triangular  than  in  the  horse.  The  temporal 
fossa  is  confined  to  this  surface.  It  is  deep  and  narrow,  and  its  boundaries  are  more 
complete.  It  is  limited  dorsally  by  a  crest  which  extends  from  the  postero-lateral 
angle  of  the  frontal  bone  to  the  supraorbital  process,  and  is  analogous  to  the  pari- 
etal crest  of  the  horse.  It  is  bounded  behind  by  the  temporal  crest.  It  is  clearly 
marked  off  from  the  orbit  by  a  rounded  ridge  and  the  pterygoid  crest.  The  zygo- 
matic arch  is  short,  weak,  and  flattened,  and  is  formed  by  the  temporal  and  malar 
only.  Its  condyle  is  convex  and  is  wide  from  before  backward.  The  glenoid  cavity 
and  postglenoid  process  are  small.  The  orbit  is  encroached  upon  below  by  the 
lacrimal  bulla,  and  presents  the  orifice  of  the  supraorbital  canal  behind.  The  or- 
bital margin  is  completed  behind  by  the  frontal  process  of  the  malar;  its  lower  part 
is  prominent  and  rough,  not  smooth  and  rounded  as  in  the  horse.  The  pterygo- 
palatine fossa  is  much  larger,  deeper,  and  more  clearly  defined.  It  has  a  long  nar- 
row recess  between  the  vertical  plate  of  the  palate  bone  medially  and  the  maxilla 
and  lacrimal  bulla  laterally;  thus  the  sphenopalatine  and  maxillary  foramina  are 
deeply  placed.  The  preorbital  region  is  short  but  relatively  high.  A  tuberosity 
and  curved  line  correspond  to  the  facial  crest  of  the  horse.  The  infraorbital  fora- 
men is  situated  above  the  first  cheek  tooth  and  is  often  double. 

The  basal  surface  (Fig.  132)  is  short  and  wide,  especially  in  its  cranial  part.  The 
occipital  condyles  are  limited  in  front  by  transverse  ridges.  The  basilar  tubercles  at 
the  junction  of  the  occipital  and  sphenoid  are  large.  The  condyloid  fossse  contain  two 
foramina,  the  hypoglossal  below  and  in  front,  and  the  condyloid  above  and  behind; 
other  inconstant  ones  occur.  The  paramastoid  processes  are  short  and  convergent. 
The  foramen  lacerum  is  slit-like.  The  bulla  ossea  is  a  large,  laterally  compressed 
prominence.  The  muscular  processes  are  usually  long  and  narrow  triangular  plates, 
with  one  or  two  sharp  points.  The  external  acoustic  process  is  directed  almost 
straight  outward.  A  curved  plate  extends  ventrally  from  it  and  joins  the  bulla 
ossea  medially,  completing  the  deep  cavity  which  receives  the  articular  angle  of 
the  hyoid  bone.  The  chief  external  opening  of  the  temporal  canal  is  in  front  of 
this  plate,  and  an  accessory  one  lies  behind  it.  The  infratemporal  fossa  is  small, 
and  presents  the  foramen  ovale.  The  posterior  nares  are  very  narrow,  and  the 
vomer  does  not  reach  to  the  level  of  their  ventral  margin.  The  hard  palate  is  wide, 
and  forms  about  three-fifths  of  the  entire  length  of  the  skull.  A  small  central  part 
only  of  its  posterior  border  enters  into  the  formation  of  the  posterior  nares;  the 
lateral  parts  are  notched  and  just  above  them  are  the  posterior  palatine  foramina. 
The  anterior  palatine  foramina  are  an  inch  or  more  from  the  posterior  margin, 
and  about  the  same  distance  apart.  The  palatine  grooves  are  distinct  for  a  short 
distance  only.  Just  beyond  the  cheek  teeth  the  palate  narrows  and  becomes  con- 
cave; beyond  this  it  widens  and  flattens. 

The  nuchal  surface  is  extensive  and  somewhat  pentagonal  in  outline  in  the 
adult.  About  its  center  is  the  external  occipital  protuberance  for  the  attachment 
of  the  ligamentum  nuchae.  From  this  a  median  occipital  crest  extends  toward  the 
foramen  magnum,  and  laterally  two  lines  (Linese  nuchse  superiores)  curve  outward, 
marking  the  upper  limit  of  the  area  which  is  roughened  for  muscular  attachment. 
The  surface  above  the  lines  is  relatively  smooth,  and  is  covered  only  by  the  skin 
and  the  thin  auricular  muscles  in  the  living  animal.  It  is  separated  from  the 
frontal  surface  by  a  thick  border,  which  forms  centrally  the  frontal  eminence,  and 
bears  at  its  extremities  the  processus  cornus — except  in  the  polled  breeds.  The  con- 
dyles are  further  apart,  and  the  articular  surfaces  are  more  clearly  divided  into 


142 


SKELETON    OF   THE    OX 


upper  and  lower  parts  than  in  the  horse.     The  mastoid  foramen  is  at  the  junction 
of  the  occipital  and  temporal  bones;  it  is  frequently  very  small. 


Fig.  138. — Cranium  of  Jersey  Cow,  Nuchal  View.    The        Fig.  139. — Cranium  op  Polled  Angus  Cow,  Nuchal 
Gre.^ter  Part  of  the  Processus  Cornus  has  been  View. 

Sawn  Off. 
1,  Foramen  magnum;   2,  occipital  condyle;   3,  parama.stoid  process;   4,  bulla  ossea;    5,  meatus  acusticus  externus; 
6,  mastoid  foramen;   7,  external  occipital  protuberance;   8,  median  occipital  crest;   9,  linea  nuchse  superior;    10,  frontal 
eminence. 

Dorsal  meatus 

Middle  meatus 


Nasal  bone 


Dorsal  part  of  ventral  turbinate 
Basal  lamella 


Ventral  part  of  ventral 
turbinate 


Fig.  140. — Cross-section  of  Nasal  Region  of  Skull  of  Ox.     Section  Passes  Through  Facial  Tuberosity  and 

Third  Cheek  Tooth. 
1,  Cartilage  of  septum  nasi;    2,  vomer;   3,  ventral  meatus;   4,  anterior  extremity  of  maxillary  sinus;    5,  palatine 
sinus;   6,  infraorbital  canal  and  nerve;   7,  palatine  process  of  maxilla.     Dotted  lines  indicate  mucous  membrane  A'hich 
closes  gap  in  bony  floor  of  nasal  cavity. 


The  cranial  cavity  is  shorter  and  its  long  axis  is  more  oblique  than  in  the  horse, 
but  it  is  relativel}^  high  and  wide.     The  anterior  fossa  lies  at  a  much  higher  level 


SKULL   OF   THE   OX   AS   A   WHOLE 


143 


than  the  rest  of  the  floor.  The  ethmoidal  fossse  are  smaller,  and  the  hypophyseal 
fossa  or  sella  turcica  is  much  deeper  than  in  the  horse.  A  deep  groove  leads  from 
the  petrous  temporal  forward  over  the  foramen  ovale  to  the  foramen  rotundum. 
Behind  the  sella  there  is  often  a  distinct  prominence  (Dorsum  sellae) .  The  internal 
parietal  crest  is  prominent  anteriorl}^,  but  subsides  further  back.  A  faintly  marked 
elevation  represents  the  internal  occipital  protuberance.  The  petrous  temporal 
bone  projects  into  the  cavity  laterally.  The  ridges  and  digital  impressions  are  very 
pronounced.  The  temporal  canal  is  formed  entirely  in  the  temporal  bone,  and 
opens  internally  at  the  apex  of  the  petrous,  where  it  is  joined  by  the  condyloid 
canal.  The  foramen  lacerum  is  divided  into  two  parts  (For.  lacerum  orale  et  ab- 
orale) . 

The  nasal  cavity  is  incompletely  divided  l)y  the  septum,  which  does  not  reach 


Dorsal  meatus 


Nasal  bone 


Dorsal  turhinaU 
Middle  meatus 


Lacrimal  bone 

Aaso-lacrimcd  canal 
Maxilla 


Fig.  141.— Cross-section  of  N.\sal  Region  of  Skull  of  Ox.     Section  is  Cut  between  Fourth  .a.nd  Fifth  Cheek 

Tooth. 
1,  Cartilage  of  septum  na.si;   2,  vomer;   3,  ventral  meatus;  4,  4',  maxillary  sinuses;   5,  5',  palatine  sinuses;  6,  infra- 
orbital canal  and  nerve;  7,  horizontal  part  of  palatine  bone;  8,  communication  between  maxillarj^  and  palatine  sinuses. 
Dotted  lines  indicate  mucous  membrane  which  closes  gap  in  bony  floor  of  nasal  cavity. 


the  floor  posteriorly.  The  floor  is  relatively  long,  and  is  more  concave  from  side  to 
side  than  in  the  horse.  In  the  dry  skull  it  has  a  large  oval  opening  (Hiatus  maxillaris) 
into  the  palatine  sinus,  which  is  closed  during  life  by  mucous  membrane.  The 
middle  meatus  is  divided  behind  into  upper  and  lower  branches  by  the  great  eth- 
moturbinate.     The  choanal  or  posterior  nares  are  narrow  and  obhque. 

The  frontal  sinus  is  very  large.  It  involves  almost  all  of  the  frontal  bone  and 
a  large  part  of  the  posterior  wall  of  the  cranium.  It  also  extends  for  a  variable  dis- 
tance into  the  horn  processes  when  these  are  present.  A  complete  median  septum 
separates  the  right  and  left  sinuses.  The  anterior  limit  is  indicated  by  a  transverse 
plane  through  the  middle  of  the  orbits.  It  extends  laterally  to  the  crest,  which 
limits  the  temporal  fossa  above,  and  into  the  root  of  the  supraorbital  process.  At 
the  highest  part  of  the  cranial  cavity  and  at  the  external  occipital  protuberance 


144 


SKELETON    OF   THE    OX 


tlie  two  plates  of  the  bone  come  together.  The  cavity  is  very  irregular  and  is  sub- 
divided into  numerous  spaces  by  ridges  and  partial  septa.  This  multilocular 
character  is  most  marked  in  the  anterior  part,  and  here  several  small  spaces  appear 
to  be  cut  off  from  the  main  cavity.  The  supraorbital  canal  passes  through  the 
sinus.  Several  small  openings  lead  from  the  sinus  to  the  ethmoidal  meatuses, 
and  thus  indirectly  to  the  upper  division  of  the  middle  meatus  nasi.  The  communi- 
cations with  the  cavity  of  the  dorsal  turbinate  and  with  the  lacrimal  part  of  the 


Fig.  142. — Skull  op  Ox;  Dorsal  View. 
The  outer  plate  of  bone  has  been  removed  to  show  the  sinuses,  a,  Frontal  sinus;  a',  cranial  plate  of  frontal  bone; 
a",  anterior  part  of  frontal  sinus,  which  is  separated  from  remainder  by  a  septum  (b) ;  c,  c',  communications  between 
frontal  sinus  and  nasal  cavity;  d,  supraorbital  foramen;  e,  supraorbital  canal;  /,  cavity  of  dorsal  turbinate  bone, 
and  fir,  its  opening  into  the  nasal  cavity;  h.  lacrimal  sinus;  i,  its  communication  with  the  maxillary  sinus;  k,  maxillary 
sinus;  Z,  orbit;  i,  frontal  bone;  /',  processus  cornus;  ^,  nasal  bone;  3,  premaxilla  (nasal  process) ;  4.  maxilla;  5,  lacri- 
mal bone;  6,  malar  bone;  7,  dotted  line  indicating  course  of  nasolacrimal  duct.  (After  Ellenberger,  in  Leisering's 
Atlas.) 


maxillary  sinus  which  are  seen  in  the  macerated  skull  are  closed  in  the  fresh  state 
by  mucous  membrane. 

The  maxillary  sinus  is  excavated  chiefly  in  the  maxilla,  lacrimal,  and  malar, 
and  is  not  divided  by  a  septum  as  in  the  horse.  It  extends  forward  as  far  as  the 
facial  tuberosity,  or  a  little  further  in  old  animals.  Its  dorsal  limit  is  indicated 
approximately  by  a  line  drawn  from  the  infraorbital  foramen  to  the  upper  margin 
of  the  orbit.     It  is  continued  into  the  lacrimal  bulla  to  a  point  nearly  opposite  to 


BONES    OF    THE    THORACIC    LIMB  145 

the  bifurcation  of  the  zygomatic  process  of  the  malar.  It  also  extends  upward  and 
backward  through  a  large  opening  into  a  cavity  formed  by  the  lacrimal,  frontal, 
ethmoid,  and  turbinal  bones,  at  the  medial  side  of  the  orbit. ^  The  floor  of  the  cavity 
is  irregular  and  the  roots  of  the  last  three  or  four  cheek  teeth  project  up  into  it, 
covered  by  a  plate  of  bone.  The  sinus  communicates  with  the  palatine  sinus  freely 
over  the  infraorbital  canal  through  an  oval  opening  about  two  to  three  inches  (ca. 
5  to  7.5  cm.)  long.  Above  this  it  communicates  by  a  shorter  and  much  narrower 
opening  with  the  middle  meatus  nasi. 

The  palatine  sinus  is  excavated  in  the  hard  palate,  and  is  separated  from  that 
of  the  opposite  side  by  a  median  septum.  It  extends  from  the  posterior  border  of 
the  palate  to  a  plane  an  inch  or  more  (2.5  to  3  cm.)  in  front  of  the  first  cheek  tooth. 
As  mentioned  above,  there  is  a  large  communication  with  the  maxillary  sinus  over 
the  infraorbital  canal,  so  that  the  cavity  is  sometimes  regarded  as  a  part  of  that  sinus. 
The  large  defect  in  the  bony  roof  of  the  sinus  is  closed  by  two  layers  of  mucous 


Fig.  143. — Skull  op  Ox;  Lateral  View  without  Mandible. 
The  maxillary,  lacrimal,  and  turbinate  sinuses  have  been  opened,  and  part  of  the  orbital  margin  removed,  a.  Cavity 
of  dorsal  turbinate  bone;  6,  lacrimal  sinus;  c,  maxillary  sinus;  d,  communication  between  maxillary  and  palatine 
sinuses;  e,  opening  between  maxillary  and  lacrimal  sinuses;  /,  thin  osseous  bulla;  g,  lacrimal  bulla;  h,  orbit;  1-6,  cheek 
teeth;  7,  nasal  bone;  8,  premaxilla  (nasal  process);  9,  maxilla;  9',  infraorbital  foramen;  10,  frontal  bone;  11,  lacri- 
mal bone;  12,  malar  bone;  13,  fissure  between  nasal  bone  and  maxilla;  74,  temporal  bone  (squamous) ;  75,  external 
acoustic  meatus;  75,  paramastoid  process;  77,  occipital  condyle;  7,?,  palate  bone  (perpendicular  part);  7 S,  pterygoid 
bone  (hamulus);  ^0,  tympanic  part  of  temporal;  ^0',  muscular  process  of  petrous  temporal.  (After  EUenberger,  in 
Leisering's  Atlas.) 

membrane  in  the  fresh  state.  The  palatine  canal  passes  obliquely  through  the 
posterior  part  of  the  sinus. 

The  sphenoidal  sinus  is  almost  entirely  in  the  sphenoid  bone  and  does  not 
communicate  with  the  palatine  sinus.  It  has  one  or  two  openings  into  the  ventral 
ethmoidal  meatuses.  There  is  no  cavity  in  the  perpendicular  part  of  the  palate 
bone. 

There  are  several  small  air-cavities  between  the  lateral  mass  of  the  ethmoid 
and  the  anterior  part  of  the  frontal  sinus,  which  communicate  separately  with 
ethmoidal  meatuses. 

BONES  OF  THE  THORACIC  LIMB 

The  scapula  is  more  regularly  triangular  than  in  the  horse,  relatively  wider  at 

the  vertebral  end  and  narrower  at  the  distal  end.     The  scapular  index  is  about 

1  : 0.6.     The  spine  is  more  prominent  and  is  placed  further  forward,  so  that  the 

supraspinous  fossa  is  narrow  and  does  not  extend  to  the  lower  part  of  the  bone. 

1  This  is  termed  the  lacrimal  sinus  by  some  authors.     It  is  similar  in  location  and  in  the  posi- 
tion of  its  orifice  to  the  turbinate  part  of  the  frontal  sinus  of  the  horse  with  the  important  differ- 
ence that  it  does  not  communicate  with  the  frontal  sinus  in  the  ox. 
10 


146 


SKELETON    OF    THE    OX 


The  spine  is  sinuous,  bent  backward  in  its  middle,  forward  below.  Its  free  border 
is  somewhat  thickened  in  its  middle,  but  bears  no  distinct  tuber.  Instead  of  sub- 
siding below  as  in  the  horse,  the  spine  becomes  a  little  more  prominent,  and  is  pro- 
longed by  a  pointed  projection,  the  acromion,  from  which  part  of  the  deltoid  muscle 
arises.  The  subscapular  fossa  is  shallow.  The  areas  for  the  attachment  of  the 
serratus  muscle  are  not  very  distinct.  The  nutrient  foramen  is  usually  in  the 
lower  third  of  the  posterior  border.  The  glenoid  cavity  is  almost  circular  and 
without  any  distinct  notch.     The  tuberosity  is  small  and  close  to  the  glenoid  cavity. 


Fig.  144. — Left  Sc.\pul.\  of  Ox;  L.\teral  View. 

1,  Anterior  angle;  2,  posterior  angle;  3,  supra.spinous  fossa;  4,  infraspinous  fossa;    5,  anterior  border;    6,  posterior 

border;  7,  spine;  8,  acromion;  9,  tuber  scapulae;   10,  glenoid  cavity;   11,  nutrient  foramen. 


The  coracoid  process  is  short  and  rounded.  The  cartilage  resembles  that  of 
the  horse.  The  tuberosity  unites  with  the  rest  of  the  bone  at  seven  to  ten  months. 
The  humerus  has  a  shallow  musculo-spiral  groove.  The  deltoid  tuberosity 
is  less  prominent  than  in  the  horse,  and  the  curved  line  running  from  it  to  the  neck 
bears  a  well-marked  tubercle  on  its  upper  part.  The  nutrient  foramen  is  usually 
in  the  distal  third  of  the  posterior  surface.  The  lateral  tuberosity  is  very  large, 
and  rises  an  inch  or  more  (ca.  3  cm.)  above  the  level  of  the  head.  Its  anterior  part 
curves  medially  over  the  intertuberal  or  bicipital  groove,  and  below  it  laterally 
there  is  a  prominent  circular  rough  area  for  the  insertion  of  the  tendon  of  the  infra- 
spinatus.    The  anterior  part  of  the  medial  tuberosity  has  a  small  projection  which 


BONES    OF   THE   THORACIC    LIMB 


147 


curves  over  the  groove.  The  groove  is  undivided.  The  distal  articular  surface 
is  decidedly  oblique,  and  the  grooves  and  ridge  are  very  well  marked.  The  coro- 
noid  and  olecranon  fossae  are  deep  and  wide.  The  condyloid  crest  is  represented  by 
a  rough  raised  area.  The  proximal  end  unites  with  the  shaft  at  three  and  one-half 
to  four  years,  and  the  distal  at  about  one  and  one-half  years. 

The  radius  is  short  and  relatively  broad.  It  is  somewhat  oblique,  the  distal 
end  being  nearer  the  median  plane  than  the  proximal.  The  curvature  is  more 
pronounced  below  than  above.     The  shaft  is  prismatic  in  its  middle  part  and  has 


Fig.  14.5. — Left  Humerus  of  Ox; 
Lateral  View. 
1,  Head;  2,  neck;  3,  3',  lateral 
tuberosity;  4,  rough  prominence  for 
attachment  of  infraspinatus  tendon; 
5,  deltoid  tuberosity;  6,  coronoid 
fossa;  7,  lateral  condyle;  8,  lateral 
epicondyle;  9,  medial  epicondyle; 
10,  olecranon  fossa. 


Fig.  146. — Left  Humerus  of  Ox; 
Anterior  View. 
1,  Lateral  tuberosity;  2,  medial 
tuberosity;  3,  intertuberal  groove; 
4,  rough  prominence  for  attach- 
ment of  infraspinatus  tendon;  5, 
deltoid  tuberosity;  6,  teres  tubercle; 
7,  musculo-spiral  groove;  8,  coro- 
noid fossa;  9,  medial  condyle;  10, 
lateral  condyle. 


Fig.  147. — Left  Radius  and  Ulna 
OF  Ox;  PosTERO-MEDiAL  View. 
1,  Olecranon;  2,  processus  an- 
conaeus;  3,  semilunar  notch;  4, 
proximal  extremity  of  radius;  5,  5', 
proximal  and  distal  interosseous 
spaces;  6,  shaft  of  radius;  7,  shaft 
of  ulna;  8,  vascular  groove;  9,  sty- 
loid process  of  ulna. 


dorsal,  volar,  and  lateral  faces.  There  is  a  marked  increase  in  width  and  thickness 
distally.  The  proximal  articular  surface  presents  a  synovial  fossa  which  extends 
medially  from  the  deep  groove  between  the  two  glenoid  cavities.  The  radial 
tuberosity  is  represented  by  a  slightly  elevated  rough  area.  The  facets  for  the  ulna 
are  larger  than  in  the  horse.  The  two  bones  commonly  fuse  above  the  proximal 
interosseous  space  and  always  fuse  below  it,  except  near  the  distal  end,  where  there 
is  a  small  distal  interosseous  space.  A  groove  connects  the  two  spaces  laterally. 
The  distal  extremity  is  large,  and  is  thickest  medially.  Its  articular  surface  is 
oblique  in  two  directions,  i.  e.,  from  within  upward  and  backward.     The  grooves 


148 


SKELETON    OF   THE   OX 


for  the  extensor  tendons  are  shallow.     The  proximal  end  unites  with  the  shaft  at 
one  to  one  and  one-half  years,  and  the  distal  at  three  and  one-half  to  four  years. 

The  approximation  of  the  lower  ends  of  the  forearms  and  the  carpi  gives  the  "knock-kneed" 
appearance  in  cattle.  The  obliquity  of  the  joint  surfaces  produces  lateral  deviation  of  the  lower 
part  of  the  hmb  in  flexion.  The  facets  for  the  radial  and  intermediate  carpals  are  narrower  than 
in  the  horse  and  run  obliquely  dorso-laterally.  The  surface  for  the  ulnar  carpal  is  extensive  and 
saddle-shaped;  its  lateral  part  is  furnished  by  the  ulna. 

The  ulna  is  more  fully  developed  than  in  the  horse.  The  shaft  is  complete, 
three-sided,  and  strongly  curved.  It  is  fused  with  the  radius  in  the  adult,  except 
at  the  two  interosseous  spaces  mentioned  above.  Its  proximal  part  contains  a 
medullary  cavity  which  extends  somewhat  into  the  proximal  end.     The  olecranon  is 


i 

—u 

3 

i 
3 

J 

Fig.  148. — Left  Carpus  and  Adjacent  Bones  op  Ox; 
Front  View. 
if,  Radius;  XJ ,  ulna;  C  r.,  radial  carpal;  C.  u., 
ulnar  carpal;  C.  2+3,  fused  second  and  third  carpals; 
C.  4,  fourth  carpal;  1,S,  3,  grooves  for  extensor  tendons; 
4,  metacarpal  tuberosity;  6,  vascular  groove.  Inter- 
mediate carpal  bone  (between  radial  and  ulnar)  not 
marked. 


Mc.  3+4 


Fig.  149. — Left  Carpus  and  Adjacent  Bones  of 
Ox;  Lateral  View. 
R,  Distal  end  of  radius;  U,  styloid  process  of 
ulna;  I,  distal  interosseous  space;  C.  i.,  intermediate 
carpal;  C.  u.,  ulnar  carpal;  C.  a.,  accessory  carpal; 
C.  2  +  3,  fused  second  and  third  carpals;  C.  4,  fourth 
carpal;  Mc.  3+4.  fused  third  and  fourth  (large) 
metacarpal;  Mc.  5,  fifth  (small)  metacarpal;  T,  meta- 
carpal tuberosity. 


large  and  bears  a  rounded  tuberosity.  The  distal  end  is  fused  with  the  radius;  it 
projects  below  the  level  of  the  latter,  forming  the  styloid  process  of  the  ulna  (Pro- 
cessus styloideus  ulna?),  which  furnishes  part  of  the  facet  for  the  ulnar  carpal. 
The  summit  of  the  olecranon  and  the  distal  end  unite  with  the  shaft  at  three  and 
one-half  to  four  years. 

The  carpus  consists  of  six  bones,  four  in  the  proximal  row  and  two  in  the  distal. 
The  proximal  row  is  oblique  in  conformity  with  the  carpal  articular  surface  of  the 
radius.  The  radial  and  intermediate  resemble  in  general  those  of  the  horse,  but 
are  less  regular  in  shape,  and  their  long  axes  are  directed  obliquely  backward  and 
medially.  The  radial  is  narrower  than  in  the  horse  and  curves  upward  behind.  The 
intermediate  is  constricted  in  its  middle,  and  wider  behind  than  in  front.  The 
ulnar  is  large  and  very  irregular.  Its  proximal  surface  is  extensive  and  sinuous  and 
articulates  with  both  radius  and  ulna;  it  has  a  large  oval  facet  behind  for  articula- 
tion with  the  accessory  carpal.     The  accessory  is  short,  thick,  and  rounded;    it 


BONES   OF  THE   THORACIC  LIMB 


149 


articulates  with  the  ulnar  carpal  only.  The  first  carpal  is  absent.  The  second  and 
third  carpals  are  fused  to  form  a  large  quadrilateral  bone.  The  fourth  carpal  is  a 
smaller  quadrilateral  bone. 

The  metacarpus  consists  of  a  large  metacarpal  and  a  lateral  small  metacarpal 
bone.  The  large  metacarpal  bone  (Mc.  3+4)  results  from  the  fusion  of  the  third 
and  fourth  bones  of  the  foetus,  and  bears  evidences  of  its  double  origin  even  in  the 
adult  state.  The  shaft  is  shorter  than  in  the  horse,  and  is  relatively  wider  and 
flatter.  The  dorsal  surface  is  rounded,  and  is  marked  by  a  vertical  vascular 
groove  connecting  two  canals  which  traverse  the  ends  of  the  shaft  from  before 
backward.  The  volar  surface  is  flat  and  presents  a  similar  but  much  fainter  groove. 
The  borders  are  rough  in  the  proximal  third.  The  proximal  end  bears  two  slightly 
concave  facets  for  articulation  with  the  bones  of  the  lower  row  of  the  carpus;  the 
medial  area  is  the  larger,  and  they  are  separated  by  a 
ridge  in  front  and  a  notch  behind.  The  lateral  angle 
has  a  facet  behind  for  the  small  metacarpal  bone.  The 
medial  part  of  the  extremity  has  anterior  and  posterior 
tuberosities.  The  distal  end  is  divided  into  two  parts 
by  a  sagittal  notch.  Each  division  bears  an  articular 
surface  similar  to  that  in  the  horse,  but  much  smaller. 
The  medullary  cavity  is  divided  into  two  parts  by  a  ver- 
tical septum  which  is  usually  incomplete  in  the  adult. 
The  small  metacarpal  bone  (Mc.  5)  is  a  rounded  rod 
about  an  inch  and  a  half  (ca.  3.5  to  4  cm.)  in  length, 
which  lies  against  the  proximal  part  of  the  lateral  bor- 
der of  the  large  bone.  Its  proximal  end  articulates  with 
the  latter,  but  not  with  the  carpus.  The  distal  end  is 
pointed. 

Four  cartilaginous  metacarpals  are  present  in  the  early  foetal 
state,  viz.,  the  second,  third,  fourth,  and  fifth.  The  second  com- 
monly either  disappears  or  unites  with  the  third;  sometimes  it 
develops  as  a  small  rod  of  bone.  The  third  and  fourth  gradually 
unite,  but  can  be  cut  apart  at  birth.  Each  has  three  centers  of 
ossification;  the  proximal  epiphysis  fuses  with  the  shaft  before 
birth,  the  distal  at  two  to  two  and  one-half  years. 

Four  digits  are  present  in  the  ox.  Of  these,  two — 
the  third  and  fourth — are  fully  developed  and  have 
three  phalanges  and  three  sesamoids  each.  The  second 
and  fifth  are  vestiges  and  are  placed  behind  the  fetlock; 
each  contains  one  or  two  small  bones  which  do  not  ar- 
ticulate with  the  rest  of  the  skeleton. 

The  first  phalanx  is  shorter  and  narrower  than  in 
the  horse  and  is  three-sided.  The  interdigital  surface  is 
flattened  and  its  volar  part  bears  a  prominence  for  the 

attachment  of  the  interdigital  ligaments.  The  proximal  extremity  is  relatively 
large,  and  is  somewhat  compressed  from  side  to  side.  The  articular  surface  is  con- 
cave from  before  backward  and  is  cUvided  by  a  sagittal  groove  into  two  areas,  of 
which  the  abaxial  one  is  the  larger  and  higher.  Behind  these  are  two  facets  for 
articulation  with  the  sesamoid  bones.  The  volar  surface  bears  two  tuberosities 
separated  by  a  deep  depression.  The  distal  extremity  is  smaller  than  the  proximal, 
especially  in  the  dorso-volar  direction.  Its  articular  surface  is  divided  by  a  sagittal 
groove  into  two  convex  facets,  of  which  the  abaxial  one  is  decidedly  the  larger. 
There  are  depressions  on  either  side  for  ligamentous  attachment.  The  bone  con- 
sists at  birth  of  two  pieces— the  distal  end  and  the  fused  shaft  and  proximal  ex- 
tremity.    Union  occurs  at  one  and  one-half  to  two  years. 

The  second  phalanx  is  about  two-thirds  of  the  length  of  the  first  and  is  dis- 


FiG.       1.50. — Left       Metacarpal 

Bones   of  Ox;   Front  View. 

The   Small  Bone   has   been 

Moved  Laterally. 

1,  Metacarpal  tuberosity;  2, 
vascular  groove;  3,  3',  foramina; 
4,  4',  condyles;  5,  articular  facet 
of  fifth  (small)  metacarpal  bone. 


150 


SKELETON    OF   THE    OX 


tinctly  three-sided.  The  proximal  articular  surface  is  divided  by  a  sagittal  ridge 
into  two  glenoid  cavities,  of  which  the  abaxial  one  is  much  the  larger.  There  is  a 
central  dorsal  prominence  and  two  tubercles  are  present  on  the  volar  face.  The 
cUstal  extremity  is  smaller  than  the  proximal.  Its  articular  surface  encroaches  con- 
siderably on  the  dorsal  and  volar  surfaces,  and  is  divided  into  two  parts  by  a 
sagittal  groove.  There  is  a  deep  depression  for  ligamentous  attachment  on  the  inter- 
digital  side.  The  bone  contains  a  small  medullary  canal.  The  distal  end  unites 
^^dth  the  rest  of  the  bone  about  the  middle  of  the  second  year. 

The  third  phalanges  resemble  in  a  general  way  one-half  of  the  bone  of  the  horse. 
Each  has  four  surfaces.  The  dorsal  surface  is  marked  in  its  distal  part  by  a  shal- 
low groove,  along  which  there  are  several  foramina  of  considerable  size;  the 
posterior  one  of  the  series  is  the  largest,  and  conducts  to  a  canal  in  the  interior  of 
the  bone.      Distal  to  the  groove  the   surface  is  prominent,  rough,  and   porous. 


Fig.  lol. — Boxes  of  Distal  Part  of  Fore  Limb  of 
Ox;  Lateral  View. 
1,  Distal  end  of  metacarpal  bone;  2,  first  phalanx; 
3,  proximal  sesamoid  bone;  4,  second  phalanx;  5,  ex- 
tensor process  of  third  phalanx;  6,  dorsal  surface;  7, 
angle;    S,  distal  sesamoid  bone. 


Fio.  152. — Bones  of  Distal  Part  of  Fore  Limb  of 
Ox;  Volar  View. 
1,  Metacarpal  bone;    2,  proximal  sesamoid  bones; 
3,  first  phalanx;    4,  second  phalanx;    5,  distal  sesamoid 
bone;  6,  third  phalanx. 


Near  and  on  the  extensor  process  are  several  relatively  large  foramina.  The  slope 
of  the  surface  is  very  steep  posteriorly,  but  in  front  it  forms  an  angle  of  25  to  30  de- 
grees with  the  ground  plane.  The  articular  surface  is  narrow  from  side  to  side,  and 
slopes  downward  and  backward.  It  is  also  oblique  transversely,  the  interdigital 
side  being  the  lower.  It  is  adapted  to  the  distal  surface  of  the  second  phalanx,  with 
the  exception  of  a  facet  behind  for  the  distal  sesamoid.  The  extensor  process  is 
very  rough.  The  volar  surface  is  narrow  and  slightly  concave,  and  presents  two 
or  three  foramina  of  considerable  size.  It  is  separated  from  the  dorsal  surface 
by  a  border  which  is  sharp  in  front,  rounded  behind.  There  is  no  semilunar  crest, 
since  the  deep  flexor  tendon  is  attached  to  the  thick  posterior  border  of  the  volar 
surface.  The  interdigital  surface  is  smooth  and  grooved  below,  rough  and  porous 
above.  At  the  proximal  angle  it  is  perforated  by  a  large  foramen,  which  is  equiva- 
lent to  the  volar  foramen  of  the  horse  and  leads  to  a  cavity  in  the  middle  of  the  bone. 
The  surface  is  separated  by  a  rounded  border  from  the  dorsal  surface,  and  by  a  sharp 


BONES    OF   THE   PELVIC    LIMB  151 

edge  from  the  volar  surface.  The  angle  is  very  short  and  blunt,  and  there  is  no 
cartilage. 

Four  proximal  sesamoids  are  present,  two  for  each  digit.  They  are  much 
smaller  than  in  the  horse.  The  bones  of  each  pair  articulate  with  the  correspond- 
ing part  of  the  distal  end  of  the  large  metacarpal  bone  by  their  dorsal  surfaces, 
with  each  other  and  with  the  first  phalanx  by  small  facets. 

The  two  distal  sesamoids  are  short  and  their  ends  are  but  little  narrower  than 
the  middle. 

BONES  OF  THE  PELVIC  LIMB 

The  ilia  are  almost  parallel  to  each  other  and  are  also  less  oblique  with  regard 

to  the  horizontal  plane  than  in  the  horse.     They  are  relatively  small.     The  gluteal 

line  is  prominent  and  is  nearly  parallel  to  the  lateral  border;   it  joins  the  ischiatic 

spine.     A  rounded  ridge  separates  the  two  parts  of  the  pelvic  surface.     The  surface 


Tuber  sacrule 


Greater 
Lesfier  sciatic  Ischiatic  sciatic 

Tuber  ischii  notch  spine  notch 


]^^s 


Tuber 
coxce 


"  Sliajt  of  ilium 


Ischium 

^-  '  I  I         Acetabulum 

Ji'tili/i      Ohlurator     Puliis 
J'oramen 

Fig.  153. — Right  Os  Cox«  of  Ox;  Lateral  View. 
1,  Gluteal  line;    2,  fossa  acetabuli. 

for  articulation  with  the  sacrum  is  triangular.  The  tuber  sacralc  is  truncated,  does 
not  extend  as  high  as  the  vertebral  spines,  and  is  separated  from  the  opposite  angle 
by  a  wider  interval  than  in  the  horse.  The  tuber  coxse  is  relatively  large  and  prom- 
inent; it  is  not  so  oblique  as  in  the  horse,  and  is  wide  in  the  middle,  smaller  at  either 
end.     The  shaft  is  short  and  compressed  from  side  to  side. 

The  ischium  is  large.  Its  long  axis  is  directed  obliquely  upward  and  back- 
ward, forming  an  angle  of  about  45  to  50  degrees  with  the  horizontal  plane.  The 
transverse  axis  is  oblique  downward  and  inward  at  a  similar  angle,  so  that  this 
part  of  the  pelvic  floor  is  deeply  concave  from  side  to  side.  The  middle  of  the 
ventral  surface  bears  a  rough  ridge  or  imprint  for  muscular  attachment.  The 
ischiatic  spine  is  high  and  thin,  and  bears  a  series  of  almost  vertical  rough  lines 
laterally.  The  tuber  ischii  is  large  and  three-sided,  bearing  dorsal,  ventral,  and 
lateral  tuberosities.  The  ischial  arch  is  narrow  and  deep.  The  symphysis  bears  a 
ventral  ridge,  which  fades  out  near  the  ischial  arch. 

The  acetabular  branch  of  the  pubis  is  narrow,  and  is  directed  laterally  and  a 


152 


SKELETON    OF   THE    OX 


little  forward.  The  anterior  border  is  marked  by  a  transverse  groove  which  ends 
below  the  rough  ilio-pectineal  eminence.  The  symphyseal  branch  is  wide  and 
■/hin. 

The  acetabulum  is  smaller  than  in  the  horse.  The  rim  is  rounded  and  is 
usually  marked  by  two  notches.  One  of  these  is  postero-medial  and  is  narrow 
and  deep;  it  leads  to  the  deep  acetabular  fossa  and  is  often  almost  converted 
into  a  foramen  by  a  bar  of  bone.  The  other  notch  is  antero-medial,  small,  and 
sometimes  replaced  by  a  foramen  or  absent. 

The  obturator  foramen  is  large  and  elliptical.  Its  medial  border  is  thin  and 
sharp. 

Fusion  of  the  three  bones  occurs  at  seven  to  ten  months. 

The  pelvic  inlet  is  elliptical  and  is  more  oblique  than  in  the  horse.     In  a  cow 


Median 
Wing  of         crest  of     Tuber 
sacrum         sacrum     sacrale 


Ilio-pectineal  eminence 

Sym-physis  pubis 


Acetabulum 
Tuber  ischii 


Obturator  foramen 


Ventral  ridge 
Fig.  154. — Pelvic  Bones  of  Cow,  Viewed  from  in  Front  and  Somewhat  from  Below. 


of  medium  size  the  conjugate  diameter  is  about  nine  and  a  half  inches  (ca.  23  to  24 
cm.),  and  the  transverse  diameter  about  seven  inches  (ca.  18  cm.).  The  anterior 
end  of  the  symphysis  lies  in  a  transverse  plane  through  the  junction  of  the  third  and 
fourth  sacral  segments.  The  dorsal  wall  or  roof  is  concave  in  both  directions.  The 
ventral  wall  or  floor  is  deeply  concave,  particularly  in  the  transverse  direction. 
The  cavity  is  narrower  and  its  axis  is  inclined  strongly  upward  in  the  posterior  part. 
The  distance  between  the  acetabulum  and  the  tuber  coxae  is  only  a  little  (ca.  3  to 
4  cm.)  more  than  the  distance  between  the  former  and  the  tuber  ischii. 

The  femur  has  a  relatively  small  shaft,  which  is  cylindrical  in  its  middle,  pris- 
matic distally.  The  trochanter  minor  has  the  form  of  a  rough  tuberosity,  and  is 
situated  higher  up  than  in  the  horse  and  encroaches  on  the  posterior  surface.  The 
trochanteric  ridge  (Crista  intertrochanterica  posterior)  connects  it  with  the  tro- 


BONES   OF   THE   PELVIC    LIMB 


153 


chanter  major.  The  third  trochanter  is  absent.  The  supracondyloid  fossa  is 
shallow.  The  proximal  extremity  is  very  wide.  The  head  is  smaller  than  in  the 
horse,  and  the  articular  surface  extends  considerably  on  the  upper  surface  of  the 
neck.  The  fovea  capitis  is  a  small  depression  on  the  middle  of  the  head  for  the 
attachment  of  the  round  ligament.  The  neck  is  well  defined  except  above.  The 
trochanter  major  is  very  massive  and  is  undivided;  its  lateral  surface  is  very  rough. 


Fig.  1.55. — Right  Femur  of  Ox;  Poste- 
rior View. 
1,  Head;  2,  neck;  3,  trochanter  ma- 
jor; 4,  trochanteric  fossa;  5,  trochanter 
minor;  6,  nutrient  foramen;  7,  vascular 
groove;  8,  lateral  supracondyloid  crest; 
9,  supracondyloid  fossa;  10,  10',  medial 
and  lateral  condyles;  11,  11',  medial  and 
lateral     epicondyles;     12,    intercondyloid 


Fig.  1.50.— liuaii-  Ji.MLii  of  Ox; 
Lateral  View. 
Numbers  around  bone:  1, 
Head;  2,  neck;  3,  trochanter 
major;  4,  lateral  border;  5,  lateral 
supracondyloid  crest;  6,  supra- 
condyloid fossa;  7,  lateral  condyle; 
8,  trochlea.  Numbers  on  bone:  1, 
Eminence  for  attachment  of  gluteus 
profundus;  2,  lateral  epicondyle; 
3,  depression  for  origin  of  popliteus 
muscle;   4,  extensor  fossa. 


Fig.  157. — Left  Tibia  and  Prox- 
imal Part  of  Fibula  of  Ox; 
Posterior  View. 
Numbers  around  bones:  1,  1', 
Medial    and   lateral    condyles    of 
tibia;    2,    nutrient    foramen;    3, 
lateral  border;    4,  distal  extrem- 
ity; 5,  medial  malleolus;  6,  shaft 
of  fibula.    Numbers  on  bone:  1,  1', 
Tubercles  of  spine;  2,  intercondy- 
loid    fossa;     3,     muscular    lines. 
Arrow  indicates  groove  for  flexor 
digitalis  longus. 


The  trochanteric  fossa  is  deep,  but  does  not  extend  so  far  distally  as  in  the  horse. 
The  distal  end  presents  no  very  striking  differential  features,  but  the  ridges  of  the 
trochlea  are  less  oblique  than  in  the  horse,  and  converge  very  slightly  below.  The 
proximal  extremity  unites  with  the  shaft  at  about  three  and  one-half  years,  the 
distal  at  three  and  one-half  to  four  years. 

The  tibia  resembles  that  of  the  horse  rather  closely,  but  is  somewhat  shorter. 


154 


SKELETON    OF   THE    OX 


The  shaft  is  distinctly  curved,  so  that  the  medial  side  is  convex.  The  posterior 
surface  is  not  divided  into  two  areas,  and  the  linese  musculares  are  fewer  and  extend 
up  higher  than  in  the  horse.  The  articular  grooves  and  ridge  of  the  distal  end  are 
almost  sagittal  in  direction,  and  present  an  extensive  but  shallow  synovial  fossa. 
The  lateral  groove  is  separated  by  a  sharp  ridge  from  an  outer  area  which  is  for 
articulation  with  the  lateral  malleolus.  The  anterior  part  of  the  medial  malle- 
olus is  prolonged  do'vvnward  and  has  a  pointed  end.  The  groove  behind  it  is  broad 
and  well  defined.  Laterally  there  is  a  deep  narrow  groove  which  separates  two 
prominences.  The  proximal  extremity  fuses  with  the  shaft  at  three  and  one-half 
to  four  years,  the  distal  at  two  to  two  and  one-half  years. 

Tuber  calcis 


M.m. 


M.l. 


Mt.  5+4 


Fig.    15S. — Right    Tarsus    and    Adjacent    Boxes    of    Ox;        Fig.  1.59. — Right  Tarsus  and  Adjacent  Bones  op 
AIedial  View.  Ox;  Dorso-l.\teral  View. 

M.  m.,  Medial  malleolus;  .1/.  I.,  lateral  malleolus  (distal  end  of  fibula) ;  T,  tibia;  T.  t.,  tibial  tarsal  bone;  T.  /.,  fibulai 
tarsal  bone  (sustentaculum);  T.  c+-J,  fused  central  and  fourth  tarsal  bones;  T.  i,  first  tarsal  bone;  T.2+S,  fused 
second  and  third  tarsal  bones;  Mt.  2,  small  or  second  metatarsal  bone;  Mt.  S+  4.  large  metatarsal  or  fused  third  and 
fourth  metatarsal  bones;   1,  groove  for  tendon  of  flexor  digitalis  longus;   S,  groove  for  deep  flexor  tendon. 


The  fibula  usually  consists  of  the  two  extremities  onlj\  The  head  is  fused  with 
the  lateral  condyle  of  the  tibia  and  is  continued  by  a  small,  blunt-pointed  prolonga- 
tion below.  The  distal  end  remains  separate  and  forms  the  lateral  malleolus  (some- 
times called  the  os  malleolare).  It  is  quadrilateral  in  outline  and  compressed  from 
side  to  side.  The  proximal  surface  articulates  with  the  distal  end  of  the  tibia,  and 
bears  a  small  spine  which  fits  into  the  groove  on  that  bone.  The  distal  surface 
rests  on  the  fibular  tarsal,  and  the  medial  articulates  with  the  lateral  ridge  of  the 
tibial  tarsal  bone.     The  lateral  surface  is  rough  and  irregular. 

The  early  cartilaginous  fibula  is  complete,  but  later  the  shaft  is  reduced  to  the 
small  prolongation  noted  in  speaking  of  the  head  and  a  fibrous  cord  which  connects 
it  with  the  distal  end  (lateral  malleolus).  In  some  cases,  however,  the  upper  part 
undergoes  partial  ossification,  forming  a  slender  rod  which  is  usually  united  with 
the  lateral  border  of  the  tibia  and  is  joined  to  the  head  by  fibrous  tissue. 


BONES    OF  THE    PELVIC    LIMB 


155 


The  patella  is  long,  narrow,  and  very  thick.  The  free  surface  is  strongly  con- 
vex and  very  rough  and  irregular.  The  articular  surface  is  convex  from  side  to 
side  and  nearly  straight  in  the  vertical  direction.  The  large  prominence  on  the 
medial  side  for  the  attachment  of  the  fibro-cartilage  allows  prompt  determination 
of  the  side  to  which  the  bone  belongs.     The  apex  is  more  pointed  than  in  the  horse. 

The  tarsus  consists  of  five  pieces;  the  central  and  fourth  and  the  second  and 
third  tarsal  bones  are  fused. 

The  tibial  tarsal  bone  is  relatively  long  and  narrow,  and  is  somewhat  flattened 
from  before  backward.  It  bears  a  trochlea  at  either  end.  The  groove  and  ridges 
of  the  proximal  trochlea  are  not  spiral,  but  almost  sagittal;  the  lateral  ridge  is  the 
wider,  and  articulates  with  both  tibia  and  fibula.  The  distal  trochlea  consists 
of  two  condyles  divided  by  a  groove,  and  articulates  with  the 
combined  central  and  fourth  tarsals.  The  plantar  surface  bears 
a  large  oval  facet  for  articulation  with  the  fibular  tarsal;  this 
occupies  most  of  the  surface,  and  is  convex  and  grooved  from 
above  downward.  The  lateral  surface  presents  two  facets  for 
articulation  with  the  fibular  tarsal,  and  is  excavated  and  rough 
elsewhere.  The  medial  surface  bears  a  tuberosity  at  its  upper 
part,  and  is  flattened  below. 

The  fibular  tarsal  ])one  is  longer  and  more  slender  than  in 
the  horse.  The  distal  part  of  the  body  is  compressed  laterally, 
and  bears  a  projection  in  front  which  articulates  with  the  lateral 
malleolus.  The  tuber  calcis  is  marked  posteriorly  by  a  wide 
shallow  groove,  which  is  coated  with  cartilage  in  the  fresh  state. 

The  central  and  fourth  tarsals  are  fused  to  form  a  large 
bone  (Os  centrotarsale  quartum,  scapho-cuboid),  which  extends 
across  the  entire  width  of  the  tarsus  and  articulates  with  all  of 
the  other  bones.  The  greater  part  of  the  proximal  surface  is 
molded  on  the  distal  trochlea  of  the  tibial  tarsal,  and  its  medial 
part  rises  high  above  the  rest  posteriorly.  Laterally  there  is  a 
narrow,  undulating  surface  for  articulation  with  the  distal  end 
of  the  fibular  tarsal  bone.  The  plantar  surface  bears  two  tuber- 
osities, of  which  the  lateral  one  is  rounded,  the  medial  more 
prominent  and  narrower. 

The  first  tarsal  bone  is  quadrilateral  and  small.  It  articu- 
lates with  the  central  above,  the  metatarsus  below,  and  the 
second  tarsal  in  front. 

The  second  and  third  tarsals  are  fused  to  form  a  rhomboid 
piece.  The  proximal  surface  is  concavo-convex,  and  articulates 
with  the  central  component.  The  distal  surface  is  undulating 
and  rests  on  the  metatarsus.  The  lateral  surface  bears  a  small 
facet  in  front  for  the  fourth  tarsal  component,  and  the  plantar 
surface  a  very  small  one  for  the  first  tarsal  bone. 

The  large  metatarsal  bone  is  about  one-seventh  (ca.  3  cm.)  longer  than  the 
corresponding  metacarpal.  Its  shaft  is  compressed  transversely  and  is  distinctly 
four-sided.  The  groove  on  the  dorsal  surface  is  deep  and  wide.  The  plantar 
surface  is  marked  by  variable  grooves.  The  proximal  foramen  on  this  surface  does 
not  perforate  the  shaft,  but  passes  obliquely  through  the  extremity,  opening  on  the 
posterior  part  of  its  proximal  surface.  The  medio-plantar  angle  of  the  proximal 
end  bears  a  facet  for  articulation  with  the  small  metatarsal  bone. 

The  small  metatarsal  bone  is  a  quadrilateral  disc  a  little  less  than  an  inch  in 
width  and  height.  Its  anterior  face  bears  a  facet  for  articulation  with  the  large 
metatarsal  bone. 


Fig.  160. — L  a  r  g  e 
Metatarsal  Bone 
OF  Ox;  Dorsal 
View. 

1,  Vascular  groove; 
2,  foramen;  3,  3',  con- 
dyles. 


156  SKELETON    OF   THE    SHEEP 

The  large  metatarsal  bone  is  usually  regarded  as  consisting  of  the  fused  third  and  fourth 
metatarsal  bones,  and  the  small  bone  as  the  second  metatarsal.  The  medullary  cavity  is  subdivided 
like  that  of  the  large  metacarpal  bone.  Some  anatomists,  however,  consider  that  the  ridges  at 
the  upper  end  of  each  border  represent  the  second  and  fifth  metatarsals  (Rosenberg  and  Retterer). 
On  this  basis  the  small  bone  would  be  the  first  metatarsal. 

The  phalanges  and  sesamoids  resemble  those  of  the  thoracic  limb  so  closely 
as  to  render  separate  description  unnecessary. 


SKELETON  OF  THE  SHEEP 

VERTEBRAL  COLUMN 

The  vertebral  formula  may  be  given  as  C7Ti3L6_7S4Cyi6-i8,  but  it  should  be 
noted  that,  except  in  the  cervical  region,  variation  in  number  is  common. 

It  is  not  very  rare  to  find  twelve  thoracic  and  seven  lumbar,  or  an  ambiguous  intermediate 
vertebra.  More  commonly  there  are  seven  lumbar  vertebriE  without  reduction  in  the  thoracic 
region.  In  some  cases  there  are  fourteen  thoracic  and  five  or  six  lumbar  vertebrae,  and  Lesbre 
records  a  case  in  which  twelve  thoracic  and  seven  lumbar  were  present.  In  some  cases  the  fourth 
sacral  vertebra  remains  separate,  and  in  others  the  first  coccygeal  unites  with  the  sacrum,  although 
the  fusion  here  is  rarely  complete.  Nathusius  states  that  the  number  of  coccygeal  vertebrae 
varies  from  tliree  to  twenty-four  or  more. 

The  cervical  vertebrae  are  relatively  longer  than  those  of  the  ox.  The  atlas 
differs  chiefly  in  that  the  prominence  on  the  dorsal  arch  is  much  less  developed. 
The  anterior  articular  cavities  are  often  separated  by  a  central  ridge.  The  wings 
are  produced  to  form  blunt  points  behind.  The  spinous  process  of  the  axis  is  not 
enlarged  posteriorly;  those  of  the  succeeding  vertebrae  are  less  developed  than  in 
the  ox;  they  increase  in  length  from  the  third  to  the  last.  The  ventral  spines  are 
rudimentar5\     The  arches  are  separated  dorsally  by  interarcuate  spaces. 

The  thoracic  vertebrae  are  usually  thirteen  in  number,  but  fourteen  may  be 
present,  or,  more  rarely,  only  twelve.  Their  bodies  are  relatively  wider  and  less 
constricted  than  those  of  the  ox,  and  their  extremities  are  not  so  strongly  curved, 
especially  toward  the  end  of  the  series.  The  intervertebral  foramina  are  larger,  in 
correlation  with  the  absence  of  the  foramina  which  usually  occur  in  the  arches  of 
these  vertebrae  in  the  ox. 

The  limibar  vertebrae  number  six  or  seven,  the  former  being  a  little  more  fre- 
quent than  the  latter.  It  is  not  common  to  find  the  number  reduced  to  five.  In 
some  cases  there  is  an  ambiguous  vertebra  at  the  junction  of  the  thoracic  and  lum- 
bar regions.  The  bodies  are  more  flattened  dorso-ventrally  than  those  of  the  ox; 
their  anterior  ends  are  somewhat  concave  transversely,  and  the  posterior  ends  are 
almost  flat.  The  anterior  articular  processes  are  strongly  curved  and  overlap  the 
posterior  ones.     The  transverse  processes  curve  forward  and  have  expanded  ends. 

The  sacrum  consists  ordinarily  of  four  segments,  but  the  last  vertebra  may  re- 
main separate  or  undergo  orfly  partial  fusion.  There  is  no  vascular  groove  on  the 
pelvic  surface.  The  spines  are  not  fused,  ^vith  the  exception  of  the  flrst  and  second, 
which  may  be  partially  united.  The  transverse  processes  of  the  last  segment  are 
distinct  and  outstanding. 

The  coccygeal  vertebrae  vary  in  number  from  three  (in  short-tailed  sheep)  to 
twenty-four  or  more.  The  bodies  have  no  hemal  processes  on  the  ventral  surface. 
The  transverse  processes  are  long  and  thin  and  project  backward. 


THE  RIBS 
The  ribs  usually  number  thirteen  pairs,  but  the  occurrence  of  fourteen  pairs  is 
not  at  all  unconmion.     The  thirteenth  rib  is  floating  and  has  a  cartilage  about  an 


THE    STERNUM — THE    SKULL  157 

inch  long.  The  fourteenth  rib,  when  present,  is  also  floating.  As  compared  with 
those  of  the  ox,  they  are  narrower  and  are  more  strongly  curved  in  the  anterior  part 
of  the  series.  The  lateral  surface  is  in  general  smooth  and  rounded.  The  second 
to  the  eleventh  form  diarthroses  with  their  cartilages. 

The  thirteenth  rib  may  be  more  or  less  rudimentary  on  one  side  or  both,  and  may  be  fused 
with  the  corresponding  vertebra;  the  latter  may,  therefore,  be  ambiguous  in  character. 

THE  STERNUM 
The  sternum  resembles  in  general  that  of  the  ox.  The  number  of  segments 
may  be  reduced  to  six,  and  the  primitive  division  of  the  next  to  the  last  sternebra 
into  two  lateral  halves  may  persist  for  a  long  time.  The  first  segment  is  cylindrical, 
with  enlarged  ends;  the  second  and  third  are  wide  and  flat;  the  last  is  long  and  nar- 
row. 

THE  SKULL 

The  more  important  differences  in  the  skull  of  the  sheep  as  compared  with 
that  of  the  ox  are  in  regard  to  the  cranium.  Viewed  from  above,  the  cranium  is 
irregularly  hexagonal  in  outline;  it  is  widest  in  the  frontal  region,  between  the 
posterior  parts  of  the  orbits,  and  narrows  greatly  both  anteriorly  and  posteriorly. 
In  profile  the  roof  of  the  cranium  is  strongly  convex;  the  highest  part  of  the  curve 
coincides  with  the  greatest  width,  and  the  posterior  part  slopes  at  an  angle  of  about 
45  degrees  with  the  basal  plane. 

The  occipital  bone  forms  all  of  the  nuchal  surface  of  the  cranium,  except  a 
small  lateral  area  occupied  by  the  mastoid  part  of  the  temporal  bone.  A  narrow 
part  (about  1.5  cm.  in  width)  enters  into  the  formation  of  the  roof  of  the  cranium 
also;  it  joins  the  parietal  bones  at  a  transverse  suture.  The  parietal  and  nuchal 
surfaces  are  separated  by  a  rough  transverse  ridge,  the  central  part  of  which  is 
united  below  with  the  external  occipital  protuberance,  to  which  the  ligamentum 
nuchse  is  attached.  The  mastoid  foramen  is  situated  between  the  lateral  border 
and  the  petro-mastoid  part  of  the  temporal  bone.  The  paramastoid  process  is 
grooved  laterally,  has  a  concave  anterior  border,  and  tapers  to  a  blunt  point.  The 
basilar  part  is  wide;  the  tubercles  at  its  junction  with  the  sphenoid  are  placed 
laterally,  and  are  broad  and  short. 

The  sphenoid  bone  resembles  that  of  the  ox.  The  posterior  wall  of  the  deep 
hypophyseal  or  pituitary  fossa  is  formed  by  a  plate  (Dorsum  sellae)  which  is  di- 
rected forward  and  upward,  and  bears  a  projection  (Processus  clinoideus  posterior) 
at  each  side  of  its  upper  part.  The  sphenoidal  sinus  is  commonly  absent  or  rudi- 
mentary. 

The  ethmoid  bone  resembles  that  of  the  ox. 

The  parietal  bone  fuses  soon  after  birth  with  its  fellow  and  with  the  inter- 
parietal. From  this  union  there  result  a  central  quadrilateral  curved  plate  which 
forms  part  of  the  roof  of  the  cranium,  and,  separated  from  it  by  a  curved  line,  a 
narrower  lateral  part,  which  extends  forward  on  either  side  as  part  of  the  medial 
wall  of  the  temporal  fossa.  The  frontal  sinus  does  not  extend  into  the  parietal  bone. 
There  is  no  internal  occipital  protuberance. 

The  frontal  bone  is  relatively  less  extensive  than  in  the  ox.  The  naso-frontal 
part  is  strongly  curved,  but  varies  considerably  in  contour  in  different  breeds.  In 
horned  breeds  the  processus  cornus  projects  from  the  lateral  part  of  the  external 
surface  a  little  (ca.  1.5  cm.)  behind  a  transverse  plane  through  the  posterior  margin 
of  the  orbit.  The  process  varies  in  size  and  shape,  and  does  not  contain  an  extension 
of  the  frontal  sinus.  In  other  cases  there  is  a  rounded  tuberosity  or  a  slight  rough- 
ened elevation.  The  supraorbital  foramen  is  further  forward  than  in  the  ox,  being 
just  behind  a  transverse  plane  through  the  middle  of  the  orbit;  it  is  a  little  nearer 


158 


SKELETON    OF   THE    SHEEP 


to  the  orbital  margin  than  to  the  median  line.  The  groove  which  leads  forward 
from  it  is  often  rather  faint.  The  orbital  part  is  deeply  concave.  The  infraorbital 
canal  opens  on  the  medial  wall  of  the  orbit  as  in  the  ox.  The  frontal  sinus  extends 
backward  to  a  transverse  plane  through  the  posterior  part  of  the  temporal  con- 
dyle, and  forward  to  one  through  the  anterior  margin  of  the  orbit. 

The  temporal  bone  consists  of  distinct  squamous,  tympanic,  and  petro-mastoid 
parts.  The  squamous  part  in  general  resembles  that  of  the  ox,  but  has,  like  that  of 
the  horse,  a  notch  through  which  the  external  acoustic  process  protrudes.  The  root 
of  the  zygomatic  process  is  perforated  by  a  foramen  which  opens  ventrally  behind 
the  postglenoid  process,  in  front  of  the  chief  external  opening  of  the  temporal  canal. 
The  latter  extends  upward  and  backward  between  the  petro-mastoid  and  squamous 
parts  and  the  parietal  l:)one,  and  opens  into  the  cranial  cavity  in  front  of  the  apex 
of  the  petrous.     The  tympanic  part  includes  the  external  acoustic  process,  the  bulla 


Fig.  161. — Skull  of  Sheep;  Lateral  View. 
A,  Occipital  bone;  B,  parietal  bone;  C,  squamous  temporal  bone;  D,  frontal  bone;  S,  nasal  bone;  F,  lacrimal  bone; 
G,  malar  bone;  H,  maxilla;  I,  premaxilla;  J,  mandible;  K,  perpendicular  part  of  palatine  bone;  L,  hyoid  bone;  1, 
occipital  condyle;  2,  paramastoid  process;  3,  mastoid  process;  4,  meatus  acusticus  externus;  5,  bulla  ossea;  6,  zygo- 
matic process  of  temporal  bone;  7,  condyle  of  mandible;  S,  coronoid  process;  9,  supraorbital  process;  10,  processus 
cornus;  11,  11',  openings  of  supraorbital  canal;  12,  ethmoidal  foramen;  13,  optic  foramen;  14,  fossa  sacci  lacrimalis; 
15,  bulla  lacrimalis;   16,  external  lacrimal  fossa;    17,  facial  tuberosity;   18,  infraorbital  foramen;    19,  mental  foramen. 


ossea,  and  the  muscular  process;  the  first  resembles  that  feature  in  the  horse,  the 
others  those  of  the  ox,  but  the  cavity  of  the  bulla  is  undivided.  The  cerebral  sur- 
face of  the  petrous  part  presents  the  floccular  fossa  on  its  upper  part,  and  a  round 
eminence  behind  the  internal  acoustic  meatus. 

The  bones  of  the  face  present,  aside  from  the  difference  in  size,  few  important 
special  features. 

In  regard  to  the  maxilla  it  may  be  noted  that  the  junction  with  the  lacrimal  and 
malar  is  less  oblique  than  in  the  ox,  since  the  facial  parts  of  these  bones  are  quadri- 
lateral and  not  produced  to  a  point  anteriorly.  The  facial  tuberosity  and  the  infra- 
orbital foramen  are  a  little  further  back,  and  lie  about  over  the  second  and  fourth 
cheek  tooth  respectively.  The  palatine  sinus  extends  from  a  point  opposite  to  the 
fir.st  cheek  tooth  backward  to  the  transverse  palatine  suture.  The  defect  (in  the 
dry  skull)  in  its  nasal  wall  is  quite  small — in  marked  contrast  to  that  of  the  ox — 


THE    SKULL 


159 


Occipital  huno 

\ 


Temporal  crest 
( 'oronoid  process 

Frontal  bone 


Orbit 

Supraorbital 
foramen 


Malar  bone 
Lacrimal  bone 


since  the  basal  lamella  of  the  ventral  turbinate  bone  curves  ventro-medially,  joins 
the  palatine  bone,  and  is  separated  only  by  a  narrow  hiatus  from  the  nasal  plate  of 
the  palatine  process  of  the  maxilla.  The  anterior  palatine  foramen  is  at  the  trans- 
verse palatine  suture.  The  anterior  end  of  the  palatine  process  tapers  to  a  point. 
The  maxillary  sinus  resembles  that  of  the  ox,  but  is  relatively  small. 

The  premaxilla  has  a  narrow  and  pointed  body.  The  palatine  process  is  ex- 
tremely narrow  in  front  and  is  grooved  laterally.  The  palatine  fissure  is  long  and 
narrows  to  a  very  acute  angle  behind. 

The  palatine  bone  resembles  that  of  the  ox,  but  there  is  no  air-cavity  in  its 
horizontal  part.     The  spheno- 
palatine foramen  is  large  and  Occipital  hum        Parietal  bom 
oval. 

The  pterygoid  bone  is 
very  broad  above  and  narrow 
below,  where  it  ends  in  a  sharp- 
pointed  hamulus. 

The  nasal  bone  tapers  to 
a  point  at  its  anterior  end, 
which  is  not  notched. 

The  facial  part  of  the 
lacrimal  bone  has  an  elongated 
quadrilateral  outline;  in  front 
of  the  orbit  it  forms,  with  the 
adjacent  part  of  the  malar,  the 
external  lacrimal  fossa  (Fossa 
lacrimalis  externa)  which 
lodges  a  cutaneous  cul-de-sac 
known  as  the  infraorbital  or 
lacrimal  pouch.  The  bone  here 
may  be  more  or  less  cribriform. 
The  lacrimal  bulla  is  relatively 
small,  is  usually  cribriform, 
and  has  a  pointed  posterior 
end;  the  maxillary  sinus  ex- 
tends into  it.  The  orbital 
margin  forms  a  distinct  promi- 
nence, and  behind  the  latter  is 
the  fossa  for  the  lacrimal  sac. 

The  facial  part  of  the 
malar  bone   is  extensive  and 

quadrilateral.  Its  upper  part  concurs  in  the  formation  of  the  external  lacrimal 
fossa;  this  area  is  limited  below  by  a  curved  crest  which  continues  backward  on 
the  zygomatic  process.     The  latter  divides  into  two  branches,  as  in  the  ox. 

The  turbinates  and  the  vomer  resemble  those  of  the  ox. 

The  mandible  differs  from  that  of  the  ox  chiefly  in  that  the  ventral  border  of 
the  ramus,  from  the  body  to  the  angle,  is  only  slightly  curved. 

On  account  chiefly  of  the  limited  extent  of  the  frontal  sinuses,  the  cranial 
cavity  corresponds  to  the  external  form  of  the  cranium  more  closely  than  is  the  case 
in  the  ox.  It  is  ovoid,  and  is  much  longer  relatively,  but  has  a  much  shorter  dorso- 
ventral  diameter  than  that  of  the  ox.  The  parietal  bone  forms  a  distinct  ridge  on 
the  lateral  wall  between  the  cerebral  and  cerebellar  compartments,  but,  on  the  other 
hand,  the  petrous  temporal  projects  very  little  into  the  cavity. 

The  nasal  cavity  resembles  that  of  the  ox,  but  is  relatively  narrow  (especially 
anteriorly),  and  there  is  no  large  hiatus  in  the  nasal  plate  of  the  maxilla. 


Facial  tuberosity 
Maxilla 

Nasal  hone 

Nasal  process  of  pre- 
maxilla 

Palatine  process  of  pre- 
maxilla 
Palatine  fissure 

of  premaxilla 


Incisor  teeth 


Fig.  162. — Skull  of  Sheep;  Dorsal  View. 


160  SKELETON    OF   THE    SHEEP 


BONES  OF  THE  THORAaC  LIMB 

The  scapula  differs  chiefly  from  that  of  the  ox  in  the  following  points :  The  ver- 
tebral border  is  longer  and  the  neck  narrower.  The  spine  is  less  sinuous.  The 
glenoid  extremity  is  relatively  long,  since  the  tuber  scapulae  is  connected  with  the 
rim  of  the  glenoid  cavity.     The  subscapular  fossa  is  more  extensive. 

The  humerus  is  relatively  longer  and  more  slender  than  that  of  the  ox.  The 
anterior  part  of  the  lateral  tuberosity  is  blunt  and  less  incurved,  while  the  posterior 
part  is  small.  The  deltoid  tuljerosity  is  nearer  to  the  proximal  end  and  is  less 
prominent. 

The  bones  of  the  forearm  are  relatively  longer  than  those  of  the  ox.  The 
radius  is  a  little  more  curved  than  that  of  the  ox,  and  its  dorsal  surface  is  more 
regularly  rounded.  The  shaft  of  the  ulna  is  more  slender,  especially  in  its  distal 
half;  its  fusion  with  the  radius  occurs  later  and  is  usually  much  less  extensive  than 
in  the  ox. 

The  carpal  bones  resemble  those  of  the  ox  except  in  size.  The  accessory  is 
long  and  less  tuberous. 

The  large  metacarpal  bone  (Mc.  3  +  4)  is  long  and  slender.  The  lateral  small 
metacarpal  bone  (Mc.  5)  is  often  absent  or  is  represented  by  a  ridge  on  the  large 
metacarpal. 

The  phalanges  of  the  chief  digits  are  relatively  long  and  narrow.  The  third 
phalanx  in  particular  is  much  flattened  on  its  abaxial  side,  so  as  to  form  a  prominent 
dorsal  border.  Of  the  proximal  sesamoids,  the  abaxial  ones  are  compressed  from 
side  to  side,  and  the  axial  ones  from  before  backward.  The  flexor  surface  of  the 
distal  sesamoids  forms  a  shallow  groove,  not  divided  by  a  ridge.  The  accessory 
digits  usually  have  no  phalanges. 

BONES  OF  THE  PELVIC  LIMB 

The  OS  coxae  differs  greatly  from  that  of  the  ox.  The  long  axis  of  the  ilium 
is  almost  in  a  line  with  that  of  the  ischium.  The  gluteal  line  appears  as  a  ridge 
which  is  nearly  parallel  with  the  lateral  border.  The  tuber  coxa  is  only  slightly 
thickened,  and  the  tuber  sacrale  is  pointed.  The  crest  is  concave  medially,  convex 
laterally.  The  shaft  is  relatively  long  and  is  flattened  laterally.  The  superior 
ischiatic  spine  is  low  and  everted.  The  pubis  resembles  that  of  the  ox,  but  its  an- 
terior border  (pecten)  is  thin  and  sharp.  The  ischium  slopes  downward  and  back- 
ward, and  forms  a  much  larger  angle  with  its  fellow  than  in  the  ox.  The  lesser 
sciatic  notch  is  very  shallow.  The  tuber  ischii  is  flattened  and  everted;  it  bears  a 
long,  blunt-pointed  lateral  process,  and  a  verj''  short  and  blunt  dorsal  prominence. 
There  is  a  very  low  ventral  ridge  on  the  symphysis.  The  latter  is  not  usually  com- 
pletely ossified,  even  in  old  animals.  The  acetabulum  is  further  back  than  in  the 
ox,  and  is  relatively  larger  and  deeper;  it  has  a  deep  notch  posteriorly.  The 
pelvic  inlet  is  very  oblique,  so  that  a  vertical  plane  from  the  anterior  end  of  the 
symphysis  cuts  the  first  coccygeal  vertebra.  The  brim  is  elliptical;  the  conjugate 
cUameter  is  about  five  inches  (ca.  12  cm.),  and  the  transverse  about  three  and  a 
half  to  four  inches  (ca.  9.5  cm.).  The  floor  of  the  pelvic  cavity  is  wide  and  shallow 
as  compared  with  the  ox,  and  the  pelvic  axis  inclines  downward  posteriorly. 

The  shaft  of  the  femur  is  slightly  curved,  the  convexity  being  anterior.  A  dis- 
tinct line  separates  the  lateral  and  posterior  surfaces.  The  supracondyloid  fossa 
is  very  shallow.  The  head  has  a  shallow  fovea  and  the  neck  is  distinct.  The  tro- 
chanter major  is  little  higher  than  the  head.  The  ridges  of  the  trochlea  are  similar 
and  parallel,  but  slightly  oblique. 

The  tibia  is  long  and  slender,  but  otherwise  resembles  that  of  the  ox.  The 
fibula  has  no  shaft,  and  its  proximal  end  is  represented  by  a  small  prominence  be- 


SKELETON    OF   THE    PIG VERTEBRAL    COLUMN 


161 


low  the  lateral  margin  of  the  lateral  condyle  of  the  tibia;  the  distal  end  forms  the 
lateral  malleolus,  as  in  the  ox. 

The  patella  is  relatively  longer  and  narrower  than  that  of  the  ox. 

The  tarsal  bones  resemble  those  of  the  ox  except  in  size. 

The  metatarsal  and  digital  bones  present  special  characters  similar  to  those  of 
the  corresponding  part  of  the  thoracic  limb. 


SKELETON  OF  THE  PIG 

VERTEBRAL  COLUMN 

The  vertebral  formula  is  C7Ti4_i5L6-7S4Cy2o-23. 

The  cervical  vertebrae  are  short  and  wide.  The  bodies  are  elliptical  in  cross- 
section,  the  long  diameter  being  transverse.  The  anterior  articular  surfaces  are 
slightly  convex  from  side  to  side  and  concave  dorso-ventrally ;   the  posterior  ones 


Fig.  163. — Skeleton  of  Pig;  Lateral  View. 
o.  Cranium;  b,  maxilla;  c,  mandible;  1H.-7H.,  cervical  vertebrae;  IR.iv.,  first  thoracic  vertebra;  13  Rav.,  thir- 
teenth thoiacic  vertebra  (uext  to  last);  IL.,  first  lumbar  vertebra;  6L.,  sixth  lumbar  vertebra  (next  to  last  usually); 
A'.,  sacrum;  S.,  coccygeal  vertebrse;  IR.,  first  rib;  I4R.,  last  rib;  R.hi.,  costal  cartilages;  St.,  sternum;  d,  supraspin- 
ous fossa;  rf',  infraspinous  fossa;  i,  spine  of  scapula;  ^,  neck  of  scapula;  e,  humerus;  3,  head  of  humerus;  4,  tuberosities 
of  humerus;  5,  deltoid  tuberosity;  6,  lateral  epicondyle  of  humerus;  /.radius;  g,  ulna;  7,  olecranon;  /j,  carpus:  18-26, 
carpal  bones;  i-i"",  metacarpus;  Z;-^"",  proximal  phalanges;  Z-Z"",  middle  phalanges;  m-m"",  distal  phalanges;  n,  o, 
sesamoids;  p,  ilium;  5,  tuber  coxse;  S,  tuber  sacrale;  1  ,  superior  ischiatic  spine;  g,  ischium;  ??,  tuber  ischii;  r,  pubis; 
12,  acetabulum;  s,  femur;  13,  trochanter  major;  14,  trochanter  minor;  lo,  lateral  epicondyle;  t.  patella;  u.  tibial- 
is, crest  of  tibia;  i 7,  lateral  condyle  of  tibia;  w,  fibula;  m),  tarsus;  ^^-37,  tarsal  bones;  ^6',  tuber  calcis.  (After  Ellen- 
berger,  in  Leisering's  Atlas). 


are  slightly  concave.  A  ventral  spine  is  not  present.  The  arches  are  wide  trans- 
versely, but  the  laminae  are  narrow,  so  that  a  considerable  interval  (Spatium  inter- 
arcuale)  separates  adjacent  arches  dorsally.  The  pedicles  are  perforated  by  a 
foramen  in  addition  to  the  usual  intervertebral  foramina.  The  transverse  processes 
divide  into  two  branches,  both  of  which  increase  in  size  from  the  third  to  the  sixth. 
The  dorsal  branch  projects  outward  and  backward;  it  is  short  and  is  thickened  at 
its  free  end.  The  other  branch  is  a  quadrilateral  plate  cUrected  ventrally;  each 
overlaps  the  succeeding  one  to  a  small  extent,  and  the  series  forms  the  lateral 
boundary  of  a  deep  and  wide  ventral  groove.  The  spines  increase  in  height  from  the 
11 


162 


SKELETON    OF   THE   PIG 


third  to  the  last;  the  anterior  ones  are  incHned  backward,  the  posterior  ones  for- 
ward. The  last  cervical  is  recognized  by  the  great  length  of  its  spine  (ca.  10  cm. 
in  the  adult),  the  absence  of  the  ventral  plate  of  the  transverse  process,  and  the  flat- 
ness of  the  body,  which  bears  a  pair  of  small  facets  on  its  posterior  margin  for  the 


r 


.  S" 


■?:i 


Fig.  164. — Fouhth  Cervical 
Vertebra  of  Pig;  Lat- 
eral View. 

1,  1',  Anterior  and  pos- 
terior ends  of  body;  2,  arch; 
3,  foramen  of  arch;  4,  anterior 
articular  process;  5,  spinous 
process;  6,  ventral  branch  of 
transverse  process. 


— Sixth  Cervical  Vertebra 

OF  Pig;  Anterior  ^'IEW. 

1,    Body;     2,    transverse    process; 

foramen   transversarium ;     4,    addi- 

nal  foramen  of  arch;  5,  articular  proc- 

;    6,  arch;   7,  spinous  process. 


^■» 

1^.  5' 

^^ 

3 

^,^ 

1 

4—^ 

^'^ 

1-^^^^ 

) 

Fig.   166.— Seventh 

Cervical 

Vertebra  op 

Pig 

Lateral 

View. 

1,  1',  Anterior  and  posterior 
ends  of  body;  2,  facet  for  head  of 
first  rib;  3,  arch;  4,  transverse 
process;  5,  5',  articular  processes; 
6,  spinous  process;  1  (number  on 
bono),  foramina  of  arch. 


Fig.  1()7. — Atlas  of  Pig;  Dorsal  View. 
1,  Dorsal    tuberosity;    2,    alar  foramen;    3,  wing; 
4,  intervertebral  foramen;    5,  dorsal  arch;    6,  ventral 
tubercle;   7,  surface  for  dens. 


-Atlas  of  Pig;  Anterior  View. 
1,  Dorsal  tuberosity;  2,  wing;   3,  alar  foramen;  4,  ante- 
rior articular  cavity;   5,  ventral  tubercle. 


heads  of  the  first  ribs.     It  has  foramina  transversaria,  and  usually  two  foramina  in 
each  side  of  the  arch. 

The  dorsal  tuberosity  of  the  atlas  is  large.  The  ventral  tubercle  is  long,  com- 
pressed laterally,  and  projects  back  under  the  axis.  The  wing  is  flattened  and 
bears  a  posterior  tuberosity.     The  foramen  transversarium  passes  through  the 


VERTEBRAL   COLUMN 


163 


Fig.  169. — Axis  of  Pig;  Lateral  View. 
1,    Dens;     2,   2',    anterior   and   posterior  articular 
processes;  3,  posterior  end  of  body;  4,  transverse  proc- 
ess;    5,  foramen    transversarium ;  6,  arch;  7,  spinous 
process.     Arrow  indicates  intervertebral  foramen. 


Fig.  170. — Axis  op  Pig;  Anterior  View. 
1,    Dens;     2,   2',   anterior   and    posterior  articular 
processes;  3,  foramen   transversarium;   4,   arch;  o,  spi- 
nous process. 


posterior  border  of  the  wing  to  the  fossa  under  the  latter, 
it  is  sometimes  very  small  or  absent.  The 
sides  of  the  vertebral  foramen  bear  two  lat- 
eral projections  which  partially  divide  it 
into  a  ventral  narrow  part,  which  receives 
the  dens,  and  a  dorsal  larger  part  for  the 
spinal  cord.  In  the  fresh  state  the  division 
is  completed  by  the  transverse  ligament, 
which  is  attached  to  the  projections. 

The  axis  has  a  large  spinous  process, 
which  is  directed  upward  and  backward. 
The  dens  is  a  thick  cylindrical  rod.  The 
transverse  process  is  very  small  and  the 
foramen  transversarium  is  often  incom- 
plete. 

The  thoracic  vertebrae  are  commonly 
fourteen  or  fifteen  in  number.  Their 
bodies  are  relatively  long,  constricted  in 
the  middle,  and  without  ventral  spines. 
Their  extremities  are  elliptical,  depressed 
in  the  middle,  and  prominent  at  the  peri- 
phery. The  arch  is  perforated  by  a  fora- 
men on  each  side  and  in  most  of  the  series 
there  is  also  a  foramen  in  the  posterior 
part  of  the  root  of  the  transverse  process 
which  communicates  with  the  former  or 
with  the  posterior  intervertebral  foramen. 
Sometimes  there  is  a  foramen  in  the  an- 
terior part  of  the  process  also.  There  are 
mammillary  processes  except  on  the  first 
two ;  in  the  posterior  five  or  six  vertebrae 
they  project  from  the  anterior  articular 
processes.  The  facet  for  the  tubercle  of  the 
rib  is  absent  or  fused  with  that  for  the 
head  in  the  last  five  or  six.    The  last  trans- 


(1  is  not  visi1)lc  dorsally; 


Fig.  171. — Second  and  Third  Thoracic  Vertebr.e 
OF  Pig;  Lateral  View. 
Numbers  around  bones:  1,  1',  Anterior  and  poster- 
ior ends  of  bodies ;  2,  cavities  for  heads  of  ribs ;  3,  3',  artic- 
ular process;  4,  facet  for  head  of  rib;  5,  spinous  process. 
Numbers  on  bones:  1,  1',  Foramina  of  arches;  2,  2', 
transverse  procesaes;  3,  3',  facets  for  tubercles  of  ribs. 


Jg4  SKELETON    OF   THE    PIG 

verse  process  is  lumbar  in  character,  plate-like,  and  about  an  inch  (2  cm.)  long. 
Small  accessory  processes  occur  in  the  posterior  part  of  the  region.  The  first 
spinous  process  is  broad,  very  high,  and  inclined  a  little  forward.  The  others  di- 
minish very  gradually  in  length  to  the  tenth,  beyond  which  they  are  about  equal. 
The  seconcl  to  the  ninth  are  inclined  backward,  the  tenth  is  vertical  (anticlinal),  and 
the  rest  incline  forward.  The  width  decreases  decidedly  from  the  fourth  to  the 
tenth,  beyond  which  there  is  a  gradual  increase.  The  summits  are  slightly  enlarged 
and  lie  almost  in  a  straight  line. 

The  lumbar  vertebrae  are  six  or  seven  in  number.  The  bodies  are  longer  than 
in  the  thoracic  region  and  bear  a  ventral  crest.  They  become  wider  and  flatter 
in  the  posterior  part  of  the  series.  The  arches  are  deeply  notched,  and  are  separated 
by  an  increasing  space  dorsally.  The  mammillary  processes  project  outward  and 
backward.  The  transverse  processes  are  bent  downward  and  incline  a  little  for- 
ward. Their  length  increases  to  the  fifth  and  is  much  diminished  in  the  last.  They 
form  no  articulation  with  each  other  or  with  the  sacrum.  The  posterior  edge  of  the 
root  of  the  process  is  marked  by  a  notch  in  the  anterior  part  of  the  series,  a  fora- 


FiG.  172. — Fourth  Lttmbar  Vertebra  of  Pig;  Anterior  View. 
1,  Body;  2,  transverse  process;  3,  anterior  articular  process;  4,  mammillary  process;  5,  posterior  articular  process; 

6,  spinous  process. 

men  in  the  posterior  part.     The  spines  are  broad  and  incline  forward,  with  the  ex- 
ception of  the  last,  which  is  narrow  and  vertical. 

Lesbre  states  that  six  and  seven  lumbar  vertebra?  occur  with  almost  equal  frequency.  The 
number  may  be  reduced  to  five,  and  the  number  of  presacral  vertebra;  varies  from  twenty-six  to 
twenty-nine. 

The  sacrum  consists  usually  of  four  vertebrae,  which  fuse  later  and  less  com- 
pletely than  in  the  other  domesticated  animals.  It  is  less  curved  than  in  the  ox. 
The  spines  are  little  developed  and  commonly  in  part  absent.  The  middle  of  the 
dorsal  surface  is  flattened  and  smooth,  and  presents  openings  into  the  sacral  canal 
between  adjacent  arches  (Spatia  interarcualia) .  On  either  side  are  the  dorsal 
sacral  foramina,  and  tubercles  which  indicate  the  fused  articular  processes.  The 
wings  resemble  those  of  the  ox.  The  anterior  articular  processes  are  very  large. 
The  pelvic  surface  resembles  that  of  the  ox,  but  is  not  so  strongly  curved,  and  the 
transverse  lines  are  very  distinct. 

The  coccygeal  vertebrae  are  specially  characterized  by  the  presence  of  func- 
tional articular  processes  on  the  first  four  or  five,  beyond  which  these  processes 
become  non-articular  and  smaller.  The  arches  of  the  first  five  or  six  are  complete. 
The  transverse  processes  are  broad  and  plate-like  in  the  anterior  part  of  the  series 


THE    RIBS 


165 


and  diminish  very  gradually.     Not  rarely  the  first  coccygeal  vertebra  unites  with 
the  sacrum. 

Vertebral  Curves. — The  cei-vical  region  is  practically  straight.  The  thoracic 
and  lumbar  regions  form  a  gentle  curve,  concave  ventrally,  the  highest  point  of 
which  is  at  the  junction  of  the  two  regions.  The  sacral  promontory  is  not  so  pro- 
nounced as  in  the  ox,  and  the  sacral  curve  is  flatter. 


Fig.  173. — Sacrum  and  First  Coccygeal  Vertebra  op 
^Pig;  Dorsal  View. 
/-/]',  Arches  of  sacral  vertebrae;  1,  2,  3,  dorsal  sacral 
foramina;  4,  similar  foramen  between  sacrum  and  first 
coccygeal  vertebra;  A,  body  of  first  sacral  vertebra;  B, 
articular  process;  C,  wing;  D,  auricular  surface;  E,  articu- 
lar processes;    F,  first  coccygeal  vertebra. 


Fig.  174. — Sacrum  and  First  Coccygeal  Vertebra  of 
Pig;  Ventral  View. 
7-7  F,  Sacral  vertebrae  (bodies) ;  1,  2,  3,  ventral  sacral 
foramina;  4,  similar  foramen  between  sacrum  and  first 
coccygeal  vertebra;  A,  body  of  first  sacral  vertebra;  B, 
articular  process;  C,  wing;  D,  auricular  surface;  E,  first 
coccygeal  vertebra. 


Length. — The  regional  lengths  of  the  vertebral  column  of  a  large  Berkshire  sow  were  as  fol- 
lows: Cervical,  24  cm.;  thoracic,  53.5  cm.;  lumbar,  31  cm.;  sacral,  17  cm.;  coccygeal,  35  cm. 

Variations. — The  occurrence  of  fifteen  thoracic  vertebrse  is  quite  common,  and  the  existence 
of  sixteen  or  even  seventeen  has  been  recorded.  Reduction  to  thirteen  is  very  rare.  Six  and 
seven  lumbar  vertebrse  seem  to  occur  with  about  equal  frequency,  and  reduction  to  five  is  on  rec- 
ord. The  number  of  coccygeal  vertebrae  varies  from  twenty  to  twenty-six  according  to  the  records 
of  several  observers.     Lesbre  states  that  he  has  found  twenty-three  most  frequently. 


THE  RIBS 
The  ribs  number  fourteen  or  fifteen  pairs,  of  which  seven  are  sternal  and  seven 
or  eight  asternal  usually.     They  are  in  general  strongly  curved  in  the  improved 
breeds,  so  that  there  is  a  fairly  distinct  angle,  except  toward  the  end  of  the  series. 


166 


SKELETON    OF   THE    PIG 


The  backward  slope  of  the  posterior  ribs  is  slight.     The  first  rib  is  prismatic,  has  a 
large  sternal  end,  and  a  very  short  cartilage.     The  width  is  greatest  in  the  third 
to  the  sixth,  and  the  length  in  the  sixth  and  seventh  usually.     The  tubercle  fuses 
A\dth  the  head  on  the  last  five  or  six.     The  second 
3  to  the  fifth  form  diarthrodial  joints  mth  their  car- 

tilages, which  are  wide  and  plate-like. 

The  fifteenth  rib,  when  present,  may  be  fully  developed 
and  its  cartilage  enter  into  the  formation  of  the  costal  arch; 
but  in  most  cases  it  is  floating,  and  in  some  cases  it  is  only 
about  an  inch  (ca.  2-3  cm.)  in  length. 


THE  STERNUM 
The  sternum  consists  of  six  segments  and  re- 
sembles that  of  the  ox  in  general  form.     The  first 
segment  (Manubrium)  is   long,  flattened  laterally^ 


Fig.  175. — Eighth  Rib  of  Pig;  Lat- 
eral View. 
1,  Head;   2,  neck;  3,  tubercle;  4,  ante- 
rior border;   5,  sternal  extremity. 


Fig.   176. — First  Rib  or  Pig;  Lateral  View. 
neck;  3,  tubercle;  4,  anterior  border;  o,  vascular  impression; 
6,  sternal  extremity. 


and  bears  a  blunt-pointed  cartilage  on  its  anterior  end;  its  posterior  end  forms  a 
diarthrodial  joint  with  the  body.  The  latter  is  flattened,  wide  in  its  middle,  narrow 
at  either  end.  The  widest  segments  are  formed  of  two  lateral  parts,  w^hich  are 
not  completely  fused  in  the  adult.  The  last  segment  has  a  long,  narrow  part  which 
bears  the  xiphoid  cartilage. 

The  thorax  is  long  and  is  more  barrel-shaped  than  in  the  horse  or  ox,  since  the 
ribs  are  more  strongly  curved  and  differ  less  in  relative  length. 


BONES  OF  THE  SKULL 
Cranium 

The  occipital  bone  has  an  extensive  squamous  part,  which  forms  a  very  broad 
and  prominent  nuchal  crest.  The  latter  is  concave,  and  is  thick  and  rough  above, 
where  it  forms  the  highest  part  of  the  skull;    laterally  it  becomes  thinner,  turns 


BONES  OF  THE  SKULL — CRANIUM 


167 


downward,  and  is  continuous  with  the  temporal  crest.  Two  divergent  ridges  pass 
upward  from  the  foramen  magnum,  and  the  surface  between  them  is  concave  and 
smooth.  The  greater  part  of  the  cerebral  surface  of  the  squamous  part  is  united 
with  the  parietal  bones,  but  a  ventral  concave  area  faces  into  the  cranial  cavity. 
The  foramen  magnum  is  almost  triangular,  and  is  narrow  above,  where  it  is  flanked 
by  two  small  tuberosities.  The  paramastoid  processes  are  extremely  long  and  pro- 
ject almost  straight  ventrally.  The  hypoglossal  foramen  is  at  the  medial  side  of 
the  root  of  the  process.     The  basilar  part  is  short  and  wide;    its  ventral  surface 


Fig.  177. — Skull  of  Pig;  Lateral  View. 
A,  Occipital  bone;  B,  squamous  temporal  bone;  C,  parietal  bone;  D,  frontal  bone;  E,  lacrimal  bone;  F,  malar 
bone;  G,  maxilla;  H,  premaxilla;  I,  nasal  bone;  J,  os  rostri;  A',  mandible;  1,  occipital  condyle;  2,  paramastoid  proc- 
ess; 3,  condyle  of  mantlible;  4,  meatus  acusticus  externus;  5,  temporal  fossa;  6,  parietal  crest;  7,  supraorbital  process; 
8,  orbital  part  of  frontal  bone;  9,  fossa  for  origin  of  ventral  oblique  muscle  of  eyeball;  10,  orbital  opening  of  supraorbital 
canal;  11,  lacrimal  foramina;  12,  supraorbital  foramen  and  groove;  13,  infraorbital  foramen;  14,  zygomatic  process  of 
temporal  bone;  15,  temporal,  and  15',  zygomatic,  process  of  malar  bone;  16,  incisor  teeth;  17,  canine  teeth;  18,  18', 
premolars;    19,  19',  molars;   20,  mental  foramina;  21,  mental  prominence;  22,  angle  of  mandible. 


bears  a  thin  median  ridge  and  two  lateral  imprints  or  tubercles  which  converge  at 
the  junction  with  the  sphenoid  bone. 

The  interparietal  bone  fuses  before  birth  with  the  occipital.  The  internal 
occipital  protuberance  is  absent. 

The  parietal  bone  is  overlapped  by  the  occipital  bone  behind  and  concurs  in  the 
formation  of  the  nuchal  crest.  Its  external  surface  is  divided  by  the  parietal  crest 
into  two  parts.  The  medial  part  (Planum  parietale)  faces  upward  and  forward, 
and  is  flattened  and  smooth.  Its  medial  border  is  short  and  straight  and  unites 
early  with  the  opposite  bone.     Its  anterior  border  is  concave  and  joins  the  frontal 


168 


SKELETON    OF   THE    PIG 


bone.  The  lateral  part  (Planum  temporale)  faces  outward  and  is  more  extensive; 
it  is  concave,  forms  a  large  part  of  the  temporal  fossa,  and  is  overlapped  ventrally 
by  the  squamous  temporal.  The  parietal  crest  extends  in  a  curve  from  the  nuchal 
crest  forward  and  outward  to  the  supraorbital  process.  The  cerebral  surface  is  con- 
cave and  is  marked  by  digital  impressions.  The  ventral  border  projects  into  the 
cranial  cavity  and  forms  a  crest  w^hich  separates  the  cerebral  and  cerebellar  compart- 


Squamous  -part 
of  occipital  hone 


Occipital  condyle 
Paramastoid  process  (tip) 


Basilar  part  of 
occipital  bone 

Mastoid  process 

Temporal  condyle 


Maxillary  recess 

Zygomatic  proces. 
of  malar  hone 

Maxilla 


Molar  teeth 


Premolar  teeth 


Canine  tooth 


Prcmaxilla 


Fig.  178. — Skull  of  Pig,  Ventral  View,  without  Mandible  and  Htoid. 
1,  Hypoglossal  foramen;  2,  foramen  lacerum  anterius;  3,  foramen  lacerum  posterius;  4,  bulla  ossea;  5,  body  of 
sphenoid;  6,  pterygoid  bone,  and  6',  hamulus  of  same;  7,  vomer;  8,  horizontal,  and  8',  perpendicular,  part  of  palatine 
bone;  9,  pterygoid  process  of  palatine  bone;  10,  pterygoid  process  of  sphenoid  bone;  11,  supraorbital  process;  12,  or- 
bital opening  of  supraorbital  canal;  13,  choanae  or  posterior  nares;  14,  11',  anterior  palatine  foramen  and  groove;  15, 
palatine  fissure. 


ments  laterally.     The  interior  is  excavated  and  forms  part  of  the  frontal  sinus  in 
the  adult.     There  is  no  temporal  canal. 

The  frontal  bone  is  long.  The  frontal  surface  slopes  downward  and  forward, 
the  inclination  varying  in  different  subjects.  The  anterior  part  is  concave  and  is 
marked  by  the  supraorbital  foramen  and  the  groove  leading  forward  from  the 
foramen  to  the  nasal  bone.     The  supraorbital  canal  opens  into  the  orbit  at  the 


CRANIUM  169 

upper  part  of  the  medial  wall  of  the  latter.  The  supraorbital  process  is  short  and 
blunt-pointed,  and  is  not  connected  with  the  zygomatic  arch.  The  gap  in  the  or- 
bital margin  is  closed  by  the  orbital  ligament  in  the  fresh  state.  The  orbital  part 
is  extensive  and  forms  the  greater  part  of  the  medial  wall  of  the  orbit.  Its  upper 
part  is  perforated  by  the  orbital  orifice  of  the  supraorbital  canal,  in  front  of  which 
is  the  distinct  fovea  trochlearis.  The  ethmoidal  foramen  is  situated  in  the  ventral 
part  near  the  junction  with  the  orbital  wing  of  the  sphenoid.  The  temporal  part 
is  very  narrow  and  is  separated  from  the  orbital  plate  by  a  ridge  which  joins  the 


Parietal  bone 
Temporal  fossa 

Squamous  temporal 
bone 

External  acoustic 
meatus 


Zygom.atic  process 
of  temporal  bone 
Supraorbital  pro- 
cess 
Frontal  bone 

Supraorbital  fora- 
men 
Zygomatic  process 
of  malar  bone 
Lacrimal  bone 


Infraorbital  foramen 

Nasal  process  of  premaxilla 

Nasal  bone 

Canine  tooth 

Palatine  fissure 
Body  of  premaxilla 


Nuchal  crest 
Temporal  crest 
Parietal  crest 


y,^ — ^ —  Lacrimal  foramen 
Preorbital  fossa 


Fig.  179. — Skull  of  Pig;  Dorsal  View. 


pterygoid  crest  below.  The  interior  of  the  bone  is  excavated  by  the  frontal  sinus  in 
practically  its  entire  extent  in  the  adult.  In  the  young  subject  the  cavity  is  con- 
fined to  the  anterior  part  and  the  rest  of  the  bone  is  thick. 

The  temporal  bone  has  a  general  resemblance  to  that  of  the  ox.  The  zygo- 
matic process  is  short  and  stout  and  is  bent  at  a  right  angle.  The  dorsal  border  of 
the  process  is  thin;  traced  from  before  backward  it  curves  sharply  upward  and 
forms  a  high  prominence  in  front  of  the  external  acoustic  meatus;  beyond  this 
it  drops  rather  abruptly  and  is  then  continued  upward  to  the  nuchal  crest.  The 
anterior  part  of  the  ventral  border  joins  the  zygomatic  process  of  the  malar,  which 


170  SKELETON    OF   THE   PIG 

is  deeply  notched.  The  condyle  is  concave  in  the  transverse  direction.  The  post- 
glenoid  process  is  absent,  but  the  articular  surface  is  bounded  behind  and  medially 
by  a  crest.  There  is  no  temporal  canal.  The  external  acoustic  meatus  is  very 
long  and  is  directed  dorso-laterally.  The  bulla  ossea  is  large,  compressed  laterally, 
and  bears  a  pointed  muscular  process  in  front.  A  narrow  space  intervenes  between 
the  bulla  and  the  basilar  part  of  the  occipital  bone,  so  that  the  foramen  lacerum 
resembles  that  of  the  horse.  The  small  hyoid  process  is  situated  in  a  deep  de- 
pression in  front  of  the  root  of  the  paramastoid  process,  and  the  stylo-mastoid 
foramen  is  lateral  to  it.  The  petrous  part  presents  no  important  differential  fea- 
tures. The  squamous  part  (including  the  root  of  the  zygomatic  process)  contains 
an  air-cavity,  which  is  continuous  with  the  sphenoidal  sinus. 

The  sphenoid  bone  is  short  and  resembles  that  of  the  ox  in  general.  The  body 
is  narrow.  The  hypophyseal  or  pituitary  fossa  is  very  deep,  and  is  limited  behind 
by  a  prominent  dorsum  sellse;  the  dorsum  bears  lateral  projections,  the  posterior 
clinoid  processes  (Processus  clinoidei  aborales).  The  foramen  ovale  is  absent, 
being  included  in  the  foramen  lacerum  anterius.  The  other  foramina  are  like  those 
of  the  ox.  The  pterygoid  process  is  broad  and  twisted.  Its  base  is  not  perforated 
and  its  free  edge  is  thin  and  sharp.  It  concurs  with  the  pterygoid  and  palate  bones 
in  the  formation  of  the  pterygoid  fossa  (Fossa  pterygoidea),  which  opens  backward 
and  is  not  present  in  the  horse  or  ox.  The  sphenoidal  sinus  is  very  large  and  oc- 
cupies the  body,  the  temporal  wings,  and  a  great  part  of  the  pterj^goid  processes 
in  the  adult;  it  is  continued  into  the  temporal  Ijone  as  mentioned  above. 

The  ethmoid  bone  has  a  relatively  long  perpendicular  plate,  which  is  marked 
by  ridges  corresponding  to  the  ethmoidal  meatuses.  The  cribriform  plate  is  ex- 
tensive and  very  oblique,  so  that  it  and  the  crista  galli  are  almost  in  line  with  the 
basi-cranial  axis.  A  linear  series  of  relatively  large  foramina  is  found  on  either 
side  of  the  crista.  The  lateral  mass  consists  of  five  endoturbinates  and  eighteen 
ectoturbinates  (Paulli).  The  lamina  lateralis  concurs  in  the  formation  of  the 
pterygo-palatine  fossa.  The  lamina  transversalis  separates  the  fundus  of  the 
nasal  cavity  from  the  naso-pharyngeal  meatus. 

Face 

The  maxilla  is  extensive.  Its  facial  surface  forms  a  longitudinal  groove, 
which  is  continued  upon  the  premaxilla  in  front  and  the  facial  parts  of  the  lacrimal 
and  malar  behind.  The  infraorbital  foramen — sometimes  double — is  large  a,nd 
is  situated  above  the  third  or  fourth  cheek  tooth.  The  alveolus  for  the  canine 
tooth  produces  a  ridge  (Juga  canina)  at  the  anterior  end  which  is  very  pronounced 
in  the  boar.  The  facial  crest  extends  forward  from  the  root  of  the  zygomatic  proc- 
ess and  fades  out  behind  the  infraorbital  foramen;  in  some  specimens  it  is  prom- 
inent and  thin-edged,  in  others  it  is  rounded  and  projects  little.  The  zygomatic 
process  is  short  but  stout  and  buttress-like;  it  is  overlapped  laterally  by  the  malar. 
The  maxillary  tuberosity  forms  in  the  young  subject  a  long  bulla,  which  occupies 
most  of  the  pterygo-palatine  fossa  and  contains  the  developing  permanent  molars; 
after  the  eruption  of  the  teeth  the  tuberosity  flattens  and  joins  the  vertical  part  of 
the  palate  bone.  The  palatine  process  is  very  long  and  is  marked  in  its  anterior 
part  by  transverse  grooves  (Sulci  palatini  transversi)  corresponding  with  those  of 
the  mucous  membrane  of  the  palate.  The  anterior  palatine  foramen  is  near  the 
junction  with  the  palate  bone;  from  it  the  palatine  groove  can  be  traced  distinctly 
along  the  entire  length  of  the  process.  The  alveolar  border  presents  a  large  alveolus 
for  the  canine  tooth  at  its  anterior  end;  behind  this  are  seven  alveoli  for  the  cheek 
teeth,  which  increase  in  size  from  first  to  last.  The  maxillary  foramen  and  infraor- 
bital canal  are  very  large.     The  maxillary  sinus  is  small. 

The  body  of  the  premaxilla  is  narrow  and  prismatic.  It  presents  three  alveoli 
for  the  incisor  teeth,  which  are  separated  by  short  intervals  and  diminish  in  size 


FACE  171 

from  before  backward.  As  in  the  ox,  a  narrow  space  separates  the  right  and  left 
bones  and  takes  the  place  of  the  foramen  incisivum.  The  palatine  process  is  long 
and  narrow.  The  nasal  process  is  very  extensive  and  is  somewhat  rhomboid  in 
outline.  Its  dorsal  border  forms  a  very  long  suture  with  the  nasal  bone,  and  the 
ventral  articulates  to  about  the  same  extent  with  the  maxilla.  The  palatine  fissure 
is  relatively  wide. 

The  horizontal  part  of  the  palatine  bone  forms  a  fourth  to  a  fifth  of  the  length  of 
the  palate;  its  palatine  surface  is  triangular,  the  apex  being  anterior;  its  nasal 
surface  is  deeply  grooved  and  smooth.  A  pterygoid  process  (Processus  pyramidalis 
of  man)  projects  backward  and  downward,  and  its  thick  rounded  end  is  received 
between  the  pterygoid  process  of  the  sphenoid  and  the  pterygoid  bone.  The 
perpendicular  part  is  largely  overlapped  laterally  by  the  maxilla  and  concurs  in 


Fig.  180. — Sagittal  Section  op  Skull  op  Pig,  without  Mandible. 
A,  A',  Basilar  and  squamous  parts  of  occipital  bone;  B,  body,  B',  temporal  wing,  B",  orbital  wing,  of  sphenoid 
bone;  C,  parietal  bone;  D,  D',  internal  and  external  plates  of  frontal  bone;  E,  E',  cribriform  and  perpendicular  plates 
of  ethmoid  bone;  F,  pterygoid  bone;  G,  G',  perpendicular  and  horizontal  parts  of  palatine  bone;  H.  palatine  process  of 
maxilla;  /,  vomer;  J,  nasal  bone;  K,  body  of  premaxilla;  L,  dorsal  turbinate  bone;  M,  ventral  turbinate  bone; 
I,  II,  III,  fossse  cranii;  1,  hypoglossal  foramen;  2,  foramen  lacerum  posterius;  3,  meatus  acusticus  internus;  4,  fora- 
men lacerum  anterius;  5,  hypophyseal  or  pituitary  fossa;  6,  foramen  orbito-rotundum;  7,  lateral  crest  between  cerebral 
and  cerebellar  parts  of  cranial  cavity;  8,  optic  foramen;  9,  ethmoidal  foramen;  10,  frontal  sinus;  11,  meatus  naso- 
pharyngeus;  12,  13,  14,  dorsal,  middle,  and  ventral  nasal  meatuses;  15,  incisor  teeth;  16,  canine  tooth;  17,  premolar 
teeth;    18,  molar  teeth;    19,  paramastoid  process;   20,  bulla  ossea. 


forming  part  of  the  palatine  canal.  The  two  plates  separate  dorsally  and  inclose 
an  air-cavity  which  opens  into  an  ethmoidal  meatus.  The  inner  plate  curves 
inward  and  unites  with  the  vomer  and  ethmoid  to  form  a  horizontal  plate,  the 
lamina  transversalis,  which  divides  the  posterior  part  of  the  nasal  cavity  into  a 
dorsal  olfactory  part  and  a  ventral  respiratory  part. 

The  pterygoid  bone  is  nearly  vertical  in  direction,  and  is  narrow  in  its  middle, 
wide  at  each  end.  The  lateral  surface  is  free  below  and  forms  the  medial  wall  of 
the  pterygoid  fossa.     The  ventral  end  is  notched  and  forms  a  distinct  hamulus. 

The  nasal  bone  is  very  long  and  its  width  is  almost  uniform,  except  at  the 
anterior  end,  which  is  pointed  and  reaches  almost  as  far  forward  as  the  premaxilla. 
The  facial  surface  is  flattened  from  side  to  side.  In  profile  it  is  nearly  straight  in 
some  subjects,  variably  concave  in  others.  The  lateral  border  is  free  to  a  small 
extent  in  front  only;    otherwise  it  is  firmly  connected  with  the  premaxilla  and 


172 


SKELETON    OF   THE    PIG 


maxilla.     In   the   adult   the   frontal    sinus   extends    into   the    posterior   part   of 
the  bone. 

The  lacrimal  bone  is  very  sharply  bent.  Its  facial  surface  presents  a  deep 
depression,  surmounted  by  a  ridge  or  tubercle.  On  or  close  to  the  orbital  margin 
are  two  lacrimal  foramina  which  lead  to  the  lacrimal  canals.  The  orbital  surface 
presents  a  fossa  in  which  the  inferior  oblique  muscle  of  the  eyeball  arises,  and  its 
lower  part  bears  a  crest,  which  is  crossed  obliquely  by  a  vascular  furrow.  The 
dorsal  border  articulates  with  the  frontal  only.  The  bone  concurs  in  the  formation 
of  the  maxillary  sinus. 

The  malar  bone  is  strongly  compressed  from  side  to  side.     Its  facial  surface 

is  small  and  presents  a  fossa  which  is  con- 
tinuous with  the  depressions  of  the  maxilla 
and  lacrimal.  The  orbital  surface  is  still 
smaller  and  is  smooth  and  deeply  grooved. 
The  zygomatic  process  is  very  extensive, 
especially  in  the  vertical  direction.  Its 
lateral  surface  is  convex  and  free,  and 
bears  a  rough  eminence  in  its  middle.  Its 
medial  surface  is  concave;  it  is  over- 
lapped in  front  by  the  maxilla,  and  in  the 
remainder  of  its  extent  is  free  and  smooth. 
The  dorsal  border  is  thick  and  rounded  in 
front,  where  it  forms  the  lower  part  of  the 
orbital  margin;  behind  this  it  forms  an 
extensive  notch  which  receives  the  zygo- 
matic process  of  the  temporal.  (It  might 
be  regarded  as  dividing  into  frontal  and 
temporal  branches.)  The  ventral  border 
is  convex  and  becomes  thinner  behind. 

The  turbinate  bones  resemble  those 
of  the  ox.  The  dorsal  turbinate  is,  how- 
ever, relatively  longer,  less  fragile,  and 
more  firmly  attached  to  the  nasal  bone. 
There  is  no  middle  turbinate. 

The  vomer  is  very  long.  The  anter- 
ior extremity  reaches  to  the  body  of  the 
premaxilla  or  very  close  to  it.  The  ven- 
tral border  is  received  into  a  groove 
formed  by  the  nasal  crest  of  the  maxillge 
and  palatine  bones  and  in  front  by  the 
palatine  processes  of  the  premaxillse.  The 
posterior  border  is  concave,  thin,  and 
sharp. 

The  OS  rostri  (or  prenasal  bone)  is 
situated  in  the  snout  between  the  nostrils. 
It  has  the  form  of  a  short,  three-sided  prism.  The  dorsal  surface  is  convex  and  is 
notched  at  each  end.  The  lateral  surfaces  are  concave,  smooth,  and  converge 
below,  forming  a  grooved  ventral  border.  The  posterior  surface  is  triangular, 
notched  centrally,  and  rough  laterally.  The  anterior  surface  is  deeply  pitted  and 
is  surrounded  by  an  irregular  sharp  border. 

The  mandible  is  very  strong,  and  differs  very  much  from  that  of  the  horse  or 
ox.  The  body  narrows  decidedly  in  front;  the  lingual  surface  is  deeply  concave; 
the  mental  surface  is  strongly  convex,  slopes  downward  and  backward,  and  forms 
a  distinct  prominence  (Tuber  mentale)  at  the  point  of  divergence  of  the  rami. 


Fig.  181. — MandibixE  of  Pig;  Dorsal  View. 

A,  Body;  B,  B',  horizontal  and  vertical  parts  of 
ramus;  C,  condyle;  D,  coronoid  process;  1,  2,  3,  in- 
cisor teeth;  4,  canine  tooth;  5,  6,  7,  premolar  teeth 
(first  absent) ;   8,  9,  10,  molar  teeth. 


THE   SKULL   AS   A   WHOLE  173 

Above  this  prominence  is  a  pair  of  foramina.  The  alveolar  border  presents  six 
alveoli  for  the  incisor  teeth,  and  a  little  further  back  two  large  cavities  for  the 
canine  teeth.  There  are  two  pairs  of  mental  foramina  of  considerable  size  and  a 
variable  number  of  smaller  ones.  The  rami  diverge  more  than  in  the  horse  or  ox, 
and  the  upper  part  is  somewhat  incurved.  The  horizontal  part  is  very  thick  and 
strong.  Its  lateral  surface  is  strongly  convex  from  above  downward.  The  medial 
surface  is  prominent  over  the  roots  of  the  molar  teeth  and  overhangs  the  concave 
lower  part.  The  alveolar  border  is  thin  in  front  and  widens  behind;  it  does  not 
follow  the  axis  of  the  ramus,  but  runs  nearly  straight  and  produces  the  marked  over- 
hang noted  above.  There  are  seven  alveoli  for  the  lower  cheek  teeth,  which  in- 
crease in  size  from  before  backward.  The  first  is  small,  not  always  present  in  the 
adult,  and  is  separated  by  short  spaces  from  the  second  and  the  canine  alveolus. 
The  vertical  part  is  relatively  wide  above.  The  condyle  is  convex  in  both  direc- 
tions, wide  in  front,  narrow  and  declivitous  behind.  The  very  small  and  thin- 
edged  coronoid  process  is  not  quite  so  high  as  the  condyle,  from  which  it  is  separated 
by  a  very  wide  notch.  The  mandibular  foramen  is  large.  The  two  halves  of  the 
bone  unite  soon  after  birth  in  the  improved  breeds. 

The  body  of  the  hyoid  bone  is  broad  from  before  backward,  short  transversely, 
and  bears  on  its  ventral  aspect  a  very  short  pointed  lingual  process.  The  thyroid 
cornua  are  wide  and  curved,  concave  and  grooved  dorsally;  their  ends  are  attached 
to  the  thyroid  cartilage  of  the  larynx  by  rather  long  bars  of  cartilage.  The  small 
cornua  are  short,  wide,  and  flattened  dorso-ventrally ;  they  are  attached  to  short 
bars  which  project  from  the  junction  of  the  body  and  thyroid  cornua.  The  middle 
cornu  is  a  little  longer  than  the  small  cornu,  but  is  relatively  slender;  it  is  largely 
cartilaginous  in  the  young  subject  and  does  not  ossify  at  either  end.  The  great 
cornu  is  a  very  slender  rod,  slightly  enlarged  at  either  end;  the  dorsal  extremity  is 
attached  to  the  hyoid  process  of  the  temporal  by  a  rather  long  and  wide  bar  of 
cartilage. 

THE  SKULL  AS  A  WHOLE 

The  length  and  the  profile  vary  greatly  in  different  subjects.  Primitively 
the  skull  is  long — especially  in  its  facial  part — and  the  frontal  profile  is  almost 
straight.  The  condition  is  very  pronounced  in  wild  or  serai-feral  pigs,  and  exists 
also — though  in  less  degree — in  the  improved  breeds  during  extreme  youth.  Most 
of  the  latter  are  decidedly  brachycephalic  when  fully  developed;  the  face  is 
"dished"  in  a  pronounced  fashion.  The  frontal  region  slopes  sharply  upward, 
and  the  nasal  region  is  shortened,  and  in  some  specimens  even  distinctly  concave 
in  profile.  The  supraorbital  foramina  are  about  midway  between  the  orbital  mar- 
gin and  the  frontal  suture.  The  supraorbital  grooves  extend  forward  from  the 
foramina  to  the  nasal  region  and  turn  ventro-laterally  toward  the  infraorbital 
foramina  over  the  ridges  which  separate  the  nasal  and  lateral  regions. 

The  lateral  surface  is  triangular  when  the  mandible  is  included.  The  tem- 
poral fossa  is  entirely  lateral  and  its  long  axis  is  almost  vertical.  It  is  bounded 
above  by  the  nuchal  crest,  behind  by  the  temporal  crest,  in  front  by  the  parietal 
crest,  and  is  marked  off  from  the  orbital  cavity  by  the  supraorbital  process  and  a 
curved  crest  which  extends  from  it  to  the  root  of  the  pterygoid  process.  The 
zygomatic  arch  is  strong,  high,  and  flattened  from  side  to  side.  Its  root  is  notched 
dorsally  and  bears  a  projection  ventrally.  It  curves  sharply  upward  behind  and 
forms  a  pointed  recurved  projection  above  and  in  front  of  the  external  acoustic 
meatus.  The  orbit  is  small.  Its  margin  is  deficient  behind  in  the  dry  skull,  thick 
and  rounded  in  front  and  below.  The  cavity  is  limited  below  by  a  ridge  on  the 
frontal  and  lacrimal  bones,  and  is  separated  by  a  crest  from  the  temporal  fossa. 
The  medial  wall  is  perforated  above  by  the  orbital  opening  of  the  supraorbital 
canal,  and  below  by  the  optic  and  ethmoidal  foramina;  on  its  antero-inferior  part 


174 


SKELETON    OF   THE   PIG 


is  the  fossa  in  which  the  inferior  oblique  muscle  of  the  eye  takes  origin.  Two  lac- 
rimal foramina  are  found  on  or  close  to  the  anterior  margin.  The  pterygo-palatine 
fossa  is  well  defined ;  its  upper  part  forms  a  deep  groove  which  leads  from  the  fora- 
men orbito-rotundum  to  the  very  large  maxillary  foramen.  The  preorbital  region 
is  deeply  grooved  in  its  length  and  is  clearly  marked  off  by  a  ridge  from  the  nasal 
and  frontal  regions.  The  facial  crest  is  short,  usually  thin-edged,  and  lies  above  the 
fifth  and  sixth  cheek  teeth.     A  little  (ca.  2  cm.)  in  front  of  it  is  the  infraorbital  fora- 


Nuchal  crest 


Fig.  182. — Skull  of  Pig;  Posterior  View. 
1,  2,  3,  Squamous,  lateral,  and  basilar  parts  of  occipital  bone;  4,  foramen  magnum;  .5,  occipital  condyle;  6,  para- 
mastoid  process;  7,  squamous  temporal  bone;  8,  meatus  acusticus  externus;  9,  temporal  condyle;  10,  zygomatic 
process  of  malar  bone;  11,  bulla  ossea;  12,  12',  perpendicular  and  horizontal  parts  of  palatine  hone;  13,  13',  choanae  or 
posterior  nares;  14,  vomer;  15,  pterygoid  process  of  sphenoid  bone;  16,  pterygoid  process  of  palatine  bone;  17,  con- 
dyle of  mandible;   18,  mandibular  foramen;    19,  body  of  mandible. 


men.     There  is  a  ritlged  prominence  over  the  canine  alveolus.     In  some  skulls  the 
anterior  part  of  the  upper  jaw  is  inclined  upward. 

The  most  striking  features  of  the  basal  surface  are  as  follows:  The  basioc- 
cipital  is  wide  and  flattened;  it  bears  a  median  crest  and  two  lateral  tubercles. 
The  paramastoid  process  is  extremely  long,  less  flattened  than  in  the  horse  and  ox, 
and  nearly  vertical.  At  the  medial  side  of  its  root  is  the  h3'poglossal  foramen, 
and  in  front  of  it  are  the  stylo-mastoid  foramen  and  a  deep  cavity  in  which  the 
hyoid  process  is  concealed.  The  bulla  ossea  is  long,  compressed  lateral!}',  and  bears 
a  sharp,  short,  muscular  process.  The  posterior  nares  are  small  and  are  wider  be- 
low than  above.     On  either  side  of  them  is  the  tuberosity  of  the  palate  bone,  and 


THE   SKULL   AS   A   WHOLE  175 

above  this  is  the  pterygoid  fossa.  The  palate  constitutes  about  two-thirds  of  the 
entire  length  of  the  skull,  and  is  relatively  narrow.  It  is  widest  between  the  canines 
and  premolars  and  narrow  at  each  end.  It  is  marked  by  a  crest  medially  and  by 
the  palatine  foramen  and  groove  laterally.  The  anterior  part  bears  transverse 
ridges.  It  is  moderately  arched  from  side  to  side.  In  some  specimens  it  is  nearly 
straight  or  slightly  concave  in  its  length;  in  others  it  curves  upward  to  a  variable 
degree  in  front.     The  posterior  end  always  slopes  upward  more  or  less. 

The  nuchal  surface  is  remarkable  for  its  height  and  the  breadth  of  the  nuchal 
crest.  The  central  part  above  the  foramen  magnum  is  smooth  and  concave  from 
side  to  side,  and  is  bounded  laterally  by  ridges,  which  converge  ventrally  and  end 
on  two  tubercles  at  the  upper  margin  of  the  foramen  magnum.  The  surface  is 
separated  from  the  temporal  fossse  by  the  temporal  crests,  which  curve  downward 
and  outward  and  blend  with  the  external  acoustic  meatus.  The  mastoid  process 
has  the  form  of  a  plate  which  overlaps  the  root  of  the  paramastoid  process  and  bears 
a  crest  on  its  anterior  part. 

The  cranial  cavity  is  small,  in  spite  of  the  great  size  of  the  cranium;  the 
discrepancy  is  due  to  the  enormous  development  of  the  frontal  sinuses  in  the  adult. 
It  is  relatively  longer,  but  much  lower  than  that  of  the  ox.  Its  width  is  greatly 
diminished  between  the  orbits.  The  olfactory  fossse  are  extensive  and  very  ob- 
lique. The  floor  resembles  that  of  the  ox,  but  the  foramen  ovale  is  absent,  the 
dorsum  sellse  is  more  developed,  and  the  foramen  lacerum  is  like  that  of  the  horse. 
Two  oblique  lateral  crests  clearly  mark  the  limit  between  the  cerebral  and  cerebellar 
compartments.  The  internal  occipital  protuberance  and  the  temporal  canal  are 
absent. 

The  nasal  cavity  is  very  long.  Its  posterior  part  is  divided  by  the  lamina 
transversalis  into  olfactory  and  respiratory  parts.  The  olfactory'  part  or  fundus  is 
dorsal,  and  contains  the  ethmoturbinates  and  ethmoidal  meatuses.  The  ventral 
part  is  continuous  with  the  ventral  meatus  and  leads  to  the  pharyngeal  orifice; 
hence  it  is  called  the  naso-pharyngeal  meatus.  The  bony  roof  is  almost  complete 
in  front  on  account  of  the  great  length  of  the  nasal  bones. 

The  frontal  sinus  is  a  vast  excavation  in  the  adult  animal.  It  involves  all  of 
the  roof  and  almost  all  of  the  sides  of  the  cranium,  and  extends  forward  into  the 
roof  of  the  nasal  cavity  a  variable  distance — sometimes  as  far  as  a  transverse  plane 
through  the  infraorbital  foramina.  The  septum  between  the  right  and  left  sinuses 
is  usually  deflected  in  an  irregular  manner  in  its  middle  part,  but  is  practically 
median  at  either  end.  Each  sinus  is  sul^divided  by  numerous  septa,  some  of  which 
are  complete.  Thus  the  sinus  is  divided  into  compartments,  each  of  which  com- 
municates with  an  ethmoidal  meatus. 

In  the  young  pig  the  sinus  is  small  and  is  confined  to  the  anterior  part  of  the  frontal  bone. 
Later  it  extends  backward,  outward,  and  to  a  less  extent  forward.  In  the  old  subject  it  penetrates 
laterally  into  the  supraorbital  process  and  the  root  of  the  zygomatic  process  of  the  temporal  bone, 
and  behind  almost  down  to  the  foramen  magnum  and  the  occipital  condyles.  It  then  consists 
of  six  to  eight  compartments  usually. 

The  maxillary  sinus  is  relatively  small.  Its  anterior  end  is  a  little  less  than 
an  inch  (ca.  2  cm.)  behind  the  infraorbital  foramen,  and  it  extends  upward  into 
the  lacrimal  and  backward  into  the  malar  bone.  The  infraorl^ital  canal  passes 
along  its  floor,  and  the  roots  of  the  molar  teeth  do  not  project  up  into  it.  It  does 
not  communicate  with  the  frontal  and  sphenoidal  sinuses,  but  with  the  posterior 
part  of  the  middle  meatus  nasi  by  means  of  a  considerable  orifice. 

The  sphenoidal  smus  is  very  large.  It  involves  the  body,  pterygoid  processes, 
and  temporal  wings  of  the  sphenoid  bone,  and  extends  into  the  squamous  temporal. 
It  communicates  with  the  ventral  ethmoidal  meatus. 

There  is  a  small  sinus  in  the  perpendicular  part  of  the  palatine  bone  which 
communicates  with  an  ethmoidal  meatus. 


176 


SKELETON    OF   THE    PIG 


BONES  OF  THE  THORACIC  LIMB 
The  scapula  is  very  wide,  the  index  being  about  1  :  0.7.  The  spine  is  tri- 
angular and  is  verj^  wide  in  its  middle,  which  curves  backward  over  the  infra- 
spinous  fossa  and  bears  a  large  tuberosity.  Its  lower  part  bears  a  small  projection 
(rudimentary  acromion).  The  anterior  border  is  strongly  convex  in  profile,  sinuous 
when  viewed  from  the  front,  and  thick  and  rough  in  its  middle.  The  posterior 
border  is  wide,  slightly  concave,  and  bears  a  rough  outer  lip.  The  vertebral  border 
is  convex,  and  the  cartilage  is  not  so  extensive  as  in  the  horse  and  ox.  The  anteri- 
or angle  is  thin  and  bent  medially  a  little.     The  posterior  angle  is  thick  and  is  about 


Fig.  183. — Left  Scapula  of  Pig;  Lateral  View. 
Anterior  angle;    6,  posterior  angle;    c,  anterior  border;    d,  posterior  border;  e,  neck;   /,  glenoid  cavity;  g,  tuber 
scapulae;   1,  spine;  2,  tuber  spinas ;   3,  acromion;   4,  supraspinous  fossa;   5,  inf raspinou3  f ossa ;  6,  cartilage. 


a  right  angle.  The  neck  is  well  defined.  The  rim  of  the  glenoid  cavity  is  rounded 
and  not  notched.  The  tuber  scapulae  is  just  above  the  antero-medial  part  of 
the  glenoid  cavity  and  bears  no  distinct  coracoid  process;  it  unites  with  the  rest  of 
the  bone  at  about  one  year. 

The  humerus  has  an  appearance  in  profile  somewhat  like  an  italic  /  minus  the 
cross-bar;  this  is  due  to  the  marked  backward  and  forward  inclination  of  the  prox- 
imal and  distal  ends  respectively.  The  shaft  is  decidedly  compressed  from  side  to 
side.  The  medial  surface  is  extensive  and  flattened;  it  is  separated  from  the 
anterior  surface  by  a  distinct  border,  and  bears  no  teres  tubercle.  The  musculo- 
spiral  groove  is  shallow.  The  deltoid  tuberosity  is  small,  and  there  is  a  larger 
rounded  eminence  midway  between  it  and  the  lateral  tuberosity.     The  nutrient 


BONES    OF   THE   THORACIC    LIMB  177 

foramen  is  on  the  posterior  surface  below  its  middle.  The  head  is  more  strongly 
curved  and  the  neck  better  marked  than  in  the  horse  or  ox.  The  lateral  tuber- 
osity is  very  large  and  extends  upon  the  front  of  the  extremity.  It  is  divitled  into 
two  high  prominences  by  a  wide  deep  groove.  There  is  a  third  eminence  below 
and  laterally  for  the  attachment  of  the  supraspinatus  muscle.  The  intertuberal  or 
bicipital  groove  is  at  the  front  of  the  medial  side;  it  is  undivided  and  is  almost  con- 
verted into  a  canal.  The  lateral  groove  on  the  distal  articular  surface  is  so  shallow 
as  to  give  the  appearance  of  two  condyles  of  similar  size.  The  olecranon  fossa  is 
very  deep,  and  the  plate  of  bone  which  separates  it  from  the  coronoid  fossa  is  thin 
and  sometimes  perforated.  The  proximal  end  unites  with  the  shaft  at  three  and  a 
half  years,  the  distal  at  one  year. 


£7 

Fig.  184. — Left  Scapula  of  Pig;  Medial  View. 

a.  Anterior  angle;    h,  posterior  angle;    c,  anterior  border;    d,  posterior  border ;  e,  neck;   /,  vascular  groove;  g,  glenoid 

cavity;  /i,  tuber  scapulae;    1,  subscapular  fossa;  2,  serratus  area;   3,  cartilage. 

The  radius  is  short  and  narrow,  but  thick.  The  shaft  increases  in  size  distally. 
The  greater  part  of  the  volar  surface  is  in  apposition  with  the  ulna;  this  part  is 
marked  by  a  vascular  furrow  which  runs  distally  from  the  proximal  interosseous 
space,  and  has  the  nutrient  foramen  at  its  proximal  end.  The  radial  tuberosity  is 
represented  by  a  rough  area.  The  distal  end  is  relatively  large.  Its  carpal  sur- 
face consists  of  concavo-convex  facets  for  the  radial  and  intermediate  carpal  bones. 
There  is  a  wide  shallow  groove  on  the  middle  of  the  front.  The  proximal  end  fuses 
with  the  shaft  at  one  year,  the  distal  at  three  and  a  half  years. 

The  ulna  is  massive.     It  is  much  longer  and  considerably  heavier  than  the 

radius.     The  shaft  is  curved.     The  dorsal  surface  is  convex  and  most  of  it  is  rough 

and  attached  to  the  radius  by  the  interosseous  ligament.     There  is  a  smooth  area 

on  the  upper  third,  which  concurs  with  the  radius  in  forming  the  proximal  inter- 

12 


178 


SKELETON    OF   THE    PIG 


Deltoid 
tuberosity 


Lateral 
tuberosity 


Medial 
condyle 

Lateral 
condyle 


Head 


Lateral 
epicondyle 


Nutrient 
foramen 

Lateral  con- 
dyloid crest 

Olecranon 
fossa 

Medial  epi- 
condyle 


Intertuberal 

Lateral  

tuberosity 
Head 


Medial 
condyle 


Fia.    185. — Left   Humerus   of  Pig;    Lateral  View. 


Medial         Lateral 
epicondyle         condyle 
Fig.    186. — Left    Humerus    of   Pig;    Medial   Vi 


Olecranon 


-r  Olecranon 
I 


Shaft  of  -I    \  '^:     1 ^V/«/^  of  ulna 

radiuH 


Carpal  surface 
of  radius 
-Left  Radius  and  Ulna  of  Pig;  Lateral 
View. 


Distal  end 
of  radius 
-Left  Radius  and  Ulna  of  Pig;  Medial 
View. 


BONES    OF   THE   THORACIC    LIMB 


179 


osseous  space,  and  is  marked  in  its  upper  part  by  the  nutrient  foramen.  From  this 
space  a  vascular  furrow  descends  to  the  distal  part  of  the  shaft,  where  there  is  often 
a  distal  interosseous  space  for  the  passage  of  vessels.  The  medial  surface  is  exten- 
sive, concave,  and  smooth.  The  lateral  surface  is  slightly  convex,  and  its  proximal 
part  is  marked  by  an  oblique  rough  line  or  ridge.  The  proximal  extremity  is 
large  and  is  bent  medially  somewhat;  its  length  is  more  than  one-third  of  that  of 
the  entire  bone.  The  distal  extremity  is  relatively  small;  it  articulates  with  the 
ulnar  and  accessory  carpal  bones,  and  is  notched  in  front  to  accommodate  the  ridge 


Fig.  189. — Skeleton  of  Distal  Part  of  Left  Thor- 
acic Limb  of  Pig;  Dorsal  View. 
R,  Distal  end  of  radius;  U,  distal  end  (styloid  proc- 
ess) of  ulna;  C.  r.,  radial  carpal;  C.  i.,  intermediate 
carpal;  C.  u.,  ulnar  carpal;  C.  2,  C.  3,  C.  4,  second, 
third,  and  fourth  carpal  bones;  Mc.  2-5,  metacarpal 
bones;  Ph.l,  Ph.  2,  Ph.  3,  first,  second,  and  third  pha- 
langes. 


Fig.  190. —  Skeleton  of  Distal  Part  of  Left 
Thoracic  Limb  of  Pig;  Volar  View. 
R,  Distal  end  of  radius;  U,  distal  end  (styloid  proc- 
ess) of  ulna;  C.  r.,  C.  i.,  C.u.,  C.  a.,  radial,  intermedi- 
ate, ulnar,  and  accessory  carpal  bones;  C.  1-4,  first  to 
fourth  carpal  bones;  Mc.  2-5,  metacarpal  bones;  Ph.  1, 
Ph.  2,  Ph.  3,  first,  second,  and  third  phalanges;  S,  prox- 
imal, and  <S',  distal  sesamoid  bones. 


on  the  radius.     The  bone  contains  a  considerable  medullary  canal,  and  is  con- 
solidated at  three  to  three  and  a  half  years. 

The  carpus  comprises  eight  bones,  four  in  each  row.  The  bones  of  the  prox- 
imal row  resemble  those  of  the  ox,  with  the  exception  of  the  accessory,  which  is  more 
like  that  of  the  horse,  but  has  no  lateral  groove.  The  first  carpal  is  small,  elon- 
gated from  before  backward,  rounded,  and  articulates  in  front  with  the  second  carpal. 
The  latter  is  high  and  narrow,  and  articulates  with  the  second  and  third  metacarpal 
bones  distally.  The  third  carpal  articulates  with  the  radial  and  intermediate 
above,  the  third  metacarpal  bone  below.  The  fourth  is  the  largest  bone  of  the  row; 
it  articulates  with  the  intermediate  and  ulnar  above,  the  fourth  and  fifth  meta- 
carpals below,  and  bears  a  tuberosity  on  its  volar  aspect. 


180 


SKELETON    OF   THE   PIG 


Four  metacarpal  bones  are  present.  The  first  is  absent,  the  third  and  fourth 
are  large  and  carry  the  chief  chgits,  while  the  second  and  fifth  are  much  smaller  and 
bear  the  accessory  digits.  Their  proximal  ends  articulate  with  each  other  and  with 
the  carpus  as  indicated  above.  The  distal  ends  fuse  with  the  shafts  at  about  two 
years  of  age. 

The  third  and  fourth  metacarpals  are  flattened  from  before  backward,  three-sided,  and 
placed  close  together.  The  distal  end  of  each  bears  a  trochlea  for  articulation  with  the  first 
phalanx  and  the  sesamoids.  The  third  is  the  wider  of  the  two,  and  articulates  with  all  of  the  distal 
row  of  the  carpus  except  the  first.  The  fourth  articulates  with  the  fourth  carpal  chiefly,  but  has  a 
small  facet  for  the  third.  The  second  and  fifth  metacarpals  are  placed  further  back  than  the  chief 
bones.  The  fifth  is  considerably  the  thicker  of  the  two.  The  proximal  ends  are  small  and  articu- 
late with  the  corresponding  carpal  and  metacarpal  bones.  The  distal  end  is  relatively  large;  its 
articular  surface  is  condyloid  in  front,  trochlear  behind. 

Each  chief  digit  comprises  three  phalanges  and  three  sesamoids.  The  bones 
of  the  chief  digits  resemble  those  of  the  ox  in  form,  but  there  is  no  foramen  on  the 
interdigital  side  of  the  extensor  process  and  the  proximal  sesamoids  are  narrow  and 
ridged  behind.  The  phalanges  of  the  accessory  digits  (which  do  not  reach  the 
ground  ordinarily)  are  similar  in  form  but  much  smaller.  Fusion  of  the  proximal 
ends  with  the  shafts  takes  place  at  about  two  years  for  the  fir.st  phalanges,  at  about 
one  year  for  the  second  phalanges. 


Crest  of  ilium         Gluteal  line 

V  /   ... ^ 

\  ^  5*p^-    Tuber  sacrale 


Ischiatic  Lesser  sciatic     Tuber 

sjiinv  notch  ischii 


Tuber  coxcr 


i? 


Ilium  (shaft) 

Acetabulum  Ischium 

Fig.  191. — Left  Os  Cox.e  of  Pig;   Lateral  View. 


Tuber  sarmh 


( 'n  st  of  ilium 


Lesser 
Tuber        sciatic  Ischiatic 

ischii        notch  spine 


Tuber  coxce 


\    Ilio-pectineal 
eminence 
Pubis  (acstah- 
ular  branch) 
Fig.  192. — Left  Os  Cox.e  of  Pig;  Medial  View. 


BONES  OF  THE  PELVIC  LIMB 
The  OS  coxae  is  long  and  narrow.     The  ilium  and  ischium  are  almost  in  line 
with  each  other  and  nearly  sagittal  in  direction.     The  wing  of  the  ilium  bends  out- 
ward much  less  than  in  the  horse  or  ox.    The  gluteal  surface  is  divided  into  two  fossa? 


BONES    OF   THE    PELVIC    LIMB 


181 


by  a  ridge,  which  is  continuous  with  the  superior  ischiatic  spine  behind.  The 
pelvic  surface  presents  an  extensive  rough  area  behind,  which  is  in  apposition  with 
the  wing  of  the  sacrum.  The  smooth  iliac  area  is  narrow,  and  is  bounded  above 
by  a  ridge.  The  crest  is  convex,  and  is  thick,  rough,  and  prominent  in  its  middle, 
which  forms  the  highest  point  of  the  bone.  The  tuber  sacrale  is  lower  than  the 
crest,  is  directed  backward,  and  articulates  internally  with  the  sacrum.  The  tuber 
coxffi  is  lower  still  and  is  very  little  thickened.  The  ischia  in  the  female  are  some- 
what divergent  and  flattened  behind.  The  tubera  are  everted  and  bear  three  prom- 
inences. There  is  a  crest  or  tuberosity  on  the  ventral  surface.  The  superior 
ischiatic  spine  is  like  that  of  the  cow,  but  is  slightly  incurved  and  the  muscular 


Trochant'T 

major  //<  nd 


Trochan- 
taric  Trochanter 

Head      fossa      /  major 


Lateral  Trochlea      Medial 


condyle  condyle 

Fig.    193. — Right   Femur  of   Pig;    Anterior    View. 


hd  r-      \ 

Medial  condyL-     condyloid      Lateral  condyle 
fossa 

Fig.    194. — Right  Femur  of  Pig;   Posterior  View. 


ridges  on  its  lateral  face  are  more  pronounced.  The  symphyseal  part  of  the  pubis 
is  thick  and  the  two  bones  are  almost  in  a  horizontal  plane.  The  ilio-pectineal 
eminence  is  prominent  and  the  psoas  tubercle  is  well  marked. 

The  acetabulum  is  placed  a  little  further  back  than  in  the  ox.  The  rim  is 
thick  and  is  cut  into  posteriorly  by  a  narrow  fissure,  which  leads  into  the  deep  fossa 
acetabuli.  The  three  pieces  of  the  os  coxse  are  fused  by  the  end  of  the  first  year, 
but  the  crest  and  the  tuber  ischii  are  partially  separate  till  the  sixth  or  seventh  year. 
The  symphysis  does  not  usually  undergo  complete  ankylosis.  Interischial  bones 
are  present. 

The  inlet  of  the  pelvis  is  elliptical  and  very  oblique.  In  a  sow  of  full  size  the 
conjugate  diameter  measures  five  to  six  inches  (12.5-15  cm.),  and  the  transverse 


182 


SKELETON    OF    THE    PIG 


about  three  and  a  half  to  four  inches  (ca.  8.75  to  10  cm.).  In  the  female  the  tloor 
is  relatively  wide  and  flattened,  especially  at  the  outlet,  where  the  tubera  are 
everted;  it  also  has  a  decided  ventral  inclination  behind.  The  pelvic  axis  is  there- 
fore correspondingly  oblique.  The  ischial  arch  is  wide.  In  the  boar  the  pubis  is 
much  thicker  and  the  ischia  are  not  everted  posteriorly.  The  inlet  is  smaller;  the 
conjugate  diameter  is  about  four  and  a  half  to  five  inches  (ca.  11-12.5  cm.),  and  the 
transverse  three  to  three  and  a  half  inches  (ca.  7.5-8.75  cm.).  The  floor  is  concave 
from  side  to  side  and  slopes  decidedly  less  than  in  the  sow.  The  superior  ischiatic 
spines  are  more  incurved,  and  the  ischial  arch  is  much  narrower  and  deeper. 

The  femur  has  a  relatively  wide  and  massive  shaft,  on  which  four  surfaces 
might  be  recognized.     The  principal  nutrient  foramen  is  situated  in  the  proximal 


Spine  of  tibia     Tuberositi/ 

Lateral  condyle  Js./.-.^      Medial 

'condyle 

Head  of 
fibula 


Crest  of  tibia 


Medial  condyle         Spine  of  tibia 

I  ateral  condyle 


Groove  for 
tendons 

Lateral 
malleolus 


Fig.   195. — Right  Tibia  and  Fibula  of  Pig;   Ante- 
rior View. 
Arrow  indicates    muscular    notch  of    proximal    end  of 
tibia. 


Distal  end  of  tibia 


Fig.   196. — Right    Tibia    and  Fibula   of  Pig;    Pos- 
terior View. 
o,  Groove  on  medial  malleolus  for  tendon  of  flexor  dig- 
italis longus. 


third  of  the  anterior  surface.  The  posterior  surface  is  wide,  and  is  limited  laterally 
by  a  ridge  which  extends  from  the  trochanter  major  to  the  large  lateral  supra- 
condyloid  crest.  There  is  no  supracondyloid  fossa.  The  head  is  strongly  curved, 
and  is  marked  toward  the  medial  side  by  a  rather  large  fovea  for  the  attachment  of 
the  round  ligament.  The  neck  is  distinct.  The  trochanter  major,  although  massive, 
does  not  extend  above  the  level  of  the  head.  The  trochanteric  ridge  and  fossa  re- 
semble those  of  the  ox.  The  third  trochanter  is  absent.  The  ridges  of  the  trochlea 
are  similar  and  almost  sagittal.  The  extremities  unite  with  the  shaft  at  about 
three  and  a  half  years. 

The  shaft  of  the  tibia  is  slightly  curved,  convex  medially.  The  tuberosity 
is  grooved  in  front,  and  a  narrow  sulcus  separates  it  from  the  lateral  condyle. 
The  facet  for  the  fibula  is  on  the  posterior  border  of  the  latter,  and  is  bounded 


BONES    OF   THE   PELVIC    LIMB 


183 


medially  by  an  eminence.  The  proximal  part  of  the  crest  is  very  prominent  and 
curves  outward.  The  distal  end  resembles  in  general  that  of  the  ox,  but  is  rela- 
tively narrower  transversely  and  thicker  from  before  backward.  The  proximal 
end  unites  with  the  shaft  at  about  three  and  a  half  years,  the  distal  at  about  two 
years. 

The  fibula  extends  the  entire  length  of  the  region,  and  is  separated  from  the 
tibia  by  a  wide  interosseous  space.  The  shaft  is  flattened  from  side  to  side;  the 
proximal  part  is  wide  and  deeply  grooved  laterally;    the  distal  part  is  narrower 


Tuber  calcis 


Tuber  calcis 


T.  t 


T,c. 


ML  2 


ML  5 


Fig.  197. — Skeleton  op  Right  Pes  of  Pig;  Dorsal 
View. 
T.  t.,  Tibial  tarsal;  T.  /.,  fibular  tarsal;  T.  c,  cen- 
tral tarsal;  T.  3,  third  tarsal;  T.  4,  fourth  tarsal;  Mt. 
2-5,  metatarsal  bones;  Ph.  1,  Ph.  2,  Ph.  S,  first,  second, 
and  third  phalanges. 


Fig.  198. — Skeleton  of  Right  Pes  of  Pig;  Plantar 
View. 
T.t.,  Tibial  tarsal;  T.  /.,  fibular  tarsal;  T.c,  cen- 
tral tarsal;  T.l,  T.4,  first  and  fourth  tarsal  bones; 
Mt.  2-5,  metatarsal  bones;  Ph.  1,  Ph.  2,  Ph.  3,  first,  sec- 
ond, and  third  phalanges;  .S,  proximal  sesamoid  bones; 
distal  sesamoids  shown  but  not  marked;  a,  tarsal 
sesamoid  bone. 


and  thicker.  The  proximal  end  is  flattened,  grooved  laterally,  and  articulates 
medially  with  the  lateral  condyle  of  the  tibia.  The  distal  end  forms  the  lateral 
malleolus.  It  is  grooved  laterally,  and  articulates  with  the  tibia  and  tibial  tarsal 
medially,  with  the  fibular  tarsal  bone  distally.  The  proximal  end  unites  with  the 
shaft  at  about  three  and  a  half  years,  the  distal  at  about  two  and  a  half  years. 

The  patella  is  very  much  compressed  transversely  and  presents  three  surfaces. 

The  tarsus  comprises  seven  bones.  The  tibial  and  the  fibular  tarsals  resemble 
in  general  those  of  the  ox.  The  axis  of  the  tibial  is,  however,  slightly  oblique  (ven- 
tro-medial),  and  its  distal  end  bears  a  double  trochlea  for  articulation  with  the  cen- 


184  SKELETON    OF   THE   DOG 

tral  and  fourth  tarsals.  The  tuber  calcis  is  deeply  grooved  posteriorly.  The 
central  tarsal  is  narrow  transversely  and  thick.  Its  proximal  surface  is  deeply 
concave,  and  the  plantar  bears  a  large  tubercle.  The  first  tarsal  is  high  and 
narrow;  it  articulates  with  the  central  and  second  tarsals  and  the  second  metatarsal 
bone.  The  second  tarsal  is  small  and  somewhat  prismatic;  it  articulates  with 
the  central  above,  the  third  in  front,  the  first  behind,  and  the  second  and  third 
metatarsals  below.  The  third  tarsal  is  much  larger,  and  is  compressed  from  above 
downward,  wide  in  front,  narrow  behind.  It  articulates  with  the  central  tarsal 
above,  the  third  metatarsal  below,  the  second  tarsal  medially,  and  the  fourth  tarsal 
laterally.  The  fourth  tarsal  is  large.  Its  lateral  face  is  crossed  by  an  oblique 
groove  for  the  tendon  of  the  peroneus  longus.  The  medial  surface  articulates 
with  the  central  and  third  tarsals.  The  proximal  surface  supports  the  tibial  and 
fibular  tarsal  bones,  and  the  distal  surface  rests  on  the  fourth  and  fifth  metatarsals. 
It  ossifies  from  two  centers.  The  summit  of  the  tuber  calcis  fuses  with  the  rest 
of  the  bone  at  two  to  two  and  a  half  years. 

The  four  metatarsal  bones  resemble  the  corresponding  bones  of  the  fore  limb, 
but  are  somewhat  longer.  The  proximal  ends  of  the  third  and  fourth  each  have  a 
considerable  plantar  projection;  the  process  on  the  third  has  a  facet  for  articulation 
with  a  discoid  sesamoid  bone.  The  second  and  fifth  are  placed  more  toward  the 
plantar  aspect  of  the  large  bones  than  is  the  case  in  the  fore  limb. 

The  first  and  second  phalanges  are  a  little  longer  and  narrower  than  those  of 
the  fore  limb. 


SKELETON  OF  THE  DOG 

VERTEBRAL  COLUMN 

The  vertebral  formula  is  CTTisLrSsCy^o-os- 

The  cervical  vertebrae  are  relatively  longer  than  in  the  ox  and  the  pig.  The 
bodies  of  the  typical  vertebrae  diminish  in  length  from  first  to  last  and  are  com- 
pressed dorso-ventrally.  The  anterior  extremity  is  moderately  convex  and  the 
posterior  slightly  concave;  both  are  oblique.  The  median  ridge  and  lateral  grooves 
on  the  dorsal  surface  of  the  body  are  very  well  marked.  The  second,  third,  and 
fourth  have  distinct  ventral  spines.  The  spinous  process  of  the  third  has  the 
form  of  a  long  low  crest;  in  the  remainder  it  is  higher,  blunt-pointed,  and  inclined 
forward.  The  transverse  processes  of  the  third,  fourth,  and  fifth  project  ventrally 
and  backward,  and  divide  into  two  branches;  of  these,  the  anterior  one  is  thin, 
and  the  posterior  is  thick  and  tuberculate  at  its  free  end.  The  process  of  the 
sixth  has  two  parts;  one  of  these  is  an  extensive  quadrilateral  plate  which  is  di- 
rected ventro-laterally  and  is  ridged  on  its  medial  surface;  the  other  part  is  short  and 
blunt,  and  is  directed  outward  and  a  little  backward  and  upward.  The  seventh  is 
readily  distinguished  by  its  shortness,  the  length  of  its  spine,  and  the  single  trans- 
verse process.  The  posterior  articular  processes  bear  tubercles  which  are  large  on 
the  third,  fourth,  and  fifth. 

The  ventral  arch  of  the  atlas  is  narrow  from  before  backward,  and  bears  a 
small  tubercle  posteriorly.  The  dorsal  surface  of  the'  dorsal  arch  is  strongly  convex 
and  rough  centrally.  The  wings  are  wide,  flattened,  and  almost  horizontal.  The 
dorsal  surface  is  rough.  There  is  an  alar  notch  (Incisura  alaris)  on  the  anterior 
border  instead  of  the  alar  foramen.     The  foramen  transversarium  is  present. 

The  body  of  the  axis  is  flattened  dorso-ventrally,  especially  in  front.  The 
dens  is  rounded  and  relatively  long,  reaching  almost  to  the  occipital  bone;  it  is 
inclined  upward  a  little.  The  articular  surfaces  which  flank  it  are  condyloid  in 
form  and  very  oblique.     The  ventral  surface  is  wide,  and  is  divided  by  a  median 


VERTEBRAL    COLUMN 


185 


*■   I 


Fig.  199. — Skeleton  or  Dog;  Lateral  View. 
a.  Cranium;  6,  face;  c,  mandible;  1H-7H,  cervical  vertebrse;  13B,  last  thoracic  vertebra;  1L-7L,  lumbar  verte- 
bra; K,  sacrum;  S,  coccygeal  vertebrae;  1R-13R,  ribs;  R.kn.,  costal  cartilages;  St.,  sternum;  d,  scapula;  d' ,  supia- 
spinous  fossa;  d",  infraspinous  fossa;  i,  spine  of  scapula;  ^.acromion;  3,  tuberosity  of  scapula;  S',  articular  end  of 
scapula;  e,  humerus;  4,  head  of  humerus;  o,  lateral  tuberosity  of  humerus;  5',  deltoid  ridge;  6,  6',  epicondyles  of 
humerus;  7,  lateral  condyloid  crest ;  7',  coronoid  fossa;  /.radius;  ff,  ulna;  S,  olecranon;  5,  "beak"  of  ulna;  /»,  carpus; 
i,  metacarpus;  k,  proximal  phalanges;  I,  middle  phalanges;  m,  distal  phalanges;  n,  sesamoid;  p,  iUum;  10,  wing  of 
ilium;  ii,  shaft  of  ilium;  i^,  crest  of  ilium;  i5,  tuber  coxse;  i^i  tuber  sacrale;  i5,  superior  ischiatic  spine;  g,  pubis; 
r,  ischium;  iff,  tuber  ischii;  7  7,  acetabulum;  s,  femur;  i 5,  head  of  femur;  iS,  trochanter  major;  ^0,  trochanter  minor; 
^i,  trochanter  tertius;  ^^,  ^S,  condyles;  ^4,  ;g5,  epicondyles;  ^ff,  trochlea;  /.patella;  m,  tibia;  ^7,  tuberosity  of  tibia; 
;25,  ^5,  condyles  of  tibia;  SO,  medial  malleolus;  u,  fibula;  S/,  lateral  malleolus;  S^,  head  of  fibula;  w),  tarsus;  x,  meta- 
tarsus; y,  phalanges;  33,  occipital  bone;  34,  paramastoid  process;  35,  parietal  bone;  36,  frontal  bone;  37,  lacrimal 
bone;  SS,  malar  bone ;  SS,  squamous  temporal;  ^0,  maxilla;  4"',  infraorbital  foramen;  4?.  premaxilla;  4^,  nasal  bone: 
43,  external  acoustic  meatus;  44 ■  canine  tooth;  45,  masseteric  fossa;  4^i  angular  process  of  mandible.  (After  Ellra- 
berger,  in  Leisering's  Atlas.) 


Fig.  200. — Third  Cervical  Vertebra  of  Dog;  Left 
Lateral  View. 
.t,  S,  Anterior  and  posterior  ends  of  body;    3,  3, 
articular  processes;  4,  spinous  process;  5,  6,  transverse 
process;  7,  foramen  transversarium. 


Fig.    201. — Fourth    Cervical   Vertebra    of    Dog; 
Left  Lateral  View. 
1,  1',  Anterior  and  posterior  ends  of  body;    2,  2', 
articular  processes;    3,  transverse  process;    4,  spinous' 
process. 


186 


SKELETON    OF   THE   DOG 


crest  into  two  fossae.     The  transverse  processes  are  single,  pointed,  directed  back- 
ward and  outward,  and  perforated  by  relatively  large  foramina  transversaria.     The 

spinous  process  is  thin  and  of  moderate 
height,  but  very  long;  it  is  prolonged  for- 
ward so  as  to  overhang  the  dorsal  arch  of 
the  atlas,  and  is  terminated  behind  by  a 
tuberosity  which  is  connected  by  two 
crests  with  the  posterior  articular  proc- 
esses. The  anterior  notches  are  large 
and  are  never  converted  into  foramina. 


Fig.    202. — Seventh    Cervical   Vertebra    of   Dog; 
Posterior  View. 
1,  Body;    2,  costal  facet;    3,  transverse  process; 
4,  notch;   5,  5',  articular  processes;   6,  spinous  process. 


Fig.  203. — Atlas  of  Dog;  Dorsal  View. 
1,  Dorsal  arch;    2,  2,  posterior  articular  cavities;    3, 
ventral  tubercle;  4,  4'  intervertebral  foramina;  5,  5',  wings; 
6,  6',  alar  notches;   7,  7',  foramina  transversaria. 


The  bodies  of  the  thirteen  thoracic  vertebrae  are  wide  and  compressed  dorso- 
ventrally,  especially  at  each  end  of  the  region.  Their  con- 
vex anterior  surfaces  are  depressed  in  the  middle.  The 
posterior  facets  for  the  heads  of  the  ribs  are  absent  on  the 
last  three  or  four.  The  transverse  processes  resemble  those 
of  the  horse.  They  bear  mammillary  processes  except  at 
the  anterior  end  of  the  region.  The  facets  for  the  tubercles 
of  the  ribs  are  large  and  concave  in  the  anterior  part  of  the 
series,  and  become  smaller  and  slightly  convex  further  back. 


Fig.  204. — Axis  or  Dog;  Left  Lateral  View. 
1,  Dens;  2,  anterior  articular  process;  3,  posterior  end  of  body;  4,  arch;  5,  pos- 
terior notch;  6,  transverse  process;  7,  intervertebral  foramen;  8,  posterior  articular 
process;  9,  spinous  process. 


Fig.  205. — Fourth  Thoracic 
Vertebra  of  Dog;  Left 
View. 

1,  Body;  2,  2',  costal  facets 
of  body;  3,  posterior  notch; 
4,  4',  articular  processes;  5, 
transverse  process;  6,  facet  for 
tubercle  of  rib;  7,  mammillary 
process;  8,  spinous  process. 


VERTEBRAL    COLUMN  187 

The  last  three  have  accessory  processes  also.  The  first  three  or  four  spinous  proc- 
esses are  about  equal  in  length.  Behind  this  they  become  gradually  shorter  to  the 
tenth,  and  then  remain  equal.  The  backward  slope  is  most  marked  in  the  ninth 
and  tenth.  The  eleventh  is  practically  vertical  (anticlinal  vertebra),  and  the  last 
two  incline  slightly  forward. 

The  bodies  of  the  seven  lumbar  vertebrae  are  decidedly  flattened  dorso-ventrally, 
and  increase  in  width  from  first  to  last.  The  length  increases  to  the  sixth.  The 
transverse  processes  are  plate-like  and  are  directed  forward  and  downward.  Their 
length  increases  to  the  fifth  and  sixth.  They  form  no  joints  with  each  other  or 
with  the  sacrum.  Their  extremities  are  enlarged,  with  the  exception  of  the  last. 
The  accessory  processes  project  backward  over  the  posterior  notches  of  the  first 
five.  The  anterior  articular  processes  are  large,  compressed  laterally,  and  bear 
mammillary  processes.  The  spinous  processes  are  broad  below,  narrower  above, 
and  with  the  exception  of  the  last,  incline  a  little  forward.  Their  height  diminishes 
behind  the  fourth. 

The  sacrum  results  from  the  early  fusion  of  three  vertebrae.     It  is  short, 


Fig.  206. — Fifth  Lumbar  Vertebra  op  Dog;   Dorsal  View.  Fig.  207. — Sacrum  of  Dog;    Ventral  View. 

1,  Anterior  end  of  body;    2,  spinous  process;    3,  3',  artic-  I,  II,  III,  Bodies  of  vertebrse;  1,  2,  ventral  sac- 

ular  processes;  4,  transverse  process;  5,  accessory  process;  ral  foramina;  3,  4,  lineae  transversae;  5,  anterior  end 
6,  groove  for  spinal  nerve.  of  body  of  first  sacral  vertebra;  6,  6',  anterior  artic- 

ular processes;  7,  7',  wings;  8,  posterior  end  of  body 
of  last  sacral  vertebra;  9,  9',  posterior  articular  proc- 
esses; 10,  sacral  canal;  11,  spinous  ^'process;  12, 
12',  transverse  processes;  13,  auricular  surface. 

wide,  and  quadrangular.  The  spines  are  fused  to  form  a  median  crest,  which  is 
notched,  however,  between  the  summits  of  the  spines.  On  either  side  are  two 
tubercles,  vestiges  of  the  fused  articular  processes.  The  pelvic  surface  is  deeply 
concave  and  presents  two  pairs  of  foramina.  The  wings  are  prismatic  and  very 
high.  Their  lateral  surfaces  are  extensive,  face  almost  directly  outward,  and  bear 
an  auricular  surface  on  the  lower  part.  The  anterior  surface  of  the  body  of  the 
first  vertebra  is  extensive,  depressed  in  its  middle,  and  bears  a  prominent  lip  below. 
The  anterior  articular  processes  are  large  and  have  extensive,  slightly  concave 
facets  which  face  dorso-medially.  The  posterior  articular  processes  are  small. 
The  transverse  processes  of  the  last  vertebra  project  backward  and  may  articulate 
or  fuse  with  those  of  the  first  coccygeal.  The  sacral  canal  is  strongly  compressed 
dorso-ventrally. 

The  coccygeal  vertebrae  are  fully  developed  in  the  anterior  part  of  the  region. 
The  arch  is  complete  in  the  first  six  usually.  The  first  three  or  four  have  well  de- 
veloped articular  processes  at  each  end.  Behind  this  the  posterior  processes 
quickly  disappear,  and  the  anterior  ones  become  non-articular  and  gradually  re- 


188  SKELETON    OF   THE    DOG 

duced  in  size.  The  transverse  processes  of  the  first  five  or  six  are  relatively  large; 
behind  this  they  quickly  disappear.  Hemal  arches  (or  chevron  bones)  in  the  form 
of  a  V  or  Y  occur  ventrall}^  at  the  intercentral  junctions  of  the  third,  fourth,  and 
fifth  usualh^  They  transmit  the  middle  coccygeal  artery,  which  passes  between 
pairs  of  ventral  tubercles  further  back. 

Curves. — A  gentle  curve,  convex  ventrally,  is  formed  by  the  cervical  and  the 
anterior  part  of  the  thoracic  region.  The  posterior  thoracic  and  the  lumbar 
vertebrae  form  a  second  curve,  concave  ventrally.  The  sacral  promontory  is  well 
marked.  The  sacrum  and  the  anterior  part  of  the  coccygeal  region  constitute 
a  third  and  more  pronounced  curve,  concave  ventrally.  In  long-tailed  dogs  the 
sacro-coccygeal  region  is  somewhat  S-shaped. 

Variations. — Numerical  variations  are  not  common  except  in  the  coccygeal  region.  Tlie 
number  of  thoracic  vertebrae  may  be  twelve  or  fourteen,  with  or  without  compensatory  change  in 
the  lumbar  region.  Girard  recorded  a  case  with  eight  lumbar  and  the  usual  number  of  thoracic 
vertebrae.  Six  lumbar  with  foiu-teen  thoracic  vertebrae  have  been  met  with.  The  first  coccygeal 
sometimes  unites  with  the  sacrum. 

THE  RIBS 

Thirteen  pairs  of  ribs  are  present,  of  which  nine  are  sternal  and  four  asternal. 
They  are  strongly  curved,  narrow,  and  thick.  Those  in  the  middle  of  the  series 
are  the  longest.  The  first  eight  or  nine  increase  in  width  in  their  lower  part.  I'he 
last  rib  is  usually  floating.  The  costal  cartilages  are  long  and  curve  ventrally  and 
forward;  the  length  and  curvature  of  the  first  pair  are  striking  special  features. 


THE  STERNUM 

This  is  long,  laterally  compressed,  and  consists  of  eight  sternebrae,  which  fuse 
only  in  exceptional  cases  and  in  extreme  old  age.  The  first  segment  is  the  longest-; 
its  anterior  end  is  blunt-pointed  and  bears  a  short  conical  cartilage.  It  widens 
at  the  point  of  articulation  of  the  first  pair  of  cartilages.  The  last  segment  is 
also  long,  thinner  than  its  predecessors,  wide  in  front,  and  narrow  behind,  where  it 
bears  a  narrow  xiphoid  cartilage. 

The  thorax  is  distinctly  barrel-like  and  is  not  decidedly  compressed  anteriorly 
like  that  of  the  horse  and  ox.  The  inlet  is  oval  and  is  relatively  wide  on  account 
of  the  marked  curvature  of  the  first  pair  of  ribs  and  cartilages. 


BONES  OF  THE  SKULL  i 

Cranium 
The  occipital  bone  is  similar  in  position  to  that  of  the  horse.  The  nuchal  crest 
is  prominent,  angular,  and  directed  backward.  Just  below  the  crest  are  two  rough 
imprints  or  tubercles  for  muscular  attachment.  The  surface  below  these  is  convex 
from  side  to  side  and  concave  dorso-ventrally.  On  each  side,  at  the  junction 
with  the  squamous  temporal,  is  the  mastoid  foramen  which  opens  into  the  cranial 
cavity.  The  condyles  are  somewhat  flattened  and  are  widely  separated  above; 
at  the  medial  side  of  each  is  a  short  condyloid  canal,  which  opens  into  the  temporal 
canal.  The  paramastoid  processes  are  very  short.  The  basilar  part  is  wide  and 
joins  the  bulla  ossea  on  either  side;  its  ventral  surface  is  flattened  and  the  tubercles 
are  at  the  junction  with  the  bulla.  The  hypoglossal  foramen  is  small  and  is  close 
to  the  foramen  lacerum  posterius ;  the  latter  is  bounded  in  front  by  the  bulla  ossea, 
behind  and  medially  by  the  occipital  bone. 

^In  the  following  descriptions  of  the  separate  bones  an  intermediate  type — e.  g.,  a  fox  terrier, 
— is  selected,  and  the  most  striking  differences  in  the  brachycephalic  and  dolichocephalic  breeds 
will  be  considered  in  the  section  on  the  skull  as  a  whole. 


BONES    OF   THE   SKULL — CRANIUM 


189 


The  interparietal  bone  fuses  with  the  occipital  before  birth.  It  bears  the  high 
posterior  part  of  the  parietal  crest,  and  is  wedged  in  between  the  two  parietal  bones. 
It  forms  the  central  part  of  the  tentorium  osseum,  which  is  thin  and  curved,  con- 
cave ventrally.  Its  base  concurs  with  the  occipital  and  parietal  bones  in  the  for- 
mation of  a  transverse  canal  which  is  continuous  with  the  temporal  canals. 

The  parietal  bone  is  rhomboid  in  outline  and  is  strongly  curved.  It  is  exten- 
sive and  forms  the  greater  part  of  the  roof  of  the  cranial  cavity.  At  the  junction 
of  the  right  and  left  bones  there  is  a  prominent  parietal  crest  which  is  continued 
upon  the  frontal  bones.  The  ventral  border  articulates  with  the  temporal  wing 
of  the  sphenoid  by  its  anterior  part  and  with  the  squamous  temporal  in  the  remain- 
der of  its  extent.     The  external  surface  enters  into  the  formation  of  the  temporal 

r 


-V*^ 


-14 


Fig.  208. — Sktjll  of  Dog;  Lateral  View. 
A,  Occipital  bone;  5,  parietal  bone;  C,  squamous  temporal  bone;  D,  frontal  bone;  E,  lacrimal  bone;  F,  malar 
bone;  G,  perpendicular  part  of  palatine  bone;  H,  maxilla;  /,  premaxilla;  J ,  nasal  bone;  K,  mandible;  1,  parietal 
crest;  2,  occipital  condyle;  3,  paramastoid  process;  4,  stylo-mastoid  foramen;  5,  bulla  ossea;  6,  meatus  acusticus 
externus;  7,  external  opening  of  temporal  canal;  8,  postglenoid  process;  9,  zygomatic  process  of  temporal  bone;  10, 
zygomatic  process  of  malar  bone;  11,  supraorbital  process;  12,  entrance  to  lacrimal  canal;  13,  infraorbital  foramen; 
14,  mental  foramina;  1.5,  condyle  of  mandible;  16,  coronoid  process;  17,  mandibular  notch;  18,  angular  process;  19, 
masseteric  fossa;    i.  i',  incisor  teeth     c,  c',  canine  teeth. 


fossa.  The  cerebral  surface  is  marked  by  digital  impressions,  and  by  grooves  for 
the  middle  meningeal  artery  and  its  branches. 

The  external  surface  of  the  frontal  bone  is  crossed  by  a  frontal  crest,  which 
extends  in  a  curve  from  the  parietal  crest  to  the  supraorbital  process,  and  separates 
the  frontal  and  temporal  parts.  The  frontal  parts  of  the  two  bones  form  a  central 
depression  and  slope  downward  and  forward.  The  supraorbital  process  is  very 
short,  so  that  the  supraorbital  margin  is  incomplete  as  in  the  pig.  The  supraor- 
bital foramen  is  absent.  In  front  there  is  a  narrow  pointed  nasal  part  which  fits 
in  between  the  nasal  bone  and  the  maxilla.  The  orbital  and  temporal  parts  are 
relatively  extensive.  Two  ethmoidal  foramina  are  commonly  present.  The 
frontal  sinus  is  confined  to  the  frontal  bone. 

The  parts  of  the  temporal  bone  fuse  early.  The  zygomatic  process  curves 
widely  outward  and  forward.     Its  anterior  part  is  beveled  ventrally  and  articulates 


190 


SKELETON    OF   THE   DOG 


extensively  with  the  corresponding  process  of  the  malar.  The  articular  surface 
for  the  condyle  of  the  mandible  consists  of  a  transverse  groove  which  is  continued 
upon  the  front  of  the  large  postglenoid  process.  Behind  the  latter  is  the  lower 
opening  of  the  temporal  canal.  There  is  no  condyle.  The  mastoid  part  is  small, 
but  bears  a  distinct  mastoid  process.  The  external  acoustic  meatus  is  wide  and 
verj^  short,  so  that  one  can  see  into  the  tympanum  in  the  dry  skull.  The  bulla  ossea 
is  very  large  and  is  rounded  and  smooth;  its  medial  side  is  united  to  the  basilar 
part  of  the  occipital  bone.  Above  this  junction  and  roofed  in  by  the  union  of  the 
petrous  part  and  the  basioccipital  is  the  petro-basilar  canal  (Canalis  petrobasilaris) ; 
this  transmits  a  vein  from  the  floor  of  the  cranium  to  the  foramen  lacerum  posterius. 
The  latter  opens  into  a  narrow  depression  behind  the  bulla  ossea.     It  transmits  the 


Interparietal  bone 


Parietal  crest 


Zygomatic  process  of 

temporal  hone 

Coronoid  process 

Frontal  crest 
Supraorbital  process 


Zygomatic  process  of 

malar  bone 

Lacrimal  bone 


Infraorbital  foramen 

Nasal  process  of  premaxilla 
Canine  tooth 
Incisor  teeth 


Parietal  bone 
Squamous  temporal  bone 
Frontal  bone 


Body  of  premaxilla 


Fig.  209. — Skull  of  Doa;  Dorsal  View. 


ninth,  tenth,  and  eleventh  cranial  nerves.  The  carotid  canal  branches  off  from 
the  petro-basilar,  passes  forward  lateral  to  it  through  the  medial  part  of  the  bulla 
ossea,  and  opens  in  front  at  the  carotid  foramen;  it  transmits  the  internal  carotid 
artery.  The  Eustachian  opening  is  immediately  lateral  to  the  carotid  foramen. 
The  muscular  and  hyoid  processes  are  extremely  rudimentary.  The  petrous  part 
projects  into  the  cranial  cavity  and  forms  a  sharp  prominent  petrosal  crest.  The 
medial  surface  presents  a  deep  floccular  fossa  above  the  internal  acoustic  meatus. 
The  anterior  surface  is  also  free.  The  anterior  angle  is  perforated  by  a  canal  for 
the  fifth  cranial  nerve  (Canalis  nervi  trigemini). 

The  body  of  the  sphenoid  bone  is  flattened  dorso-ventrally.  The  hypophyseal 
fossa  is  shallow,  but  the  dorsum  sellse  is  well  developed  and  bears  posterior  clinoid 
processes.     A  pair  of  anterior  clinoid  processes  (Processus  clinoidei  orales)  pro- 


FACE  191 

ject  back  from  tlie  roots  of  the  orbital  wings.  The  latter  are  relatively  small  and 
are  crossed  laterally  by  a  crest,  which  is  continued  forward  upon  the  palatine  bone. 
The  temporal  wings  are  extensive  and  articulate  dorsally  with  the  parietals.  Per- 
forating the  roots  of  the  wings  are  the  following  foramina,  named  from  before  back- 
ward :  The  optic  passes  through  the  orbital  wing.  The  foramen  orbitale  is  a  little 
lower  and  is  at  the  junction  of  the  wings.  The  foramen  rotundum  opens  into  the 
alar  canal,  which  passes  through  the  root  of  the  short  but  wide  pterygoid  process. 
The  foramen  ovale  is  near  the  posterior  border  of  the  temporal  wing.  There  is  no 
sphenoidal  sinus. 

The  ethmoid  bone  is  highly  developed.  The  cribriform  plate  is  extensive, 
and  the  olfactory  fossae  are  very  deep.  The  crista  galli  is  little  developed,  and  often 
incomplete.  The  perpendicular  plate  is  long.  The  lateral  masses  are  greatly 
developed  and  project  into  the  frontal  sinus.     There  are  four  large  endoturbinates 


Fig.  210. — Cranial  and  Orbital  Regions  of  Skull  of  Dog.  The  Zygomatic  Arch  Has  Bi^en  Sawn  Off. 
.4,  Occipital  bone;  B,  interparietal  bone;  C,  parietal  bone;  D,  squamous  temporal  bone;  E,  E',  temporal  and 
orbital  parts  of  frontal  bone;  F,  F',  orbital  and  temporal  wings  of  sphenoid  bone;  G,  perpendicular  part  of  palatine  bone; 
ff,  pterygoid  bone ;  J,  lacrimal  bone;  /.maxilla;  1,  parietal  crest;  2,  nuchal  crest;  3,  occipital  condyle;  4,  paramastoid 
process;  5,  stylo-mastoid  foramen;  6,  bulla  ossea;  7,  meatus  acusticus  externus;  8,  articular  surface  for  condyle  of 
mandible;  9,  section  of  root  of  zygomatic  process  of  temporal  bone;  10,  alar  canal;  11,  foramen  orbitale;  12,  optic 
foramen;  13,  ethmoidal  foramen;  14,  posterior  palatine  foramen;  15,  sphenopalatine  foramen;  16,  entrance  to  lacrimal 
canal;  17,  supraorbital  process;  18,  zygomatic  process  of  malar  bone  (section);  19,  maxillary  foramen;  20,  last  molar 
tooth. 

and  six  ectoturbinates.  The  lamina  lateralis  is  extensive  and  forms  the  medial  wall 
of  the  maxillary  sinus.  Its  ventral  border  joins  the  palatine  process  of  the  maxilla 
and  the  horizontal  part  of  the  palate  bone.  A  shelf-like  plate  extends  inward  from 
its  lower  part  and  concurs  with  the  similarly  incurved  part  of  the  palatine  bone  in 
forming  the  lamina  transversalis,  which  divides  the  olfactory  fundus  of  the  nasal 
cavity  from  the  naso-pharyngeal  meatus. 


Face 
The  maxilla  is  short,  but  very  high  posteriorly.  The  facial  crest  is  absent. 
The  infraorbital  foramen  is  over  the  alveolus  for  the  third  premolar.  The  frontal 
process  fits  into  a  deep  notch  between  the  nasal  and  orbital  parts  of  the  frontal 
bone,  and  the  middle  part  of  the  posterior  border  lies  along  the  orbital  margin. 
There  are  more  or  less  pronounced  ridges,  juga  alveolaria,  over  the  canine  and 
molar  teeth.  The  zygomatic  process  is  short  and  thin ;  it  is  completely  overlapped 
laterally  by  the  malar,  and  is  perforated  by  a  number  of  foramina  (Foramina 


192 


SKELETON    OF   THE    DOG 


alveolaria).  A  maxillary  tuberosity  is  not  present  in  the  adult,  but  there  is  a 
pointed  projection,  the  pterygoid  process,  behind  the  last  alveolus.  The  nasal 
surface  bears  a  short  turbinate  crest  on  its  anterior  part,  behind  which  it  is  deeply 
concave  and  forms  the  lateral  wall  of  the  maxillary  sinus.  The  palatine  process  is 
short,  wide  behind,  and  moderately  arched  from  side  to  side.     The  anterior  palatine 


Foramen    Foramen  Occipital 
hypoglossi  magnum  condyle 


Foramen  lacerum  posterius  ^^  ^ 
Stylo-mastoid  foramen 
Meatus  acusticus  externus 


Parnmnstoid  process 

Bulla  ossea 
mporal  canal 


Molar  teeth 


Premolar  teeth 


Canine  tooth 


Zygomatic  process  of  malar 
bone 


Palatine  process  of  rnaxilla 


Prcmaxilla 


Incisor  teeth 


Fig.  211. — Skull  of  Dog;  Vkntral  View,  Without  Mandible. 
A,  Basilar  part  of  occipital  bone;  B,  body  of  sphenoid  bone;  C,  vomer;  D,  D',  perpendicular  and  horizontal  parts 
of  palatine  bone;  E,  pterygoid  bone;  1,  Eustachian  opening;  2,  external  carotid  foramen;  3,  foramen  ovale;  4,  5, 
posterior  and  anterior  openings  of  alar  canal ;  6,  foramen  orbitale ;  7,  postglenoid  process;  8,  articular  groove  of  temporal 
bone;  9,  supraorbital  process;  10,  meatus  naso-pharyngeus ;  11,  anterior  palatine  foramen;  12,  palatine  groove;  13, 
palatine  fissure;    14,  foramen  incisivum. 


foramen  is  situated  at  or  close  to  the  transverse  palatine  suture  and  about  midway 
between  the  median  suture  and  the  alveolar  border.  The  palatine  groove  is  dis- 
tinct. The  large  alveolus  for  the  canine  tooth  is  completed  by  the  premaxilla. 
The  small  alveolus  for  the  first  premolar  is  separated  from  the  preceding  one  by  a 
small  interval.  The  next  two  consist  of  anterior  and  posterior  parts  for  the  roots 
of  the  teeth.     The  fourth  and  fifth  are  much  larger  and  are  divided  into  three 


FACE  193 

parts.     The  last  is  small  and  consists  of  three  divisions.     The  infraorbital  canal  is 
short. 

The  body  of  the  premaxilla  is  compressed  dorso-ventrally,  and  contains  three 
alveoli  for  the  incisor  teeth,  which  increase  in  size  from  first  to  third;  it  also  com- 
pletes the  medial  wall  of  the  large  alveolus  for  the  canine  tooth.  The  foramen 
incisivum  is  very  small  except  in  large  skulls.  The  interalveolar  border  is  wide 
and  very  short.  The  nasal  process  is  wide  at  its  origin  and  tapers  to  a  sharp  point 
behind;  the  anterior  part  curves  upward,  backward,  and  a  little  inward,  and  forms 
the  lateral  margin  of  the  osseous  nasal  aperture;  the  posterior  part  extends  back- 
ward a  long  distance  between  the  nasal  bone  and  the  maxilla.  The  palatine  process 
turns  upward  and  outward,  forming  with  its  fellow  a  wide  groove  for  the  septal 
cartilage;   the  posterior  end  is  pointed  and  fits  into  a  notch  between  the  palatine 


Fig.  212. — Sagittal  Section  ok  Skull  of  Dog,  Without  Mandible. 
A,  A',  Basilar  and  squamou.s  parts  of  occipital  bone;  B,  B',  presphenoid  and  postsphenoid;  C,  C,  perpendicular 
and  cribriform  plates  of  ethmoid  bone;  i>,  parietal  bone;  £?,  frontal  bone;  i'',  pterygoid  bone;  G,  G",  vertical  and  hori- 
zontal parts  of  palatine  bone;  //.vomer;  /.premaxilla;  J,  nasal  bone;  /C,  dorsal  turbinate  bone;  L,  ventral  turbinate 
bone;  /,  //,  ///,  anterior,  posterior  and  middle  fossae  of  cranium;  1,  occipital  condyle;  2,  opening  of  condyloid  canal; 
3,  canal  for  intertransverse  sinus  of  dura  mater;  4,  internal  occipital  protuberance;  5,  internal  opening  of  temporal 
canal;  6,  mastoid  foramen;  7,  floccular  fossa;  8,  meatus  acusticus  internus;  9,  canal  for  trigeminal  nerve;  10,  internal 
carotid  foramen;  11,  12,  openings  into  petro-basilar  canal;  13,  foramen  hypoglossi;  14,  petrosal  crest;  15,  dorsum  sellae; 
16,  hypophyseal  or  pituitary  fossa;  17,  optic  foramen;  18,  ethmoid  foramen;  19,  meatus  naso-pharyngeus;  20,21,22, 
dorsal,  middle,  and  ventral  meatus  nasi;  23,  incisor  teeth;  24,  canine  tooth;  25,  premolar  teeth;  26,  molar  teeth;  27, 
septum  between  frontal 


processes  of  the  maxillae,  and  supports  the  end  of  the  vomer.  The  palatine  fissare 
is  short  but  wide. 

The  horizontal  part  of  the  palatine  bone  is  extensive,  forming  about  one-third 
of  the  hard  palate.  It  presents  a  variable  number  of  accessory  palatine  foramina. 
There  is  usually  a  pointed  posterior  nasal  spine  (Spina  nasalis  aboralis)  at  the  end 
of  the  median  suture.  The  palatine  canal  is  sometimes  formed  entirely  in  this  bone. 
The  perpendicular  part  is  even  more  extensive.  Its  lateral  surface  is  chiefly  free 
and  forms  most  of  the  medial  wall  of  the  large  pterygo-palatine  fossa.  The  max- 
illary foramen  is  situated  in  a  deep  recess  between  this  bone  and  the  zygomatic 
process  of  the  maxilla.  Just  above  it  there  is  commonly  another  foramen  which 
opens  into  the  nasal  cavity.  The  posterior  palatine  and  sphenopalatine  foramina 
are  situated  further  back  and  a  little  lower;  the  former  is  ventral  to  the  latter.  A 
horizontal  plate  extends  from  the  nasal  surface,  meets  that  of  the  opposite  bone,  and 
completes  the  lamina  transversalis  spoken  of  in  the  description  of  the  ethmoid  bone. 
There  is  no  palatine  sinus. 

The  pterygoid  bones  are  very  wide  and  short.  They  form  a  considerable  part 
13 


194 


SKELETON    OF   THE    DOG 


of  the  lateral  boundaries  of  the  posterior  nares.  The  lower  and  posterior  borders 
are  free  and  at  their  angle  of  junction  there  is  a  variable  hamulus. 

The  nasal  bones  are  (in  most  breeds)  long  and  wider  in  front  than  behind. 
The  facial  surface  is  variably  concave  in  its  length  and  is  inclined  toward  the 
median  suture  so  as  to  form  a  central  groove.  The  medial  borders  turn  downward 
and  form  an  internal  nasal  crest  which  becomes  very  prominent  behind.  The  pos- 
terior parts  fit  into  a  notch  formed  by  the  frontal  bones.  The  anterior  ends  form 
an  almost  semicircular  nasal  notch. 

The  lacrimal  bone  is  very  small.  The  facial  part  extends  very  little  or  not 
at  all  beyond  the  orbital  margin.  The  orbital  surface  is  small  and  triangular, 
and  presents  the  entrance  to  the  lacrimal  canal. 

The  large  zygomatic  process  constitutes  the  bulk  of  the  malar  bone.  It  is 
very  long  and  is  strongly  curved.  The  dorsal  border  is  convex,  free  in  front,  where 
it  forms  part  of  the  orbital  margin,  beveled  behind  for  articulation  with  the  similar 
process  of  the  temporal  bone.  Between  these  it  bears  an  eminence,  the  processus 
frontalis,  to  which  the  orbital  ligament  is  attached.  The  body  of  the  bone  may  be 
considered  to  consist  of  a  lacrimal  process  directed  dorsally  and  fitting  in  between 


Symphyseal 
surface 


Fig.  213. — Right  Half  of  Mandible  of  Dog;  Medial  View. 


the  lacrimal  and  maxilla,  and  a  maxillary  process  directed  ventrally.  The  facial 
surface  is  convex. 

The  dorsal  turbinate  bone  is  in  its  anterior  part  a  simple  plate,  attached  by 
one  edge  to  the  nasal  bone;  it  curves  ventro-medially,  and  its  free  border  is  thick- 
ened and  everted.  The  posterior  part  is  wider  and  resembles  the  ethmoturbinates, 
with  which  it  is  connected. 

The  ventral  turbinate  bone  is  short  and  very  complex.  It  is  attached  to  the 
nasal  surface  of  the  maxilla  by  a  basal  lamina,  which  divides  into  two  secondary 
lamellae.  The  latter  detach  numerous  tertiary  lamellae,  which  are  coiled  and  have 
thick  free  edges. 

The  vomer  is  not  in  contact  with  the  posterior  part  of  the  floor  of  the  nasal 
cavity,  and  does  not  divide  the  posterior  nares.  The  posterior  end  is  narrow  and 
deeply  notched.  Near  the  posterior  nares  the  two  plates  curve  outward  and  join 
the  palatine  bones  and  assist  in  forming  the  lamina  transversalis. 

The  two  halves  of  the  mandible  do  not  fuse  completely  even  in  old  age,  so  that 
there  is  a  permanent  symphysis  mandibulae.  The  body  presents  six  alveoli  for  the 
incisor  teeth  and  two  for  the  canines.  The  incisor  alveoli  increase  in  size  from  first 
to  third.  The  canine  alveoli  extend  deeply  downward  and  backward.  The  rami 
diverge  less  than  in  the  pig.  The  ventral  border  of  the  horizontal  part  is  convex 
in  its  length  and  is  thick  and  rounded.     The  alveolar  border  is  slightly  concave  in 


THE   SKULL   AS   A   WHOLE  195 

its  length  and  is  a  little  everted,  especialty  in  its  middle;  it  presents  seven  alveoli 
for  the  lower  cheek  teeth,  which  resemble  those  of  the  upper  jaw  except  that  the 
fourth  and  sixth  are  much  smaller  and  the  fifth  is  like  the  fourth  of  the  upper  series. 
The  interalveolar  space  is  very  short  or  even  absent.  There  are  two  or  three  men- 
tal foramina  on  either  side.  The  vertical  part  is  relatively  small.  Its  lateral  sur- 
face presents  a  deep  masseteric  fossa  (Fossa  masseterica)  which  encroaches  on  the 
coronoid  process  and  is  limited  by  ridges  in  front  and  below.  The  medial  surface 
is  convex  and  is  marked  by  the  usual  mandibular  foramen.  At  about  the  same 
level  as  the  latter  is  the  rough  angular  process  (Processus  angularis),  which  pro- 
jects backward  from  the  posterior  border,  and  is  equivalent  to  the  angle  of  the 
other  animals.  The  condyle  is  placed  very  low — not  much  higher  than  the  apex 
of  the  canine  tooth  when  the  bone  is  resting  on  a  flat  surface.  It  is  long  trans- 
versely and  the  medial  part  of  the  articular  surface  is  much  the  wider  and  extends 
over  the  posterior  surface.  Its  long  axis  is  a  little  oblique,  the  medial  end  being 
inclined  somewhat  downward  and  forward.  The  coronoid  process  is  very  exten- 
sive and  is  bent  slightly  outward  and  backward. 

The  body  of  the  hyoid  bone  is  a  slightly  curved  transverse  rod;  it  is  compressed 
from  before  backward,  and  bears  no  lingual  process.  The  thyroid  cornua  are  per- 
manently attached  to  the  body  by  cartilage;  they  diverge  widely,  curve  inward,  and 
are  compressed  laterally.  The  small  cornua  are  short,  prismatic,  and  strong.  The 
middle  cornua  are  commonly  a  little  longer  than  the  great  cornua;  they  are  com- 
pressed laterally,  and  are  slightly  enlarged  at  the  ends,  which  are  joined  by  cartilage 
to  the  adjacent  cornua.  The  great  cornua  are  bent  outward  and  are  somewhat 
twisted. 

THE  SKULL  AS  A  WHOLE 
The  different  breeds  of  dogs  display  great  variations  in  the  form  and  size  of 
the  skull.  Those  which  have  a  long  narrow  skull  (e.  g.,  greyhound,  collie)  are 
designated  dolichocephalic.  Other  dogs  (e.  g.,  bulldog,  small  spaniels,  pugs)  have 
very  broad,  short  skulls  and  are  termed  brachycephalic.  Intermediate  forms 
(e.  g.,  fox  terrier,  dachshund)  are  mesaticephalic. 

The  length  is  usually  measured  from  the  nuchal  crest  to  the  anterior  end  of  the  premaxil- 
lary  suture,  and  the  breadth  between  the  summits  of  the  zygomatic  arches.  The  cephaUc  index 
is  the  relation  of  the  breadth  to  the  length,  assuming  the  latter  equal  100;    the  formula  is: 

1     P?h ^  cephalic  index.     The  index  of  extreme  dolichocephalic  breeds  is  about  50, 

as  in  the  greyhound,  and  that  of  brachycephalic  specimens  may  be  as  high  as  90,  as  in  the  pug  and 
some  toy  terriers.  Among  the  mesaticephalic  types  are  the  fox  terrier,  with  an  index  of  about 
70,  and  the  white  Pomeranian,  with  one  about  72  to  75.  The  cranio-facial  index  is  the  relation  of 
the  distance  between  the  nuchal  crest  and  the  fronto-nasal  sutvu-e  to  that  between  the  latter  and 
the  nasal  notch.  It  varies  from  10  :  3  in  extreme  brachycephalic  breeds  to  10  :  7  in  extreme 
dolichocephalic  subjects. 

The  frontal  surface  shows  the  wide  outward  curve  of  the  zygomatic  arches 
and  the  great  extent  of  the  temporal  fossae.  The  latter  are  separated  bj^  the  parietal 
crest,  which  in  the  larger  breeds  is  very  strong  and  prominent,  and  is  continued  by 
the  diverging  frontal  crests  to  the  supraorbital  processes.  The  frontal  and  nasal 
regions  are  centrally  depressed,  and  are  more  or  less  concave  in  profile.  The  nasal 
region  is  narrow  and  is  terminated  in  front  by  a  nasal  notch.  In  the  extreme 
brachycephalic  breeds  the  differences  are  very  striking.  The  cranium  is  strongly 
convex  in  both  directions  and  is  considerably  longer  than  the  face.  The  parietal 
crest  is  more  or  less  effaced  posteriorly  and  is  formed  by  the  interparietal  onl3\  The 
parietofrontal  crests  are  separated  by  an  interval  behind  and  diverge  to  the  supra- 
orbital processes,  so  that  the  temporal  fossae  are  widely  separated.  The  frontal 
region  is  wide,  strongly  convex,  and  has  a  shallow  central  depression.  The  nasal 
region  is  very  short,  relatively  wide,  and  centrally  depressed.     In  profile  there  is  a 


196 


SKELETON    OF   THE   DOG 


marked  depression  at  the  fronto-nasal  junction,  producing  what  is  termed  by  fan- 
ciers the  "stop"  of  the  face. 

On  the  lateral  surface  the  great  extent  of  the  temporal  fossa  is  seen.  The 
orbit  communicates  freely  with  the  fossa,  the  posterior  part  of  the  orbital  margin 
being  absent  in  the  dry  skull.  The  axis  of  the  orbital  cavity  forms  a  much  smaller 
angle  with  the  median  plane  than  in  the  horse  and  ox.  A  distinct  crest  marks  the 
limit  between  the  orbital  cavity  and  the  extensive  pterygo-palatine  fossa.  The 
preorbital  region  is  somewhat  triangular,  concave  in  its  length,  and  convex  dorso- 
ventrally ;  the  infraorbital  foramen  is  on  its  lower  part  above  the  third  cheek  tooth. 
In  extreme  brachycephalic  breeds  the  orbit  is  relatively  very  large  and  the  preor- 
bital region  extremely  short  but  high.  In  the  bulldog  the  lower  jaw  protrudes  be- 
yond the  upper — a  condition  known  as  prog- 
nathism. The  opposite  condition,  l^rachygna- 
thism,  is  seen  in  the  dachshund. 

Striking  features  on  the  basal  surface  of 
the  cranium  are  the  width  and  flatness  of  the 
basilar  part  of  the  occipital  bone,  the  small  size 
of  the  paramastoid  processes,  the  large  size  and 


Fig.  214. — Skull  or  Dolichocephalic  Dog; 
Dorsal  View. 


Fig.  215. — Skull  of  Brachycephalic  Dog;  Dorsal  View. 


rounded  shape  of  the  bulla  ossea,  and  the  grooved  form  of  the  articular  surfaces 
for  the  mandible.  The  posterior  nares  are  long  and  narrow  and  are  not  divided 
b}'  the  vomer.  The  hard  palate  is  usually  about  half  the  length  of  the  skull.  It 
is  commonly  marked  b}^  a  median  crest  or  rough  line,  and  on  each  side  are  the 
anterior  and  accessory  palatine  foramina  and  the  palatine  grooves.  The  width 
is  greatest  between  the  fourth  pair  of  cheek  teeth,  and  here  there  is  in  most  skulls 
a  pronounced  depression  on  either  side.  The  length,  width,  and  contour  vary 
greatly  in  different  breeds. 

The  angle  of  divergence  of  the  rami  of  the  mandible  varies  from  25  to  30  de- 
grees; it  is  smallest  in  the  greyhound,  largest  in  extreme  brachycephalic  types, 
e.  g.,  bulldog,  pug. 

The  nuchal  surface  is  somewhat  triangular,  with  the  base  ventral.  The  sum- 
mit is  formed  l)y  the  nuchal  crest,  which  projects  very  stronglv  l)ackward  in  the 
large  breeds.  Below  it  there  are  two  very  distinct  rough  imprints  for  muscular 
attachment.  In  some  skulls  there  is  a  thin  median  occipital  crest,  in  others  a 
rounded  elevation.     Laterally  are  the  temporal  crests  and  the  mastoid  processes. 


BONES    OF   THE   THORACIC    LIMB  197 

The  mastoid  foramen  is  at  the  junction  of  the  occipital  and  temporal  bones,  above 
the  root  of  the  paramastoid  process;  it  opens  directly  into  the  cranial  cavity. 
The  foramen  magnum  varies  greatly  in  form ;  most  often  the  transverse  diameter  is 
the  greater,  but  in  some  skulls  it  is  equaled  or  exceeded  by  the  vertical  diameter. 

The  cranial  cavity  (Fig.  212)  corresponds  in  form  and  size  with  the  cranium, 
especially  in  those  breeds  in  which  the  various  crests  are  more  or  less  effaced  and  the 
frontal  sinuses  are  small.  The  basi-cranial  axis  is  almost  parallel  with  the  palate, 
and  the  floor  is  flattened.  The  anterior  fossa  is  narrow  and  is  only  slightly  higher 
than  the  middle  one.  The  ethmoidal  fossae  are  very  deep  and  the  crista  galli  is 
little  developed.  The  hj^pophyseal  fossa  is  variable  in  depth,  and  the  dorsum  sellse 
is  relatively  high  and  bears  clinoid  processes  laterally.  The  cerebral  and  cerebellar 
compartments  are  well  marked  off  laterally  by  the  petrosal  crests  and  dorsally  by 
the  tentorium  osseum.  The  base  of  the  latter  is  traversed  by  a  canal  which  con- 
nects the  two  temporal  canals.  The  anterior  angle  of  the  petrous  temporal  is 
perforated  by  a  canal  for  the  fifth  cranial  nerve. 

The  nasal  cavity  (Fig.  212)  conforms  to  the  shape  of  the  face.  Its  anterior 
aperture  is  large  and  nearly  circular  in  most  dogs.  The  complex  ventral  turbinates 
occupy  the  anterior  part  of  the  cavity  to  a  large  extent,  except  near  the  aperture. 
Behind  the  ventral  turbinate  is  the  large  opening  of  the  maxillary  sinus.  Behind 
this  the  cavity  is  divided  by  the  lamina  transversalis  into  a  large  upper  olfactory 
region  or  fundus  nasi  and  a  lower  naso-pharyngeal  meatus.  The  fundus  is  occupied 
largely  by  the  ethmoturbinates.  The  posterior  nares  are  undivided  and  are  in 
general  long  and  narrow,  but  vary  with  the  shape  of  the  skull. 

The  frontal  sinus  is  of  considerable  size  in  the  large  breeds,  but  is  confined  to 
the  frontal  bone.  It  is  usually  divided  into  a  small  anterior  and  a  much  larger 
posterior  compartment,  each  of  which  opens  into  the  dorsal  ethmoidal  meatus. 
The  sinus  is  very  small  in  extreme  brachycephalic  types. 

The  maxillary  sinus  is  small,  and  is  in  such  free  communication  with  the  nasal 
cavity  as  to  make  it  rather  a  recess  than  a  true  sinus.  It  is  bounded  medially  by 
the  lamina  lateralis  of  the  ethmoid,  and  its  lateral  wall  is  crossed  obliquely  by  the 
naso-lacrimal  canal.     The  roots  of  the  molar  teeth  do  not  project  up  into  it. 


BONES  OF  THE  THORACIC  LIMB 

The  clavicle  is  a  small,  thin,  irregularly  triangular  bony  or  cartilaginous  plate. 
It  is  embedded  in  the  brachiocephalicus  muscle  in  front  of  the  shoulder-joint  and 
forms  no  articulation  with  the  rest  of  the  skeleton.  (It  is  nearly  an  inch  long  in 
a  large  cat  and  is  a  slender  curved  rod.) 

The  scapula  is  relatively  long  and  narrow.  The  spine  increases  gradually 
in  height  from  above  downward  and  divides  the  lateral  surface  into  two  nearly 
equal  fossae.  Its  free  edge  is  thick  and  rough  above,  and  at  the  lower  part  is  thin 
and  bent  backward.  The  acromion  is  short  and  blunt  and  is  opposite  the  rim  of 
the  glenoid  cavity.  The  subscapular  fossa  is  very  shallow  and  is  marked  by  rough 
lines  (Linese  musculares).  The  rough  area  above  it  for  the  attachment  of  the  ser- 
ratus  ventralis  is  large  and  quadrilateral  in  front,  narrow  and  marginal  behind. 
The  anterior  border  is  thin,  strongly  convex,  and  sinuous.  The  posterior  border 
is  straight  and  thick.  The  vertebral  border  is  convex  and  thick  and  bears  a  band 
of  cartilage.  The  anterior  angle  is  rounded.  The  posterior  angle  is  thick  and  square. 
The  neck  is  well  defined  and  bears  a  rough  eminence  posteriorly,  from  which  the 
long  head  of  the  triceps  arises.  The  glenoid  cavity  is  continued  forward  upon  the 
lower  face  of  the  tuber  scapulae,  which  is  blunt  and  bears  no  coracoid  process.  The 
cervical  angle  is  opposite  the  first  thoracic  spine;  the  dorsal  angle  lies  above  the  ver- 
tebral end  of  the  fourth  rib,  and  the  glenoid  angle  at  a  point  just  in  front  of  the 
sternal  end  of  the  first  rib  in  the  ordinary  standing  position.     The  tuber  scapulae 


198 


SKELETON    OF    THE    DOG 


unites  with  the  rest  of  the  bone  at  six  to  eight  months.     The  shoulder  has  a  great 
range  of  movement  on  the  chest  wall. 

The  humerus  is  relatively  very  long,  rather  slender,  and  has  a  slight  spiral 
twist.  The  shaft  is  somewhat  compressed  laterally,  especially  in  its  proximal  two- 
thirds;  this  part  is  curved  in  varying  degree,  convex  in  front.  The  deltoid  tuber- 
osity has  the  form  of  a  low  ridge,  and  it  is  continued  by  a  crest  which  runs  up- 
ward and  backward  and  bears  a  tubercle  on  its  proximal  part.  Another  line  runs 
from  it  down  the  anterior  aspect  and  forms  .the  medial  boundary  of  the  very  shallow 
musculo-spiral  groove.  The  nutrient  foramen  is  about  in  the  middle  of  the  posterior 
surface.  A  slight  elevation  on  the  proximal  third  of  the  medial  surface  represents 
the  teres  tubercle.  The  head  is  long  and  strongly  curved  from  before  backward. 
The  neck  is  better  marked  than  in  the  horse.  The  undivided  lateral  tuberosity  is 
placed  well  forward  and  extends  little  above  the  level  of  the  head.     The  medial  tu- 


Cartilage 


Tuber 
scapulce 


Cartilage 


Pos- 
terior 
angle 


I     Glenoid  catnty 
Acromion 


Fig.  21G. — Left  Scapula  of  Dog;  Lateral  Viei 


Glenoid  cavity 
Fig.  217. — Right  Scapula  of  Dog;  Medial  View. 


berosity  is  small.  The  intertuberal  or  bicipital  groove  is  undivided  and  is  displaced 
to  the  medial  side  by  the  extension  forward  of  the  lateral  tuberosity.  The  distal 
end  bears  an  oblique  trochlear  articular  surface  for  articulation  with  the  radius  and 
ulna,  the  lateral  part  of  which  is  the  more  extensive  and  is  faintl}^  grooved.  The  epi- 
condyles  are  prominent.  The  coronoid  and  olecranon  fossae  often  communicate 
through  a  large  supratrochlear  foramen.  The  proximal  end  unites  with  the  shaft 
at  about  one  year,  the  distal  at  six  to  eight  months. 

The  two  bones  of  the  forearm  are  relatively  long  and  articulate  with  each  other 
at  each  end  in  such  a  manner  as  to  allow  of  slight  movement.  A  narrow  inter- 
osseous space  separates  their  shafts.  The  radius  is  flattened  from  before  back- 
ward and  increases  in  size  distally.  The  shaft  forms  two  curves,  so  that  it  is  con- 
vex dorsally  and  medially.  The  dorsal  surface  is  convex  in  both  directions  and  is 
marked  in  its  distal  half  by  a  groove  for  the  oblique  extensor  of  the  carpus.  The 
volar  surface  presents  the  nutrient  foramen  in  its  proximal  third,  and  bears  a  rough 


BONES   OF   THE   THORACIC    LIMB 


199 


line  (Crista  interossea)  laterally  for  the  attachment  of  the  interosseous  ligament. 
The  proximal  end  (Capitulum  radii)  is  relativel}^  small  and  is  supported  by  a  dis- 
tinct neck  (Collum  radii).  It  bears  a  concave  surface  (Fovea  capituli)  for  articu- 
lation with  the  humerus,  and  a  convex  marginal  area  (Circumferentia  articularis) 
behind  for  the  ulna.  The  radial  tuberosity  is  small.  There  is  a  large  lateral  tuber- 
osity and  below  this  a  rough  eminence.  The  distal  extremity  is  much  wider. 
It  has  an  extensive  concave  carpal  articular  surface.  Its  medial  border  projects 
downward,  forming  the  styloid  process  of  the  radius.  Laterally  there  is  a  concave 
facet  (Incisura  ulnaris  racUi)  for  articulation  with  the  ulna.  Dorsally  are  three 
distinct  grooves  for  the  extensor  tendons.     The  ulna  is  well  developed,  but  dimin- 


Lateral 
tuber  ositij 


Medial 


I  tdert  liberal 


tuberosity     ^'l'"'' 


Head 


A 


Neck 
Deltoid  tuberosity 


Musculo-spiral 
groove 


Coronoid  fossa 


Lateral  condyloid 
crest 

Olecranon  fossa 


Lateral  epicondyle       ^"^'"^  epicondyle 
FiQ.  218. — Left  Humerus  of  Dog;  Lateral  View. 


tH- 


Medial  condyle 


Fig.  219. — Left    Humerus  op    Dog;  Medial  View. 

1,   Attachment  of  medial  ligament   of  elbow  joint;   2, 

attachment  of  flexor  muscles  to  medial  epicondyle. 


ishes  in  size  distally.  It  crosses  the  volar  surface  of  the  radius  medio-laterally. 
The  shaft  is  large  and  three-sided  in  its  proximal  two-thirds,  smaller  and  more 
rounded  below.  Its  dorsal  surface  is  in  general  rough.  The  nutrient  foramen  is 
near  the  proximal  end.  A  vascular  groove  descends  from  it  and  indicates  the  course 
of  the  interosseous  artery.  The  proximal  end  is  relatively  short.  It  is  concave 
and  smooth  mediall}',  convex  and  rough  laterally.  The  olecranon  is  grooved  and 
bears  three  prominences,  of  which  the  posterior  one  is  large  and  rounded.  The 
semilunar  notch  is  wide  below  and  completes  the  surface  for  articulation  with  the 
trochlea  of  the  humerus.  Below  it  is  a  concave  surface  (Incisura  radialis),  which 
articulates  with  the  back  of  the  head  of  the  radius,  and  below  this  is  a  fossa,  which 
receives  a  tuberosity  of  the  radius.     The  distal  end  (Capitulum  ulnae)  is  small  and 


200 


SKELETON    OF   THE   DOG 


Olecranon 


Processus  anconceus 


Semilunar  notch 
y^  Fovea  capituli 


Shaft  of  ulna 


Shaft  of 
radius 


is  produced  to  a  blunt  point  (Processus  styloideus  ulnae).  It  articulates  with  the 
ulnar  carpal  distally,  and  has  a  convex  facet  on  its  dorso-medial  aspect  for  the  radius. 
The  proximal  end  of  the  radius  unites  with  the  shaft  at  six  to  eight  months,  the 
distal  at  about  one  and  a  half  years  of  age.  The  olecranon  and  the  distal  end  of  the 
ulna  fuse  with  the  rest  of  the  bone  at  about  fifteen  months. 

The  carpus  comprises  seven  bones — -three  in  the  proximal  row  and  four  in  the 
distal.  The  numerical  reduction  in  the  proximal  row  is  apparently  due  to  the 
fusion  of  the  radial  and  intermediate,  constituting  a  large  bone  (radio-intermediate) 

which  articulates  with  almost  all  of  the 
distal  surface  of  the  radius  and  with  the 
bones  of  the  distal  row.  It  projects  promi- 
nently on  the  volar  surface  of  the  carpus. 
The  ulnar  carpal  is  long;  it  articulates  with 
the  radius  and  ulna  above  and  the  acces- 
sory behind;  below  it  rests  on  the  fourth 
carpal  and  is  prolonged  downward  to  ar- 
ticulate with  the  fifth  metacarpal  also. 
The  accessory  is  cylindrical,  constricted 
in  its  middle  and  enlarged  at  each  end;  the 
anterior  extremity  articulates  with  the 
ulna  and  ulnar  carpal  bone.  The  first  car- 
pal is  the  smallest  bone  of  the  lower  row; 
it  articulates  ^vith  the  second  carpal  later- 
ally and  the  first  metacarpal  distall3^  The 
second  carpal  is  wedge-shaped,  the  base  be- 
ing posterior;  its  proximal  surface  is  con- 
vex, and  its  distal  is  concave  and  rests  on 
the  second  metacarpal.  The  third  carpal 
is  somewhat  like  the  second ;  its  distal  sur- 
face is  concave  and  articulates  chieflj^  with 
the  third  metacarpal.  The  fourth  carpal 
is  the  largest  of  the  row;  it  articulates  with 
the  fourth  and  fifth  metacarpals.  Two 
small  bones  or  cartilages  may  be  found  on 
the  volar  surface  at  the  junction  of  the  two 
rows,  and  a  third  small  bone  articulates 
with  the  medial  side  of  the  radio-inter- 
mediate.^ 

Five  metacarpal  bones  are  present. 
The  first  is  much  the  shortest;  the  third 
and  fourth  are  the  longest,  and  are  about 
one-fifth  longer  than  the  second  and  fifth. 
The  fifth  is  the  widest  at  the  proximal  end 
and  is  slightly  shorter  than  the  second. 
They  are  close  together  above,  but  diverge 
somewhat  distally;  the  first  is  separated 
from  the  second  by  a  considerable  interosseous  space.  They  are  so  arranged  as  to 
form  a  convex  dorsal  surface  and  a  concave  volar  surface,  which  corresponds  to 
the  hollow  of  the  palm  of  the  hand  in  man.  Each  consists  of  a  shaft  and  two  ex- 
tremities. The  shaft  is  compressed  from  before  backward.  In  the  third  and  fourth 
it  is  almost  four-sided,  in  the  second  and  fifth  three-sided,  in  the  first  rounded. 
The  proximal  ends  (Bases)  articulate  with  each  other  and  with  the  corresponding 

1  The  third  bone  was  termed  the  phacoid  in  the  cat  by  Strauss-Durckeim,  and  is  regarded 
by  some  authors  as  the  vestige  of  an  additional  digit,  the  prepollex. 


Styloid  process 
of  ulna 


Carpal  articular 
surfaces 


Fig.  220.- 


-Left  Radius  and  Ulna  of  Dog;  Medial 
View. 
o,  Rough  area  for  attachment  of  biceps  brachii 
and  brachialis  muscles;  b,  groove  for  tendon  of  exten- 
sor carpi  obUquus. 


BONES    OF    THE   THORACIC    LIMB 


201 


carpal  bones.  The  carpal  articular  surface  formed  by  them  is  concave  from  side 
to  side,  convex  from  before  backward.  The  distal  ends  (Capitula)  have  articular 
surfaces  of  the  nature  of  a  head,  but  bear  a  sagittal  ridge  on  the  volar  aspect,  ex- 
cept the  first,  which  is  grooved.  Ossification  is  complete  at  five  or  six  months  of 
age. 

The  five  digits  have  three  phalanges  each,  except  the  first,  which  has  two. 
The  third  and  fourth  digits  are  the 
longest ;  the  first  is  very  short  and  does 
not  come  in  contact  with  the  ground 
in  walking.  The  first  phalanges  of  the 
chief  digits  have  four-sided  shafts, 
which  are  slightly  curved  dorsally. 
The  proximal  end  of  each  has  a  con- 
cave surface  for  articulation  with  the 
metacarpal  bone  and  is  deeply  notched 
behind.  The  distal  end  has  a  trochlea 
for  articulation  with  the  second  pha- 
lanx, and  depressions  on  each  side  for 
ligamentous  attachment.  The  second 
phalanges  are  about  two-thirds  of  the 
length  of  the  first  phalanges.  The 
proximal  articular  surface  consists  of 
two  cavities  separated  by  a  sagittal 
ridge.  The  distal  extremity  is  wider 
and  flatter  than  that  of  the  first.  The 
third  phalanges  correspond  in  general 
to  the  form  of  the  claws.  The  base  has 
an  articular  surface  adapted  to  the 
second  phalanx  and  is  encircled  by  a 
collar  of  bone  (Crista  unguicularis). 
The  volar  surface  bears  a  wing  or  tuber- 
osity, and  on  each  side  of  this  is  a  fora- 
men. The  ungual  part  is  a  curved  rod 
with  a  blunt-pointed  free  end.  It  is 
rough  and  porous.  Its  base  forms  with 
the  collar  previously  mentioned  a  deep 
groove,  into  which  the  proximal  border 
of  the  claw  is  received.  The  two  pha- 
langes of  the  first  digit  resemble  in  ar- 
rangement the  first  and  third  phalanges 
of  the  other  digits.  Ossification  is 
complete  at  five  or  six  months. 

Nine  volar  sesamoids  are  usually 
present.  Two  are  found  at  each  meta- 
carpo-phalangeal  joint  of  the  chief 
digits.  They  are  high  and  narrow, 
articulate  with  the  distal  end  of  the 

metacarpal  bone  in  front,  and  have  a  small  facet  on  the  base  for  the  first  phalanx. 
On  this  joint  of  the  first  digit  there  is  usually  a  single  flattened  sesamoid,  but  ex- 
ceptionally two  are  present.  The  distal  volar  sesamoids  remain  cartilaginous.  A 
nodular  dorsal  sesamoid  occurs  in  the  capsule  of  the  metacarpo-phalangeal  joints, 
and  cartilaginous  nodules  are  found  in  a  similar  position  in  connection  with  the 
joints  between  the  first  and  second  phalanges. 


Fig.  221. — Skeleton  of  Distal  Part  op  Right  Thoracic 
Limb  of  Dog;  Dorsal  View. 
The  digits  are  spread.  J,  Distal  end  of  interosseous 
space;  R,  distal  end  of  radius;  C.  r.+  i.,  radio-intermediate 
carpal;  C  u.,  ulnar  carpal;  C.  a.,  accessory  carpal  (very 
small  part  \asible) ;  C.  1,C.  2,  C.  S,  C.  4,  first  to  fourth  car- 
pal bones;  Mc.  I,  metacarpal  bone  of  first  digit;  P.  1  +  2, 
fused  first  and  second  phalanges  of  same;  P.  3,  third  phalanx 
of  same;  Mc.  V,  fifth  metacarpal  bone;  P.  UP.  2,  P.  3, 
phalanges  of  fifth  digit;   S,  dorsal  sesamoid;    C,    C,   volar 


202 


SKELETON    OF   THE   DOG 


BONES  OF  THE  PELVIC  LIMB 

The  ilium  is  nearly  parallel  with  the  median  plane  and  its  axis  is  only  slightly 
oblique  with  regard  to  the  horizontal  plane.  The  gluteal  surface  is  concave.  The 
pelvic  surface  is  almost  flat.  The  auricular  surface  faces  almost  directly  inward, 
and  in  front  of  it  there  is  an  extensive  rough  area.  The  ilio-pectineal  line  is  very 
distinct  and  is  uninterrupted.  The  crest  is  strongly  convex,  thick,  and  rough. 
The  tuber  sacrale  is  represented  by  a  thickened  part  which  bears  two  eminences, 
homologous  with  the  posterior  superior  and  posterior  inferior  iliac  spines  of  man. 
The  tuber  coxse  also  has  two  prominences,  which  are  equivalent  to  the  two  anterior 
spines  present  in  man.  The  shaft  is  almost  sagittal  and  is  compressed  laterally. 
It  is  smooth  and  rounded  dorsally,  and  it  bears  a  ventro-lateral  crest  (Linea  glu- 
tae  ventralis),  which  terminates  at  a  tuberosity  in  front  of  the  acetabulum. 

The  ischium  has  a  twisted  appearance,  owing  to  the  fact  that  its  acetabular 
part  is  nearly  sagittal  while  the  posterior  part  is  almost  horizontal.     The  two  bones 


Fig.  222.— Rk 
1,  Gluteal  surface  of  ilium;   2,  crest  of  i 


HT  Os  Cox«  OP  Dog;  Lateral  View. 

3,  tuber  sacrale;   4,  tuber  coxa;   5,  shaft  of  ilium;   6,  nutrient  fora- 

10,  ilio-pectineal 


uum; 
Tnen;  7,  greater  sciatic  notch;  S,  ventral  gluteal  line;  9,  tubercle  to  which  rectus  femoris  is  attached; 
eminence;  11,  11',  acetabular  and  symphyseal  branches  of  pubis;  12,  articular  surface  of  acetabulum;  12',  fossa  acetab- 
uli;  13,  obturator  foramen;  14,  ischiatic  spine;  15,  lesser  sciatic  notch;  16,  16',  acetabular  and  symphyseal  branches 
of  ischium:   17,  tuber  ischii. 


also  diverge  behind  and  the  tubera  are  flattened  and  everted.  The  superior  ischiatic 
spine  is  low  and  thick ;  its  posterior  part  is  marked  by  transverse  grooves  and  has  a 
prominent  outer  lip.  The  greater  sciatic  notch  is  elongated  and  very  shallow.  There 
is  no  lesser  sciatic  notch.     The  ischial  arch  is  relatively  small  and  is  semi-elliptical. 

The  symphyseal  part  of  the  pubis  is  thick  and  fuses  late  with  the  opposite  bone. 
There  is  no  subpubic  groove. 

The  acetabulum  is  about  twice  as  far  from  the  tuber  coxae  as  from  the  tuber 
ischii.  The  fossa  acetabuli  is  deep,  and  is  bounded  medially  by  a  flat  plate  of  bone; 
its  floor  is  so  thin  as  to  be  translucent.     There  is  a  small  notch  behind. 

The  obturator  foramen  resembles  in  outline  an  equilateral  triangle  with  the 
angles  rounded  off. 

Union  of  the  three  parts  of  the  os  coxse  has  usually  taken  place  at  six  months, 
but  the  epiphyses  of  the  ilium  and  ischium  do  not  fuse  with  the  main  part  of  these 
bones  till  about  the  end  of  the  second  year. 

The  inlet  of  the  pelvis  is  very  oblique.  It  is  almost  circular  in  the  female, 
but  in  the  male  it  is  elliptical  and  the  conjugate  diameter  is  the  longer.  The  cavity 
is  narrowest  between  the  acetabula,  and  very  wide  behind.  The  floor  is  concave 
and  relatively  narrow  in  front,  wide  and  flat  behind. 


BONES    OF   THE    PELVIC    LIMB 


203 


The  femur  is  relatively  much  longer  than  in  the  horse  or  ox.  The  shaft  is  regu- 
larly cylindrical,  except  near  the  extremities,  where  it  is  wider  and  compressed  froiiz 
before  backward.  It  is  strongly  curved  in  its  distal  two-thirds,  convex  in  front. 
The  posterior  surface  is  flattened  transversely,  narrow  in  the  middle,  and  widens 
toward  each  end.  It  is  bounded  by  two  rough  lines  (Labium  laterale,  mediale) 
which  diverge  toward  the  extremities.  The  third  trochanter  and  the  supracondyloid 
fossa  are  absent.  There  are  two  supracondyloid  crests,  the  medial  one  being  small. 
The  nutrient  foramen  is  in  the  proximal  third  of  the  posterior  surface.  The  head 
is  a  little  more  than  a  hemisphere  and  has  a  shallow  fovea  behind  and  lateral  to  its 
center.     The  neck  is  well  defined.     The  trochanter  major  does  not  extend  as  high 


Crest  of  ilium  Tir  ■        /•  •,  • 

V_  n  mg  of  ilium 


Tuber  coxce 


Shaft  of  ilium 


Ilio-pedineal 
eminence 


Acetabular  branch  of 
pubis 

Symphyseal  branch  of 
pubis 
Symphyseal  branch  of  _ 
ischium 


Vascular  impression 


-  Sacro-iliac  articulation 

Nutrient  foramen 
Ilio-pectineal  line 

Tubercle 
Acetabulum 


Obturator  foramen 

Acetabular  branch  of 
ischium 

Tuber  ischii 


Ischial  arch 
Fig.  223. — Pelvic  Bones  of  Dog;  Ventral  View. 
1,  Body  of  first  sacral  vertebra;    2,  wing  of  sacrum;    3,  sacral  canal;    4,  median  crest  of  sacrum;  5,  pelvic  surface  of 


as  the  head;  a  thick  ridge  runs  from  its  anterior  surface  to  the  neck.  The  trochanter 
minor  has  the  form  of  a  blunt  tuberosity.  The  trochanteric  fossa  is  round  and 
deep.  The  ridges  of  the  trochlea  are  practically  sagittal  in  direction  and  are  al- 
most similar.  The  intercondyloid  fossa  is  wide.  Just  above  each  condyle  pos- 
teriorly there  is  a  facet  for  articulation  with  the  sesamoid  bone  which  is  developed 
in  the  origin  of  the  gastrocnemius  muscle.  Union  of  shaft  and  extremities  takes 
place  at  about  one  and  a  half  years. 

The  tibia  is  about  the  same  length  as  the  femur.  The  shaft  forms  a  double 
curve;  the  proximal  part  is  convex  medially,  the  chstal  part  laterally.  The  prox- 
imal third  is  prismatic,  but  is  compressed  laterally  and  is  long  from  before  backward. 
The  remainder  is  almost  regularly  cylindrical.     The  crest  is  short  but  very  prom- 


204 


SKELETON    OF   THE    DOG 


inent.  The  nutrient  foramen  is  usually  in  the  proximal  third  of  the  lateral  border. 
The  tuberosity  is  not  grooved,  but  bears  a  distinct  mark  where  the  ligamentum 
patellae  is  attached.  There  is  a  small  facet  for  the  fibula  on  the  postero-lateral  part 
of  the  lateral  condyle,  and  a  small  sesamoid  bone  in  the  tendon  of  origin  of  the 
popliteus  is  in  contact  with  the  posterior  angle  of  the  latter.  The  distal  end  is  quad- 
rangular and  relatively  small.  The  articular  grooves  and  ridge  are  almost  sagittal. 
There  is  a  facet  laterally  for  articulation  with  the  fibula.  There  is  a  vertical  groove 
medially  and  a  shallower  one  behind — both  for  tendons.  The  proximal  end  unites 
with  the  shaft  at  about  eighteen  months,  the  distal  at  fourteen  or  fifteen  months. 


Head 


Trochanteric 
fossa 


\,.  .    —  ^[ed^al 

Lateral  _i  £.       ( jncondyle 

epicondyle      ""  \_^,      ,^* 

Trochlea 
Fig.  224. — Right  Femur  of   Dog:  Anterior  View. 


Lateral 
condyle 


I  ntercondyloid 

fossa 


Fig.  225. — Right  Femur  of  Dog;  Posterior  View. 
1,  2,  Sesamoid  bones. 


The  fibula  extends  the  entire  length  of  the  region.  It  is  slender,  somewhat 
twisted,  and  enlarged  at  either  end.  The  proximal  part  of  the  shaft  is  separated 
from  the  tibia  by  a  considerable  interosseous  space,  but  the  distal  part  is  flattened 
and  closely  applied  to  the  tibia.  The  proximal  extremity  is  flattened  and  articu- 
lates with  the  lateral  condyle  of  the  tibia.  The  distal  end  is  somewhat  thicker  and 
forms  the  lateral  malleolus.  It  articulates  medially  with  the  tibia  and  the  tibial 
tarsal  bone.     Laterally  it  l)ears  two  tubercles. 

The  patella  is  long  and  narrow.  The  free  surface  is  convex  in  both  direc- 
tions. The  articular  surface  is  convex  from  side  to  side  and  slightly  concave  from 
above  downward. 


BONES    OF  THE    PELVIC    LIMB 


205 


The  tarsus  comprises  seven  bones.  The  tibial  tarsal  consists  of  a  body,  neck, 
and  head,  like  the  bone  in  man.  The  body  presents  a  proximal  trochlea  for  articula- 
tion with  the  tibia  and  fibula.  The  plantar  surface  has  three  facets  for  articulation 
with  the  fibular  tarsal  bone.  The  head  is  directed  a  little  inward  and  articulates 
with  the  central.  The  fibular  tarsal  has  a  long  anterior  process  or  "beak,"  but 
the  sustentaculum  is  short.  The  tuber  calcis  presents  a  sagittal  groove.  The 
central  has  a  concave  proximal  surface  adapted  to  the  head  of  the  tibial  tarsal. 
Its  distal  surface  articulates  with  the  first,  second,  and  third  tarsals.  It  bears  two 
plantar  tubercles.  The  first  tarsal  is  flattened  and  irregularly  quadrangular;  its 
proximal  surface  articulates  with  the  central  and  the  distal  with  the  first  metatarsal. 


Sulcus  muscu-, 
laris 


Head  of  fibula 


Tuberosity 


Medial 
condyle 


Head  of  fibula 


Shaft  of  tibia 


Interosseous  space 


Fig.  226. — Right  Tibia  and  FiBUL.'t  of  Dog;  Ante- 
rior View. 


#  ^     E-  Lateral  inalleolus 

-Right  Tibia  and  Fibula  of  Dog;  Poste- 
rior View. 


The  second  tarsal  is  the  smallest  and  is  wedge-shaped;  it  articulates  distally  with 
the  second  metatarsal  bone.  The  third  tarsal  is  also  wedge-shaped,  the  base  being 
in  front;  it  articulates  with  the  third  metatarsal  distally.  The  fourth  tarsal  is 
remarkably  high,  and  resembles  a  quadrangular  prism;  its  proximal  surface 
articulates  with  the  fibular  tarsal,  its  distal  with  the  fourth  and  fifth  metatarsal, 
and  the  medial  with  the  central  and  third  tarsal  bones.  A  groove  for  the  tendon  of 
the  peroneus  longus  crosses  its  lateral  and  plantar  surface,  and  above  it  are  one  or 
two  tubercles.  The  tuber  calcis  fuses  with  the  body  of  the  bone  at  fourteen  or 
fifteen  months. 

Five  metatarsal  bones  are  present.     The  first  is  commonly  very  small  and  has 
the  form  of  a  blunt  cone,  somewhat  compressed  laterally.     It  articulates  with  the 


206 


THE    ARTICULATIONS    OR   JOINTS 


first  tarsal  and  furnishes  insertion  to  the  tibialis  anterior  muscle.  In  some  cases 
it  fuses  with  the  first  tarsal;  when  the  first  digit  is  well  developed,  its  metatarsal 
may  resemble  the  others  (except  in  size)  or  be  reduced  in  its  proximal  part  to  a 
fibrous  band.  The  other  metatarsals  are  a  little  longer  than  the  corresponding: 
metacarpals.  Their  proximal  ends  are  elongated  from  before  backward  and  have 
plantar  projections,  which  in  the  case  of  the  third  and  fourth  usually  have  facets 


Fig.  228. — Skeleton  of  Distal  Part  of  Left  Pelvic  Limb  of  Dog;  Dorsal  View. 
L,  Lateral  malleolus  (distal  end  of  fibula);   T.  t.,  tibial  tarsal  bone;   T.  /.,  fibular  tarsal  bone;   T.  c,  central  tarsal 
bone;   T.  2,  T.  3,  T.  4,  second,  third,  and  fourth  tarsal  bones;  P.  l-\-  2,  fused  first  and  second  phalanges,  and  P.  3,  third 
phalanx,  of  first  digit;  Mc.  5,  fifth  metacarpal  bone;  P.  1,  P.  2,  P.  3,  phalanges  of  fifth  digit;    S,  dorsal  sesamoid. 


for  articulation  with  two  small  rounded  sesamoid  bones.  In  other  respects  they 
resemble  the  metacarpals. 

The  first  digit  is  often  absent.  When  present,  its  development  varies  and  it 
contains  one  or  two  phalanges.  In  other  cases — especiall}'  in  very  large  dogs — 
a  sixth  digit  is  present;  it  does  not  articulate  with  the  metatarsus,  but  is  attached 
by  fibrous  tissue.  The  phalanges  of  the  other  digits  resemble  those  of  the  tho- 
racic limb. 

Ossification  of  the  metatarsal  bones  and  phalanges  is  complete  at  five  or  six 
months. 


ARTHROLOGY 

THE  ARTICULATIONS  OR  JOINTS 

An  articulation  or  joint  is  formed  by  the  union  of  two  or  more  bones  or  carti- 
lages by  other  tissue.  Bone  is  the  fundamental  part  of  most  joints;  in  some  cases 
a  bone  and  a  cartilage,  or  two  cartilages,  form  a  joint.  The  uniting  medium  is 
chiefly  fibrous  tissue  or  cartilage,  or  a  mixture  of  these.  Union  of  parts  of  the 
skeleton  by  muscles  (Synsarcosis) ,  as  in  the  attachment  of  the  thoracic  limb  in 
the  horse,  will  not  be  considered  in  this  section. 

Joints  may  be  classified — (a)  anatomically,  according  to  their  mode  of  develop- 
ment, the  nature  of  the  uniting  medium,  and  the  form  of  the  joint  surfaces;  (6) 
physiologically,  with  regard  to  the  amount  and  kind  of  movement  or  the  absence 
of  mobility  in  them;   (c)  by  a  combination  of  the  foregoing  considerations. 

The  classification  of  joints  is  still  in  a  very  unsatisfactory  state,  and  unfortunately  the  same 
term  is  used  in  various  senses  by  different  authors.  The  two  main  subdivisions  proposed  by  Hep- 
burn are:  (1)  Those  in  which  the  uniting  medium  is  coextensive  with  the  opposed  joint  surfaces, 
and  in  which  a  direct  union  of  those  surfaces  is  thereby  effected.  (2)  Those  in  which  the  uniting 
medium  has  undergone  interruption  in  its  structural  continuity,  and  in  which  a  ca\'ity  of  greater 
or  less  extent  is  thus  formed  in  the  interior  of  the  joint.  This  distinction  is  of  considerable  im- 
portance chnically. 

Three  chief  subdivisions  of  joints  are  usually  recognized — viz.,  sjniarthroses, 
diarthroses,  and  amphiarthroses. 


SYNARTHROSES 
In  this  group  the  segments  are  united  by  fibrous  tissue  or  cartilage,  or  a  mix- 
ture of  the  two  in  such  a  manner  as  practically  to  preclude  movement;  hence  they 
are  often  termed  fixed  or  immovable  joints.  There  is  no  joint  cavity.  Most  of 
these  joints  are  temporary,  the  uniting  medium  being  invaded  by  the  process  of 
ossification,  with  a  resulting  ankylosis  or  synostosis.  The  chief  classes  in  this 
group  of  joints  are  as  follows: 

(1)  Suture.— This  term  (Sutura)  is  applied  to  those  joints  in  the  skull  in  which 
the  adjacent  bones  are  closely  united  by  fibrous  tissue — the  sutural  ligament.  In 
many  cases  the  edges  of  the  bones  have  irregular  interlocking  margins,  forming  the 
sutura  serrata,  e.  g.,  the  frontal  suture.  In  others  the  edges  are  beveled  and 
overlap,  forming  the  sutura  squamosa,  e.  g.,  the  parieto-temporal  suture.  If  the 
edges  are  plane  or  shghtly  roughened,  the  term  sutura  harmonia  is  applied  to  the 
joint,  e.g.,  the  nasal  suture. 

(2)  Syndesmosis. — In  these  the  uniting  medium  is  white  fibrous  or  elastic 
tissue  or  a  mixture.  As  examples  are  the  union  of  the  shafts  of  the  metacarpal  bones 
and  the  attachments  to  each  other  of  costal  cartilages. 

(3)  Synchondrosis.— In  these  the  two  bones  are  united  by  cartilage,  e.  g., 
the  joint  between  the  basilar  part  of  the  occipital  bone  and  the  sphenoid  bone. 
Very  few  of  these  joints  are  permanent. 

(4)  Symphysis. — This  term  is  usually  limited  to  a  few  median  joints  which 
connect  symmetrical  parts  of  the  skeleton,  e.  g.,  symphysis  pelvis,  symphysis 
mandibulge.  The  uniting  medium  is  cartilage  and  fibrous  tissue.  In  some  cases 
a  cleft-like  rudimentary  joint  cavity  occurs. 

207 


208 


THE   ARTICULATIONS 


(5)  Gomphosis. — This  term  is  sometimes  applied  to  the  implantation  of  the 
teeth  in  the  alveoli. 

The  gomphosis  is  not,  properly  considered,  a  joint  at  all,  since  the  teeth  are  not  parts  of  the 
skeleton. 

DIARTHROSES 

These  joints  are  characterized  by  the  presence  of  a  joint  cavity  and  by  their 
mobility.  They  are  often  called  movable  or  true  joints.  A  simple  joint  (Articu- 
latio  simplex)  is  one  formed  by  two  articular  surfaces;  a  composite  joint  (Articulatio 
composita),  one  formed  by  several  articular  surfaces.  The  following  structures 
enter  into  their  formation: 

1.  The  articular  surfaces  (Facies  articulares)  are  in  most  cases  smooth,  and 
vary  much  in  form.  The}^  are  formed  of  specially  dense  bone,  which  differs  his- 
tologically from  ordinary  compact  substance.  In  certain  cases  (vide  Osteology) 
the  surface  is  interrupted  by  non-articular  cavities  known  as  synovial  fossae. 

2.  The  articular  cartilages  (Cartilagines  articulares),  usually  hyaline  in  type, 
form  a  covering  over  the  articular  surfaces  of  the  bones.  They  vary  in  thick- 
ness in  different  joints;  they  are  thickest  on  those 
which  are  subject  to  the  most  pressure  and  fric- 
tion. They  usually  tend  to  accentuate  the  curva- 
ture of  the  bone,  ^.  e.,  on  a  concave  surface  the 
peripheral  part  is  the  thickest,  while  on  a  con- 
vex surface  the  central  part  is  the  thickest.  The 
articular  cartilages  are  non-vascular,  very  smooth, 
and  have  a  bluish  tinge  in  the  fresh  state.  They 
diminish  the  effects  of  concussion  and  greatly  reduce 
friction. 

3.  The  articular  or  joint  capsule  (Capsula  articu- 
laris)  is,  in  its  simplest  form,  a  tube,  the  ends  of  which 
are  attached  around  the  articulating  surfaces.  It 
consists  of  two  layers — an  external  one,  composed  of 
fibrous  tissue,  and  an  internal  one,  the  synovial  layer 
or  membrane.  The  fibrous  layer  (Stratum  fibrosum) , 
sometimes  termed  the  capsular  ligament,  is  attached 
either  close  to  the  margins  of  the  articular  surfaces  or 
at  a  variable  distance  from  them.  Its  thickness  varies 
greatly  in  different  situations:  in  certain  places  it  is  extremely  thick,  and  sometimes 
cartilage  or  bone  develops  in  it;  in  other  places  it  is  practically  absent,  the  cap- 
sule then  consisting  only  of  the  synovial  membrane.  Tendons  which  pass  over  a 
joint  may  partially  take  the  place  of  the  fibrous  layer;  in  these  cases  the  deep  face 
of  the  tendon  is  covered  by  the  synovial  layer.  Parts  of  the  capsule  may  undergo 
thickening  and  so  form  ligaments,  which  are  not  separable,  except  artificially,  from 
the  rest  of  the  capsule.  The  synovial  layer  (Stratum  synoviale)  lines  the  joint 
cavity  except  where  this  is  bounded  by  the  articular  cartilages;  it  stops  normally 
at  the  margin  of  the  latter.  It  is  a  thin  membrane,  and  is  richly  supplied  by  close 
networks  of  vessels  and  nerves.  It  frequently  forms  folds  (Plicae  synoviales)  and 
villi  (Villi  synoviales),  which  project  into  the  cavity  of  the  joint.  The  folds  com- 
monly contain  pads  of  fat,  and  there  are  in  many  places  masses  of  fat  outside  of  the 
capsule  which  fill  up  interstices  and  vary  in  form  and  position  in  various  phases  of 
movement.  The  synovial  membrane  secretes  a  fluid,  the  synovia,  which  lubricates 
the  joint;  it  resembles  white-of-egg,  but  has  a  yellowish  tinge.^     In  many  places  the 

^  It  is  doubtful  whether  the  synovia  is  a  true  secretion  or  a  transudate  containing  products  of 
friction.  The  view  given  above  is  that  which  is  more  commonly  accepted.  It  contains  albumen, 
mucin,  and  salts,  and  is  alkaline.  In  it  there  are  commonly  cells  derived  from  the  synovial  mem- 
brane, portions  of  cells,  cells  which  have  undergone  fatty  degeneration,  particles  of  articular 
cartilage,  etc. 


Fig.    229. — Diagram   op   Section   of 

DiARTHROSIS. 

f.l.,  Fibrous  layer,  s.L,  synovial 
layer  of  joint  capsule.  The  articular 
cartilages  are  white,  bones  dotted,  and 
the  joint  cavity  black  in  the  figure. 


DIARTHROSES  209 

membrane  forms  extra-articular  pouches,  which  facilitate  the  play  of  muscles  and 
tendons. 

The  articular  or  joint  cavity  (Cavum  articulare)  is  enclosed  by  the  synovial 
membrane  and  the  articular  cartilages.  Normally,  it  is,  strictly  speaking,  only  a 
potential  cavity,  which  contains  nothing  but  a  small  amount  of  synovia. 

The  student  must  guard  against  a  false  conception  of  the  joint  cavity  which  may  result  from 
dissections  and  diagrams  in  which  an  actual  cavity  of  considerable  extent  appears  to  exist.  A 
correct  idea  of  the  intimate  apposition  of  the  parts  is  best  obtained  from  the  study  of  frozen  sec- 
tions. On  the  other  hand,  it  is  instructive  to  examine  joints  which  have  been  injected  so  as  to 
distend  the  capsule  fully.  It  is  then  seen  that  the  cavity  is  often  of  much  greater  potential  extent 
than  one  might  suppose,  and  that  the  capsule  is  often  very  irregular  in  form,  i.  e.,  forms  a  variety  of 
sacculations. 

The  foregoing  are  constant  and  necessary  features  in  all  diarthroses.  Other 
structures  which  enter  into  the  formation  of  these  joints  are  ligaments,  articular 
discs  or  menisci,  and  marginal  cartilages. 

4.  Ligaments. — These  (Ligamenta)  are  strong  bands  or  membranes,  usually 
composed  of  white  fibrous  tissue,  which  bind  the  bones  together.  They  are  pli- 
able, but  practically  inelastic.  In  a  few  cases,  however,  e.  g.,  the  ligamentum 
nuchae,  they  are  composed  of  elastic  tissue.  They  may  be  subdivided,  according 
to  position,  into  periarticular  and  intraarticular.  Periarticular  ligaments  are  fre- 
quently blended  with  or  form  part  of  the  fibrous  capsule;  in  other  cases  they  are 
quite  distinct.  Those  which  are  situated  on  the  sides  of  a  joint  are  termed  col- 
lateral ligaments  (Ligamenta  collateralia) .  Strictly  speaking,  intra-articular  liga- 
ments, though  within  the  fibrous  capsule,  are  not  in  the  joint  cavity;  the  synovial 
membrane  is  reflected  over  them.  The  term  seems  justifiable,  however,  on  prac- 
tical grounds.  Those  which  connect  directly  opposed  surfaces  of  bones  are  termed 
interosseous  ligaments.  In  many  places  muscles,  tendons,  and  thickenings  of  the 
fascia3  function  as  ligaments  and  increase  the  security  of  the  joint.  Atmospheric 
pressure  and  cohesion  play  a  considerable  part  in  keeping  the  joint  surfaces  in  appo- 
sition. 

5.  Articular  discs  or  menisci  (Disci  s.  menisci  articulares)  are  plates  of  fibro- 
cartilage  or  dense  fibrous  tissue  placed  between  the  articular  cartilages,  and  divide 
the  joint  cavity  partially  or  completely  into  two  compartments.  They  render  cer- 
tain surfaces  congruent,  allow  greater  range  or  variety  of  movement,  and  diminish 
concussion. 

6.  A  marginal  cartilage  (Labrum  glenoidale)  is  a  ring  of  fibro-cartilage  which 
encircles  the  rim  of  an  articular  cavity.  It  enlarges  the  cavity  and  tends  to  pre- 
vent fracture  of  the  margin. 

Vessels  and  Nerves. — The  arteries  form  anastomoses  around  the  larger  joints, 
and  give  off  branches  to  the  extremities  of  the  bones  and  to  the  joint  capsule.  The 
synovial  membrane  has  a  close-meshed  network  of  capillaries;  the  latter  form  loops 
around  the  margins  of  the  articular  cartilages,  but  do  not  usually  enter  them. 
The  veins  form  plexuses.  The  synovial  membrane  is  also  well  supplied  with  lymph- 
vessels.  Nerve-fibers  are  especially  numerous  in  and  around  the  synovial  mem- 
brane and  there  are  special  nerve-endings,  e.  g.,  Pacinian  bodies  and  the  articular 
end-bulbs  described  by  Krause. 

Movements.— The  movements  of  a  joint  are  determined  chiefly  by  the  form 
and  extent  of  the  joint  surfaces  and  the  arrangement  of  the  ligaments.  They  are 
usually  classified  as  follows: 

1.  Gliding.— This  refers  to  the  sliding  of  one  practically  plane  surface  on 
another,  as  in  the  joints  between  the  articular  processes  of  the  cervical  vertebrse. 

2.  Angular  Movements. — In  these  cases  there  is  movement  around  one  or 
more  axes.  Motion  which  diminishes  the  angle  included  by  the  segments  forming 
the  joint  is  termed  flexion,  while  that  which  tends  to  bring  the  segments  into  line 
with  each  other  is  called  extension.     With  reference  to  the  joints  of  the  distal  parts 

14 


210  THE   ARTICULATIONS 

of  the  limbs,  it  seems  advisable  to  employ  the  terms  dorsal  and  volar  or  plantar 
flexion,  since  these  joints  can  be  "overextended."  Similarly  the  terms  dorsal  and 
ventral  flexion  are  applied  to  the  corresponding  movements  of  the  spinal  column. 
The  meaning  of  the  term  lateral  flexion  as  applied  to  the  vertebral  column  is  evi- 
dent. These  movements  are  all  rotations  around  axes  which  are  approximately 
either  transverse  or  vertical.  Depression,  elevation,  and  transverse  movement  of 
the  lower  jaw  fall  in  this  category. 

3.  Circumduction. — This  designates  movements  in  which  the  distal  end  of 
the  limb  describes  a  circle  or  a  segment  of  one.  In  man  such  movement  is  easily 
performed,  but  in  quadrupeds  it  is  possible  to  a  limited  degree  only,  and  is  to  be 
regarded  usually  as  an  indication  of  disease. 

4.  Rotation. — As  a  matter  of  convenience,  this  term  is  reserved  to  indicate 
rotation  of  one  segment  around  the  longitudinal  axis  of  the  other  segment  forming 
the  joint.     It  is  seen  typically  in  the  atlanto-axial  joint. 

5.  Adduction  and  abduction  designate  respectively  movement  of  a  limb  to- 
ward and  away  from  the  medial  plane,  or  of  a  digit  toward  and  away  from  the 
axis  of  the  limb. 

Classification. — This  is  based  on  the  form  of  the  joint  surfaces  and  the  move- 
ments which  occur.     The  following  chief  classes  may  be  recognized : 

1.  Arthrodia,  or  gliding  joint.  In  these  the  surfaces  are  practically  flat,  ad- 
mitting of  gliding  movement.  Examples:  carpo-metacarpal  joints;  joints  be- 
tween the  articular  processes  of  the  cervical  and  thoracic  vertebrse. 

2.  Ginglymus,  or  hinge-joint.  In  this  class  the  joint  surfaces  consist  usually 
of  two  condyles,  or  of  a  segment  of  a  cylinder  or  cone,  which  are  received  by  cor- 
responding cavities.  In  typical  cases  the  movements  are  flexion  and  extension, 
i.  e.,  around  a  single  transverse  axis.  Examples:  atlanto-occipital  and  elbow 
joints. 

3.  Trochoid,  or  pivot  joint.  In  these  the  movement  is  limited  to  rotation  of 
one  segment  around  the  longitudinal  axis  of  the  other.  Example:  atlanto-axial 
joint. 

4.  Enarthrosis,  or  ball-and-socket  joint.  These  are  formed  by  a  surface  of 
approximately  spherical  curvature,  received  into  a  corresponding  cavity.  They 
are  multiaxial,  and  allow  of  the  greatest  variety  of  movement,  e.  g.,  flexion, 
extension,  rotation,  abduction,  adduction,  circumduction.  Examples:  hip  and 
shoulder  joints."^ 

AMPHIARTHROSES 

These  joints,  as  the  name  indicates,  share  some  characters  with  both  of  the 
preceding  groups.  In  them  the  segments  are  directly  united  by  a  plate  of  fibro- 
cartilage,  and  usually  by  ligaments  also.  The  amount  and  kind  of  movement  are 
determined  by  the  shape  of  the  joint  surfaces  and  the  amount  and  pliability  of  the 
uniting  medium.^  These  joints  are  all  medial  in  position,  and  are  best  illustrated 
by  the  joints  between  the  bodies  of  the  vertebrse.  There  is  usually  no  joint  cavity, 
but  in  certain  situations  a  rudimentary  one  exists. 

1  This  classification  makes  no  claims  to  scientific  accuracy,  but  is  simply  a  statement  of  the 
terms  in  general  use.  A  grouping  based  on  mechanical  principles  is  desirable,  but  appears  to  be 
almost  impossible  on  account  of  the  great  variety  and  irregularity  of  form  of  the  articular  surfaces. 

2  The  movements  in  some  of  these  joints  are  more  extensive  and  varied  than  in  some  diar- 
throses.  To  illustrate  this  we  may  compare  the  movements  of  the  cervical  or  coccygeal  vertebrae 
with  those  possible  in  the  carpo-metacarpal  or  the  sacro-ihac  joints. 


THE    ARTICULATIONS    OF    THE    HORSE INTERCENTRAL    ARTICULATIONS  211 

THE  ARTICULATIONS  OF  THE  HORSE 
Joints  and  Ligaments  of  the  Vertebrae 

The  movable  vertebrae  form  two  sets  of  articulations,  viz.,  those  formed  by  the 
bodies,  and  those  formed  by  the  articular  processes  of  adjacent  vertebra;  the 
former  are  termed  intercentral,  and  the  latter  intemeural.  Associated  with  these 
are  ligaments  uniting  the  arches  and  processes;  some  of  these  are  special,  i.  e.,  con- 
fined to  a  single  joint,  while  others  are  common,  i.  e.,  extend  along  the  entire  ver- 
tebral column  or  a  considerable  part  of  it.  The  joints  between  the  atlas  and  axis 
and  between  the  former  and  the  skull  require  separate  consideration. 


Supraspi- 
nous liga- 
ment 


Fig.  230. — Sagittal  Section  of  Last  Two  Thoracic  and  First 
Lumbar  Vertebr.e,  showing  Ligaments  and  Spinal  Cord 
(Medulla).     (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


INTERCENTRAL  ARTICULATIONS 
These  are  amphiarthroses,  formed  l)y  tlie  junction  of  the  extremities  of  the 
bodies  of  adjacent  vertebrae.     The  articular  surfaces  in  the  cervical  region  consist 
of  a  cavity  on  the  posterior 
end  of  the  body  of  the  anter- 
ior vertebra,  and  a  correspond- 
ing convexity  or  head  of  the 
succeeding  vertebra.      In  the 
other  regions  the  surfaces  are 
much  flattened.     The  uniting 
media  are : 

1.  The  intervertebral 
fibro-cartilages  (Fibrocartila- 
gincs  intervertebrales).  Each 
of  these  is  a  disc  which  fits  into 
the  space  between  the  bodies 
of  two  adjacent  vertebrae,  to 
which  it  is  intimately  attached. 
The  discs  are  thinnest  in  the 
middle  of  the  thoracic  region, 
thicker  in  the  cervical  and  lum- 
bar regions,  and  thickest  in  the 

coccygeal  region.      Each  consists  of  a  peripheral  fibrous  ring   (Annulus   fibrosus) 
and  a  soft  central  pulpy  nucleus  (Nucleus  pulposus) . 

The  fibrous  ring  consists  of  laminae  of  fibrous  tissue  and  fibro-cartilage,  which  pass  obliquely 
between  the  two  vertebrae  and  alternate  in  direction,  forming  an  X-shaped  arrangement.  The 
central  part  of  the  ring  is  largely  cartilaginous,  and  gradually  assumes  the  character  of  the  pulpy 
center.  The  latter  is  very  elastic  and  is  compressed,  so  that  it  bulges  considerably  from  the  sur- 
face of  sections;  it  consists  of  white  and  elastic  fibers,  connective-tissue  cells,  and  pecuhar  clear, 
transparent  cells  of  various  sizes.  It  is  a  remnant  of  the  notochord.  There  are  joint  cavities  in 
the  cervical  intercentral  joints,  and  in  those  between  the  last  cervical  and  the  first  thoracic,  and 
between  the  last  lumbar  and  the  sacrum. 

2.  The  ventral  longitudinal  ligament  (Lig.  longitudinale  ventrale)^  lies  on  the 
ventral  surface  of  the  bodies  of  the  vertebrae  and  the  intervertebral  fibro-car- 
tilages, to  which  it  is  firmly  attached.  It  begins  to  be  distinct  a  little  behind  the 
middle  of  the  thoracic  region,  and  is  at  first  a  narrow,  thin  band.  Further  back 
it  becomes  gradually  thicker  and  wider,  and  terminates  on  the  pelvic  surface  of 
the  sacrum  by  spreading  out  and  blending  with  the  periosteum.  It  is  strongest  in 
the  lumbar  region,  where  the  tendons  of  the  crura  of  the  diaphragm  fuse  with  it. 

3.  The  dorsal  longitudinal  ligament  (Lig.  longitudinale  dorsale)-  lies  on  the 
floor  of  the  vertebral  canal  from  the  axis  to  the  sacrum.     It  is  narrow  over  the  mid- 

^  Also  termed  the  inferior  common  ligament. 
2  Also  termed  the  superior  common  ligament. 


212 


THE    ARTICULATIONS    OF    THE    HORSE 


dies  of  the  vertebral  bodies,  and  widens  over  the  intervertebral  fibro-cartilages,  to 
which  it  is  very  firmly  attached. 

This  ligament  is  in  relation  with  the  spinal  veins  on  either  side,  and  in  the  middle  of  each 
vertebra  a  transverse  anastomotic  vein  passes  under  the  hgament. 

INTERNEURAL  ARTICULATIONS 

Each  typical  vertebra  presents  two  pairs  of  articular  processes,  which  form 
diarthroses  with  the  two  adjacent  vertebrae.  The  articular  surfaces  are  extensive, 
almost  flat,  and  oval  in  the  cervical  region,  small  and  flat  in  the  thoracic  region, 


Atlas 


Funicular  part 


on  at  withers 


Last  cervical 
vertebra 


First  thoracic 
vertebra 


1,  Scapula;    /',  cartilage  of  scapul: 


Fig.  231. — Ligamentum  Nuch.e  of  Horse. 

,;    4,  lamellar  part  of  ligamentum  nuehse;    x, 

Baum,  Anat.  fiir  Kiinstler.) 


wing  of  atlas.      (After  Ellenberger- 


while  in  the  lumbar  region  the  anterior  ones  are  concave  and  the  posterior  convex. 
The  joint  capsule  is  strong  and  ample  in  the  cervical  region,  in  conformity  with  the 
large  size  and  greater  mobility  of  these  joints  in  the  neck.  In  the  thoracic  and 
lumbar  regions  the  capsule  is  small  and  close.  These  joints  are  arthrodia  in  the 
neck  and  back,  trochoid  in  the  lumbar  region. 

Associated  with  these  joints  are  the  ligamenta  flava,  which  connect  the  arches 
of  adjacent  vertebrae.     They  are  membranous  and  consist  largely  of  elastic  tissue. 

The  supraspinous  ligament  (Lig.  supraspinale)  extends  medially  from  the 
occipital  bone  to  the  sacrum.  Behind  the  withers  it  consists  of  a  strong  cord  of 
white  fibrous  tissue,  attached  to  the  summits  of  the  vertebral  spines.    In  the  neck 


SACRAL    AND    COCCYGEAL    ARTICULATIONS  213 

and  withers  it  is  remarkably  modified  to  form  the  Hgamentum  nuchse,  which  re- 
quires more  extended  notice. 

The  ligamentum  nuchae  is  a  powerful  elastic  apparatus,  the  principal  function 
of  which  is  to  assist  the  extensor  muscles  of  the  head  and  neck.  It  extends  from 
the  occipital  bone  to  the  withers,  where  it  is  directly  continuous  with  the  lumbo- 
dorsal  part  of  the  supraspinous  ligament.  It  consists  of  two  parts — funicular  and 
lamellar.  The  funicular  part  (Pars  occipitalis)  arises  from  the  external  occipital 
protuberance  and  is  inserted  into  the  summits  of  the  vertebral  spines  at  the  withers. 
Two  bursas  are  usually  found  under  it  in  the  adult.  The  atlantal  bursa  lies  be- 
tween the  ligament  and  the  dorsal  arch  of  the  atlas.  The  supraspinous  bursa  is 
usually  over  the  third  and  fourth  thoracic  spines,  but  may  be  over  the  second  or 
extend  to  the  fifth. ^  Another  bursa  may  be  present  at  the  spine  of  the  axis;  this  is 
between  the  funicular  part  and  the  large  digitation  attached  to  the  axis.  In  the 
neck  the  funicular  part  consists  for  the  greater  part  of  two  bands  closely  applied  and 
attached  to  each  other.  Near  and  at  the  withers  it  broadens  greatly,  forming  an  ex- 
pansion about  five  to  six  inches  (ca.  12  to  15  cm.)  in  width,  the  lateral  margins  of  which 
are  thin  and  turn  down  over  the  trapezius  and  rhomboideus  muscles.  Behind  the 
higher  spines  it  becomes  narrower  and  thinner,  and  is  continued  by  the  white  fibrous 
lumbo-dorsal  part.^  A  mass  of  fat  and  elastic  tissue  lies  upon  the  ligament  as  far 
back  as  the  withers.  It  varies  greatly  in  amount  in  different  subjects,  and  is  most 
developed  in  stallions  of  draft  breeds,  in  which  it  forms  the  basis  of  the  so-called 
''crest."  The  lamellar  part  (Pars  cervicalis)  consists  of  two  laminae  separated 
medially  by  a  layer  of  loose  connective  tissue.  Each  lamina  is  formed  of  digitations 
which  arise  from  the  second  and  third  thoracic  spines  and  from  the  funicular  part, 
are  directed  do^vnward  and  forward,  and  end  on  the  spines  of  the  cervical  vertebrae, 
except  the  first  and  last.  The  digitation  which  is  attached  to  the  spine  of  the  axis 
is  very  thick  and  strong.  Behind  this  they  diminish  in  size  and  strength;  the  last 
one,  which  is  attached  to  the  sixth  cervical  vertebra,  is  quite  thin  and  feeble,  or  may 
be  absent. 

The  interspinous  ligaments  (Ligg.  interspinalia)  extend  between  the  spines 
of  contiguous  vertebrae.  In  the  cervical  region  they  are  narrow  elastic  bands,  and 
in  the  thoracic  and  lumbar  regions  they  consist  of  white  fibers  directed  obliquely 
downward  and  backward. 

The  intertransverse  ligaments  (Ligg.  intertransversaria)  are  membranes 
which  connect  adjacent  transverse  processes  in  the  lumbar  region. 

INTERTRANSVERSE  ARTICULATIONS 
These  joints  (peculiar  to  equidae)  are  diarthroses  formed  by  the  transverse 
processes  of  the  fifth  and  sixth  lumbar  vertebrae  and  between  the  latter  and  the  alae 
of  the  sacrum.  A  similar  joint  between  the  fourth  and  fifth  lumbar  processes  is 
frequently  present.  The  articular  surfaces  have  an  elongated  oval  form,  the 
anterior  one  being  concave  and  the  posterior  one  convex.  The  capsule  is  tight, 
and  is  reinforced  ventrally. 

SACRAL  AND  COCCYGEAL  ARTICULATIONS 

In  the  foal  the  bodies  of  the  five  sacral  vertebrae  form  joints  which  resemble 
somewhat  those  in  the  posterior  part  of  the  lumbar  region.     These  joints  are  in- 

1  In  dissecting-room  subjects  these  bursse  and  the  adjacent  structures  are  commonly  the  seat 
of  pathological  changes.  They  appear  to  be  the  starting-point  of  "poll  evil"  and  "fistulous 
withers."     SulDCutaneous  bursa}  may  be  found  over  the  Ugament  at  the  withers. 

-  No  natural  line  of  demarcation  exists  between  the  ligamentum  nuchse  and  the  lumbo-dorsal 
part  of  the  supraspinous  ligament,  since  the  change  from  the  elastic  to  the  white  fibrous  structure 
is  gradual. 


214 


THE   ARTICULATIONS    OF   THE    HORSE 


vaded  bj^  the  process  of  ossification  early,  so  that  the  consolidation  of  the  sacrum 
is  usually  complete,  or  nearly  so,  at  three  years. 

The  coccygeal  vertebrae  are  united  by  relatively  thick  intervertebral  fibro-cartil- 
ages,  which  have  the  form  of  biconcave  discs.  Special  ligaments  are  not  present,  but 
there  is  a  continuous  sheath  of  fibrous  tissue.  The  movement  in  this  region  is  exten- 
sive and  varied.  In  old  horses  the  first  coccygeal  vertebra  is  often  fused  with  the 
sacrum. 

MOVEMENTS  OF  THE  VERTEBRAL  COLUMN 

The  movements  of  the  spine,  exclusive  of  those  at  the  atlanto-axial  joint,  are 
dorsal,  ventral,  and  lateral  flexion,  and  rotation.     The  range  of  movement  at  a 
single  joint  is  small,  but  the  sum  of  the  movements  is 
considerable.     The  movements  are  freest  in  the  cervical 
|i  I     .  yik.>i^ili     ^        and  coccygeal  regions.     Rotation  is  extremely  limited 
in  the  thoracic  and  lumbar  regions. 

ATLANTO-AXML  ARTICULATION 

This  is  a  trochoid  or  pivot  joint  of  a  rather  peculiar 
character.  The  articular  surfaces  are :  (1)  On  the  lateral 
masses  of  the  atlas,  two  somewhat  saddle-shaped  facets, 
which  are  separated  by  a  wide  notch  above  and  a  narrow 
one  below;  (2)  on  the  axis,  reciprocal  saddle-shaped  sur- 
faces which  extend  upon  the  dens  and  are  confluent  on 
its  ventral  aspect.  It  will  be  observed  that  the  joint 
surfaces  are  not  at  all  accurately  adapted  to  each  other, 
so  that  only  limited  areas  are  in  contact  at  any  time. 

The  joint  capsule  is  attached  around  the  margins 
of  the  articular  surfaces.  It  is  loose  and  ample  enough 
laterally  to  allow  extensive  movement. 

The  dorsal  atlanto-axial  ligament  (Lig.  interar- 
cuale)  is  membranous  and  reinforces  the  capsule  dor- 
sally. 

The  interspinous  ligament  (Lig.  interspinale)  con- 
sists of  two  elastic  bands  which  extend  from  the  dorsal 
arch  of  the  atlas  to  the  spine  of  the  axis. 

The  ventral  atlanto-axial  ligament  (Lig.  dentis  ex- 
ternum) arises  from  the  ventral  tubercle  of  the  atlas  and 
is  attached  by  two  branches  on  the  ventral  spine  of  the 
axis. 

The  ligament  of  the  dens  or  odontoid  ligament  (Lig. 
dentis  internum)  is  short,  very  strong,  and  somewhat  fan- 
shaped.  It  extends  from  the  rough  concave  dorsal  sur- 
face of  the  dens,  widens  in  front,  and  is  attached  to  the 
transverse  rough  area  on  the  inner  surface  of  the  ventral 
arch  of  the  atlas. 

Movements. — The  atlas  and  the  head  rotate  upon 
the  axis;  the  axis  of  rotation  passes  through  the  center 
of  the  bodv  of  the  axis. 


Fig.  232. — Atlanto-occipital  and 
Atlanto  -  AXIAL  Joints  of 
Horse;  Dorsal  View  after 
Removal  of  Dorsal  Arch  of 
Atl.\s. 

a.  Joint  capsule  of  left  part  of 
atlanto-occipital  joint;  6,  lateral 
ligament  of  same;  c,  c',  ligament  of 
the  dens;  d,  atlanto-axial  joint  cap- 
sule; e,  joint  capsule  of  articulation 
between  axis  and  third  cervical 
vertebra;  /,  interspinous  ligament; 
1,  occipital  bone;  2,  atlas;  3,  axis; 
4,  third  cervical  vertebra;  5,  dorsal 
longitudinal  ligament.  (Ellenber- 
ger-Baum,  Anat.  d.  Haustiere.) 


THE  ATLANTO-OCCIPITAL  ARTICULATION 
This  joint  may  be  classed  as  a  ginglymus.     The  articular  surfaces  of  this 
joint  are:   (1)  On  the  atlas,  two  deep  oval  cavities;   (2)  the  corresponding  condyles 
of  the  occipital  bone. 


ARTICULATIONS    OP  THE  THORAX — COSTO-VERTEBRAL  ARTICULATIONS 


215 


The  joint  surfaces  are  oblique,  coming  very  close  to  the  median  Hue  ventrally,  but  separated 
by  a  considerable  interval  dorsally.  A  triangular  rough  area  cuts  into  the  medial  part  of  each  of 
the  atlantal  articular  surfaces. 

There  are  two  roomy  joint  capsules,  which  sometimes  communicate  ventrally, 
especially  in  old  subjects. 

The  dorsal  atlanto-occipital  membrane  (Membrana  atlanto-occipitalis  dorsalis) 
extends  from  the  dorsal  arch  of  the  atlas  to  the  dorsal  margin  of  the  foramen  mag- 
num.    It  is  blended  with  the  capsules  and  contains  many  elastic  fibers. 

The  ventral  atlanto-occipital  membrane  (Membrana  atlanto-occipitalis  ven- 
tralis)  extends  from  the  ventral  arch  of  the  atlas  to  the  ventral  margin  of  the  fora- 
men magnum.  It  is  narrower  and  thinner  than  the  dorsal  membrane,  and  also 
fuses  with  the  joint  capsules. 

The  lateral  atlantal  ligaments  (Ligg.  lateralia  atlantis)  are  two  short  bands 
which  are  partially  blended  with  the  capsules.  Each  is  attached  to  the  border  of 
the  wing  of  the  atlas  near  the  intervertebral  foramen,  and  to  the  lateral  surface  of 
the  paramastoid  process  of  the  occipital  bone. 

Movements. — These  are  chiefly  flexion  and  extension.  A  small  amount  of 
lateral  oblique  movement  is  also  possible. 


Articulations  of  the  Thorax 
costo-vertebral  articulations 

Each  typical  rib  forms  two  joints  with  the  vertebral  column,  one  by  its  head, 
and  one  by  its  tubercle.  Thej^  are  termed  respectively  costo-central  and  costo- 
transverse joints. 

I,  The  costo-central  articulation  (Articulatio  capituli)  is  a  trochoid  or  rotatory 
joint,  formed  by  the  junction  of  the 
head  of  the  rib  with  the  bodies  of 
two  adjacent  vertebrae  and  the 
intervertebral  fibro-cartilage.  The 
two  facets  on  the  head  of  the  rib 
are  separated  by  a  non-articular 
groove,  and  correspond  to  the  two 
concave  facets  (Fovese  costales)  on 
the  vertebral  bodies.  The  joint 
capsule  is  rather  tight,  and  is  cov- 
ered by  the  accessory  ligaments, 
which  are  as  follows:  1.  The  radiate 
ligament  (Lig.  capituli  costae  radi- 
atum)  extends  ventrally  from  the 
neck  of  the  rib  to  spread  out  on 
the  vertebral  bodies  and  the  in- 
tervertebral fibro-cartilage.  2.  The 
conjugal  ligament  (Lig.  conjugale) 
— absent  from  the  first  joint — is 
attached  to  the  groove  on  the  head 
of  the  rib,  passes  transversely  into 
the  vertebral  canal,  and  divides 
under  the  dorsal  longitudinal  liga- 
ment into  two  branches:  one  of  these  is  attached  to  the  body  of  the  anterior  vertebra; 
the  other  is  continued  across  to  the  head  of  the  opposite  rib,  and  is  also  attached  to 
the  intervertebral  fibro-cartilage.  The  joint  cavity  is  divided  into  two  compart- 
ments by  the  conjugal  ligament.     3.  The  ligament  of  the  neck  of  the  rib  (Lig.  colli 


'\^Radiate  ligament 
Conjugal  ligamen, 


233. — Costovertebral  Articulation;  Anterior  View. 
(After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


216  THE    ARTICULATIONS    OF   THE    HORSE 

costse)  is  a  strong  band  which  crosses  the  joint  dorsally.     It  is  attached  on  the 
vertebra  above  the  costal  facet  and  on  the  neck  of  the  rib. 

II.  The  costo-transverse  articulation  (Articulatio  costo-transversaria) .  This 
is  formed  by  the  facet  on  the  tubercle  of  the  rib  and  on  the  transverse  proc- 
ess of  the  vertebra.  They  are  gliding  joints.  The  capsule  is  reinforced  by  the 
dorsal  costo-transverse  ligament  (Lig.  costo-transversarium  dorsale),  a  distinct 
strong  band  which  arises  on  the  transverse  process  and  ends  on  the  non-articular 
part  of  the  tubercle.  It  is  covered  by  the  levator  costae  muscle,  and  begins  to  be 
quite  distinct  at  the  fifth  joint. 

The  cavity  for  the  head  of  the  first  rib  is  formed  by  concave  facets  on  the  bodies  of  the  last 
cervical  and  first  thoracic  vertebrjE.  The  conjugal  ligament  is  absent,  but  the  hgament  of  the 
neck  is  short  and  strong.  The  radiate  ligament  is  very  strong,  and  consists  of  two  parts.  In  the 
case  of  the  last  two  or  three  ribs  the  costo-central  and  costo-transverse  joints  are  confluent,  and  the 
various  structures  are  correspondingly  modified. 

Movements. — The  chief  movement  is  rotation  around  an  axis  which  connects 
the  centers  of  the  head  and  tubercle  of  the  rib.  The  movement  is  very  limited  in 
the  anterior  part  of  the  series  of  joints,  but  very  considerable  in  the  posterior  part. 

In  the  case  of  the  first  rib  the  movement  is  evidently  extremely  limited.  The  facet  for  the 
tubercle  of  the  rib  is  deeply  concave,  and  the  axis  of  rotation  is  almost  transverse,  so  that  the 
movement  is  chiefly  sagittal  in  direction.  Further  back  the  facets  on  the  transverse  processes 
become  flat,  and  the  axis  of  rotation  gradually  approaches  a  longitudinal  direction.  This,  in 
connection  with  the  mobiUty  of  the  ventral  ends  of  the  asternal  ribs  and  their  elasticity,  allows  a 
great  increase  here  in  the  range  of  movement  which  is  largely  transverse,  the  effect  being  to  enlarge 
(chiefly)  the  transverse  diameter  of  the  thorax. 


COSTO-CHONDRAL  ARTICULATIONS 

The  costo-chondral  junctions  are  synarthroses.  The  rib  has  a  concave  surface 
which  receives  the  convex  end  of  the  cartilage.  They  are  united  by  the  continuity 
of  the  strong  periosteum  and  perichondrium. 


CHONDRO-STERNAL  ARTICULATIONS 

These  joints  (Articulationes  sternocostales)  are  diarthroses  formed  by  the 
junction  of  the  cartilages  of  the  sternal  ribs  with  the  sternum.  The  articular  ends 
of  the  cartilages  (except  the  first)  are  somewhat  enlarged,  and  present  surfaces  of 
cylindrical  curvature.  The  articular  surfaces  on  the  sternum  for  the  first  pair  of 
cartilages  are  placed  close  together  on  the  dorsal  border  of  the  carinif  orm  cartilage ; 
the  other  seven  are  placed  laterally  at  the  junctions  of  the  segments.  The  capsules 
are  strong  and  tight;  the  first  pair  of  joints  has  a  common  capsule,  and  the  cartil- 
ages articulate  with  each  other  medially.  The  ventral  ends  of  the  first  pair  of  ribs 
are  firmly  attached  to  each  other  by  dense  fibrous  tissue,  which  is  prolonged  for- 
ward along  the  upper  margin  of  the  carinif  orm  cartilage  and  is  continuous  behind  with 
the  sternal  ligament.  Each  of  the  other  capsules  is  reinforced  dorsally  by  the  radiate 
costo-stemal  ligament  (Ligamentum  sterno-costale  radiatum),  composed  of  radi- 
ating fibers  which  blend  with  the  sternal  ligament.  Interarticular  bands  may  be 
present.  The  movement  is  rotation  around  a  nearly  vertical  axis,  except  in  the 
case  of  the  first  pair  of  joints. 


INTERCHONDRAL  LIGAMENTS 
The  eighth  and  ninth  costal  cartilages  are  firmly  united  by  fibrous  tissue.     The 
chondro-xiphoid  ligament  attaches  the  ninth  costal  cartilage  to  the  xiphoid  carti- 
lage.    The  remaining  cartilages  are  rather  loosely  attached  to  each  other  by  elastic 
tissue. 


THE    ARTICULATIONS    OF   THE    SKULL — SYNARTHROSES   OF   THE    SKULL         217 


STERNAL  ARTICULATIONS 
In  the  new-born  foal  the  seven  bony  segments  are  united  by  persisting  cartilage 
(Synchondroses  intersternales) .  The  last  two  segments  coalesce  within  a  few  weeks 
after  birth.  In  old  subjects  there  is  more  or  less  ossification  of  the  intersternebral 
cartilage,  which  may  lead  to  fusion  of  adjacent  segments,  especially  posteriorly. 
The  internal  sternal  ligament  (Lig.  sterni  proprium  internum)  lies  on  the  thoracic 
surface  of  the  sternum.  It  arises  on  the  first  segment,  and  divides  opposite  the 
second  chondro-sternal  joint  into  three  bands.  The  median  band  passes  back- 
ward and  spreads  out  on  the  last  segment  and  the  xiphoid  cartilage.  The  lateral 
branches — thicker  and  wider — lie  along  the  lateral  borders  above  the  chondro- 
sternal  joints,  and  end  at  the  cartilage  of  the  eighth  rib;  they  are  covered  by  the 
transversus  thoracis  muscle. 


The  Articulations  of  the  Skull 
mandibular  articulation 

This  joint  (Articulatio  mandibularis)  is  a  diarthrosis  formed  between  the  ramus 
of  the  mandible  and  the  squamous  temporal  bone  on  either  side. 

The  articular  surfaces  are  dissimilar  in  form  and  size.  That  on  the  squamous 
temporal  bone  is  concavo-convex,  and  the  long  axis  is  directed  outward  and  some- 
what forward;  it  consists  of  a  condyle  in  front  and  a  glenoid  cavity,  which  is  con- 
tinued upon  the  postglenoid  process  behind.  The  mandible  presents  a  trans- 
versely elongated  condyle. 

The  articular  disc  (Discus  articularis)  is  placed  between  the  joint  surfaces, 
which  it  renders  congruent.  Its  surfaces  are  molded  upon  the  temporal  and  man- 
dibular surfaces  respectively,  and  its  circumference  is  attached  to  the  joint  capsule; 
thus  it  divides  the  joint  cavity  into  upper  and  lower  compartments,  the  former  being 
the  more  room5^ 

The  joint  capsule  is  strong  and  tight.  It  is  reinforced  by  two  ligaments.  The 
lateral  ligament  (Lig.  laterale)  extends  obliquely  across  the  anterior  part  of  the 
lateral  surface  of  the  capsule,  from  which  it  is  not  distinctly  separable.  The  pos- 
terior ligament  (Lig.  posterius)  is  an  elastic  band  which  is  attached  above  to  the 
postglenoid  process,  and  below  to  a  line  on  the  posterior  face  of  the  neck  of  the 
mandible. 

Movements. — The  chief  movements  take  place  around  a  transverse  axis  pass- 
ing through  both  joints.  Associated  with  this  hinge-like  action  is  slight  gliding 
movement,  as  in  opening  and  shutting  the  mouth.  When  the  mouth  is  shut, 
the  condyle  of  the  mandible  lies  under  the  glenoid  cavity.  When  the  mandible 
is  depressed,  the  condyle  moves  forward  under  the  articular  eminence  of  the  tem- 
poral bone,  carrying  the  disc  with  it.  In  protrusion  and  retraction  of  the  lower 
jaw  the  gliding  movement  just  described  occurs  without  the  hinge-like  rotation 
of  the  condyle.  These  movements  are  similar  in  both  joints.  In  the  transverse 
movements  (as  usually  performed  in  mastication)  the  action  consists  of  rotation 
of  the  condyles  around  a  vertical  axis,  while  the  disc  glides  forward  on  one  side  and 
backward  on  the  other. 

SYNARTHROSES  OF  THE  SKULL 
Most  of  the  bones  of  the  skull  are  united  with  the  adjacent  bones  by  sutures; 
a  few  are  united  by  cartilage.     The  difference  in  the  uniting  medium  depends  on 
the  fact  that  most  of  these  bones  are  developed  in  membrane,  but  some  are  pre- 
formed in  cartilage.     Most  of  these  joints  are  temporary,  and  are  obliterated  at 


218  THE  ARTICULATIONS  OF  THE  HORSE 

various  periods  during  development  and  groAvth.  Their  importance  lies  in  the 
fact  that  so  long  as  they  persist,  continuous  growth  is  possible.  They  are  usually 
designated  according  to  the  bones  which  enter  into  their  formation,  e.  g.,  spheno- 
squamous, naso-frontal,  etc. 

Detailed  description  of  the  sutures  has  not  sufficient  clinical  value  to  justify  much  addition 
to  the  statements  made  in  the  osteology  in  this  connection.  The  obhteration  or  closure  of  the 
sutures  is,  however,  worthy  of  brief  mention.  The  cranial  sutm-es  are.  usually  all  closed  at  seven 
years,  but  the  apex  only  of  the  petrous  temporal  is  fused  with  the  occipital  and  squamous  temporal. 
Most  of  the  facial  sutures  are  {practically  closed  at  ten  years,  although  complete  synostosis  may  in 
some  be  delayed  for  years  or  may  not  occur  at  all;  the  nasal  suture,  for  example,  usually  persists 
even  in  advanced  age,  so  far  as  its  anterior  part  is  concerned. 

The  principal  synchondroses  are:  (1)  That  between  the  basilar  part  of  the 
occipital  bone  and  the  bod}'  of  the  sphenoid  (Synchondrosis  spheno-occipitalis) ; 
(2)  that  between  the  presphenoid  and  postsphenoid  (Synchondrosis  intersphenoid- 
alis);  (3)  those  between  the  parts  of  the  occipital  bone  (Synchondroses  intraoc- 
cipitales).  The  first  is  ossified  at  four  or  five  years,  the  second  at  three  years,  and 
the  occipital  bone  is  consolidated  at  two  years. 

The  symphysis  mandibulae  ossifies  at  one  to  six  months. 

THE  HYOIDEAN  ARTICULATIONS 

The  temporo-hyoid  articulation  is  an  amphiarthrosis,  in  which  the  articular 
angle  of  the  dorsal  end  of  the  great  cornu  of  the  hyoid  bone  is  attached  by  a  short 
bar  of  cartilage  to  the  hyoid  process  of  the  petrous  temporal  bone.  The  cartilage 
(Arthrohyoid)  is  about  half  an  inch  (ca.  1-1.5  cm.)  in  length.  The  chief  move- 
ment is  hinge-like,  the  axis  of  motion  passing  transversely  through  both  joints. 

The  intercomual  articulation  is  an  amphiarthrosis  formed  by  the  junction  of 
the  ventral  extremity  of  the  great  cornu  with  the  dorsal  end  of  the  small  cornu  of 
the  hyoid  bone.  They  are  united  by  a  very  short  piece  of  cartilage,  in  which  there 
is  usually  a  small  nodule  of  bone  in  the  young  subject.  This  nodule,  the  epihyoid 
or  middle  cornu,  is  usually  fused  with  the  great  cornu  in  the  adult.  The  chief 
movement  here  is  also  hinge-like,  the  angle  between  the  cornua  being  increased  or 
diminished. 

The  basi-comual  articulation  is  a  diarthrosis  formed  b^^  the  junction  of  each 
small  cornu  with  the  body  of  the  hyoid  bone.  The  small  cornu  has  a  concave  facet 
which  articulates  with  the  convex  facet  on  either  end  of  the  dorsal  surface  of  the 
body.  The  capsule  is  ample  enough  to  allow  considerable  movement,  which  is 
chiefly  hinge-like. 

The  m.ovements  of  the  hyoid  bone  are  concerned  chiefly  in  the  acts  of  mastica- 
tion and  swallowing.  In  the  latter  the  ventral  parts  of  the  hyoid  bone  are  moved 
forward  and  upward,  carrying  the  root  of  the  tongue  and  the  larynx  with  them, 
and  then  return  to  their  former  position. 


The  Articulations  of  the  Thoracic  Limb 

In  the  absence  of  the  clavicle  the  thoracic  limb  forms  no  articulation  with  the 
trunk,  to  which  it  is  attached  by  muscles.  The  movement  of  the  shoulder  on  the 
chest-wall  is  chiefly  rotation  around  a  transverse  axis  passing  through  the  scapula 
behind  the  upper  part  of  the  spine. 

THE  SHOULDER  JOINT 

The  shoulder  or  scapulo-humeral  joint  (Articulatio  scapulo-humeralis)  is 
formed  by  the  junction  of  the  distal  end  of  the  scapula  with  the  proximal  end  of 
the  humerus.     The  articular  siufaces  are:    (1)  On  the  scapula,  the  glenoid  cavity; 


THE   ELBOW   JOINT 


219 


(2)  on  the  humerus,  the  head.  Both  surfaces  are  approximately  spherical  and 
similar  in  curvature,  but  the  humeral  surface  is  about  twice  as  extensive  as  that  of 
the  scapula. 

The  joint  capsule  is  ample  enough  to  allow  the  bones  to  be  drawn  apart  about 
an  inch  (ca.  2-3  cm.) ;  but  this  requires  a  very  considerable  amount  of  force  unless 
air  is  admitted  into  the  joint  cavity.  The  fibrous  layer  is  not  attached  to  the  mar- 
gin of  the  joint  surfaces,  but  at  a  distance  of  one  to  two  centimeters  from  it.  It  is 
strengthened  in  front  by  two  diverging  elastic  bands,  which  arise  on  the  tuber 
scapulae  and  end  on  the  tuberosities  of  the  humerus.  A  pad  of  fat  is  interposed 
between  the  capsule  and  the  tendon  of  the  biceps. 

Ligaments  are  absent  from  this  joint,  but  the  muscles  and  tendons  around  it 
afford  remarkable  security,  so  that  dislocation  very  seldom  occurs.  The  large  ex- 
tent of  the  head  of  the  humerus  is  also  of  importance  in  this  regard. 

The  principal  muscles  which  are  attached  around  the  joint  and  act  as  ligaments  are: 
laterally,  the  supraspinatus,  infraspinatus,  and  teres  minor;  medially,  the  subscapularis ;  in 
front,  the  biceps  and  supraspinatus;  behind,  the  triceps.  Fibers  of  the  brachialis  are  attached  to 
the  lower  edge  of  the  posterior  part  of  the  joint  capsule,  and  would  evidently  tense  the  latter.  In 
some  cases  the  joint  cavity  communicates  with  the  bicipital  or  intertuberal  bursa. 

Movements. — While  it  is  a  typical  enarthrosis  in  structure,  and  capable  of  the 
various  movements  of  the  ball-and-socket  joint,  the  chief  normal  movements  are 
flexion  and  extension.  In  the  position  of  rest  the  angle  formed  between  the  scapula 
and  humerus  posteriorly  is  about  110°  to  120°;  in  flexion  it  is  reduced  to  about  80°, 
and  in  extension  it  is  increased  to  about  145°.  Adduction  and  abduction  are  very 
restricted,  the  former  being  limited  chiefly  by  the  infraspinatus,  the  latter  by  the 
subscapularis  and  the  low  insertion  of  the  superficial  pectoral  muscles.  Rotation 
is  somewhat  freer,  but  does  not  exceed  33°  when 
all  the  muscles  are  removed  (Franck). 


THE  ELBOW  JOINT 

This,  the  cubital  articulation  (Articulatio 
cubiti),  is  a  ginglymus  formed  between  the  dis- 
tal extremity  of  the  humerus  and  the  proximal 
ends  of  the  radius  and  ulna. 

The  articular  surfaces  are:  (1)  A  trochlear 
surface  formed  by  the  condyles  of  the  humerus 
and  the  ridge  between  them ;  (2)  the  correspond- 
ing glenoid  cavities  and  groove  on  the  proximal 
extremity  of  the  radius,  together  with  the  semi- 
lunar notch  of  the  ulna. 

The  articular  surface  of  the  condyles  does  not  ex- 
tend upon  the  back  of  the  extremity,  but  the  groove  which 
receives  the  semilunar  notch  of  the  ulna  extends  up  into 
the  olecranon  fossa.  In  the  fore  part  of  the  gi'oove  there 
is  a  synovial  fossa.  The  surface  on  the  lateral  condyle  is 
much  smaller  than  that  of  the  medial  one,  and  is  sub- 
divided into  two  unequal  parts  by  a  shallow  furrow.  On 
the  lower  part  of  the  semilunar  notch  and  the  adjacent 
part  of  the  ridge  on  the  radius  are  synovial  fossis. 

The  joint  capsule  is  extremely  thin  behind, 
where  it  forms  a  pouch  in  the  olecranon  fossa 
under  the   anconeus  muscle   and  a  pad  of  fat. 


Fig.  231. — Left  Elbow  Joint  of  Horse; 
Posterior  View.  The  Capsule  is  Re- 
moved. (After  Schmaltz,  Atlas  d.  Anat. 
d.  Pferdes.) 


In  front  it  is  strengthened  by 
oblique  fibers  (Ijig.  ol)liquum  or  anterior  ligament),  and  on  each  side  it  fuses 
with  the  collateral  ligaments.  It  also  is  adherent  to  the  tendons  of  muscles 
which  arise  from  the  distal  end  of  the  humerus  or  end  on  the  proximal  end  of  the 
radius.     The  synovial  membrane  sends  prolongations  to   the  small  radio-ulnar 


220 


THE    ARTICULATIONS    OF   THE    HORSE 


THE    RADIO-ULNAR   ARTICULATION THE    CARPAL   JOINTS  221 

joints  and  also  pouches  downward  under  the  origins  of  the  flexors  of  the  digit  and 
the  lateral  flexor  of  the  carpus.     There  are  two  collateral  ligaments. 

The  medial  ligament  (Lig.  collaterale  radiale)  is  attached  above  to  an 
eminence  on  the  medial  epicondyle  of  the  humerus,  and  divides  into  two  parts: 
the  long,  superficial  part  ends  on  the  medial  border  of  the  radius,  just  below  the 
level  of  the  interosseous  space;  the  deep,  short  part  is  inserted  into  the  medial  tu- 
berosity of  the  radius. 

The  lateral  ligament  (Lig.  collaterale  ulnare)  is  short  and  strong.  It  is  at- 
tached above  to  a  depression  on  the  lateral  epicondyle  of  the  humerus,  and  below 
to  the  lateral  tuberosity  of  the  radius,  just  below  the  margin  of  the  articular  surface. 

Movements. — This  joint  is  a  typical  ginglymus,  the  only  movements  being 
flexion  and  extension  around  an  axis  which  passes  through  the  proximal  attachments 
of  the  collateral  ligaments.  In  the  standing  position  the  articular  angle  (in  front)  is 
about  140°  to  150°.  The  range  of  movement  is  about  55°  to  60°.  Complete  ex- 
tension is  prevented  chiefly  by  the  tension  of  the  collateral  ligaments  and  the  biceps 
muscle.  (The  axis  of  movement  is  slightly  oblique,  so  that  in  flexion  the  forearm 
is  carried  somewhat  outward.) 


THE  RADIO-ULNAR  ARTICULATION 

In  the  foal  the  shaft  of  the  ulna  is  attached  to  the  radius  above  and  below  the 
interosseous  space  by  the  interosseous  ligament  of  the  forearm  (Lig.  interosseum 
antibrachii).  Below  the  space  the  two  bones  become  fused  before  adult  age  is 
reached.  Above  the  space  the  ligament  usually  persists,  but  may  undergo  more 
or  less  ossification  in  extreme  old  age.  The  transverse  or  arciform  ligament  (Lig. 
transversum  ulnare  et  radiale  ulnae  et  radii)  consists  of  fibers  which  pass  above  the 
interosseous  space  from  each  border  of  the  shaft  of  the  ulna  to  the  posterior  sur- 
face of  the  radius.  The  proximal  radio-ulnar  articulation  (Articulatio  radio-ulnaris 
proximalis),  formed  by  two  small  convex  facets  on  the  ulna  and  the  corresponding 
facets  on  the  posterior  surface  of  the  proximal  extremity  of  the  radius,  is  inclosed 
in  the  capsule  of  the  elbow-joint  and  does  not  require  separate  consideration.  The 
distal  extremity  of  the  ulna  fuses  early  with  the  radius,  and  is  therefore  regarded 
usually  as  a  part  of  the  latter. 

Movement. — This  is  inapprecia])le,  the  forearm  being  fixed  in  the  position  of 
pronation. 

THE  CARPAL  JOINTS 

These  joints  taken  together  constitute  the  composite  articulatio  carpi,  or  what 
is  popularly  termed  the  "knee-joint"  in  animals.^  This  consists  of  three  chief 
joints,  viz.,  (1)  The  radio-carpal  or  antibrachio-carpal  joint  (Articulatio  radiocarpea) 
formed  by  the  distal  end  of  the  radius  and  the  proximal  row  of  the  carpus;  (2)  the 
intercarpal  joint  (Articulatio  intercarpea),  formed  between  the  two  rows  of  the  car- 
pus; (3)  the  carpo-metacarpal  joint  (Articulatio  carpometacarpea),  formed  between 
the  distal  row  of  the  carpus  and  the  proximal  ends  of  the  metacarpal  bones.  The 
proximal  and  middle  joints  may  be  regarded  as  ginglymi,  although  they  are  not 
typical  or  pure  examples  of  hinge-joints.  The  distal  joint  is  arthrodial.  In  addi- 
tion there  are  arthrodial  joints  formed  between  adjacent  bones  of  the  same  row 
(Articulationes  interossese).  All  these  form  a  composite  joint  with  numerous  liga- 
ments.    The  articular  surfaces  have  been  described  in  the  Osteology. 

The  joint  capsule  may  be  regarded,  so  far  as  the  fibrous  part  is  concerned,  as 
being  common  to  all  three  joints.     It  is  attached  close  to  the  margin  of  the  articu- 

^  The  term  is  a  very  unfortunate  one,  since  it  is  a  distinct  misapplication  of  the  name  as  it  is 
used  in  regard  to  man.  It  is,  however,  very  firmly  established,  and  appears  likely  to  persist  in- 
definitely in  the  absence  of  a  convenient  popular  equivalent. 


222 


THE    ARTICULATIONS    OF   THE    HORSE 


-  R 


lar  surface  of  the  radius  above  and  the  metacarpus  below;  its  deep  face  is  also 
attached  to  a  considerable  extent  to  the  carpal  bones  and  to  the  small  ligaments. 
Its  anterior  part,  the  dorsal  carpal  ligament,  is  loose,  except  during  flexion,  and 
assists  in  forming  the  fibrous  canals  for  the  extensor  tendons.  Its  posterior  part, 
the  volar  carpal  ligament  (Lig.  carpi  volare),  is  very  thick  and  dense,  and  is  closely 
attached  to  the  carpal  bones.  It  levels  up  the  irregularities  of  the  skeleton  here, 
and  forms  the  smooth  anterior  wall  of  the  carpal  canal.  It  is  continued  downward 
to  form  the  subcarpal  or  inferior  check  ligament,  which  blends  with  the  tendon  of 
the  deep  flexor  of  the  digit  about  the  middle  of  the  metacarpus,  and  may  well  be 
regarded  as  the  carpal  (tendinous)  head  of  that  muscle. 

The  synovial  membrane  forms  three  sacs  corresponding  to  the  three  joints. 

The  radio-carpal  sac  is  the 
most  voluminous;  it  includes 
the  joints  formed  by  the  acces- 
sory carpal  bone,  and  also  those 
between  the  proximal  carpal 
bones  as  far  as  the  interosseous 
ligaments.  The  intercarpal  sac 
sends  extensions  upward  and 
downward  between  the  bones 
of  the  two  rows  as  far  as  the 
interosseous  ligaments;  it  com- 
municates between  the  third 
and  fourth  carpal  bones  with 
the  carpo-metacarpal  sac.  The 
latter  is  very  limited  in  extent, 
and  is  closely  applied  to  the 
bones;  it  incloses  the  carpo- 
metacarpal joint,  and  lubri- 
cates also  the  lower  parts  of 
the  joints  between  the  distal 
carpal  bones  and  the  inter- 
metacarpal joints. 

The  lateral  ligament  (Lig. 
carpi  collaterale  ulnare)  is  at- 
tached above  to  the  lateral 
tuberosity  of  the  distal  end  of 
the  radius.  Its  long  superficial 
part  is  attached  below  to  the 
proximal  end  of  the  lateral 
small  metacarpal  chiefly,  but 
some  fibers  end  on  the  large 
metacarpal  bone.  A  canal  for  the  lateral  extensor  tendon  separates  a  short  deep 
band  which  ends  on  the  ulnar  carpal  bone.  Other  deep  fibers  connect  the  latter 
with  the  fourth  carpal  bone,  and  the  fourth  carpal  with  the  metacarpus. 

The  medial  ligament  (Lig.  carpi  collaterale  radiale)  resembles  the  preceding 
in  general,  but  is  stronger  and  wider  distally.  It  is  attached  above  to  the  medial 
tuberosity  of  the  distal  end  of  the  radius  and  ends  below  on  the  proximal  ends  of 
the  large  and  medial  small  metacarpal  bones.  Deep  fasciculi  are  detached  to  the 
radial  and  second  carpal  bones.  The  first  carpal  bone,  when  present,  is  usuall^^ 
embedded  in  the  posterior  part  of  the  distal  end  of  the  ligament.  The  posterior 
part  of  the  ligament  is  fused  with  the  transverse  ligament  of  the  carpus  (Lig.  carpi 
transversum),  and  concurs  in  the  formation  of  a  canal  for  the  tendon  of  the  flexor 
carpi  radialis. 


Fig.   238.- 


-Left   Carpal   Joints   of    Horse;    Dors 
Joint  Capsule  is  Removed. 


.L  Vii 


C.  u. 


C. 


Mc.  IV 


Mc.  Ill 


The 


R,  Lateral  distal  tuberosity  of  radius;  M,  medial  ligament;  L, 
lateral  ligament;  C.  r.,  radial  carpal  bone;  C.  u.,  ulnar  carpal  bone; 
C.  3,  third  carpal  bone;  C.  4,  fourth  -  carpal  bone;  Mc.  Ill,  Mc.  IV, 
metacarpal  bones;  1,  intermediate  carpal  bone;    2-6,  dorsal  ligaments. 


INTERMETACARPAL   JOINTS 


223 


^M 


A  number  of  special  short  ligaments  connect  two  or  more  adjacent  bones;    only  the  most 
distinct  of  these  will  be  described  here. 

The  accessory  carpal  bone  is  connected  with  adjacent  bones  by  three  hgaments  (Fig.  234). 
The  proximal  one  is  a  short  band  which  extends  from  the  accessory  carpal  in  front  of  the  groove  on 
its  lateral  face  and  is  inserted  into  the  distal  end  of  the  radius  behind  the  groove  for  the  lateral 
extensor  tendon.  A  middle  band  connects  the  accessory  with  tlie  ulnar  carpal.  The  distal  liga- 
ment consists  of  two  strong  bands  which  pass  from  the  distal  margin  of  the  accessory  to  the  fourth 
carpal  and  the  proximal  end  of  the  fourth 
metacarpal  bone;  these  bands  transmit  the 
action  of  the  muscles  which  are  inserted  into 
the  accessory  carpal  bone.  The  other  bones 
of  the  proximal  row  are  connected  by  two 
dorsal  Ugaments,  which  are  transverse  m  direc- 
tion, and  two  interosseous  Hgaments.  An 
oblique  ligament  passes  from  an  eminence  on 
the  volar  surface  of  the  radial  carpal  bone  to 
a  small  depression  on  the  radius  medial  to  the 
facet  for  the  accessory  carpal  bone. 

Two  ligaments  connect  the  proximal  and 
distal  rows  posteriorly.  The  medial  one  joins 
the  radial  to  the  second  and  third  carpal,  and 
the  lateral  one  attaches  the  ulnar  to  the  third 
and  fourth  carpals. 

The  bones  of  the  distal  row  are  con- 
nected by  two  strong  transverse  dorsal 
ligaments  and  two  interosseous  ligaments. 

There  are  four  carpo-metacarpal  liga- 
ments. Two  obHque  dorsal  Hgaments  (Ligg. 
carpometacarpea  dorsaHa)  connect  the  third 
carpal  with  the  large  metacarpal  bone.  Two 
interosseous  Hgaments  pass  downward  from 
the  interosseous  Hgaments  of  the  distal  row 
to  end  in  depressions  of  the  opposed  surfaces 
of  the  proximal  ends  of  the  metacarpal  bones. 
Volar  Hgaments  (Ligg.  carpometacarpea  vo- 
laria)  connect  the  second  and  third  carpal 
bones  with  the  metacarpus.  Other  short 
special  Ugaments  have  been  described,  but 
some  of  them  at  least  are  artefacts. 

Movements. — Taking  the  joint  as 
a  whole,  the  chief  movements  are  flex- 
ion and  extension.  In  the  standing 
position  the  joint  is  extended.  When 
the  joint  is  flexed,  shght  transverse 
movement  and  rotation  can  be  pro- 
duced by  manipulation.  The  dorsal 
part  of  the  capsule  is,  of  course,  tense 
during  flexion,  the  volar  part  in  exten- 
sion. 


The  movement  practically  all  occurs  at 
the  radio-carpal  and  intercarpal  joints,  the 
articular  surfaces  of  which  are  widely  separ- 
ated in  front  during  flexion,  but  remain  in 
contact  behind.  The  distal  row  remains  in 
contact  with  the  metacarpus.  The  inter- 
mediate and  ulnar  carpals  move  together  as 

one  piece,  but  the  radial  does  not  move  so  far  as  the  intermediate,  so  that  the  dorsal  and  inter- 
osseous Ugaments  connecting  these  bones  become  tense  and  obUque  in  direction. 


Fig.  239. — Left  Carpal  Joints  op  Horse;  Volar  View. 
Accessory  Carpal  and  Capsule  have  been  Re- 
moved. 

R,  Dist.al  end  of  radius;  M,  medial  ligament;  L, 
lateral  ligament;  1,  2,  ligaments  connecting  radial  carpal 
bone  and  radius;  3,  ligament  connecting  intermediate 
carpal  with  radius;  4,  stump  of  ligament  connecting  inter- 
mediate and  accessory  carpal ;  5,  ligament  connecting  radial 
and  second  carpal;  6,  6',  ligaments  connecting  second 
carpal  and  metacarpal  bones;  7,  7',  ligaments  connecting 
third  carpal  and  metacarpal  bone;  8,  ligament  connecting 
ulnar  and  third  and  fourth  carpal  bones;  9,  deep  short  part 
of  medial  collateral  ligament;  10,  11,  12,  radial,  inter- 
mediate, and  ulnar  carpal  bones;  13,  14,  1.5,  second,  third, 
and  fourth  carpal  bones;  16,  16',  17,  metacarpal  bones. 
(Of  the  preceding  volar  ligaments,  1,  3,  and  8  are  distinct 
from  the  capsule.) 


INTERMETACARPAL  JOINTS 

The  small  joints  formed  between  the  proximal  ends  of  the  metacarpal  bones 
(Articulationes  intermetacarpeae)  are  enclosed  by  the  carpal  joint  capsule,  as  des- 
cribed above.  The  opposed  surfaces  of  the  shafts  of  the  bones  are  closely  united  by 
an  interosseous  metacarpal  ligament  (Lig.  interosseum  metacarpi),  which  often 
undergoes  more  or  less  extensive  ossification. 


224  THE   ARTICULATIONS    OF   THE    HORSE 


THE  FETLOCK  JOINT 

This,  the  metacarpo-phalangeal  articulation  (Articulatio  metacarpo-phalangea), 
is  a  ginglymus  formed  by  the  junction  of  the  distal  end  of  the  large  (third)  meta- 
carpal bone,  the  proximal  end  of  the  first  phalanx,  and  the  proximal  sesamoid 
bones. 

Articular  Surfaces. — The  surface  on  the  large  metacarpal  bone  is  approxi- 
mately cylindrical  in  curvature,  but  is  divided  into  two  slightly  unequal  parts  by  a 
sagittal  ridge.  This  is  received  into  a  socket  formed  by  the  first  phalanx  below  and 
the  two  sesamoids  together  with  the  intersesamoid  ligament  behind.  The  latter 
is  a  mass  of  fibro-cartilage  in  which  the  sesamoid  bones  are  largely  embedded.  It 
extends  above  the  level  of  the  sesamoids,  and  is  grooved  to  receive  the  ridge  on  the 
metacarpal  bone;  its  volar  surface  forms  a  smooth  groove  for  the  deep  flexor  ten- 
don. 

The  joint  capsule  is  attached  around  the  margin  of  the  articular  surfaces.  It 
is  thick  and  ample  in  front;  here  a  bursa  is  interposed  between  it  and  the  extensor 
tendons,  but  the  tendons  are  also  attached  to  the  capsule.  Posteriorly  it  forms  a 
thin-walled  pouch  which  extends  upward  between  the  metacarpal  bone  and  the 
suspensory  ligament  about  as  high  as  the  point  of  bifurcation  of  the  latter.^  The 
capsule  is  reinforced  by  two  collateral  ligaments. 

The  collateral  ligaments,  medial  and  lateral  (Lig.  collaterale  ulnare,  radiale), 
are  partially  divided  into  two  layers :  the  superficial  layer  arises  from  the  eminence 
on  the  side  of  the  distal  end  of  the  large  metacarpal  bone,  and  passes  straight  to 
the  rough  area  below  the  margin  of  the  articular  surface  of  the  first  phalanx;  the 
deep  layer,  shorter  and  much  stronger,  arises  in  the  depression  on  the  side  of  the 
distal  end  of  the  metacarpal  bone,  and  passes  obliquely  downward  and  backward 
to  be  inserted  into  the  abaxial  surface  of  the  sesamoid  and  the  proximal  end  of  the 
first  phalanx. 

The  capsule  is  further  strengthened  by  a  layer  of  oblique  fibers  which  pass  over  the  collateral 
ligament  on  either  side  and  end  on  the  extensor  tendon  and  the  proximal  extremity  of  the  first 
phalanx.     It  may  properly  be  regarded  as  fascia  rather  than  ligament. 

Movements. — These  are  of  the  nature  of  flexion  and  extension,  the  axis  of 
motion  passing  through  the  proximal  attachments  of  the  collateral  ligaments.  In 
the  ordinary  standing  position  the  joint  is  in  a  state  of  partial  dorsal  flexion,  the 
articular  angle  (in  front)  being  about  140°  to  150°.  (In  the  hind  limb  it  is  about 
5°  greater.)  Diminution  of  this  angle  (sometimes  termed  "overextension")  is  nor- 
mally very  limited  on  account  of  the  resistance  offered  by  the  sesamoidean  appa- 
ratus, but  it  varies  considerably  in  amount  in  different  subjects.  Volar  flexion  is 
limited  only  by  contact  of  the  heels  with  the  metacarpus.  During  volar  flexion 
a  small  amount  of  transverse  movement  is  possible. 


THE  SESAMOIDEAN  LIGAMENTS 

Under  this  head  will  be  described  a  number  of  important  ligaments  which  are 
connected  with  the  sesamoid  bones  and  form  a  sort  of  stay  apparatus  or  brace. 

The  intersesamoidean  ligament  (Lig.  intersesamoideum)  not  only  fills  the 
space  between  and  unites  the  sesamoid  bones,  but  also  extends  above  them,  enter- 
ing into  the  formation  of  the  articular  surface  of  the  fetlock  joint.  Other  facts 
in  regard  to  it  have  been  given  above. 

The  collateral  sesamoidean  ligaments,  lateral  and  medial  (Ligg.  sesamoidea 

^  This  pouch  is  in  part  bound  down  by  a  layer  of  elastic  tissue  which  arises  by  two  branches 
from  the  distal  part  of  the  volar  surface  of  the  shaft  of  the  large  metacarpal  bone  and  ends  on  the 
intersesamoid  ligament.  It  was  first  described  by  Skoda  who  terms  it  the  lig.  metacarpo-inter- 
sesamoideum. 


THE   SESAMOIDEAN   LIGAMENTS 


225 


ulnare  et  radiale),  arise  on  the  abaxial  surface  of  each  sesamoid  bone,  pass  forward, 
and  divide  into  two  branches,  one  of  which  ends  in  the  depression  on  the  distal  end 
of  the  large  metacarpal  bone,  the  other  on  the  eminence  on  the  proximal  end  of  the 
first  phalanx.  They  are  partly  covered  by  the  branches  of  the  suspensory  or 
superior  sesamoidean  ligament. 

The  suspensory  ligament  or  interosseous  tendon  (Tendo  interosseus)i  lies  in 
great  part  in  the  metacarpal  groove,  where  it  has  the  form  of  a  wide,  thick 
band.     It  is  attached  above  to  the  proximal  part  of  the  posterior  surface  of  the  large 


Extensor  tendon 


Proximal  end  of  capsule  of  fetlock 
joint 

Bursa 

Collateral  ligament  of  fetlock  joint 
Fascia 

Branch  of  suspensory  ligament 


Lateral  volar  ligament  of  pastern  if^ 

joint 


Suspensory  ligament  of  navicidar 
bone 
Band  from  cartilage  to  extensor 
tendon 
Collateral  ligament  of  coffin  joint 


Superficial  flexor  tendon 
Deep  flexor  tendon 
Suspensory  ligament 
Lateral  interosseous  tendon 

Proximal  end  of  digital  sheath 
Ring  of  superficial  flexor  tendon 
I ntersesamoidean  ligament 
Posterior  annular  ligament  (cut) 


Collateral  sesamoidean  ligament 
Superficial  distal  sesamoidean 

ligaynent 
Middle  distal  sesamoidean  ligament 

Attachments  of  proximal  digital 
annular  ligament 


Pouch  of  digital  sheath 

Distal  digital  annular  ligament 
Cartilage  of  third  phalanx 


Fig.  240. — Ligaments  and  Tendons  of  Distal  Part  of  Limb  of  Horse. 

Mc.in,  Large  metacarpal  bone;    Ph. I,  first  phalanx;    Ph.H,  second  phalanx;    Ph.IH,  third  phalanx;    1,  deep  flexor 

tendon;  2,  band  from  first  phalanx  to  digital  cushion.     (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


metacarpal  bone  and  to  the  distal  row  of  carpal  bones.  At  the  distal  fourth  of  the 
metacarpus  it  divides  into  two  diverging  branches.  Each  branch  passes  to  the 
abaxial  face  of  the  corresponding  sesamoid,  on  which  a  considerable  part  is  attached. 
The  remainder  passes  obliquely  do^vnward  and  forward  to  the  dorsal  surface  of  the 
first  phalanx,  where  it  joins  the  extensor  tendon;  there  is  a  bursa  between  this  ex- 
tensor branch  and  the  proximal  end  of  the  first  phalanx.     This  ligament  possesses 

^  This  is  also  known  as  the  superior  sesamoidean  Hgament;   it  is  described  here  in  deference 
to  custom  and  on  account  of  its  Ugamentous  function. 
15 


226 


THE   ARTICULATIONS    OF   THE    HORSE 


considerable  elasticity,  and  is  the  highly  modified  interosseous  medius  muscle.  It 
consists  mainly  of  tendinous  tissue,  but  contains  a  variable  amount  of  striped  mus- 
cular tissue,  especially  in  its  deep  part  and  in  young  subjects.  Its  principal  func- 
tion is  to  support  the  fetlock,  i.  e.,  to  prevent  excessive  dorsal  flexion  of  the  joint 
when  the  weight  is  put  on  the  limb.  The  branches  which  join  the  common  exten- 
sor tendon  limit  volar  flexion  of  the  interphalangeal  joints  in  certain  phases  of  move- 
ment. ^ 

The  distal  sesamoidean  ligaments  are  three  in  number.     The  superficial  or 


Large  metacarpal  bone 

Lateral  small  metacarpal  bone 

Bifurcation  of  suspensory 
ligament 


Bifurcation  of  common  digital  artery 
Medial  digital  artery 


Oblique  or  middle  distal  sesamoid 
ligament 
Straight  or  superficial  distal 
sesamoid  ligament 


Distal  annular  ligament  of  digit  (cut 
and  reflected) 


Capsule  of  fetlock  joint  (proximal 

pouch) 
Sesarnoid  groove 

Volar  annular  ligament  of  fetlock 
(cut  and  reflected) 

Lateral  sesamoid  ligament 
Stump  of  proximal  digital  annular 

ligament 
Extensor  branch  of  suspensory 

ligament 
Volar  ligaments  of  pastern  joint 

Insertion  of  superficial  flexor 

tendon 
Fibrous  plate 
Deep  flexor  tendon 

Lateral  ligament  of  pastern  joint 
Distal  end  of  digital  sheath 
Suspensory  ligament  of  navicular 

bone 
Dorsal  branch  of  digital  artery 
Volar  branch  of  digital  artery 


Fig.  241. — Deep  Dissection  of  Distal  Part  of  Right  Fore  Limb  of  Horse,  Showing  Joints  and  Ligaments; 

Posterior  View. 
1,  Cartilage  of  third  phalanx;    2,  flexor  surface  of  navicular  bone;    3,  diatal   navicular   ligament;   4,  insertion  of 
deep  flexor  tendon.     Small  arrows  point  to  openings  made  in  capsules  of  pastern  and  coffin  joints.     (After  Schmaltz, 
Atlas  d.  Anat.  d.  Pferdes.) 


straight  sesamoidean  ligament  (Lig.  sesamoideum  rectum)  is  a  flat  band  and  is 
somewhat  wider  above  than  below. ^  It  is  attached  above  to  the  bases  of  the  sesa- 
moid bones  and  the  intersesamoid  ligament,  below  to  the  complementary  fibro- 
cartilage  of  the  proximal  end  of  the  second  phalanx.  The  middle  sesamoidean 
ligament  is  triangular,  with  thick,  rounded  margins  (Ligg.  sesamoidea  obliqua)  and 
a  thin  central  portion.^     Its  base  is  attached  to  the  sesamoid  bones  and  intersesa- 


*  This  is  often  called  the  Y-shaped  ligament — a  rather  undesirable  name,  since  it  is  not 
bifurcate. 

^  It  is  also  called  the  V-shaped  ligament. 


THE    SESAMOIDEAN    LIGAMENTS 


227 


moid  ligament,  and  its  deep  face  to  the  triangular  rough  area  on  the  volar  surface 
of  the  first  phalanx.  The  deep  or  cruciate  sesamoidean  ligaments  (Ligg.  sesamoidea 
cruciata)  consist  of  two  thin  layers  of  fibers  which  arise  on  the  base  of  the  sesa- 
moid bones,  cross  each  other,  and  end  on  the  opposite  eminence  on  the  proximal 
end  of  the  first  phalanx. 

The  two  short  sesamoidean  ligaments  (Ligg.  sesamoidea  brevia)  are  best  seen 


Skin 

Tendon  of  common  extensor 

Bursa 

Capsule  of  fetlock  joint 
Cavity  of  fetlock  joint 


Cavity  of  pastern  joint 


Cavity  of  coffin  joint 


Middle  sesamoidean  ligament 
Digital  synovial  sheath 
Cavity  of  pastern  joint 
Superficial  sesamoidean  ligament 
Deep  flexor  tendon 
Distal  end  of  digital  sheath 


11 

Digital  cushion 


Corium  of  periopl 
Periople 

Coronary  corium 

Wall 

Laminae 


Sole  Corium  of  sole 
Fig.  242. — Sagittal  Section  of  Digit  and  Distal  Part  of  Metacarpus  op  Horse. 
A,  Metacarpal  bone;  B,  first  phalanx;  C,  second  phalanx;  D,  third  phalanx;  E,  distal  sesamoid  bone;  1,  volar 
pouch  of  capsule  of  fetlock  joint;  2,  intersesamoidean  ligament;  3,  4,  proximal  end  of  digital  synovial  sheath;  5,  ring 
formed  by  superficial  flexor  tendon;  6,  fibrous  tissue  underlying  ergot;  7,  ergot;  8,  9,  9',  branches  of  digital  vessels;  10, 
distal  ligament  of  distal  sesamoid  bone;  11,  suspensory  ligament  of  distal  sesamoid  bone;  12,  12',  proximal  and  distal 
ends  of  bursa  podotrochlearis.     By  an  oversight  the  superficial  flexor  tendon  (behind  4)  is  not  marked. 


by  opening  the  joint  in  front  and  pushing  the  sesamoid  bones  backward;  they 
are  covered  by  the  synovial  membrane.  Each  is  a  short  band  which  extends  from 
the  anterior  part  of  the  base  of  the  sesamoid  bone  outward  or  inward  to  the  posterior 
margin  of  the  articular  surface  of  the  first  phalanx. 

The  distal  sesamoidean  ligaments  may  be  regarded  as  digital  continuations 
of  the  suspensory  ligament,  the  sesamoid  bones  being  intercalated  in  this  remark- 
able stay  apparatus,  by  which  the  fetlock  is  supported  and  concussion  diminished. 


228  THE    ARTICULATIONS    OF   THE    HORSE 


THE  PASTERN  JOINT 

This,  the  proximal  interphalangeal  articulation  (Articulatio  interphalangea 
proximalis  s.  phalangis  secundffi),  is  a  ginglymus  formed  by  the  junction  of  the 
distal  end  of  the  first  phalanx  and  the  proximal  end  of  the  second  phalanx. 

The  articular  surfaces  are:  (1)  On  the  first  phalanx,  two  slightly  unequal  con- 
vex areas  ^Adth  an  intermediate  shallow  groove;  (2)  on  the  second  phalanx,  a  cor- 
responding surface,  completed  behind  by  a  plate  of  fibro-cartilage. 

The  joint  capsule  is  close-fitting  in  front  and  on  the  sides,  where  it  blends  with 
the  extensor  tendon  and  the  collateral  ligaments  respectively.  Behind  it  pouches 
upward  a  little  and  is  reinforced  by  the  straight  sesamoidean  ligament  and  the 
branches  of  the  superficial  fiexor  tendon. 

There  are  two  collateral  and  four  volar  ligaments. 

The  collateral  ligaments,  medial  and  lateral  (Lig.  collaterale  rachale,  ulnare), 
are  very  short  and  strong  bands  which  are  attached  above  on  the  eminence  and  de- 
pression on  each  side  of  the  distal  end  of  the  first  phalanx,  and  below  on  the  em- 
inence on  each  side  of  the  proximal  end  of  the  second  phalanx.  The  direction  of 
the  ligaments  is  about  vertical  and,  therefore,  does  not  correspond  to  the  digital 
axis. 

The  volar  ligaments  (Ligg.  volaria)  consist  of  a  central  pair  and  lateral  and 
medial  bands  which  are  attached  below  to  the  posterior  margin  of  the  proximal  end 
of  the  second  phalanx  and  its  complementary  fibro-cartilage.  The  lateral  and 
medial  ligaments  are  attached  above  to  the  middle  of  the  borders  of  the  first  phalanx, 
the  central  pair  lower  down  and  on  the  margin  of  the  triangular  rough  area. 

These  ligaments  are  very  commonly  thickened  as  a  result  of  clironic  inflammation,  and  then 
are  not  well  defined.  The  central  ones  blend  below  with  the  branches  of  the  superficial  flexor 
tendon  and  with  the  straight  sesamoidean  Ugament. 

Movements. — These  are  very  limited,  and  consist  of  flexion  and  extension. 
The  axis  of  motion  passes  transversely  through  the  distal  end  of  the  first  phalanx. 
In  the  standing  position  the  joint  is  extended.  A  small  amount  of  volar  flexion  is 
possible,  and  in  this  position  slight  lateral  and  medial  flexion  and  rotation  can  be 
produced  by  manipulation.  Dorsal  flexion  is  prevented  by  the  lateral,  volar,  and 
straight  sesamoidean  ligaments. 

THE  COFFIN  JOINT 

This  joint,  technically  termed  the  distal  interphalangeal  articulation  (Articu- 
latio interphalangea  distalis  s.  phalangis  tertise),  is  a  ginglymus  formed  by  the  junc- 
tion of  the  second  and  third  phalanges  and  the  distal  sesamoid  bone. 

Articular  Surfaces. — The  surface  on  the  distal  end  of  the  second  phalanx  is 
convex  in  the  sagittal  direction,  concave  transversely.  The  articular  surface  of  the 
third  phalanx  slopes  sharply  upward  and  forward;  its  central  part  is  prominent, 
and  is  flanked  by  two  glenoid  cavities.  It  is  completed  behind  by  the  articular 
surface  of  the  distal  sesamoid  or  navicular  bone. 

Joint  Capsule. — This  is  attached  around  the  margins  of  the  articular  surfaces. 
In  front  and  on  the  sides  it  is  tight,  and  is  blended  with  the  extensor  tendon  and  the 
collateral  ligaments  respectively.  It  forms  a  considerable  pouch  behind,  which 
extends  upward  to  about  the  middle  of  the  second  phalanx,  where  it  is  separated  by 
a  fibrous  membrane  from  the  digital  synovial  sheath.  On  each  side  small  pouches 
project  (especially  during  volar  flexion)  against  the  cartilages  of  the  third  phalanx 
just  behind  the  collateral  ligaments.^ 

Ligaments. — The  collateral  ligaments,  medial   and  lateral   (Lig.   collaterale 

'  Tliis  should  be  noted  in  regard  to  resection  of  the  cartilage  or  other  operations  in  this 
vicinity. 


THE    ARTICULATIONS    OF   THE    PELVIC    LIMB 


229 


ulnare,  radiale),  are  short,  strong  bands  v/hich  are  attached  above  in  the  depressions 
on  either  side  of  the  lower  part  of  the  second  phalanx,  under  cover  of  the  cartilage 
of  the  third  phalanx.  They  widen  below  and  end  in  the  depressions  on  either 
side  of  the  extensor  process  and  on  the  anterior  end  of  the  cartilages. 

The  collateral  sesamoidean  or  suspensory  navicular  ligaments,  medial  and 
lateral  (Lig.  sesamoideum  coUaterale  ulnare,  radiale),i  are  strong,  somewhat  elastic 
bands,  which  form  a  sort  of  suspensory  apparatus  for  the  third  sesamoid.  They  are 
attached  superiorly  in  and  above  the  depressions  on  each  side  of  the  distal  end  of 
the  first  phalanx  and  are  here  partly  blended  with  the  collateral  ligaments  of  the 
pastern  joint.  They  are  directed  obliquely  downward  and  backward,  and  end 
chiefly  on  the  ends  and  proximal  border  of  the  distal  sesamoid,  but  detach  a 
branch  to  the  axial  surface  of  each  cartilage  and  angle  of  the  third  phalanx. 

The  phalango-sesamoidean  or  distal  navicular  ligament  (Lig.  phalangeo-sesa- 
moideum)  reinforces  the  capsule  distally.  It  is  a  strong  layer  of  fibers  which 
extend  from  the  distal  border  of  the  distal  sesamoid  to  the  flexor  surface  of  the  third 
phalanx. 

Movemenis.— 'The  chief  movements  are  flexion  ana  extension.  In  the  stand- 
ing position  the  joint  is  extended.  During  volar  flexion  a  very  small  amount  of 
lateral  movement  and  rotation  can  be  produced  by  manipulation.  Dorsal  flexion 
is  very  limited. 

Dorsal  flexion  appears  to  be  checked  mainly  by  the  deep  flexor  tendon,  since  in  cases  of  rup- 
ture of  the  latter  the  toe  turns  up.  The  mobility  of  the  posterior  part  of  the  socket  for  the  second 
phalanx  (formed  by  the  distal  sesamoid)  diminishes  concussion  when  the  weight  comes  on  the  foot 


LIGAMENTS  OF  THE  CARTILAGES  OF  THE  THIRD  PHALANX 

In  addition  to  the  bands  mentioned  above,  which  attach  the  cartilages  to  the 
extremities  of  the  navicular  bone,  there  are  three  ligaments  on  either  side  which 
attach  the  cartilages  to  the  phalanges. 

An  ill-defined  elastic  band  passes  from  the  middle  part  of  the  border  of  the  first 
phalanx  to  the  upper  part  of  the  cartilage,  detaching  a  branch  to  the  digital  cushion. 

A  short,  strong  band  connects  the  anterior  extremity  of  the  cartilage  with  the 
rough  eminence  on  the  second  pha- 
lanx in  front  of  the  attachment  of  the 
collateral  ligament  of  the  coffin  joint. 

The  lower  border  of  the  cartil- 
age is  covered  in  part  by  fibers  which 
attach  it  to  the  angle  of  the  third 
phalanx. 


The  Articulations  of  the 
Pelvic  Limb 

the  sacro-iliac  articulation 

This  joint  (Articulatio  sacro- 
iliaca)  is  a  diarthrosis  formed  be- 
tween the  auricular  surfaces  of  the 
sacrum  and  ilium.  These  surfaces 
are  not  smooth  in  the  adult,  but  are 

marked  by  reciprocal  eminences  and  depressions,  and  are  covered  by  a  thin  laj^er  of 
cartilage.     The  joint  cavity  is  a  mere  cleft,  and  is  often  crossed  by  fibrous  bands. 


Sacro-iliac 
articulation 


243. — Left  Sacro-iliac  Articulation  of  Horse;  An- 
terior View.  (Adapted  from  Schmaltz,  Atlas  d.  Anat. 
d.  Pferdes.) 


^  These  are  termed  the  postero-lateral  ligaments  by  M'Fadyean. 
suspensory  ligaments  of  the  navicular  bone. 


Functionally  they  are 


230  THE    ARTICULATIONS   OF   THE   HORSE 

The  joint  capsule  is  very  close  fitting,  and  is  attached  around  the  margins  of 
the  articular  surfaces.  It  is  reinforced  by  the  ventral  sacro-iliac  ligament  (Lig. 
sacro-iliacum  ventrale),  which  surrounds  the  joint;  this  is  exceedingly  strong  above, 
where  it  occupies  the  angle  between  the  ilium  and  the  wdng  of  the  sacrum;  it  con- 
sists chiefly  of  nearly  vertical  fibers. 

The  movements  are  inappreciable  in  the  adult — stability,  not  mobility,  being 
the  chief  desideratum. 


LIGAMENTS  OF  THE  PELVIC  GIRDLE 

The  following  ligaments  (Ligg.  cinguli  extremitatis  pelvinse)  may  be  regarded 
as  accessory  to  the  sacro-iliac  joint,  although  not  directly  connected  with  it: 


Fig.  244. — Pelvic  Ligaments  and  Hip  Joint. 
1,  Dorsal  sacro-iliac  ligament;  S,  lateral  sacro-iliac  ligament;  3,  saero-sciatic  ligament;  4.  greater  sciatic  foramen; 
S,  lesser  sciatic  foramen;  6,  line  of  attachment  of  intermuscular  septum  between  biceps  femoris  and  semitendinosus; 
7,  capsule  of  hip  joint;  8,  capsularis  muscle;  9,  lateral  tendon  of  origin  of  rectus  femoris;  10,  tuber  sacrale;  11,  tuber 
cox«;  /;?,  shaft  of  ilium;  ^i?,  superior  ischiatic  spine;  /4.  pubis;  7.J,  tuber  ischii;  iff,  trochanter  major;  / 7,  semimem- 
branosus;  IS,  fifth  lumbar  spine;   19,  20,  first  and  second  coccygeal  vertebrae. 

The  dorsal  sacro-iliac  ligament  (Lig.  sacro-iliacum  dorsale  breve)  is  a  strong 
band  which  is  attached  to  the  tuber  sacrale  and  the  summits  of  the  sacral  spines. 

The  lateral  sacro-iliac  ligament  (Lig.  sacro-iliacum  dorsale  longum)  is  a  tri- 
angular, thick  sheet  which  is  attachetl  in  front  to  the  tuber  sacrale  and  adjacent 
part  of  the  medial  border  of  the  ilium  above  the  great  sciatic  notch,  and  below  to 
the  lateral  border  of  the  sacrum.  It  blends  above  with  the  dorsal  sacro-iliac  liga- 
ment, below  with  the  sacro-sciatic  ligament,  and  behind  with  the  coccygeal  fascia. 

The  sacro-sciatic  ligament  (Lig.  sacroischiadicum  s.  sacrospinosum  et  tuber- 
osum) is  an  extensive  quadrilateral  sheet  which  completes  the  lateral  pelvic  wall. 


SYMPHYSIS    PELVIS THE    HIP   JOINT  231 

Its  dorsal  border  is  attached  to  the  border  of  the  sacrum  and  the  transverse  processes 
of  the  first  and  second  coccygeal  vertebrae.  Its  ventral  border  is  attached  to  the 
superior  ischiatic  spine  and  tuber  ischii.  Between  these  it  bridges  over  the  lateral 
border  of  the  ischium  and  completes  the  lesser  sciatic  foramen  (Foramen  ischiadi- 
cum  minus).  The  anterior  border  is  concave,  and  completes  the  greater  sciatic 
foramen  (Foramen  ischiadicum  majus).  The  posterior  border  is  fused  with  the 
vertebral  head  of  the  semimembranosus  muscle. 

The  lesser  sciatic  foramen  is  closed,  except  where  the  tendon  of  the  obturator  internus  and 
a  vein  pass  tlirough  it,  by  a  thin  fibrous  sheet  given  off  from  the  sacro-sciatic  ligament. 

The  ilio-lumbar  ligament  (Lig.  ilio-lumbale)  is  a  triangular  sheet  which  at- 
taches the  ends  of  the  lumbar  transverse  processes  to  the  ventral  surface  of  the 
ilium  below  the  attachment  of  the  longissimus  muscle  (Fig.  273) . 

SYMPHYSIS  PELVIS 
The  symphysis  pelvis  is  formed  Ijv  the  junction  of  the  two  ossa  coxarum  at 
the  ventral  median- line.  In  the  young  subject  the  bones  are  united  by  a  layer  of 
cartilage  (Lamina  fibrocartilaginea) ;  in  the  adult  the  latter  is  gradually  replaced 
by  bone,  the  process  beginning  in  the  pubic  portion  and  extending  backward, 
but  commonly  the  ischia  are  in  part  not  fused.  The  union  is  strengthened  by 
white  fibrous  tissue  dorsally  and  ventrally.  A  transverse  band  also  covers  the 
anterior  border  of  the  pubis,  and  other  fibers  (Lig.  arcuatum  ischiadicum)  extend 
across  at  the  ischial  arch.  No  appreciable  movement  occurs  even  before  synosto- 
sis takes  place. 

OBTURATOR  MEMBRANE 

This  (Membrana  obturatoria)  is  a  thin  layer  of  fibrous  tissue  which  covers  the 
obturator  foramen,  leaving,  however,  a  passage  (Canalis  obturatorius)  for  the 
obturator  vessels  and  nerve. 

THE  HIP  JOINT 

This  joint  (Articulatio  coxae)  is  an  enarthrosis  formed  by  the  proximal  end  of 
the  femur  and  the  acetabulum. 

Articular  Surfaces. — The  head  of  the  femur  presents  an  almost  hemispherical 
articular  surface,  which  is  continued  a  short  distance  on  the  upper  surface  of  the 
neck.  It  is  more  extensive  than  the  socket  which  receives  it.  It  is  cut  into  medi- 
ally by  a  deep  notch  for  the  attachment  of  the  round  and  accessory  ligaments. 
The  acetabulum  is  a  typical  cotyloid  cavity.  Its  articular  surface  is  somewhat 
crescentic,  being  deeply  cut  into  medially  by  the  acetabular  notch  and  fossa. 

The  acetabulum  is  deepened  by  a  ring  of  fibro-cartilage,  the  cotyloid  ligament 
(Labrum  glenoidale),  which  is  attached  to  the  bony  margin;  that  part  of  the  liga- 
ment which  crosses  the  notch  is  called  the  transverse  acetabular  ligament  (Lig. 
transversum  acetabuli)  (Fig.  291). 

The  joint  capsule  is  roomy.  It  is  attached  around  the  margin  of  the  acetab- 
ulum and  the  neck  of  the  femur.     It  is  thickest  laterally. 

The  attachment  on  the  femur  is  about  1  cm.  from  the  margin  of  the  articular  surface,  except 
above,  where  2  to  3  cm.  of  the  neck  is  intracapsular.  A  thin,  oblique  band  corresponding  in  direc- 
tion with  the  capsularis  muscle  reinforces  the  antero-lateral  part  of  the  capsule;  this  appears  to 
be  the  feeble  homologue  of  the  very  strong  ilio-femoral  ligament  of  man.  The  capsule  is  very 
thin  under  the  iho-psoas,  and  is  adherent  to  the  muscle.  Its  fibrous  part  is  perforated  medially 
by  the  accessory  and  round  ligaments  and  the  articular 


The  round  ligament  (Lig.  teres)  is  a  short,  strong  band  which  is  attached 
in  the  subpubic  groove  close  to  the  acetabular  notch,  passes  outward,  and  ends 
in  the  notch  on  the  head  of  the  femur  (Fig.  581). 


232  THE    ARTICULATIONS    OF   THE    HORSE 

The  accessory  ligament  (Lig.  accessorium)i  does  not  occur  in  the  domestic 
animals  other  than  the  equidse.  It  is  a  strong  band  detached  from  the  prepubic 
tendon  of  the  abdominal  muscles  (Fig.  581).  It  is  directed  outward,  backward, 
and  upward,  passes  through  the  acetabular  notch  dorsal  to  the  transverse  ligament, 
and  ends  behind  the  round  ligament  in  the  notch  on  the  head  of  the  femur.  The 
origin  of  the  pectineus  muscle  is  perforated  by  the  ligament,  which  furnishes  at- 
tachment to  many  fibers  of  the  muscle. 

The  synovial  membrane  is  reflected  over  the  intracapsular  parts  of  these  lig- 
aments and  covers  the  fossa  acetabuli.  A  pouch  also  extends  from  the  acetabular 
notch  for  a  variable  distance  along  the  subpubic  groove  above  the  accessory  liga- 
ment. 

Movements. — This  joint  is  capable  of  all  the  movements  of  a  ball-and-socket 
joint,  viz.,  flexion,  extension,  abduction,  adduction,  rotation,  and  circumduction. 
The  greatest  range  of  movement  is  displayed  in  flexion  and  extension.  When 
standing  at  rest,  the  joint  is  partially  flexed,  the  articular  angle  (in  front)  being 
about  100°  to  115°.  The  other  movements  occur  to  a  very  limited  extent  in  normal 
action.  Abduction  appears  to  be  checked  by  tension  of  the  round  and  accessory 
ligaments.  The  accessory  ligament  is  tensed  most  promptly  by  inward  rotation  of 
the  thigh. 

THE  STIFLE  JOINT 

This  joint  (Articulatio  genu),  which  corresponds  to  the  knee-joint  of  man, 
is  the  largest  and  most  elaborate  of  all  the  articulations.  Taken  as  a  whole,  it 
may  be  classed  as  a  ginglymus,  although  it  is  not  a  typical  example  of  the  group. 
In  reality  it  consists  of  two  joints — the  femoro-patellar  and  the  femoro-tibial. 

The  femoro-patellar  articulation  (Articulatio  femoro-patellaris)  is  formed 
between  the  trochlea  of  the  femur  and  the  articular  surface  of  the  patella. 

Articular  Surfaces. — The  trochlea  consists  of  two  slightly  oblique  ridges, 
with  a  wide  and  deep  groove  between  them.  The  medial  ridge  is  much  the  larger 
of  the  two,  especially  at  its  proximal  part,  which  is  wide  and  rounded.  The  lateral 
ridge  is  much  narrower,  and  is  more  regularly  curved;  its  proximal  part  lies  about 
an  inch  behind  a  frontal  plane  tangent  to  the  medial  one.  The  articular  surface 
of  the  patella  is  much  smaller  than  that  of  the  trochlea.  It  is  completed  medially 
by  a  supplementary  plate  of  fibro-cartilage  (Fibrocartilago  patellae),  which  curves 
over  the  medial  ridge  of  the  trochlea.  A  narrow  strip  of  cartilage  is  found  along 
the  lateral  border  also.  The  articular  cartilage  on  the  trochlea  completely  covers 
both  surfaces  of  the  medial  ridge,  but  extends  only  a  short  distance  on  the  lateral 
surface  of  the  outer  ridge. 

Joint  Capsule. — This  is  thin  and  is  very  capacious.  On  the  patella  it  is 
attached  around  the  margin  of  the  articular  surface,  but  on  the  femur  the  line  of 
attachment  is  at  a  varying  distance  from  the  articular  surface.  On  the  medial  side 
it  is  an  inch  or  more  from  the  articular  cartilage;  on  the  lateral  side  and  above, 
about  half  an  inch.  It  pouches  upward  under  the  quadriceps  femoris  for  a  distance 
of  two  or  three  inches,  a  pad  of  fat  separating  the  capsule  from  the  muscle.  Be- 
low the  patella  it  is  separated  from  the  patellar  ligaments  by  a  thick  pad  of  fat, 
but  inferiorly  it  is  in  contact  with  the  femoro-tibial  capsules.  The  joint  cavity  is 
the  most  extensive  in  the  body.  It  usually  communicates  with  the  medial  sac  of 
the  femoro-tibial  joint  cavity  by  a  slit-like  opening  situated  at  the  lowest  part  of 
the  medial  ridge  of  the  trochlea.  A  similar,  usually  smaller,  communication  with 
the  lateral  sac  of  the  femoro-tibial  capsule  is  often  found  at  the  lowest  part  of  the 
lateral  ridge. 

The  medial  communication  is  rarely  absent  in  adult  horses,  but  is  liable  to  be  overlooked 
on  account  of  the  fact  that  it  is  covered  by  a  valvular  fold  of  the  synovial  membrane.     It  is  about 

^  This  is  also  commonly  called  the  pubo-femoral  ligament. 


THE    STIFLE    JOINT 


233 


half  an  inch  ^vnde,  and  bes  under  the  narrow  articular  area  wliich  connects  the  trochlea  and  medial 
condyle.  Ihe  lateral  communication  occui-s  in  18  to  25  per  cent,  of  cases,  according  to  Baum;  in 
rare  cases  it  is  larger  than  the  inner  one.  It  is  instructive  to  distend  this  capsule  and  thus  obtain 
an  idea  of  its  potential  capacity  and  relations  (Fig.  246). 

Ligaments. — The  femoro-patellar  ligaments,  lateral  and  medial  (Lig.  femoro- 
patellare  fibulare,  tibiale),  are  two  thin  bands  which  reinforce  the  capsule  on  either 


Patella 


Accessory  cartilage  of  — 
patella 


Medial  ridge  of  trochlea 
Medial  patellar  ligament 

Medial  epicondyh 

Medial  femoro-tibial 
ligament 

Medial  meniscus 
Medial  condyle  of  tibia 


Tuberosity  of  tibia 


Biceps  femoris 

Lateral  patellar  ligament 


Lateral  femoro-tibial 
ligament 

Lateral  meniscus 
Lateral  condyle  of  tibia 


Interosseous  space 


Fibula 


hderosseous  ligament 


Fig.  245. — Left  Stifle  Joint  of  Horse;   Froxt  View.     The  Capsules  are  Removed. 
1,  Middle  patellar  ligament;  2,  stump  of  fascia  lata;    3,  stump  of  common  tendon  of  extensor  longus  and  peroneus 


side.  The  lateral  ligament  is  fairly  distinct;  it  arises  from  the  lateral  epicondyle  of 
the  femur  just  above  the  lateral  femoro-tibial  ligament,  and  ends  on  the  lateral 
border  of  the  patella.  The  medial  ligament  is  thinner  and  is  not  distinct  from  the 
capsule;  it  arises  above  the  medial  epicondyle,  and  ends  on  the  patellar  fibro-car- 
tilage. 

The  patellar  ligaments  (Ligg.  patellae)^  are  three  very  strong  bands  which  at- 

^  They  are  also  termed  the  straight  ligaments  of  the  patella.     This  term  seems  objectionable 
since  they  are  all  obUque  in  direction. 


234 


THE   ARTICULATIONS   OF  THE   HORSE 


tach  the  patella  to  the  tuberosity  of  the  tibia.  The  lateral  patellar  ligament  ex- 
tends from  the  lateral  part  of  the  anterior  surface  of  the  patella  to  the  lateral  part 
of  the  tubcrosit}^  of  the  tibia.  It  receives  a  strong  tendon  from  the  biceps  femoris 
muscle  and  also  part  of  the  fascia  lata.  The  middle  patellar  ligament  extends 
from  the  front  of  the  apex  of  the  patella  to  the  distal  part  of  the  groove  on  the 
tuberosit}^  of  the  tibia;  a  bursa  is  interposed  between  the  ligament  and  the  upper 
part  of  the  groove,  and  a  smaller  one  occurs  between  the  upper  part  of  the  ligament 
and  the  apex  of  the  patella.     The  medial  patellar  ligament  is  attached  above  to  the 


Proximal  end  of 
femoro- patellar 


Lateral  head  of  gastrocnemius 

Lateral  fetnoro-patellar  ligament 

Attachment  of  joint  capsule 
Lateral  condyle  of  femur 
Lateral  fejnoro-tibial  ligament- 
Popliteus 


Deep  digital  flexor 


Base  of  patella 


-Distal  end  of  capsule 
— -Middle  patellar  ligament 
ll'^^  Medial  patellar  ligament 

Lateral  patellar  ligament 

{stump) 

Tuberosity  of  tibia 
Tibialis  anterior 


Long  extensor 

Lateral  extensor 

Fig.  246. — Right  Stifle  Joint  of  Horse;  Latehal  View. 

The  femoro-patellar  capsule  was  filled  with  plaster-of-Paris  and  then  removed  after  the  cast  was  set.     The  femoro- 

tibial  capsule  and  most  of  the  lateral  patellar  ligament  are  removed.     M,  Lateral  meniscus. 


patellar  fibro-cartilage,  and  ends  on  the  tuberosity  of  the  tibia  at  the  medial  side  of 
the  groove.  It  is  joined  by  the  common  aponeurosis  of  the  gracilis  and  sartorius, 
and  its  proximal  part  furnishes  insertion  to  fibers  of  the  vastus  medialis.  These 
so-called  ligaments  are,  in  reality,  the  tendons  of  insertion  of  the  quadriceps 
femoris  and  biceps  fe-moris  muscles,  and  transmit  the  action  of  the  latter  to  the 
tibia;  they  also  function  similarly  for  the  other  muscles  attached  to  them  as  noted 
above. 

It  will  be  noticed  that  the  proximal  attachments  are  further  apart  than  the  distal  ones,  so 
that  the  ligaments  converge  below.  The  medial  ligament  is  especially  oblique.  The  middle 
ligament  is  more  deeply  placed  than  the  others,  and  therefore  cannot  usually  be  felt  so  distinctly 
in  the  living  animal.     The  lateral  ligament  is  very  largely  the  tendon  of  the  anterior  part  of  the 


THE    STIFLE   JOINT 


235 


biceps  femoris,  but  it  also  furnishes  insertion  to  the  tensor  fasciae  latse  by  means  of  the  fascia 
lata,  which  blends  with  it. 

The  femoro-tibial  articulation  (Articulatio  femoro-tibialis)  is  formed  between 
the  condyles  of  the  femur,  the  proximal  end  of  the  tibia,  and  the  interposed  articular 
menisci  or  semilunar  cartilages. 

Articular  Surfaces. — The  condyles  of  the  femur  are  slightly  oblique  in  direc- 
tion. The  articular  surface  of  the  lateral  one  is  more  strongly  curved  than  that  of 
the  medial  one;  the  latter  is  confluent  below  with  the  medial  ridge  of  the  trochlea. 


Base  of  patella 


Medial  condyle  of 
femur 
Medial  femoro-tibial 
ligament 
Medial  meniscus 

Medial  condyle  of 
tibia 


Accessory  cartilage 


'^Tf Medial  ridge  of  trochlea 

Medial  patellar  liga- 


Middle  patellar  liga- 
metd 


Tuberosity  of  tibia 


Fig.  247. — Left  Stifle  Joint  of  Horse;   Medial  View.     The  Capsules  are  Removed, 


while  the  narrow  ridge  which  connects  the  lateral  condyle  with  the  trochlea  is 
usually  non-articular.  The  saddle-shaped  surfaces  of  the  condyles  of  the  tibia  are 
not  adapted  to  the  femoral  condyles,  and  are  in  contact  with  only  a  small  part  of 
them. 

The  menisci,  lateral  and  medial  (Meniscus  lateralis,  medialis),i  are  two  C- 
shaped  or  crescentic  plates  of  fibro-cartilage  which  produce  congruence  in  the  ar- 
ticular surfaces.     Each  has  a  proximal  concave  surface  adapted  to  the  condyle  of 
the  femur,  and  a  distal  surface  which  fits  the  corresponding  condyle  of  the  tibia. 
1  These  are  also  commonly  termed  the  semilunar  cartilages,  although  they  are  not  so  shaped. 


236 


THE   ARTICULATIONS    OF   THE   HORSE 


The  lateral  meniscus  does  not  cover  the  lateral  and  posterior  part  of  the  tibial  con- 
djde,  over  which  the  tendon  of  origin  of  the  popliteus  muscle  plays.  The  peripheral 
border  is  thick  and  convex,  the  central  one  very  thin  and  concave.  The  fibrous 
ends  or  ligaments  are  attached  to  the  tibia  in  front  of  and  behind  the  spine.  The 
lateral  meniscus  has  a  third  attachment  by  means  of  an  oblique  band  (Ligamentum 
femorale  menisci  lateralis)  which  passes  from  the  posterior  end  to  the  posterior 
part  of  the  intercondyloid  fossa  of  the  femur. 


Base  of  patella 


Medial  ridge  of 
trochlea 


Lateral  patellar  liga-  : 

ment 


Middle  patellar  liga- 
ment 


Stump  of  biceps 
femoris 


La  teralfem  oro-pa  tellar 
ligament 


Lateral  condyle  of 
femur 

Lateral  femoro-tihial 

ligament 

Lateral  meniscus 


Lateral  condyle  of 
tibia 


Tvherosity  of  tibia 


Fig.   248. — Left  Stifle  Joint  of  Honsio;  Lateral  Vie-v.     The  CAPSULEa  are  Remov 


1,  Stump  of  tendon  of  origin  of  extensor  longus  and  peroneus  tertius;   2,  stump  of  fascia  lata;   3,  patellar  attachment  of 
biceps  femoris  and  lateral  patellar  ligament. 


The  ligaments  of  the  medial  meniscus  (Ligamenta  tibialia  anterius  et  posterius  menisci  m.edi- 
alis)  are  attached  in  front  of  and  beliind  the  medial  eminence  of  the  spine.  The  anterior  ligament 
of  the  lateral  meniscus  (Ligamentum  tibiale  anterius  menisci  lateraUs)  is  attached  in  front  of  the 
lateral  eminence  of  the  spine.  The  posterior  one  bifurcates;  the  lower  branch  (Ligamentum  tibiale 
posterius  menisci  lateralis)  is  inserted  at  the  popliteal  notch,  the  upper  (Ligamentum  femorale 
menisci  lateralis)  in  a  small  fossa  in  the  extreme  posterior  part  of  the  intercondyloid  fossa. 

The  joint  capsule  is  attached  to  the  margin  of  the  tibial  articular  surface, 
but  on  the  femur  the  line  of  attachment  is  for  the  greater  part  about  half  an  inch 
(ca.  1  cm.)  from  the  articular  margin.  It  is  also  attacterl  to  the  convex  borders  of 
the  menisci  and  to  the  cruciate  ligaments.     It  is  thin  in  front,  where  it  consists 


THE   STIFLE   JOINT 


237 


practically  of  the  synovial  layer  only.  It  is  much  stronger  posteriorly:  here  it 
is  reinforced  by  what  might  be  regarded  as  a  posterior  ligament.  This  is  a 
strong,  flat  band  which  arises  from  the  femur  just  lateral  to  the  origin  of  the  medial 
head  of  the  gastrocnemius,  and  extends  down  to  the  posterior  border  of  the  medial 
condyle  of  the  tibia;  it  is  wider  below  than  above.  There  are  two  synovial  sacs, 
corresponding  to  the  double  nature  of  the  articular  surfaces;  they  do  not  usually 
communicate,  and  each  is  partially  divided  into  an  upper  and  a  lower  compartment 
by  the  meniscus.     The  medial  sac  pouches  upward  about  half  an  inch  over  the  con- 


Lateral  condyle  of 

Jem  ur 


Lateral  femoro- 

tibial  ligament 

Shimp  of  pop- 

liteus  tendon 

Lateral  meniscus 


Lateral  condyle  of 
tibia 


Head  of  fibula 


Interosseous  space 


Y* —  Medial  femoro- 
'\\        tibial  ligament 


condyle  of 
femur 


Medial  meniscus 


Medial  condyle  of 
tibia 


Fig.  249. — Left  Stifle  Joint  of  Horse;  Posterior  View.     The  Capsule  is  Removed. 
1,  Femoral  ligament  of  lateral  meniscus;    2,  posterior  ligament  of  lateral  meniscus;    3,  anterior  cruciate  ligament;    4, 

posterior  cruciate  ligament. 


clyle  of  the  femur.  The  lateral  sac  invests  the  tendon  of  origin  of  the  popliteus 
muscle,  and  also  pouches  downward  about  three  inches  (ca.  7.5  cm.)  beneath  the 
peroneus  tertius  and  extensor  longus  muscles.  As  stated  above,  the  lateral  sac 
sometimes  communicates  with  the  femoro-patellar  joint  cavity,  and  the  medial 
sac  usually  does  so  in  the  adult. 

Ligaments. — There  are  four  of  these — two  collateral  and  two  cruciate. 

The  medial  ligament  (Lig.  collaterale  tibiale)  is  attached  above  to  the  prom- 
inent medial  epicondyle  of  the  femur,  and  below  to  a  rough  area  below  the  margin 
of  the  medial  condyle  of  the  tibia. 


238 


THE   ARTICULATIONS   OF   THE    HORSE 


The  lateral  ligament  (Lig.  collaterale  fibulare)  is  somewhat  thicker;  it  arises  from 
the  upper  depression  on  the  lateral  epicondj^e,  and  ends  on  the  head  of  the  fibula. 


Middle  patellar 
ligament 


Lateral  patellar 
ligament 


Medial  patellar 
ligament 


Medial  condyle 


Medial  meniscus 


Fig.  250. — Proximal  End  of  Right  Tibia  with  Menisci,  Etc. 
1,  2,  Anterior  and  posterior  cruciate  ligaments;   3,  posterior  ligament  of  medial  meniscus;   4,  femoral  ligament  of 
lateral  meniscus;    5,  5',  anterior  ligaments  of  menisci;    6,  groove  for  popliteus  tendon;   7,  spine  of  tibia;    8,  9,  medial 
and  lateral  femoro-tibial  ligaments. 


It  covers  the  tendon  of  the  origin  of  the  popliteus  muscle,  a  bursa  being  interposed 

between  the  two;  another  bursa  is  present 
between  the  lower  part  of  the  ligament  and 
the  margin  of  the  lateral  condyle  of  the  tibia. 
The  cruciate  ligaments  are  two  strong 
rounded  bands  situated  mainly  in  the  inter- 
condyloid  fossa  of  the  femur,  between  the  two 
synovial  sacs.  They  cross  each  other  some- 
what in  the  form  of  an  X,  and  are  named  ac- 
cording to  their  tibial  attachments.  The 
anterior  cruciate  ligament  (Lig.  cruciatum  an- 
terius)  arises  in  the  central  fossa  on  the  tibial 
spine,  extends  upward  and  backward,  and  ends 
on  the  lateral  wall  of  the  intercondyloid  fossa. 
The  posterior  cruciate  ligament  (Lig.  crucia- 
tum posterius)  is  medial  to  the  preceding,  and 
is  somewhat  larger.  It  is  attached  to  an  emi- 
nence at  the  popliteal  notch  of  the  tibia,  is 
directed  upward  and  forward,  and  ends  in  the 
anterior  part  of  the  intercondyloid  fossa  of 
the  femur. 

It  may  be  added  that  these  ligaments  do  not  lie  in  a  sagittal  plane,  but  are  somewhat  twisted 
across  each  other;   outward  rotation  of  the  leg  untwists  and  slackens  them. 

Movements. — The  principal  movements  of  the  stifle  joint  as  a  whole  are 


Fig.  251. — Proximal  End  of  Right  Tibia  of 
Horse,  with  Areas  of  Ligamentous  At- 
tachment. 
1,  2,  Medial  and  lateral  patellar  ligaments; 

3,  4,  anterior  ligaments  of  menisci;  5,  7,  anterior 

and  posterior    cruciate    ligaments;    6,  posterior 

ligament  of  medial  meniscus. 


TIBIO-FIBULAR   ARTICULATION THE    HOCK   JOINT  239 

flexion  and  extension.  In  the  ordinary  standing  position  the  articular  angle 
(behind)  is  about  140°  to  150°.  Flexion  is  limited  only  by  contact  of  the  leg  with 
the  thigh,  if  the  hock  is  also  flexed.  Extension  is  incomplete,  i.  e.,  the  femur  and 
tibia  cannot  be  brought  into  the  same  straight  line.  Rotation  is  limited,  and  is 
freest  during  semiflexion.  The  patella  glides  on  the  femoral  trochlea  upward  in 
extension,  downward  in  flexion. 

Extension  is  checked  mainly  by  tension  of  the  cruciate  and  collateral  ligaments.  In  extreme 
extension,  which  is  accompanied  by  slight  outward  rotation  of  the  leg,  the  patella  can  be  pushed 
upward  and  inward  so  that  its  fibro-cartilage  hooks  over  the  upper  end  of  the  medial  ridge  of  the 
trochlea,  but  it  will  not  remain  there  unless  held  in  position.  When  pressure  is  removed,  the  base 
of  the  patella  tips  forward  and  the  cartilage  lies  upon  the  most  prominent  part  of  the  trochlear 
ridge.  During  flexion,  which  is  accompanied  by  slight  inward  rotation  of  the  leg,  the  condyles 
of  the  femur  and  the  menisci  gUde  backward  on  the  tibia;  the  movement  of  the  lateral  condyle 
and  meniscus  is  gi-eater  than  that  of  the  medial  one.  In  extreme  flexion  the  patellar  and  posterior 
cruciate  ligaments  are  tense;  the  other  ligaments  are  relaxed.  The  movement  of  the  patella  is 
gliding  with  coaptation,  i.  e.,  different  parts  of  the  opposing  articular  surfaces  come  into  contact 
successively.  Only  a  narrow  transverse  strip  (ca.  1.5-2  cm.  wide)  of  the  patella  is  in  contact 
with  the  trochlea  at  a  time. 

TIBIO-FIBULAR  ARTICULATION 

This  joint  (Articulatio  tibiofibularis)  is  formed  by  the  head  of  the  fibula  ar- 
ticulating with  a  crescentic  facet  just  below  the  outer  margin  of  the  lateral  condyle 
of  the  tibia.  The  joint  capsule  is  strong  and  close.  The  shaft  of  the  fibula  is  at- 
tached to  the  lateral  border  of  the  tibia  b}^  the  interosseous  membrane  of  the  leg 
(Membrana  interossea  cruris);  this  is  perforated  about  an  inch  from  its  proximal 
end  by  an  opening  which  transmits  the  anterior  tibial  vessels  to  the  front  of  the  tibia. 
A  fibrous  cord  usually  extends  from  the  distal  end  of  the  shaft  of  the  fibula  to  the 
lateral  malleolus.  The  latter  is  the  distal  end  of  the  fibula  which  has  fused  with  the 
tibia.     No  appreciable  movement  occurs  in  this  joint. 


THE  HOCK  JOINT 

This  is  a  composite  joint  made  up  of  a  number  of  articulations  (Artie ulationes 
tarsi).  These  are:  (1)  The  tibio-tarsal  articulation;  (2)  the  intertarsal  articula- 
tions;   (3)  the  tarso-metatarsal  articulation. 

The  tibio-tarsal  articulation  (Articulatio  talocruralis)  is  a  typical  ginglymus 
formed  by  the  trochlea  of  the  tibial  tarsal  bone  and  the  corresponding  surface  of  the 
distal  end  of  the  tibia.  The  ridges  and  grooves  of  these  surfaces  are  directed  ob- 
liquel}^  forward  and  outward  at  an  angle  of  about  12°  to  15°  with  a  sagittal  plane. 
The  trochlear  surface  is  about  twice  as  extensive  as  that  on  the  tibia,  and  its  ridges 
have  a  spiral  curvature.  The  other  articulations  are  arthrodia,  which  have  joint 
surfaces  and  ligaments  of  such  a  nature  as  to  allow  only  a  minimal  amount  of  glid- 
ing motion. 

As  in  the  case  of  the  carpal  joints,  it  is  convenient  to  describe  first  the  common 
capsule  and  ligaments,  which  are  the  more  important  practically,  and  then  to 
consider  very  briefly  the  special  ligaments. 

The  fibrous  part  of  the  joint  capsule  is  attached  around  the  margin  of  the 
tibial  articular  surface  above  and  the  metatarsal  surfaces  below;  it  is  also  attached 
in  part  to  the  surfaces  of  the  bones  which  it  covers,  and  blends  with  the  collateral 
ligaments.  Its  dorsal  part  (anterior  ligament)  is  rather  thin;  in  distention  of  the 
capsule,  as  in  "bog-spavin,"  its  antero-medial  part,  which  is  not  bound  down  by 
the  tendons  passing  over  the  joint,  forms  a  fluctuating  swelling  over  the  medial 
ridge  of  the  trochlea.  The  plantar  part  (posterior  and  tarso-metatarsal  ligaments) 
is  very  thick  below,  and  is  intimately  attached  to  the  tarsal  bones.  It  is  in  part 
cartilaginous,  and  forms  a  smooth  surface  for  the  deep  flexor  tendon.  The  proximal 
part  pouches  upward  behind  the  distal  end  of  the  tibia  for  a  distance  of  about  two 


240 


THE   ARTICULATIONS    OF   THE   HORSE 


inches  (ca.  5  cm.) ;  here  it  is  thin.  It  is  continued  downward  to  form  the  sub- 
tarsal  or  check  ligament,  which  unites  with  the  deep  flexor  tendon  about  the  mid- 
dle of  the  metatarsus. 

There  are  four  synovial  sacs:  1.  The  tibio-tarsal  sac  lubricates  the  proximal 
joint,  and  is  much  the  largest  and  most  important.^  2.  The  proximal  intertarsal 
sac  lines  the  joints  formed  by  the  tibial  and  fibular  tarsal  bones  above,  and  the  cen- 
tral and  fourth  tarsals  below;  it  communicates  in  front  with  the  til)io-tarsal  sac. 
3.  The  distal  intertarsal  sac  lubricates  the  joints  formed  between  the  central  tarsal 
and  the  bones  below  and  on  either  side.     4.  The  tarso-metatarsal  sac  lubricates 

Tuber  calcis 


Medial  malleolus 

Long  medial  ligament 
Trochlea  of  tibial  tarsal  bone 


Dorsal  ligament 


ML  III 


ML  II 


Fig.  252. — Right  Hock  Joixt  of  Horse;  Medial  View.     The  Capsule  is  Removed. 

1,  2,  Branches  of  short  part  of  medial  ligament;    3,  tarso-metatarsal  ligament;    4,  proximal  tuberosity  of  tibial  tarsal 

bone;  5,  sustentaculum;  6,  groove  for  deep  flexor  tendon;  Mt.  II,  Ml.  Ill,  metatarsal  bones. 


the  joints  formed  between  the  tarsal  and  metatarsal  bones,  those  between  the 
proximal  ends  of  the  metatarsal  bones,  and  those  formed  by  the  third  tarsal  with 
the  bones  on  either  side. 

Common  Ligaments. — The  lateral  ligament  (Lig.  collaterale  fibulare)  consists 
of  two  distinct  bands  which  cross  each  other.  The  long  lateral  ligament  (Lig. 
collaterale  laterale  longum)  is  superficial ;  it  arises  on  the  posterior  part  of  the  lateral 
malleolus,  is  directed  almost  straight  downward,  and  is  attached  to  the  fibular  and 
fourth  tarsal  bones  and  the  large  and  lateral  small  metatarsal  bones.  It  forms  a 
canal  for  the  lateral  extensor  tendon.     The  short  lateral  ligament  (Lig.  collaterale 

^  It  is  this  part  of  the  capsule  which  is  chiefly  involved  in  distention  by  excess  of  fluid  in  the 
joint  cavity  (as  in  "bog-spavin"). 


THE    HOCK   JOINT 


241 


laterale  breve)  is  deeper;  it  arises  on  the  anterior  part  of  the  lateral  malleolus,  is 
directed  chiefly  backward,  and  ends  on  the  rough  excavation  on  the  lateral  surface 
of  the  tibial  tarsal  and  the  adjacent  surface  of  the  fibular  tarsal  bone. 

The  medial  ligament  (Lig.  collateral  tibiale)  also  consists  of  two  parts  which 
cross  each  other.  The  long  medial  ligament  (Lig.  collateral  mediale  longum) 
is  superficial;  it  arises  on  the  posterior  part  of  the  medial  malleolus,  becomes  wider 
below,  and  is  attached  on  the  distal  tuberosity  of  the  tibial  tarsal,  the  large  and 
medial  small  metatarsal  bones,  and  the  surface  of  the  lower  tarsal  bones  which  it 

Tuber  calcis 


Plantar  ligament 


ML  IV 


Short  lateral  ligament 
Long  lateral  ligament 


Fig.  253. — Right  Hock  .Joint  or  Hor.se;   Lateral  View.     The  Capsule  is  Removed. 
1,  Ligament  connecting  lateral  ridge  of  tibial  tarsal  with  processus  cochlearis  of  fibular  tarsal  bone;   2,  groove  for 
lateral  extensor  tendon;  T.  t.,  lateral  ridge  of  trochlea  of  tibial  tarsal  bone;  T.  c,  central  tarsal  bone;  T.  3,  third  tarsal 
bone;  Mt.  Ill,  Ml.  IV,  metatarsal  bones. 


covers.  The  short  medial  ligament  (Lig.  collaterale  mediale  breve)  lies  largely 
under  cover  of  the  long  one.  It  extends  from  the  anterior  part  of  the  medial  malleo- 
lus, runs  backward  and  somewhat  downward,  and  divides  into  two  branches;  one 
of  these  ends  on  the  proximal  tuberosity  on  the  medial  surface  of  the  tibial  tarsal 
bone,  the  other  on  the  sustentaculum  tali. 

The  plantar  ligament  (Lig.  tarsi  plantare)i  is  a  very  strong,  flat  band  which 
covers  the  outer  part  of  the  plantar  surface  of  the  tarsus.  It  is  attached  to  the 
plantar  surface  of  the  fibular  and  fourth  tarsal  bones  and  the  proximal  end  of  the 
lateral  metatarsal  bone. 

The  dorsal  ligament  (Lig.  tarsi  dorsale)^  is  a  triangular  sheet  which  is  attached 

^  Also  termed  the  calcaneo-metatarsal  ligament.         ^  Also  known  as  the  oblique  ligament. 
16 


242 


THE   ARTICULATIONS    OF   THE    HORSE 


above  to  the  distal  tuberosity  on  the  medial  face  of  the  tibial  tarsal  bone,  and 
spreads  out  below  on  the  central  and  third  tarsal  bones,  and  the  proximal  ends  of 
the  large  and  outer  small  metatarsal  bones,  to  all  of  which  it  is  attached. 

Special  Ligaments. — A  considerable  number  of  short  bands  which  connect 
adjacent  bones  of  the  tarsus  and  metatarsus  are  described  by  various  authors; 
some  of  these  are  quite  distinct;  others  are  difficult  to  isolate.  Most  of  them  are 
not  of  sufficient  importance  to  justify  detailed  description. 


Tuber  calcis 


Lateral  malleolus 


Short  lateral  ligament 


Trochlea,  of  tibial  tarsal 
bone 


Short  tncdial  ligaments 


Ml.  IV 


Fig.  254. — Right  Hock  Joint  of  Horse.     Viewed  from  the  Front  and  Slightly  Laterally  After  Removal  of 

Joint  Cap.sule  and  Long  Collateral  Ligaments. 

T.  t.,  Tibial  tarsal  bone  (distal  tuberosity);  T.  c,  central  tarsal  bone;  T.  3,  ridge  of  third  tarsal  bone;  T.f.,  fibular  tarsal 

bone  (distal  end);  T.  4,  fourth  tarsal  bone;    Mt.  Ill,  Mt.  IV,  metatarsal  bones.     Arrow  points  to  vascular  canal. 


(1)  The  tibial  and  fibular  tarsal  bones  are  united  by  four  bands  (astragalo-calcaneal  liga- 
ments). The  medial  ligament  extends  from  the  sustentaculum  tali  to  the  adjacent  part  of  the 
tibial  tarsal,  blending  with  the  short  collateral  ligament.  The  lateral  ligament  extends  from  the 
cochlear  process  of  the  fibular  tarsal  to  the  adjacent  part  of  the  lateral  ridge  of  the  trochlea. 
The  proximal  ligament  extends  from  the  posterior  margin  of  the  trochlea  to  the  fibular  tarsal. 
The  interosseous  ligament  is  deeply  placed  in  the  sinus  tarsi  between  the  two  bones,  and  is  at- 
tached in  the  rough  areas  of  the  opposed  surfaces. 

(2)  The  smaller  bones  are  attached  to  each  other  as  follows:  The  central  and  third  tarsal  are 
united  by  an  interosseous  and  an  oblique  dorsal  ligament  (scaphoido-cunean  ligaments).  The 
central  and  fourth  tarsal  are  united  by  an  interosseous  and  a  lateral  transverse  ligament  (cuboido- 
ecaphoid  ligament).  The  third  and  fourth  tarsals  are  similarly  connected  (cuboido-cunean  liga- 
ments). The  third  tarsal  is  joined  by  an  interosseous  (intercunean)  ligament  to  the  (fused)  first 
and  second  tarsals;  the  latter  are  connected  with  the  fourth  tarsal  by  a  plantar  transverse  liga- 
ment. 

(3)  The  smaller  bones  are  connected  with  the  proximal  row  as  follows;    The   central  is 


THE   HOCK   JOINT 


243 


attached  to  the  tibial  by  plantar  and  interosseous  (astragalo-scaphoid)  ligaments,  and  to  the  fibular 
tarsal  by  a  short  oblique  (calcaneo-scaphoid)  band.  The  fourth  is  attached  to  the  fibular  tarsal 
by  interosseous  and  plantar  (calcaneo-cuboid)  hgaments.  The  (fused)  first  and  second  tarsals 
are  connected  with  the  fibular  tarsal  by  a  plantar  (calcaneo-cunean)  ligament. 

(4)  The  distal  tarsal  bones  are  connected  with  the  metatarsus  by  tarso-metatarsal  hgaments, 
which  are  not  distinct  from  the  common  Hgaments,  except  in  the  case  of  the  interosseous  ligament 
between  the  third  tarsal  and  metatarsal  bones. 

Movements. — These  are  flexion  and  extension,  which  take  place  at  the  tibio- 
tarsal  joint.  The  movements  between  the  tarsal  bones,  and  between  the  latter 
and  the  metatarsus,  are  so  limited  as  to  be  negligible  so  far  as  the  action  of  the  joint 
as  a  whole  is  concerned.     In  the  standing  position  the  articular  angle  (in  front) 


Superficial  flexor  tendon 

Gastrocnemius  tendon 

Tarsal  tendon  of 
biceps  femoris 

Calcanean  bursa 

Gastrocnemius 
bursa 

Tuber  calcis- 


Upper  po^ich  of 
joint  capsule 


Tibial  tarsal  bone 

Interosseous  ligunient 

Plantar  ligament 

Fourth  tarsal  bone 

Interosseous  ligament 
Large  metatarsal  bone 

Suspensory  ligament 
Check  ligament 


Tibia 


Tibialis  anterior 
Peroneus  tertius 


Tibio-tarsal  joint  cavity 
Joint  capsule 
Central  tarsal  bone 
Third  tarsal  bone 

Distal  annular  ligament 


Fig.  255. — Sagittal  Section  of  Hock  of  Horse. 
The  section  is  cut  so  far  laterally  that  the  deep  flexor  tendon  does  not  show. 


is  about  150°  to  160°.  Complete  extension  is  prevented  by  tension  of  the  collateral 
ligaments.  Flexion  is  checked  only  by  contact  of  the  metatarsus  with  the  leg, 
provided  the  stifle  joint  is  also  flexed.  Owing  to  the  fact  that  the  axis  of  motion 
is  slightly  oblique,  the  lower  part  of  the  limb  deviates  somewhat  outward  during 
flexion.  The  long  collateral  hgaments  are  tense  in  extension,  the  short  ones  in 
flexion,  of  the  joint.  The  movements  of  the  hock  joint  must  correspond  with  those 
of  the  stifle  on  account  of  the  tendinous  bands  in  front  and  behind  (peroneus  tertius 
and  flexor  superficialis),  which  extend  from  the  lower  part  of  the  femur  to  the  tarsus 
and  metatarsus. 

The  remaining  joints  differ  in  no  material  respect  from  those  of  the  thoracic 
limb. 


244 


COMPARATIVE   ARTHROLOGY 


COMPARATIVE  ARTHROLOGY  ^ 
Joints  and  Ligaments  of  the  Vertebrje 

Ox. — The  ligamentum  nuchse  is  better  developed  than  in  the  horse.  The 
funicular  part  is  clearly  divided  into  two  lateral  halves,  which  are  round  at  their 
occipital  attachment,  but  from  the  axis  backward  become  rapidly  Avider  and  fiat. 
This  wide  portion  is  almost  sagittal,  lies  on  either  side  of  the  vertebral  spines,  and 
is  covered  by  the  trapezius  and  rhomboideus  muscles.  From  the  highest  part  of 
the  withers  (third  thoracic  spine)  it  gradually  diminishes  in  size  and  fades  out  in 
the  lumbar  region.  The  lamellar  part  is  thick,  and  consists  of  anterior  and  pos- 
terior parts.  T'he  anterior  part  is  double;  its  fibers  proceed  from  the  funicular 
part  to  the  second,  third,  and  fourth  cervical  spines.  The  posterior  part  is  single; 
its  fibers  extend  from  the  first  thoracic  spine  to  the  fifth,  sixth,  and  seventh  cervical 
spines. 

The  ventral  longitudinal  ligament  is  very  strong  in  the  lumbar  region. 


Fig.  256. — Ligamentttm  Nttch/e  of  Ox. 

o,  Funicular  part;   6,  its  wide  portion;   <?,  rf,  lamellar  part;   e,  interspinous  ligament;   ?,  spinous  process  of  first  thoracic 

vertebra;  2,  axis      (Ellenberger-Baum,  Anat.  d.  Haustiere.) 


The  intervertebral  fibro-cartilages  are  thicker  than  in  the  horse. 

The  interspinous  ligaments  of  the  back  and  loins  consist  largely  of  elastic 
tissue. 

There  are  no  intertransverse  joints  in  the  lumbar  region. 

Pig. — The  ligamentum  nuchae  is  represented  by  a  fibrous  raphe  and  thin 
layers  of  elastic  tissue  which  extend  between  the  cervical  spines. 

The  atlanto-occipital  and  atlanto-axial  joints  resemble  those  of  the  dog. 

The  interspinous  ligaments  of  the  neck  are  elastic. 

Dog. — The  ligamentum  nuchse  consists  of  a  small  fibrous  band  which  extends 
from  the  spine  of  the  axis  to  the  anterior  thoracic  spines;  it  may  be  regarded  as  a 
mere  fibrous  raphe  between  the  right  and  left  muscles. 

There  are  interspinous  muscles  instead  of  ligaments  in  the  neck. 

There  are  three  ligaments  in  connection  with  the  dens  of  the  axis.  The  two 
alar  ligaments  (Ligg.  alaria)  arise  on  either  side  of  the  dens,  diverge,  and  end  on 

^  This  section  consists  necessarily  only  of  a  brief  statement  of  the  most  important  differences 
in  the  joints  of  the  other  animals. 


ARTICULATIONS    OF   THE   THORACIC   LIMB  245 

either  side  of  the  foramen  magnum.  The  transverse  ligament  of  the  atlas  (Lig. 
transversum  atlantis)  stretches  across  the  dorsal  surface  of  the  dens  and  binds  it 
down  on  the  ventral  arch  of  the  atlas,  a  bursa  being  interposed.  It  is  attached  on 
either  side  to  the  lateral  mass  of  the  atlas. 

The  two  capsules  of  the  atlanto-occipital  joint  communicate  with  each  other, 
and  usually  with  the  capsule  of  the  atlanto-axial  joint  also. 


Articulations  of  the  Thorax 

Ox. — The  second  to  the  eleventh  costo-chondral  joints  inclusive  are  diarthroses 
with  close  capsules,  reinforced  externall}-.  (They  are  synchondroses  in  the  sheep.) 
The  upper  parts  of  the  cartilages  are  attached  to  each  other  by  cUstinct  elastic  liga- 
ments (Ligg.  intercostalia) . 

The  first  pair  of  chondro-sternal  joints  are  separate  from  each  other;  inter- 
crossing fibers  unite  the  costo-chondral  junctions  above  the  joints. 

The  first  segment  of  the  sternum  forms  ^\dth  the  body  a  diarthrodial  interstemal 
joint  (Articulatio  intersternalis) .  The  anterior  joint  surface  is  concave,  the  pos- 
terior convex.  The  joint  is  surrounded  by  a  close  capsule,  and  the  joint  surfaces 
are  attached  to  each  by  a  small  inter-articular  ligament.  Limited  lateral  move- 
ment is  possible.  (In  the  sheep  the  joint  is  a  synchondrosis.)  Both  surfaces  of  the 
sternum  are  covered  by  a  layer  of  fibrous  tissue  (Membrana  sterni). 

Pig. — The  second  to  the  fifth  or  sixth  costo-chondral  joints  are  diarthroses. 
The  intersternal  articulation  and  the  sternal  ligaments  resemble  those  of  the  ox. 

Dog. — The  first  chondro-sternal  joints  do  not  coalesce.  The  internal  sternal 
ligament  divides  into  three  bands. 


TEMPORO-MANDIBULAR  ARTICULATION 

Ox. — The  articular  surfaces  are  of  such  a  character  as  to  permit  more  extensive 
transverse  movement  than  in  the  horse  {vide  Osteology).  The  posterior  ligament 
is  absent. 

Pig. — The  considerable  longitudinal  diameter  of  the  temporal  articular  sur- 
faces and  the  very  small  size  of  the  postglenoid  process  allow  great  freedom  of 
protraction  and  retraction  of  the  lower  jaw.  Transverse  movement  is  limited. 
The  posterior  ligament  is  absent. 

Dog. — The  articular  surfaces  allow  extremely  little  transverse  or  gliding  move- 
ment. They  are  cylindrical  in  curvature,  and  the  interarticular  disc  is  very  thin. 
The  posterior  ligament  is  absent. 

The  other  articulations  of  the  skull  are  sufficiently  described  in  the  Osteology. 


Articulations  of  the  Thoracic  Limb 
shoulder  joint 

Ox. — The  articular  angle  is  about  100°. 

Pig  and  Dog. — The  joint  capsule  communicates  so  freely  with  the  bicipital 
bursa  that  the  latter  may  well  be  regarded  as  a  pouch  of  the  capsule.  There  is  a 
rudimentary  marginal  cartilage  around  the  rim  of  the  glenoid  cavity.  In  the  pig 
the  front  of  the  capsule  is  reinforced  by  cruciate  bands.  In  the  dog  there  is  usu- 
ally a  strong  band  extending  from  the  acromion  to  the  lateral  part  of  the  capsule; 
another  band  (Ligamentum  coraco-acromiale)  often  stretches  between  the  scapular 
tuberosity  and  the  acromion. 


246  COMPARATIVE  ARTHROLOGY 


ELBOW  JOINT 

Ox. — No  important  differences  exist.  The  upper  part  of  the  intero.sseous 
raclio-ulnar  hgament  is  commonly  ossified  in  the  adult. 

Pig. — There  are  no  important  differences.  The  radius  and  ulna  are  so  firmly 
united  bj^  the  interosseous  ligament  as  to  prevent  any  appreciable  movement  be- 
tween them. 

Dog. — The  joint  capsule  is  reuiforced  in  front  by  an  oblique  ligament  which 
arises  on  the  front  of  the  lateral  condyle  of  the  humerus  above  the  joint  surface, 
and  joins  the  terminal  part  of  the  biceps  and  brachialis  below.  There  is  a  strong 
reinforcement  of  the  postero-medial  part  of  the  capsule,  which  extends  obliquely 
from  the  medial  side  of  the  olecranon  fossa  to  the  ulna,  just  above  the  processus  an- 
coneus. The  lateral  ligament  is  much  stronger  than  the  medial  one.  It  is  attached 
above  to  the  lateral  epicondyle  of  the  humerus,  and  below  chiefly  to  the  eminence 
distal  to  the  neck  of  the  radius ;  but  part  of  it  inclines  backward  and  is  attached  to 
the  ulna.  The  middle  part  of  the  ligament  is  wide  and  forms  a  sort  of  cap  over  the 
proxmial  tuberosity  of  the  radius.  From  this  part  a  band,  the  annular  ligament 
of  the  radius  (Lig.  annulare  radii),  extends  across  the  front  of  the  proximal  end  of 
the  radius  and  ends  on  the  ulna;  although  incorporated  in  the  joint  capsule  it  is 
easily  defined.  The  medial  ligament  is  more  slender.  It  arises  from  the  medial 
epicondyle  of  the  hmnerus  and  passes  deeply  into  the  proximal  part  of  the  inter- 
osseous space,  ending  chiefly  on  the  posterior  surface  of  the  radius  a  little  medial  to 
the  attachment  of  the  lateral  ligament;  there  is  also  a  small  attachment  to  the 
interosseous  border  of  the  ulna.  This  ligament  is  very  oblique.  An  elastic  band 
(Ligamentum  olecrani)  extends  from  the  lateral  surface  of  the  medial  epicondyle 
to  the  anterior  border  of  the  ulna. 

There  are  two  radio-ulnar  joints.  The  proximal  radio-ulnar  joint  (Articulatio 
radioulnaris  proximalis)is  included  in  the  capsule  of  the  elbow,  but  is  provided  \\dth 
an  annular  hgament,  as  described  above.  The  distal  radio-ulnar  joint  (Articulatio 
radioulnaris  distahs)  is  formed  by  a  concave  facet  on  the  radius  and  a  convex  one  on 
the  ulna,  and  is  surrounded  by  a  tight  capsule.  The  interosseous  membrane  unites 
the  shafts  of  the  two  bones;  its  proximal  part  is  specially  strong  and  is  attached  to 
prominences  on  both  bones.  The  movements  consist  of  limited  rotation  of  the 
radius  (ca,  20°),  carrying  the  paw  with  it.  The  ordinary  position  is  termed  prona- 
tion; outward  rotation  is  supination.^ 


THE  CARPAL  JOINTS 

These  have  the  same  general  arrangement  as  in  the  horse.  Numerous  minor 
differences  naturally  exist,  but  must  be  excluded  from  this  brief  account,  which 
contains  only  important  special  features. 

The  lateral  and  medial  movements  are  freer,  especially  in  the  dog,  but  flexion  is 
not  so  complete :  the  anatomical  explanation  of  these  facts  lies  in  the  nature  of  the 
articular  surfaces  and  certain  hgamentous  differences.  The  coUateral  ligaments  are 
much  weaker,  the  long  lateral  one  being  especially  small  in  the  ox.  Two  obhque, 
somewhat  elastic  bands  cross  the  front  of  the  radio-carpal  and  intercarpal  joints. 
The  proximal  one  is  attached  to  the  distal  end  of  the  radius  and  passes  do^vnward 
and  outward  to  the  ulnar  carpal  bone ;  the  other  one  connects  the  radial  and  fourth 
carpal  bones  in  a  similar  fashion. 

In  the  ox  the  short  collateral  ligaments  are  well  defined;  a  ligament  connects 
the  accessory  carpal  with  the  distal  end  of  the  ulna,  and  strong  volar  bands  connect 

1  These  movements  are  best  seen  in  man,  in  whom  the  back  of  the  hand  may  be  turned  for- 
ward (pronation)  or  backward  (supination).  In  the  dog  the  rotation  is  much  restricted  and  is 
freest  when  the  elbow  is  flexed. 


INTERMETACARPAL    JOINTS METACARPO-PHALANGEAL    JOINTS 


247 


the  distal  bones  with  the  metacarpus 
ulnar  carpal  bone  with  the  meta- 
carpus. 

The  dorsal,  volar,  and  interos- 
seous carpal  ligaments  vary  with  the 
number  of  carpal  bones  present  in 
the  different  species. 

In  the  dog  there  are  six  dorsal 
and  six  volar  ligaments.  The  inter- 
osseous ligaments  are  not  inter- 
ordinal.  The  accessory  carpal  bone 
is  attached  l)y  ligaments  to  the  ulna, 
the  radio-intermediate,  and  the 
third,  fourth,  and  fifth  metacarpal 
bones.  The  distal  carpal  bones  are 
attached  to  the  metacarpal  bones  by 
dorsal  and  volar  ligaments. 


INTERMETACARPAL  JOINTS 

In  the  ox  the  small  (fifth)  meta- 
carpal bone  articulates  with  the  large 
metacarpal,  but  not  with  the  carpus. 
The  joint  cavity  is  connected  with 
that  of  the  carpo-metacarpal  sac. 
The  proximal  end  of  the  small  meta- 
carpal bone  is  attached  by  a  ligament 
to  the  fourth  carpal,  and  another 
band  extends  from  its  distal  part 
to  the  side  of  the  large  metacarpal. 
There  is  also  an  interosseous  liga- 
ment, which  is  permanent  and  allows 
a  small  amount  of  movement. 

The  chief  metacarpal  bones  of 
the  pig,  and  the  second  to  the  fifth  of 
the  dog,  articulate  with  each  other 
at  their  proximal  ends,  and  are  con- 
nected by  interosseous  ligaments, 
which  do  not,  however,  unite  them 
closely,  as  in  the  horse.  There  are 
feeble  dorsal  and  volar  ligaments 
(Ligg.  basium)  which  unite  the 
proximal  ends  of  the  metacarpal 
bones  in  the  dog. 


A  strong  oblique  ligament  connects  the 


Fig.  257. — Distal  Part  of  Limb  of  Ox,  Showing  Ligaments 
AND  Tendons.  One  Digit  .\nd  Corresponding  Articu- 
lar Part  of  Metacarpal  Bone  are  Removed. 
a,  Suspensory  ligament;  a',  branch  of  a  to  superficial  flexor 
tendon;  a",  a"',  lateral  and  central  branches  of  o;  b,  deep  flexor 
tendon;  6',  branch  of  6  to  digit  removed;  c,  c,  superficial  flexor 
tendon;  d,  d',  intersesamoid  hgament  (cut);  e,  interdigital  col- 
lateral hgament  of  fetlock  joint;  /,  tendon  of  common  extensor; 
g,  proximal  interdigital  hgament;  h,  digital  annular  hgament; 
i,  posterior  annular  hgament  of  fetlock;  k,  collateral  hgament 
of  pastern  joint;  I,  distal  interdigital  ligament;  m,  cruciate  inter- 
digital hgament  (cut) ;  m',  m",  attachments  of  m  to  second  pha- 
lanx and  distal  sesamoid  bone;  n,  suspensory  hgament  of  distal 
sesamoid;  o,  dorsal  elastic  ligament;  p,  lateral  volar  ligament 
of  pastern  joint;  1,  metacarpus,  sawn  off  at  /';  S,  first  phalanx; 
3,  second  phalanx;  4,  third  phalanx.  (EUenberger-Baum,  Anat. 
d.  Haustiere.) 


METACARPO-PHALANGEAL  JOINTS 
Ox. — There  are  two  joints,  one 
for  each  digit.  The  volar  parts  of 
the  two  joint  capsules  communicate. 
The  two  interdigital  collateral  liga- 
ments (Ligg.  collateralia  interdigi- 
talia)  result  from  the  bifurcation  of  a 

band  which  arises  in  the  furrow  between  the  divisions  of  the  distal  end  of  the  large 
metacarpal  bone;  they  spread  out  and  end  on  the  proximal  ends  of  the  first  pha- 


248  COMPARATIVE  ARTHROLOGY 

langes.  The  other  collateral  ligaments  are  arranged  like  those  of  the  horse.  A  strong 
interdigital  ligament  (Lig.  interdigitale) ,  consisting  of  short  intercrossing  fibers, 
unites  the  middles  of  the  interdigital  surfaces  of  the  first  phalanges  of  the  chief  digits. 
It  prevents  undue  divergence  of  the  phalanges.     It  is  not  present  in  the  sheep. 

Cruciate  ligaments  (Ligg.  phalango-sesamoidese)  connect  the  proximal  sesamoids 
with  the  proximal  end  of  the  opposite  first  phalanx. 

The  intersesamoid  ligament  connects  all  four  sesamoids,  and  extends  upward 
much  less  than  in  the  horse. 

The  laterate  and  medial  sesamoidean  ligaments  end  chiefly  on  the  first  phalanges, 
but  also  detach  a  small  part  to  the  large  metacarpal  bone. 

The  superficial  or  straight  distal  sesamoidean  ligament  is  absent.  The  middle 
distal  sesamoidean  ligaments  of  each  digit  are  two  short,  strong  bands  which  extend 
from  the  distal  margins  of  the  proximal  sesamoids  to  the  proximal  ends  of  the  first 
phalanges.  The  deep  distal  sesamoidean  ligaments  are  strong  and  distinctly 
cruciate. 

The  suspensory  ligament  or  interosseus  tendon  contains  more  muscular 
tissue  than  in  the  horse — indeed,  in  the  young  animal  it  consists  almost  entirely  of 
muscular  tissue.  At  the  distal  third  of  the  metacarpus  it  divides  into  three  branches. 
These  give  rise  to  five  subdivisions,  either  by  bifurcation  of  the  lateral  and  medial 
branches  or  trifurcation  of  the  middle  branch.  The  two  lateral  and  two  medial 
bands  end  on  the  proximal  sesamoid  bones  and  the  distal  end  of  the  large  meta- 
carpal bone,  and  cletach  slips  to  the  extensor  tendons.  The  middle  band  passes 
through  the  groove  between  the  two  divisions  of  the  distal  end  of  the  metacarpus, 
and  divides  into  two  branches  which  join  the  tendons  of  the  proper  extensors  of  the 
digits;  it  sends  fibers  also  to  the  interdigital  collateral  ligaments  and  to  the  central 
sesamoids.  About  the  middle  of  the  metacarpus  the  suspensory  ligament  detaches 
a  band  which  unites  lower  down  with  the  superficial  flexor  tendon,  thus  inclosing 
the  tendon  of  the  deep  flexor  of  the  digit ;  it  also  blends  with  the  thick  fascia  of  the 
region.  The  latter  gives  off  a  band  on  either  side  to  the  accessory  digits,  and  a  ten- 
dinous band  descends  from  each  accessory  digit  to  the  third  phalanx  and  distal  sesa- 
moid bone,  blending  with  the  tendon  of  the  corresponding  proper  extensor. 

Pig. — There  are  four  metacarpo-phalangeal  joints,  each  of  which  has  a  capsule, 
collateral,  intersesamoidean,  and  cruciate  sesamoidean  ligaments.  Since  distinct 
interosseous  muscles  are  present,  there  are,  of  course,  no  suspensory  ligaments. 

Dog. — There  are  five  metacarpo-phalangeal  joints,  each  having  its  own  capsule 
and  indistinct  collateral  ligaments.  A  small  sesamoid  bone  occurs  in  the  anterior 
part  of  each  capsule,  over  which  the  corresponding  extensor  tendon  plays.  The 
intersesamoidean  ligaments  do  not  extend  above  the  sesamoids.  The  cruciate 
ligaments  are  present,  as  well  as  a  fibrous  layer  which  attaches  the  distal  margins 
of  the  sesamoids  to  the  posterior  surface  of  the  proximal  end  of  the  first  phalanx. 


INTERPHALANGEAL  JOINTS 

Ox. — The  two  proximal  joints  have  separate  capsules,  and  broad,  but  rather 
indistinct,  collateral  ligaments.  Each  joint  has  also  central  and  collateral  volar 
ligaments.  The  central  ligaments  are  largely  fused  to  form  a  strong  band  which  is 
attached  by  two  branches  to  the  distal  end  of  the  first  phalanx  and  to  the  depression 
on  the  volar  surface  of  the  proximal  end  of  the  second  phalanx.  The  collateral  ones 
extend  from  the  borders  of  the  first  phalanx  to  the  proximal  end  of  the  second 
phalanx;  those  on  the  interdigital  side  are  weak  and  indistinct. 

The  distal  interphalangeal  joints  have,  in  addition  to  the  capsules  and  collateral 
ligaments,  bands  which  reinforce  them  on  either  side.  The  interdigital  pair  arise 
in  the  depressions  on  the  distal  ends  of  the  first  phalanges,  receive  fibers  from  the 
second  phalanges,  and  end  on  the  interdigital  surfaces  of  the  third  phalanges  at  the 


INTERPHALANGEAL   JOINTS 


249 


margin  of  the  articular  surface.  The  abaxial  pair  have  a  similar  course,  but  are 
thinner,  and  end  on  the  corresponding  third  sesamoid.  An  elastic  band  crosses  the 
front  of  the  second  phalanx  obliquely,  from  the  distal  end  of  the  first  phalanx  to  the 
extensor  process  of  the  third  phalanx. 

The  cruciate  or  distal  interdigital  ligaments  (Ligg.  cruciata  interdigitalia)  are 
two  strong  bands  which  limit  the  separation  of  the  digits.  They  are  attached  above 
to  the  abaxial  emmences  on  the  proximal  ends  of  the  second  phalanges  (blending 
with  the  collateral  ligaments),  cross  the  deep  flexor  tendon  obliquely,  and  reach  the 


Fig.  2,58. — Ligaments  axd  Tendoxs  of  Digits  of  Pig; 
VoLAB  View. 
a,  Superficial  flexor  tendon;  6,  deep  flexor  tendon;  b', 
branches  of  6  to  accessorj'  digits;  c,  c',  annular  ligaments; 
d-d'",  ligaments  of  accessory  digits;  e,  cruciate  interdigital 
ligaments;  /,  /',  spiral  band  around  the  flexor  tendons  of 
the  accessory  digits;  g,  abductor  of  accessory  digit.  (Ellen- 
berger-Baum,  Anat.  d.  Haustiere.) 


Fig.  259. — Ligaments  and  Tendons  of  Digits  of 
Dog,  Hind  Limb;  Volak  View. 
a,  a',  Superficial  flexor  tendon;  b,  tendon  to 
large  pad;  c,  lumbricales  muscles;  d,  interossei 
muscles;  e,  f,  annular  ligaments  at  metatarso- 
phalangeal joints;  g,  suspensory  ligament  of  large 
pad;  /(,  digital  annular  ligaments;  i,  deep  flexor 
tendon;  k,  distal  sesamoid;  I,  suspensory  ligament 
of  k;  m,  suspensory  ligament  of  digital  pad;  n, 
digital  pads.  (Ellenberger-Baum,  Anat.  d.  Haus- 
tiere.) 


interdigital  space,  where  they  intercross  and  blend.  Most  of  the  fibers  end  on  the 
distal  sesamoid  of  the  opposite  side,  but  some  are  attached  to  the  interdigital  as- 
pect of  the  second  phalanx  and  the  distal  sesamoid  of  the  same  side.  In  the  sheep 
there  is,  instead  of  the  foregoing,  a  transverse  ligament  which  is  attached  on  either 
side  to  the  interdigital  surfaces  of  the  second  and  third  phalanges  and  the  distal  sesa- 
moid bone.     It  is  related  below  to  the  skin,  above  to  a  pad  of  fat. 

Pig. — The  interphalangeal  joints  of  the  chief  digits  resemble  in  general  those 
of  the  ox.  The  distal  interdigital  ligament  resembles,  however,  that  of  the  sheep, 
and  is  intimately  adherent  to  the  skin.     There  is,  besides,  a  remarkable  arrange- 


250  COMPARATIVE  ARTHROLOGY 

ment  of  ligaments  which  connect  the  small  digits  with  each  other  and  with  the 
chief  digits  (Fig.  258). 

This  apparatus  is  somewhat  complex,  but  its  chief  features  are  as  follows :  A  proximal  inter- 
digital  ligament  is  attached  on  either  side  to  the  third  phalanges  of  the  small  digits,  while  centrally 
it  blends  with  the  annular  ligaments  of  the  flexor  tendons  behind  the  metacarpo-phalangeal 
joints  of  the  chief  digits.  Two  bands  (central  longitudinal  interdigital  Ugaments)  arise  on  the 
bases  of  the  small  digits,  cross  the  flexor  tendons  obhquely  downward  and  centrally,  pass  through 
the  proximal  interdigital  hgament,  and  blend  below  with  the  distal  interdigital  hgament.  Two 
collateral  bands  (collateral  longitudinal  interdigital  ligaments)  are  attached  in  common  with  the 
proximal  interdigital  Ugaments  to  the  third  phalanges  of  the  small  digits,  and  blend  below  with 
the  outer  part  of  the  distal  interdigital  hgament. 

Dog. — Each  joint  has  a  capsule  and  two  collateral  ligaments.  The  distal 
joints  have  also  two  elastic  dorsal  ligaments  (Ligg.  dorsaha),  which  extend  from 
the  proximal  end  of  the  second  phalanx  to  the  ridge  at  the  base  of  the  third 
phalanx.  They  produce  dorsal  flexion  of  the  joint,  and  thus  raise  or  retract  the 
claws  when  the  flexor  muscles  relax.  The  distal  sesamoids  are  represented  by 
complementary  cartilages  attached  to  the  volar  margins  of  the  articular  surfaces 
of  the  third  phalanges. 

Three  interdigital  ligaments  restrict  the  spreading  apart  of  the  digits  (Fig.  259). 
Two  of  these  cross  the  volar  surface  of  the  proximal  parts  of  the  chief  digits,  i.  e., 
one  for  the  second  and  third,  the  other  for  the  fourth  and  fifth ;  they  blend  with  the 
annular  ligaments  on  either  side.  The  third  ligament  is  attached  on  either  side  to 
the  foregoing  ligaments  and  the  annular  ligaments  of  the  third  and  fourth  digits, 
and  curves  downward  centrally,  ending  in  the  large  pad  on  the  paw. 


Articulations  of  the  Pelvic  Limb 
sacro-iliac  joint 

This  joint  and  the  pelvic  ligaments  present  no  very  striking  differences  in  the 
other  animals  except  that  the  sacro-sciatic  ligament  in  the  dog  is  a  narrow  but 
strong  band  which  extends  from  the  posterior  part  of  the  lateral  margin  of  the 
sacrum  to  the  tuber  ischii;  it  is  the  homologue  of  the  ligamentum  sacro-tuberosum 
of  man. 

HIP  JOINT 

Ox. — The  shallowness  of  the  acetabulum  is  compensated  by  the  greater  size 
of  the  marginal  cartilage,  which  is  specially  large  laterally.  The  head  of  the  femur 
has  a  smaller  radius  of  curvature  than  that  of  the  horse,  and  the  articular  surface 
extends  a  considerable  distance  outward  on  the  upper  surface  of  the  neck.  The 
round  ligament  is  entirely  intra-articular;  it  is  small,  and  sometimes  absent.  The 
accessory  ligament  is  absent. 

There  are  no  important  differences  in  the  other  animals. 

STIFLE  JOINT 

Ox. — There  is  a  considerable  communication  between  the  femoro-patellar 
and  medial  femoro-tibial  joint  cavities;  this  is  situated  as  in  the  horse,  but  is  wider. 
A  small  communication  with  the  lateral  femoro-tibial  capsule  sometimes  occurs. 
The  two  femoro-tibial  capsules  usually  communicate.  The  middle  patellar  liga- 
ment is  not  sunken,  as  there  is  no  groove  on  the  tuberosity  of  the  tibia  where  it  is 
attached.  The  lateral  patellar  ligament  fuses  completely  with  the  tendon  of  in- 
sertion of  the  biceps  femoris,  and  a  large  synovial  bursa  is  interposed  between  them 
and  the  lateral  condyle  of  the  femur. 

Pig. — The  femoro-patellar  capsule  is  strongly  reinforced  on  both  sides  by  bands 


TIBIO-FIBULAR   JOINTS — HOCK   JOINT  251 

which  blend  with  the  collateral  femoro-tibial  ligaments.  The  cavity  is  continuous 
below  with  that  of  the  femoro-tibial  joint.  A  sagittal  synovial  fold  (rudimentum 
septi)  extends  up  a  short  distance  from  the  anterior  cruciate  ligament.  The  supra- 
patellar pouch  extends  an  inch  or  more  (ca.  2-3  cm.)  above  the  trochlea;  from  this 
a  pouch  extends  up  beneath  the  quadriceps  femoris  almost  an  inch  and  communi- 
cates through  a  large  round  opening  with  the  joint  cavity.  There  is  a  strong 
ligamentum  patellae,  which  has  a  bursa  under  its  distal  part.  The  tendon  of  the 
biceps  femoris  takes  the  place  of  the  lateral  patellar  ligament.  A  small  ligamentum 
transversum  connects  the  anterior  faces  of  the  menisci. 

Dog. — The  joint  in  general  resembles  that  of  the  pig.  The  posterior  part  of 
the  capsule  contains  two  sesamoid  bones,  which  are  imbedded  in  the  origin  of  the 
gastrocnemius. 

TmiO-FIBULAR  JOINTS 

Ox. — The  proximal  end  of  the  fibula  fuses  with  the  lateral  condyle  of  the 
tibia.  The  distal  end  remains  separate,  and  forms  an  arthrosis  with  the  distal  end 
of  the  tibia;  the  movement  here  is  imperceptible,  as  the  two  bones  are  closely 
united  by  strong  peripheral  fibers. 

Pig. — The  proxunal  joint  is  provided  with  a  capsule  which  is  reinforced  in 
front  and  behind  by  fibrous  tissue.  The  interosseous  ligament  attaches  the  shaft 
of  the  fibula  to  the  lateral  border  of  the  tibia.  The  distal  joint  is  included  in  the 
capsule  of  the  hock  joint,  and  is  strengthened  by  dorsal  and  plantar  ligaments 
(Lig.  malleoli  lateralis  dorsalis,  plantaris),  which  extend  almost  transversely  from 
one  bone  to  the  other.     There  is  also  an  interosseous  ligament. 

Dog. — The  arrangement  is  essentially  the  same  as  in  the  pig,  but  there  is  no 
interosseous  ligament  in  the  distal  joint.  Not  uncommonly  the  distal  part  of  the 
shaft  of  the  fibula  and  tibia  are  ankylosed. 


HOCK  JOINT 

Ox. — There  is  very  considerable  mobility  at  the  proximal  intertarsal  joint,  the 
capsule  of  which  is  correspondingly  roomy.  The  short  lateral  ligament  is  attached 
distally  on  the  tibial  tarsal  only.  A  strong  transverse  ligament  attaches  the  lateral 
malleolus  (distal  end  of  the  fibula)  to  the  back  of  the  tibial  tarsal  bone.  The  dorsal 
ligament  is  narrow  and  thin. 

Pig. — The  arrangement  in  general  resembles  that  of  the  ox.  The  medial  liga- 
ment consists  of  a  thin  superficial  part  which  extends  almost  vertically  from  malleo- 
lus to  metatarsus,  and  a  very  strong  deep  part,  which  runs  from  the  malleolus  back- 
ward and  downward  to  the  sustentaculum  and  tibial  tarsal.  The  lateral  ligament 
also  consists  of  two  parts.  The  small  superficial  part  exi;ends  from  the  malleolus 
down  to  the  lateral  face  of  the  body  of  the  fil^ular  tarsal  bone.  The  stronger  deep 
part  arises  from  the  anterior  part  of  the  malleolus,  passes  cheifly  backward,  ^videns, 
and  ends  on  a  ridge  on  the  lateral  surface  of  the  fibular  tarsal.  A  strong  band  ex- 
tends from  the  lateral  face  of  the  medial  malleolus  to  a  depression  on  the  medial 
surface  of  the  proximal  part  of  the  tibial  tarsal  bone.  An  oblique  dorsal  band  con- 
nects the  central  and  fourth  tarsal  bones. 

Dog. — The  long  collateral  ligaments  are  very  small,  and  the  short  ones  double. 
The  plantar  ligament  is  weak,  and  ends  on  the  fourth  metacarpal  bone.  No  dis- 
tinct dorsal  Hgament  is  present,  unless  we  regard  as  such  a  ligament  which  extends 
from  the  neck  of  the  tibial  tarsal  to  the  fourth  tarsal  and  third  metatarsal  bones. 

The  remaining  joints  resemble  those  of  the  thoracic  limb. 


MYOLOGY 

Myology  deals  with  the  muscles  and  their  accessory  structures.  The  muscles 
(Musculi)  are  highly  specialized  organs,  which  are  characterized  by  their  property 
of  contracting  in  a  definite  manner  when  stimulated.  They  are  the  active  organs 
of  motion.  The  contractile  part  of  the  muscle  is  the  muscular  tissue.  Three  kinds 
of  muscular  tissue  are  recognized,  viz.:  (1)  Striated  or  striped;  (2)  non-striated, 
unstriped  or  smooth;  (3)  cardiac,  which  may  be  regarded  as  a  specialized  variety 
of  striated  muscle.  Only  the  first  of  these  will  be  considered  in  this  section.  The 
striated  muscles  are  for  the  most  part  connected  directly  or  indirectly  with  the 
skeleton,  upon  which  they  act,  and  are  hence  often  designated  as  skeletal  muscles 
(Musculi  skeleti),  in  distinction  from  non-striated  muscle,  which  is  often  spoken 
of  as  visceral.  The  striated  muscles  cover  the  greater  part  of  the  skeleton,  and  play 
an  important  part  in  determining  the  form  of  the  animal.  They  are  red  in  color, 
the  shade  varying  in  different  muscles  and  under  various  conditions.  Some  are  in- 
timately associated  with  and  attached  to  the  skin,  and  are  called  cutaneous  mus- 
cles (Musculi  cutanei) .  The  muscular  part  of  each  is  composed  of  bundles  of  con- 
tractile fibers  surrounded  by  a  thin  sheath  of  connective  tissue,  the  perimysium. 

The  description  of  the  muscles  may  be  arranged  under  the  following  heads:  (1) 
Name;  (2)  shape  and  position;  (3)  attachments;  (4)  action;  (5)  structure;  (6) 
relations;    (7)  blood  and  nerve  supply. 

(1)  The  name  is  determined  by  various  considerations,  e.  g.,  the  action,  at- 
tachments, shape,  position,  direction,  etc.  In  most  cases  two  or  more  of  these  are 
combined  to  produce  the  name,  e.  g.,  flexor  carpi  radialis,  longus  colli,  obliquus 
externus  abdominis. 

A  satisfactory  comparative  nomenclature  is  exceedingly  difficult  to  work  out,  and  much 
confusion  exists  in  this  respect.  This  is  due  in  great  part  to  the  lack  of  a  uniform  basis  for  the 
formation  of  names  and  the  difficulty  in  determining  homologies  in  various  species. 

(2)  The  shape  is  in  many  cases  sufficiently  definite  and  regular  to  allow  the 
use  of  such  terms  as  triangular,  quadrilateral,  fan-shaped,  fusiform,  etc.  Some 
muscles  are  characterized  as  long,  broad,  short,  etc.  Orbicular  or  ring-like  muscles 
circumscribe  openings;  since  the  contraction  of  such  a  muscle  closes  the  orifice,  it  is 
often  termed  a  sphincter.  The  position  and  direction  are  usually  stated  with  refer- 
ence to  the  region  occupied  and  to  adjacent  structures  which  may  be  presumed  to  be 
already  known. 

(3)  The  attachments  are  in  most  cases  to  bone,  but  many  muscles  are  attached 
to  cartilage,  ligaments,  fascia,  or  the  skin.  As  a  matter  of  convenience,  the  term 
origin  (Origo)  is  applied  to  the  attachment  which  always  or  more  commonly  re- 
mains stationary  when  the  muscle  contracts;  the  more  movable  attachment  is 
termed  the  insertion  (Insertio).  Such  a  distinction  is  often  quite  arbitrary,  and 
cannot  always  be  made,  as  the  action  may  be  reversible  or  both  attachments  may  be 
freely  movable.  With  respect  to  the  muscles  of  the  limbs,  the  proximal  attaclmient 
is  regarded  as  the  origin  and  the  distal  one  as  the  insertion.  In  all  cases  the  attach- 
ment is  made  by  fibrous  tissue,  the  muscular  tissue  not  coming  into  direct  relation 
with  the  point  of  attachment.  But  when  the  intermediate  fibrous  tissue  is  not  evi- 
dent to  the  naked  eye,  it  is  customary  to  speak  of  a  ''fleshy  attachment."  The 
term  "tendinous  attachment"  is  applied  to  those  cases  in  which  the  intermediate 
fibrous  tissue — tendon  or  aponeurosis — is  evident.     A  tendon  (Tendo)  is  a  band  of 

252 


MYOLOGY  253 

dense  white  fibrous  tissue  by  means  of  which  a  muscle  is  attached;  an  aponeurosis 
is  a  broad  fibrous  sheet  which  fulfils  a  similar  function. 

(4)  The  action  belongs  rather  to  physiological  study,  but  the  main  points  are 
usually  given  in  anatomical  descriptions.  In  some  cases  the  action  is  simple,  in 
others,  complex.  Muscles  which  concur  in  action  are  termed  synergists;  those 
which  have  opposite  actions  are  antagonists. 

(5)  The  consideration  of  structure  includes  the  direction  of  the  muscular  fibers, 
the  arrangement  of  the  tendons,  the  synovial  membranes,  and  any  other  accessory 
structures.  The  terms  fleshy  and  tendinous  are  sometimes  used  to  indicate  the 
relative  amounts  of  muscular  and  tencUnous  tissue.  In  the  case  of  the  long  muscles 
of  the  limbs,  the  origin  is  termed  the  head  (Caput),  and  when  the  muscle  is  fusi- 
form, the  large  fleshy  part  is  often  called  the  belly  (Venter)  of  the  muscle.  Some 
muscles  have  two  or  more  heads,  and  are  hence  designated  as  biceps,  triceps,  etc.  A 
digastric  muscle  is  one  having  two  bellies  and  an  intermediate  tendon.  In  most 
muscles  the  muscle-fibers  join  the  tendon  at  an  acute  angle,  like  the  relation  of  the 
barbs  of  a  feather  to  its  shaft ;  hence  the  term  pennate  is  applied  to  such  an  arrange- 
ment. When  the  fibers  are  so  arranged  on  one  side  of  the  tendon  the  muscle  is 
unipennate  (M.  unipennatus) ;  while  one  in  which  this  arrangement  exists  on  both 
sides  is  bipennate  (M.  bipennatus).  The  structure  may  be  still  more  complex,  re- 
sulting in  a  multipennate  muscle.  The  structure  of  many  muscles  is  much  more 
complex  than  a  superficial  examination  would  lead  one  to  suppose.     Frequently 


Fibrous  sheath 


Ji^esotendpn         J^ibrous  ^heafk. 

fSyntwial  sheath 


A  B 

Fig.  260. — Diagrams  of  Cross-sections  of  Synovial  Bursa  (A)  and  Synovial  Sheath  (B);    T,  Tendon. 
In  both  the  synovial  sac  is  represented  for  the  sake  of  clearness  as  though  somewhat  distended. 


they  are  intersected  by  tendinous  layers  or  bands,  known  as  tendinous  intersec- 
tions. Intersecting  bands  or  tracts  which  appear  on  the  surface — usually  as  zig- 
zag lines — are  termed  tendinous  inscriptions  (Inscriptiones  tendinese). 

(6)  The  relations  constitute  a  very  important  part  of  anatomical  topography, 
and  a  knowledge  of  them  is  fundamental  to  further  study  in  this  respect. 

(7)  The  blood  and  nerve  supply  are,  of  course,  important  on  clinical  grounds. 
The  nerve  supply  is  often  of  value  in  the  determination  of  homologies.  As  might 
be  expected,  the  muscles  have  a  large  blood  supply.  They  are  also  provided  with 
lymph-vessels.  The  nerves  to  the  muscles  are  motor,  sensory,  and  vasomotor  in 
function. 

The  accessory  structures  associated  with  the  muscles  are  the  synovial  mem- 
branes and  the  fascise. 

The  sjrnovial  membranes  are  thin-walled  sacs,  similar  to  the  synovial  mem- 
branes of  the  joints,  and  having  a  similar  function.  Two  forms  are  recognized. 
A  S5niovial  bursa  (Bursa  synoviafis)  is  a  simple  sac  which  is  interposed  at  a  point  of 
unusual  pressure  between  a  tendon  or  muscle  and  some  underlying  structure,  com- 
monly a  prominence  of  the  skeleton.  A  synovial  sheath  (Vagina  synovialis  ten- 
dinis) differs  from  a  bursa  in  the  fact  that  the  sac  is  folded  around  the  tendon  so  that 
two  layers  can  be  distinguished:  the  inner  one  is  adherent  to  the  tendon,  while  the 
outer  one  lines  the  canal  in  which  the  tendon  lies.  The  two  layers  are  continuous 
along  a  fold  termed  the  mesotendon.  The  arrangement  is  showai  in  the  annexed 
diagrams.     The  synovial  membranes  of  joints  in  some  places  form  extra-articular 


254  FASCIA    AND   MUSCLES    OF   THE    HORSE 

pouches  which  act  as  bursse.     The  sj-novial  sheath  is  not  to  be  confused  with  the 
fibrous  sheath  of  a  tendon  (Vagina  fibrosa  tendinis) . 

The  student  will  note  in  dissection  that  intermediate  forms  of  these  sacs  occur.  A  synovial 
sheath  may  belong  to  two  or  more  tendons  in  common;  in  such  cases  the  synovial  membrane  is 
reflected  from  one  tendon  to  the  other,  forming  a  secondary  mesotendon.  In  the  normal  state 
these  sacs  cannot  be  recognized  on  external  examination  of  the  subject.  It  is  only  when  they  are 
distended  that  their  presence  is  evident. 

The  fasciae  are  sheets  of  connective  tissue,  composed  mainly  of  bundles  of  white 
fibers,  Avith  a  greater  or  less  admixture  of  elastic  fibers  in  some  cases.  At  least  two 
layers  may  usually  be  distinguished.  The  superficial  fascia  (Fascia  superficialis) 
is  subcutaneous,  and  is  composed  of  loose  connective  tissue  which  usually  contains 
more  or  less  fat.  The  deep  fascia  is  composed  of  one  or  more  layers  of  dense  fibrous 
tissue.  Its  deep  face  may  be  very  slightly  adherent  to  the  underlying  structures, 
but  in  many  places  it  is  attached  to  the  skeleton,  Hgaments,  and  tendons.  In  many 
places  laminae  are  given  off  from  the  deep  face  of  the  fascia,  pass  between  muscles, 
and  are  attached  to  bones  or  ligaments;  such  layers  are  termed  intermuscular  septa 
(Septa  intermuscularia) .  The  groove  in  which  a  tendon  lies  is  converted  into  a 
canal  by  a  band  or  fascial  sheet  known  as  a  vaginal  or  annular  ligament  (Lig. 
vaginale).  Many  fasciae  furnish  origin  or  insertion  to  muscles  and  thus  act  as 
tendons;  such  are  tendinous  in  structure,  so  as  to  render  the  distinction  between 
fascia  and  aponeurosis  in  these  cases  arbitrary.  Bursse  occur  in  certain  situations 
between  the  fascia  and  underlying  structures,  and  are  distinguished  as  subfascial 
bursae.     Those  between  the  fascia  and  the  skin  are  subcutaneous  bursae. 


FASCIA  AND  MUSCLES  OF  THE  HORSE 

The  cutaneous  muscle  or  panniculus  camosus  (Musculus  cutaneus)  is  a  thin 
muscular  layer  developed  in  the  superficial  fascia.  It  is  intimately  adherent  in 
great  part  to  the  skin,  but  has  very  little  attachment  to  the  skeleton.  It  does  not 
cover  the  entire  body,  and  may  be  conveniently  divided  into  facial,  cervical,  omo- 
brachial,  and  abdominal  parts. 

The  facial  part,  m.  cutaneus  faciei,  consists  of  a  thin  and  usually  incomplete 
muscular  layer,  which  extends  over  the  mandibular  space  and  the  masseter  muscle. 
A  distinct  branch  of  it  passes  forward  to  the  angle  of  the  mouth  and  blends  with  the 
orbicularis  oris.  This  part,  the  m.  cutaneus  labiorum,  retracts  the  angle  of  the 
mouth,  and  has  therefore  been  termed  the  retractor  anguli  oris. 

The  cervical  part,  m.  cutaneus  colli,  is  situated  on  the  ventral  region  of  the  neck. 
It  arises  from  the  cariniform  cartilage  and  a  median  fibrous  raphe.  The  fibers  are 
directed  forward  and  diverge  from  the  raphe  to  the  sides  of  the  neck  in  pennate 
fashion.  It  is  thick  at  its  sternal  origin,  but  thins  out  in  front  and  laterally.  On 
the  side  of  the  neck  it  is  attached  to  the  cervical  fascia,  which  acts  as  its  aponeurosis. 
It  is  related  deeply  to  the  sterno-cephalicus,  the  brachio-cephalicus  (in  part)  and 
the  jugular  vein.  Some  bundles  extend  upon  the  parotid  gland,  and  in  well- 
developed  subjects  it  is  continuous  with  the  facial  part. 

The  omo-brachial  part,  m.  cutaneus  omo-brachialis,  covers  the  lateral  surface 
of  the  shoulder  and  arm.  Its  fibers  begin  over  the  upper  part  of  the  scapula  and 
extend  to  the  proximal  part  of  the  forearm.  Most  of  its  fibers  are  vertical,  but 
posteriorly  they  become  oblique  and  are  continued  by  the  abdominal  part. 

The  abdominal  part,  m.  cutaneus  tnmci,  covers  a  large  part  of  the  body  be- 
hind the  shoulder  and  arm.  Its  fibers  are  largely  longitudinal.  It  is  continuous 
in  front  with  the  omo-brachial  part,  and  a  tendinous  layer  from  it  passes  forward 


THE    FASCIA    AND    MUSCLES    OF   THE    HEAD  255 

with  the  posterior  deep  pectoral  muscle  to  the  medial  tuberosity  of  the  humerus. 
Posteriorly  it  forms  a  fold,  which,  covered  by  the  skin,  forms  the  fold  of  the  flank, 
and  ends  on  the  fascia  above  the  stifle.  The  dorsal  limit  of  the  muscle  corresponds 
approximately  with  a  line  drawn  from  the  posterior  angle  of  the  scapula  to  the  fold 
of  the  flank.  Ventrally  the  two  muscles  are  about  a  handbreadth  apart  in  the  um- 
bilical region.  Further  forward  they  diverge,  so  as  to  overlap  the  posterior  deep 
pectoral  muscle  only  to  a  small  extent.  Here  the  cutaneous  muscle  is  closely  ad- 
herent to  the  pectoral  and  contains  the  external  thoracic  vein.  Posteriorly  they 
diverge  to  the  fold  of  the  flank. 

The  muscle  is  in  general  closely  adherent  to  the  skin  and  its  contraction  twitches 
the  skin,  thus  getting  rid  of  insects  or  other  irritants. 


The  Fascia  and  Muscles  of  the  Head 

The  muscles  of  the  head  (Mm.  capitis)  may  be  divided  into  three  groups,  viz.: 
(1)  Superficial  muscles,  including  the  cutaneous  muscle  and  those  of  the  lips,  cheeks, 
nostrils,  eyelids,  and  external  ear;  (2)  the  orbital  muscles;  (3)  the  mandibular 
muscles;    (4)  the  hyoid  muscles. 

The  superficial  fascia  forms  an  almost  continuous  layer,  but  is  very  scanty 
around  the  natural  orifices.  It  contains  a  number  of  the  thin  superficial  muscles, 
so  that  care  must  be  exercised  in  removing  the  skin.  Over  the  frontal  and  nasal 
bones  the  fascia  blends  with  the  periosteum. 

The  deep  fascia  is  of  special  interest  in  three  regions.  The  temporal  fascia 
(Fascia  temporalis)  covers  the  temporalis  muscle,  and  is  attached  to  the  parietal 
and  frontal  crests  medially,  and  to  the  zygomatic  arch  laterally.  The  buccal  fascia 
(F.  buccalis)  covers  the  buccinator  muscle  and  the  free  part  of  the  outer  surface  of 
the  ramus  of  the  mancUble.  It  is  attached  to  the  facial  crest,  and  posteriorly  it 
forms  a  band  (Raphe  pterygomandibulare)  which  stretches  from  the  hamulus  of  the 
pterygoid  bone  to  the  mandible  behind  the  last  molar  tooth.  It  is  directly  continu- 
ous with  the  pharyngeal  fascia  (F.  pharyngea),  which  is  attached  to  the  great  and 
thyroid  cornua  of  the  hyoid  bone  and  the  thyroid  cartilage  of  the  larynx ;  it  covers 
the  lateral  walls  of  the  pharynx,  and  blends  dorsally  with  the  mecUan  raphe  of  the 
constrictor  muscles  of  the  latter. 

Cutaneus  faciei. — This  has  been  described  (p.  254). 


MUSCLES  OF  THE  LIPS  AND  CHEEKS 

1.  Orbicularis  oris. — This  is  the  sphincter  muscle  of  the  mouth;  it  is  con- 
tinuous with  the  other  muscles  which  converge  to  the  lips.  It  lies  between  the 
skin  and  the  mucous  membrane  of  the  lips,  and  is  intimately  adherent  to  the 
former.  Most  of  the  fibers  run  parallel  to  the  free  edges  of  the  lips  and  have  no 
direct  attachment  to  the  skeleton. 

Action.— It  closes  the  lips. 

Blood-supply  — Palato-labial,  facial,  and  mental  arteries. 

Nerve-supphj. — Facial  nerve. 

2.  Levator  nasolabialis.^ — This  thin  muscle  lies  directly  under  the  skin,  and 
chiefly  on  the  lateral  surface  of  the  nasal  region. 

Origin. — The  frontal  and  nasal  bones. 

Insertion. — (1)  The  upper  lip  and  the  lateral  wing  of  the  nostril;  (2)  the  com- 
missure of  the  lips. 

Action. — (1)  To  elevate  the  upper  lip  and  the  commissure;  (2)  to  cUlate  the 
nostril. 

^A.lso  termed  the  levator  labii  superioris  ala'que  nasi. 


256 


FASCIA    AND    MUSCLES    OF    THE    HORSE 


Structure. — The  muscle  arises  b}-  a  thin  aponeurosis.  The  belly  is  also  thin, 
and  divides  into  two  branches,  between  which  the  lateral  dilator  of  the  nostril  passes. 
The  dorsal  branch  reaches  the  nostril  and  upper  lip,  blending  vdih.  the  lateral  di- 
lator; the  ventral  one  is  much  smaller,  and  blends  at  the  labial  commissure  ^^^th 
the  orbicularis  and  buccinator. 

Relations. — Superficially,  the  skin,  fascia,  and  lateral  dilator  (in  part) ;  deeply, 


Fig.  261. — Muscles  of  Head  of  Horse;  Lateral  View.  The  M.  ctttaneus  is  Removed. 
o,  Levator  labii  superioris  proprius;  6,  levator  nasolabialis;  c,  brachiocephalicus;  d,  sterno-cephalicus ;  d', 
tendon  of  d;  e,  omo-hyoideus;  /,  dilatator  naris  lateralis;  g,  zygomaticus;  h,  buccinator;  i,  depressor  labii  inferioris; 
k,  orbicularis  oris;  I,  lateralis  nasi,  dorsal  part;  m,  masseter;  n,  parotido-auricularis;  o,  zygomatico-auricularis;  p, 
interscutularis;  p',  fronto-scutularis,  pars  temporalis;  q,  cervico-auricularis  profundus  major;  r,  cervico-auricularis 
superficialis;  s,  obliquus  capitis  anterior;  <,  splenius;  r,  occipito-mandibularis;  i/,  mastoid  tendon  of  brachiocephalicus; 
.2,  posterior,  3,  anterior,  border  of  external  ear;  S,  scutiform  cartilage;  9,  zygomatic  arch;  70,  orbital  fat;  7S,  temporo- 
mandibular articulation;  27,  facial  crest;  30',  angle  of  jaw;  37,  external  maxillary  vein;  38,  jugular  vein;  39,  facial 
vein;  .40,  parotid  duct;  4 A  transverse  facial  vein;  4^,  masseteric  vein;  45,  facial  nerve;  44.  parotid  gland;  40,  chin; 
X,  wing  of  atlas.  By  an  oversight  the  superior  buccal  branch  of  the  facial  nerve  is  shown  crossing  over  instead  of  under 
the  zygomaticus.     (After  EUenberger-Baum,  Anat.  fiir  Kiinstler.) 


the  levator  labii  superioris  proprius,  lateral  dilator  (in  part),  buccinator,  branches 
of  the  facial  vessels  and  nerve,  and  the  infraorbital  arterj'  and  nerve. 

Blood-sup  pi  y. — Facial  and  palato-labial  arteries. 

Nerve-supphj. — Facial  nerve. 

3.  Levator  labii  superioris  proprius.^This  lies  on  the  dorso-lateral  aspect  of 
the  face,  partly  covered  by  the  preceding  muscle. 

Origin. — The  lacrimal,  malar,  and  maxillary  bones  at  their  junction. 


MUSCLES    OF   THE    LIPS   AND    CHEEKS 


257 


Insertion. — The  upper  lip,  by  a  common  tendon  with  its  fellow. 

Action.— Kcimg  with  its  fellow,  to  elevate  the  upper  lip.     This  action,  if 
carried  to  the  fullest  extent,  results  in  eversion  of  the  lip.     In  unilateral  action  the 
lip  is  drawn  upward  and  to  the  side  of 
the  muscle  acting. 

Structure.- — The  muscle  has  a  short, 
thin  tendon  of  origin.  The  belly  is  at 
first  flattened,  but  becomes  narrower 
and  thicker,  then  tapers  over  the  nasal 
diverticulum,  to  terminate  in  a  tendon. 
The  tendons  of  the  two  muscles  unite 
over  the  alar  cartilages  of  the  nostrils, 
forming  an  expansion  which  spreads 
out  in  the  substance  of  the  upper 
lip.i 

Relations. — Superficially,  the  skin, 
the  levator  nasolabialis,  and  the  angu- 
lar vessels  of  the  eye ;  deeply,  the  later- 
alis nasi,  the  transversus  nasi,  and  the 
infraorbital  artery  and  nerve. 

Blood-supply. — Facial  artery. 

Nerve-supply. — Facial  nerve. 

4.  Zygomaticus. — This  very  thin 
muscle  lies  immediately  under  the  skin 
of  the  cheek. 

Origin. — The  fascia  covering  the 
masseter  muscle  below  the  facial 
crest. 

Insertion. — The  commissure  of  the 
lips,  blending  with  the  buccinator. 

Action. — To  retract  and  raise  the 
angle  of  the  mouth. 

Structure. — Fleshy,  with  a  thin 
aponeurotic  origin. 

Relatio7is. — Superficially,  the  skin; 
deeply,  the  buccinator. 

Blood-supply. — Facial  artery. 

Nerve-supply. — Facial  nerve. 

5.  Incisivus  superior. — This  lies 
under  the  mucous  membrane  of  the 
upper  lip. 

Origin. — The  alveolar  border  of 
the  premaxilla  from  the  second  incisor 
to  the  first  cheek  tooth. 

Insertion. — The  upper  lip. 

Action. — To  depress  the  upper 
lip. 

6.  Incisivus  inferior. — This  is  ar- 
ranged in  the  lower  lip  like  the  pre- 
ceding muscle  in  the  upper  one. 

Origin. — The  alveolar  border  of  the  mandible  from  the  second  incisor  to  a 
point  near  the  first  cheek  tooth. 

^  In  rare  cases  a  branch  is  given  off  from  the  ventral  border  of  the  muscle.     It  passes  forward 
and  ends  in  the  subcutaneous  tissue  at  the  posterior  end  of  the  diverticulum  nasi. 
17 


Fig.  262. — Muscles  of  Head  of  Horse;  Dorsal  View. 
The  M.  cutaneus  is  Removed. 
a,  Levator  labii  superioris  proprius;  a',  common 
tendon  of  a  with  opposite  muscle;  6,  levator  nasolabialis; 
/,  dilatator  naris  lateralis;  g,  zygomaticus;  I,  lateralis 
nasi;  ?i,  parotido-auricularis;  o",  scutulo-auricularis  super- 
ficialis  superior;  p,  interscutularis ;  p',  fronto-scutularis, 
pars  temporalis;  r,  cervico-auricularis  superficialis;  u, 
corrugator  supercilii;  x,  transversus  nasi;  2,  posterior, 
S,  anterior,  border  of  external  ear;  8,  scutiform  cartilage; 
9,  zygomatic  arch;  10,  supraorbital  depression;  S3,  medial 
wing  of  nostril,  containing  lamina  of  alar  cartilage;  39, 
facial  vein.     (After  EUenberger-Baum,  Anat.  fur  Kiinstler.) 


258  FASCIA    AND    MUSCLES    OF   THE    HORSE 

Insertion. — The  skin  of  the  lower  hp  and  the  prominence  of  the  chin. 
Action. — To  raise  the  lower  lip.     The  two  incisivi  bring  the  lips  together, 
concurring  with  the  orbicularis  oris  in  prehension  of  food. 

7.  Mentalis.^ — This  is  situated  in  the  prominence  of  the  chin.  Its  fibers  arise 
from  each  side  of  the  body  of  the  mandible  and  are  inserted  into  the  skin  of  the 
chin.  It  is  mingled  with  fat  and  strands  of  connective  tissue,  in  which  the  roots 
of  the  tactile  hairs  are  embedded.  It  raises  and  corrugates  the  skin  to  which  it  is 
attached. 

8.  Depressor  labii  inferioris. — This  muscle  lies  on  the  lateral  surface  of  the 
ramus  of  the  mandible,  along  the  ventral  border  of  the  buccinator. 

Origin. — The  alveolar  border  of  the  mandible  near  the  coronoid  process  and 
the  maxillary  tuberosity,  in  common  with  the  buccinator. 

Insertion. — The  lower  lip. 

Action. — To  depress  and  retract  the  lower  lip. 

Structure. — The  tendon  of  origin  and  the  belly  are  fused  with  the  buccinator 
as  far  forward  as  the  first  cheek  tooth.  From  this  point  forward  the  belly  is  dis- 
tinct and  rounded,  terminating  in  a  tendon  which  spreads  out  in  the  lower  lip, 
blending  with  the  orbicularis  and  the  muscle  of  the  opposite  side. 

Relations. — Superficially,  the  skin,  masseter,  facial  vessels,  and  parotid  duct; 
deeply,  the  mandible  and  inferior  labial  artery. 

Blood-supply. — Facial  artery. 

Nerve-supply. — Facial  nerve. 

9.  Buccinator. — This  muscle  lies  in  the  lateral  wall  of  the  mouth,  extending 
from  the  angle  of  the  mouth  to  the  maxillary  tuberosity. 

Origin. — The  lateral  surface  of  the  maxilla  above  the  interalveolar  space  and 
the  molar  teeth ;  the  alveolar  border  of  the  mandible  at  the  interalveolar  space  and 
also  posteriorly  where  it  turns  upward  to  the  coronoid  process;  the  pterygo-mandib- 
ular  raphe. 

Insertion. — The  angle  of  the  mouth,  blending  with  the  orbicularis  oris. 

Action. — To  flatten  the  cheeks,  thus  pressing  the  food  between  the  teeth; 
also  to  retract  the  angle  of  the  mouth. 

Structure. — Two  layers  ma}^  be  recognized.  The  superficial  layer  (Pars  buc- 
calis)  extends  from  the  angle  of  the  mouth  to  the  masseter.  It  is  incompletely  pen- 
nate,  having  a  longitudinal  raphe  on  which  most  of  the  muscle-fibers  converge. 
The  upper  fibers  are  directed  chiefly  downward  and  backward,  the  lower  ones  up- 
ward and  backward.  The  deep  layer  (Pars  molaris)  consists  mainly  of  longitudinal 
fibers.  It  blends  in  part  with  the  superficial  layer  of  the  orbicularis;  it  has  a 
small  tendinous  attachment  to  the  coronoid  process  behind,  and  is  united  ventrally 
with  the  depressor  labii  inferioris. 

Relations. — Superficially,  the  skin  and  fascia,  the  zygomaticus,  levator  naso- 
labialis,  lateral  dilator  of  the  nostril,  the  superior  buccal  glands,  the  parotid  duct, 
the  facial  vessels,  and  branches  of  the  facial  nerve;  deeply,  the  mucous  membrane 
of  the  mouth  and  the  inferior  buccal  glands. 

Blood-supply. — Facial  and  buccinator  arteries. 

Nerve-supply. — Facial  nerve. 


MUSCLES  OF  THE  NOSTRILS 

1.  Levator  nasolabialis. — This  has  been  descriljed  (p.  255). 

2.  Dilatator  naris  lateralis  (M.  caninus). — This  thin,  triangular  muscle  lies 
on  the  lateral  nasal  region,  and  passes  between  the  two  branches  of  the  levator 
nasolabialis. 

1  Also  known  as  the  levator  menti. 


MUSCLES    OF   THE    NOSTRILS 


259 


Origin. — The  maxilla,  close  to  the  anterior  extremity  of  the  facial  crest. 

Insertion. — The  lateral  wing  of  the  nostril. 

Action. — To  dilate  the  nostril. 

Structure. — The  muscle  has  a  flat  tendon  of  origin,  passes  between  the  two 
branches  of  the  levator  nasolabialis,  and  spreads  out  in  the  lateral  wing  of  the 
nostril.     The  lower  fibers  blend  with  the  orbicularis  oris. 

Relations. — Superficially,  the  skin,  fascia,  and  the  labial  branch  of  the  levator 
nasolabialis;  deeply,  the  maxilla  and  the  nasal  branch  of  the  levator  nasolabialis. 

Blood-supply. — Facial  artery. 

Nerve-supply. — Facial  nerve. 

3.  Transversus  nasi.^^ — This  is  an  unpaired,  quadrilateral  muscle,  which  lies 
bet^veen  the  nostrils.     It  consists  of  two  layers. 


Fig.  263. — Nasal  and  Superior  Labial  Muscles  of  Horse. 
a,  a',  Transversus  nasi;  b,  levator  labii  superioris  proprius;  6',  tendon  of  b;  b",  common  tendon  of  two 
levatores  labii  superioris  proprii;  c,  c',  c",  d,  ventral  part  of  lateralis  nasi;  e,  dorsal  part  of  lateralis  nasi;  /,  or- 
bicularis oris;  g,  levator  nasolabialis,  a  portion  of  which  is  removed;  h,  dilatator  naris  lateralis  (the  terminal  part  of 
which  is  removed);  i,  cornu  of  alar  cartilage;  k,  nostril;  k',  upper  commissure  of  nostril;  I,  nasal  diverticulum;  m, 
nasal  bone.     (After  EUenberger-Baum,  Top.  Anat.  d.  Pferdes.) 


Attachments. — Superficial  layer,  the  superficial  faces  of  the  laminae  of  the  alar 
cartilages;  deep  layer,  the  convex  edges  of  the  cornua  of  the  same. 

Action. — To  dilate  the  nostrils. 

Structure. — It  is  composed  of  transverse  fleshy  fibers,  which  blend  below  with 
the  orbicularis. 

Relations. — Superficially,  the  skin,  fascia,  and  tendinous  expansion  of  the 
levator  labii  superioris  proprius;  deeply,  the  alar  cartilages,  the  extremity  of  the 
septum  nasi,  and  the  palato-labial  artery. 

Blood-supply. — Palato-labial  artery. 

Nerve-supply. — Facial  nerve. 

Lateralis  nasi. — This  is  situated  along  the  margins  of  the  naso-maxillary  notch, 
and  may  be  regarded  as  consisting  of  dorsal  and  ventral  parts. 

The  dorsal  part  (Pars  dorsalis  m,  lateralis  nasi)-  is  a  thin  layer  which  lies  along 

^  Also  called  the  dilatator  naris  transversus.  ^  Also  known  as  the  dilatator  naris  superior. 


260  FASCIA   AND   MUSCLES    OF   THE   HORSE 

the  dorsal  border  of  the  naso-maxillary  notch.  Its  fibers  arise  from  the  nasal  bone 
and  pass  outward  and  downward  to  the  parietal  cartilage  and  the  adjacent  part  of 
the  soft  lateral  wall  of  the  nasal  cavity. 

The  ventral  part  (Pars  ventralis  m.  lateralis  nasi)^  is  much  thicker  and  lies 
along  the  ventral  border  of  the  notch.  It  arises  from  the  nasal  process  of  the  pre- 
maxilla  and  the  adjacent  part  of  the  maxilla,  and  its  fibers  curve  inward  to  end  on 
the  cartilaginous  prolongations  of  the  turbinate  bones  (chiefly  the  ventral  one)  and 
on  the  lateral  wall  of  the  vestibule  of  the  nasal  cavity.  A  few  bundles  pass  from 
the  cornu  of  the  alar  cartilage  to  the  lateral  wing  of  the  nostril. 

Action. — To  dilate  the  vestibule  of  the  nasal  cavity,  to  rotate  the  turbinal  car- 
tilages outward,  and  to  assist  in  dilating  the  nostril. 

Relations. — Superficially,  the  skin,  fascia,  nasal  diverticulum,  the  levator  labii 
superioris  proprius,  the  levator  nasolabialis,  and  the  lateral  nasal  artery;  deeply, 
the  nasal  bone,  the  parietal  cartilage,  the  maxilla,  the  premaxilla,  the  nasal  mucous 
membrane,  and  the  anterior  nasal  branch  of  the  infraorbital  nerve. 

Blood-supply. — Facial  and  palato-labial  arteries. 

Nerve-supply. — Facial  nerve. 

The  preceding  muscle  does  not  dilate  the  so-called  "false  nostril"  or  nasal  diverticulum,  aa 
is  commonly  stated.  Both  act  on  the  lateral  wall  of  the  vestibule  of  the  nasal  cavity  so  as  to  draw 
it  outward,  thus  tending  to  constrict,  rather  than  dilate,  the  nasal  diverticulum.  The  thick  part 
of  the  ventral  muscle  which  is  attached  to  the  cartilage  of  the  turbinate  bone  has  a  similar  effect. 
When  the  nostril  is  fully  dilated,  the  so-called  "false  nostril,"  i.  e.,  the  entrance  to  the  nasal  diver- 
ticulum, is  closed.     The  newer  term  seems  preferable. 


MUSCLES  OF  THE  EYELIDS 

1.  Orbicularis  oculi. — This  is  a  flat,  elliptical,  sphincter  muscle,  situated  in  and 
around  the  eyelids,  the  portion  in  the  upper  lid  being  much  broader  than  that  in 
the  lower.  The  chief  attachment  is  to  the  skin  of  the  lids,  but  some  bundles  are 
attached  to  the  palpebral  ligament  at  the  medial  canthus  and  to  the  lacrimal  bone. 
Its  action  is  to  close  the  lids. 

2.  Corrugator  supercilii.— This  is  a  very  thin,  small  muscle,  which  arises  over 
the  root  of  the  supraorbital  process  and  spreads  out  in  the  upper  eyelid,  blending 
with  the  orbicularis  ocuh  (Fig.  262).  Its  action  is  to  assist  in  raising  the  upper  lid 
or,  especially  in  pathological  conditions,  to  wrinkle  the  skin. 

3.  Malaris. — This  is  a  very  thin  muscle,  which  varies  much  in  different  sub- 
jects. It  extends  from  the  fascia  in  front*  of  the  orbit  to  the  lower  lid.  Its  action 
is  to  depress  the  lower  lid. 

The  foregoing  muscles  receive  their  blood-supply  from  the  facial,  transverse 
facial,  supraorbital,  and  infraorbital  arteries;  the  nerve-supply  is  derived  from  the 
facial  nerve. 

4.  Levator  palpebrae  superioris. — This  slender,  flat  muscle  is  almost  entirely 
within  the  orbit  (Fig.  561).  It  arises  on  the  pterygoid  crest,  passes  forward  above 
the  rectus  oculi  superior  and  below  the  lacrimal  gland,  and  terminates  in  a  thin  ten- 
don in  the  upper  lid. 

Action. — To  elevate  the  upper  lid. 
Blood-supply. — Ophthalmic  artery. 
Nerve-supply. — Oculomotor  nerve. 


MANDIBULAR  MUSCLES 

The  muscles  of  this  group  (Mm.  mandibulae)  are  six  in  number  in  the  horse. 
They  arise  from  the  upper  jaw  and  the  cranium,  and  are  all  inserted  into  the  man- 
dible. 

1  Also  known  as  the  dilata'  or  naris  inferior. 


MANDIBULAR   MUSCLES  261 

1.  Masseter. — This  muscle  extends  from  the  zygomatic  arch  and  facial  crest 
over  the  broad  part  of  the  mandibular  ramus.     It  is  semi-elliptical  in  outline. 

Origin. — By  a  strong  tendon  from  the  zygomatic  arch  and  the  facial  crest. 

Insertion. — The  lateral  surface  of  the  broad  part  of  the  ramus  of  the  mandible. 

Action. — Its  action  is  to  bring  the  jaws  together.  Acting  singly,  it  also  carries 
the  lower  jaw  toward  the  side  of  the  contracting  muscle. 

Structure. — The  superficial  face  of  the  muscle  in  its  upper  part  is  covered  by  a 
strong,  glistening  aponeurosis,  and  several  tendinous  intersections  partially  divide 
the  muscle  into  layers.  The  fibers  of  the  superficial  layer  take  origin  from  the 
malar  and  maxilla  only,  and  diverge  somewhat  to  their  insertion  close  to  the  thick 
ventral  border  of  the  lower  jaw.  The  fibers  of  the  deep  layer  arise  from  the  entire 
area  of  origin,  and  pass  straight  to  the  border  of  the  mandible;  it  will  be  noted  that 
a  small  part,  near  the  temporo-mandibular  joint,  is  not  covered  by  the  superficial 
layer.  The  two  layers  are  separable  only  above  and  behind;  elsewhere  they  are 
fused. 

Relations. —  Superficially,  the  skin  and  cutaneus,  the  parotid  gland,  the 
transverse  facial  and  masseteric  vessels,  and  the  facial  nerve;  deeply,  the  ramus  of 
the  mandible,  the  buccinator  and  depressor  labii  inferioris  muscles,  the  superior 
buccal  glands,  the  buccinator  vessels  and  nerve,  and  the  vena  reflexa,  which  joins 
the  facial  vein  at  the  anterior  edge  of  the  muscle.  The  facial  vessels  and  parotid 
duct  run  along  the  anterior  edge  of  the  muscle;  the  duct,  however,  bends  for- 
ward about  the  middle  of  the  border  and  leaves  the  muscle. 

Blood-supply. — Transverse  facial  and  masseteric  arteries. 

Nerve-supply. — Mandibular  nerve. 

2.  Temporalis. — This  muscle  occupies  the  temporal  fossa. 

Origin. — The  rough  part  of  the  temporal  fossa  and  the  crests  which  limit  it. 

Insertion. — The  coronoid  process  of  the  mandible,  which  it  envelops. 

Action. — Chiefly  to  raise  the  lower  jaw,  acting  with  the  masseter  and  medial 
pterygoid  muscles. 

Structure. — The  surface  of  the  muscle  is  covered  with  a  glistening  aponeurosis, 
and  strong  tendinous  intersections  are  found  in  its  substance.  The  medial  edge  of 
the  muscle  is  quite  thin,  but  as  the  fibers  converge  toward  the  much  smaller  area 
of  insertion,  the  muscle  becomes  nearly  an  inch  thick.  It  fuses  partly  with  the 
masseter. 

Relations. — Superficially,  the  scutiform  cartilage,  the  anterior  muscles  of  the 
external  ear,  and  the  auricular  and  orbital  fat;  deeply,  the  temporal  fossa  and  the 
deep  temporal  vessels  and  nerves. 

Blood-supply. — Superficial  and  deep  temporal,  and  posterior  meningeal  arteries. 

Nerve-supply. — Mandibular  nerve. 

3.  Pterygoideus  medialis  (s.  internus).- — This  muscle  occupies  a  position  on 
the  medial  surface  of  the  ramus  of  the  mandible  similar  to  that  of  the  masseter 
laterally. 

Origin. — The  crest  formed  by  the  pterygoid  process  of  the  sphenoid  and  the 
palatine  bone. 

Insertion. — The  concave  medial  surface  of  the  broad  part  of  the  ramus  of  the 
mandible  and  the  medial  lip  of  the  ventral  border. 

Action. — Acting  together,  to  raise  the  lower  jaw;  acting  singly,  to  produce  also 
lateral  movement  of  the  jaw. 

Structure. — The  muscle  is  capable  of  division  into  two  parts.  The  principal 
part  is  superficial  (medial),  and  its  fibers  are,  for  the  most  part,  vertical  in  direc- 
tion. It  contains  much  tendinous  tissue  (septa).  The  smaller  portion  is  lateral 
to  the  foregoing,  and  its  fibers  are  directed  do^vnward  and  backward. 

Relations. — Laterally,  the  ramus  of  the  mandible,  the  lateral  pterygoid  muscle, 
the  inferior  alveolar  vessels  and  nerve,  and  the  lingual  and  mjdo-hyoid  nerves; 


262 


FASCIA   AND    MUSCLES    OF   THE    HORSE 


medially,  the  great  cornu  of  the  hyoid  bone,  the  pharynx,  the  larynx,  the  tensor 
palati,  mylo-hyoideus,  digastricus,  and  stylo-hyoideus  muscles,  the  guttural  pouch, 
the  external  maxillary  vessels,  the  ninth  and  twelfth  nerves,  the  mandibular  salivary 
gland,  the  mandibular  and  parotid  ducts,  and  the  mandibular  and  pharyngeal  lymph- 
fflands. 

Blood-supply. — Internal  maxillary,  masseteric,  and  inferior  alveolar  arteries. 

Nerve-supply. — Mandibular  nerve. 

4.  Pterygoideus  lateralis  (s.  externus). — This  muscle  is  considerably  smaller 
than  the  preceding  one,  and  is  situated  lateral  to  its  upper  part. 

Origin. — The  lateral  surface  of  the  pterygoid  process  of  the  sphenoid  bone. 

Insertion. — The  medial  surface  of  the  neck,  the  medial  part  of  the  anterior 
border  of  the  condyle  of  the  mandible  and  the  articular  disc. 

Actio7i. — Acting  together,  to  draw  the  lower  jaw  forward;    acting  singly,  to 


Ethmo- 
turhinates 
Dorsal  meatus 
Dorsal  turbinate 
Middle  meatus 
Ventral  iurhitiate 
Ventral  meatus 


Septum  of 
frontal  sinuses 


Digastricus, 
posterior 
belly 


Digastricus, 
anterior  belly 


Intermediate  tendon 


Fig.  264. — Sagittal  Section  of  Head  op  Horse,  Showing  Deep  Pterygo-mandibular  Region  and  Nasal  and 

Cra.nial  Cavities. 
1,  Cerebral   compartment   of   cranial    cavity;   £,  cerebellar  compartment  of  same;    3,  tentorium  osseum;   4i  ten- 
torium cerebelli;    5,  sphenoidal  sinus;    6,  hamulus  of  pterygoid  bone-tendon  of  tensor  palati  cut  off  short  at  anterior 
border  of  hamulus;    7,  mylo-glossus.     The  olfactory  mucous  membrane  is  shaded. 


move  the  jaw  also  toward  the  side  opposite  to  the  muscle  acting.  The  latter  action 
is  due  to  the  fact  that  the  origin  is  nearer  to  the  median  plane  than  the  insertion. 

Structure. — The  muscle  is  almost  entirely  fleshy,  and  the  fibers  are  almost 
longitudinal  in  direction.  Some  of  them  are  inserted  into  the  edge  of  the  articular 
disc. 

Relations. — Laterally,  the  temporo-mandibular  articulation  and  the  temporalis 
muscle;  medially,  the  medial  pterygoid  and  tensor  palati  muscles.  The  internal 
maxillary  artery  crosses  the  ventral  face  of  the  muscle  and  dips  in  between  it  and 
the  tensor  palati.  The  mandibular  nerve  lies  on  the  ventral  surface,  and  the  buc- 
cinator nerve  perforates  the  origin  of  the  muscle. 

Blood-supply. — Internal  maxillary  and  inferior  alveolar  arteries. 

Nerve-supply. — Mandibular  nerve. 

5.  Occipito-mandibularisi  (M.  jugulomandibularis).— This  is  a  short,  fusiform 

^  This  muscle  is  also  known  as  the  stylo-maxillaris,  stylo-mandibularis,  etc. 


MANDIBULAR   MUSCLES 


263 


muscle  extending  from  the  paramastoid  process  of  the  occipital  bone  to  the  posterior 
border  of  the  lower  jaw;  it  is  covered  by  the  parotid  gland. 


Fig  265  -Mandibular  and  Laryngeal  Regions  of  Horse,  after  Removal  of  Skin  and  Cutaneub. 
c  Brachiocephalicus:  d.  sterno-cephalicus;  e.  omo-hyoideus  and  sterno-hyoideus;  h,  buccinator;  ^,  depressor 
labiiWerLris-  m,  masseter;  «.  occipito-mandibularis;  u,  mylo-hyoideus;  ...  posterior.  3.  anterior,  border  of  external 
ear  SO'  angi;  o  jaw;  36  mandibular  lymph-glands;  ^7.  external  maxillary  vein;  3^.  facial  continuation  of  ^7; 
ro'parolid  duct;  L  parotid  gland;  4o,  prominence  of  chin;  x.  wing  of  atlas.  (After  EUenberger-Baum.  Anat.  fur 
Kiinstler.) 


Origin.— The  paramastoid  process  of  the  occipital  bone,  in  common  with  the 
posterior  belly  of  the  digastricus. 

Insertion.— The  posterior  border  of  the  ramus  of  the  mandible. 
Action.— To  depress  the  lower  jaw  and  open  the  mouth. 


264  FASCIA    AND    MUSCLES    OF   THE    HORSE 

Structure. — The  muscle  contains  a  good  deal  of  tendinous  tissue.  It  blends 
with  the  posterior  belly  of  the  digastricus. 

/?e/'a^^ons.— Superficially,  the  parotid  gland,  the  tendon  of  the  sterno-cephalicus, 
and  the  fibrous  expansion  which  connects  it  with  the  tendon  of  the  brachiocephali- 
cus;  deeply,  the  guttural  pouch,  the  external  carotid  artery,  the  ninth  and  twelfth 
nerves,  the  pharynx,  and  the  mandibular  salivary  gland. 

Blood-supply. — External  carotid  artery. 

Nerve-supply. — Facial  nerve. 

6.  Digastricus. — This  muscle  is  composed  of  two  fusiform,  flattened  bellies, 
united  by  a  round  tendon. 

Origin. — The  paramastoid  process  of  the  occipital  bone,  in  common  with  the 
preceding  muscle. 

Insertion.- — The  medial  surface  of  the  ventral  border  of  the  molar  part  of  the 
ramus  of  the  mandible. 

Action. — It  assists  in  depressing  the  lower  jaw  and  opening  the  mouth.  If  the 
mandible  be  fixed  and  both  bellies  contract,  the  hyoid  bone  and  the  base  of  the 
tongue  are  raised,  as  in  the  first  phase  of  deglutition. 

Structure. — The  posterior  belly  has  the  appearance  of  a  branch  detached  from 
the  medial  surface  of  the  occipito-mandibularis.  It  passes  downward  and  forward, 
and  is  succeeded  by  a  small  rounded  tendon.  The  latter  perforates  the  tendon  of 
insertion  of  the  stylo-hyoideus,  and  is  provided  with  a  synovial  sheath.  The  an- 
terior belly  is  larger  and  terminates  by  thin,  tendinous  bundles. 

Relations.- — The  posterior  belly  has  practically  the  same  relations  as  the  oc- 
cipito-mandibularis. The  intermediate  tendon  is  in  contact  laterally  with  the  me- 
dial pterygoid  muscle,  the  mandibular  gland  and  duct,  and  the  external  maxillary 
artery.  The  anterior  belly  lies  in  the  mandibular  space  between  the  ramus  of  the 
jaw  and  the  mylo-hyoideus  muscle;  the  sublingual  vessels  run  along  its  dorsal 
border. 

Blood-supply.- — External  carotid  and  sublingual  arteries. 

Nerve-supply. — Facial  and  mandibular  nerves. 

THE  HYOID  MUSCLES 

This  group  consists  of  eight  muscles  (Mm.  ossis  hyoidei),  one  of  which,  the 
hyoideus  transversus,  is  unpaired. 

1.  Mylo-hyoideus.^ — This  muscle,  together  with  its  fellow,  forms  a  sort  of 
sling  between  the  rami  of  the  mandible,  in  which  the  tongue  is  supported. 

Origin. — The  medial  surface  of  the  alveolar  border  of  the  mandible. 

Insertion.- — (1)  A  median  fibrous  raphe  extending  from  the  symphysis  to  the 
hyoid  bone;   (2)  the  lingual  process,  body,  and  thyroid  cornu  of  the  hj'oid  bone. 

Action.- — It  raises  the  floor  of  the  mouth,  the  tongue,  and  the  hyoid  bone. 

Structure. — Each  muscle  consists  of  a  thin  curved  sheet,  the  fibers  passing 
ventrally  from  their  origin  and  then  curving  toward  the  median  raphe.  It  is 
chiefly  fleshy,  and  is  thickest  behind.  There  is  a  tendinous  intersection  between  this 
muscle  and  the  omo-hyoideus,  to  which  both  muscles  are  attached.  The  anterior 
superficial  part  of  the  muscle  is  termed  the  mylo-glossus. 

Relations. — On  the  superficial  surface  of  the  muscles  are  the  ramus,  the  metlial 
pterygoid  and  digastricus  muscles,  and  the  mandibular  lymph-glands.  The  deep 
surface  is  in  contact  with  the  mucous  membrane  of  the  mouth,  the  stylo-glossus, 
hyo-glossus,  and  genio-hyoideus  muscles,  the  sublingual  gland  and  vessels,  the 
mandibular  duct,  and  the  lingual  and  hypoglossal  nerves.  The  sublingual  vein 
passes  through  the  posterior  part. 

Blood-supply. — Sublingual  artery. 

^  Also  known  as  the  transversus  mandibulae. 


THE    HYOID    MUSCLES  265 

Nerve-supply. — Mylo-hyoid  branch  of  the  mandibular  nerve. 

2.  Stylo-hyoideus. — This  is  a  slender,  fusiform  muscle,  having  a  direction 
nearly  parallel  to  that  of  the  great  cornu  of  the  hyoid  bone  (Fig.  559) . 

Origin. — The  muscular  angle  of  the  dorsal  extremity  of  the  great  cornu  of  the 
hyoid  bone. 

Insertion. — The  anterior  part  of  the  thyroid  cornu  of  the  hyoid  bone. 

Action. — It  draws  the  base  of  the  tongue  and  the  larynx  upward  and  backward. 

Structure.— It  arises  by  a  thin,  short  tendon,  and  has  a  fusiform  belly.  The 
tendon  of  insertion  is  perforated  for  the  passage  of  the  intermediate  tendon  of  the 
cUgastricus,  and  at  this  point  there  is  a  small  synovial  sheath. 

Relations. — Superficially,  the  medial  pterygoid  muscle  and  the  parotid  gland; 
deeply,  the  guttural  pouch,  the  pharynx,  the  external  carotid  and  maxillary  arteries, 
and  the  hypoglossal  nerve. 

Blood-supply. — External  carotid  artery. 

Nerve-supply. — Facial  nerve  (stylo-hyoid  branch). 

In  rare  cases  an  anomalous  arrangement  is  present  in  which  the  stylo-hyoideus  is  not  at- 
tached to  the  thyroid  cornu  but  is  continuous  with  the  intermediate  tendon  of  the  digastricus, 
and  no  fibrous  ring  is  formed.  The  posterior  belly  of  the  digastricus  is  inserted  chiefly  on  the 
thyroid  cornu,  but  also  sends  a  dehcate  tenchnous  shp  to  the  intermediate  tendon. 

3.  Occipito-hyoideus  (M.  jugulo-hyoideus). — This  is  a  small  triangular  muscle, 
which  lies  in  the  space  between  the  paramastoid  process  and  the  great  cornu  of  the 
hyoid  bone. 

Origin. — The  paramastoid  process  of  the  occipital  bone. 

Insertion. — The  dorsal  extremity  and  ventral  edge  of  the  great  cornu  of  the 
hyoid  bone. 

Action. — It  carries  the  ventral  extremity  of  the  great  cornu  backward. 

Structure. — The  muscle  is  somewhat  triangular,  its  fibers  being  longer  as  the 
ventral  border  is  approached.     It  blends  with  the  posterior  belly  of  the  digastricus. 

Relations. — Superficially,  the  parotid  gland;  deeply,  the  guttural  pouch. 

Blood-supply.- — Occipital  artery. 

Nerve-supply. — Facial  nerve. 

4.  Genio-hyoideus. — This  is  a  long,  spindle-shaped  muscle,  which  lies  under 
the  tongue  in  contact  with  its  fellow  of  the  opposite  side  (Fig.  330) . 

Origin. — A  small  depression  on  the  medial  surface  of  the  ramus  of  the  mandible, 
close  to  the  symphysis. 

Insertion. — The  extremity  of  the  lingual  process  of  the  hyoid  bone. 

Action. — It  draws  the  hyoid  bone  and  tongue  forward. 

Structure. — The  muscle  arises  by  a  short  tendon,  which  is  succeeded  by  the 
belly,  composed  of  long  bundles  of  parallel  fibers. 

Relations. — Ventrally,  the  mylo-hyoideus;  dorsally,  the  hyo-glossus,  stylo- 
glossus, genio-glossus,  the  sublingual  gland,  mandibular  duct,  and  the  lingual  nerve. 

Blood-supply. — Sublingual  artery. 

Nerve-supply. — Hypoglossal  nerve. 

5.  Kerato-hyoideus. — This  small  triangular  muscle  lies  in  the  space  between 
the  thyroid  and  small  cornu,  under  cover  of  the  hyo-glossus  (Fig.  331). 

Origin. — The  posterior  edge  of  the  small  cornu  and  the  adjacent  part  of  the 
ventral  border  of  the  great  cornu. 

Insertion. — The  dorsal  edge  of  the  thyroid  cornu. 

Action.- — It  raises  the  thyroid  cornu  and  the  larynx. 

Relations. — The  muscle  is  crossed  laterally  by  the  lingual  artery. 

Blood-supply. — Lingual  artery. 

Nerve-supply. — Glosso-pharyngeal  nerve. 

6.  Hyoideus  transversus. — This  is  a  small,  unpaired  muscle,  which  extends 
transversely  between  the  two  small  cornua  of  the  hyoid  bone. 


266  FASCIA    AND    MUSCLES    OF   THE    HORSE 

Attachments. — The  small  cornua  close  to  the  junction  with  the  great  cornua. 
Action. — When  relaxed,  its  dorsal  surface  is  concave;  when  it  contracts,  it 
elevates  the  root  of  the  tongue. 

Structure. — Fleshy,  composed  of  parallel  transverse  bundles. 
Blood-supply. — Lingual  artery. 
Nerve-supply. — Glosso-pharyngeal  nerve. 

7.  Stemo-thyro-hyoideus,  and 

8.  Omo-hyoideus. — These  are  described  with  the  muscles  on  the  ventral  sur- 
face of  the  neck  (p.  268). 


The  Fascia  and  Muscles  of  the  Neck 

It  is  convenient  to  divide  the  muscles  of  the  neck  (Mm.  colli)  into  ventral  and 
lateral  groups,  the  two  lateral  groups  being  separated  from  each  other  by  the  liga- 
mentum  nuchse. 

THE  FASCIA  OF  THE  NECK 

The  superficial  fascia  is  in  part  two-layered,  and  contains  the  cervical  cutaneous 
muscle.  The  fasciae  of  the  right  and  left  sides  are  attached  along  the  dorsal  line 
of  the  neck  to  the  ligamentum  nuchas,  while  along  the  ventral  line  they  meet  in  a 
fibrous  raphe.  A  deep  layer  is  detached  which  passes  underneath  the  cutaneous 
muscle,  bridges  over  the  jugular  furrow,  and  crosses  over  the  deep  face  of  the  brachio- 
cephalicus  and  omo-hyoideus  to  join  the  superficial  layer.  It  again  separates  to 
pass  under  the  cervical  trapezius,  and  become  attached  to  the  ligamentum  nuchse. 
Along  the  ventral  line  a  septum  is  detached  which  separates  the  sterno-cephalici. 
Two  other  layers  in  front  of  the  shoulder  enclose  the  prescapular  lymph-glands. 

The  deep  fascia  also  forms  two  layers.  The  superficial  layer  is  attached  to 
the  wing  of  the  atlas  and  the  ventral  edge  of  the  longissimus  capitis  et  atlantis  and 
scalenus.  Passing  downward  it  encloses  the  trachea,  and,  together  with  the  deep 
layer,  furnishes  sheaths  for  the  vagus  and  sympathetic  nerves  and  the  carotid 
artery.  Passing  upward  it  detaches  septa  between  the  extensor  muscles  of  the  spine. 
Anteriorly  it  covers  the  thyroid  gland,  the  guttural  pouch,  the  adjacent  vessels  and 
nerves,  and  the  larynx,  and  is  attached  to  the  mastoid  process  of  the  temporal  bone 
and  the  thyroid  cornel  of  the  hyoid  bone.  Posteriorly  it  is  attached  to  the  first 
rib  and  the  cariniform  cartilage  of  the  sternum.  The  deep  layer  (prevertebral 
fascia)  covers  the  ventral  surface  of  the  longus  colli,  and  encloses  the  trachea  and 
oesophagus.  Anteriorly  it  forms,  with  the  corresponding  layer  of  the  opposite 
side,  a  septum  between  the  guttural  pouches;  posteriorly  it  becomes  continuous 
with  the  endothoracic  fascia.  A  fascia  propria  forms  a  tubular  sheath  around  the 
trachea,  enclosing  also  the  recurrent  nerves. 


VENTRAL  CERVICAL  MUSCLES 

This  group  consists  of  twelve  pairs  of  muscles  which  lie  ventral  and  lateral  to 
the  vertebrae. 

1.  Cutaneus  colli. — This  has  been  described  (p.  254). 

2.  Brachiocephalicus. — This  is  described  on  p.  294. 

3.  Stemo-cephalicus.i — This  is  a  long,  narrow  muscle  which  extends  along  the 
ventral  and  lateral  aspects  of  the  trachea  from  the  sternum  to  the  angle  of  the  jaw. 
It  forms  the  ventral  boundary  of  the  jugular  furrow. 

^  This  muscle  is  probably  the  homologue  of  the  sternal  part  of  the  sterno-cleido-mastoid 
of  man.  On  account  of  the  differences  in  its  insertion  in  the  various  animals,  it  seems  desirable 
to  adopt  the  name  sterno-cephalicus.  It  is  also  known  as  the  sterno-mandibularis  or  sterno- 
maxillaris. 


VENTRAL    CERVICAL   MUSCLES 


267 


Origin .  — The  cariniform  cartilage  of  the  sternum. 
Insertion. — The  posterior  border  of  the  ramus  of  the  mandible. 
Action. — Acting  together,  to  flex  the  head  and  neck;    acting  singly,  to  incUne 
the  head  and  neck  to  the  side  of  the  muscle  contracting. 

Structure. — The  two  muscles  are  fused  at  their  origin,  which  is  fleshy.     Near 


A 


V 


r    ' 


Fig.  266. — Antero-lateral  View  of  Muscles  and  Skeleton  of  Horse. 
a,  Trapezius;  c,  brachiocephalicus;  d,  sterno-cephalicus;  /,  long  head  of  triceps;  /',  lateral  head  of  triceps; 
g,  anterior  superficial  pectoral  muscle;  g',  posterior  superficial  pectoral;  h' ,  anterior  deep  pectoral;  i),  cutaneus  colli; 
z,  supraspinatus;  29,  omo-hyoideus;  30,  steruo-th>TO-hyoideus;  31,  jugular  vein;  32,  cephalic  vein;  1,  scapula; 
7',  cartilage  of  scapula;  ;?,  spine  of  scapula;  4.  shaft  of  humerus;  4'  lateral  epicondyle;  5,  lateral  tuberosity  of  humerus; 
e,  deltoid  tuberosity;  74,  ventral  border  ("keel")  of  sternum;  i^'.  cariniform  cartilage;  7. iJ.,  first  rib.  (After  Ellen- 
berger-Baum,  Anat.  fiir  Kiinstler.) 


the  middle  of  the  neck  they  separate,  and,  becoming  narrower  and  thinner,  each 
muscle  passes  under  the  parotid  gland  and  terminates  by  a  flat  tendon.  The  latter 
is  connected  by  a  thin  aponeurosis  with  that  of  the  brachiocephalicus. 

Relations. — Superficially,  the  cutaneous  muscle;  deeply,  the  sterno-thyro- 
hyoideus  and  omo-hyoideus  muscles.  The  dorsal  edge  of  the  muscle  is  related  to 
the  jugular  vein,  which  lies  in  the  jugular  furrow.     The  carotid  artery,  the  vagus, 


268  FASCIA    AND    MUSCLES    OF    THE    HORSE 

sjTnpathetic,  and  recurrent  nerves  also  lie  along  the  upper  edge  at  the  root  of  the 
neck.  The  tendon  passes  under  the  external  maxillary  vein  and  the  parotid  gland, 
having  the  mandibular  gland  and  occipito-mandibularis  muscle  on  its  medial  side. 

Blood-supply. — Carotid  artery. 

Nerve-supply. — Ventral  branch  of  the  spinal  accessor}'  nerve. 

4.  Stemo-thyro-hyoideus  (Sterno-thyreoideus  et  sterno-hyoideus). — This  is  a 
long,  slender,  digastric  muscle,  applied  to  the  ventral  surface  of  the  trachea  and 
its  fellow  of  the  opposite  side. 

Origin. — The  cariniform  cartilage  of  the  sternum. 

Insertion. — (1)  A  prominence  on  the  posterior  border  of  the  lamina  of  the  thy- 
roid cartilage  of  the  larynx  at  the  ventral  end  of  the  oblique  line;  (2)  the  body 
and  lingual  process  of  the  hyoid  bone. 

Action. — To  retract  and  depress  the  hyoid  bone,  the  base  of  the  tongue,  and 
the  larynx,  as  in  deglutition.  It  may  also  fix  the  hyoid  bone  when  the  depressors 
of  the  tongue  are  acting,  as  in  sucking. 

Structure. — The  origin  of  the  muscle  is  fleshy,  and  as  far  as  the  middle  of  the 
neck,  it  blends  with  its  fellow.  The  common  belly  is  then  interrupted  by  a  tendon, 
or  sometimes  two  tendons,  from  which  arise  three  or  four  fleshj^  bands.  The  lat- 
eral small  bands  (Sterno-thyroidei)  diverge  to  reach  their  insertion  into  the  thy- 
roid cartilage  by  a  delicate  tendon;  while  the  medial  and  larger  bands  (Sterno- 
hyoidei),  closely  applied  to  each  other  and  blending  with  the  omo-hyoideus,  pass 
straight  forward  to  reach  the  ventral  surface  of  the  hyoid  bone. 

Relations. — At  the  root  of  the  neck  the  common  belly  is  related  ventrall}'  to 
the  sterno-cephalicus,  and  the  carotid  arteries  and  recurrent  nerves  dorsally. 
Further  forward  the  trachea  becomes  the  dorsal  relation,  and  near  the  head  the 
omo-hyoideus,  skin  and  fascia,  the  ventral  one. 

Blood-supply. — Carotid  artery. 

Nerve-supply. — Ventral  branches  of  the  first  and  second  cervical  nerves. 

5.  Omo-hyoideus.^ — This  is  a  thin,  ribbon-like  muscle,  almost  entirely  fleshy, 
which  crosses  the  trachea  very  obliquel}^ 

Origin. — The  subscapular  fascia  close  to  the  shoulder  joint. 

Insertion. — The  body  and  adjacent  part  of  the  lingual  process  of  the  hyoid 
bone,  in  common  with  the  hyoid  branch  of  the  preceding  muscle. 

Action.- — To  retract  the  hyoid  bone  and  the  root  of  the  tongue. 

Structure. — The  muscle  is  composed  of  parallel  fleshy  fibers,  except  at  its  origin, 
where  it  has  a  thin  tendon. 

Relations. — The  posterior  part  of  the  muscle  is  related  laterally  to  the  supra- 
spinatus,  anterior  deep  pectoral,  and  brachiocephalicus  and  the  prescapular  lymph- 
glands;  and  medially  to  the  scalenus.  It  is  intimately  adherent  to  the  brachio- 
cephalicus. In  the  middle  of  the  neck  it  is  related  superficially  to  the  brachio- 
cephalicus, sterno-cephalicus,  and  the  jugular  vein;  deeply,  to  the  rectus  capitis 
ventralis  major,  the  carotid  artery,  the  vagus,  sympathetic,  and  recurrent  nerves, 
the  trachea,  and,  on  the  left  side,  the  oesophagus.  In  its  anterior  part  the  muscle 
blends  with  the  sterno-hyoideus,  the  two  covering  the  sterno-thyroideus,  the  thy- 
roid gland  in  part,  and  the  ventral  face  of  the  larynx. 

Blood-supply. — Carotid  and  inferior  cervical  arteries. 

Nerve-supply. — Ventral  l^ranch  of  the  first  cervical  nerve. 

6.  Scalenus  (M.  scalenus  primse  costae).^ — This  muscle  is  deeply  situated  on 
the  side  of  the  posterior  half  of  the  neck.  It  is  composed  of  two  parts,  between 
which  the  cervical  roots  of  the  brachial  plexus  of  nerves  emerge. 

Origin. — The  anterior  border  and  lateral  surface  of  the  first  rib. 
Insertion. — (1)  The  dorsal  (smaller)  part  (M.  scalenus  dorsalis)  is  attached  to 
the  transverse  process  cf  the  seventh  cervical  vertebra;    (2)  the  ventral  part  (M. 
1  Also  termed  the  subscapulo-hyoideus. 


VENTRAL    CERVICAL   MUSCLES  269 

scalenus  ventralis)  is  attached  to  the  transverse  processes  of  the  sixth,  fifth,  and 
fourth  cervical  vertebrae. 

Action. — The  neck  is  flexed  or  inclined  laterally,  according  as  the  muscles  act 
together  or  singly.  If  the  neck  be  the  fixed  point,  the  muscle  may  have  a  respira- 
tory action  by  pulling  forward  or  fixing  the  first  rib. 

Structure. — The  dorsal  part  is  composed  of  several  small  fleshy  bundles.  The 
ventral  portion,  which  is  much  larger,  is  almost  entirely  fleshy,  and  not  so  divided. 

Relations. — Superficially,  the  anterior  deep  pectoral,  brachiocephalicus,  and 
omo-hyoideus  muscles,  the  phrenic  nerve,  and  branches  of  the  brachial  plexus; 
deeply,  the  vertebrae,  the  longus  colli  and  intertransversales  muscles,  the  oesoph- 
agus (on  the  left  side),  the  trachea  (on  the  right  side),  the  vertebral  vessels, 
the  vagus,  sympathetic,  and  recurrent  nerves.  The  roots  of  the  brachial  plexus 
form  a  flat  anastomosis,  which  lies  between  the  two  parts  of  the  muscle.  The 
brachial  vessels  cross  the  ventral  edge  close  to  the  first  rib. 

Blood-supply. — Carotid,  vertebral,  and  inferior  cervical  arteries. 

Nerve- supply. — Ventral  branches  of  the  cervical  nerves. 

7.  Cervicalis  ascendens.^ — This  muscle  is  the  cervical  continuation  of  the 
longissimus  costarum,  and  is  sometimes  regarded  as  a  part  of  the  scalenus,  with 
which  it  is  partially  united.  It  consists  of  three  or  four  bundles  which  are  attached 
to  the  transverse  processes  of  the  last  three  or  four  cervical  vertebrae  and  the  first 
rib. 

Action. — To  extend  the  neck  or  to  flex  it  laterally. 

Relations. — Superficially,  the  brachiocephalicus  and  anterior  deep  pectoral; 
deeply,  the  scalenus  and  intertransversales. 
Blood-supply. — Vertebral  artery. 
Nerve-supply. — Cervical  nerves. 

8.  Rectus  capitis  ventralis  major  (M.  longus  capitis). — This  is  the  largest 
of  the  three  special  flexors  of  the  head,  and  lies  along  the  ventro-lateral  surface 
of  the  anterior  cervical  vertebrae  and  the  base  of  the  cranium. 

Origin. — The  transverse  processes  of  the  fifth,  fourth,  and  third  cervical  ver- 
tebrae. 

Insertion. — The  tubercles  at  the  junction  of  the  basilar  part  of  the  occipital 
bone  with  the  body  of  the  sphenoid. 

Action. — Acting  together,  to  flex  the  head;  acting  singly,  to  incline  it  to  the 
same  side  also. 

Structure. — ^The  origin  of  the  muscle  is  by  fleshy  digitations.  The  belly  in- 
creases in  size  by  the  union  of  these  digitations,  reaching  its  maximum  at  the  axis. 
It  then  diminishes,  passes  toward  the  median  plane,  and  terminates  on  a  rounded 
tendon. 

Relations. — Superficially,  the  brachiocephalicus  and  omo-hyoideus,  the  mandib- 
ular gland,  the  carotid  artery  (which  lies  along  the  ventral  border),  the  occipital 
and  internal  carotid  arteries,  and  the  tenth,  eleventh,  and  sympathetic  nerves; 
deeply,  the  vertebrae,  the  longus  colli,  intertransversales,  and  the  rectus  capitis 
ventralis  minor.  The  terminal  part  of  the  muscle  lies  in  contact  with  its  fellow 
above  the  pharynx  and  between  the  guttural  pouches. 

Blood-supply. — Carotid,  vertebral,  and  occipital  arteries. 

Nerve-supply. — Ventral  branches  of  the  cervical  nerves. 

9.  Rectus  capitis  ventralis  minor  (M.  rectus  capitis  ventralis). — This  is  a  small 
muscle  which  lies  dorsal  to  and  under  cover  of  the  preceding  one. 

Origin.- — The  ventral  arch  of  the  atlas. 

Insertion. — The  basilar  part  of  the  occipital  bone,  close  to  the  preceding  muscle. 

Action. — To  flex  the  atlanto-occipital  articulation. 

Structure. — Fleshy . 

1  This  muscle  is  also  known  as  the  ilio-costalis  cervicis. 


270  FASCIA   AND   MUSCLES    OF   THE    HORSE 

Relations. — Ventrally,  to  the  preceding  muscle;  dorsall}-,  to  the  atlas,  atlanto- 
occipital  articulation,  and  the  basilar  part  of  the  occipital  bone;  laterally,  to  the 
rectus  capitis  lateralis  and  the  guttural  pouch. 

Blood-supply. — Occipital  artery. 

Nerve-supply. — Ventral  branch  of  the  first  cervical  nerve. 

10.  Rectus  capitis  lateralis. — This  is  a  still  smaller  muscle,  which  lies  for  the 
most  part  under  the  obliquus  capitis  anterior. 

Origin. — The  atlas,  lateral  to  the  preceding  muscle. 
Insertion. — The  paramastoid  process  of  the  occipital  bone. 
Action. — The  same  as  the  preceding  muscle. 
Structure. — Fleshy. 

Relations. — Superficially,  the  obliquus  capitis  anterior,  the  occipital  vessels, 
and  the  ventral  branch  of  the  first  cervical  nerve. 
Blood-supply. — Occipital  artery. 
Nerve-supply. — Ventral  branch  of  the  first  cervical  nerve, 

11.  Longus  colli. — This  muscle  covers  the  ventral  surfaces  of  the  vertebrae, 
from  the  sixth  thoracic  to  the  atlas,  and  is  united  with  its  fellow.  It  consists  of 
two  parts,  thoracic  and  cervical. 

Origin. — (1)  Thoracic  part,  the  bodies  of  the  first  six  thoracic  vertebrae;  (2) 
cervical  part,  the  transverse  processes  of  the  cervical  vertebrae. 

Insertion. — (1)  Thoracic  part,  the  bodies  and  transverse  processes  of  the  last 
two  cervical  vertebrae;  (2)  cervical  part,  the  bocUes  of  the  cervical  vertebrae  and 
the  ventral  tubercle  of  the  atlas. 

Action. — To  flex  the  neck. 

Structure. — The  muscle  is  composed  of  a  succession  of  bundles.  The  largest 
of  these  constitute  the  thoracic  part  of  the  muscle,  which  has  a  strong  tendon  in- 
serted into  the  last  two  cervical  vertebrae.  A  bursa  is  interposed  between  the  ten- 
don and  the  spine  at  the  first  costo-vertebral  articulation.  The  cervical  part  con- 
sists of  a  number  of  smaller  bundles,  each  of  which  passes  from  its  origin  on  the 
transverse  process  of  one  vertebra  forward  and  medially  to  its  insertion  into  a  ver- 
tebra further  forward.  The  most  anterior  bundle  is  inserted  by  a  strong  tendon  into 
the  ventral  tubercle  of  the  atlas. 

Relations. — The  principal  relations  of  the  two  muscles  in  the  thorax  are: 
ventrally,  the  pleura,  and,  further  forward,  the  trachea  and  oesophagus;  dorsally, 
the  vertebrae  and  the  costo-vertebral  joints;  laterally,  the  dorsal,  deep  cervical, 
and  vertebral  vessels,  the  sympathetic  nerve,  and  the  thoracic  roots  of  the  brachial 
plexus.  In  the  neck  important  relations  are:  ventrally,  the  trachea  and  oesophagus, 
the  carotid  artery,  the  vagus,  sympathetic,  and  recurrent  nerves;  dorsally,  the 
vertebrae  and,  in  the  middle  third  of  the  neck,  the  intertransversales  muscles;  lat- 
erally, the  scalenus,  the  rectus  capitis  ventralis  major,  and  the  intertransversales 
(in  the  anterior  third).  The  terminal  part  of  the  muscle  is  separated  from  the 
trachea  by  the  oesophagus,  which  is  here  median  in  position. 

Blood-supply. — Subcostal  and  vertebral  arteries. 

Nerve-supply. — Ventral  branches  of  the  spinal  nerves. 

12.  Intertransversales  colli  (Mm.  intertransversarii  cervicis). — These  are  six 
fasciculi  which  occupy  the  spaces  between  the  lateral  aspects  of  the  vertebrae  and 
the  transverse  and  articular  processes.  There  is  thus  a  bundle  for  each  inter- 
vertebral articulation  except  the  first.  Each  bundle  consists  of  a  dorsal  and  ven- 
tral part. 

Attachments. — The  dorsal  bundles  pass  from  transverse  process  to  articular 
process;  the  ventral  bundles  extend  between  adjacent  transverse  processes. 
Action. — To  flex  the  neck  laterally. 

Structure. — They  contain  strong  tendinous  intersections. 
Relations. — Superficially,  the  brachiocephalicus,  rectus  capitis  ventralis  ma- 


LATERAL   CERVICAL   MUSCLES  271 

jor,  obliquus  capitis  posterior,  complexus,  longissimus  capitis  et  atlantis,  splenius, 
scalenus,  and  longissimus  dorsi  et  costarum  muscles;  deeply,  the  vertebrae,  the 
longus  colli  muscle,  and  the  vertebral  vessels.  The  muscles  are  perforated  by 
branches  of  these  vessels  and  by  the  primary  branches  of  the  cervical  nerves. 

Blood-supply. — Vertebral  artery. 

Nerve-supply. — The  cervical  nerves. 

LATERAL  CERVICAL  MUSCLES 
This  group  consists  of  twelve  pairs  of  muscles  arranged  in  layers. 

First  Layer 

1.  Trapezius  cervicalis. — Described  on  p.  293. 

Second  Layer 

2.  Rhomboideus  cervicalis. — Described  on  p.  293. 

3.  Serratus  cervicis. — Described  on  p.  297. 

Third  Layer 

4.  Splenius. — This  is  an  extensive,  fiat,  triangular  muscle,  partly  covered  by 
the  preceding  three  muscles. 

Origin. — The  second,  third,  and  fourth  thoracic  spines  by  means  of  the  dorso- 
scapular  ligament  and  the  funicular  part  of  the  ligamentum  nucha?. 

Insertion. — The  nuchal  crest,  the  mastoid  process,  the  wing  of  the  atlas, 
and  the  transverse  processes  of  the  third,  fourth,  and  fifth  cervical  vertebrse. 

Action. — Acting  together,  to  elevate  the  head  and  neck;  acting  singly,  to  in- 
cline the  head  and  neck  to  the  side  of  the  muscle  acting. 

Structure. — The  muscle  arises  in  the  withers  from  the  anterior  part  of  the 
dorso-scapular  ligament,  which  also  affords  attachment  to  the  rhomboideus,  ser- 
ratus dorsalis,  and  complexus  muscles.  The  fibers  pass  upward  and  forward 
toward  the  head  and  the  first  cervical  vertebra.  The  insertion  on  the  occipital 
bone  and  the  mastoid  process  is  by  means  of  a  thin  aponeurosis  common  to  the 
brachiocephalicus  and  longissimus  capitis.  The  atlantal  insertion  is  by  a  strong, 
flat  tendon,  in  common  with  the  longissimus  atlantis  and  the  brachiocephalicus. 
The  remaining  insertions  are  fleshy  digitations. 

Relations. — Superficially,  the  skin  and  fascia,  the  trapezius,  rhomboideus 
cervicalis,  serratus  ventralis,  and  posterior  auricular  muscles'  deeply  the  com- 
plexus and  longissimus  dorsi  muscles. 

Blood-supply. — Deep  cervical  and  dorsal  arteries. 

Nerve-supply. — Dorsal  branches  of  the  last  six  cervical  nerves. 

Fourth  Layer 

5.  Longissimus  capitis  et  atlantis.^ — This  muscle  consists  of  two  parallel,  fusi- 
form portions.  It  lies  between  the  deep  face  of  the  splenius  and  the  ventral  part 
of  the  complexus. 

Origin. — (1)  The  transverse  processes  of  the  first  two  thoracic  vertebrse;  (2) 
the  articular  processes  of  the  cer'Mcal  vertebrse. 

Insertion.- — (1)  The  mastoid  process;   (2)  the  wing  of  the  atlas. 

^di'on.— Acting  together,  to  extend  the  head  and  neck;  acting  singly,  to  flex 
the  head  and  neck  laterally  or  to  rotate  the  atlas. 

Structure. — The  origin  from  the  thoracic  vertebrse  is  by  aponeurotic  slips 
which  blend  with  the  complexus.  The  succeeding  fleshy  part,  in  passing  along 
lAIso  termed  the  trachelo-mastoideus. 


272 


FASCIA   AND    MUSCLES    OF   THE    HORSE 


the  neck,  receives  fasciculi  from  each  of  the  cervical  vertebra  except  the 
first  two.  The  dorsal  division  of  the  muscle  (M.  longissimus  capitis)  is 
inserted  into  the  mastoid  process  by  a  flat  tendon  which  fuses  with  that  of 
the  splenius;  the  ventral  division  (M.  longissimus  atlantis)  is  inserted  into  the 


LATERAL   CERVICAL   MUSCLES  273 

wing  of  the  atlas  by  a  ribbon-like  tendon  in  common  with  the  splenius  and 
brachiocephalicus. 

Relations. — Superficially,  the  splenius  muscle  and  dorsal  branches  of  the 
cervical  nerves;  deeply,  the  complexus,  the  spinalis  colli,  and  the  oblique  muscles 
of  the  head.  The  deep  cervical  vessels  cross  the  deep  face  of  the  muscle  obliquely 
at  the  level  of  the  sixth  and  seventh  cervical  vertebrae. 

Blood-supply. — Vertebral  and  deep  cervical  arteries. 

Nerve-supply. — Dorsal  branches  of  the  last  six  cervical  nerves. 

6.  Complexus  (M.  semispinalis  capitis). — This  is  a  large  triangular  muscle 
which  lies  chiefly  on  the  ligamentum  nuchse,  under  cover  of  the  splenius. 

Origin. — (1)  The  second,  third,  and  fourth  thoracic  spines,  in  common  with 
the  splenius  and  serratus  dorsalis;  (2)  the  transverse  processes  of  the  first  six  or 
seven  thoracic  vertebrae ;    (3)  the  articular  processes  of  the  cervical  vertebrae. 

Insertion. — A  rough  area  on  the  occipital  bone  just  ventral  to  the  nuchal  crest. 

Action. — It  is  the  chief  extensor  of  the  head  and  neck.  Acting  singly,  the 
muscle  inclines  the  head  to  the  same  side. 

Structure. — The  origin  of  the  muscle  at  the  withers  is  aponeurotic.  In  the 
neck  the  bundles  arising  from  the  articular  processes  run  obliquely  upward 
and  forward,  giving  the  lower  part  of  the  muscle  a  distinct  pennate  character. 
The  dorsal  part  of  the  belly  is  crossed  obliquely  by  four  or  five  tendinous 
intersections.     The  insertion  is  by  a  strong  tendon. 

Relations. — Superficially,  the  rhomboideus,  serratus  ventralis,  splenius,  and 
longissimus  capitis  et  atlantis;  deeply,  the  ligamentum  nuchae,  the  multifidus 
cervicis,  longissimus  dorsi,  and  the  oblique  and  dorsal  straight  muscles  of  the  head, 
the  deep  cervical  vessels,  and  the  dorsal  cutaneous  branches  of  the  cervical  nerves. 

Blood-supply. — Deep  cervical,  vertebral,  and  occipital  arteries. 

Nerve-supply. — Dorsal  branches  of  the  last  six  cervical  nerves. 

7.  Multifidus  cervicis. — This  muscle  lies  on  the  arches  of  the  last  five  cervical 
vertebrae.     It  consists  of  five  or  six  segments. 

Origin. — The  articular  processes  of  the  last  four  or  five  cervical  and  the  first 
thoracic  vertebrae. 

Insertion. — The  spinous  and  articular  processes  of  the  cervical  vertebrae. 

Action. — Acting  together,  to  extend  the  neck;  acting  singly,  to  flex  the  neck  on 
the  side  of  the  muscle  contracting  and  to  rotate  the  neck  to  the  opposite  side. 

Structure. — The  muscle  is  composed  of  two  sets  of  bundles.  The  superficial 
bundles  are  directed  obliquely  forward  and  inward,  each  passing  from  an  articular 
process  to  the  spine  of  the  preceding  vertebra.  The  deep  bundles  are  shorter  and 
run  straight  from  an  articular  process  to  that  of  the  preceding  vertebra. 

Relations.- — Superficially,  the  complexus,  longissimi,  and  obliquus  capitis  poster- 
ior; deeply,  the  spinalis,  the  ligamentum  nuchae,  and  the  arches  of  the  vertebrae. 

Blood-supply. — Deep  cervical  and  vertebral  arteries. 

Nerve-supply. — Dorsal  branches  of  the  last  six  cervical  nerves. 

8.  Spinalis. — Described  with  the  longissimus  on  p.  278. 

9.  Obliquus  capitis  posterior  (s.  caudalis) .— This  is  a  strong,  quadrilateral 
muscle,  which  covers  the  dorso-lateral  aspect  of  the  atlas  and  axis. 

Origin. — The  side  of  the  spine  and  the  posterior  articular  process  of  the  axis. 

Insertion. — The  dorsal  surface  of  the  wing  of  the  atlas. 

Action. — Chiefly  to  rotate  j^fe  atlas,  and  with  it  the  head,  to  the  same  side; 
also  to  assist  in  extending  and  fixing  the  atlanto-axial  joint. 

Structure. — The  muscle  is  composed  almost  entirely  of  parallel  fleshy  fibers 
directed  obliquely  forward  and  outward.     It  is  covered  by  a  special  fascia. 

Relations. — Superficially,  the  splenius,  complexus,  longissimus  capitis,  and 
brachiocephalicus  muscles;  deeply,  the  arch  and  spine  of  the  axis,  the  wing  of 
the  atlas,  the  atlantoaxial  joint,  the  rectus  capitis  dorsalis  minor,  the  occipital  and 
18 


274 


FASCIA   AND    MUSCLES    OF   THE    HORSE 


vertebral  vessels,  and  the  first  and  second  cervical  nerves.  The  terminal  part  of 
the  vertebral  arterj^  joins  the  posterior  branch  of  the  occipital  artery  under  cover 
of  the  muscle. 

Blood-supply. — Occipital  and  vertebral  arteries. 


m  no  °^ 
3  3  9 
m     C   ■*! 


iiJI'lli 


I  ".  s  -^- 


O     05      O    — 
^    I3J    73    H 


LATERAL    CERVICAL   MUSCLES 


275 


Nerve-supply. — Dorsal  branch  of  the  second  cervical  nerve. 

10.  Obliquus  capitis  anterior  (s.  craniahs). — This  short,  thick,  quadrilateral 
muscle  lies  on  the  side  of  the  atlantooccipital  articulation. 

Origin. — The  anterior  edge  and  ventral  surface  of  the  vnng  of  the  atlas. 

Insertion. — The  paramastoid  process  and  nuchal  crest  of  the  occipital  bone 
and  the  mastoid  process. 

Action. — Acting  together,  to  extend  the  head  on  the  atlas;  acting  singly,  to 
flex  the  head  laterally. 

Structure. — The  muscle  contains  a  good  deal  of  tendinous  tissue.  The  direction 
of  its  fibers  is  forward,  upward,  and  inward. 


Fig.  269. — Deepest  Layer  of  Muscles  of  Neck  of  House. 
a,  Obliquus  capitis  anterior;  b,  obliquus  capitis  posterior;  c,  rectus  capitis  lateralis;  d,  rectus  capitis  ventralia 
minor;  e,  rectus  capitis  ventralis  major;  /,  longus  colli;  s,  s',  scalenus;  A,  longissimus  costarum;  j,  longissimus  dorsi; 
fc,  spinalis  et  semispinalis;  ?,  multifidus  dorsi ;  m,  multifidus  cervicis;  n,  intertransversales;  o,  o',  rectus  capitis  dorsalis 
major;  p,  rectus  capitis  dorsalis  minor;  q,  tendon  of  insertion  of  complexus;  1,  lamellar  part,  1',  funicular  part  of  liga- 
mentum  nuchae;  2,  nuchal  crest;  3,  paramastoid  process;  4.  edge  of  wing  of  atlas;  o,  transverse,  and  6,  articular, 
processes  of  cervical  vertebrae;   7,  nerves  of  brachial  plexus  (cut) ;   S,  first  rib.    (Ellenberger-Baum,  Anat.  d.  Haustiere.) 


Relations. — Superficially,  the  complexus,  the  aponeurosis  of  the  splenius,  longus 
capitis,  and  brachiocephalicus,  overlying  which  are  the  posterior  auricular  muscles, 
artery,  and  nerve,  and  the  parotid  gland;  deeply,  the  dorsal  straight  muscles, 
the  occipito-hyoideus,  the  atlanto-occipital  articulation,  the  posterior  meningeal 
artery,  and  a  branch  of  the  occipital   nerve. 

Blood-supply.— Occipital  artery. 

Nerve-supply. — Dorsal  branch  of  the  first  cervical  nerve. 

11.  Rectus  capitis  dorsalis  major. — This  muscle  extends  from  the  axis  to  the 
occipital  bone,  in  contact  with  the  ligamentum  nuchse. 

Origin. — The  edge  of  the  spinous  process  of  the  axis. 


276  FASCIA   AND   MUSCLES    OF   THE    HORSE 

Insertion. — The  occipital  bone,  below  the  complexus;  the  tendon  of  insertion 
of  the  complexus. 

Action. — To  extend  the  head. 

Structure. — The  muscle  is  fleshy  and  may  be  divided  into  two  parallel  parts, 
superficial  and  deep.  The  former  blends  somewhat  with  the  terminal  part  of  the 
complexus.  The  deep  part  may  be  termed  the  rectus  capitis  dorsalis  medius. 
Bundles  frequently  arise  from  the  fascia  over  the  obliquus  capitis  posterior. 

Relations. — Superficially,  the  obliquus  capitis  anterior,  splenius,  and  com- 
plexus; medially,  the  ligamentum  nuchse;  deeply,  the  atlas,  the  atlanto-occipital 
articulation,  and  the  rectus  capitis  dorsalis  minor.  The  dorsal  branch  of  the  first 
cervical  nerve  appears  between  this  muscle  and  the  obliquus  capitis  anterior. 

Blood-supply. — Occipital  artery. 

Nerve-supply. — Dorsal  branch  of  the  first  cervical  nerve. 

12.  Rectus  capitis  dorsalis  minor. — This  small  muscle  lies  under  cover  of  the 
preceding. 

Origin. — The  dorsal  surface  of  the  atlas. 

Insertion. — The  occipital  bone  beneath  the  preceding  muscle  and  lateral  to  the 
funicular  part  of  the  ligamentum  nuchse. 

Action. — To  assist  the  preceding  muscle. 

Structure. — It  is  fleshy  and  varies  a  good  deal  in  volume,  being  sometimes 
small  and  difficult  to  recognize.^     On  the  other  hand,  it  is  sometimes  double. 

Relations. — Superficially,  the  preceding  muscle  and  the  obliquus  capitis  an- 
terior;  deeply,  the  atlas  and  the  atlanto-occipital  articulation. 

Blood-supply. — Occipital  artery. 

Nerve-supply. — Dorsal  branch  of  the  first  cervical  nerve. 


The  Fascije  and  Muscles  of  the  Back  and  Loins 

(fascia  et  musculi  dorsi  et  lumborum) 

The  superficial  fascia  presents  no  special  features.  The  lumbo-dorsal  fascia 
(Fascia  lumbo-dorsalis)  closely  invests  the  muscles,  but  is  easily  stripped  off  the 
longissimus.  It  is  attached  medially  to  the  supraspinous  ligament  and  the  spinous 
processes  of  the  vertebrae;  it  divides  laterally  into  two  layers.  The  superficial 
layer  is  practically  the  aponeurosis  of  the  latissimus  dorsi.  The  deep  layer  gives 
origin  to  the  serratus  dorsalis,  the  lumbar  part  of  the  obliquus  abdominis  externus, 
the  transversus  abdominis,  and  the  retractor  costae.  Its  lateral  edge  curves  under 
the  longissimus  and  is  attached  to  the  ribs  and  lumbar  transverse  processes.  Pos- 
teriorly it  is  continuous  with  the  gluteal  fascia.  At  the  withers  it  forms  an  impor- 
tant structure,  the  dorso-scapular  ligament.  This  is  a  strong  tendinous  sheet, 
attached  to  the  third,  fourth,  and  fifth  thoracic  spines.  Its  upper  part  is  very 
thick  and  gives  origin  by  its  superficial  surface  to  the  rhomboideus  thoracalis,  by 
its  anterior  part  to  the  splenius.  The  lower  part  is  thin  and  elastic,  and  furnishes 
numerous  lamellae  which  intersect  the  scapular  part  of  the  serratus  ventralis  and 
are  attached  to  the  scapula.  Three  lamellae  are  detached  from  the  ligament. 
The  deepest  of  these  passes  between  the  longissimus  and  spinalis  and  is  attached  to 
the  transverse  processes  of  the  first  seven  thoracic  vertebrae;  it  gives  attachment 
to  the  complexus.  The  middle  one  dips  in  between  the  longissimus  dorsi  and 
longissimus  costarum.  The  superficial  one  gives  origin  to  the  serratus  dorsalis. 
A  strong  fascial  layer,  the  ilio-lumbar  ligament,  extends  from  the  last  rib  to  the 
tuber  coxae. 

There  are  nine  pairs  of  muscles  in  this  region,  arranged  in  four  layers. 

^  This  seems  due  to  pressure  produced  by  pathological  changes  in  the  supra-atloid  bursa, 
which  are  frequently  extensive  in  dissecting-room  subjects. 


the  fascia  and  muscles  of  the  back  and  loins  277 

First  Layer 

1.  Trapezius  thora  calls. 

2.  Latlsslmus  dorsl. 

Second  Layer 

3.  Rhomboldeus  thoracalls. 

The  foregoing  are  described  with  the  other  muscles  which  attach  the  thoracic 
limb  to  the  trunk  (p.  293). 

4.  Serratus  dorsalis  anterior  (s.  cranialis). — This  is  a  thin  quadrilateral  muscle, 
named  from  its  serrated  ventral  border.  It  lies  under  cover  of  the  rhomboideus, 
serratus  ventralis,  and  latissimus  dorsi. 

Origin. — The  lumbo-dorsal  fascia  and  dorso-scapular  ligament. 

Insertion. — The  lateral  surfaces  of  the  fifth  or  sixth  to  the  eleventh  or  twelfth 
ribs  inclusive. 

Action. — To  draw  the  ribs  on  which  it  is  inserted  forward  and  outward,  thus 
assisting  in  inspiration. 

Structure. — The  muscle  arises  by  means  of  a  thin  aponeurosis.  The  muscle- 
fibers  pass  ventrally  and  backward  to  be  attached  to  the  ribs  by  seven  or  eight 
digitations  below  the  lateral  edge  of  the  longissimus  costarum. 

Relations. — Superficially,  the  rhomboideus,  serratus  ventralis,  latissimus  dorsi, 
and  serratus  dorsalis  posterior;  deeply,  the  longissimus  dorsi,  longissimus  costarum, 
external  intercostal  muscles,  and  the  ribs. 

Blood-supply. — Intercostal  arteries. 

Nerve-supply. — Thoracic  nerves. 

5.  Serratus  dorsalis  posterior  (s.  caudalis). — This  muscle  resembles  the  pre- 
ceding one,  which  it  partly  covers. 

Origin. — The  lumbo-dorsal  fascia. 

Insertion. — The  lateral  surfaces  of  the  last  seven  or  eight  ribs. 

Action. — To  draw  the  ribs  backward,  thus  assisting  in  expiration. 

Structure. — Similar  to  the  preceding  muscle.  The  fibers  are  directed  ventrally 
and  forward  and  terminate  in  seven  or  eight  digitations,  one  or  two  of  which  cover 
the  posterior  teeth  of  the  anterior  muscle.  The  aponeurosis  blends  with  that  of 
the  latissimus  dorsi. 

Relations. — Superficially,  the  latissimus  dorsi  and  external  oblique;  deeply, 
the  longissimus  dorsi,  longissimus  costarum,  external  intercostals,  serratus  dorsalis 
anterior,  and  the  ribs. 

Blood-supply. — Intercostal  and  lumbar  arteries. 

Nerve-supply. — Thoracic  nerves. 

Third  Layer 

6.  Longissimus  costarum.^ — This  long,  segmental  muscle  extends  across  the 
series  of  ribs,  in  contact  with  the  outer  edge  of  the  longissimus  dorsi. 

Origin. — (1)  The  deep  layer  of  the  lumbo-dorsal  fascia  as  far  back  as  the  third 
or  fourth  lumbar  transverse  process.  (2)  The  anterior  borders  and  lateral  surface 
of  the  last  fifteen  ribs.^ 

Insertion. — The  posterior  borders  of  the  ribs  and  the  transverse  processes  of 
the  last  cervical  vertebra. 

Action. — Chiefly  to  depress  and  retract  the  ribs  and  so  help  in  expiration. 

1  This  muscle  is  also  known  as  the  long  costal,  ilio-costaUs,  or  transversalis  costarum.  The 
name  given  above  was  introduced  by  the  International  Commission  for  the  Reform  of  Myological 
Nomenclature  and  appears  worthy  of  general  adoption. 

2  The  lumbar  part  of  this  muscle  is  subject  to  variation.  It  may,  in  quite  exceptional  case^ 
extend  as  far  as  the  ilium,  and  sometimes,  on  the  other  hand,  it  does  not  arise  quite  as  far  back  as 
given  above.  In  some  subjects  the  origin  can  be  traced  distinctly  to  the  tips  of  lumbar  transverse, 
processes. 


278 


FASCIA   AND   MUSCLES    OF   THE    HORSE 


Acting  together,  they  may  assist  in  extending  the  spine,  acting  singly  in  inchning 
it  laterally. 

Structure. — This  muscle  presents  a  distinct  segmental  arrangement.  It  is 
composed  of  a  series  of  bundles,  the  fibers  of  which  are  directed  forward  and  a  little 
ventro-laterally.  From  these  are  detached  two  sets  of  tendons.  The  superficial 
tendons  spring  from  the  lateral  edge  of  the  muscle.  They  are  flat  and  are  about 
half  an  inch  in  width.  Each  crosses  two  or  three  intercostal  spaces,  to  be  inserted 
on  the  posterior  border  of  a  rib.  The  deep  tendons  are  detached  from  the  dorsal 
part  of  the  deep  face  of  the  muscle.  Each  passes  backward  across  one  or  two  inter- 
costal spaces  to  its  origin  on  the  anterior  border  or  lateral  surface  of  a  rib.     Small 

bursae  may  be  found  between  the  ribs  and 
tendons. 

Relations. — Superficially,  the  dorsal  and 
ventral  serrati;  deeply,  the  external  inter- 
costals  and  the  ribs.  The  lumbar  origin  is 
covered  by  the  longissimus  dorsi.  The  deep 
cervical  and  dorsal  vessels  cross  the  surface  of 
the  muscle  at  the  first  and  second  intercostal 
spaces  respectively,  and  branches  of  the  in- 
tercostal vessels  and  nerves  emerge  between 
it  and  the  longissimus  dorsi;  here  a  fascial 
layer  dips  in  between  the  two. 

Blood-supply. — Intercostal  arteries. 
Nerve-supply. — Dorsal  branches  of  the 
thoracic  nerves. 

7.  Longissimus  dorsi.^ — This  is  the 
largest  and  longest  muscle  in  the  body.  It 
extends  from  the  sacrum  and  ilium  to  the 
neck,  filling  up  the  space  between  the  spinous 
processes  medially  and  the  lumbar  trans- 
verse processes  and  the  upper  ends  of  the 
ribs  ventrally ;  consequently  it  has  the  form 
of  a  three-sided  prism. 

Origin. — (1)  The  tubera,  crest,  and  ad- 
jacent part  of  the  ventral  surface  of  the  ilium ; 
(2)  the  first  three  sacral  spines ;  (3)  the  lum- 
bar and  thoracic  spines  and  the  supraspinous 
ligament. 

Insertion. — (1)  The  lumbar  transverse 
and    articular  processes;    (2)   the    thoracic 
transverse  processes;     (3)  the  spinous  and 
transverse  processes  of  the  last  four   cer- 
vical vertebrae;  (4)  the  lateral  surfaces  of  the  ribs,  except  the  first. 

Action. — Acting  with  its  fellow,  it  is  the  most  powerful  extensor  of  the  back 
and  loins;  by  its  cervical  attachment  it  assists  in  extending  the  neck.  By  its  costal 
attachment  it  may  also  assist  in  expiration.  Acting  singly,  it  flexes  the  spine 
laterally. 

Structure. — This  is  quite  complex.  The  posterior  part  of  the  muscle  is  greatly 
developed  and  constitutes  the  common  mass  of  the  loins.  This  is  covered  by  a 
strong  aponeurosis  which  blends  with  the  supraspinous  and  sacro-iliac  ligaments, 
and  is  attached  to  the  crest  and  sacral  angle  of  the  ilium  and  the  first  and  second 
sacral  spines;    it  furnishes  origin  to  the  lumbar  portion  of  the  middle  gluteus.     In 

'  The  muscle  as  here  described  includes  the  longissimus  dorsi  et  cervicis  and  the  spinalis  and 
semispinalis  components,  as  the  separation  of  these  is  largely  artificial  in  the  horse. 


Fig.  270. — Right  Portion  op  Cross-section  op 
Back  op  Horse.  Section  is  Cut  Through 
Seventh  Thoracic  Vertebra. 
a,  Ligamentum  nuchae;  6,  trapezius  mus- 
cle; c,  cartilage  of  scapula;  d,  latissimus  dorsi;  e, 
cutaneus;  /,  rhomboideus  thoracalis;  g,  ser- 
ratus  ventralis;  h,  serratus  dorsalis;  h',  lumbo- 
dorsal  fascia,  which  divides  below  into  three 
layers;  i,  longissimus  costarum;  k,  levator  costae; 
k',  internal  intercostal  muscle;  I,  longissimus  dorsi; 
m,  m',  seventh  thoracic  vertebra;  n,  head  of 
eighth  thoracic  vertebra;  o,  head  of  eighth  rib; 
p,  seventh  rib;  r,  intercostal  artery  and  nerve;  s, 
skin.  The  fascise  are  indicated  by  dotted  lines. 
(After  Ellenberger,  in  Leisering's  Atlas.) 


THE    FASCIA    AND    MUSCLES    OF   THE   TAIL  279 

its  course  further  forward  the  muscle  receives  fasciculi  from  the  lumbar  and  thoracic 
spines,  but  diminishes  somewhat  in  volume.  About  the  twelfth  thoracic  vertebra 
it  divides  into  two  parts.  The  dorsal  division  (m.  spinalis  et  semispinalis),  rein- 
forced by  bundles  from  the  first  four  thoracic  spines,  passes  forward  under  the  com- 
plexus  to  be  inserted  into  the  spines  of  the  last  four  cervical  vertebrae.  The  ventral 
division  passes  forward  and  downward  underneath  the  serratus  ventralis  to  be  in- 
serted into  the  ribs  and  the  transverse  processes  of  the  last  four  cervical  vertebrae. 
Three  sets  of  fasciculi  may  be  distinguished,  viz. :  (1)  spinal,  which  are  superficial 
and  medial;  (2)  transverse,  attached  to  the  transverse  and  articular  processes, 
which  are  medial  and  deep;   (3)  costal,  which  are  lateral. 

Relations. — Superficially,  the  middle  gluteus,  the  lumbo-dorsal  fascia,  the 
latissimus  dorsi,  serrati  dorsales,  serratus  ventralis,  and  complexus;  deeply,  the 
multifidus,  intertransversales,  external  intercostals,  levatores  costarum,  the  liga- 
mentum  nuchse,  and  its  fellow  of  the  opposite  side  (in  the  neck). 

Blood-supply. — Dorsal,  deep  cervical,  intercostal,  and  lumbar  arteries. 

Nerve-supply. — Dorsal  branches  of  the  thoracic  and  lumbar  nerves. 

8.  Multifidus  dorsi. — This  is  a  long  segmental  muscle  which  lies  along  the  sides 
of  the  spinous  processes  of  the  vertebrae  from  the  sacrum  to  the  neck. 

Origin. — (1)  The  lateral  part  of  the  sacrum;  (2)  the  articular  processes  of 
the  lumbar  vertebrae;   (3)  the  transverse  processes  of  the  thoracic  vertebrae. 

Insertion. — The  spinous  processes  of  the  first  two  sacral,  the  lumbar,  thoracic, 
and  last  cervical  vertebrae. 

Action. — Acting  with  its  fellow,  it  is  an  extensor  of  the  spine;  acting  singly, 
it  flexes  it  laterally. 

Structure. — It  is  composed  of  a  series  of  bundles  which  are  directed  obliquely 
forward  and  upward.  Each  fasciculus  passes  over  several  vertebrae  to  its  insertion. 
In  the  posterior  part  of  the  series  the  bundles  cross  two  or  three  vertebrae  and  are 
inserted  into  the  summits  of  the  spines.  Anteriorly  the  bundles  have  a  more 
horizontal  direction,  cross  three  to  five  vertebrae,  and  are  inserted  into  the  sides 
of  the  spines  considerably  below  their  summits.  A  further  complication  consists 
in  the  fusion  of  several  bundles  into  a  common  insertion. 

Relations. — Superficially,  the  longissimus  dorsi;  deeply,  the  vertebral  spines. 

Blood-supply. — Intercostal  and  lumbar  arteries. 

Nerve-supply. — Dorsal  branches  of  the  thoracic  and  lumbar  nerves. 

9.  Intertransversales  lumborum. — These  are  very  thin  muscular  and  tendin- 
ous strata,  which  occupy  the  spaces  between  the  transverse  processes  of  the  lumbar 
vertebrae  except  the  fifth  and  sixth. 

Action. — To  assist  in  flexing  the  loins  laterally  or  in  rendering  the  region  rigid. 
Relations. — Superficially,  the  longissimus  dorsi;    deeply,  the  quadratus   lum- 
borum. 

Blood-supply. — Lumbar  arteries. 
Nerve-supply. — Lumbar  nerves. 


The  Fascia  and  Muscles  of  the  Tail 
(fascia  et  musculi  caud^) 

The  muscles  of  the  tail  are  inclosed  in  the  strong  coccygeal  fascia,  which  is 
continuous  in  front  with  the  gluteal  fascia  and  blends  with  the  lateral  sacro-iliac 
ligament.  At  the  root  of  the  tail  it  is  loosely  attached  to  the  subjacent  muscles, 
l^ut  further  back  it  is  intimately  adherent  to  them.  From  its  deep  face  are  de- 
tached septa  which  pass  between  the  muscles  to  become  attached  to  the  vertebrae. 

1.  Coccygeus.^ — This  is  a  flat,  triangular  muscle  which  lies  chiefly  between  the 
sacro-sciatic  ligament  and  the  rectum. 

^  Also  termed  the  ischio-coccygeus  or  compressor  coccygis. 


280 


FASCIA    AND    MUSCLES    OF   THE    HORSE 


Origin. — The  pelvic  surface  of  the  sacro-sciatic  ligament  near  the  ischiatic  spine. 

Insertion. — The  first  four  coccygeal  vertebrae  and  the  coccygeal  fascia. 

Action. — Acting  together,  to  de- 
press (flex)  the  tail,  compressing  it 
over  the  perineum;  acting  singly, 
to  depress  and  incline  it  to  the 
same  side. 

Structure. — The  origin  of  the 
muscle  is  aponeurotic.  Becoming 
fleshy,  its  fibers  pass  upward  and 
backward  and  divide  into  two 
layers.  The  lateral  layer  is  at- 
tached to  the  vertebrae,  the  medial 
to  the  fascia;  included  between 
the  two  lie  the  intertransversales. 
When  the  tail  is  raised,  the  ventral 
edges  of  the  muscles  produce  a  dis- 
tinct ridge  at  either  side  of  the  anus. 
Relations.  —  Laterally,  the 
sacro-sciatic  ligament  and  the  semi- 
membranosus ;  medially,  the  rectum 
and  the  sacro-coccygeus  ventralis 
muscle.  The  internal  pudic  artery 
crosses  the  origin  of  the  muscle, 
sacrococcygeus   dorsalis   medialis).^ — This 


Fig.  271. — Cross-section  of  Tail  of  Horse. 
1,  2,  Branches  of  lateral  coccygeal  vessels  and  nerve;  3,  mid- 
dle coccygeal  artery;  4,  sacro-coccygeus  dorsalis;  4',  sacro-coccy- 
geus  lateralis;  5,  5',  intertransversales;  6,  sacro-coccygeus  ven- 
tralis; 7,  recto-coccygeus;  8,  coccygeal  fascia;  9,  fibro-cartilage 
between  fourth  and  fifth  coccygeal  vertebrae.  The  veins  are  black. 


2.  Sacro-coccygeus    dorsalis    (M. 
muscle  lies  along  the  dorso-median  aspect  of  the  tail,  in  contact  with  its  fellow 

Origin. — The  last  three  sac- 
ral spines  and  some  of  the  coccy- 
geal spines. 

Insertion . — The  dorsal  sur- 
face of  the  coccygeal  vertebrae. 

Action. — Acting  together,  to 
elevate  (extend)  the  tail;  acting 
singly,  to  elevate  and  incline  it 
laterally. 

Structure. — The  muscle  has 
a  strong  rounded  belly.  It  is  in- 
serted by  means  of  short  tendons 
which  fuse  with  those  of  the  next 
muscle. 

Relations. — Superficially,  the 
coccygeal  fascia;  medially,  its 
fellow;  laterally,  the  sacro-coccy- 
geus lateralis;  deeply,  the  verte- 
brae. 

3.  Sacro-coccygeus  lateralis 
(M.  sacro-coccygeus  dorsalis  later- 
alis).^— This  muscle  hes  immedi- 
ately lateral  to  the  preceding. 

Origin. — The    sides    of    the 

1  Also  termed  the  erector  coccy- 
gis. 

■  Also  known  as  the  curvator 
coccygis. 


Fig.  272.- 
a,  Coccygeus;  b 
d,  recto-coccygeus;  e 
tor  penis;  g,  bulbo 
pudic  artery;  k,  anus;  I,  penis. 
Anat.  d.  Pferdes.) 


Muscles  of  Perineum  of  Horse. 
retractor  ani;    c,  c',  sphincter   ani  externus; 


■geus  ventralis  lateralis;  /,  retrac- 
h,  ischio-cavernosus;  i,  internal 
(After   EUenberger-Baum,  Top. 


THE    MUSCLES    OF   THE   THORAX  281 

sacral  spines,  with  the  multifidus,  and  the  transverse  processes  of  the  sacral  and 
coccygeal  vertebrse. 

Insertion. — The  lateral  surface  of  the  coccygeal  vertebrae,  except  the  first  four. 

Action. — Acting  with  its  fellow,  to  assist  the  preceding  muscle  in  elevating  the 
tail;  acting  singly,  to  incline  it  to  the  same  side. 

Structure.— This,  muscle  appears  to  be  a  direct  continuation  of  the  multifidus 
dorsi.  The  belly  is  fusiform  and  receives  reinforcing  fasciculi  from  the  transverse 
processes  of  the  sacrum.  This  is  succeeded  by  bundles  of  tendons,  as  many  as  four 
lying  alongside  of  each  other. 

Relations. — Superficially,  the  lateral  sacro-iliac  ligament  and  the  coccygeal 
fascia;  dorsally,  the  sacro-coccygeus  dorsalis;  ventrally,  the  intertransversales; 
deeply,  the  vertebrae  and  a  branch  of  the  lateral  coccygeal  artery  and  accompanying 
vein  and  nerve. 

4.  Intertransversales  caudae  (Mm.  intertransversarii  caudse). — These  con- 
sist of  muscular  bundles  which  lie  on  the  lateral  aspect  of  the  tail,  between  the 
preceding  muscle  and  the  sacro-coccygeus  ventralis.  They  begin  on  the  lateral 
edge  of  the  sacrum  and  occupy  the  spaces  between  the  transverse  processes,  to  which 
they  are  attached.     They  are,  however,  not  arranged  in  a  strict  segmental  manner. 

Action. — Acting  together,  to  fix  the  coccygeal  vertebrae;  acting  singly,  to  assist 
in  lateral  flexion. 

5.  Sacro-coccygeus  ventralis  (Mm.  sacro-coccygei  ventrales).^ — This  muscle 
lies  on  the  ventral  aspect  of  the  sacrum  and  coccyx.  It  is  composed  of  two  parts, 
described  by  Bourgelat  and  the  German  anatomists  as  separate  muscles. 

(a)  The  lateral  part  (M.  coccygeus  ventralis  lateralis)  is  much  the  larger  of 
the  two.  It  arises  from  the  lateral  part  of  the  ventral  surface  of  the  sacrum,  about 
as  far  forward  as  the  third  foramen,  and  is  inserted  into  the  transverse  processes 
and  ventral  surface  of  the  coccygeal  vertebrae. 

(6)  The  medial  part  (M.  sacro-coccygeus  ventralis  medialis)  arises  from  the 
ventral  surface  of  the  sacrum  medial  to  the  preceding  muscle  and  the  first  eight 
coccygeal  vertebrse,  and  is  inserted  into  the  ventral  surfaces  of  the  coccygeal  ver- 
tebrae. 

Action. — Acting  together,  to  depress  (flex)  the  tail;  acting  singly,  to  incline 
it  laterally  also. 

Structure. — The  lateral  part  has  a  somewhat  compressed  belly,  and  receives 
bundles  from  the  transverse  processes  of  the  coccygeal  vertebrae.  The  medial  part 
is  much  smaller  and  shorter,  reaching  only  about  to  the  middle  of  the  tail. 

Relations.- — Ventrally,  the  pelvic  and  coccygeal  fasciae;  dorsally,  the  sacrum, 
coccygeal  vertebrae,  and  the  intertransversales;  laterally,  the  sacro-sciatic  liga- 
ment, the  coccygeus,  and  the  coccygeal  fascia;  medially,  its  fellow,  the  recto- 
coccygeus,  and  the  middle  coccygeal  vessels.  Branches  of  the  lateral  coccygeal 
vessels  and  nerves  lie  between  the  lateral  division  of  the  muscle  and  the  intertrans- 
versales. 

Blood-supply. — Middle  and  lateral  coccygeal  arteries. 

Nerve-supply. — Coccygeal  nerves. 


The  Muscles  of  the  Thorax 
(muscuu  thoracis) 

These  consists  of  seven  muscles  or  sets  of  muscles,  which  are  attached  to  the 
thoracic  vertebrae,  to  the  ribs  and  their  cartilages,  and  to  the  sternum.  They  are 
muscles  of  respiration. 

1.  Levatores  costarum. — These  constitute  a  series  of  small  muscles  which  oc- 
cupy and  overhe  the  dorsal  ends  of  the  intercostal  spaces. 
1  Also  known  as  the  depressor  coccygis. 


282 


FASCIA   AND    MUSCLES    OF   THE    HORSE 


Origin. — The  transverse  processes  of  the  thoracic  vertebrse. 

Insertion. — The  lateral  surfaces  of  the  upper  ends  of  the  ribs  posterior  to  the 
A'ertebral  origin. 

Action.— To  draw  the  ribs  forward  in  inspiration. 

Structure. — Arising  by  tendinous  fibers,  each  muscle  passes  backward  and  out- 
ward and  expands  at  its  insertion.     Some  fibers  pass  over  one  rib  and  are  inserted 


Seventh  cervical  vertebra-' 
First  thoracic  vertebra- 


Section  of  scapula 


Intertransversales 


Intercostal  f 

nervet<  *i 


Retractor  co. 

Intertransverse  luja, 

Ilio-lumbar  ligament,. 


Levatores  costarum 


External 
intercostal 
XT"-   J  muscles 


Lateral  border  of  lon- 
gissimus  dor  si 


Tuber  coxce 


Fig.  273. — Deep  Dissection  op  Dorsal  and  Lumbar  Regions  of  Horse;   Dorsal  View.     (After  Schmaltz,  Atlas 

d.  Anat.  d.  Pferdes.) 


on  a  succeecUng  one.  At  the  beginning  and  end  of  the  series  the  muscle  cannot  be 
distinguished  from  the  external  intercostal,  of  which  it  is  in  reality  only  a  specially 
developed  part. 

Relations. — Superficially,  the  longissimus  dorsi;  deeply,  the  ribs,  internal  in- 
tercostal muscles,  and  the  intercostal  vessels  and  nerves. 

Blood-supply. — Intercostal  arteries. 


THE   MUSCLES    OF   THE    THORAX  283 

Nerve-supply. — Intercostal  nerves. 

2.  External  intercostals  (Mm.  intercostales  externi). — Each  of  these  occupies 
an  intercostal  space,  from  the  levatores  to  the  sternal  extremity  of  the  rib.  They 
do  not  occupy  the  intercartilaginous  spaces. 

Origin. — The  posterior  borders  of  the  ribs. 

Insertion. — The  anterior  borders  and  lateral  surfaces  of  the  succeeding  ribs. 

Action. — To  draw  the  ribs  forward  in  inspiration. 

Structure. — The  fibers  are  directed  downward  and  backward.  There  is  a 
considerable  admixture  of  tendinous  tissue.  The  thickness  of  the  muscles  grad- 
ually diminishes  toward  the  lower  ends  of  the  spaces. 

Relations. — Superficially,  the  serratus  ventralis,  latissimus  dorsi,  serratus 
dorsalis,  longissimus  dorsi,  longissimus  costarum,  rectus  thoracis,  deep  pectoral, 
obliquus  abdominis  externus,  and  cutaneous  muscles;  deeply,  the  internal  inter- 
costals and  (in  the  upper  part  of  the  spaces)  the  intercostal  vessels  and  nerves. 

Blood-supply. — Intercostal  and  internal  thoracic  arteries. 

Nerve-supply . — I nter costal  nerves . 

3.  Internal  intercostals  (Mm.  intercostales  interni). — These  extend  the  en- 
tire length  of  the  intercostal  spaces,  including  their  interchondral  portion. 

Origin. — The  anterior  borders  of  the  ribs  and  their  cartilages. 

Insertion. — The  posterior  borders  of  the  preceding  ribs  and  cartilages. 

Action.- — To  draw  the  ribs  backward  in  expiration.  It  seems  probable,  how- 
ever, that  the  intercartilaginous  portion  is  inspiratory.'- 

Structure. — The  direction  of  the  fibers  is  oblique  downward  and  forward. 
There  is  a  smaller  amount  of  tendinous  tissue  than  in  the  external  set,  and  the 
thickness  diminishes  dorsally.  In  the  upper  part  of  the  spaces  fibers  sometimes 
cross  a  rib  in  a  fashion  similar  to  the  subcostals  of  man.  A  thin  fascia  separates 
the  internal  from  the  external  intercostal  muscle  in  each  space. 

Relations. — Superficially,  the  levatores  costarum  and  the  external  intercostals; 
deeply,  the  endothoracic  fascia  and  pleura,  the  transversus  thoracis,  diaphragm, 
transversus  abdominis,  and  the  internal  thoracic  and  musculo-phrenic  vessels. 
In  the  upper  part  of  the  intercostal  spaces  the  intercostal  vessels  and  nerves  lie 
between  the  internal  and  external  intercostal  muscle,  but  below  they  lie  chiefly  on 
the  deep  face  of  the  internal  muscle. 

Blood-supply. — Intercostal  and  internal  thoracic  arteries. 

Nerve-supply. — Intercostal  nerves. 

The  muscles  in  connection  with  the  costal  cartilages  are  sometimes  distinguished  as  Mm. 
intercartilaginei ;  their  direction  is  similar  to  that  of  the  internal  intercostal,  and  they  cover  the 
cartilages  of  the  asternal  ribs  more  or  less.  At  the  ventral  ends  of  some  of  the  intercostal  spaces 
there  is  a  layer  of  longitudinal  muscle. 

4.  Retractor  costae. — This  is  a  small  triangular  muscle  which  lies  behind  the 
last  rib,  chiefly  under  cover  of  the  serratus  dorsalis. 

Origra. — The  transverse  processes  of  the  first  three  or  four  lumbar  vertebrae 
by  means  of  the  lumbar  fascia. 

Insertion. — The  posterior  border  of  the  last  rib. 

Action. — To  retract  the  last  rib. 

Structure. — The  muscle  arises  by  a  thin  aponeurosis.  Its  fibers  are  parallel 
to  those  of  the  adjacent  internal  oblique. 

Relations. — Superficially,  the  serratus  dorsalis  and  external  oblique;  deeply, 
the  transversus  abdominis. 

Blood-supply. — Lumbar  arteries. 

Nerve-supply. — Lumbar  nerves. 

5.  Rectus  thoracis.^ — This  is  a  thin  muscle  which  lies  under  cover  of  the  deep 

^  The  function  of  the  intercostal  muscles  is  still  a  subject  of  much  discussion.     The  state- 
ments made  above  seem  to  represent  the  view  most  commonly  held  in  regard  to  their  action. 
2  Also  known  as  the  transversus  costarum  or  lateralis  sterni. 


284 


FASCIA   AND    MUSCLES    OF   THE    HORSE 


pectoral  muscles.  It  is  directed  obliquely  backward  and  downward,  and  crosses 
the  lower  part  of  the  first  three  intercostal  spaces. 

Origin. — The  lateral  surface  of  the  first  rib,  below  the  scalenus. 

Insertion. — The  cartilage  of  the  fourth  rib.  The  aponeurosis  usually  joins  the 
rectus  abdominis.     It  may  reach  the  fifth  rib  or  the  sternum. 


Cariniform  cartilage 


Sternal  ligament 


First  rib 
Internal  thoracic  vessels 


Internal  intercostal  muscle 


Fig.  274. — Dissection  of  Floor  of  Thorax  op  Horse. 
The  ribs  have  been  sawn  off  near  their  sternal  ends  and  the  diaphragm  and  transversus  abdominis  cut  off  close  to  their 

attachment. 
1,  Eighth  rib;   2,  3,  cartilages  of  ninth  and  tenth  ribs;   4,  xiphoid  cartilage;    5,  apex  of  pericardium. 


Action. — It  may  assist  in  inspiration  or  concur  with  the  rectus  abdominis. 
Relations. — Superficially,  the  deep  pectoral  muscles;    deeply,  the  intercostal 
muscles  and  the  ribs. 

Blood-supphj. — Internal  and  external  thoracic  arteries. 
Nerve-supply. — Intercostal  nerves. 


THE   MUSCLES   OF   THE   THORAX  285 

6.  Transversus  thoracis.— This  is  a  flat  muscle  situated  on  the  thoracic  sur- 
face of  the  sternum  and  the  cartilages  of  the  sternal  ribs. 

Origin.- — The  sternal  ligament,  meeting  the  opposite  muscle. 

Insertion. — The  cartilages  of  the  ribs,  from  the  second  to  the  eighth  inclusive, 
and  the  adjacent  part  of  some  of  the  ribs. 

Action. — It  draws  the  ribs  and  costal  cartilages  inward  and  backward,  thus 
assisting  in  expiration. 

Structure. — Each  muscle  has  the  form  of  a  scalene  triangle,  of  which  the  base 
is  the  strongly  serrated  lateral  border.  The  muscle  contains  a  good  deal  of  ten- 
dinous tissue.  The  anterior  bundles  are  directed  forward  and  outward;  the  poste- 
rior, backward  and  outward. 

Relations. — Dorsally,  the  endothoracic  fascia  and  pleura;  ventrally,  the 
costal  cartilages,  the  internal  intercostal  muscles,  and  the  internal  thoracic  vessels. 

Blood-supply. — Internal  thoracic  artery. 

Nerve-supply. — The  intercostal  nerves. 

7.  Diaphragm. — This  is  a  broad,  unpaired  muscle  which  forms  a  partition  be- 
tween the  thoracic  and  abdominal  cavities. ^  In  outline  it  has  some  resemblance  to 
a  palm-leaf  fan.  In  form  it  is  dome-shaped,  compressed  laterally.  On  a  median 
section  it  is  seen  to  have  a  general  direction  downward  and  forward  from  the  lumbar 
vertebrae  to  the  xiphoid  cartilage.  The  thoracic  surface  is  strongly  convex,  and 
is  covered  by  the  pleura.  The  abdominal  surface  is  deeply  concave,  and  is  covered 
for  the  most  part  by  the  peritoneum.  The  muscle  consists  of  a  fleshy  rim  which 
may  be  subdivided  into  costal  and  sternal  parts;  a  lumbar  part,  composed  of  two 
crura;  and  a  tendinous  center. 

Attachments. — (1)  Costal  part  (Pars  costalis):  The  cartilages  of  the  eighth, 
ninth,  and  tenth  ribs,  and  behind  this  to  the  ribs  at  an  increasing  distance  from  their 
sternal  ends. 

(2)  Sternal  part  (Pars  sternalis) :  The  upper  surface  of  the  xiphoid  cartilage. 

(3)  Lumbar  part  (Pars  lumbalis):  (a)  The  right  crus  (Crus  dextrum)  is  at- 
tached to  the  ventral  longitudinal  ligament,  and  by  this  means  to  the  first  four  or 
five  lumbar  vertebrae.  (6)  The  left  crus  (Crus  sinistrum)  is  attached  in  a  similar 
fashion  to  the  first  and  second  lumbar  vertebrae. 

Action. — It  is  the  principal  muscle  of  inspiration  and  increases  the  longitu- 
dinal diameter  of  the  chest.  The  contraction  produces  a  general  lessening  of  the 
curvature  of  the  diaphragm.  In  the  expiratory  phase  the  costal  part  and  crura  lie 
almost  entirely  on  the  body  walls,  so  that  the  bases  of  the  lungs  are  in  contact  with 
the  tendinous  center  almost  exclusively.  In  orcUnary  inspiration  the  fleshy  rim 
recedes  from  the  chest-wall,  so  that  the  bases  of  the  lungs  move  backward  to  a  line 
about  parallel  with  the  costal  arches,  and  about  four  or  five  inches  (ca.  10-12  cm.) 
therefrom. 

It  is  stated  that  the  inspiratory  movement  affects  the  tendinous  center  much  less  than  the 
fleshy  part,  and  that  the  foramen  venaj  cava;  scarcely  moves  at  all,  since  the  posterior  vena  cava 
is  firmly  attached  to  it.  It  should  be  noted,  however,  that  the  direction  of  the  thoracic  part  of 
the  vena  cava  in  the  expiratory  phase  is  oblique  upward  and  backward.  Thus  it  would  seem  that 
there  is  no  anatomical  reason  why  the  diaphragm  should  not  move  as  a  whole  in  ordinary  inspira- 
tion at  least;  examination  of  formahn-hardened  subjects  in  which  the  diaphragm  appears  to  be 
fixed  in  the  inspiratory  phase  indicates  that  such  is  the  case. 

Structure. — The  costal  part  consists  of  a  series  of  digitations  which  meet,  or 
are  separated  by  a  very  narrow  interval  from,  the  transversus  abdominis;  between 
the  two  are  the  musculo-phrenic  vessels.  From  the  tenth  rib  backward  the  at- 
tachments to  the  ribs  are  at  an  increasing  distance  above  the  costo-chondral  junc- 
tions. Thus  at  the  last  rib  the  upper  limit  of  the  attachment  is  four  to  five  inches 
(10-12  cm.)  from  the  ventral  end.     Anteriorly  the  origin  extends  along  the  eighth 

1  It  should  be  noted,  however,  that  in  the  embryo  the  diaphragm  appears  as  a  paired  struc- 
ture, extending  from  the  lateral  walls  of  the  ccelom  to  fuse  with  the  septum  transversum. 


286 


FASCIA    AND    MUSCLES    OF   THE    HORSE 


and  ninth  costal  cartilages  to  the  xiphoid  cartilage.  From  these  points  of  origin 
the  fibers  curve  inward  and  forward  to  join  the  tendinous  center.^  The  right  cms 
is  about  twice  as  thick  as  the  left  one  and  is  also  longer.     It  arises  by  a  strong  tendon 


Longissimus  dorsi 

Lumbar  transverse 
process 


Costal  arch 
Musculo-phrenic 
artery 

Transvcrsus 

abdominalis  {cut 

edge) 
Xiphoid  cartilage 
(depressed) 


Fig.  275. — Diaphr.^gm  of  Horse;  Abdominal  Surface. 
i,  Ventral  longitudinal  ligament;  .2,  ;2',  tendons  of  crura;  3,  lumbar  sympathetic  trunks;  4,  external  spermatic 
nerve;  o,  5,  great  splanchnic  nerves;  6,  cisterna  chyli  (opened);  7,  7,  ce.sophageal  continuations  of  vagus  nerves; 
8,  lymph-gland;  9,  coronary  ligament  of  liver  (cut);  10,  right  lateral  ligament  of  Uver  (cut);  11,  left  lateral  ligament  of 
liver  (cut);  12,  falciform  ligament  of  liver  (cut);  A.I.,  lumbo-costal  arch;  N.i.,  intercostal  nerve;  C.d.,  right  crus; 
C.S.,  left  crus;  A,  aorta;  Ca,  coeliac  artery;  Oe.,  oesophagus;  V.c,  posterior  vena  cava;  V.p.,  phrenic  veins.  (After 
Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


which  blends  with  the  ventral  longitudinal  ligament.     The  tendon  is  succeeded  by 
a  rounded  belly  which  leaves  the  vertebral  column  at  the  last  thoracic  vertebra. 

1  It  is  interesting  to  note  that  when  a  nineteenth  rib  is  present  (even  when  it  is  well  developed) 
the  diaphragm  has  no  connection  with  it,  but  ends  on  the  eighteenth  rib  at  a  point  a  Uttle  more 
ventral  than  usual. 


THE    ABDOMINAL   FASCIiE   AND    MUSCLES  287 

Passing  downward  and  forward,  its  fibers  spread  out  and  join  the  tendinous  center. 
The  left  cms  arises  by  a  thin  tendon  from  the  ventral  longitudinal  ligament  at  the 
first  and  second  lumbar  vertebrae.  This  is  succeeded  by  a  triangular  belly  which 
joins  the  central  tendon.  Between  the  crura  and  the  attachment  to  the  last  rib 
the  edge  of  the  muscle  crosses  the  ventral  surface  of  the  psoas  muscles  without  at- 
tachment, forming  the  so-called  lumbo-costal  arch  (Arcus  lumbocostalis) ;  here  the 
thoracic  and  abdominal  cavities  are  separated  only  by  the  serous  membranes  and 
some  areolar  tissue.  The  tendinous  center  (Centrum  tendineum)  resembles  the 
periphery  in  outline,  but  is  more  elongated.  It  is  partially  divided  into  right  and 
left  parts  by  the  descent  of  the  crura  into  it.  It  is  composed  largely  of  radiating 
fibers,  but  many  interlace  in  various  directions;  this  is  speciallj^  evident  around  the 
foramen  venae  cavae,  which  is  encircled  by  fibers.  A  strong  tendinous  layer  extends 
across  below  the  hiatus  oescphageus. 

Schmaltz  and  others  describe  the  lumbar  part  as  consisting  of  four  crura,  two  medial  and  two 
lateral.  On  this  basis  the  left  crus  of  the  preceding  description  becomes  the  crus  lalerale  sinistrum, 
and  the  corresponding  part  of  the  right  side  is  the  crus  laterale  dextrtim.  The  central  part  is  divided 
by  the  hiatus  oesophageus  and  the  sht  which  extends  from  it  dorsally  into  a  crus  mediale  dextrum 
and  a  crus  mediale  sinistrum.     Both  modes  of  division  are  in  part  artificial. 

The  diaphragm  is  pierced  by  three  foramina.  (1)  The  hiatus  aorticus  is  an 
interval  between  the  two  crura  and  below  the  last  thoracic  vertebra.  It  contains 
the  aorta,  vena  azygos,  and  cisterna  chyH.  (2)  The  hiatus  oesophageus^  perforates 
the  right  crus  near  its  junction  with  the  tendinous  center.  It  is  situated  a  little  to 
the  left  of  the  median  plane  and  about  a  hand  breadth  ventral  to  the  thirteenth 
and  fourteenth  thoracic  vertebrae.  It  transmits  the  oesophagus,  the  vagus  nerves, 
and  the  oesophageal  branch  of  the  gastric  artery.  (3)  The  foramen  venae  cavae^ 
pierces  the  tendinous  center  about  an  inch  (ca.  2-3  cm.)  to  the  right  of  the  median 
plane,  and  about  six  to  eight  inches  (ca.  15-20  cm.)  below  the  eleventh  and 
twelfth  thoracic  vertebrae.  The  vena  cava  is  firmly  attached  to  the  margin  of  the 
opening.'^ 

Relations. — The  thoracic  surface  is  related  to  the  endothoracic  fascia,  pleurae, 
pericardium,  the  bases  of  the  lungs,  and  the  ribs  in  part.  The  abdominal  surface 
is  in  great  part  covered  by  the  peritoneum,  and  is  related  chiefly  to  the  liver,  stom- 
ach, intestine,  spleen,  pancreas,  kidneys,  and  adrenals.  The  sympathetic  trunk  and 
splanchnic  nerve  pass  between  the  crus  and  the  psoas  muscles  on  each  side.  The 
musculo-phrenic  vessels  perforate  the  edge  of  the  muscle  at  the  ninth  costo-chondral 
joint. 

Blood-supply. — Phrenic  and  musculo-phrenic  arteries. 

Nerve-supply. — Phrenic  nerves. 


The  Abdominal  Fasci^e  and  Muscles 
(fascle  et  musculi  abdominis) 

The  superficial  fascia  of  the  abdomen  is  in  part  fused  dorsally  with  the  lumbo- 
dorsal  fascia;  in  front  it  is  continuous  with  the  superficial  fascia  of  the  shoulder  and 
arm,  behind  with  that  of  the  gluteal  region.  In  the  inguinal  region  it  forms  part 
of  the  fascia  of  the  penis  or  of  the  mammary  glands.  At  the  lower  part  of  the  flank 
it  forms  a  fold  which  is  continuous  mth  the  fascia  of  the  thigh  near  the  stifle  joint. 

1  Formerly  termed  the  foramen  sinistrum.  ^  Formerly  termed  the  foramen  dextrum. 

^  In  order  to  get  a  clear  idea  of  the  relative  positions  of  these  foramina  and  of  the  form  of 
the  diaphragm,  the  thoracic  surface  of  the  latter  should  be  examined  in  properly  preserved  sub- 
jects while  the  abdominal  idscera  remain  in  situ.  It  will  be  observed  that  the  distances  of  the 
hiatus  oesophageus  and  foramen  vense  cavae  from  the  vertebral  column  vary  according  to  the  ful- 
ness of  the  abdominal  viscera  and  the  degree  of  contraction  of  the  diaphragm.  The  statements 
given  above  are  averages. 


288  FASCIA   AND    MUSCLES    OF   THE    HORSE 

In  this  fold  are  the  prefemoral  lymph-glands.  Medially  it  blends  with  the  linea 
alba.     It  contains  the  abdominal  cutaneous  muscle  (described  on  p.  254). 

The  deep  fascia  is  represented  chiefly  by  the  abdominal  tunic  (Tunica  flava 
abdominis) .  This  is  a  sheet  of  elastic  tissue  which  assists  the  muscles  in  supporting 
the  great  weight  of  the  abdominal  viscera.  It  is  practically  coextensive  with  the 
obliquus  externus,  which  it  covers.  Ventrally  it  is  thick,  and  is  intimately  ad- 
herent to  the  aponeurosis  of  the  muscle.  Laterally  it  becomes  thinner  and  is  more 
easily  separated,  although  fibers  from  it  dip  in  between  the  muscle-bundles.  It  is 
continued  for  some  distance  upon  the  inter costals  and  serratus  ventralis.  Traced 
forward,  it  passes  as  a  thin  layer  beneath  the  posterior  deep  pectoral  muscle.  Pos- 
teriorly it  is  attached  to  the  tuber  coxae.  In  the  inguinal  region  it  forms  the  deep 
fascia  of  the  prepuce  or  of  the  mammary  glands. 

The  linea  alba  is  a  median  fibrous  raphe  which  extends  from  the  xiphoid  car- 
tilage to  the  prepubic  tendon.  It  is  formed  chiefly  by  the  junction  of  the  aponeu- 
roses of  the  oblique  and  transverse  muscles,  but  partly  by  longitudinal  fibers.  A 
little  behind  its  middle  (about  in  a  transverse  plane  tangent  to  the  last  pair  of  ribs) 
is  a  cicatrix,  the  iimbilicus,  which  indicates  the  position  of  the  umbilical  opening 
of  the  foetus. 

1.  Obliquus  abdominis  externus, — This  is  the  most  extensive  of  the  abdominal 
muscles.  It  is  a  broad  sheet,  irregularly  triangular  in  shape,  widest  behind.  Its 
fibers  are  directed  chiefly  downward  and  backward. 

Origin. — (1)  The  lateral  surfaces  of  the  last  fourteen  ribs,  and  the  fascia  over 
the  external  intercostal  muscles;    (2)  the  lumbo-clorsal  fascia. 

Insertion. — (1)  The  linea  alba  and  the  prepubic  tendon;  (2)  the  tuber  coxae  and 
shaft  of  the  ilium;  (3)  the  medial  femoral  fascia. 

Action. — (1)  To  compress  the  abdominal  viscera,  as  in  defecation,  micturition, 
parturition,  and  expiration;  (2)  to  flex  the  trunk  (arch  the  back) ;  (3)  acting  singly, 
to  flex  the  trunk  laterally. 

Structure. — The  muscle  is  composed  of  a  muscular  part  and  an  aponeurosis. 
The  muscular  part  lies  on  the  lateral  wall  of  the  thorax  and  abdomen.  It  arises 
by  a  series  of  digitations,  the  anterior  four  of  which  alternate  with  those  of  the  ser- 
ratus ventralis.  The  origin  may  be  indicated  by  a  slightly  curved  line  (concave 
dorsally)  drawn  from  the  lower  part  of  the  fifth  rib  to  the  tuber  coxae.  The  fibers 
are  directed  downward  and  backward  and  terminate  on  the  aponeurosis,  except  in 
the  upper  part  of  the  flank,  where  they  are  less  oblique  in  direction  and  end  on  the 
tuber  coxae.  The  line  of  junction  is  a  curve  (concave  dorsally)  extending  from  the 
upper  edge  of  the  posterior  deep  pectoral  muscle  toward  the  point  of  the  hip.  The 
aponeurosis  is  intimately  attached  to  the  abdominal  tunic,  and  its  fibers  are  largely 
interwoven  ventrally  with  those  of  the  aponeurosis  of  the  internal  oblique.  By 
this  fusion  is  formed  the  outer  sheath  of  the  rectus  abdominis,  which  blends  at  the 
linea  alba  with  that  of  the  opposite  side.  In  the  inguinal  region  the  aponeurosis 
divides  into  two  chief  layers;  one  of  these  curves  dorsally  and  backward  and  is  in- 
serted into  the  tuber  coxae  and  the  prepubic  tendon.  Between  these  points  the 
aponeurosis  is  much  strengthened  and  is  called  the  inguinal  ligament  (Ligamentum 
inguinale).^  This  curves  upward  and  somewhat  forward,  becomes  thin,  and  blends 
with  the  iliac  fascia.  It  forms  the  posterior  wall  of  the  inguinal  canal.  About  an 
inch  (ca.  2  to  3  cm.)  in  front  of  the  pubis  and  about  two  inches  (ca.  4  to  5  cm.) 
from  the  mecUan  plane  the  aponeurosis  is  pierced  by  a  slit-like  opening,  the 
subcutaneous  or  external  inguinal  ring  (Annulus  inguinalis  subcutaneus).^    This  is 

1  Also  commonly  known  as  Poupart's  ligament — based  on  a  false  historical  allusion.  It  is 
in  no  proper  sense  a  ligament,  but  is  the  inguinal  part  of  the  aponeurosis  of  the  obliquus  externus; 
it  might  therefore  well  be  termed  the  lamina  inguinalis. 

-  It  is  narrow  and  slit-like  in  the  natural  condition,  but  may  appear  oval  in  the  dissecting- 
room,  especially  if  the  hind  limb  is  drawn  back  and  abducted. 


THE    ABDOMINAL   FASCIA    AND   MUSCLES 


289 


the  external  orifice  of  the  inguinal  canal.     Its  long  axis  is  directed  outward,  for- 
ward, and  somewhat  ventrally,  and  is  four  to  five  inches  (ca.  10-12  cm.)  in  length. 


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The  medial  angle  is  rounded  and  is  well  defined  by  the  junction  of  the  aponeurosis 
with  the  prepubic  tendon,  but  the  lateral  angle  is  not  so  sharply  defined.     The  bor- 
ders or  crura  are  constituted  by  arciform  fibers  of  the  aponeurosis  (Crus  mediale, 
19 


290  FASCIA   AND   MUSCLES    OF   THE   HORSE 

laterale).  The  femoral  lamina  of  the  aponeurosis  (Lamina  femoralis)  passes  on 
to  the  medial  surface  of  the  thigh,  where  it  blends  with  the  femoral  fascia.  A 
thin  iliac  lamina  (Lamina  iliaca)  passes  over  the  lateral  margin  of  the  iliacus  and 
is  attached  to  the  lateral  border  of  the  ilium. 

Relations. — Superficially,  the  skin,  the  abdominal  cutaneus,  the  abdominal 
tunic,  and  the  posterior  deep  pectoral  muscle;  deeply,  the  ribs  and  their  cartilages, 
the  intercostal  muscles,  the  obliquus  abdominis  internus,  the  contents  of  the  inguinal 
canal,  and  the  sartorius  and  gracilis. 

Blood-supply. — Intercostal  and  lumbar  arteries. 

Nerve-supply. — Intercostal  and  lumbar  nerves. 

2.  Obliquus  abdominis  internus. — This  muscle  is  situated  under  the  preceding 
one.  Its  fibers  are  directed  do^\aiward,  forward,  and  inward.  It  forms  a  triangular 
curved  sheet  with  the  base  behind. 

Origin. — The  tuber  coxse  and  the  adjacent  part  of  the  inguinal  ligament. 

Insertion. — (1)  The  cartilages  of  the  last  four  or  five  ribs;  (2)  the  linea  alba 
and  the  prepubic  tendon. 

Action. — Similar  to  that  of  the  preceding  muscle. 

Structure. — Like  the  external  oblique,  it  is  composed  of  a  fleshy  portion  and 
an  aponeurosis.  The  muscular  part  is  fan-shaped,  and  is  situated  chiefly  in  the 
flank.  At  its  iliac  origin  it  is  covered  by  a  glistening  aponeurosis.  Traced  medially 
and  ventrally  along  the  abdominal  surface  of  the  inguinal  ligament,  the  muscular 
origin  is  found  to  become  much  thinner,  and  also  becomes  looselj''  attached  to  the 
ligament.  This  medial  part  of  the  muscle  forms  the  anterior  wall  of  the  inguinal 
canal.  The  abdominal  orifice  of  the  canal,  the  abdominal  or  internal  inguinal 
ring^  (Annulus  inguinalis  abdominalis),  is  found  here.  It  is  normally  a  narrow 
slit,  bounded  in  front  by  the  edge  of  the  internal  oblique,  and  behind  by  the  in- 
guinal ligament.  Near  the  last  rib  the  muscle  divides  into  two  parts.  The  small 
dorsal  part  is  inserted  by  four  or  five  thin  tendinous  strips  to  the  medial  surface  of 
the  last  four  or  five  costal  cartilages.  The  aponeurosis  of  the  large  ventral  part 
is  to  a  great  extent  blended  with  that  of  the  external  oblique,  being,  indeed,  consider- 
ably interwoven  Avith  it  ventrally.  Where  it  covers  the  rectus  abdominis  it  is  at- 
tached to  the  tendinous  inscriptions  of  that  muscle.  It  may  be  noted  that  the  dor- 
sal margin  of  the  aponeurosis  varies  in  different  subjects  in  the  fact  that  it  may 
cover  the  costal  arch  or  lie  ventral  to  it. 

Relations. — Superficially,  the  obliquus  externus;  deeply,  the  rectus  abdominis^ 
transversus  abdominis,  and  the  peritoneum. 

Blood-supply. — Circumflex  iUac,  lumbar,  and  intercostal  arteries. 

Nerve-supply. — Ventral  branches  of  the  lumbar  nerves. 

3.  Rectus  abdominis. — This  muscle  is  confined  to  the  ventral  part  of  the  ab- 
dominal wall ;  it  extends  from  the  sternal  region  to  the  pubis. 

Origin. — The  cartilages  of  the  fourth  or  fifth  to  the  ninth  ribs  inclusive,  and  the 
adjacent  surface  of  the  sternum. 

Insertion. — The  pubis,  by  means  of  the  prepubic  tendon. 

Action. — Similar  to  that  of  the  oblique  muscles.  It  is  especially  adapted  to 
flex  the  lumbo-sacral  joints  and  the  lumbar  and  thoracic  parts  of  the  spine. 

Structure. — The  fibers  of  the  muscle  are  directecl  longitudinally.  Nine  to 
eleven  transverse  bands  of  fibrous  tissue  extend  in  an  irregular  maimer  across  the 

1  It  must  be  admitted  that  the  term  "ring"  is  rather  misleading  as  applied  to  the  abdomi- 
nal opening  of  the  canal,  since  normally  it  is  a  mere  dilatable  slit.  The  ring-hke  constriction 
which  exists  here  in  the  male  is  constituted  by  the  peritoneum,  which  descends  into  the  canal 
to  form  the  tunica  vaginalis.  This  peritoneal  ring  is  termed  the  vaginal  ring  (Annulus  vagi- 
nalis), and  must  not  be  confused  with  the  subperitoneal  ring,  i.  e.,  the  abdominal  or  internal 
inguinal  ring.  The  internal  inguinal  ring  is  six  or  seven  inches  (ca.  16  cm.)  in  length.  Its 
direction  corresponds  approximately  to  a  line  from  the  lateral  margin  of  the  prepubic  tendon  to  the 
ventral  part  of  the  tuber  coxa;. 


THE    ABDOMINAL    FASCIA    AND    MUSCLES  291 

muscle.  These  are  termed  inscriptiones  tendineaB.  They  strengthen  the  muscle 
and  serve  to  prevent  separation  of  its  fibers.  The  width  of  the  muscle  is  greatest 
about  its  middle.     The  anterior  part  blends  with  the  rectus  thoracis. 

Relations. — Superficially,  the  aponeuroses  of  the  oblique  muscles  (which  con- 
stitute the  external  rectus  sheath)  and  the  posterior  deep  pectoral;  deeply,  the 
transversus  abdominis,  intercostals,  the  cartilages  of  the  ribs,  and  the  sternum. 
The  posterior  abdominal  artery  runs  along  the  lateral  edge  of  the  muscle  posteriorly, 
and  the  anterior  abdominal  artery  on  or  in  its  anterior  part. 

Blood-supply. — Anterior  and  posterior  abdominal  arteries. 

Nerve-supply. — Intercostal  and  lumbar  nerves. 

4.  Transversus  abdominis. — This  muscle,  named  from  the  general  direction 
of  its  fibers,  is  a  triangular  curved  sheet.  Its  lateral  part  is  muscular,  its  ventral 
aponeurotic. 

Origin. — (1)  The  medial  surfaces  of  the  distal  ends  or  the  cartilages  of  the 
asternal  ribs,  meeting  the  costal  attachment  of  the  diaphragm;  (2)  the  transverse 
processes  of  the  lumbar  vertebrae,  by  means  of  the  deep  layer  of  the  lumbo-dorsal 
fascia. 

Insertion. — The  xiphoid  cartilage  and  the  linea  alba. 

Action. — Similar  to  that  of  the  oblique  muscles. 

Structure. — The  muscular  part  is  a  sheet  of  parallel  bundles  of  fibers,  directed 
ventro-medially.  It  is  thickest  along  the  cartilages  of  the  ribs,  and  from  here  it 
thins  out  greatly  toward  the  aponeurosis  and  the  lumbar  region.  The  fibers  of  the 
aponeurosis  directly  continue  those  of  the  fleshy  part.  Posteriorly  it  becomes  ex- 
tremely thin  and  fades  out  without  reaching  the  pelvis.  It  covers  the  deep  face 
of  the  rectus,  so  forming  the  internal  rectus  sheath. 

Relations. — Superficially,  the  oblique  and  straight  muscles,  the  retractor  costae, 
the  cartilages  of  the  asternal  ribs,  and  the  internal  intercostal  muscles;  deeply,  the 
fascia  transversalis  and  the  peritoneum.  The  fascia  transversalis  is  little  de- 
veloped in  the  horse,  and  is  very  thin  in  emaciated  subjects,  but  in  animals  in  good 
condition  it  contains  a  good  deal  of  fat.  It  blends  with  the  iliac  fascia  and  de- 
scends into  the  inguinal  canal.  The  musculo-phrenic  artery  runs  along  the  inter- 
val between  the  origin  of  the  transversus  and  the  costal  part  of  the  diaphragm. 
The  intercostal  nerves  pass  down  over  the  lateral  surface  of  the  muscle,  to  which 
they  give  branches.  Branches  of  the  first  three  lumbar  nerves  are  similarly  cUs- 
posed  further  back. 

Blood-supply. — Intercostal,  lumbar,  and  musculq|phrenic  arteries. 

Nerve-supply. — Intercostal  and  lumbar  nerves. 

5.  Cremaster  extemus. — This  small  muscle  may  be  regarded  as  a  detached 
portion  of  the  obliquus  abdominis  internus,  with  which  it  blends  at  its  origin  (Figs. 
370,  575). 

Origin. — The  iliac  fascia,  near  the  origin  of  the  sartorius. 

Insertion. — The  tunica  vaginalis  communis. 

Action. — To  raise  the  tunica  vaginalis,  and  with  it  the  testicle. 

Structure.- — The  muscle  arises  by  a  thin  aponeurosis  which  is  succeeded  by  a 
flat  muscular  belly  about  two  inches  (ca.  5  cm.)  in  width  in  the  stallion.^  It  passes 
down  the  inguinal  canal  on  the  postero-lateral  surface  of  the  tunica  vaginalis,  to 
which  it  is  very  loosely  attached.  On  reaching  the  point  where  the  tunic  is  reflected 
on  to  the  tail  of  the  epididymis,  the  muscle  is  inserted  into  the  outer  surface  of  the 
tunic  by  short  tendinous  fibers. 

Relations. — The  muscle  lies  between  the  peritoneum  and  the  fascia  trans- 
versalis in  front  and  the  iliac  fascia  and  inguinal  ligament  behind.     On  reaching 

1  As  might  be  expected,  the  cremaster  usually  undergoes  more  or  less  atrophy  and  is  paler 
In  the  castrated  subject.  In  the  mare  the  muscle  is  very  small,  and  ends  in  the  connective  tissue 
in  the  inguinal  canal. 


292  FASCIA   AND   MUSCLES    OF   THE    HORSE 

the  abdominal  ring  it  descends  the  inguinal  canal  on  the  postero-lateral  surface  of 
the  tunica  vaginalis  communis. 

Blood-supply. — External  spermatic  artery. 

Nerve-supply. — External  spermatic  nerve. 

The  Inguinal  Canal. — This  term  (Canalis  inguinalis)  is  applied  to  an  oblique 
passage  through  the  posterior  part  of  the  abdominal  wall.^  It  begins  at  the  ab- 
dominal inguinal  ring,  and  extends  obliquely  ventro-medially,  and  somewhat  for- 
ward, to  end  at  the  subcutaneous  inguinal  ring.  Its  anterior  wall  is  formed  by  the 
fleshy  posterior  part  of  the  internal  oblique  muscle,  and  the  posterior  wall  by  the 
strong  tendinous  inguinal  ligament.  The  average  length  of  the  canal,  measured 
along  the  spermatic  cord,  is  about  four  inches  (ca.  10  cm.).  The  abdominal  or 
internal  inguinal  ring  (Annulus  inguinalis  abdominalis)  is  the  internal  opening  of 
the  canal;  it  is  bounded  in  front  by  the  thin  margin  of  the  internal  oblique  muscle, 
and  behind  by  the  inguinal  ligament.  It  is  directed  from  the  edge  of  the  prepubic 
tendon  approximately  toward  the  tuber  coxae.  Its  length  is  about  six  or  seven 
inches  (ca.  15-17.5  cm.).  The  edge  of  the  muscle  is  attached  to  the  surface  of  the 
ligament  here  by  delicate  connective  tissue,  except  where  structures  intervene  be- 
tween the  walls  of  the  canal.  The  lateral  limit  of  the  ring  is  determined  by  the 
muscle  becoming  firmly  attached  to  the  ligament,  i.  e.,  actually  arising  from  the 
latter.  The  subcutaneous  or  external  inguinal  ring  (Annulus  inguinalis  subcutan- 
eus)  is  a  well-defined  slit  in  the  aponeurosis  of  the  external  oblique  muscle,  lateral 
to  the  prepubic  tendon.  Its  long  axis  is  directed  from  the  edge  of  the  prepubic 
tendon  outward,  forward,  and  slightly  ventrally,  and  its  length  is  about  four  or  five 
inches  (ca.  10-12  cm.).  The  canal  contains  in  the  male  the  spermatic  cord,  the 
tunica  vaginalis,  the  external  cremaster  muscle,  the  external  pudic  artery  (and  in- 
constantly a  small  sateUite  vein),  and  the  inguinal  lymph  vessels  and  nerves.  In 
the  female  it  contains  the  mammary  vessels  and  nerves;  in  the  bitch  it  also  lodges 
the  round  ligament  of  the  uterus,  enclosed  in  a  tubular  process  of  peritoneum. 

The  two  rings  do  not  correspond  in  direction,  but  diverge  laterally,  so  that  the  length  of  the 
canal  varies  greatly  when  measured  at  different  points.  The  medial  angles  of  the  two  rings  are 
separated  only  by  a  distance  equal  to  the  thickness  of  the  prepubic  tendon  (about  a  centimeter), 
but  the  lateral  angles  are  about  seven  inches  (ca.  17.5  cm.)  apart.  The  distance  measured  along 
the  spermatic  cord  is  about  four  inches  (ca.  10  cm.).  The  medial  angle  of  the  subcutaneous  ring 
is  well  defined  and  distinctly  palpable  at  the  side  of  the  prepubic  tendon;  from  here  the  direction 
of  the  ring  is  traceable. 

The  Prepubic  Tendon. — The  prepubic  tendon  (Tendo  prsepubicus)  is  essentially 
the  tendon  of  insertion  of  the  two  recti  abdominis,  but  also  furnishes  attachment  to 
the  obliqui,  the  graciles,  and  the  pectinei.  It  is  attached  to  the  anterior  borders  of 
the  pubic  bones,  including  the  ilio-pectineal  eminences.  It  has  the  form  of  a  very 
strong  thick  band,  with  concave  lateral  borders  which  form  the  medial  boundaries 
of  the  subcutaneous  inguinal  rings.  Its  direction  is  oblique  upward  and  backward.^ 
Its  structure  is  somewhat  complex.  Most  of  the  fibers  of  the  posterior  part  extend 
from  one  ilio-pectineal  eminence  to  the  other.  The  fibers  which  belong  to  the  recti 
curve  in  to  the  median  line.  The  aponeuroses  of  the  internal  oblique  muscles  are 
inserted  into  its  abdominal  surface,  and  the  inguinal  ligaments  are  attached  to  and 
continue  across  it  in  arciform  fashion.  The  anterior  part  of  the  tendon  of  origin 
of  the  gracilis  is  fused  with  it  ventrally,  and  many  of  the  fibers  of  the  pectineus 
arise  from  it.  It  gives  off  on  either  side  a  strong  round  band,  the  so-called  accessory 
ligament,  which  is  inserted  into  the  fovea  of  the  head  of  the  femur  with  the  round 

^  The  term  canal  is  somewhat  misleading;  it  is  rather  a  slit-like  passage  or  space  between 
the  two  obUque  muscles,  since  the  inguinal  ligament  is  that  part  of  the  aponeurosis  of  the  exter- 
nal obhque  muscle  which  stretches  between  the  tuber  coxa;  and  the  prepubic  tendon. 

-  The  obliquity  of  the  tendon  and  the  angle  which  it  forms  with  the  pelvic  floor  are  of  clinical 
importance  in  regard  to  manipulation  of  the  fcstus  in  obstetrical  cases.  The  slope  varies  in 
different  subjects.     In  some  cases  the  tendon  forms  about  a  right  angle  with  the  pubic  bones. 


THE   MUSCLES    OF   THE    THORACIC    LIMB  293 

ligament  {vide  hip  joint).     A  band  from  the  ventral  surface  extends  backward  and 
blends  with  the  tendon  of  origin  of  the  gracilis  on  each  side. 


The  Muscles  of  the  Thoracic  Limb 

L  the  muscles  of  the  shoulder  girdle  (Figs.  266.  267,  268,  276) 
This  group  (Mm.  cinguli  extremitatis  thoracalis)   consists  of  those  muscles 
which  connect  the  thoracic  limb  with  the  head,  neck,  and  trunk.     It  may  be  re- 
garded as  consisting  of  two  divisions — dorsal  and  ventral.^ 

A.  Dorsal  Dfvision 

This  division  consists  of  two  layers  which  overlie  the  proper  muscles  of  the 
neck  and  back. 

First  Layer 

L  Trapezius. — This  is  a  flat,  triangular  muscle,  the  base  of  which  extends 
along  the  supraspinous  ligament.  It  is  divided  by  an  aponeurotic  portion  into  two 
parts : 

(a)  Trapezius  cervicalis. — Origin. — The  funicular  part  of  the  ligamentum 
nuchae,  from  the  second  cervical  to  the  third  thoracic  vertebra. 

Insertion. — The  spine  of  the  scapula  and  the  fascia  of  the  shoulder  and  arm. 

(b)  Trapezius  thoracalis  (s.  dorsalis). — Origin. — The  supraspinous  ligament, 
from  the  third  to  the  tenth  thoracic  vertebra. 

Insertion. — The  tuber  spinse  of  the  scapula. 

Action. — Acting  as  a  whole,  to  elevate  the  shoulder;  the  cervical  part  draws 
the  scapula  forward  and  upward  and  the  thoracic  part  draws  it  backward  and  up- 
ward. 

Structure. — The  muscle  arises  by  a  narrow,  thin  aponeurosis,  from  which  the 
fibers  of  the  flat  fleshy  part  converge  to  the  spine  of  the  scapula  and  the  aponeurosis 
which  separates  the  two  portions.  The  cervical  fascia  joins  the  ventral  edge  of  the 
cervical  portion  to  the  brachiocephalicus,  or  the  two  muscles  may  unite  or  overlap 
here. 

Relations. — Superficially,  the  skin  and  fascia;  deeply,  the  rhomboideus, 
latissimus  dorsi,  supraspinatus,  infraspinatus,  deltoid,  splenius,  serratus  ventralis, 
and  anterior  deep  pectoral  muscles,  and  the  cartilage  of  the  scapula. 

Blood-supply. — Deep  cervical  and  intercostal  arteries. 

Nerve-supply. — Spinal  accessory  nerve. 

Second  Layer 

This  consists  of  two  muscles — the  rhomboideus  and  latissimus  dorsi. 
2.  Rhomboideus. — This  consists  of  two  parts: 

(a)  Rhomboideus  cervicalis. — Origin. — The  funicular  part  of  the  ligamentum 
nuchse,  from  the  second  cervical  to  the  second  thoracic  vertebra. 

Insertion. — The  medial  surface  of  the  cartilage  of  the  scapula. 

(b)  Rhomboideus  thoracalis  (s.  dorsalis). — Origin. — The  spinous  processes  of 
the  second  to  the  seventh  thoracic  vertebra  by  means  of  the  dorso-scapular  liga- 
ment. 

Insertion. — The  medial  surface  of  the  cartilage  of  the  scapula. 
Action.- — To  draw  the  scapula  upward  and  forward.     When  the  limb  is  fixed 
the  cervical  part  will  elevate  the  neck. 

^  The  terms  dorsal  and  ventral  are  here  used  in  the  topographic  and  not  in  the  ixiorpho- 
logical  sense;   all  the  muscles  of  the  group  are  ventral  in  the  latter  sense. 


294  FASCIA   AND    MUSCLES    OF   THE   HORSE 

Structure. — The  cervical  part  is  narrow,  pointed  at  its  anterior  extremity,  and 
lies  along  the  funicular  part  of  the  ligamentum  nuchse,  to  which  it  is  attached  by 
short  tendon  bundles.  The  fibers  are  directed  for  the  most  part  longitudinally. 
The  thoracic  part  is  quadrilateral  in  shape,  and  its  fibers  are  nearly  vertical.  Its 
deep  face  is  intimately  attached  to  the  dorso-scapular  ligament. 

Relations. — Superficially,  the  skin  and  fascia  (over  a  small  area  in  front),  the 
trapezius,  and  the  cartilage  of  the  scapula;  deeply,  the  dorso-scapular  ligament, 
the  splenius,  complexus,  longissimus  dorsi,  and  serratus  dorsalis. 

Blood-supply. — Dorsal  and  deep  cervical  arteries. 

Nerve-supply. — Sixth  and  seventh  cervical  nerves. 

3.  Latissimus  dorsi. — This  is  a  ^vide  muscle  which  has  the  form  of  a  right- 
angled  triangle.  It  lies  for  the  most  part  under  the  skin  and  cutaneous  muscle, 
on  the  lateral  wall  of  the  thorax,  from  the  spine  to  the  arm. 

Origin. — The  lumbo-dorsal  fascia — and  by  this  means  from  the  lumbar  and 
thoracic  spines  as  far  forward  as  the  highest  point  of  the  withers. 

Insertion. — The  teres  tubercle  of  the  humerus,  in  common  with  the  teres 
major. 

Action. — To  draw  the  humerus  upward  and  backward  and  flex  the  shoulder- 
joint.     If  the  limb  is  advanced  and  fixed,  it  draws  the  trunk  forward. 

Structure. — The  muscle  arises  by  a  wide  aponeurosis,  which  fuses  with  that 
of  the  serratus  dorsalis  and  with  the  lumbo-dorsal  fascia.  The  muscular  part 
is  at  first  rather  thin,  but  by  the  convergence  of  its  fibers  becomes  thicker  as  it 
approaches  the  arm.  The  anterior  fibers  pass  almost  vertically  downward  over 
the  dorsal  angle  of  the  scapula  and  its  cartilage.  The  posterior  fibers  are  directed 
downward  and  forward.  The  thick  belly  formed  by  the  convergence  of  these 
passes  under  the  triceps  to  end  on  the  flat  tendon  of  insertion,  which  is  common 
to  this  muscle  and  the  teres  major.  The  tendon  of  insertion  furnishes  origin  to  the 
anterior  part  of  the  tensor  fasciae  antibrachii. 

Relations. — Superficially,  the  superficial  fascia,  skin,  cutaneus,  trapezius, 
and  triceps;  deeply,  the  cartilage  of  the  scapula,  the  rhomboideus,  the  serrati,  the 
external  intercostals,  and  the  lumbo-dorsal  fascia. 

Blood-supply. — Subscapular,  intercostal,  and  lumbar  arteries. 

Nerve-supply .  — Thoraco-dorsal  nerve . 

B.  Ventral  Division 

1.  Brachiocephalicus.^ — This  muscle  extends  along  the  side  of  the  neck  from 
the  head  to  the  arm.     It  is  incompletely  divisible  into  two  portions. 

Origin. — (1)  The  mastoid  process  of  the  temporal  bone  and  the  nuchal  crest; 
(2)  the  wing  of  the  atlas  and  the  transverse  processes  of  the  second,  third,  and 
fourth  cervical  vertebrae. 

Insertion. — The  deltoid  tuberosity,  the  curved  rough  line  which  extends  from 
this  almost  to  the  distal  extremity  of  the  humerus,  and  the  fascia  of  the  shoulder 
and  arm. 

Action. — When  the  head  and  neck  are  fixed,  to  draw  the  limb  forward,  ex- 
tending the  shoulder  joint.  When  the  limb  is  fixed,  to  extend  the  head  and  neck, 
if  the  muscles  act  together;  acting  separately,  to  incline  the  head  and  neck  to 
the  same  side.  By  means  of  its  attachment  to  the  strong  fascia  which  extends 
from  the  deltoid  tuberosity  to  the  outer  face  of  the  elbow  the  muscle  also  acts  as 
an  extensor  of  the  elbow  joint  (e.  g.,  in  standing). 

Structure. — As  already  mentioned,  the  muscle  is  capable  of  incomplete  di- 
vision into  two  parts,  the  line  of  division  being  indicated  by  the  emergence  of  sup- 
erficial branches  of  the  ventral  divisions  of  the  cervical  nerves.     The  mastoid  part 

^  This  muscle  is  also  called  the  mastoido-humeralis,  humero-mastoideus,  dero-brachialis  and 
levator  humeri. 


THE   MUSCLES    OF   THE    SHOULDER   GIRDLE  295 

(M.  cleido-mastoideus)  partly  overlaps  the  other  (M.  cleido-transversarius),  which 
lies  dorsal  to  it.  The  former  is  attached  to  the  mastoid  process  and  the  occipital 
bone  by  a  broad  tendon  which  fuses  at  its  terminal  part  with  that  of  the  splenius 
and  longissimus  capitis  et  atlantis;  it  is  also  attached  to  the  tendon  of  insertion  of 
the  sterno-cephalicus  by  aponeurosis.  The  dorsal  part  is  attached  to  the  transverse 
processes  by  four  fleshy  digitations.  The  belly  of  the  muscle  is  adherent  superfi- 
cially to  the  cervical  fascia  and  the  cutaneous  muscle,  and  deeply  to  the  omo- 
hyoideus.  In  front  of  the  shoulder  its  deep  face  may  present  a  tendinous  inter- 
section of  variable  development.^  Here  the  muscle  becomes  wider,  covers  the 
shoulder  joint,  passes  between  the  brachialis  and  biceps,  and  is  inserted  by  means 
of  a  wide  tendon  which  it  shares  with  the  superficial  pectoral  muscle. 

Relations. — Superficially,  the  skin,  cervical  fascia,  the  parotid  gland,  the  cuta- 
neus,  the  brachialis,  and  branches  of  the  cervical  nerves;  deeply,  the  splenius, 
longissimus  capitis  et  atlantis,  rectus  capitis  ventralis  major,  omo-hyoideus,  ser- 
ratus  ventralis,  anterior  deep  pectoral  and  biceps  muscles,  the  inferior  cervical 
artery,  the  prescapular  lymph  glands,  and  branches  of  the  cervical  nerves.  The  ven- 
tral edge  of  the  muscle  forms  the  dorsal  boundary  of  the  jugular  furrow.  The 
dorsal  border  may  be  in  contact  with  the  cervical  trapezius,  or  be  separated  from 
it  by  a  variable  interval. 

Blood-supply. — Inferior  cervical,  carotid,  and  vertebral  arteries. 

Nerve-supply.- — Spinal  accessory,  cervical,  and  axillary  nerves. 

The  pectoral  fascia  is  a  thin  membrane  covering  the  surface  of  the  pectoral 
muscles,  to  which  it  is,  for  the  most  part,  closely  attached.  It  detaches  a  layer 
which  passes  between  the  superficial  and  deep  pectorals.  At  the  posterior  edge  of 
the  triceps  another  layer  is  given  off,  which  passes  on  the  lateral  surface  of  this 
muscle  to  blend  with  the  scapular  fascia;  the  deeper  layer  becomes  continuous  with 
the  subscapular  and  cervical  fasciae. 

The  pectoral  muscles  form  a  large  fleshy  mass  which  occupies  the  space  be- 
tween the  ventral  part  of  the  chest-wall  and  the  shoulder  and  arm.  They  are 
clearly  divisible  into  a  superficial  and  a  deep  layer.  The  superficial  layer  may  be 
subdivided  into  two  parts  by  careful  dissection;  the  deep  layer  is  clearly  made  up 
of  two  muscles. 

2.  Superficial  pectoral  muscle  (M.  pectoralis  superficialis) . 

(a)  Anterior  superficial  pectoral  muscle  (pars  descendens)  .^ — This  is  a  short, 
thick,  somewhat  rounded  muscle,  which  extends  from  the  manubrium  sterni  to 
the  front  of  the  arm.  It  forms  a  distinct  prominence  on  the  front  of  the  breast, 
which  is  easily  recognized  in  the  living  animal. 

Origin. — The  cariniform  cartilage  of  the  sternum. 

Insertion. — (1)  The  curved  line  of  the  humerus  with  the  brachiocephalicus;  (2) 
the  fascia  of  the  arm. 

Action. — To  adduct  and  advance  the  limb. 

Structure. — The  belly  of  the  muscle  is  convex  on  its  superficial  face,  but  deeply 
it  is  flattened  where  it  overlaps  the  posterior  superficial  pectoral.  Here  the  two 
muscles  are  usually  closely  attached  to  each  other,  and  care  must  be  exercised  in 
making  the  separation.  The  tendon  of  insertion  blends  with  that  of  the  brachio- 
cephalicus and  with  the  fascia  of  the  arm.  At  the  middle  line  of  the  breast  a  fur- 
row occurs  between  the  two  muscles;  laterally,  another  furrow,  containing  the 
cephalic  vein,  lies  between  the  muscle  and  the  brachiocephalicus. 

i^eZa^tows.— Superficially,  the   skin,  fascia,  and  panniculus;  deeply,  the  pos- 

1  This  is  regarded  as  a  vestige  of  the  clavicle.  On  this  basis  the  portion  of  the  muscle  from 
the  vestige  to  the  arm  represents  the  clavicular  part  of  the  deltoid  and  perhaps  the  clavicular  part 
of  the  pectoraUs  major  of  man. 

^  Also  termed  the  pectoralis  anticus  or  pars  clavicularis. 


296  FASCIA   AND   MUSCLES    OF   THE    HORSE 

terior  division,  the  deep  pectoral,  and  the  biceps.  The  cephahc  vein  hes  in  the 
groove  between  this  muscle  and  the  brachiocephalicus. 

(b)  Posterior  superficial  pectoral  muscle  (pars  transversa). ^^ — This  is  a  wide 
muscular  sheet  which  extends  from  the  ventral  edge  of  the  sternum  to  the  medial 
surface  of  the  elbow. 

Origin. — (1)  The  ventral  edge  of  the  sternum  as  far  back  as  the  sixth  car- 
tilage; (2)  a  fibrous  raphe  common  to  the  two  muscles. 

Insertion. — (1)  The  fascia  on  the  proximal  third  of  the  forearm;  (2)  the 
curved  line  of  the  humerus  with  the  preceding  muscle. 

Action. — To  adduct  the  limb  and  to  tense  the  fascia  of  the  forearm. 

Structure. — It  is  thin  and  pale,  and  mixed  with  a  good  deal  of  fibrous  tissue. 
The  right  and  left  muscles  fuse  at  a  median  fibrous  raphe.  The  tendon  of  inser- 
tion unites  with  the  fascia  on  the  medial  side  of  the  forearm  for  the  most  part; 
only  a  small  part  in  front,  about  an  inch  in  width,  is  attached  to  the  humerus. 

Relations. — Superficially,  the  skin,  fascia,  and  the  preceding  muscle;  deeply, 
the  deep  pectoral,  the  biceps,  and  the  brachialis;  at  the  elbow,  the  median  vessels 
and  nerve,  and  the  medial  and  middle  flexors  of  the  carpus. 

3.  Deep  pectoral  muscle  (M.  pectoralis  profundus). — This  muscle  is  much 
thicker  and  more  extensive  in  the  horse  than  the  superficial  pectoral.  It  consists 
of  two  distinct  parts. 

(a)  Anterior  deep  pectoral  muscle  (pars  scapularis).- — This  is  prismatic  and 
extends  from  the  anterior  part  of  the  lateral  surface  of  the  sternum  to  the  cervical 
angle  of  the  scapula. 

Origin. — The  anterior  half  of  the  lateral  surface  of  the  sternum  and  the  car- 
tilages of  the  first  four  ribs. 

Insertion.- — The  aponeurosis  which  covers  the  supraspinatus  at  its  dorsal 
end,  and  the  scapular  fascia. 

Action. — To  adduct  and  retract  the  limb;  when  the  limb  is  advanced  and 
fixed,  to  draw  the  trunk  forward. 

Structure.- — The  muscle  is  almost  entirely  fleshy.  It  describes  a  curve  (con- 
vex anteriorly),  passing  at  first  forward,  then  upward  over  the  front  of  the  shoulder, 
a  little  to  its  medial  side,  and  finally  inclines  somewhat  backward  along  the  anterior 
border  of  the  supraspinatus.  It  is  loosely  attached  to  the  latter  muscle,  and 
terminates  in  a  pointed  end  which  becomes  more  firmly  attached  near  the  cer- 
vical angle  of  the  scapula. 

Relations. — Superficially,  the  skin  and  fascia,  the  cutaneus,  superficial  pec- 
toral, trapezius,  and  brachiocephalicus  muscles,  the  cephalic  vein,  and  the  in- 
ferior cervical  artery;  deeply,  the  posterior  deep  pectoral,  biceps,  supraspinatus, 
omo-hyoideus,  and  serratus  ventralis  muscles,  the  brachial  vessels,  and  the  branches 
of  the  brachial  plexus  of  nerves. 

(b)  Posterior  deep  pectoral  muscle  (pars  humeralis  s.  ascendens).^ — This  is 
much  the  largest  of  the  pectoral  group  in  the  horse.  It  is  somewhat  triangular  or 
fan-shaped. 

Origin. — (1)  The  abdominal  tunic;  (2)  the  xiphoid  cartilage  and  ventral 
aspect  of  the  sternum ;  (3)  the  cartilages  of  the  fourth  to  the  ninth  ribs. 

Insertion. — (1)  The  posterior  part  of  the  medial  tuberosity  of  the  humerus;  (2) 
the  anterior  part  of  the  lateral  tuberosity  of  the  humerus;  (3)  the  tendon  of  origin 
of  the  coraco-brachialis. 

Action. — To  adduct  and  retract  the  limb;  if  the  limb  is  advanced  and  fixed, 
to  draw  the  trunk  forward. 

Structure. — This  muscle  is  almost  entirely  fleshy.     Its  posterior  part  is  wide 

^  Also  termed  the  pectoralis  transversus  or  pars  sternocostalis. 
^  Also  tenned  the  pectoralis  parvus  or  pars  praescapularis. 
'  Also  known  as  the  pectoralis  magnus. 


THE    MUSCLES    OF   THE    SHOULDER    GIRDLE  297 

and  thin,  but  as  the  muscle  is  traced  forward,  it  becomes  narrower  and  much 
thicker.  It  passes  forward  and  slightly  upward  in  a  gentle  curve  to  its  insertion. 
The  humeral  insertion  is  just  below  that  of  the  medial  division  of  the  supraspinatus. 
Part  of  the  fibers  are  inserted  by  means  of  a  tendinous  band  which  binds  down  the 
tendon  of  the  biceps  and  is  attached  to  the  lateral  lip  of  the  intertuberal  or  bicipital 
groove,  and  a  small  part  is  attached  to  the  tendon  of  origin  of  the  coraco-brachialis. 

Relations. — Superficially,  the  skin,  cutaneus,  and  superficial  pectoral;  deeply, 
the  abdominal  tunic,  the  external  oblique,  the  rectus  abdominis  et  thoracis,  the 
brachial  vessels,  and  branches  of  the  brachial  plexus  of  nerves.  The  external 
thoracic  vein  lies  along  the  lateral  border. 

Blood-supply. — Internal  and  external  thoracic,  inferior  cervical,  anterior 
circumflex,  and  intercostal  arteries. 

N erve-siipply . — Pectoral  nerves,  from  the  brachial  plexus. 

3.  Serratus  ventralisi  (Figs.  267,  268).— This  is  a  large,  fan-shaped  muscle, 
situated  on  the  lateral  surface  of  the  neck  and  thorax.  It  derives  its  name  from 
the  serrated  ventral  edge  of  its  thoracic  portion.  It  consists  of  cervical  and  tho- 
racic parts. 

(a)  Serratus  cervicis. 

Origin. — The  transverse  processes  of  the  last  four  or  five  cervical  vertebrae. 
Insertion. — The  anterior  triangular  area  on  the  costal  surface  of  the  scapula 
(facies  serrata)  and  the  adjacent  part  of  the  cartilage. 

(b)  Serratus  thoracis. 

Origin. — The  lateral  surfaces  of  the  first  eight  or  nine  ribs. 

Insertion. — The  posterior  triangular  area  on  the  costal  surface  of  the  scapula 
(facies  serrata)  and  the  adjacent  part  of  the  cartilage. 

Action. — The  two  muscles  form  an  elastic  support,  which  suspends  the  trunk  be- 
tween the  two  scapulae."  Contracting  together,  they  raise  the  thorax;  contracting 
singly,  the  weight  is  shifted  to  the  limb  on  the  side  of  the  muscle  acting.  The  two 
parts  can  act  separately  and  are  antagonistic  in  their  effect  on  the  scapula.  The 
cervical  part  draws  the  base  of  the  scapula  toward  the  neck,  while  the  thoracic 
part  has  the  opposite  action;  these  effects  concur  in  the  backward  and  forward 
swing  of  the  limb  respectively.  With  the  limb  fixed,  the  cervical  part  extends 
(raises)  the  neck  or  inclines  it  laterally.  The  thoracic  part  may  act  as  a  muscle  of 
forced  inspiration. 

Structure. — In  the  domesticated  animals  there  is  no  such  clear  division  of 
the  muscle  as  is  found  in  man  and  the  apes.  On  account  of  the  difference  in  action, 
however,  it  seems  desirable  to  distinguish  the  two  portions.  The  serratus  cervicis  is 
thick  aiKl  almost  entirely  fleshy.  The  serratus  thoracis  has  on  its  superficial  face  a 
thick,  tendinous  layer  which  may  sustain  the  weight  of  the  trunk  when  the  muscle 
substance  relaxes.  The  ventral  edge  presents  distinct  digitations,  the  last  four  of 
which  alternate  with  those  of  the  obliquus  externus  abdominis,  and  are  covered  by 
the  abdominal  tunic.  The  fourth  and  fifth  digitations  extend  nearly  to  the  sternal 
ends  of  the  ribs.  The  ninth  digitation  is  small  and  may  be  absent.  Exceptionally 
additional  digitations  may  be  attached  to  the  tenth  or  eleventh  rib  or  to  the  fascia 
over  the  intercostal  muscles.  The  fibers  converge  to  the  insertion,  which  is  thick 
and  is  intersected  by  elastic  lamellae  derived  from  the  dorso-scapular  ligament. 

Relations. — Superficially,  the  brachiocephalicus,  trapezius,  deep  pectoral, 
subscapularis,  teres  major,  latissimus  dorsi,  cutaneus,  the  abdominal  tunic,  the 
brachial  vessels,  and  the  long  thoracic  nerve;     deeply,  the  splenius,  complexus, 

1  Formerly  termed  the  serratus  magnus. 

2  It  has  been  commonly  stated  that  these  muscles  form  a  sort  of  sling  in  which  the  trunk  is 
suspended.  This  is  not  quite  correct  as  the  two  muscles  do  not  meet  ventrally.  The  arrange- 
ment is  admirable,  since  the  pull  of  the  thorax  on  the  muscles  presses  the  scapula?  against  the  body 
wall. 


298  FASCIA   AND    MUSCLES    OF   THE    HORSE 

serratus  dorsalis,  longissimi,  the  ribs  and  external  intercostal  muscles,  and  branches 
of  the  deep  cervical  and  dorsal  arteries. 

Blood-supply. — Deep  cervical,  dorsal,  vertebral,  and  intercostal  arteries. 

Nerve-supply. — Fifth  to  eighth  cervical  nerves. 


n.  THE  MUSCLES  OF  THE  SHOULDER 

The  muscles  of  this  group  (Mm.  omi)  arise  on  the  scapula  and  end  on  the  arm; 
the}'  may  be  divided  into  two  groups — one  covering  the  lateral,  the  other  the  costal, 
surface  of  the  scapula. 

The  superficial  fascia  of  the  shoulder  and  arm  contains  the  cutaneous  muscle 
of  this  region  (vide  p.  254),  and  may  be  considered  to  be  continued  on  the  medial 
side  of  the  limb  by  the  subscapular  fascia. 

The  deep  fascia  of  the  shoulder  and  arm  (Fascia  omobrachialis)  is  strong  and 
tendinous,  and  is  intimately  adherent  to  the  muscles  on  the  lateral  surface  of  the 
scapula,  between  which  it  detaches  intermuscular  septa,  which  are  attached  to  the 
spine  and  borders  of  the  scapula.  The  brachial  portion  is,  for  the  most  part,  only 
loosely  attached  to  the  underlying  muscles,  for  which  it  forms  sheaths;  it  is  attached 
to  the  proximal  and  deltoid  tuberosities  of  the  humerus.  A  specially  strong  part 
extends  from  the  deltoid  tuberosity  to  the  lateral  surface  of  the  elbow;  it  furnishes 
insertion  to  part  of  the  brachiocephalicus  and  gives  origin  to  fibers  of  the  lateral 
head  of  the  triceps  and  of  the  extensor  carpi  radialis.  The  fascia  blends  distally 
•with  the  tendon  of  insertion  of  the  biceps,  and  is  continued  by  the  antibrachial 
fascia. 

A.  Lateral  Group  (Figs.  267, 268) 

1.  Deltoideus. — This  lies  partly  on  the  triceps  in  the  angle  between  the  scap- 
ula and  humerus,  partly  on  the  infraspinatus  and  teres  minor. 

Origin. — (1)  The  upper  part  of  the  posterior  border  of  the  scapula;  (2)  the 
spine  of  the  scapula,  by  means  of  the  strong  aponeurosis  which  covers  the  infra- 
spinatus. 

Insertion. — The  deltoid  tuberosity  of  the  humerus. 

Action. — To  flex  the  shoulder  joint  and  abduct  the  arm. 

Structure. — The  origin  of  the  muscle  is  partly  aponeurotic,  partly  fleshy. 
The  aponeurosis  fuses  with  that  which  covers  the  infraspinatus;  the  posterior  part 
is  attached  to  the  scapula  immediately  in  front  of  the  origin  of  the  long  head  of  the 
triceps.  The  belly  of  the  muscle  lies  for  the  most  part  in  a  cavity  formed  in  the 
triceps.     It  is  widest  about  its  middle. 

i?e?a^ions.— Superficially,  the  skin,  fascia,  cutaneus,  and  brachiocephalicus; 
deeply,  the  infraspinatus,  teres  minor,  triceps,  and  brachialis  muscles,  and  branches 
of  the  posterior  circumflex  artery  and  axillary  nerve. 

Blood-supply. — Subscapular  artery  (chiefly  through  the  posterior  circumflex). 

Nerve-supply. — Axillary  nerve. 

2.  Supraspinatus. — This  muscle  occupies  the  supraspinous  fossa,  which  it 
fills,  and  beyond  which  it  extends,  thus  coming  in  contact  ^vith  the  subscapularis. 

Origin. — The  supraspinous  fossa,  the  spine,  and  the  lower  part  of  the  car- 
tilage of  the  scapula. 

Insertion. — The  anterior  parts  of  the  proximal  tuberosities  of  the  humerus. 

Action. — To  extend  the  shoulder  joint.  It  also  assists  in  preventing  dislo- 
cation. 

Structure. — The  surface  of  the  muscle  is  covered  by  a  strong  aponeurosis, 
from  the  deep  face  of  which  many  fibers  arise.  The  muscle  is  thin  at  its  origin 
from  the  cartilage,  but  becomes  considerably  thicker  distally.  At  the  neck  of  the 
scapula  it  divides  into  two  branches,  between  which  the  tendon  of  origin  of  the 


THE   MUSCLES    OF   THE    SHOULDER  299 

biceps  emerges.  These  branches,  fleshy  superficially,  tendinous  deeply,  are  united 
by  a  fibrous  membrane  already  mentioned  in  connection  with  the  deep  pectoral 
muscle;  some  fibers  are  attached  to  this  membrane  and  the  capsule  of  the  shoulder 
joint.     A  bursa  is  often  present  under  the  muscle  at  the  tuber  scapulae. 

Relations. — Superficially,  the  skin,  fascia,  cutaneus,  trapezius,  and  brachio- 
cephalicus;  deeply,  the  scapula  and  its  cartilage,  the  subscapularis  muscle,  and  the 
suprascapular  vessels  and  nerve;  in  front,  the  anterior  deep  pectoral  muscle;  be- 
hind, the  spine  of  the  scapula  and  infraspinatus  muscle. 

Blood-supply. — Suprascapular  and  posterior  circumflex  arteries. 

Nerve-supply. — Suprascapular  nerve. 

3.  Infraspinatus. — This  muscle  occupies  the  greater  part  of  the  infraspinous 
fossa  and  extends  beyond  it  posteriorly. 

Origin. — The  infraspinous  fossa  and  the  scapular  cartilage. 

Insertion. — (1)  The  lateral  tuberosity  of  the  humerus,  distal  to  the  lateral 
insertion  of  the  supraspinatus ;    (2)  the  posterior  eminence  of  the  lateral  tuberosity. 

Action. — To  abduct  the  arm  and  rotate  it  outward.^  It  also  acts  as  a  lateral 
ligament. 

Structure. — This  muscle  is  also  covered  by  a  strong  aponeurosis,  from  which 
many  fibers  arise,  and  by  means  of  which  the  deltoid  is  attached  to  the  spine  of 
the  scapula.  A  thick  tendinous  layer  partially  divides  the  muscle  into  two  strata, 
and,  coming  to  the  surface  at  the  shoulder  joint,  constitutes  the  chief  means  of  in- 
sertion. This  tendon,  an  inch  or  more  (3  cm.)  in  width,  passes  over  the  posterior 
eminence  of  the  lateral  tuberosity  of  the  humerus;  it  is  bound  do^\^l  by  a  fibrous 
sheet,  and  a  synovial  bursa  is  interposed  between  the  tendon  and  the  bone.  The 
portion  of  the  tendon  which  crosses  the  lateral  tuberosity  is  in  part  cartilagi- 
nous. When  the  long  insertion  is  cut  and  reflected,  the  short  insertion,  partly 
tenchnous,  partly  fleshy,  is  exposed. 

Relations. — Superficially,  the  skin,  fascia,  cutaneus,  trapezius,  and  deltoid; 
deeply,  the  scapula  and  its  cartilage,  the  shoulder  joint  and  capsule,  the  long  head 
of  the  triceps,  the  teres  minor,  and  branches  of  the  posterior  circumflex  artery  of  the 
scapula. 

Blood-supply. — Subscapular  artery. 

Nerve-supply. — Suprascapular  nerve. 

4.  Teres  minor. — This  is  a  much  smaller  muscle  than  the  foregoing.  It 
lies  chieflj^  on  the  triceps,  under  cover  of  the  deltoid  and  infraspinatus. 

Origin. — (1)  The  rough  lines  on  the  distal  and  posterior  part  of  the  infra- 
spinous fossa;  (2)  a  small  part  of  the  posterior  border  of  the  scapula,  about  its 
middle;   (3)  a  tubercle  near  the  rim  of  the  glenoid  cavity. 

Insertion. — The  deltoid  tuberosity  and  a  small  area  just  above  it. 

Action. — To  flex  the  shoulder  joint  and  to  abduct  the  arm;  also  to  assist  in 
outward  rotation. 

Structure. — The  muscle  is  not  rounded,  but  flat  and  triangular  in  the  horse. 
Its  origin  from  the  posterior  border  of  the  scapula  is  by  means  of  a  fascicular  aponeu- 
rosis which  also  gives  origin  to  fibers  of  the  infraspinatus  and  triceps.  The  short, 
deep  part  of  the  muscle  which  lies  on  the  joint  capsule  behind  the  lateral  tuberosity 
of  the  humerus  is  covered  at  its  origin  by  the  distal  edge  of  the  tendon  of  origin  of 
the  long  head  of  the  triceps.  A  bursa  is  commonly  found  between  the  terminal 
part  of  the  muscle  and  the  capsule  of  the  shoulder  joint,  and  is  often  continuous 
with  that  of  the  infraspinatus. 

Relations. — Superficially,  the  deltoid  and  infraspinatus  muscles;  deeply,  the 
scapula,  the  shoulder  joint,  and  the  triceps  muscle. 

Blood-supply. — Subscapular  artery. 

Nerve-supply. — Axillary  nerve. 

1  Giinther  states  that  this  muscle  assists  in  extension  or  flexion  according  to  the  position 
of  the  head  of  the  humerus  relative  to  the  glenoid  cavity. 


300  FASCIiE   AND    MUSCLES    OF   THE    HORSE 


B.  Medial  Group 

1.  Subscapularis. — This  muscle  occupies  the  subscapular  fossa,  beyond  which, 
however,  it  extends  both  before  and  behind. 

Origin. — The  subscapular  fossa. 

Insertion. — The  posterior  eminence  of  the  medial  tuberosity  of  the  humerus. 

Action. — To  adduct  the  humerus. 

Structure. — The  muscle  is  flat  and  triangular.  The  base  is  thin  and  inter- 
digitates  with  the  scapular  attachments  of  the  serratus  ventralis.  Distally  the 
belly  thickens  and  becomes  narrower.  It  is  covered  by  an  aponeurosis,  and  con- 
tains a  considerable  amount  of  tendinous  tissue.  The  tendon  of  insertion  is  crossed 
by  the  tendon  of  origin  of  the  coraco-brachialis;  it  is  intimately  adherent  to  the  cap- 
sule of  the  shoulder  joint,  and  may  be  regarded  as  replacing  the  medial  ligament  of 
the  latter.  A  small  bursa  usually  is  present  between  the  tendon  and  the  tuberosity 
of  the  humerus. 

Relations. — Superficially,  the  scapula  and  shoulder  joint,  the  supraspinatus, 
triceps,  and  teres  major  muscles;  deeply,  the  serratus  ventralis  muscle,  the  bra- 
chial vessels,  and  the  chief  branches  of  the  brachial  plexus.  The  subscapular 
vessels  run  along  or  near  the  posterior  edge  of  the  muscle. 

Blood-supply. — Subscapular  artery. 

Nerve-supply. — Subscapular  nerves. 

2.  Teres  major. — This  muscle  is  flat,  widest  about  its  middle,  and  lies  chiefly 
on  the  medial  face  of  the  triceps. 

Origin. — The  dorsal  angle  and  the  adjacent  part  of  the  posterior  border  of 
the  scapula. 

Insertion. — The  teres  tubercle  of  the  humerus,  in  common  with  the  latissimus 
dorsi. 

Action. — To  flex  the  shoulder  joint  and  adduct  the  arm. 

Structure. — It  is  for  the  most  part  fleshy,  but  the  origin  consists  of  an  apo- 
neurosis which  blends  with  that  of  the  tensor  fasciae  antibrachii.  The  insertion 
is  by  a  flat  tendon  which  fuses  with  that  of  the  latissimus  dorsi. 

Relations. — Laterally,  the  triceps;  medially,  the  serratus  ventralis.  The  sub- 
scapular vessels  lie  in  a  groove  between  the  anterior  edge  of  this  muscle  and  the 
posterior  border  of  the  subscapularis;  near  the  shoulder  joint  the  posterior  cir- 
cumflex artery  and  the  axillary  nerve  emerge  between  the  two  muscles.  The 
medial  face  of  the  muscle  is  crossed  by  the  thoracic  branches  of  the  brachial  plexus, 
and  by  the  artery  which  supplies  the  latissimus  dorsi. 

Blood-supply. — Subscapular  artery. 

Nerve-supply.- — Axillary  nerve. 

3.  Coraco-brachialis.^ — This  muscle  lies  on  the  medial  surface  of  the  shoulder 
joint  and  the  arm. 

Origin. — The  coracoid  process  of  the  scapula. 

Insertion. — (1)  A  small  area  above  the  teres  tubercle  of  the  humerus;  (2)  the 
middle  third  of  the  anterior  surface  of  the  humerus. 

Action. — To  adduct  the  arm  and  to  flex  the  shoulder  joint. 

Structure. — The  long  tendon  of  origin  emerges  between  the  subscapularis  and 
the  medial  branch  of  the  supraspinatus.  It  passes  over  the  terminal  part  of  the 
subscapularis  and  is  provided  with  a  synovial  sheath.  The  belly  spreads  out  and 
divides  into  two  parts.  The  small,  short  part  is  inserted  into  the  proximal  third  of 
the  medial  surface  of  the  shaft  of  the  humerus ;  the  large,  long  part  is  inserted  into 
the  middle  third  of  the  humerus,  in  front  of  the  teres  tubercle  and  the  medial  head  of 
the  triceps. 

^  Also  termed  the  coraco-humeralis. 


THE  MUSCLES  OF  THE  SHOULDER 


301 


Relations. — Laterally,  the  subscapularis,  the  brachialis,  the  tendon  of  insertion 
of  the  latissimus  dorsi,  and  the  humerus;  medially,  the  deep  pectoral;  in  front, 
the  biceps  brachii.  The  anterior  circumflex  artery  and  the  nerve  to  the  biceps 
pass  between  the  two  parts,  or  between  the  muscle  and  the  bone,  and  the  brachial 
vessels  lie  along  the  posterior  border  of  the  muscle. 


Subscdpularis 

Ankrior  deep  pectoral 


Latissimus  dorsi 


Teres  major 


Tensor  fascice  antihrachii. 


Deep  fascia  of  forearm 


"ipraspmatus 

Posterior  deep 
pectoral 


Cora  co-brach  ialis 
Biceps  brachii 


Extensor  carpi  radialis 

Brachialis 

Long  medial  ligament  of  elbow 


Fig.  277. — Muscles  of  Shoulder  and  Arm  op  Horse;  Medial  View. 
1,  Long  head  of  triceps  brachii;  2,  medial  head  of  triceps;  3,  distal  end  of  humerus. 


Blood-supply. — Anterior  circumflex  artery. 
Nerve-supply. — Musculo-cutaneous  nerve. 

4.  Capsularis.^ — This  is  a  very  small  muscle,  which  lies  on  the  flexion  surface 
of  the  capsule  of  the  shoulder  joint. 

1  Also  known  as  the  scapulo-humeralis  posticus  s.  gracilis. 


302  FASCIA   AND   MUSCLES    OF   THE   HORSE 

Origin. — The  scapula,  close  to  the  rim  of  the  glenoid  cavity. 

Insertion. — The  posterior  surface  of  the  shaft  of  the  humerus,  a  short  distance 
below  the  head. 

Action. — It  has  been  held  that  it  tenses  the  capsule  of  the  shoulder  joint  and 
prevents  its  being  pinched  during  flexion,  but  there  does  not  appear  to  be  any 
attachment  of  the  muscle  to  the  joint  capsule. 

Structure. — It  is  fleshy  and  usually  about  the  breadth  of  a  finger.  It  may, 
however,  consist  of  only  a  few  bundles  of  fibers ;  sometimes  it  is  double.  It  passes 
through  the  brachialis  muscle  to  reach  its  insertion. 

Relations. — Laterally,  the  teres  minor  and  triceps  muscles;  medially,  the  teres 
major  and  subscapularis  muscles,  and  the  capsule  of  the  joint. 

Blood-supply. — Posterior  circumflex  artery. 

Nerve-supply. — Axillary  nerve. 


m.  THE  MUSCLES  OF  THE  ARM 
This  group  consists  of  five  muscles  (Mm.  brachii)  which  are  grouped  around  the 
humerus.     They  arise  from  the  scapula  and  the  humerus,  and  are  inserted  into  the 
forearm.     They  act  on  the  elbow  joint  and  the  fascia  of  the  forearm. 

1.  Biceps  brachii.^ — This  is  a  strong  fusiform  muscle,  which  lies  on  the  anterior 
surface  of  the  humerus  (Fig.  277). 

Origin. — The  tuber  scapulae. 

Insertion. — (1)  The  radial  tuberosity;  (2)  the  medial  ligament  of  the  elbow 
joint;  (3)  the  fascia  of  the  forearm  and  the  tendon  of  the  extensor  carpi  radialis. 

Action. — To  flex  the  elbow  joint;  to  fix  the  shoulder,  elbow,  and  carpus  in 
standing;  to  assist  the  extensor  carpi  radialis,  and  to  tense  the  fascia  of  the  fore- 
arm. 

Structure. — The  muscle  is  inclosed  in  a  double  sheath  of  fascia,  which  is  attached 
to  the  tuberosities  and  the  deltoid  ridge  of  the  humerus.  The  tendon  of  origin 
is  molded  on  the  intertuberal  or  bicipital  groove;  it  is  very  strong  and  dense  and 
is  partly  cartilaginous.  Its  play  over  the  groove  is  facilitated  by  the  large  inter- 
tuberal or  bicipital  bursa  (Bursa  intertubercularis).^  The  synovial  membrane 
covers  not  only  the  deep  face  of  the  tendon,  but  extends  somewhat  around  the  edges 
to  the  superficial  face.  A  well-marked  tendinous  intersection  runs  through  the  belly 
of  the  muscle  and  divides  distally  into  two  portions.  Of  these,  the  short,  thick 
one  is  inserted  into  the  radial  tuberosity  and  detaches  fibers  to  the  medial  collat- 
eral ligament  of  the  elbow  joint.  The  long  tendon  (Lacertus  fibrosus)  is  thinner, 
blends  with  the  fascia  of  the  forearm,  and  ends  by  fusing  with  the  tendon  of  the 
extensor  carpi  radialis;  thus  the  action  is  continued  to  the  metacarpus. 

Relations. — Laterally,  the  brachiocephalicus  and  brachialis  muscles;  medially, 
the  posterior  deep  pectoral  and  the  superficial  pectoral  muscles;  in  front,  the  an- 
terior deep  pectoral  muscle;  behind,  the  humerus,  the  coraco-brachialis  muscle, 
the  anterior  circumflex  and  anterior  radial  vessels,  and  the  musculo-cutaneous 
nerve. 

Blood-supply. — Branches  of  the  brachial  and  anterior  radial  arteries. 

Nerve-supply. — Musculo-cutaneous  nerve. 

2.  Brachialis.^ — This  muscle  occupies  the  musculo-spiral  groove  of  the  humerus. 
Origin.- — The  proximal  third  of  the  posterior  surface  of  the  humerus. 
Insertion. — The  medial  surface  of  the  neck  of  the  radius  (under  cover  of  the 

long  collateral  ligament)  and  the  transverse  radio-ulnar  ligament. 
Action. — To  flex  the  elbow  joint. 

^  Also  known  as  the  coraco-radialis  or  flexor  brachii. 

^  In  some  cases  the  bursa  communicates  with  the  cavity  of  the  shoulder  joint. 

'  Also  known  as  the  humeralis  obliquus  s.  externus  and  as  the  brachialis  anticus. 


THE   MUSCLES    OF   THE   ARM  303 

Structure. — The  peculiar  spiral  course  of  this  muscle  gave  rise  to  the  name 
often  applied  to  it— humeralis  obliquus.  Beginning  on  the  posterior  surface  of  the 
shaft,  close  to  the  head  of  the  humerus,  it  winds  over  the  lateral  surface,  crosses  the 
biceps  very  obliquely,  and  finally  reaches  the  medial  side  of  the  forearm  by  passing 
between  the  biceps  and  the  extensor  carpi.  It  is  entirely  fleshy,  with  the  exception 
of  its  relatively  slejider  tendon  of  insertion.  Some  fibers  at  the  proximal  end  are 
attached  to  the  capsule  of  the  shoulder  joint,  which  may  thereby  be  tensed  during 
flexion. 

Relations. — Laterally,  the  skin  and  fascia,  the  teres  minor,  deltoid,  triceps 
(lateral  head),  and  brachiocephalicus  muscles.  Deeply,  the  teres  major,  the  bi- 
ceps, and  the  humerus.  The  anterior  radial  artery  crosses  the  deep  face  of  the 
muscle  in  its  distal  third,  and  the  radial  nerve  accompanies  the  muscle  in  the  distal 
half  of  the  musculo-spiral  groove. 

Blood-supply. — Brachial  artery. 

Nerve-supply. — Musculo-cutaneous  nerve;  frequently  radial  nerve  also. 

3.  Tensor  fasciae  antibrachii  (Fig.  277). ^ — This  is  a  thin  muscle  which  lies 
chiefly  on  the  medial  surface  of  the  triceps. 

Origin. — The  tendon  of  insertion  of  the  latissimus  dorsi  and  the  posterior 
border  of  the  scapula. 

Insertion. — (1)  The  deep  fascia  of  the  forearm;   (2)  the  olecranon. 

Action. — (1)  To  tense  the  fascia  of  the  forearm  and  to  extend  the  elbow  joint. 

Structure. — The  origin  consists  of  a  very  thin  aponeurosis  which  blends  with 
those  of  the  caput  longum  and  the  latissimus  dorsi.  In  most  cases  there  is  a  dis- 
tinct division  into  anterior  and  posterior  heads.  The  muscular  portion  is  thin  in 
its  anterior  part,  somewhat  thicker  behind,  and  is  narrower  than  the  aponeurotic 
origin.  It  is  succeeded  by  an  aponeurotic  insertion,  which  ends  chiefly  by  blending 
with  the  fascia  of  the  forearm  a  little  below  the  elbow.  There  is,  however,  a  small 
but  constant  tendinous  attachment  to  the  olecranon. 

Relations. — Laterally,  the  cutaneus,  triceps  (long  and  medial  heads),  the  medial 
and  middle  flexors  of  the  carpus,  and  the  ulnar  vessels  and  nerve;  medially,  the 
latissimus  dorsi,  serratus  ventralis,  and  posterior  pectoral  muscles. 

Blood-supply. — Subscapular,  ulnar,  and  deep  brachial  arteries. 

Nerve-supply. — Radial  nerve. 

4.  Triceps  brachii  (Figs.  267,  268,  277).— This,  together  with  the  preceding 
muscle,  constitutes  the  large  muscular  mass  which  fills  the  angle  between  the  pos- 
terior border  of  the  scapula  and  the  humerus.  It  is  clearly  divisible  into  three 
heads. 

(a)  Long  head  (Caput  longum  tricipitis).' — This,  the  largest  and  longest  of 
the  three  heads,  is  a  powerful,  thick,  triangular  muscle,  which  extends  from  the 
posterior  border  of  the  scapula  to  the  olecranon. 

Origin. — The  posterior  border  of  the  scapula. 

Insertion. — The  lateral  and  posterior  part  of  the  summit  of  the  olecranon. 

Action. — (1)  To  extend  the  elbow  joint;   (2)  to  flex  the  shoulder  joint. 

Structure.— The  muscle  arises  by  a  wide,  strong  aponeurosis  from  the  posterior 
border  of  the  scapula.  From  this  the  bundles  of  the  fleshy  portion  converge  to 
the  short,  strong  tendon  of  insertion.  A  careful  examination  will  show  that  the 
muscle  is  penetrated  by  a  tendinous  intersection  from  which  many  fibers  take  origin 
obliquely.  The  superficial  face  is  covered  by  an  aponeurosis  which  is  specially 
developed  at  its  distal  part.     A  small  bursa  occurs  under  the  tendon  of  insertion. 

1  M'Fadyean  and  Vaughan  term  this  muscle  the  scapulo-ulnaris,  while  Arloing  and  Lesbre 
term  it  "Ancone  accessoire  du  grand  dorsal."  The  above  name  seems  to  agree  best  with  the 
chief  insertion  and  action,  although  it  certainly  arises  largely  from  the  tendon  of  insertion  of  the 
latissimus  dorsi. 

*  Also  known  as  the  anconaeus  longus  or  caput  magnum. 


304  FASCI.E    AND    MUSCLES    OF   THE    HORSE 

Relations. — Laterally,  the  cutaneus,  deltoid,  infraspinatus,  teres  minor,  and 
the  lateral  head;  medially,  the  tensor  fasciae  antibrachii,  teres  major,  latissimus  dorsi 
and  posterior  deep  pectoral  muscles,  and  the  subscapular  vessels;  in  front,  the 
brachialis  and  the  medial  head,  the  deep  brachial  and  posterior  circumflex  vessels, 
and  the  axillary  and  radial  nerves;  behind,  the  skin  and  fascia. 

J5/ood-SMpp??/.— Subscapular  and  deep  brachial  arteries. 

Nerve-supply. — Radial  nerve. 

(b)  Lateral  head  (Caput  laterale  tricipitis).' — This  is  a  strong,  quadrilateral 
muscle,  which  lies  on  the  lateral  surface  of  the  arm.  Its  proximal  third  is  covered 
by  the  deltoid  and  teres  minor  muscles,  the  remainder  only  by  the  thin  cutaneous 
muscle  and  the  skin. 

Origin. — (1)  The  deltoid  tuberosity  and  the  curved  rough  line  which  extends 
from  it  to  the  neck  of  the  humerus;  (2)  the  strong  fascia  which  extends  from  the 
deltoid  tuberosity  to  the  lateral  surface  of  the  elbow  joint. 

Insertion. — (1)  A  small  prominent  area  on  the  lateral  surface  of  the  olecranon; 
(2)  the  tendon  of  the  long  head. 

Action. — To  extend  the  elbow  joint. 

Structure. — The  origin  consists  of  short  tendinous  fibers.  The  belly  is  thick, 
and  is  composed  of  parallel  bundles  which  are  directed  obliquely  downward  and 
backward.  They  are  inserted  partly  into  the  tendon  of  the  long  head  and  partly 
into  the  olecranon  below  and  in  front  of  that  tendon. 

Relations. — Laterally,  the  deltoid,  teres  minor,  and  cutaneus  muscles ;  medially, 
the  long  and  medial  heads  and  the  brachialis  muscle.  Branches  of  the  circumflex 
vessels  and  axillary  nerve  emerge  between  the  posterior  edge  of  the  muscle  and  the 
long  head.  The  deep  face  of  the  muscle  is  related  to  the  branches  of  the  deep  bra- 
chial artery  and  of  the  radial  nerve. 

Blood-supply. — Posterior  circumflex  and  deep  brachial  arteries. 

Nerve-supply. — Radial  nerve. 

(c)  Medial  head  (Caput  mediale  tricipitis)  (Fig.  277). ^ — This  is  much  the  small- 
est of  the  three  heads.  It  is  situated  on  the  medial  surface  of  the  arm,  and  extends 
from  the  middle  third  of  the  humerus  to  the  olecranon. 

Origin. — The  middle  third  of  the  medial  surface  of  the  shaft  of  the  humerus, 
behind  and  below  the  teres  tubercle. 

Insertion. — The  medial  and  anterior  part  of  the  summit  of  the  olecranon,  be- 
tween the  insertion  of  the  long  head  and  the  origin  of  the  ulnar  head  of  the  deep 
digital  flexor. 

Action. — To  extend  the  elbow  joint. 

Structure. — The  muscle  is  fleshy  except  at  its  insertion,  where  it  has  a  flat  ten- 
don, under  which  a  small  bursa  may  be  found. 

Relations. — Laterally,  the  humerus,  brachialis,  anconeus,  and  the  lateral  head; 
medially,  the  posterior  deep  pectoral,  coraco-brachialis,  teres  major,  latissimus  dorsi, 
and  tensor  fascise  antibrachii  muscles,  the  brachial  and  deep  brachial  vessels,  and 
the  median  and  ulnar  nerves;  behind,  the  long  head,  branches  of  the  deep  brachial 
vessels,  and  the  radial  nerve. 

Blood-supply. — Deep  brachial  and  ulnar  arteries. 

Nerve-supply. — Radial  nerve. 

5.  Anconeus. — This  is  a  small  muscle  which  covers  the  olecranon  fossa  and 
is  covered  by  the  triceps.     It  is  somewhat  difficult  to  separate  from  the  lateral  head. 

Origin. — The  distal  third  of  the  posterior  surface  of  the  humerus. 

Insertion. — The  lateral  surface  of  the  olecranon. 

Action. — To  extend  the  elbow  joint,  and  to  raise  the  capsule  of  the  joint  and 
prevent  its  being  pinched  during  extension. 

*  Also  known  as  the  anconi3eiis  lateralis  s.  externus  or  caput  medium. 
2  Also  known  as  the  anconjeus  mediahs  s.  internus  or  caput  parvum. 


FASCIA    AND    MUSCLES    OF   THE    FOREARM    AND    MANUS 


305 


Structure. — It  is  almost  entirely  fleshy.  The  deep  face  is  adherent  to  the  joint 
capsule. 

Relations. — Superficially,  the  triceps  muscle;  deeply,  the  humerus  and  the 
elbow  joint. 

Blood-supply. — Deep  brachial  artery. 

Nerve-supply. — Radial  nerve. 


-Ul 


•Deep  flexor  tendon 

■•Distal  end  of  small  metacarpal  bone 
•'Suspensory  ligament 


Branch  of  superficial  flexor  tendon 
Distal  digital  annular  ligament 
Upper  border  of  cartilage 
of  third  phalanx 


IV.  FASCIA  AND  MUSCLES  OF  THE  FOREARM  AND  MANUS 
(FASCIA  ET  MUSCULI  ANTIBRACHII  ET  MANUS) 

The  forearm  is  covered  on  three  sides  by  the  muscles  of  this  group,  leaving 
the  medial  surface  of  the  radius  for  the  most  part  subcutaneous.    The  extensors  of 
the  carpus  and  digit  lie  on  the 
dorsal  and  lateral  parts  of  the 
region,  while  the  flexors  oc- 
cupy the  volar  surface. 

The  fascia  of  the  fore- 
arm (Fascia  antibrachii) 
forms  a  very  strong  and  com- 
plete investment  for  all  the 
muscles  of  the  region.  The 
superficial  fascia  is  thin,  and 
blends  at  the  carpus  with  the 
deep  fascia ;  it  furnishes  inser- 
tion to  the  posterior  super- 
ficial pectoral  muscle.  The 
deep  fascia  is  very  strong  and 
tendinous  in  character.  It 
furnishes  insertion  at  its 
proximal  and  medial  part  to 
the  tensor  fasciae  antibrachii 
muscle;  at  its  proximal  anter- 
ior and  lateral  part  to  the 
brachiocephalicus  and  biceps. 
It  is  attached  at  the  elbow  to 
the  lateral  tuberosities  of  the 
humerus  and  radius,  to  the 
ulna,  and  to  the  collateral 
ligaments.  On  '  the  medial 
surface  of  the  forearm  it 
blends  with  the  periosteum 
on  the  subcutaneous  surface 

of  the  radius.  It  is  closely  adherent  to  the  surface  of  the  extensor  muscles,  but  is 
rather  loosely  attached  to  the  flexors;  near  the  carpus  it  blends  with  the  tendons 
attached  to  the  accessory  carpal  bone.  From  its  deep  face  are  detached  intermus- 
cular septa,  which  form  sheaths  for  the  muscles  and  are  attached  to  the  underlying 
bones.  The  principal  septa  are:  (a)  One  which  passes  between  the  common  digital 
extensor  and  the  lateral  extensor  and  ulnaris  laterahs;  (h)  one  between  the  com- 
mon extensor  and  the  extensor  carpi  radialis;  (c)  one  between  the  medial  and  middle 
flexors  of  the  carpus. 

The  carpal  fascia  (Fascia  carpi)  is  a  direct  continuation  of  that  of  the  forearm. 
It  is  attached  chiefly  to  the  tuberosities  at  the  distal  end  of  the  radius,  to  the  ac- 
cessory carpal  bone,  and  to  the  carpal  collateral  ligaments.     In  front  it  forms  the 
so-called  dorsal  annular  ligament  of  the  carpus  (Lig.  carpi  dorsale),  bridging  over 
20 


Fia.   278. — Digit  of  Horse;  Volar  View. 
14,  Deep  flexor  tendon;    15,  superficial  flexor  tendon;    16,  volar  an- 
nular ligament  of  fetlock;    17,  proximal  digital  annular  or  vaginal  liga- 
ment;   11,  cartilage  of  third  phalanx;   34,  digital  cushion.     (After  Ellen- 
berger-Baum,  Anat.  fiir  Kiinstler.) 


306  FASCIA   AND   MUSCLES    OF   THE    HORSE 

the  grooves  and  binding  down  the  extensor  tendons  and  their  synovial  sheaths.  Be- 
hind it  is  greatly  thickened  and  forms  the  volar  annular  or  transverse  ligament  of 
the  carpus  (Lig.  carpi  transversum) .  This  stretches  across  from  the  accessory  car- 
pal bone  to  the  medial  collateral  ligament  and  the  proximal  extremity  of  the  medial 
metacarpal  bone.  It  thus  completes  the  carpal  canal  (Canalis  carpi),  in  which  lie 
the  flexor  tendons,  the  carpal  synovial  sheath,  the  common  digital  artery,  and 
the  medial  volar  nerve. 

The  superficial  fascia  of  the  metacarpus  and  digit  presents  no  special  features, 
but  the  deep  fascia  (Fascia  metacarpea  et  digitalis)  is  complicated  by  the  existence 
of  several  annular  ligaments.  In  the  metacarpus  it  is  hardly  distinguishable  from 
the  periosteum  in  front.  On  the  proximal  part  of  the  volar  surface  it  forms  a  strong 
and  close  sheath  for  the  flexor  tendons,  and  is  attached  to  the  metacarpal  bone 
on  each  side.  Lower  down  and  between  the  annular  ligaments  it  is  thin.  On  the 
flexion  surface  of  the  fetlock  joint  it  is  much  thickened  by  fibers  passing  transversely 
from  one  sesamoid  bone  to  the  other,  forming  the  volar  annular  ligament  of  the  fet- 
lock, which  binds  down  the  flexor  tendons  in  the  sesamoid  groove  and  converts  the 
latter  into  a  canal.  Distal  to  this  is  a  second  thick  quadrilateral  sheet,  the  prox- 
imal digital  annular  ligament  (Lig.  vaginale),  which  covers  and  is  adherent  to  the 
tendon  of  the  superficial  flexor.  It  is  attached  on  either  side  by  two  bands  to  the 
ends  of  the  borders  of  the  first  phalanx,  thus  firmly  binding  down  the  flexor  tendons. 
A  little  further  down  a  crescentic  fibro-elastic  sheet,  the  distal  digital  annular  liga- 
ment, covers  the  terminal  expansion  of  the  deep  flexor  tendon.  It  is  attached 
on  either  side  by  a  strong  band  to  the  side  of  the  first  phalanx  about  its  middle;  its 
superficial  face  is  largely  covered  by  the  digital  cushion  and  its  deep  surface  is  in 
great  part  adherent  to  the  deep  flexor  tendon.  It  is  also  connected  with  the  so- 
called  tendon  or  ligament  of  the  ergot  (Fig.  572).  This  is  a  thin  and  narrow 
fibrous  band,  which  begins  in  the  fibrous  basis  of  the  ergot,  as  the  mass  of  horn  at  the 
fetlock  is  called.  It  descends  to  the  side  of  the  pastern  joint,  crossing  over  the 
digital  artery  and  nerve;  here  it  widens  out  and  blends  with  the  fibro-elastic  sheet 
just  described. 

A.  Extensor  Division 

1.  Extensor  carpi  radialis  (M.  radialis  dorsalis).^ — This  is  the  largest  muscle 
of  the  extensor  division,  and  lies  on  the  dorsal  surface  of  the  radius. 

Origin. — (1)  The  lateral  condyloid  crest  of  the  humerus;  (2)  the  coronoid 
fossa;  (3)  the  deep  fascia  of  the  arm  and  forearm  and  the  intermuscular  septum 
between  this  muscle  and  the  common  extensor. 

Insertion. — The  metacarpal  tuberosity. 

Action. — To  extend  and  fix  the  carpal  joint  and  to  flex  the  elbow  joint. 

Structure. — The  tendon  of  origin  blends  with  that  of  the  common  extensor 
and  is  adherent  to  the  capsule  of  the  elbow  joint.  The  belly  of  the  muscle  is  rounded 
and  runs  out  to  a  point  at  the  distal  third  of  the  forearm.  The  tendon,  which  runs 
nearly  the  whole  length  of  the  fleshy  portion,  appears  on  the  surface  of  the  latter 
about  its  middle;  here  the  muscle  shows  a  distinctly  pennate  arrangement.  The 
tendon  passes  through  the  middle  groove  at  the  distal  extremity  of  the  radius  and 
over  the  capsule  of  the  carpal  joint,  bound  down  by  the  dorsal  annular  ligament  and 
invested  with  a  synovial  sheath.  The  latter  begins  three  to  four  inches  (ca.  8- 
10  cm.)  above  the  carpus  and  extends  to  the  middle  of  the  carpus.  Distal  to  this 
the  tendon  is  attached  to  the  joint  capsule,  but  there  is  usually  a  small  bursa  at  the 
level  of  the  third  carpal  bone.  In  the  distal  half  of  the  forearm  the  deep  fascia 
blends  with  the  tendon,  and  here  the  latter  is  joined  by  the  long  tendon  of  the  biceps. 

Relations. — Superficially,  the  skin,  fascia,  and  the  oblique  extensor;  deeply, 
the  capsule  of  the  elbow  joint,  the  short  biceps  tendon,  the  radius,  the  carpal  joint 

1  Also  commonly  termed  the  extensor  metacarpi  magnus. 


EXTENSOR   DIVISION  307 

capsule,  the  anterior  radial  artery,  and  the  radial  nerve;  laterally,  the  common  ex- 
tensor;   medially,  at  the  elbow,  the  brachialis  and  biceps. 

Blood-supply. — Anterior  radial  artery. 

Nerve-supply. — -Radial  nerve. 

2.  Common  digital  extensor  (M.  extensor  digitalis  communis). ^ — This  muscle 
lies  lateral  to  the  foregoing,  which  it  resembles  in  general  form,  although  less  bulky. 

Origin. — (1)  The  front  of  the  distal  extremity  of  the  humerus,  in  and  lateral 
to  the  coronoid  fossa;  (2)  the  lateral  tuberosity  on  the  proximal  extremity  of  the 
radius,  the  lateral  ligament  of  the  elbow,  and  the  lateral  border  of  the  radius  at  the 
junction  of  its  proximal  and  middle  thirds;  (3)  the  lateral  surface  of  the  shaft  of 
the  ulna;    (4)  the  fascia  of  the  forearm. 

Insertion. — (1)  The  extensor  process  of  the  third  phalanx;  (2)  the  dorsal  sur- 
face of  the  proximal  extremities  of  the  first  and  second  phalanges. 

Action. — To  extend  the  digital  and  carpal  joints,  and  to  flex  the  elbow  joint. 

Structure. — The  muscle  is  a  compound  one,  representing  the  common  extensor, 
together  with  vestiges  of  the  proper  extensors  of  the  digits.  Usually  at  least  two 
heads  may  be  distinguished,  although  the  division  is  always  more  or  less  artificial 
so  far  as  the  muscular  part  is  concerned.  The  humeral  head  (Caput  humerale), 
which  constitutes  the  bulk  of  the  muscle,  arises  from  the  front  of  the  lateral  epi- 
condyle  of  the  humerus  in  common  with  the  extensor  carpi;  the  tendon  of  origin 
is  adherent  to  the  capsule  of  the  elbow  joint.  Its  belly  is  fusiform,  and  terminates 
in  a  point  near  the  distal  third  of  the  radius.  The  tendon  appears  on  the  surface 
of  the  muscle  about  the  middle  of  the  belly,  the  arrangement  being  pennate.  The 
tendon  passes  downward  through  the  outer  of  the  two  large  grooves  on  the  front  of 
the  distal  end  of  the  radius,  and  over  the  capsule  of  the  carpal  joint.  Passing  down 
over  the  front  of  the  metacarpus,  it  gradually  inclines  medially,  reaching  the  middle 
line  of  the  limb  near  the  fetlock.  A  little  below  the  middle  of  the  first  phalanx  it 
is  joined  by  the  branches  of  the  suspensory  ligament,  and  the  tendon  thus  becomes 
much  wider.  Two  synovial  membranes  facilitate  the  play  of  the  tendon.  The 
proximal  one  is  a  synovial  sheath  which  begins  about  three  inches  (ca.  7-8  cm.) 
above  the  carpus,  and  terminates  at  the  proximal  end  of  the  metacarpus.  At  the 
fetlock  a  bursa  occurs  between  the  tendon  and  the  joint  capsule,  but  otherwise 
the  two  are  adherent.  The  smaller  head,  arising  chiefly  from  the  radius  and  ulna, 
is  often  divisible  into  two  parts  (Fig.  568).  The  larger  of  these  is  the  radial  head 
(Caput  radiale) ;-  it  arises  from  the  lateral  tuberosity  and  border  of  the  radius,  and 
from  the  lateral  ligament  of  the  elbow  joint.  The  flat  belly  is  succeeded  by  a  deli- 
cate tendon,  which  accompanies  the  principal  tendon  over  the  carpus  (included  in 
the  same  sheath),  and  then  passes  outward  to  fuse  with  the  tendon  of  the  lateral 
extensor,  or  it  may  continue  downward  between  the  common  and  lateral  extensor 
tendons  to  the  fetlock.  Usually  a  slip  is  detached  which  is  inserted  on  the  prox- 
imal extremity  of  the  first  phalanx,  or  ends  in  the  fascia  here.  The  smaller  and 
deeper  division  is  the  ulnar  head  (Caput  ulnare)  f  it  is  usually  somewhat  difficult 
to  isolate.  It  arises  from  the  ulna  close  to  the  interosseous  space.  It  has  a  small 
rounded  belly  and  is  provided  with  a  deficate  tendon  which  may  fuse  with  the 
principal  tendon  or  may  be  inserted  into  the  joint  capsule  and  the  fascia  in  front  of 
the  fetlock  joint. 

Relations. — The  chief  relations  of  the  belly  of  the  muscle  are :  superficially,  the 
skin  and  fascia;  deeply,  the  elbow  joint,  the  radius  and  ulna,  the  extensor  carpi 
obliquus,  and  the  anterior  radial  vessels  and  radial  nerve;    in  front  and  medially, 

^  Termed  also  the  anterior  extensor  of  the  phalanges  or  extensor  pedis. 

2  This  (formerly  called  the  muscle  of  PhilUps)  is  considered  to  represent  the  part  of  the 
common  extensor  for  the  fourth  and  fifth  digits. 

'  Martin  considers  that  this  muscle  (formerly  termed  the  muscle  of  Thiernesse)  represents 
the  extensor  indicis  proprius  and  the  part  of  the  common  extensor  for  the  second  digit. 


308 


FASCIA   AND   MUSCLES    OF   THE    HORSE 


the  extensor  carpi  radialis;    behind,  the   lateral   extensor  and  the  interosseous 
vessels. 

Blood-supply. — Radial  and  interosseous  arteries. 

Nerve-supply. — Radial  nerve. 

Lesbre  reports  that  he  has  found  in  one  case  a  brachioradialis  muscle  in  the  horse.  It 
was  a  delicate  fleshy  bundle,  superposed  on  the  medial  border  of  tlie  common  extensor,  and  ex- 
tended from  the  lateral  condyloid  crest  to  the  distal  part  of  the  medial  border  of  the  radius. 


Extensor  carpi  obliquus 


Metacarpal  tuberosity  -^  '  H 
Tendon  from  common  to  lateral  extensor  '^' 


Lateral  small  metacarpal  hone 


Branch  of  suspensory  ligament  to 
extensor  tendon 


Olecranon 
Ulnar  head  of  deep  flexor 


Lateral  extensor 
Deep  flexor  {humeral  head) 

Tendon  of  ulnaris  lateralis 
Accessory  carpal  bone 


Check  ligament 

Suspensory  ligament 
Flexor  tendons 


Flexor  tendons 
Cartilage  of  tJiird  j)halanx 


Fig.  279. — Muscles  of  Left  Thoracic  Limb  of  Horse  from  Elbow  Downward;   Lateral  View. 

O,  Extensor  carpi  radialis;   g,  brachialis;   g',  anterior  superficial  pectoral;    c,  common  digital  extensor;    e,  ulnaris  la - 

eralis.     (After  EIlenberger-Baum,  Anat.  fiir  Kiinstler.) 

3.  Lateral  digital  extensor  (M.  extensor  digitalis  lateralis  s.  digiti  quinti  pro- 
prius).^— This  muscle  is  much  smaller  than  the  preceding,  behind  which  it  is  situated. 
Origin.— The  lateral  tuberosity  of  the  radius  and  the  lateral  ligament  of  the 
^  Also  known  as  the  lateral  extensor  of  the  phalanges. 


EXTENSOR   DIVISION 


309 


elbow  joint,  the  shaft  of  the  uhia,  the  lateral  border  of  the  radius,  and  the  inter- 
muscular septum. 

Insertion. — An  eminence  on  the  front  of  the  proximal  extremity  of  the  first 
phalanx. 

Action. — To  extend  the  digit  and  carpus. 

Structure.— TliG:  muscle  is  pennate,  and  is  enclosed  in  a  sheath  formed  by  the 
deep  fascia,  from  which  many  fibers  arise.  The  belly  is  thin  and  fusiform  and 
terminates  at  the  distal  third  of  the  forearm.  From  here  the  tendon  (at  first 
small  and  round)  passes  downward  through  the  groove  on  the  lateral  tuberosity 
of  the  distal  end  of  the  radius,  then  over  the  carpus,  and,  gradually  inclining  toward 


Intermuscular  septum 


Common  digital  extensor 

Extensor  carpi  obliquus 

Intermuscular  septum 

Lateral  digital  extensor 
Intermuscular  septum 


Deep  digital  flexor 
{humeral  head) 

Ulnaris  lateralis 


Deep  digital  flexor 
{ulnar  head) 


Extensor  carpi  radialis 


Cutaneous  branch  of  mv 
culo-cutaneous  nerve 
Cephalic  vein 


Median  nerve 
Flexor  carpi  radialis 


Flexor  carpi  ulnaris 


Ulnar  vessels  and  nerve 


Superficial  digital  flexor 


Fig.  280. — Cross-section  of  Left  Forearm  of  Horse. 

Section  is  cut  a  little  above  middle  of  region  and  the  figure  is  a  proximal  view. 

1,  Median  artery  and  satellite  veins;   2,  3,  branches  of  deep  brachial  and  anterior  radial  vessels;   4,  dorsal  interosseous 

vessels. 


the  front,  but  not  reaching  the  middle  line  of  the  limb,  it  passes  over  the  meta- 
carpus and  fetlock  to  its  insertion.  Two  synovial  membranes  occur  in  connection 
with  the  tendon.  A  synovial  sheath  envelops  the  tendon,  beginning  about  three 
inches  (ca.  6-8  cm.)  above  the  carpus,  and  reaching  to  the  proximal  end  of  the 
metacarpus.  At  the  fetlock  a  small  bursa  lies  between  the  tendon  and  the  joint 
capsule,  but  otherwise  the  tendon  is  adherent  to  the  capsule.  The  tendon  becomes 
flat  and  much  larger  below  the  carpus,  having  received  the  tendon  of  the  radial 
head  of  the  common  extensor  and  a  strong  band  from  the  accessory  carpal  bone. 

Relations. — Superficially,  the  skin  and  fascia;    deeply,  the  lateral  face  of  the 
radius  and  ulna;     in  front,  the  common  extensor,  the  oblique  extensor,  and  the 


310  FASCIiE   AND   MUSCLES    OF   THE    HORSE 

interosseous  artery;  behind,  the  lateral  flexor  of  the  carpus  and  the  deep  flexor  of 
the  digit. 

Blood-supply. — Interosseous  artery. 

Nerve-supply. — Radial  nerve. 

4.  Extensor  carpi  obliquus  (M.  abductor  pollicis  longus  et  extensor  pollicis 
brevis).^ — This  is  a  small  muscle  which  curves  obliquely  over  the  distal  half  of  the 
radius  and  the  carpus. 

Origin. — The  lateral  border  and  adjacent  part  of  the  dorsal  surface  of  the 
radius  (the  attachment  area  begimiing  at  a  point  above  the  middle  of  the  bone  and 
extending  down  to  its  distal  fourth). 

Insertion. — The  head  of  the  medial  (second)  metacarpal  bone. 

Action. — To  extend  the  carpal  joint. 

Structure. — The  muscle  is  pennate  and  has  a  flat  belly  which  curves  downward, 
forward,  and  medially  over  the  distal  part  of  the  radius.  The  tendon  continues 
the  direction  of  the  muscle,  and  passes  over  the  tendon  of  the  extensor  carpi  radialis ; 
it  then  occupies  the  oblique  groove  at  the  distal  end  of  the  radius,  and  crosses  the 
medial  face  of  the  carpus.     It  is  provided  with  a  sjmovial  sheath. 

Relations. — Superficially,  the  skin  and  fascia,  the  lateral  extensor,  and  the 
common  extensor;  deeply,  the  radius,  the  extensor  carpi  radialis,  the  carpal  joint 
capsule,  and  the  medial  ligament  of  the  carpus. 

Blood-supply.- — Interosseous  and  anterior  radial  arteries. 

Nerve-supply. — Radial  nerve. 

B.  Flexor  Division 

1.  Flexor  carpi  radialis  (or  medial  flexor  of  the  carpus).- — This  muscle  lies  on 
the  medial  surface  of  the  forearm,  behind  the  border  of  the  radius. 

Origin. — The  medial  epicondyle  of  the  humerus,  below  and  behind  the  col- 
lateral ligament. 

Insertion. — The  proximal  end  of  the  medial  (second)  metacarpal  bone. 

Action. — To  flex  the  carpal  joint  and  to  extend  the  elbow. 

Structure. — The  muscle  has  a  short  tendon  of  origin,  which  is  succeeded  by  a 
somewhat  flattened,  fusiform  belly.  The  tendon  of  insertion  begins  near  the  distal 
fourth  of  the  radius  and  descends  in  a  canal  in  the  transverse  carpal  ligament.  It 
is  provided  with  a  synovial  sheath  which  begins  two  or  three  inches  (ca.  5-8  cm.) 
above  the  carpus  and  extends  almost  to  the  insertion  of  the  tendon. 

Relations. — Superflcially,  the  skin  and  fascia,  the  posterior  superficial  pectoral, 
and  the  tensor  fasciae  antibrachii;  deeply,  the  elbow  joint,  the  radius,  the  deep 
flexor,  the  flexor  carpi  ulnaris,  the  median  vessels,  and  the  median  nerve.  At  the 
elbow  the  artery  and  nerve  lie  in  front  of  the  muscle,  but  below  they  dip  beneath  it. 

Blood-supply. — Median  artery. 

Nerve-supply. — Median  nerve. 

On  removing  the  deep  fascia  on  the  medial  surface  of  the  elbow  the  student  may  notice  a 
small  muscle  lying  along  the  collateral  ligament.  This  is  the  pronator  teres,  which  is  usually 
not  present  or  a  mere  vestige  in  the  horse.  It  arises  by  a  small,  flat  tendon  from  the  medial  epi- 
condyle of  the  humerus,  and  is  inserted  into  the  medial  ligament  of  the  elbow.  On  account  of  its 
small  size  and  the  fact  that  the  forearm  is  fixed  in  the  po.sition  of  pronation,  the  muscle  can  have 
no  appreciable  function.     It  is  usually  represented  by  a  tendinous  band. 

2.  Flexor  carpi  ulnaris  (or  middle  flexor  of  the  carpus).^ — This  muscle  lies  on  the 
medial  and  posterior  aspect  of  the  forearm,  partly  under,  partly  behind,  the  preced- 
ing muscle.     It  arises  by  two  heads — humeral  and  ulnar. 

1  Also  known  as  the  extensor  metacarpi  obliquus. 

2  Also  known  as  the  flexor  carpi  s.  metacarpi  internus  or  radialis  volaris. 

2  Also  known  as  the  flexor  carpi  (s.  metacarpi)  medius  or  ulnaris  medialis. 


FLEXOR   DIVISION 


311 


Origin. — (1)  The  medial  epicondyle  of  the  humerus  just  behind  the  preceding 
muscle;  (2)  the  medial  surface  and  posterior  border  of  the  olecranon. 


Long  head  of  triceps 
Medial  head  of  triceps 

Olecranon 
Ulnar  head  of  deep  flexor 


Flexor  carpi  idnaris 
Flexor  carpi  radialis 


Accessory  carpal  bone 
Medial  ligament  of  carpus 


Superficial  flexor  tendon 

Deep  flexor  tendon 
Suspensory  ligament 

Distal  end  of  Mc.  II 
Annular  ligament 

Superficial  flexor  tendon 
Deep  flexor  tendon 


Biceps  brachii 


Extensor  carpi  radialis 
Long  tendon  of  biceps 
Brachialis 

Long  medial  ligament 


Radius 


Tendon  of  extensor  carpi 
obliquus 


Metacarpal  tuberosity 


Mc.  in 


Fetlock  joint 

E.vtensor  branch  of  suspensory 
ligament 

Common  extensor  tendon 

Pastern  joint 

Cartilage  of  third  phalanx 


Fig.  2S1. — Muscles  of  Left  Thoracic  Limb  of  Horse  from  Elbow  Downward;  Medial  View. 
The  fascia  and  the  ulnar  head  of  the  flexor  carpi  ulnaris  have  been  removed.      1,  Distal  end  of  humerus;    2,  median 


Insertion. — The  proximal  edge  of  the  accessory  carpal  bone. 
Action. — To  flex  the  carpal  joint  and  to  extend  the  elbow. 


312 


FASCIiE   AND   MUSCLES    OF   THE    HORSE 


Structure. — The  humeral  head  is  much  the  larger,  constituting,  in  fact,  the 
bulk  of  the  muscle.  It  is  flattened,  curved,  and  tapers  at  both  ends.  The  ulnar 
head,  much  smaller  and  very  thin,  is  covered  by  an  aponeurosis  from  which  many  of 
its  fibers  arise.     It  joins  the  large  head  a  little  above  the  middle  of  the  forearm. 


Ulnar  head  of  deep  flexor 
Stump  of  flexor  carpi  radialis 

Stump  of  flexor  carpi  idnaris 


Superficial  digital  flexor 
Deep  digital  flexor 

Tendon  of  ulnar  head 

Radial  head  of  superficial  flexor 
Insertion  of  flexor  carpi  idnaris 
Accessory  carpal  bone 


Deep  flexor  tendon 
Superficial  flexor  tendon 

Check  ligament 
Suspensory  ligament 


Biceps  brachii 

Brachialis 

Long  medial  ligament 

Extensor  carpi  radialis 


Radius 


Annular  ligament 


Deep  flexor  tendon 
Cartilage  of  third  phalanx 


Tendon  of  flexor  carpi  radialis 
Tendon  of  extensor  carpi  obliquus 


Mc.  Ill 


Fetlock  joint 

Extensor  branch  of  suspensory 
ligament 


Fig.  282. — Muscles  of  Left  Thoracic  Limb  of  Horse,  fhom  Elbow  Downward;  Medial  View. 
Parts  of  superficial  muscles  have  been  removed,  carpal  canal  opened  up,  and  flexor  tendons  drawn  backward. 


The  tendon  of  insertion  is  short  and  strong;    it  blends  with  the  posterior  annular 
ligament  of  the  carpus. 

Relations. — Superficially,  the  tensor  fascise  antibrachii,  superficial  pectoral,  and 
flexor  carpi  radialis,  the  skin  and  fascia,  and  cutaneous  branches  of  the  ulnar 
nerve;    deeply,  the  superficial  and  deep  flexors  of  the  digit.     In  the  cUstal  half  of 


FLEXOR   DIVISION  313 

the  forearm  the  ulnar  vessels  and  nerve  lie  between  the  lateral  edge  of  this  muscle 
and  the  lateral  flexor  of  the  carpus. 

Blood-supply. — Ulnar  and  median  arteries. 

Nerve-supply. — Ulnar  and  median  nerves. 

3.  Ulnaris  lateralis  (or  lateral  flexor  of  the  carpus).^ — This  muscle  lies  on  the 
lateral  face  of  the  forearm,  behind  the  lateral  extensor  of  the  digit. 

Origin. — The  lateral  epicondyle  of  the  humerus,  behind  and  below  the  lateral 
ligament. 

Insertion. — (1)  The  lateral  surface  and  proximal  border  of  the  accessory  carpal 
bone ;   (2)  the  proximal  extremity  of  the  lateral  (fourth)  metacarpal  bone. 

Action.- — To  flex  the  carpal  joint  and  to  extend  the  elbow. 

Structure.- — The  belly  of  the  muscle  is  flattened  and  is  intersected  by  a  good 
deal  of  tendinous  tissue.  There  are  two  tendons  of  insertion.  The  short  tendon 
is  inserted  into  the  accessory  carpal  bone.  The  long  tendon  is  detached  just  above 
the  carpus;  it  is  smaller  and  rounded;  it  passes  downward  and  a  little  forward 
through  a  groove  on  the  lateral  surface  of  the  accessory  carpal  bone,  enveloped  by 
a  synovial  sheath,  to  reach  its  insertion  on  the  lateral  metacarpal  bone.  A  synovial 
pouch  lies  under  the  origin  of  the  muscle  at  the  elbow  joint,  with  the  cavity  of 
which  it  communicates. 

Relations. — Superficially,  the  skin,  fascia,  and  cutaneous  branches  of  the  ulnar 
nerve;  deeply,  the  elbow  joint,  the  ulna,  and  the  flexors  of  the  digit;  in  front,  the 
lateral  extensor  of  the  digit;  behind,  the  middle  flexor  of  the  carpus,  the  ulnar  head 
of  the  deep  flexor,  and  the  ulnar  vessels  and  nerve. 

Blood-supply. — Interosseous,  ulnar,  and  median  arteries. 

Nerve-supply. — Radial  nerve. 

4.  Superficial  digital  flexor-  (M.  flexor  digitalis  superficialis) . — This  muscle  is 
situated  in  the  middle  of  the  flexor  group,  chiefly  under  cover  of  the  middle  flexor 
of  the  carpus. 

Origin. — (1)  The  medial  epicondyle  of  the  humerus;  (2)  a  ridge  on  the  pos- 
terior surface  of  the  radius,  below  its  middle  and  near  the  medial  border. 

Insertion. — (1)  The  eminences  on  the  proximal  extremity  of  the  second  phalanx, 
behind  the  collateral  ligaments;  (2)  the  distal  extremity  of  the  first  phalanx,  also 
behind  the  collateral  ligaments. 

Action. — To  flex  the  digit  and  carpus  and  to  extend  the  elbow. 

Structure. — The  fleshy  part  of  the  muscle  is  the  humeral  head  (Caput  humerale) ; 
it  takes  origin  from  the  humerus.  The  radial  head  (Caput  tendineum)  consists  of 
a  strong  fibrous  band,  usually  termed  the  radial  or  superior  check  Ugament,  which 
fuses  with  the  tendon  near  the  carpus.  The  belly  of  the  muscle  is  intersected  by 
tendinous  strands,  and  fuses  more  or  less  with  that  of  the  deep  flexor,  from  which 
it  is  therefore  somewhat  difficult  to  separate.  Near  the  carpus  it  is  succeeded  by  a 
strong,  thick  tendon  which  passes  down  through  the  carpal  canal  and  is  enveloped 
by  a  synovial  sheath,  in  common  with  the  deep  flexor.  This,  the  carpal  sheath 
(Vagina  carpea),  begins  three  or  four  inches  (8-10  cm.)  above  the  carpus,  and  ex- 
tends downward  nearly  to  the  middle  of  the  metacarpus.  Below  the  carpus  the 
tendon  becomes  flattened  and  broader  and  at  the  fetlock  it  widens  greatly.  Near 
the  fetlock  it  forms  a  ring  through  which  the  tendon  of  the  deep  flexor  passes  (Fig. 
286) .  Here  the  two  tendons  are  bound  down  in  the  sesamoid  groove  by  the  volar 
annular  ligament,  which  fuses  more  or  less  with  the  superficial  flexor  tendon.  At 
the  distal  end  of  the  first  phalanx  the  tendon  divides  into  two  branches  which  di- 
verge to  reach  their  points  of  insertion,  and  between  these  branches  the  tendon  of 

1  Also  known  as  the  flexor  carpi  (s.  metacarpi)  externus  or  extensor  carpi  ulnaris.  Morpho- 
logically it  belongs  to  the  extensor  group. 

2  Also  commonly  known  as  the  flexor  perforatus  or  superficial  flexor  of  the  phalanges. 


314 


FASCIA    AND    MUSCLES    OF   THE    HORSE 


the  deep  flexor  emerges  (Fig.  278).     A  second  synovial  membrane,  the  digital 
synovial  sheath  (Vagina  digitalis),  begins  at  the  distal  fourth  of  the  metacarpus, 


183. — Synovial  Sheaths  and  Burs^  of  Distal 
Part  op  Right  Fore  Limb  of  Horse;  Medial 
View. 


Fig.  284. — Synovial  Sheaths  and  Burs^  of  Distal 
Part  of  Right  Fore  Limb  op  Horse;  Lateral 
View. 
The  synovial  sheaths  (colored  yellow)  and  the  joint  capsules  (colored  pink)  are  injected. 


a.  Sheath  of  extensor  carpi  obliquus;  b,  sheath 
of  flexor  carpi  radialis;  c,  carpal  sheath;  d,  d',  d",  d'", 
digital  sheath;  e,  bursa  under  common  extensor  ten- 
don; /,  capsule  of  fetlock  joint;  1,  extensor  carpi  ra- 
dialis; 2,  tendon  of  extensor  carpi  obliquus;  3,  flexor 
carpi  radialis;  4>  flexor  carpi  ulnaris;  5,  superficial 
flexor  tendon;  6,  deep  flexor  tendon;  7,  suspensory  liga- 
ment; 8,  small  metacarpal  bone;  9,  large  metacarpal 
bone;  10,  volar  annular  ligament  of  fetlock;  11, 
proximal  digital  annular  ligament;  12,  radius;  13, 
radiocarpal  joint;  14,  fetlock  joint;  1.5,  cartilage  of 
third  phalanx;  16,  band  from  first  phalanx  to  cartilage. 
(After  Ellenberger,  in  Leisering's  Atlas.) 


a,  Sheath  of  extensor  carpi  radialis:  b,  sheath 
of  common  extensor;  c,  sheath  of  lateral  extensor;  d, 
sheath  of  outer  tendon  of  ulnaris  lateralis;  e,  e',  carpal 
sheath;  /,  /',  /",  digital  sheath;  g,  bursa  under  com- 
mon extensor  tendon;  h,  bursa  under  lateral  extensor 
tendon;  i,  capsule  of  fetlock  joint;  1,  extensor  carpi 
radialis;  3,  common  digital  extensor;  3,  lateral  digital 
extensor;  4.  ulnaris  lateralis;  4'<  4",  tendons  of  4;  5, 
superficial  flexor  tendon;  6,  deep  flexor  tendon;  7, 
suspensory  ligament;  8,  lateral  metacarpal  bone;  9, 
large  metacarpal  bone;  10,  volar  annular  ligament 
of  fetlock;  11,  digital  annular  ligament;  12,  fetlock 
joint;  13,  cartilage  of  third  phalanx;  14,  band  from 
first  phalanx  to  cartilage.  (After  Ellenberger,  in 
Leisering's  Atlas.) 


two  or  three  inches  (ca.  5-8  cm.)  above  the  fetlock,  and  extends  to  the  middle  of 
the  second  phalanx. 

Relations. — The  belly  of  the  muscle  is  related  superficially  to  the  ulnar  head 
of  the  deep  flexor,  the  flexor  carpi  ulnaris,  and,  at  its  origin,  to  the  ulnar  vessels 


FLEXOR   DIVISION 


315 


and  nerve;  deeply,  to  the  humeral  head  of  the  deep  flexor.  The  tendon  is  re- 
lated superficially  to  the  skin  and  fascia;  deeply,  to  the  deep  flexor  tendon. 

Blood-supply. — Median  artery. 

Nerve-supply. — Ulnar  and  median  nerves. 

5.  Deep  digital  fiexori  (M.  flexor  digitaUs  profundus). — The  fleshy  part  of 
this  muscle  lies  on  the  posterior  surface  of  the  radius,  and  is  almost  entirely  under 
cover  of  the  preceding  muscles.     It  is  the  largest  muscle  of  the  flexor  group. 

Origin. — (1)  The  medial  epicondyle  of  the  humerus;  (2)  the  medial  surface  of 
the  olecranon;  (3)  the  middle  of  the  posterior  surface  of  the  radius  and  a  small  ad- 
jacent area  of  the  ulna. 

Insertion. — The  semilunar  crest  and  the  adjacent  surface  of  the  cartilage  of 
the  third  phalanx. 

Action. — -To  flex  the  digit  and  carpus  and  to  extend  the  elbow. 

Structure. — This  muscle  consists  of  three  heads.  The  humeral  head  (Caput 
humerale)  constitutes  the  bulk  of  the  muscle.  It  is  marked  by  tendinous  inter- 
sections, and  is  separable  into  three  secondary  heads.  A  synovial  pouch  from  the 
elbow  joint  descends  under  its 


Tendon  of 
lateral  extensor 


Tendon  of 
common  extensor 


origin  about  two  inches.  The 
ulnar  head  (Caput  ulnare)  is 
much  smaller,  and  is  at  first 
superficially  situated  between 
the  lateral  and  middle  flexors 
of  the  carpus.  The  radial  head 
(Caput  radiale)  is  the  smallest, 
and  is  not  always  present;  it 
is  situated  on  the  distal  two- 
thirds  of  the  posterior  surface 
of  the  radius,  under  the  humer- 
al head.  Each  of  these  heads 
is  provided  with  a  tendon.  The 
principal  tendon — that  of  the 
humeral  head — begins  about 
three  or  four  inches  (8-10 
cm.)  above  the  carpus  and  is 
joined  at  the  carpus  by  the 
tendons  of  the  other  two  heads. 
The  conjoined  tendon  passes 
downward  through  the  carpal 

canal,  being  included  in  the  carpal  synovial  sheath  with  the  superficial  flexor  ten- 
don, as  previously  described.  The  tendon  is  at  first  broad  and  three-sided,  but 
becomes  narrower  and  rounded  below.  Continuing  downward,  it  is  joined  about 
the  middle  of  the  metacarpus  by  a  strong  fibrous  band,  the  so-called  inferior  or 
subcarpal  check  ligament  (Caput  carpale  s.  tendineum).^  This  is  a  direct  continua- 
tion of  the  posterior  ligament  of  the  carpus.  Below  this  the  tendon  passes  through 
the  ring  formed  by  the  superficial  flexor  tendon,  then  in  succession  over  the  sesa- 
moid groove,  the  chstal  sesamoidean  ligaments,  and  the  flexor  surface  of  the  distal 
sesamoid,  to  its  insertion  (Figs.  241  and  242).  At  the  fetlock  it  widens  consider- 
ably, narrows  again  in  the  middle  of  the  digital  region,  again  widens  at  the  pulley 


Tendon  of  superficial  flexor 
Fig.  285. 


Cross-sectiox  of  Distal  Part  of  Lej 
Horse,  Just  Above  Sesamoids 


Intersesamoi- 
dean  ligament 

Digital  vein 
Digital  artery 
Digital  nerve 


Tendon  of  deep  flexor 

Metacarpus  of 


1  Also  commonly  knowTi  as  the  flexor  perforans  or  deep  flexor  of  the  phalanges. 

-  This  might  appropriately  be  termed  the  carpal  head  (caput  carpale)  or  tendinous  head 
(caput  tendineum).  At  its  upper  end  it  is  broad,  occup>ang  the  entire  width  of  the  space  between 
the  small  metacarpal  bones;  below  it  becomes  narrower  and  thicker.  It  is  related  in  front  to 
the  suspensory  ligament,  and  its  posterior  face,  which  is  related  to  the  deep  flexor  tendon,  is 
covered  by  the  deep  layer  of  the  carpal  sheath. 


316 


FASCIA   AND   MUSCLES    OF   THE    HORSE 


of  the  second  phalanx,  and  forms  a  terminal  fan-like  expansion.  At  the  pulleys 
of  the  digit  the  tendon  contains  cartilage  and  is  thickened.  From  the  distal  fourth 
of  the  metacarpus  to  the  distal  end  of  the  second  phalanx  it  is  inclosed  in  the  dig- 
ital synovial  sheath  described  in  connection  with  the  superficial  flexor.  The  bursa 
podotrochlearis  or  navicular  bursa  is  found  between  the  tendon  and  the  distal  sesa- 
moid or  navicular  bone.  The  terminal  part  of  the  tendon  is  bound  down  by  the 
distal  digital  annular  ligament  described  with  the  fascia. 

Relations. — The  belly  of  the  muscle  is  related  posteriorly  to  the  superficial 


Extensor  tendon 


Proximal  end  of  capside  of  fetlock 
joint 

Bursa 

Collateral  ligament  of  fetlock  joint  — ^ "^  ' 

Fascia 


Branch  of  suspc7isory  ligament- 


Lateral  volar  ligament  of  pastem 
joint 


\    ^"l" 


^hl\ 


Superficial  flexor  tendon 
Deep  flexor  te?idon 
Suspensory  ligament 
.Lateral  interosseus  tendon 

'  Proximal  end  of  digital  sheath 
'  Ring  of  superficial  flexor  tendon 
•  Intersesamoidean  ligame7it 
Posterior  annular  ligament  {cut) 


.      .Collateral  sesamoidean  ligament 
ij'/l    Superficial  distal  sesamoidean 
ligament 
Middle  distal  sesamoidean  ligament 

>  Attachments  of  proximal  digital 
'  annular  ligament 


Pouch  of  digital  sheath 


llti^^rff^ 

^  ^Cartilage 

Suspensory  ligament  of  navicidar 
bone 

Ba?id  from  cartilage  to  extensor 

tendon 
Collateral  ligament  of  coffin  joint  -{- 

i 

> 

Fig.  286. — Ligaments  and  Tendons  or  Distal  Part  of  Limb  of  Horse. 

Mc.  Ill,  Large  metacarpal  bone;  Ph.  I,  first  phalanx;  Ph.  II,  second  phalanx;  Ph.  III.  third  phalanx;   1,  deep  flexor 

tendon;  2,  band  from  first  phalanx  to  digital  cushion.     (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


flexor  and  to  the  middle  flexor  of  the  carpus;  medially,  to  the  flexor  carpi  radialis, 
the  radial  check  ligament,  and  the  median  vessels  and  nerve;  laterally,  to  the 
ulnaris  lateralis;  anteriorly,  to  the  radius  and  ulna  and  branches  of  the  median 
artery  and  nerve.  Below  the  carpus  the  tendon  is  accompanied  by  the  vessels  and 
nerves  of  the  digit.  It  may  also  be  noted  that  the  muscle  is  not  entirely  covered 
by  the  other  flexors;  it  comes  in  contact  with  the  skin  and  fascia  on  the  postero- 
lateral aspect  of  the  proximal  half  of  the  forearm,  and  also  on  the  lateral  aspect  of 
the  distal  fourth. 

Blood-supply. — Median  and  ulnar  arteries. 


FASCIA   AND   MUSCLES   OF   THE   PELVIC   LIMB — THE   FASCIA  317 

Nerve-supply. — Median  and  ulnar  nerves. 

The  five  muscles  of  the  metacarpus  and  digit  are  either  reduced  to  vestiges  or 
modified  greatly  in  structure. 

1,  2.  Lvimbricales  (medialis  et  lateralis). — These  are  two  very  slender  fusiform 
muscles  which  lie  on  either  side  of  the  flexor  tendons  above  the  fetlock.  They  arise 
from  the  deep  flexor  tendon,  and  end  in  the  fibrous  tissue  which  lies  under  the  nod- 
ule of  horn  at  the  fetlock  which  is  known  as  the  ergot  (Fig.  572).  Their  action  is 
inappreciable.  The  size  of  these  muscles  is  subject  to  much  variation.  Often  very 
little  muscular  tissue  can  be  foimd,  but  the  small  tendon  is  constantly  present. 

Blood-supply. — Volar  metacarpal  arteries. 

Nerve-supply. — Median  and  ulnar  nerves. 

3,  4,  5.  Interossei. — These  are  three  in  number  in  the  horse,  and  are  situated 
chiefly  in  the  metacarpal  groove.  Two,  the  medialis  and  lateralis,  are  very  small 
muscles,  each  of  which  arises  from  the  corresponding  small  metacarpal  bone  near 
its  proximal  extremity,  and  is  provided  with  a  delicate  tendon  which  is  usually  lost 
in  the  fascia  at  the  fetlock  (Fig.  240).  They  have  no  appreciable  action.  Their 
blood-  and  nerve-supply  is  the  same  as  that  of  the  preceding  muscles. 

The  interosseus  medius  is  so  much  modified  that  it  is  usually  termed  the 
suspensory  or  superior  sesamoidean  ligament.  It  contains  little  muscular  tissue, 
being  transformed  very  largely  into  a  strong  tendinous  band  (Tendo  interosseus), 
bifurcate  below,  and  having  for  its  chief  function  the  supporting  of  the  fetlock.  It 
has  been  described,  in  deference  to  common  usage,  with  the  ligaments. 


Fascle  and  Muscles  of  the  Pelvic  Limb 
The  FASCiiE 

The  iliac  fascia  (Fascia  iliaca)  covers  the  ventral  surface  of  the  iliacus  and  psoas 
muscles,  over  which  it  is  tightly  stretched  (Fig.  575).  It  is  attached  medially  to 
the  tendon  of  the  psoas  minor;  laterally  it  is  attached  to  the  tuber  coxae  and  blends 
with  the  deep  layer  of  the  lumbo-dorsal  fascia.  Its  anterior  part  is  thin.  Pos- 
teriorly it  is  continuous  with  the  inguinal  ligament  and  the  pelvic  fascia.  It  fur- 
nishes surfaces  of  origin  for  the  sartorius,  cremaster  externus,  and  transversus  ab- 
dominis muscles. 

The  pelvic  fascia  (Fascia  pelvis)  lines  the  cavity  as  the  parietal  layer  and 
at  the  pelvic  outlet  is  reflected  on  the  viscera  to  form  the  visceral  layer.  Laminae 
are  detached  from  it  to  strengthen  the  various  peritoneal  folds. 

The  superficial  fascia  of  the  gluteal  region  is  thin  and  is  closely  adherent  to 
the  deep  fascia.  A  subcutaneous  bursa  may  be  found  on  the  tuber  coxae.  The 
gluteal  fascia  (Fascia  glutea)  covers  the  superficial  muscles  of  the  region,  and  de- 
taches intermuscular  septa,  which  pass  between  the  muscles.  It  is  attached  to  the 
sacral  spines,  the  dorsal  sacro-iliac  ligament,  and  the  tubera  of  the  ilium,  and  is  con- 
tinuous in  front  with  the  lumbo-dorsal  fascia,  behind  with  the  coccygeal  fascia. 
Its  deep  face  gives  origin  to  fibers  of  the  superficial  and  middle  glutei,  the  biceps 
femoris,  and  the  semitendinosus,  so  that  care  is  necessary  in  dissecting  it  off  these 
muscles.  The  chief  intermuscular  septa  are:  (1)  One  which  passes  between  the 
superficial  gluteus  and  the  biceps  femoris;  (2)  one  between  the  biceps  and  semi- 
tendinosus, from  which  a  lamella  is  detached  which  passes  between  the  middle  and 
posterior  parts  of  the  biceps  and  is  attached  to  the  tuber  ischii;  (3)  one  between  the 
semitendinosus  and  semimembranosus,  which  is  attached  to  the  sacro-sciatic  liga- 
ment and  tuber  ischii;  it  furnishes  origin  for  fibers  of  the  long  head  of  the  semi- 
membranosus. 

The  superficial  fascia  of  the  thigh  presents  no  exceptional  features,  but  the  deep 


318  FASCIA    AND    MUSCLES    OF   THE    HORSE 

fascia  is  very  thick  and  strong  on  the  front  and  lateral  surface.  This  part,  the 
fascia  lata  (Fig.  267),  is  continuous  mth  the  gluteal  fascia;  it  is  tendinous  in  char- 
acter, and  easily  separable  from  the  underlying  muscles.  It  furnishes  insertion  to 
the  tensor  fascise  latse  and  to  the  biceps  femoris  (in  part),  by  both  of  which  it  is 
tensed.  At  the  stifle  it  is  attached  to  the  patella  and  the  lateral  and  medial  patellar 
ligaments.  Medially  it  is  continuous  with  the  medial  femoral  fascia.  It  furnishes 
the  following  intermuscular  septa:  (1)  One  which  passes  between  the  vastus  lat- 
eralis and  biceps  femoris  to  be  attached  to  the  third  trochanter  of  the  femur;  (2) 
two  which  pass  between  the  three  branches  of  the  biceps  femoris;  (3)  a  fourth  be- 
tween the  biceps  femoris  and  semitendinosus.  The  medial  femoral  fascia  (Fascia 
femoralis  medialis)  covers  the  superficial  muscles  on  the  medial  surface  of  the  thigh. 
At  its  upper  part  it  is  joined  by  the  femoral  lamina  of  the  aponeurosis  of  the  external 
oblique  muscle  (Fig.  575).  The  posterior  part  is  thin.  It  is  continuous  with  the 
fascia  lata  in  front  and  the  fascia  cruris  below.  At  the  stifle  it  fuses  with  the  ten- 
dons of  the  sartorius  and  gracilis. 

The  fascia  cruris,  or  fascia  of  the  leg,  consists  of  three  layers.  Two  of  these 
invest  the  entire  region  and  may,  therefore,  be  termed  the  common  fasciae.  The 
superficial  layer  is  a  continuation  of  that  of  the  thigh,  while  the  second  layer  may  be 
regarded  chiefly  as  a  continuation  of  the  tendons  of  the  superficial  muscles  of  the 
hip  and  thigh  (biceps  femoris,  semitendinosus,  tensor  fascise  latse,  sartorius,  and 
gracilis).  The  two  layers  frequently  fuse,  and  are  attached  chiefly  to  the  medial 
and  lateral  patellar  ligaments  and  the  crest  and  medial  surface  of  the  tibia.  About 
the  middle  of  the  leg  the  two  layers  unite  behind  the  deep  flexor  of  the  digit  and 
form  a  strong  band  which  passes  dowTiward  in  front  of  the  tendons  of  the  gastroc- 
nemius and  superficial  flexor,  to  be  attached  with  the  latter  to  the  anterior  and 
medial  part  of  the  tuber  calcis.  This  constitutes  a  tarsal  tendon  of  insertion  of  the 
biceps  femoris  and  semitendinosus.  A  strong  band,  about  two  inches  in  width, 
arises  from  the  lateral  supracondyloid  crest,  descends  over  the  lateral  head  of  the 
gastrocnemius,  and  blends  with  the  foregoing  and  the  superficial  flexor  tendon. 
The  third  layer  forms  sheaths  for  the  muscles,  furnishing  origin  in  part  to  their 
fibers.  Two  important  intermuscular  septa  are  detached,  viz.:  (1)  One  which 
passes  between  the  long  and  lateral  digital  extensors  to  be  attached  to  the  fibula 
and  the  lateral  border  of  the  tibia;  (2)  one  between  the  lateral  digital  extensor  and 
the  deep  digital  flexor. 

The  tarsal  fascia  (Fascia  tarsi)  fuses  with  the  ligaments  and  bony  prominences 
of  the  region.  It  is  strong  and  tendinous  in  front,  and  joins  the  tendon  of  the  long 
extensor  below  the  joint.  On  the  sides  it  is  thin  and  fuses  with  the  ligaments. 
Posteriorly  it  is  very  thick  and  strong,  forming  an  annular  ligament  which  stretches 
from  the  medial  ligament  to  the  fibular  tarsal  bone  and  the  plantar  ligament.  This 
converts  the  groove  at  the  back  of  the  hock  into  a  canal,  in  which  are  the  deep  flexor 
tendon  with  its  synovial  sheath  and  the  plantar  vessels  and  nerves.  In  this  vicinity 
there  are  three  annular  ligaments  (Ligamenta  transversa).  The  proximal  one  binds 
down  the  tendons  of  the  long  extensor,  peroneus  tertius,  and  tibialis  anterior  on 
the  distal  end  of  the  shaft  of  the  tibia.  The  middle  one  stretches  from  the  fibular 
tarsal  bone  to  the  lateral  tendon  of  the  peroneus  tertius,  forming  a  loop  around  the 
tendon  of  the  long  extensor.  The  distal  band  stretches  across  the  proximal  ex- 
tremity of  the  large  metatarsal  bone  and  incloses  the  tendons  (and  sheaths)  of  the 
two  extensors  of  the  digit. 

The  metatarsal  and  digital  fasciae  do  not  differ  materially  from  those  of  the 
corresponding  regions  of  the  thoracic  limb. 


THE  MUSCLES THE  SUBLUMBAR  MUSCLES  319 

The  Muscles  1 

I.  THE  SUBLUMBAR  MUSCLES  (Figs.  287,  575) 
The  muscles  of  this  group  are  not  confined  to  the  sublumbar  region,  but  ex- 
tend beyond  it  both  before  and  behind.     Their  chief  function  is  to  flex  the  hip 
joint.     Two,  however, — the  psoas  minor  and  the  quadratus  lumborum,^ — have  not 
this  action. 

1.  Psoas  minor. — This  is  a  fusiform,  flattened,  pennate  muscle,  which  lies 
along  the  ventro-lateral  aspect  of  the  bodies  of  the  last  three  thoracic  and  the 
lumbar  vertebrae. 

Origin. — The  bodies  of  the  last  three  thoracic  and  first  four  or  five  lumbar 
vertebrae,  and  the  vertebral  ends  of  the  sixteenth  and  seventeenth  ribs. 

Insertion. — The  psoas  tubercle  on  the  shaft  of  the  ilium. 

Action. — To  flex  the  pelvis  on  the  loins,  or  to  incline  it  laterally. 

Structure. — The  muscle  arises  by  a  series  of  digitations  which  pass  backward 
and  outward  to  join  the  tendon  at  an  acute  angle.  The  latter  lies  along  the  lateral 
border  of  the  fleshy  portion  and  is  flattened.  It  appears  on  the  surface  of  the  mus- 
cle at  the  third  lumbar  process  and  increases  gradually  in  width  until  it  reaches  the 
pelvic  inlet,  where  it  becomes  narrower. 

Relations. — The  ventral  surface  of  the  thoracic  part  of  the  muscle  is  related 
to  the  pleura,  crura  of  the  diaphragm,  and  sympathetic  and  splanchnic  nerves. 
In  the  abdomen  the  chief  ventral  relations  are  the  peritoneum,  the  vena  cava 
(right  side),  the  aorta  and  left  kidney  (left  side),  the  sympathetic  nerves,  and  the 
ureters.  Dorsally,  the  chief  relations  are  the  vertebrae,  the  psoas  major,  and  lum- 
bar nerves.  The  lumbar  arteries  pass  through  the  medial  edge.  Near  its  insertion 
the  tendon  is  crossed  medially  by  the  external  iliac  artery,  and  laterally  by  the  fem- 
oral nerve. 

Blood-supply. — Intercostal  and  lumbar  arteries. 

Nerve-supply. — Lumbar  nerves. 

2.  Psoas  major. — This  is  much  larger  than  the  preceding  muscle,  by  which  it 
is  partly  covered.     It  is  triangular,  with  the  base  anterior. 

Origin. — The  ventral  surfaces  of  the  transverse  processes  of  the  lumbar  ver- 
tebrae and  the  last  two  ribs. 

Insertion. — The  trochanter  minor  of  the  femur,  by  a  common  tendon  with 
the  iliacus. 

Action. — To  flex  the  hip  joint  and  to  rotate  the  thigh  outward. 

Structure. — The  origin  of  the  muscle  is  fleshy,  the  belly  being  in  general  flat- 
tened, thick  in  its  middle,  thin  at  its  edges.  The  thoracic  part  is  small,  the  abdom- 
inal part  much  thicker  and  wider,  extending  laterally  beyond  the  extremities  of  the 
lumbar  transverse  processes.  From  the  lumbo-sacral  articulation  it  lies  in  a  deep 
groove  formed  in  the  iliacus  (with  which  it  is  partly  united),  becomes  smaller  and 
rounded,  and  passes  downward  and  backward  to  terminate  by  a  strong  tendon 
common  to  it  and  the  iliacus.  On  account  of  the  intimate  union  between  the  psoas 
major  and  iliacus  they  are  frequently  considered  a  single  muscle,  to  which  the  name 
ilio-psoas  is  applied ;  some  anatomists  include  the  psoas  minor  also  under  this  term. 

Relations. — Dorsally,  the  last  two  ribs  and  thoracic  vertebrae,  the  lumbar 
vertebrae,  the  internal  intercostals,  quadratus  lumborum,  longissimus  dorsi,  and 
iliacus,  and  the  lumbar  vessels  and  nerves;  ventrally,  the  pleura  and  peritoneum, 
the  iliac  fascia,  inguinal  ligament,  the  diaphragm,  psoas  minor  and  sartorius, 
and  the  circumflex  iliac  vessels. 

^  On  account  of  the  very  slight  mobihty  of  the  sacro-iUac  articulation,  the  muscles  of  the 
pelvic  girdle  are  much  reduced,  and  almost  all  of  those  which  might  be  included  in  this  group 
extend  to  the  femur  or  even  to  the  leg.  It  seems  undesirable,  therefore,  to  attempt  a  morpho- 
logical grouping. 


320  FASCIA   AND    MUSCLES    OF   THE    HORSE 

Blood-supply. — Lumbar  and  circumflex  iliac  arteries. 
Nerve-supply. — Lumbar  and  femoral  nerves. 

3.  Iliacus. — This  muscle  covers  the  ventral  surface  of  the  ilium  lateral  to  the 
sacro-iliac  articulation,  and  extends  beyond  the  lateral  border  of  the  bone,  under- 
neath the  middle  gluteus. 

Origin. — The  ventral  surface  of  the  ilium  lateral  to  the  ilio-pectineal  line,  the 
ventral  sacro-iliac  ligament,  the  ^\^ng  of  the  sacrum,  and  the  tendon  of  the  psoas 
minor. 

Insertion. — The  trochanter  minor  of  the  femur,  by  a  common  tendon  with 
the  psoas  major. 

Action. — To  flex  the  hip  joint  and  to  rotate  the  thigh  outward. 

Structure.- — The  belly  of  the  muscle  is  so  deeply  grooved  for  the  psoas  major 
as  to  give  the  appearance  of  being  completely  divided  into  medial  and  lateral  parts. 
When  the  psoas  is  removed,  it  is  seen,  however,  that  the  two  heads  are  not  entirely 
separated.  The  lateral,  larger  head  arises  from  the  wing  of  the  ilium  chiefly;  the 
medial,  smaller  head  arises  chiefly  from  a  small  area  on  the  shaft  of  the  ilium,  be- 
tween the  psoas  tubercle  and  the  depression  for  the  medial  tendon  of  the  rectus 
femoris,  and  from  the  tendon  of  the  psoas  minor.  The  two  parts  inclose  the  psoas 
major  in  front  of  the  hip  joint. 

Relations. — Dorsally,  the  ilium,  sacrum,  sacro-iliac  articulation,  the  gluteus 
medius,  the  ilio-lumbar  and  external  circumflex  vessels;  ventrally,  the  iliac  fascia, 
inguinal  ligament,  the  psoas  major,  sartorius,  and  abdominal  muscles.  At  the 
level  of  the  hip  joint  the  chief  relations  are:  medially,  the  femoral  vessels,  the  fem- 
oral nerve,  and  the  sartorius  muscle ;  laterally,  the  rectus  femoris  and  tensor  fasciae 
latse;  in  front,  the  abdominal  muscles;  behind,  the  hip  joint. 

Blood-supply. — Lumbar,  circumflex  iliac,  and  deep  femoral  arteries. 

Nerve-supply. — Lumbar  and  femoral  nerves. 

4.  Quadratus  lumborum. — This  thin  muscle  lies  on  the  lateral  part  of  the  ven- 
tral surfaces  of  the  lumbar  transverse  processes. 

Origin. — The  ventral  surface  of  the  upper  part  of  the  last  two  ribs  and  the 
lumbar  transverse  processes. 

Insertion. — The  ventral  surface  of  the  wing  of  the  sacrum  and  the  ventral 
sacro-iliac  ligament. 

Action. — Acting  together,  to  fix  the  last  two  ribs  and  the  lumbar  vertebrae; 
acting  singly,  to  produce  lateral  flexion  of  the  loins. 

Structure. — The  muscle  is  pennate,  and  is  curved  with  the  convexity  lateral. 
It  is  thin,  largely  mixed  with  tendinous  fibers,  and  is,  in  general,  little  developed  in 
the  horse  in  comparison  with  some  of  the  other  animals  (e.  g.,  dog,  sheep). 

Relations. — Ventrally,  the  psoas  major  and  the  last  thoracic  and  first  three 
lumbar  nerves;  dorsally,  the  last  two  ribs,  the  lumbar  transverse  processes,  and 
the  lateral  branches  of  the  lumbar  arteries. 

Blood-supply. — Lumbar  arteries. 

Nerve-supply. — Lumbar  nerves. 

5.  Intertransversales  lumborum.^ — (See  p.  279.) 


11.  THE  LATERAL  MUSCLES  OF  THE  HIP  AND  THIGH 

Under  this  head  the  muscles  of  the  lateral  surface  of  the  pelvis  and  thigh,  and 
those  which  form  the  posterior  contour  of  the  latter,  will  be  described. 

1.  Tensor  fasciae  latae  (Fig.  267). — This  is  the  most  anterior  muscle  of  the 
superficial  layer.     It  is  triangular  in  form,  with  its  apex  at  the  tuber  coxae. 

Origin. — The  tuber  coxae. 

Insertion. — The  fascia  lata  and  thus  indirectly  to  the  patella,  the  lateral  patel- 
lar ligament,  and  the  crest  of  the  tibia. 


THE    LATERAL   MUSCLES    OF   THE    HIP    AND    THIGH  321 

Action. — To  tense  the  fascia  lata,  flex  the  hip  joint,  and  extend  the  stifle  joint. 

Structure. — The  muscle  arises  by  a  rather  small  head,  about  two  inches  (ca. 
5  cm.)  wide,  on  the  antero-inferior  eminence  of  the  tuber  coxae.  Below  this  the 
belly  spreads  out  and  terminates  in  the  aponeurosis  about  midway  between  the 
point  of  the  hip  and  the  stifle.  Many  fibers  arise  from  an  intermuscular  septum 
between  this  muscle  and  the  superficial  gluteus;  this  septum  is  attached  to  the  lat- 
eral border  of  the  ilium.  The  aponeurosis  fuses  with  the  fascia  lata,  which  may  be 
regarded  practically  as  the  tendon  of  insertion;  it  detaches  a  lamina  which  passes 
with  the  tendon  of  insertion  of  the  superficial  gluteus  to  the  lateral  border  of  the 
femur. 

Relations. — Laterally,  the  skin  and  fascia;  medially,  the  obliquus  abdominis 
externus,  the  iliacus,  superficial  gluteus,  rectus  femoris,  and  vastus  lateralis,  branches 
of  the  circumflex  iliac,  ilio-lumbar,  and  iliaco-femoral  arteries,  and  the  anterior 
gluteal  nerve;  anteriorly,  the  prefemoral  lymph-glands.  A  considerable  quantity 
of  connective  tissue  is  found  between  the  deep  face  of  the  muscle  and  the  abdominal 
wall. 

Blood-supply. — Circumflex  iliac,  ilio-lumbar,  and  iliaco-femoral  arteries. 

Nerve-supply.- — Anterior  gluteal  nerve. 

2.  Gluteus  superficialis  (Fig.  267). — This  muscle  lies  behind  and  partly 
underneath  the  tensor  fasciae  latse.  It  is  triangular  and  consists  of  an  anterior  and 
a  posterior  head  united  by  the  gluteal  fascia. 

Origin. — (1)  The  tuber  coxae  and  the  adjacent  part  of  the  lateral  border  of 
the  ilium;    (2)  the  gluteal  fascia. 

Insertion. — The  third  trochanter  of  the  femur. 

Action. — To  abduct  the  limb,  flex  the  hip  joint,  and  tense  the  gluteal  fascia. 

Structure. — The  anterior  head  of  the  muscle  is  not  completely  separable  (ex- 
cept artificially)  from  the  tensor  fasciae  latse,  since  both  muscles  are  attached  to  an 
intermuscular  septum.  The  attachment  to  the  border  of  the  ilium  is  by  means  of 
an  intermuscular  septum,  which  passes  beneath  the  thick  lateral  border  of  the 
gluteus  medius  and  furnishes  origin  to  fibers  of  both  muscles.  The  posterior  head 
arises  from  the  deep  face  of  the  gluteal  fascia,  and  so  indirectly  from  the  dorsal 
sacro-iliac  ligament.  The  two  heads  unite  and  terminate  on  a  strong  flat  tendon, 
which  is  inserted  into  the  edge  of  the  third  trochanter  of  the  femur,  under  cover  of 
the  biceps  femoris. 

Relations. — Superficially,  the  skin,  fascia,  and  biceps  femoris;  deeply,  the 
gluteus  medius,  iliacus,  rectus  femoris,  and  branches  of  the  iliaco-femoral  vessels; 
in  front,  the  tensor  fasciae  latae;  behind,  the  biceps  femoris. 

Blood-supply. — Gluteal  and  iliaco-femoral  arteries. 

Nerve-supply. — Anterior  gluteal  nerve. 

3.  Gluteus  medius  (Figs.  268,  580).— This  is  a  very  large  muscle  which  covers 
the  gluteal  surface  of  the  ilium  and  the  greater  part  of  the  lateral  wall  of  the  pelvis, 
and  extends  forward  also  on  the  lumbar  part  of  the  longissimus  dorsi. 

Origin. — (1)  The  aponeurosis  of  the  longissimus  dorsi,  as  far  forward  as  the 
first  lumbar  vertebra;  (2)  the  gluteal  surface  and  tubera  of  the  ilium;  (3)  the  dorsal 
and  lateral  sacro-iliac  and  sacro-sciatic  ligaments,  and  the  gluteal  fascia. 

Insertion. — (1)  The  summit  of  the  trochanter  major  of  the  femur;  (2)  the  crest 
below  the  trochanter;    (3)  the  lateral  aspect  of  the  trochanteric  ridge. 

Action.— To  extend  the  hip  joint  and  abduct  the  limb.  By  its  connection 
with  the  longissimus  a  muscular  mass  is  formed  which  is  one  of  the  chief  factors  in 
rearing,  kicking,  and  propulsion. 

Structure. — The  anterior  extremity  of  the  muscle  is  narrow  and  thin,  and  lies 

in  a  depression  on  the  surface  of  the  longissimus,  from  the  strong  aponeurosis  of 

which  the  fibers  take  origin.     The  pelvic  portion  of  the  muscle  is  very  voluminous, 

and  forms  the  bulk  of  the  muscular  mass  which  gives  the  haunch  its  rounded  con- 

21 


322  FASCIA   AND   MUSCLES    OF   THE   HORSE 

tour.  This  part  of  the  muscle  is  intersected  by  several  tendinous  sheets.  One  of 
these  is  particularly  distinct,  and  is  attached  to  the  gluteal  line  on  the  ilium.  This 
divides  the  muscle  incompletely  into  superficial  and  deep  strata.  The  superficial 
part  is  inserted  by  a  strong  tendon  into  the  summit  of  the  great  trochanter,  and 
by  a  pointed  fleshy  mass  with  a  tendinous  border  into  the  lateral  surface  of  the 
trochanteric  ridge.  The  deep  part  is  termed  the  gluteus  accessorius ;  it  is  smaller, 
and  arises  entirely  from  the  ilium  between  the  gluteal  line  and  the  tuber  coxae  (Fig. 
580).  It  has  a  strong  flat  tendon  which  passes  over  the  anterior  part  or  convexity 
of  the  trochanter  to  be  inserted  into  the  crest  below  it.  The  trochanter  is  covered 
here  A\dth  cartilage,  and  the  trochanteric  bursa  (Bursa  trochanterica)  is  interposed 
between  the  tendon  and  the  cartilage.^ 

Relations. — Superficially,  the  skin,  lumbo-dorsal  and  gluteal  fasciae,  the  tensor 
fasciae  latse,  gluteus  superficialis,  and  biceps  femoris;  deeply,  the  longissimus,  the 
ilium,  sacro-iliac  and  sacro-sciatic  ligaments,  the  gluteus  profundus,  iliacus  and 
rectus  femoris,  the  iliaco-femoral  vessels,  the  gluteal  and  internal  pudic  vessels  and 
nerves,  and  the  great  sciatic  nerve. 

Blood-supply. — Gluteal,  ilio-lumbar,  lumbar,  and  iliaco-femoral  arteries. 

Nerve-supply.— Gluteal  nerves. 

4.  Gluteus  profundus.^^ — This  much  smaller  quadrilateral  muscle  lies  under 
the  posterior  part  of  the  preceding  muscle,  and  extends  over  the  hip  joint,  from  the 
superior  ischiatic  spine  to  the  anterior  part  of  the  trochanter  major  (Fig.  580). 

Origin. — The  superior  ischiatic  spine  and  the  adjacent  part  of  the  shaft  of  the 
ilium. 

Insertion. — The  edge  of  the  anterior  part  or  convexity  of  the  trochanter  major 
of  the  femur. 

Action. — To  abduct  the  thigh  and  to  rotate  it  inward. 

Structure. — The  muscle  is  short  and  thick  and  contains  numerous  tendinous 
intersections.  The  fibers  are  directed  almost  transversely  outward  over  the  capsule 
of  the  hip  joint  and  converge  at  the  convexity  of  the  trochanter. 

Relations.- — Superficially,  the  gluteus  medius  and  branches  of  the  gluteal  vessels 
and  nerves;  deeply,  the  shaft  of  the  ilium,  the  hip  joint,  and  the  rectus  femoris 
and  capsularis. 

Blood-supply.- — Gluteal  artery. 

Nerve-supply. — Anterior  gluteal  nerve. 

5.  Biceps  femoris.^ — This  large  muscle  lies  behind  and  in  part  upon  the  super- 
ficial and  middle  glutei.  It  extends  in  a  curved  direction  from  the  sacral  and 
coccygeal  spines  to  the  lateral  surface  of  the  stifle  and  leg  (Figs.  267,  292,  580). 

Origin.-^{l)  The  dorsal  and  lateral  sacro-iliac  ligaments,  the  gluteal  and 
coccygeal  fasciae,  and  the  intermuscular  septum  between  this  muscle  and  the  semi- 
tendinosus;    (2)  the  tuber  ischii. 

Insertion. — (1)  A  rough  eminence  on  the  posterior  surface  of  the  femur  near 
the  trochanter  tertius;  (2)  the  free  (anterior)  surface  of  the  patella  and  the  lateral 
patellar  ligament;  (3)  the  tibial  crest;  (4)  the  crural  fascia  and  the  tuber  calcis. 

Action. — The  action  is  somewhat  complex,  because  the  muscle  is  composed 
of  three  parts,  has  several  points  of  insertion,  and  acts  on  all  the  joints  of  the 
limb  except  those  of  the  digit.  The  general  action  is  to  extend  the  limb,  as  in  pro- 
pelling the  body,  rearing  or  kicking,  and  to  abduct  it.  The  anterior  part,  by  its 
attachment  to  the  posterior  surface  of  the  femur  and  to  the  patella,  would  extend 

^  By  most  anatomists  the  portion  inserted  into  the  crest  is  termed  the  gluteus  accessorius, 
but  Lesbre  considers  this  to  be  the  deep  gluteus,  homologous  with  the  gluteus  minimus  of  man. 
The  portion  inserted  into  the  trochanteric  ridge  apparently  represents  the  piriformis  of  man. 

^  Lesbre  considers  this  to  be  the  scansorius. 

*  Apparently  the  muscle  represents  the  biceps,  together  with  part  of  the  gluteus  super- 
ficialis of  man.     Hence  the  names,  gluteo-biceps  and  paramero-biceps  have  been  suggested. 


THE    LATERAL   MUSCLES    OF   THE    HIP   AND    THIGH  323 

the  stifle  and  hip  joints  and  abduct  the  hmb.  The  middle  part,  being  inserted 
chiefly  on  the  tibial  crest  and  the  lateral  patellar  ligament,  would  extend  the  hip, 
and  may,  with  the  semitendinosus,  flex  the  stifle.  The  posterior  part,  by  virtue 
of  its  attachment  to  the  tuber  calcis,  assists  in  extending  the  hock.  It  is  to  be  noted, 
however,  that  extension  of  the  hock  joint  can  occur  only  when  the  stifle  is  also  ex- 
tended, and  vice  versa. 

Structure. — The  muscle  has  two  heads  of  origin.  The  long  or  vertebral  head 
arises  chiefly  from  the  dorsal  and  lateral  sacro-iliac  ligaments,  the  coccygeal  fascia, 
and  the  intermuscular  septum.  There  is  often  a  large  bursa  between  this  head  and 
the  trochanter  major.  The  short  or  ischiatic  head  arises  by  a  strong  tendon  from 
the  ventral  spine  on  the  tuber  ischii,  which  also  furnishes  origin  to  part  of  the  semi- 
tendinosus. They  unite,  and  a  short  tendon,  detached  from  the  deep  face  of  the 
muscle,  is  inserted  into  the  posterior  surface  of  the  femur  near  the  third  trochanter; 
here  a  bursa  is  interposed  between  the  tendon  and  the  bone.  The  muscle  then 
divides  into  three  parts,  which  terminate  on  a  strong  aponeurosis  over  the 
junction  of  the  thigh  and  leg.  The  anterior  part  is  directed  toward  the  patella, 
the  middle  one  toward  the  tibial  crest,  while  the  posterior  one  assists  in  the  forma- 
tion of  the  posterior  contour  of  the  limb.  The  aponeurosis  blends  with  the  deep 
layer  of  the  fascia  cruris,  as  already  described.  A  synovial  bursa  occurs  under  the 
patellar  insertion,  and  in  some  cases  there  is  also  one  between  the  muscle  and  the 
third  trochanter. 

Relations. — Superficially,  the  sldn  and  fascia;  deeply,  the  sacro-iliac  and  sacro- 
sciatic  ligaments,  the  coccygeal  fascia,  the  femur,  the  gluteus  medius,  obturator, 
gemellus,  quadratus  femoris,  adductor,  semimembranosus,  vastus  lateralis,  and 
gastrocnemius  muscles,  branches  of  the  lateral  sacral,  gluteal,  obturator,  femoral 
and  deep  femoral  vessels,  the  great  sciatic,  tibial,  peroneal,  and  posterior  gluteal 
nerves;  in  front,  the  superficial  and  middle  glutei;  behind  and  medially,  the  semi- 
tendinosus. 

Blood-supply. — Gluteal,  obturator,  and  posterior  femoral  arteries. 

Nerve-supply. — Posterior  gluteal  and  great  sciatic  nerves. 

6.  Semitendinosus. — This  is  a  long  muscle  which  extends  from  the  first  two 
coccygeal  vertebrae  to  the  proximal  third  of  the  medial  surface  of  the  tibia.  It  lies 
at  first  behind  the  biceps,  then  passes  downward  on  the  back  of  the  thigh,  between 
that  muscle  and  the  semimembranosus  (Figs.  268,  288,  580).  It  has  two  heads  of 
origin. 

Origin. — (1)  The  transverse  processes  of  the  first  and  second  coccygeal  ver- 
tebrae, the  coccygeal  fascia,  and  the  intermuscular  septum  between  this  muscle  and 
the  biceps  femoris;   (2)  the  ventral  surface  of  the  tuber  ischii. 

Insertion. — (1)  The  tibial  crest;   (2)  the  crural  fascia  and  the  tuber  calcis. 

Action. — To  extend  the  hip  and  hock  joints,  acting  wdth  the  biceps  and  semi- 
membranosus in  propulsion  of  the  trunk,  rearing,  etc.;  also  to  flex  the  stifle  and  ro- 
tate the  leg  inward.^ 

Structure. — The  long  or  vertebral  head  is  small  at  its  origin,  but  becomes  larger 
by  the  accession  of  fibers  arising  on  the  intermuscular  septum.  Below  the  tuber 
ischii  it  unites  mth  the  short  head,  which  arises  partly  by  fleshy  fibers,  partly  by  a 
common  tendon  with  the  biceps.  The  muscle  then  passes  downward  on  the  back 
of  the  thigh,  and  terminates  on  a  wide  tendon  on  the  medial  surface  of  the  proximal 
third  of  the  leg.  A  distinct  band  passes  forward  to  be  inserted  on  the  tibial  crest 
(a  bursa  lying  between  the  tendon  and  the  tibia),  part  fuses  with  the  fascia  of  the 
leg,  while  the  remainder  joins  the  biceps  tendon  and  concurs  in  the  formation  of  the 
tendinous  band,  which,  as  before  described,  terminates  on  the  tuber  calcis  (Fig. 
583) .     A  bursa  may  occur  under  the  long  head  where  it  passes  over  the  tuber  ischii. 

1  It  should  be  remembered,  however,  that  the  stifle  can  be  flexed  only  when  the  hock  is  also 
flexed  and  vice  versa. 


324 


FASCIiE   AND    MUSCLES    OF   THE    HORSE 


Relations. — Laterally,  the  skin  and  fascia,  the  biceps,  and  the  medial  head 
of  the  gastrocnemius;  medially,  the  coccygeal  fascia,  the  sacro-sciatic  ligament, 
the  semimembranosus;  anteriorly,  the  biceps  femoris,  branches  of  the  femoral 
artery,  and  the  great  sciatic  nerve. 

Blood-supply. — Posterior  gluteal,  obturator,  and  posterior  femoral  arteries. 

Nerve  supply. — Posterior  gluteal  and  great  sciatic  nerves. 


Origin  of  obhquus  ab- 
dominis internus 
Inguinal  ligament  (part 
removed) 

Iliacus 

Tensor  facice  latoe  -- 

Rectus  femoris 


Vastus  medialis ^B* 

Sartorius 

Gracilis 


Patella 


Medial  patellar  ligament     _ 
Tendon  of  sartorius  ^ 

Tendon  of  gracilL 


Fascia  cruris 


Fig.  287. — Muscles  of  Pelvis  and  Thigh  of  Young  Horse,  Right  Side;  Medial  View. 
1,  Psoas  minor,  and  1',  its  insertion;    2,  psoas  major;    3,  3',  h3ads  of  obturator  internus;    4,  sacro-coccygeus  ven- 
tralis;   5,  coccygeus;   6,  retractor  ani  (cut) ;   7,  sacro-sciatic  ligament;    8,  lesser  sciatic  foramen;  9,  semimembranosus; 
10,  lumbo-sacral  plexus;    11,  obturator  nerve  and  vessels  (cut);    12,  femoral  vessels  (origin);    13,  pubis;    14,  prepubic 
tendon;    15,  deep  inguinal  lymph  glands;    16,  opening  for  external  pudic  vein.     Vertebrae  are  numbered  by  regions. 


7.  Semimembranosus^  (Figs.  276,  287,  288,  576).— This  very  large,  three- 
sided  muscle  lies  on  the  medial  surface  of  the  preceding  muscle  and  the  gastroc- 
nemius, and  has  two  heads  of  origin. 

Origin. — (1)  The  posterior  border  of  the  sacro-sciatic  ligament;  (2)  the  ventral 
surface  of  the  tuber  ischii. 

1  This  muscle  was  incorrectly  designated  the  adductor  magnus  by  Percivall  and  Strange- 
ways.     Its  name,  however,  is  not  at  all  descriptive  of  its  structure  in  the  domesticated  animals. 


THE    MEDIAL   MUSCLES    OF   THE   THIGH  325 

Insertion. — The  medial  epicondyle  of  the  femur,  behind  the  collateral  ligament. 

Action. — To  extend  the  hip  joint  and  to  adduct  the  limb. 

Structure.— The  long  head,  small  and  pointed  above,  extends  toward  the  root 
of  the  tail,  fusing  with  the  sacro-sciatic  ligament.  Passing  downward,  it  becomes 
larger  and  covers  in  part  the  posterior  aspect  of  the  tuber  ischii.  A  bursa  may  be 
found  here.  Below  this  it  joins  the  short  head,  which  is  larger.  The  large  belly 
so  formed  passes  downward  and  forward,  covered  in  great  part  by  the  gracilis,  and 
terminates  on  a  short,  flat  tendon  of  insertion  at  the  distal  end  of  the  femur. 

Relations. — The  upper  part  of  the  muscle  concurs  with  the  sacro-sciatic  liga- 
ment in  forming  the  lateral  boundary  of  the  pelvic  outlet.  It  is  related  posteriorly 
and  laterally  to  the  skin  and  fascia  and  the  semitendinosus ;  medially,  to  the  anus 
and  its  muscles,  the  vulva  in  the  female,  and  the  internal  pudic  artery  and  nerve 
(Figs.  577,  578).  Below  the  pelvis  the  chief  relations  are:  laterally,  the  semi- 
tencUnosus,  biceps,  and  gastrocnemius,  branches  of  the  obturator,  femoral,  and 
posterior  femoral  arteries,  and  the  great  sciatic  nerve  and  its  chief  branches; 
medially,  the  crus  penis  and  ischio-cavernosus  muscle  (in  the  male)  and  the 
gracilis;  in  front,  the  adductor  and  the  femoral  vessels;  behind,  the  skin  and  fascia. 

Blood-supphj. — Obturator  and  femoral  arteries. 

Nerve-supply. — Great  sciatic  nerve. 


m.  THE  MEDIAL  MUSCLES  OF  THE  THIGH 

The  muscles  of  this  group  are  arranged  in  three  layers. 

First  Layer 

1.  Sartorius  (Figs.  287,  288,  576). — This  long  and  rather  narrow  muscle  is  the 
most  anterior  one  of  the  first  layer.  It  extends  from  the  posterior  part  of  the  sub- 
lumbar  region  to  the  lower  and  medial  part  of  the  stifle,  and  is  directed  downward 
and  somewhat  backward. 

Origin. — The  iliac  fascia  and  the  tendon  of  the  psoas  minor. 

Insertion. — The  medial  patellar  ligament  and  the  tuberosity  of  the  tibia. 

Action. — To  flex  the  hip  joint  and  adduct  the  limb. 

Structure. — The  muscle  is  thin  at  its  origin,  but  becomes  thicker,  narrower, 
and  three  sided  distally.  It  terminates  near  the  stifle  joint  on  an  aponeurosis  which 
blends  with  that  of  the  gracilis  and  with  the  fascia  of  the  leg. 

Relations. — Medially,  the  inguinal  ligament,  the  abdominal  muscles,  the  skin 
and  fascia;  laterally,  the  ilio-psoas,  quadriceps  femoris,  and  femoral  nerve.  It 
forms  the  anterior  boundary  of  the  femoral  canal,  in  which  the  femoral  artery  and 
vein  and  the  deep  inguinal  lymph  glands  are  situated  (Fig.  576). 

Blood-supply.- — Femoral  artery. 

Nerve-supply. — Saphenous  nerve. 

A  rare  variation  is  the  existence  of  a  small  accessory  head  which  arises  from  the  anterior 
border  of  the  pubis  or  from  the  prepubic  tendon  and  joins  the  normal  muscle  near  the  middle  of 
the  thigh. 

2.  Gracilis  (Figs.  276,  287,  575). — This  is  a  wide,  quadrilateral  muscle, 
which  is  situated  behind  the  sartorius,  and  covers  the  greater  part  of  the  medial 
surface  of  the  thigh. 

Origin. — The  middle  third  of  the  pelvic  symphysis,  the  prepubic  tendon  and 
accessory  ligament,  and  the  ventral  surface  of  the  pubis  behind  the  prepubic  ten- 
don. 

Insertion. — The  medial  patellar  hgament,  the  medial  surface  of  the  tibia  in 
front  of  the  medial  femoro-tibial  ligament,  and  the  crural  fascia. 

Action. — To  adduct  the  limb. 

Structure. — The  muscle  arises  by  a  strong  tendon,  chiefly  in  common  with  the 


326  FASCIA    AND    MUSCLES    OF   THE   HORSE 

opposite  muscle.  Its  direct  attachment  to  the  ventral  surface  of  the  pelvis  is  not 
so  extensive  as  a  superficial  inspection  would  suggest.  The  tendon  of  origin  pre- 
sents anteriorly  a  foramen  for  the  passage  of  the  external  pudic  vein.  The  belly- 
is  composed  of  parallel  bundles,  and  is  marked  by  a  superficial  furrow  which,  how- 
ever, does  not  indicate  a  muscular  division.  It  terminates  on  the  medial  surface 
of  the  stifle  on  a  thin  wide  tendon  which  blends  in  front  with  that  of  the  sartorius, 
below  with  the  crural  fascia. 

Relations. — Superficially,  the  skin  and  fascia,  the  penis  or  mammary  gland, 
and  the  saphenous  vessels  and  nerve;  deeply,  the  pectineus,  adductor,  semimem- 
branosus and  semitendinosus,  and,  at  the  middle  of  the  femur,  the  femoral  vessels; 
anteriorly,  the  sartorius.  In  the  proximal  third  of  the  thigh  the  sartorius  and  gracili 
are  separated  by  a  triangular  interval  (femoral  triangle),  in  which  lie  the  deep  in- 
guinal lymph  glands  and  the  femoral  vessels. 

Blood-supply. — Femoral  and  deep  femoral  arteries. 

Nerve-supply. — Obturator  nerve. 

Second  Layer 

1.  Pectineus  (Figs.  276,  288,  576). — This  muscle  is  fusiform  and  extends  from 
the  anterior  border  of  the  pubis  to  the  middle  of  the  medial  border  of  the  femur. 

Origin. — The  prepubic  tendon,  the  accessory  ligament,  and  the  anterior  border 
of  the  pubis. 

Insertion. — The  middle  of  the  medial  border  of  the  femur,  near  the  nutrient 
foramen. 

Action. — To  adduct  the  limb  and  flex  the  hip  joint. 

Structure. — The  belly  is  cylindrical  and  contains  little  fibrous  tissue.  Its 
origin  is  perforated  by  the  accessory  ligament — from  which  many  fibers  arise — 
and  is  thus  divided  into  two  unequal  parts.  The  large  upper  part  arises  largely 
from  the  prepubic  tendon — only  a  small  part  gaining  direct  attachment  to  the 
pubis.  The  small  lower  part  does  not  reach  the  bone.  The  insertion  is  pointed 
and  tendinous. 

Relations. — Medially,  the  gracilis;  laterally,  the  femur,  the  vastus  medialis, 
the  terminal  part  of  the  psoas  major  and  iliacus,  and  the  deep  femoral  artery;  an- 
teriorly, the  sartorius,  the  femoral  vessels,  the  saphenous  nerve,  and  the  deep  in- 
guinal lymph  glands;  posteriorly,  the  adductor  and  obturator  externus,  and  the 
obturator  nerve  (anterior  division). 

Blood-supply. — Femoral  and  deep  femoral  arteries. 

Nerve-supply. — Obturator  nerve. 

The  femoral  canal  is  exposed  in  the  dissection  of  the  preceding  muscles  (Figs. 
288,  290).  It  is  bounded  anteriorly  by  the  sartorius,  posteriorly  by  the  pectineus, 
and  laterally  by  the  ilio-psoas  and  vastus  medialis.  Its  medial  wall  is  formed  by 
the  femoral  fascia  and  the  gracilis.  Its  upper  or  abdominal  opening,  the  femoral 
ring  (Lacuna  vasorum),  lies  behind  the  medial  part  of  the  internal  inguinal  ring  and 
is  bounded  anteriorly  by  the  inguinal  ligament,  posteriorly  by  the  anterior  border 
of  the  pubis,  and  laterally  by  the  tendon  of  the  psoas  minor.  The  canal  termi- 
nates below  at  the  insertion  of  the  pectineus.  It  contains  the  deep  inguinal  lymph 
glands,  the  femoral  artery  and  vein,  and  the  saphenous  nerve. 

2.  Adductofi  (Figs.  276,  288,  576).— This  fleshy,  prismatic  muscle  lies  behind 
the  pectineus  and  vastus  medialis.  It  extends  downward  and  forward  from  the 
ventral  surface  of  the  pelvis  to  the  medial  epicondyle  of  the  femur. 

Origin. — The  ventral  surface  of  the  pubis  and  ischium  and  the  tendon  of  ori- 
gin of  the  gracilis. 

1  It  has  been  customary  to  describe  two  adductors — a  parvus  or  brevis,  and  a  longus  or 
magnus.  This  division  is  partly  artificial,  and  has  been  abandoned  in  the  new  nomenclature — 
a  return  to  the  views  of  Bourgelat  and  Girard. 


THE    MEDIAL   MUSCLES    OF    THE    THIGH 


327 


Insertion. — (1)  The  posterior  surface  of  the  femur  from  the  level  of  the  third 
trochanter  to  the  groove  for  the  femoral  vessels;  (2)  the  medial  epicondyle  of  the 
femur  and  the  medial  ligament  of  the  stifle  joint. 

Action. — To  adduct  the  limb  and  extend  the  hip  joint.  It  also  rotates  the  fe- 
mur inward. 

Structure. — It  is  almost  entirely  fleshy,  and  is  composed  of  parallel  bundles 


Psoas  minor 
Sartorius  (origin) 

Iliopsoas 

Tensor  JascivE  latce 

Rectus  fetnoris 


Semimembranosus 
Adductor 


Vastus  medialis 


Patella 


Middle  patellar  ligament      ^^ 
Medial  patellar  ligament  --'^^^ 
Tendon  of  sartorius 

Tendon  of  gracilis 


Tibial  insertion  of  semitendinosus 


Semitendinosus 


Medial  head  of  gastroc- 
nemius 
Tibial  nerve 


Fig.  288. — iMuscles  of  Pelvis  and  Thigh  of  Horse,  Right  Side;  Medial  View. 
Figure  represents  deeper  dissection  of  specimen  shown  in  preceding  figure. 
1,  Tendon  of  insertion  of  psoas  minor;  2,  lumbo-sacral  plexus;  3,  3',  heads  of  obturator  internus;  4,  sacro-coccy- 
geus  ventralis;  5,  coccygeus;  C,  retractor  ani  (origin) ;  7,  sacro-sciatic  hgament;  8,  lesser  sciatic  foramen;  9,  femoral 
nerve;  10,  femoral  vessels;  11,  11,  pectineus;  12,  accessory  ligament;  13,  external  pudic  vein;  14,  pubis;  15,  femoro- 
patellar  joint  capsule;  16,  distal  end  of  femur;  17,  medial  meniscus;  18,  medial  ligament  of  stifle  joint;  19,  medial 
femoro-patellar  ligament. 


united  rather  loosely.  It  is  usually  possible  to  separate  from  the  principal  mass  a 
small  anterior  short  part/  which  is  inserted  into  the  femur  behind  the  pectineus. 
The  principal  mass-  is  perforated  just  below  the  insertion  of  the  pectineus  by  an 
opening  for  the  femoral  vessels  (hiatus  adductorius),  and  is  thus  divided  into  two 

^  This  has  been  termed  by  various  authors  the  adductor  parvus  or  brevis. 
2  Termed  by  various  authors  the  adductor  magnus  or  longus. 


328  FASCIA    AND    MUSCLES    OF   THE    HORSE 

branches.  The  lateral  branch  is  inserted  into  the  back  of  the  femur  with  the  short 
portion,  while  the  medial  branch  is  attached  to  the  medial  epicondyle  and  col- 
lateral ligament.  There  is  often  a  superficial  slip  which  ends  partly  on  the  femoro- 
patellar  joint  capsule  and  may  reach  the  accessory  cartilage  or  medial  ligament  of 
the  patella.  Some  fibers  pass  under  the  collateral  ligament  and  end  on  the  tendon 
of  the  semimembranosus. 

Relations. — Medially,  the  gracilis,  and  branches  of  the  femoral  artery  and 
of  the  obturator  nerve;  laterally,  the  femur,  the  obturator  extern  us,  quadratus 
femoris,  biceps  femoris,  and  the  femoral,  deep  femoral,  and  obturator  arteries;  an- 
teriorly, the  pectineus,  vastus  medialis,  and  a  large  branch  of  the  obturator  nerve; 
posteriorly,  the  semimembranosus  and  the  great  sciatic  nerve. 

Blood-supply. — Femoral,  deep  femoral,  and  obturator  arteries. 

Nerve-supply. — Obturator  nerve. 

3.  Semimembranosus. — Described  on  p.  324. 

Third  Layer 

1.  Quadratus  femoris.^ — This  is  a  narrow,  three-sided  muscle,  which  lies  under 
cover  of  the  upper  part  of  the  adductor  (Fig.  581). 

Origin. — The  ventral  surface  of  the  ischium,  just  in  front  of  the  semimembrano- 
sus. 

Insertion. — An  oblique  line  on  the  posterior  surface  of  the  femur,  near  the 
lower  part  of  the  trochanter  minor. 

Action. — To  extend  the  hip  joint  and  to  adduct  the  thigh. 

Structure. — It  is  composed  of  parallel  bundles  of  fibers  directed  do\\Tiward, 
forward,  and  outward. 

Relations. — Postero-medially,  the  adductor,  semimembranosus,  and  the  ob- 
turator vessels;  antero-laterally,  the  obturator  externus  and  biceps  femoris,  the 
deep  femoral  vessels,  and  the  great  sciatic  nerve. 

Blood-supply. — Deep  femoral  and  obturator  arteries. 

Nerve-supply.- — Great  sciatic  nerve. 

2.  Obturator  externus  (Fig.  581). — This  is  a  pyramidal  muscle  which  extends 
across  the  back  of  the  hip  joint  from  the  ventral  surface  of  the  pelvis  around  the 
obturator  foramen  to  the  trochanteric  fossa. 

Origin. — The  ventral  surface  of  the  pubis  and  ischium,  and  the  margin  of  the 
obturator  foramen. 

Insertion. — The  trochanteric  fossa. 

Action. — To  adduct  the  thigh  and  to  rotate  it  outward. 

Structure. — It  is  almost  entirely  fleshy,  the  muscle-bundles  being  rather  loosely 
connected.  The  insertion  is  pointed,  flattened,  and  partly  tendinous.  The  origin 
is  perforated  by  the  obturator  vessels  and  nerve. 

Relations. — Medially,  the  adductor  and  quadratus  femoris  and  the  deep 
femoral  vessels;  laterally,  the  gemellus,  the  tendon  of  the  obturator  internus,  the 
biceps  femoris,  and  the  great  sciatic  nerve;  anteriorly,  the  hip  joint,  the  pectineus, 
and  the  external  pudic  vein. 

Blood-supply. — Deep  femoral  and  obturator  arteries. 

Nerve-supply. — Obturator  nerve. 

3.  Obturator  internus  (Fig.  288). — This  arises  within  the  pelvic  cavity  by  two 
heads,  the  tendon  emerging  through  the  lesser  sciatic  foramen. 

Origin. — (1)  The  pelvic  surface  of  the  pubis  and  ischium  around  the  obturator 
foramen;  (2)  the  pelvic  surface  of  the  shaft  of  the  ilium  and  the  wing  of  the  sacrum. 
Insertion. — The  trochanteric  fossa. 
Action. — To  rotate  the  femur  outward. 

1  Also  known  as  the  ischio-femoralis. 


ANTERIOR   MUSCLES    OF   THE    THIGH  329 

Structure. — The  ischio-pubic  head  Ues  on  the  pelvic  floor  and  covers  the  ob- 
turator foramen.  It  is  thin  and  fan-shaped.  The  iliac  head  extends  along  the 
lateral  wall  of  the  pelvis,  and  is  pennate,  with  a  central  tendon  throughout.  Both 
terminate  on  a  flat  tendon  which  passes  outward  through  the  lesser  sciatic  fora- 
men to  be  inserted  into  the  trochanteric  fossa.  The  tendon  furnishes  insertion  to 
fibers  of  the  gemeflus.  A  synovial  bursa  facilitates  the  play  of  the  tendon  over  the 
lateral  border  of  the  ischium.^ 

Relations. — The  pelvic  surface  is  covered  by  the  pelvic  fascia  and  in  part  by 
the  peritoneum.  The  obturator  vessels  and  nerve  lie  between  the  two  heads,  and 
the  internal  pudic  vessels  and  nerve  lie  along  the  dorsal  edge  of  the  iliac  head.  The 
tendon  is  crossed  by  the  great  sciatic  nerve. 

Blood-supply. — Obturator  and  internal  pudic  arteries. 

Nerve-supply. — Great  sciatic  nerve. 

4.  Gemellus-  (Fig.  580).— This  is  a  thin,  triangular  muscle,  which  extends 
from  the  lateral  border  of  the  ischium  to  the  trochanteric  fossa  and  ridge. 

Origin. — The  lateral  border  of  the  ischium  near  the  ischiatic  spine. 

Insertion. — The  trochanteric  fossa  and  ridge. 

Action. — To  rotate  the  femur  outward. 

Structure. — The  thin  tendon  of  origin  is  attached  to  a  line  on  the  lateral  border 
of  the  ischium,  which  begins  just  below  the  posterior  end  of  the  superior  ischiatic 
spine.  Many  superficial  fibers  are  inserted  into  the  tendon  of  the  obturator  in- 
ternus. 

Relations. — Superficially,  the  biceps  femoris,  the  tendon  of  the  obturator  in- 
ternus,  the  gluteus  medius,  and  the  great  sciatic  nerve;  deeply,  the  obturator  ex- 
ternus  and  the  hip  joint. 

Blood-supply. — Obturator  artery. 

Nerve-supply. — Great  sciatic  nerve. 


IV.  ANTERIOR  MUSCLES  OF  THE  THIGH 

This  group  consists  of  the  sartorius,  quadriceps  femoris,  and  capsularis. 

1.  Sartorius. — This  is  described  on  p.  325. 

2.  Quadriceps  femoris  (Figs.  268,  289,  291). — This  constitutes  the  large  mus- 
cular mass  which  covers  the  front  and  sides  of  the  femur.  It  has  four  heads,  one 
of  which,  the  rectus,  arises  from  the  ilium;  the  other  three  arise  from  the  femur. 
All  are  inserted  into  the  patella. 

(1)  Rectus  femoris. — This  is  fusiform  and  rounded.     It  arises  by  two  tendons. 

Origin. — Two  depressions  on  the  shaft  of  the  ilium  above  and  in  front  of  the 
acetabulum. 

Insertion. — The  base  and  anterior  surface  of  the  patella. 

Action. — To  extend  the  stifle  joint  and  to  flex  the  hip  joint. 

Structure. — It  has  two  short  strong  tendons  of  origin;  beneath  the  lateral  one 
is  a  bursa.  The  belly  is  rounded  and  rests  in  a  groove  formed  by  the  other  portions 
of  the  quadriceps.     Its  sides  are  covered  by  a  strong  tendinous  layer  which  fur- 

1  The  iliac  head  has  been  described  as  a  separate  muscle,  and  termed  the  piriformis.  This 
does  not  seem  desirable,  especially  since  it  is  probable  that  the  homologue  of  the  piriformis  of 
man  is  that  portion  of  the  middle  gluteus  which  is  inserted  into  the  trochanteric  ridge. 

^  The  name  is  based  on  the  arrangement  in  man,  in  whom  the  muscle  usually  consists  of  two 
fascicuh  forming  a  groove  between  them  for  the  tendon  of  the  obturator  internus.  In  the  horse 
it  is  usually  undivided  at  its  origin,  but  toward  the  insertion  the  upper  part  is  separated  from  the 
rest  of  the  muscle  or  is  readily  isolated.  The  muscle  is  subject  to  much  variation  in  size.  When 
well  developed,  the  insertion  extends  from  the  proximal  end  of  the  trochanteric  fossa  to  a  point 
just  above  the  femoral  attachment  of  the  biceps  femoris;  in  such  cases  the  upper  part,  which 
occupies  the  space  behind  the  hip  joint  between  the  gluteus  profundus  and  obturator  externus, 
is  much  thicker  than  the  remainder,  which  covers  the  latter  muscle.  The  gemellus  may  be  re- 
garded as  the  extrapelvic  head  of  the  obturator  internus  (Gegenbaur). 


330 


FASCIA    AND   MUSCLES    OF   THE    HORSE 


nishes  insertion  to  fibers  of  the  vasti.  The  tendon  of  insertion  is  formed  by  the 
union  of  these  tendinous  layers  on  the  lower  part  of  the  muscle.  The  lower  portion 
of  the  muscle  is  pennate,  the  fibers  on  either  side  converging  on  the  tendon  at  an 
acute  angle. 

Relations. — Medially,  the  iliacus,  sartorius,  and  vastus  medialis;  laterally, 
the  tensor  fasciae  latae,  glutei,  and  vastus  lateralis;  posteriorly,  the  hip  joint  and 
the  vastus  intermedins;  anteriorly,  the  fascia  lata  and  the  skin.  The  anterior 
femoral  artery  and  branches  of  the  femoral  nerve  descend  into  the  interspace  be- 


\'  Shaft  of  ilium 
y  Medial  tendon  of  origin 
-^         of  rectus  femoris 


Gluteus  profundus 

Vastus  lateralis 
Rectus  femoris 


Prepubic  tendon  (ir, 
median  section) 
Obturator  externus 

Iliopsoas  {insertion) 
Adductor 

Vastus  medialis 


Medial  femoro-tibial  ligament 
Medial  vieniscus 


Lateral  patellar  ligament 


Tuberosity  of  tibia 


Fig.  289. — Muscles  of  Right  Thigh  of  Horse,  Deep  Dissection.     The  Preparation  is  Viewed  fro.m  in  Front 

AND  Somewhat  Medially. 

1,  Accessory  ligament  of  hip  joint;   2,  transverse  ligament  of  same;   3,  head  of  femur;   4,  patella;   5,  trochlea  of  femur; 

6,  7,  middle  and  medial  patellar  ligaments. 


tween  the  upper  part  of  the  rectus  and  the  vastus  medialis;  similarly,  the  iliaco- 
femoral  artery  dips  in  between  the  rectus  femoris  and  vastus  lateralis. 

Blood-supply. — Femoral  and  iliaco-femoral  arteries. 

Nerve-supply. — Femoral  nerve. 

(2)  Vastus  lateralis. — This  lies  on  the  lateral  surface  of  the  femur,  extending 
from  the  great  trochanter  to  the  patella.     It  is  wide  in  its  middle,  smaller  at  each  end. 

Origin. — The  lateral  border  and  surface  of  the  femur,  from  the  trochanter 
major  to  the  supracondyloid  fossa. 


ANTERIOR   MUSCLES    OF   THE   THIGH 


331 


Insertion.— (1)  The  lateral  part  of  the  anterior  surface  of  the  patella;  (2)  the 
tendon  of  the  rectus  femoris. 

Action. — To  extend  the  stifle  joint.  . 

Structure.— The  fibers  are  directed  downward  and  forward,  many  being  in- 
serted into  the  tendinous  sheet  which  covers  the  side  of  the  rectus.  A  bursa  is 
usually  present  between  the  distal  end  and  the  patella. 

i^e/a«ions.— Laterally,  the  fascia  lata  and  skin,  tensor  fascia  lata,  superficial 


Fold  of  flank 
Tensor  fasci(r  latcB 


Vastus  lateralis 

]■  T  v^^^^^-        oV         Tl^^^^^^x    ^  Vastus  intermedium 

Vastus  mediahs  *  ^i—  i  ■■  ow  »^^^^^^^    ^ 

Sartorius 
Saphenous  vein  —-.^^jM 
Saphenous  nerve         ''^ 
Femoral  artery 
Gracilis 


Peroneal  nerve 
Tibial  nerve 


SemitendinosH 


Fig.  290.— Cross-section  of  Middle  of  Right  Thigh  of  Horse. 

gluteus,  and  biceps  femoris;  medially,  the  femur  and  femoro-patellar  joint  capsule, 
the  rectus  femoris,  vastus  intermedins,  and  the  iliaco-femoral  artery. 

Blood-supply.— llisico-iemoral  artery. 

Nerve-supply.— Femoral  nerve.  j  r  „  :„  „  oir,. 

(3)  Vastus  mediaUs.— This  resembles  the  preceding  muscle,  and  lies  m  a  sim- 
ilar position  on  the  medial  side  of  the  femur.  ,    ^    ^u     r  +„i  +i.;rri 

Onom.-The  medial  surface  of  the  femur,  from  the  neck  to  the  distal  third. 

Insertion.-{l)  The  medial  border  of  the  patella  and  its  cartilage,  and  the 


332 


FASCIA    AND    MUSCLES    OF   THE    HORSE 


proximal  part  of  the  medial  patellar  ligament.  (2)  The  tendon  of  the  rectus 
femoris. 

Action. — To  extend  the  stifle  joint. 

Structure. — This  is  very  similar  to  that  of  the  vastus  lateralis.  It  is,  how- 
ever, more  difficult  to  separate  from  the  intermedins,  because  many  fibers  of  the 
latter  arise  on  the  tendinous  sheet  which  covers  the  contact  surface-  of  the  medial 


Shaft  of  ilium 


Gluteus  profundus 


Trochanter  major 
{anterior  part) 


Vastus  lateralis 
Vastus  intermedium 

Rectus  femoris 

Vastus  lateralis 

Biceps  femoris 

Patella 


Lateral  femoro-tibial 
ligament 
Lateral  patellar  ligament 


Prepubic  tendon 
Obturator  externum 


Vastus  medialis 


Adductor 


r  Medial  femoro-tibial  ligament 
Medial  meniscus 
Middle  patellar  ligament 

Tuberosity  of  tibia 


Fig.  291. — Mi  s.  i.ks  <>f  Right  Thigh  of  Horse;  Deep  Dissection. 
The  preparation  is  viewed  from  tiie  front  and  somewhat  medially.     Most  of  rectus  femoris  and  vastus  lateralis 
has  been  removed.     1,  Stump  of  origin  of  rectus  femoris;   2,  capsularis;    3,  accessory  ligament;   4,  cotyloid  ligament; 
5,  head  of  femur;   6,  trochlea  of  femur. 


vastus.  Its  insertion  into  the  patella  is  chiefly  by  means  of  a  broad,  strong  tendon. 
From  the  deep  face  fleshy  fibers  are  inserted  also  into  the  femoro-patellar  joint  cap- 
sule. 

Relations. — Medially,  the  skin  and  fascia,  the  iliacus,  sartorius,  pectineus,  and 
adductor,  the  femoral  vessels,  and  saphenous  nerve;  laterally,  the  femur,  femoro- 
patellar  joint  capsule,  rectus  femoris,  and  vastus  intermedins,  the  anterior  femoral 
artery,  and  branches  of  the  femoral  nerve. 


THE    MUSCLES    OF   THE   LEG   AND    FOOT  333 

Blood-supply. — Femoral  and  anterior  femoral  arteries. 

Nerve-supply. — Femoral  nerve. 

(4)  Vastus  intermedius. — This  muscle  is  deeply  situated  on  the  anterior  face 
of  the  femur,  and  is  entirely  covered  by  the  preceding  heads. 

Origin.— {1)  The  anterior  surface  of  the  femur,  from  the  proximal  to  the  distal 
fourth;  (2)  the  tendinous  covering  of  the  vastus  medialis. 

Insertion. — (1)  The  base  of  the  patella;    (2)  the  femoro-patellar  joint  capsule. 

Action. — (1)  To  extend  the  stifle  joint;  (2)  to  tense  (raise)  the  femoro-patellar 
capsule  during  extension  of  the  joint. 

Structure.- — The  muscle  is  usually  quite  difficult  to  isolate  from  the  other  vasti, 
so  that  many  since  Glinther  have  declared  it  an  artefact.^  It  is  entirely  fleshy,  and 
is  small  at  its  proximal  end,  but  when  traced  downward  increases  in  bulk  by  the 
accession  of  fibers  arising  on  the  femur  and  the  tendinous  covering  of  the  vastus 
medialis.  The  terminal  part  is  intimately  adherent  to  the  femoro-patellar  joint 
capsule,  where  the  latter  bulges  above  the  level  of  the  patella. 

Relations. — Medially,  the  vastus  medialis;  laterally,  the  vastus  lateralis; 
anteriorly,  the  rectus ;  posteriorly,  the  femur  and  femoro-patellar  capsule. 

Blood-supply. — Iliaco-femoral  and  anterior  femoral  arteries. 

Nerve-supply. — Femoral  nerve. 

The  patellar  ligaments  are  to  be  regarded  as  tendons  of  the  quadriceps  which  communicate 
the  action  of  the  latter  to  the  tibia,  the  patella  being  intercalated  as  a  sesamoid  bone. 

3.  Capsularis  (Fig.  291). ^ — This  is  a  small  fusiform  muscle  (scarcely  as  large 
as  one's  finger),  which  arises  by  a  thin  tendon  on  the  ilium  immediately  above  the 
outer  tendon  of  the  rectus  femoris.  Its  delicate  tendon  of  insertion  dips  in  between 
the  vastus  intermedius  and  lateralis  and  is  attached  to  the  proximal  third  of  the 
anterior  surface  of  the  femur.  It  passes  over  the  outer  side  of  the  hip  joint,  to  the 
capsule  of  which  some  fibers  are  attached.  Sometimes  the  muscle  has  two  dis- 
tinct heads,  in  which  case  the  additional  head  arises  between  the  two  tendons  of 
origin  of  the  rectus  femoris.  Its  action  may  be  to  raise  the  capsule  during  flexion 
of  the  joint.  It  is  related  laterally  to  the  gluteus  profundus  and  vastus  lateralis, 
medially  to  the  rectus  femoris  and  vastus  intermedius  and  the  hip  joint. 


V.  THE  MUSCLES  OF  THE  LEG  AND  FOOT 
The  muscles  of  this  region  cover  almost  all  of  the  tibia  except  its  medial  face, 
which  is  largely  subcutaneous.     As  in  the  forearm,  the  muscles  fall  into  two  groups, 
a  dorso-lateral  and  a  plantar.     The  muscles  of  the  first  group  are  extensors  of  the 
digit  and  flexors  of  the  hock,  those  of  the  second  have  the  opposite  action. 

A.  Dorso-lateral  Group 

1.  Long  digital  extensor  (M.  extensor  digitalis  longus).^ — This  muscle  is  sit- 
uated superficially  on  the  dorso-lateral  aspect  of  the  leg,  and  is  provided  with  a  long 
tendon  which  passes  dowTi  over  the  front  of  the  tarsus,  metatarsus,  and  digit. 

Origin.— The  extensor  fossa  of  the  femur. 

Insertion.— {1)  The  extensor  process  of  the  third  phalanx;  (2)  the  dorsal  sur- 
face of  the  proximal  extremities  of  the  first  and  second  phalanges. 

Action.- — To  extend  the  digit  and  flex  the  hock.  It  also  assists  in  fixing  the 
stifle  joint. 

^  While  it  is  true  that  the  separation  of  the  intermedius  is  never  entirely  a  natural  one  in  the 
horse,  it  varies  in  individual  cases,  and  is  usually  clear  on  cross-sections.  In  some  subjects  it  is 
possible  to  separate  another  slip  which  may  represent  the  articularis  genu  of  man. 

^  Also  known  as  the  rectus  parvus. 

3  Also  termed  the  extensor  pedis  or  the  anterior  extensor  of  the  phalanges. 


334 


FASCIA   AND    MUSCLES    OF   THE    HORSE 


Structure. — The  origin  is  by  means  of  a  strong  tendon  in  common  with  the 
peroneus  tertius,  on  which  also  many  fibers  arise.  The  common  tendon  passes 
downward  in  the  groove  between  the  lateral  condyle  and  the  tuberosity  of  the  tibia, 

f 


Patella  -  — 


\ 


Crest  of  tibia 

Long  digital  extensor 
Lateral  digital  extensor  ■ 


Proximal  annular  ligament  - 
Lateral  malleolus 


Middle  annular  ligament 

Distal  annular  ligament 

Tendon  of  long  extensor 

Tendon  of  lateral  extensor 


Branch  of  suspensory  ligament  to 
extensor  tendon 


~  Gastrocnemius,  lateral  head 
Soleus 
\,\  Tendon  of  gastrocnemius 

-  Tarsal  tendon  of  biceps  femoris 

-  Deep  flexor 


Superficial 
flexor  tendon 


Superficial  flexor 
teridon 


Deep  flexor  tendon 


Suspensory 
ligament 


Fig.  292. — Muscles  of  Lower  Part  of  Thigh,  Leg,  and  Foot  of  Horse;  Lateral  View. 

</,  Faacia  lata;  g,  g',  g",  biceps  femoris;  r,  semitendinosus;   .27',  lateral  condyle  of  tibia.     The  extensor  brevis  is  visible 

in  the  angle  between  the  long  and  lateral  extensor  tendons,  but  by  an  oversight  it  is  not  marked.     (After  EUen- 

berger-Baum,  Anat.  fiir  Ktinstler.) 


where  a  pouch  from  the  femoro-tibial  capsule  descends  three  or  four  inches  (ca. 
7.5  to  10  cm.)  beneath  the  tendon.  The  belly  is  fusiform  and  somewhat  flattened. 
The  long  tendon  of  insertion  begins  in  the  belly  about  its  middle,  and  is  clear  of  the 


THE   MUSCLES    OF   THE    LEG    AND    FOOT  335 

fleshy  part  near  the  tarsus.  It  passes  downward  over  the  front  of  the  hock,  bound 
down  by  the  three  annular  ligaments  already  described  (see  tarsal  fascia),  and  en- 
veloped by  a  sjmovial  sheath  which  begins  a  little  above  the  level  of  the  lateral 
malleolus,  and  extends  nearly  to  the  junction  with  the  lateral  extensor  tendon. 
This  union  occurs  usually  about  a  hand's  breadth  below  the  tarsus.  In  the  angle 
of  union  the  extensor  brevis  also  joins  the  principal  tendon.  Beyond  this  point 
the  arrangement  is  the  same  as  in  the  fore  limb. 

Relations. — Superficially,  the  skin  and  fascia;  deeply,  the  femoro-tibial  joint, 
peroneus  tertius,  and  tibialis  anterior;  behind,  the  lateral  extensor  and  the  super- 
ficial and  deep  peroneal  nerves.  In  front  of  the  tarsus  the  anterior  tibial  artery 
crosses  the  deep  face  of  the  tendon  (Fig.  585). 

Blood-supply. — Anterior  tibial  artery. 

Nerve-supply. — Peroneal  nerve. 

2.  Lateral  digital  extensor  (M.  extensor  digitalis  lateralis).^ — This  muscle  lies 
on  the  lateral  surface  of  the  leg,  behind  the  preceding  one. 

Origin. — The  lateral  ligament  of  the  stifle  joint,  the  fibula,  the  lateral  border 
of  the  tibia,  and  the  interosseous  ligament. 

Insertion.— The  tendon  of  the  long  extensor,  about  a  third  of  the  way  down 
the  metatarsus. 

Action. — To  assist  the  long  extensor. 

Structure. — The  belly  is  fusiform,  flattened,  and  pennate.  The  tendon  runs 
through  the  entire  length  of  the  belly  and  becomes  free  from  it  at  the  distal  fourth 
of  the  tibia.  It  descends  through  the  groove  on  the  lateral  malleolus,  bound  down 
by  an  annular  ligament,  and,  inclining  forward,  blends  (usually)  with  the  tendon 
of  the  long  extensor.  It  is  provided  with  a  synovial  sheath,  which  begins  about 
an  inch  (ca.  2  to  3  cm.)  above  the  lateral  malleolus  and  ends  about  one  and  one- 
half  inches  (ca.  3  to  4  cm.)  above  the  junction.  Sometimes  the  fusion  does  not 
occur;  the  tendon  then  descends  alongside  of  that  of  the  long  extensor,  and  is  in- 
serted into  the  first  phalanx  like  the  corresponding  muscle  of  the  thoracic  limb. 

Relations.— Laierally,  the  skin  and  fascia  and  the  superficial  peroneal  nerve; 
medially,  the  tibia  and  fibula;  anteriorly,  the  intermuscular  septum,  the  long 
extensor,  and  the  tibialis  anterior;  posteriorly,  the  deep  digital  flexor  and  the  soleus. 

Blood-supply. — Anterior  tibial  artery. 

Nerve-supply. — Peroneal  nerve. 

3.  Peroneus  tertius  (Tendo  f emoro-metatarseus)  .^ — This  consists  in  the  horse 
of  a  strong  tendon  which  lies  between  the  long  extensor  and  the  tibialis  anterior. 

Origin. — The  extensor  fossa  (between  the  lateral  condyle  and  the  trochlea 
of  the  femur),  in  common  with  the  long  extensor. 

Insertion. — (1)  The  proximal  extremity  of  the  large  (third)  metatarsal  bone 
and  the  third  tarsal  bone ;   (2)  the  fibular  and  fourth  tarsal  bones. 

Action.- — Mechanically  to  flex  the  hock  when  the  stifle  joint  is  flexed. 

Structure. — It  is  entirely  tendinous.  The  proximal  end  and  the  underlying 
prolongation  of  the  synovial  membrane  of  the  femoro-tibial  joint  have  been  men- 
tioned in  the  description  of  the  long  extensor.  The  superficial  face  gives  origin 
to  fibers  of  the  long  extensor  in  the  upper  part  of  the  leg,  and  the  deep  face  is  fused 
with  the  tibialis  anterior  except  at  either  end  of  the  region.  At  the  distal  end  of  the 
tibia  the  tendon  is  perforated  for  the  emergence  of  the  tendon  of  the  tibialis  anterior 
and  divides  into  two  branches.  The  anterior  branch  is  attached  to  the  third  tarsal 
and  third  metatarsal  bones,  while  the  lateral  one  curves  outward,  bifurcates,  and 

^  Also  known  as  the  peroneus  or  the  lateral  extensor  of  the  phalanges.  Lesbre  considers  it 
to  be  the  homologue  of  the  peroneus  brevis  of  man  and  other  pentadactyls. 

2  It  seems  inadvisable  to  retain  the  old  term,  tendinous  part  of  the  flexor  metatarsi,  since  it 
is  inapphcable  to  other  domesticated  animals  in  which  the  muscle  is  well  developed  (e.  g.,  pig). 
Schmaltz  uses  the  term  tendo  femoro-tarseus,  and  Varaldi  and  Lesbre  designate  it  the  femoro- 
metatarsal  cord.     The  name  peroneus  anterior  has  also  been  proposed. 


336 


FASCIA    AND    MUSCLES    OF    THE    HORSE 


is  inserted  into  the  fibular  and  fourth  tarsal  bones.      The  lateral  tendon  gives  off 
a  branch  which  forms  a  loop  around  the  long  extensor  tendon  (Fig.  293). 

Relations. — Superficially,  the  long  extensor;  deeply,  the  tibialis  anterior.     The 
anterior  tibial  vessels  cross  the  deep  face  of  the  outer  branch. 


Lateral  ridge  of  trochlea  of  femur 
Lateral  femoro-tibial  ligament 

Lateral  meniscus 
Lateral  condyle  of  tibia  "^ 

Long  extensor  (stump) 

Peroneus  tertius 
Tibialis  anterior 
Lateral  extensor 


Tendinous  loop 
Extensor  brevis 


Tendon  of  lateral  extensor 
Tendon  of  long  extensor 


Medial  ridge  of  trochlea  of  femur 


Medial  meniscus 

Medial  femoro-tibial  ligament 


Tendon  of  long  extensor 
Annular  ligament 
Peroneus  tertius 

Medial  tendon  of  tibialis  anterior 

Anterior  tendon  of  tibialis  anterior 
Anterior  tendon  of  peroneus  tertius 

Annular  ligament 
Ml.  Ill 


Fig.  293. — Muscles  of  Right  Leg  of  Horse;  Front  View. 
The  greater  part  of  the  long  extensor  has  been  removed.     \,  2,  3,  Stumps  of  patellar  ligaments;  4,  tuberosity  of  tibia. 


4.  Tibialis  anterior.^ — This  lies  on  the  dorso-lateral  face  of  the  tibia;  it  is  wide 
and  flattened  above,  pointed  below. 

Origin. — The  lateral  condyle  and  border  of  the  tibia  and  a  small  area  on  the 
lateral  surface  of  the  tuberosity. 

^  This  is  also  known  as  the  muscular  part  of  the  flexor  metatarsi. 


THE  MUSCLES  OF  THE  LEG  AND  FOOT 


337 


Insertion. — (1)  The  ridge  on  the  front  of  the  proximal  end  of  the  large  meta- 
tarsal bone;    (2)  the  first  and  second  tarsal  bones. 

Action. — To  flex  the  hock  joint. 

Structure. — The  origin  is  fleshy,  and  forms  a  groove  in  which  lie  the  common 
tendon  of  the  long  extensor  and  peroneus  tertius  and  a  synovial  pouch  which  de- 
scends from  the  femoro-tibial  joint.  Many  superficial  fibers  arise  from  the  deep 
fascia  at  the  proximal  part  of  the  leg  and  thus  from  the  tibial  crest.  Passing  down- 
ward on  the  tibia,  the  belly  is  united  by  tendinous  and  fleshy  fibers  with  the  per- 
oneus tertius,  and  terminates  close  to  the  tarsus  in  a  point  on  the  tendon  of  inser- 


FiG.   294. — Injected   Synovial  Sheaths  and   Burs.*; 

OF  Tarsal  Region  of  Horse;  Medial  View. 

a,  Synovial  sheath  of  peroneus  tertius  and  tibialis 
anterior;  h,  bursa  under  medial  (cunean)  tendon  of 
tibiahs  anterior;  c,  synovial  sheath  of  flexor  longus; 
d,  tarsal  sheath  of  deep  flexor;  e,  e',  bursa  under 
superficial  flexor  tendon;  /,  /',  tibio-tarsal  joint  capsule; 
1,  long  extensor;  2,  tibialis  anterior;  2',  medial  (cun- 
ean) tendon  of  2;  3,  flexor  longus;  4,  deep  digital 
flexor;  o,  superficial  flexor  tendon;  6,  gastrocnemius 
tendon;  7,  tibia;  S,  tarsus;  9,  tuber  calcis;  10,  large 
metatarsal  bone;  11,  medial  small  metatarsal  bone; 
12,  12',  fascial  bands.  (After  Ellenberger,  in  Leisering's 
Atlas.) 


Fig.  295. — Injected  Synovial  Sheaths  and  Burs« 
OF  Tarsal  Region  of  Horse;  Lateral  View. 
o,  Synovial  sheath  of  long  digital  extensor;  6, 
synovial  sheath  of  lateral  digital  extensor;  c,  c',  bursa 
under  superficial  flexor  tendon;  d,  capsule  of  hock  joint; 
1.  long  extensor;  2,  lateral  extensor;  3,  3,  3,  annular 
ligaments;  4,  deep  digital  flexor;  5,  tendon  of  gastroc- 
nemius; 6,  superficial  flexor  tendon;  7,  tibia;  8,  tarsus; 
9,  tuber  calcis;  10,  metatarsus.  (After  Ellenberger, 
in  Leisering's  Atlas.) 


tion.  The  latter  emerges  between  the  branches  of  the  peroneus  tertius  and  bi- 
furcates, the  anterior  branch  being  inserted  into  the  large  metatarsal  bone,  the 
medial  one  into  the  first  tarsal  bone.  The  tendon  is  provided  with  a  s3aiovial  sheath 
at  its  emergence,  and  a  bursa  is  interposed  between  the  medial  branch  and  the 
medial  ligament  of  the  hock.^ 

Relations. — Superficially,  the  long  and  lateral  extensors,  the  peroneus  tertius, 
and  the  deep  peroneal  nerve;  deeply,  the  tibia,  the  deep  flexor,  and  the  anterior 
tibial  vessels. 

^  In  surgical  works  the  medial  branch  is  termed  the  cunean  tendon;  it  is  sometimes  resected 
for  the  relief  of  bone  spavin. 
22 


338 


FASCIAE    AND    MUSCLES    OF   THE    HORSE 


Blood-supply. 
Nerve-supply. 


-Anterior  tibial  artery 
-Peroneal  nerve. 


third  of  the  femur  to  the  point  of  the  hock. 


Sluifl  of  fcmu 


Medial  head  of 
gastroc7ierniits 


Fascial  hand 


Latind  head  of 
(jdst  roc  tic  till  us 


B.  Plantar  Group 
1.  Gastrocnemius  (Fi^s.  268,  292,  296).^This  muscle  extends  from  the  distal 

It  arises  by  two  heads. 

Origin. — (1)  Lateral  head, 
from  the  lateral  supracondj^- 
loid  crest  (margin  of  the  supra- 
condyloid  fossa);  (2)  medial 
head,  from  the  medial  supra- 
condyloid  crest. 

Insertion. — The  posterior 
part  of  the  tuber  calcis. 

Action. — To  extend  the 
hock  and  to  flex  the  stifle 
joint;  these  two  actions,  how- 
ever, cannot  occur  simulta- 
neously. 

Structure. — The  two  bel- 
lies are  thick,  fusiform,  and 
somewhat  flattened.  They 
are  covered  by  a  strong  apo- 
neurosis and  contain  tendinous 
intersections.  They  terminate 
toward  the  middle  of  the  leg 
on  a  common  tendon,  which  at 
first  lies  posterior  to  that  of  the 
superficial  flexor,  but,  by  a 
twist  in  both,  comes  to  lie  in 
front  of  the  latter.  The  deep 
fascia  blends  with  the  tendon 
throughout  its  length,  and  the 
soleus  muscle  is  inserted  into 
its  anterior  edge.  A  small 
bursa  (Bursa  tendinis  m.  gas- 
trocncmii)  lies  in  front  of  the 
insertion  on  the  tuber  calcis, 
and  a  large  bursa  (calcanea 
subtendinea)  is  interposed  be- 
tween the  two  tendons  from 
the  twist  downward  to  the 
middle  of  the  hock.  The  super- 
ficial digital  flexor  lies  between 
the  two  heads  and  is  adherent 
to  the  lateral  one  (Fig.  584). 
The  term  tendo  calcaneus  or 
tendo  Achillis  is  a  convenient 
designation  for  the  aggregated 
tendons  in  the  distal  part  of  the 
leg  which  are  attached  to  the 
tuber  calcis. 
Rclations.—Antoviorly,  the  stifle  joint,  the  superficial  digital  flexor,  popliteus, 
deep  digital  flexor,  popliteal  vessels,  and  tilnal  nerve;   medially  (above),  the  semi- 


Soleiis 


Ural  cxlcn- 
sor 

■.ror  }i<dlucis 

Tendon  of  (/os- 
trocnctniua 


Snpcrficiid 
Jlcvor  tendon 


A 

Tendon  of  deep  flexor 
Fig.  20G. — Musci.es  op  Right  Leo  of  Horse:  PosTEnioR  View 


Tendon  of  long 
digital  flexor 


THE    MUSCLES    OF   THE   LEG    AND    FOOT  339 

tenclinosus,  semimembranosus,  and  adductor,  (below)  the  fascia  and  skin;  laterally 
(above),  the  biceps  femoris  and  peroneal  nerve,  (below)  the  fascia  and  skin.  The 
popliteal  lymph  lands  lie  on  the  upper  part  of  the  nmscle. 

Blood-supply. — Popliteal  artery, 

Nerve-iiupph). — Tibial  nerve. 

2.  Soleus  (Fig.  29G). — This  muscle  is  very  small  in  the  horse.  It  lies  along 
the  lateral  border  of  the  gastrocnemius  under  the  common  deep  fascia,  on  the  prox- 
imal half  of  the  lateral  surface  of  the  leg. 

Origin. — The  head  of  the  fibula. 

Insertion. — The  tendon  of  the  gastrocnemius,  about  the  middle  of  the  leg. 

Action. — To  assist  the  gastrocnemius. 

Structure. — It  is  a  thin,  fleshy  band,  usually  about  an  inch  (ca.  2  to  3  cm.)  in 
width,  and  terminates  on  a  thin  tendon  which  fuses  with  that  of  the  gastrocnemius.^ 

Relations. — Superficially,  the  skin,  fascia,  and  peroneal  nerve;  deeply,  the 
lateral  extensor  and  deep  flexor. 

Blood-supply. — Posterior  tibial  artery. 

Nerrc-supply. — Ti])ial  nerve. 

3.  Superficial  digital  flexor  (M.  flexor  digitalis  pedis  superficialis)  (Figs.  292, 
296,  297).- — The  proximal  part  of  this  muscle  lies  between  and  under  cover  of 
the  two  heads  of  the  gastrocnemius.  It  consists  almost  entirely  of  a  strong  tendon, 
the  belly  being  very  little  developed. 

Origin. — The  supracondyloid  fossa  of  the  femur. 

Insertion. — (1)  The  tuber  calcis;  (2)  the  eminences  on  each  side  of  the  prox- 
imal extremity  of  the  second  phalanx,  and  the  distal  extremity  of  the  first  phalanx 
behind  the  collateral  ligaments  of  the  pastern  joint. 

Action. — To  flex  the  digit  and  extend  the  hock  joint.  On  account  of  the  ex- 
ceedingly small  amount  of  muscular  tissue  the  action  is  to  be  regarded  chiefly  as  a 
mechanical  effect  which  results  from  the  action  of  other  muscles  on  the  stifle  joint. 

Structure. — The  origin  is  by  means  of  a  strong  round  tendon  which  is  incom- 
pletely covered  with  fleshy  fibers  as  far  as  the  upper  third  of  the  leg.  Here  it  is 
intimately  attached  to  the  gastrocnemius,  especially  to  the  lateral  head.  At  the 
distal  third  of  the  tibia  it  winds  around  the  medial  surface  of  the  gastrocnemius 
tendon,  and  then  occupies  a  position  behind  the  latter.  At  the  point  of  the  hock 
it  witlens  out,  forming  a  sort  of  cap  over  the  tuber  calcis,  and  detaches  on  either  side 
a  strong  band  which  is  inserted  into  the  tuber  calcis  with  the  tarsal  tendons  of  the 
l)iceps  and  semitendinosus.  It  then  passes  downward  over  the  plantar  ligament, 
l)ecomes  narrower,  and  is  arranged  distally  as  in  the  thoracic  limb.  A  large  syno- 
vial bursa  (B.  calcanea  su])tcndinea)  lies  untler  the  t(»ndon  from  the  distal  fourth  of 
the  tibia  to  the  middle  of  the  tarsus.  A  subcutaneous  bursa  (B.  calcanea  su])cu- 
tanea)  is  sometimes  present  on  the  wide  part  of  the  tendon  at  the  point  of  the  hock. 

Relations. — Posteriorly,  the  gastrocnemius,  fascia,  and  skin;  anteriorly,  the 
femoro-patellar  capsule,  the  popliteus,  the  deep  flexor,  and  the  popliteal  vessels; 
medially,  the  tibial  nerve. 

Blood-supply. — Posterior  femoral  artery. 

Nerve-supply. — Til^ial  nerve. 

4.  Deep  digital  flexor  (M.  flexor  digitalis  pedis  profundus)  (Figs.  292,  298).^ — 
The  belly  of  this  nuiscle  lies  on  the  posterior  surface  of  the  tibia,  and  is  divisible 
into  three  heads,  which,  however,  finally  unite  on  a  common  tendon  of  insertion. 

Origin. — (1)  The  posterior  edge  of  the  lateral  condyle  of  the  tibia;  (2)  the 
border  of  the  lateral  condyle  of  the  tibia,  just  behind  the  facet  for  the  fibula;    (3) 

^The  soleus  is  sometimes  included  with  the  two  heads  of  the  gastrocnemius  under  the 
name  triceps  suric. 

2  This  is  also  known  as  the  flexor  pedis  perforatus  or  superficial  flexor  of  the  phalanges. 
'  This  muscle  is  also  commonly  termed  the  flexor  pedis  perforans. 


340 


FASCIA   AND    MUSCLES    OF   THE    HORSE 


the  middle  third  of  the  posterior  surface  and  the  upper  part  of  the  lateral  border  of 
the  tibia,  the  posterior  border  of  the  fibula,  and  the  interosseous  ligament. 

Insertion. — The  semilunar  crest  and  the  adjacent  surface  of  the  cartilage  of 
the  third  phalanx. 

Action. — To  flex  the  digit  and  to  extend  the  hock  joint. 

Structure. — (1)  The  medial  head  is  termed  the  long  digital  flexor  (M.  flexor 
digitalis  longus  s.  flexor  accessorius) ;  it  is  easily  isolated  (Figs.  298,  584).  It  has  a 
fusiform  belly,  which  crosses  the  leg  obliquely  and  lies  in  a  groove  formed  by  the 

Peroneus  tertius 


Long  digital 
extensor 


Superficial  -peroneal 


Tibialis  ayiterior 


Cutaneous  branch  of 
enous  nerve 


Saphenous  vessels 
'  nerve 


Lateral  head  of  gastroc- 
nemius 

Recurrent  tarsal  vein 


Flexor  digitalis  longus 
Vein 

Tibial  nerve 
Superficial  digital  flexor 

Medial  head  of  gastroc- 
nemius 


Fig.  297. — Cross-ssction  of  Left  Leg  of  Horse. 
The  section  is  cut  about  the  junction  of  the  proximal  and  middle  thirds  of  the  region.      1,  .\nterior  tibial  vessels; 
2,  deep  peroneal  nerve;    3,  fibula;    4,  posterior  tibial  vessels;    5,  recurrent  tibial  vessels.     A  cutaneous  branch  of  the 
saphenous  nerve  is  shown  medial  to  the  popliteus,  but  is  not  marked. 


other  heads  and  the  popliteus.  This  terminates  near  the  lower  third  of  the  tibia 
on  a  round  tendon  which  descends  in  a  canal  in  the  medial  ligament  of  the  hock, 
and  joins  the  common  tendon  about  a  third  of  the  way  down  the  metatarsus.  In 
its  course  over  the  medial  surface  of  the  hock  the  tendon  is  provided  with  a  S3mo- 
vial  sheath  which  extends  from  the  distal  fourth  of  the  tibia  to  the  junction  with 
the  principal  tendon.  (2)  The  superficial  head  is  the  tibialis  posterior  (M.  tibialis 
posterior);  it  is  only  partially  separable  from  the  deep  head.  It  has  a  flattened 
belly,  terminating  near  the  distal  third  of  the  tibia  on  a  flat  tendon  which  soon  fuses 


THE  MUSCLES  OF  THE  LEG  AND  FOOT 


341 


with  the  principal  tendon.  (3)  The  deep  head,  the  flexor  haUucis  (M.  flexor 
hallucis  longus),  is  much  the  largest.  It  lies  on  the  posterior  surface  of  the  tibia, 
from  the  popliteal  line  outward  and  downward.  The  belly  contains  much  tendi- 
nous tissue,  and  terminates  behind  the  distal  end  of  the  tibia  on  a  strong  round  ten- 


Shaft  of  femur - 

Medial  head  of  gastrocnemius - 

Medial  condyle  of  femur. 

Medial  femoro-tibial  ligament-.^ 
Medial  meniscus. 
Medial  condyle  of  tibia. 

PopliteuS- 
Flexor  digitalis  longus_ 


'Lateral  head  of  gastrocnemius 
'Superficial  digital  flexor 

-Lateral  condyle  of  femur 
Lateral  femoro-tibial  ligament 
Lateral  condyle  of  tibia 

■  Tibialis  posterior 
-Lateral  digital  extensor 


Flexor  hallucis 


Pouch  of  joint  capsule 


Deep  flexor  tendon . 
Tendon  of  flexor  digitalis  longus 


Tendon  of  gastrocnemius 


Superficial  flexor  tendon 


Fig.  298.— Muscles  of  Right  Leg  or  Horse,  Deep  Dissection;  Posterior  View. 

don  The  latter  receives  the  tendon  of  the  tibialis  posterior,  descends  in  the  tarsal 
groove,  bound  do^vn  by  the  strong  plantar  annular  ligament  (Ligamentum  lacmi- 
atum)  and  enveloped  in  a  synovial  sheath,  receives  the  tendon  of  the  medial  head 
below  the  hock,  and,  a  little  further  down,  the  so-called  check  ligament  (Caput 
tendinemn).     The  tendon  is  partly  cartilaginous  where  it  plays  over  the  hbular 


342 


FASCIA    AND    MUSCLES    OF   THE    HORSE 


tarsal  bone.  The  tarsal  sheath  (Vagina  tarsea)  begins  two  to  three  inches  (ea. 
5  to  7.5  cm.)  above  the  level  of  the  medial  malleolus,  and  extends  about  one-fourth 
of  the  way  dowTi  the  metatarsus.  The  check  ligament  resembles  that  of  the  fore 
limb,  except  that  it  is  longer  and  very  much  weaker;  it  may  be  absent.^  The  re- 
mainder of  the  tendon  is  arranged  like  that  of  the  thoracic  limb. 


Tarsal  sheath 


Tibial  tarsal  bone 


Medial  tendon  of 
tibialis  anterior 


Joint  canty 
Dorsal  ligament 
Central  tarsal  bone 
Third  tarsal  bone 

Mt.  in 


Superficial  flexor 
tendon- 


Joint  capsule  {tarso- 
metatarsal ligament) 

Fourth  tarsal 
Perforating  tarsal  vein 
Check  ligament 
Suspensory  ligament 


Fig.  299. — Sagittal  Section  of  Right  Hock  of  Horse. 
through  the  middle  of  the  groove  of  the  trochlea  of  the  tibial  tarsal  bone 


The  section 

of  cavity  of  hock  joint;   3,  thick  part  of  joint  capsule  over  which  deep  flexor  tendon  play 
tentaculum).     A  large  vein  crosses  the  upper  part  of  the  joint  capsule  (in  front  of  1). 


1,  2,  Proximal  ends 
4,  fibular  tarsal  bone  (sus- 


Relations.- — Anteriorly,  the  tibia  and  fibula,  the  popliteus,  lateral  extensor, 
tibialis  anterior,  and  the  tibial  vessels;  posteriorly,  the  gastrocnemius,  superficial 
flexor,  and  the  tibial  nerve;  laterally,  the  fascia,  skin,  and  the  soleus;  medially, 
the  fascia  and  skin. 


1  This  might  well  be  called  the  tarsal  (tendinous)  head  of  the  deep  flexor. 


MUSCLES    OF   THE   METATARSUS    AND    DIGIT  343 

Blood-supply. — Posterior  tibial  artery. 

Nerve-supply. — Tibial  nerve. 

5.  Popliteus  (Fig.  298). — This  thick,  triangular  muscle  lies  on  the  posterior 
surface  of  the  tibia  above  the  popliteal  line. 

Origin. — A  small  depression  on  the  lateral  epicondjde  of  the  femur,  close  to 
the  articular  surface  and  under  the  lateral  ligament. 

Insertion. — A  triangular  area  on  the  posterior  surface  of  the  tibia,  proximal  and 
medial  to  the  popliteal  line;  also  the  proximal  half  of  the  medial  border  and  a 
narrow  adjacent  part  of  the  medial  surface  of  the  tibia. 

Action. — To  flex  the  femoro-tibial  joint  and  to  rotate  the  leg  inward. 

Structure. — The  strong  tendon  of  origin  lies  at  first  under  the  lateral  ligament, 
and  curves  backward  and  inward  over  the  lateral  condyle  of  the  tibia  in  contact 
with  the  lateral  meniscus;  it  is  invested  by  a  reflection  of  the  synovial  membrane 
of  the  joint  (Fig.  584).  The  tendon  is  succeeded  by  a  thick  triangular  belly,  the 
fibers  of  which  are  directed  medially  in  the  proximal  part,  but  incline  downward 
below. 

Relations. — Superficially,  the  fascia  and  skin,  semitendinosus,  gastrocnemius, 
superficial  flexor;  deeply,  the  femoro-tibial  joint,  the  tibia,  the  popliteal  vessels 
and  their  divisions.  The  saphenous  vessels  and  nerve  lie  along  the  medial  border 
of  the  muscle,  separated  from  it,  however,  by  the  deep  fascia. 

Blood-supply. — Popliteal  and  posterior  tibial  arteries. 

Nerve-supply. — Tibial  nerve. 

MUSCLES  OF  THE  METATARSUS  AND  DIGIT 

Extensor  digitalis  brevis. — This  small  muscle  lies  in  the  angle  of  union  of  the 
tendons  of  the  long  and  lateral  extensors  of  the  digit.     (Fig.  293.) 

Origin. — The  lateral  tendon  of  the  peroneus  tertius,  the  middle  annular  liga- 
ment, and  the  lateral  ligament  of  the  hock. 

Insertion. — The  tendon  of  the  long  extensor. 

Action. — To  assist  the  long  extensor. 

Structure. — It  is  principally  fleshy,  having  a  superficial  origin  from  the  annular 
ligament,  and  a  deep  one  (by  a  thin  tendon)  from  the  lateral  tendon  of  the  peroneus 
tertius.     The  insertion  is  by  a  thin  tendon. 

Relations. — Superficially,  the  skin  and  fascia  and  the  tendons  of  the  long  and 
lateral  extensors;  deeply,  the  tarsal  joint  capsule,  the  great  metatarsal  artery,  and 
the  deep  peroneal  nerve. 

Blood-supply. — Great  metatarsal  artery. 

Nerve-supply. — Deep  peroneal  nerve. 

The  interossei  and  lumbricales  are  arranged  like  those  of  the  thoracic  limb, 
the  only  noticeable  difference  being  the  greater  development  of  the  lumbricales  in 
the  pelvic  limb. 


THE  MUSCLES  OF  THE  OX 
Muscles  of  the  Face 

The  cutaneus  is  much  more  developed  than  in  the  horse,  presenting  as  a  special 
feature  the  extensive  frontalis  muscle,  which  covers  the  frontal  and  nasal  regions. 

The  orbicularis  oris  does  not  form  a  complete  ring,  the  defect  being  in  the 
middle  of  the  upper  lip. 

The  levator  nasolabialis  is  extensive,  thin,  and  not  very  distinct  from  the 


344 


THE    MUSCLES    OF   THE    OX 


frontalis;  it  divides  into  two  layers,  between  which  the  levator  labii  superioris 
proprius  and  the  lateral  dilator  of  the  nostril  pass.  The  superficial  layer  ends  in 
the  nostril  and  upper  lip,  the  deep  layer  on  the  accessory  (lateral)  nasal  cartilages 
and  on  the  nasal  process  of  the  premaxilla. 

The  levator  labii  superioris  proprius  arises  on  and  before  the  facial  tuberosity 
and  terminates  by  several  tendons  in  the  muzzle.  It  passes  between  the  two  layers 
of  the  preceding  muscle,  blending  in  part  with  the  deep  layer. 

The  zygomaticus  is  much  stronger  than  in  the  horse.  It  arises  on  the  masse- 
teric fascia,  and  ends  chiefly  in  the  upper  lip. 


Fig.  300. — Muscles  of  Head  of  Ox;  Lateral  View. 
o,  Levator  labii  superioris  proprius;  b,  levator  nasolabialis;  c,  trapezius;  c',  brachiocephalicus;  d,  d',  sterno- 
cephalicus;  e,  omo-hyoideus;  /,  dilatator  naris  lateralis;  g,  zygomaticus;  y',  malaris;  h,  buccinator;  i,  depressor  labii 
inferioris;  k,  orbicularis  oris;  to,  masseter;  n,  parotido-auricularis ;  o',  zygomatico-auricularis  and  scutulo-auricularis 
superficialis  inferior;  o",  scutulo-auricularis  superfioialis  superior;  o'",  scutulo-auricularis  superficialis  accessorius; 
p,  p',  soutularis;  u,  frontalis;  w,  mylo-hyoideus;  1,  concha;  2,  3,  posterior  and  anterior  borders  of  1;  8,  scutiform 
cartilage;  9,  zygomatic  arch;  2S',  ramus  of  mandible;  37,  external  maxillary  vein;  3S,  jugular  vein;  39,  facial  vein; 
44,  parotid  gland;  50,  51',  mandibular  gland;  dotted  line  at  50  indicates  position  of  atlantal  lymph  gland,  and  the 
parotid  lymph  gland  lies  partly  under  parotid  gland,  just  in  front  of  44;  58,  medial  palpebral  ligament;  69,  laryngeal 
prominence.     (After  Ellenberger-Baum,  Anat.  fiir  Kunstler.) 


The  depressor  labii  superioris  arises  just  in  front  of  the  facial  tuberosity,  and 
divides  usually  into  two  branches,  which  terminate  in  a  number  of  tendons  that 
form  a  network  in  the  muzzle  and  upper  lip. 

The  incisivus  inferior  is  a  small,  rounded  muscle,  which  arises  on  the  body  of 
the  mandible  below  the  second  and  third  incisors,  and  ends  in  the  lower  lip,  blending 
with  the  orbicularis. 

The  depressor  labii  inferioris  is  thin,  and  does  not  extend  as  far  backward 
as  in  the  horse;  only  the  anterior  end  is  distinct  from  the  buccinator. 


MUSCLES    OF    THE    FACE 


345 


The  buccinator  shows  no  marked  variation,  but  its  superficial  layer  is  well 
developed. 

The  dilatator  naris  lateralis  arises  in  front  of  the  facial  tuberosity,  passes  for- 
ward between  the  branches  of  the  levator  nasolabialis,  and  terminates  in  the  lat- 
eral wing  of  the  nostril. 

The  dilatator  naris  apicalis  is  situated  in  the  muzzle  and  joins  its  fellow  at  a 
median  raphe.     It  arises  on  the  border  and  upper  surface  of  the  body  of  the  pre- 


FiG.  301. — Muscles  op  Head  of  Ox;  Dorsal  View. 
a,  a'.  Levator  labii  superioris  propriiis;  h,  levator  nasolabialis;  /,  dilatator  naris  lateralis;  g',  malaris;  o,  zygo- 
matico-auricularis  and  scutulo-auricularis  superficialis  inferior;  o",  scutulo-auricularis  superficialis  superior;  o'", 
scutulo-auricularis  superficialis  accessorius;  p,  scutularis;  u,  frontalis;  z,  orbicularis  oculi;  1,  concave  surface  of 
concha;  3,  2,  anterior  and  posterior  borders  of  concha;  8,  scutiform  cartilage;  34,  parietal  cartilage;  39,  facial  vein; 
49,  muzzle;  58,  medial  palpebral  ligament.     (/Vfter  EUenberger-Baum,  Anat.  filr  Kunstler.) 


maxilla,  the  fibers  passing  obliquely  upward  and  outward  to  the  medial  wing  of  the 
nostril. 

The  dorsal  part  of  the  lateralis  nasi  arises  from  the  alar  cartilage  of  the  nostril 
and  ends  in  the  medial  wing  of  the  nostril. 

The  ventral  part  of  the  lateralis  nasi  consists  of  two  layers  which  arise  on  the 
nasal  process  of  the  premaxilla  and  the  lateral  nasal  cartilage  and  end  in  the  lateral 
^\^ng  of  the  nostril. 

The  orbicularis  oculi  is  well  developed. 

The  corrugator  supercilii  is  not  present  as  a  separate  muscle,  its  place  and 
function  being  taken  by  the  frontalis. 

The  malaris  is  broad,  and  spreads  out  below  on  the  fascia  over  the  buccinator 
and  masseter;   it  is  divided  into  two  parts. 


346 


THE   MUSCLES    OF   THE    OX 


MANDIBULAR  MUSCLES 

The  masseter  is  not  so  large  as  in  the  horse;  a  considerable  part  of  it  arises 
on  the  facial  tuberosity  and  is  directed  obliquely  backward  and  downward,  so  that 
it  would  draw  the  lower  jaw  forward  as  well  as  upward. 

The  temporalis  conforms  to  the  temporal  fossa,  and  is  therefore  longer  and 
entirely  lateral  in  position. 

The  pterygoideus  medialis  arises  from  the  lateral  surface  of  the  perpendicular 
part  of  the  palatine  bone  and  from  the  pterygoid  process.     Since  the  origin  is  nearer 


Fig.  302. — Muscles  of  Head  of  Ox;  Ventral  View. 
d,  d',  Sterno-cephalicus;  e,  omo-hyoideus;  5,  zygomaticus;  A,  buccinator;   i,  depressor  labii  inferioris;  ^•,  orbicularis 
oris;   m,  masseter;    n,  parotido-auricularis;    o',  zygomatico-auricularis;    w,  mylo-hyoideus;    1,  concha,  convex  surface; 
2,  anterior  border  of  concha;   30',  angle  of  jaw;   39,  facial  vein;   44,  parotid  gland;   43,  lower  lip;   48,  angle  of  mouth; 
60,  50',  mandibular  gland;   69,  larynx;    X,  wing  of  atlas.     (After  EUenberger-Baum,  Anat.  fur  Kunstler.) 

the  median  plane  and  the  insertion  further  from  it  than  in  the  horse,  the  muscle  pro- 
duces more  marked  lateral  movement  of  the  mandible. 

The  pterygoideus  lateralis  is  flattened  transversely,  wide  and  thin  in  front, 
narrower  and  thicker  behind.  It  has  an  extensive  origin  in  the  pterj^go-palatine 
fossa,  where  it  is  partly  covered  by  the  pterygoideus  medialis. 

The  occipito-mandibularis  is  absent. 

The  digastricus  has  a  tendinous  origin  on  the  paramastoid  process  of  the 
occipital  bone;  its  bellies  are  short  and  thick.  The  intermediate  tendon  is  round  and 
thick;  it  does  not  perforate  the  stylo-hyoideus.  The  anterior  bellies  are  connected 
beneath  the  root  of  the  tongue  by  a  layer  of  transverse  muscle-fibers  termed  the 
transversus  mandibulse. 


MUSCLES    OF   THE    NECK — VENTRAL   GROUP — LATERAL    GROUP  347 


HYOm  MUSCLES 

The  mylo-hyoideus  is  thicker  and  more  extensive  than  in  the  horse. 

The  stylo-hyoideus  has  a  long,  slender  tendon  of  origin  which  is  attached  to  the 
muscular  angle  of  the  great  cornu  of  the  hyoid  bone.  The  insertion  is  fleshy  and 
is  not  perforated  by  the  digastricus. 

The  genio-hyoideus  is  much  more  developed  than  in  the  horse. 

The  kerato-hyoideus  has  an  additional  attachment  on  the  middle  cornu  of  the 
hyoid  bone. 

The  hyoideus  transversus  is  bifid. 

The  stemo-thyro-hyoideus  has  no  intermediate  tendon  and  is  thicker. 

The  omo-hyoideus  arises  as  a  thin  band  from  the  fascia  over  the  third  and 
fourth  cervical  vertel^rse.     It  blends  here  with  the  rectus  capitis  ventralis  major. 

The  occipito-hyoideus  is  thick.  Its  large  lateral  part  entirely  covers  the  para- 
mastoid  process  (from  which  it  arises)  and  is  inserted  into  the  muscular  angle  of 
the  great  cornu.  The  smaller  medial  part  arises  from  the  ventral  end  of  the  para- 
mastoid  process  and  ends  on  the  medial  face  of  the  great  cornu  below  the  dorsal 
end. 


Muscles  of  the  Neck 
a.  ventral  group 

The  cervical  cutaneus  is  absent. 

The  stemo-cephalicus  consists  of  two  muscles.  They  arise  from  the  manu- 
brium sterni  and  first  rib.  The  superficial  muscle  is  the  stemo-mandibularis ;  it 
is  inserted  on  the  anterior  border  of  the  masseter,  the  ramus  of  the  mandible,  and 
the  buccal  fascia.  The  deep  muscle  is  the  stemo-mastoideus ;  it  crosses  under  the 
preceding  and  ends  on  the  mastoid  processes,  the  mandible,  and,  in  common  with 
the  rectus  capitis  ventralis  major,  on  the  basilar  part  of  the  occipital  bone. 

There  are  two  scaleni.  The  scalenus  ventralis  (s.  primse  costse)  arises  from 
the  transverse  processes  of  the  third  to  the  seventh  cervical  vertebrae  and  ends  on 
the  first  rib.  It  is  traversed  by  the  roots  of  the  brachial  plexus,  which  divide  it 
into  bundles.  The  emerging  brachial  artery  separates  a  narrow  part  below  from 
the  main  mass.  The  scalenus  dorsalis  (s.  supracostalis)  arises  usually  on  the 
transverse  processes  of  the  fourth,  fifth,  and  sixth  cervical  vertebrae.  Its  wide 
posterior  part  lies  on  the  ventral  part  of  the  serratus  thoracis;  it  is  attached  to  the 
third  rib  and  to  the  serratus  thoracis. 

The  rectus  capitis  ventralis  major  arises  on  the  third  to  the  sixth  cervical 
transverse  processes,  and  blends  at  its  insertion  with  the  sterno-mastoideus  and 
the  cleido-mastoideus. 

The  rectus  capitis  ventralis  minor  is  larger  than  in  the  horse. 

The  rectus  capitis  lateralis  and  longus  colli  resemble  those  of  the  horse. 

The  intertransversales  are  large.  From  the  sixth  cervical  vertebra  forward 
they  form  a  muscular  mass  (M.  intertransversarius  longus)  which  is  inserted  into 
the  wing  of  the  atlas. 

B.  LATERAL  GROUP 
The  splenius  is  thin.  It  arises  directly  from  the  first  three  or  four  thoracic 
spines,  and  ends  by  a  thin  tendon  on  the  occipital  bone,  the  wing  of  the  atlas, 
and  the  transverse  process  of  the  axis,  blending  with  the  brachiocephalicus,  longis- 
simus  capitis,  and  omo-transversarius.  The  remaining  muscles  present  no  very 
marked  differential  features. 


348 


THE    MUSCLES    OF   THE    OX 


MUSCLES  OF  THE  THORAX — ABDOMINAL  MUSCLES  349' 


Muscles  of  the  Thorax 

The  levatores  costarum  number  ten  or  eleven  pairs. 

The  external  intercostal  muscles  are  thick;  they  terminate  at  the  costo- 
chondral  junctions.  The  internal  intercostals  are  specially  thick  in  relation  to  the 
cartilages  of  the  sternal  ribs;  here  there  exist  bundles  (comparable  to  the  levatores 
costarum)  which  are  attached  in  front  to  the  sternum,  behind  to  a  costal  cartilage. 
The  interosseous  part  thins  toward  the  upper  end  of  the  spaces. 

The  diaphragm  presents  several  important  differential  features.  Its  slope  is 
much  steeper  and  its  width  is  greater  than  in  the  horse.  The  upper  limit  of  the 
costal  attachment  extends  almost  in  a  straight  line  from  the  last  rib  about  a  hand- 
breadth  above  its  middle  to  the  junction  of  the  eighth  rib  with  its  cartilage,  and 
along  the  latter  to  the  sternum.  The  midline  slopes  from  the  twelfth  thoracic 
vertebra  obliquely  as  far  as  the  foramen  vense  cavae,  beyond  which  it  is  almost 
vertical.  The  right  crus  divides  into  two  branches,  which  circumscribe  the  hiatus 
oesophageus,  unite  below,  and  then  spread  out  in  the  tendinous  center.  The  left 
crus  is  small.  The  hiatus  a?sophageus  is  situated  about  four  to  five  inches  (10  to 
12  cm.)  below  the  eighth  thoracic  vertebra,  a  little  to  the  left  of  the  median  plane. 
The  foramen  vense  cavae  is  a  little  more  ventral  and  almost  in  the  median  plane. ^ 

In  the  sheep  the  costal  attachment  differs  from  that  of  the  ox.  The  upper 
limit  of  the  attachment  extends  in  a  gentle  curve  (convex  ventrally)  from  the 
last  rib  about  the  junction  of  its  middle  and  ventral  thirds  to  the  ventral  end  of 
the  ninth  rib. 

MUSCLES  OF  THE  BACK  AND  LOINS 

The  serratus  dorsalis  anterior  is  very  thin.  It  is  inserted  on  the  fifth  to  the 
eighth  ribs  when  fully  developed,  but  it  may  be  reduced  to  two  or  three  digitations 
or  may  be  absent.  The  serratus  dorsalis  posterior  is  inserted  on  the  last  three  or 
four  ribs. 

The  longissimus  costarum  has  a  distinct  lumbar  portion  which  is  attached  to 
the  lumbar  transverse  processes  and  the  tuber  coxae. 

The  longissimus  dorsi  resembles  that  of  the  horse,  but  it  is  more  fleshy  anter- 
iorly, and  the  spinalis  dorsi  is  clearly  distinguishable  from  the  common  mass.  In 
the  lumbar  region  the  tendons  meet  across  the  summits  of  the  spines. 

Intertransversales  are  present  in  the  back,  and  interspinales  in  the  back  and 
loins. 

Muscles  of  the  Tail 

These  resemble  in  general  those  of  the  horse;  the  coccygeus  is,  however,  much 
more  developed. 

Abdominal  Muscles 

The  obliquus  abdominis  extemus  is  somewhat  thinner  and  has  a  less  extensive 
origin,  which  begins  at  the  lower  part  of  the  fifth  intercostal  space  and  ends  on 
the  last  rib  above  its  middle.  The  direction  of  the  fibers  in  the  flank  is  horizontal, 
and  they  do  not  reach  to  the  tuber  coxae,  nor  as  high  as  the  lumbar  transverse  proc- 
esses.    (In  this  region  the  abdominal  tunic  has  a  strong  attachment  to  the  point 

1  The  sternal  part  is  clearly  separable  from  the  costal  part.  The  costal  attachment  is  much 
higher  posteriorly  than  in  the  horse,  thus  diminishing  the  capacity  of  the  thorax  in  comparison 
with  that  animal.  The  last  digitation  is  thus  some  seven  or  eight  inches  (ca.  18  to  20  cm.)  above  the 
corresponding  digitation  of  the  transversus  abdominis.  There  are  small  intermediate  digitations- 
at  the  last  two  intercostal  spaces. 


350 


THE   MUSCLES    OF   THE    OX 


of  the  hip  and  the  lumbo-dorsal  fascia.)  The  aponeurosis  is  intimately  united  with 
the  abdominal  tunic,  and  does  not  detach  a  femoral  lamina. 

The  obliquus  abdominis  intemus  is  more  developed  and  has  an  additional 
origin  from  the  lumbo-dorsal  fascia.  The  aponeurosis  blends  with  that  of  the 
external  oblique  near  the  linea  alba,  and  detaches  a  layer  which  assists  in  the  for- 
mation of  the  internal  sheath  of  the  rectus. 

The  rectus  abdominis  arises  on  the  lateral  border  of  the  sternum  as  far  for- 
ward as  the  third  costal  cartilage.  The  two  muscles  are  separated,  except  near 
the  pelvis,  by  an  interval  varying  from  two  to  four  inches  (ca.  5  to  10  cm.),  so  that 
this  part  of  the  abdominal  wall  is  entirely  fibrous.  (The  umbilicus  is  in  a  trans- 
verse plane  through  the  third  lumbar  vertebra.)  There  are  five  tendinous  inscrip- 
tions, at  the  third  of  which  is  a  foramen  for  the  passage  of  the  subcutaneous  ab- 
dominal vein.     The  prepubic  tendon  has,  in  addition  to  lateral  branches  inserted 


Fig.  304. — Deeper  Muscles  of  Neck,  Shoulder,  and  Thorax  op  Ox. 
c',  Cleido-oceipitalis  muscle;  d,  sterno-cephalicus;  /,  /',  long  and  lateral  heads  of  triceps;  g,  superficial  pectoral 
muscle;  h,  h',  deep  pectoral  muscle;  i,  i',  serratus  ventralis;  k,  latissimus  dorsi;  I,  obliquus  abdominis  externus;  »', 
biceps  brachii;  w,  splenius;  x,  rhomboideus;  y,  longissimus  capitis  et  atlantis;  z,  supraspinatus ;  z',  infraspinatus; 
z",  tendon  of  insertion  of  z';  1',  cartilage  of  scapula;  2,  tuberosity  of  spine  of  scapula;  S,  acromion;  5,  lateral  tuberosity 
of  humerus;  6,  deltoid  tuberosity;  S,  olecranon;  £6,  transverse  processes  of  cervical  vertebrae;  27,  posterior  auricular 
muscles:    X,  wing  of  atlas.     (After  EUenberger-Baum,  Anat.  fiir  Kunstler.) 

into  the  ilio-pectineal  eminences,  a  strong  attachment  to  the  median  common  ten- 
don of  the  adductors  of  the  thigh,  so  that  the  abdominal  wall  is  strongly  retracted 
and  almost  vertical  at  its  junction  with  the  pubis. 

The  transversus  abdominis  presents  no  striking  differential  features.     The 
transversalis  fascia  is  strong  and  distinct  except  over  the  diaphragm. 


Muscles  of  the  Thoracic  Limb 
i.  muscles  of  the  shoulder  girdle 

The  trapezius  is  much  thicker  and  broader  than  in  the  horse,  and  is  undivided. 
It  arises  on  the  ligamentum  nuchae  and  supraspinous  ligament,  from  the  atlas  to 
the  twelfth  thoracic  vertebra. 


MUSCLES    OF   THE    SHOULDER — MUSCLES    OF   THE   ARM  351 

The  omo-transversarius  arises  on  the  wing  of  the  atlas,  and,  inconstantly, 
the  transverse  process  of  the  axis,  and  is  inserted  into  the  scapular  spine  and  fascia. 

The  rhomboideus  is  clearly  divided  into  cervical  and  thoracic  parts,  the  latter 
extending  further  than  in  the  horse. 

The  latissimus  dorsi  has  a  broad  tendon  of  origin,  which  blends  with  the 
lumbo-dorsal  fascia;  it  is  also  attached  to  the  eleventh  and  twelfth  ribs  and  the 
fascia  over  the  external  intercostal  and  oblique  abdominal  muscles.  The  anterior 
fibers  end  on  the  tendon  of  the  teres  major,  the  middle  part  on  an  aponeurosis  on 
the  medial  surface  of  the  caput  longum,  and  the  posterior  part  on  a  tendon  which  is 
common  to  this  muscle  and  the  deep  pectoral. 

The  brachiocephalicus  has  two  distinct  parts.  The  dorsal  division,  the  cleido- 
occipitalis,  arises  on  the  occipital  bone  and  the  ligamentum  nuchas.  The  ventral 
part,  the  cleido-mastoideus,  is  smaller  and  arises  by  a  round  tendon  on  the  mastoid 
process  and  the  rectus  capitis  ventralis  major,  and  by  a  thin  tendon  on  the  mandible. 

The  superficial  pectoral  muscle  is  thinner  than  in  the  horse  and  its  two  parts 
are  not  so  clearly  separal^le. 

The  deep  pectoral  muscle  arises  as  far  forward  as  the  second  rib  and  is  un- 
divided. However,  the  scapular  portion  may  be  considered  to  be  represented  by  a 
small  branch  which  arises  from  the  anterior  part  of  the  sternum  and  the  first  rib 
and  passes  upward  to  end  on  the  deep  face  of  the  brachiocephalicus  in  front  of  the 
shoulder  joint. ^  A  tendon  detached  from  the  dorsal  edge  blends  with  the  latissimus 
dorsi  and  coraco-brachialis. 

The  serratus  ventralis  is  clearly  divided  into  cervical  and  thoracic  parts. 
The  former  is  large  and  extends  from  the  third  (or  second)  cervical  vertebra  to 
the  fifth  rib,  being  overlapped  behind  by  the  thoracic  part.  It  is  inserted  on  a 
large  triangular  area  on  the  antero-superior  part  of  the  costal  surface  of  the  scapula. 
The  thoracic  part  is  relatively  thin  and  is  covered  by  a  very  strong  aponeurosis; 
it  is  attached  to  the  fourth  to  the  ninth  ribs  by  six  digitations,  and  is  inserted  by  a 
flat  tendon  which  insinuates  itself  between  the  middle  and  posterior  parts  of  the 
subscapularis  to  end  on  a  rough  line — equivalent  to  the  posterior  serratus  area  of 
the  horse — and  also  on  the  cartilage  of  the  scapula  in  continuity  with  this  line. 


n.  MUSCLES  OF  THE  SHOULDER 

The  deltoid  is  clearly  divided  into  acromial  and  scapular  parts.  The  former 
(Pars  acromialis)  arises  on  the  acromion,  the  latter  (Pars  scapularis)  on  the  posterior 
border  of  the  scapula  and  the  aponeurotic  covering  of  the  infraspinatus.  The 
scapular  part  of  the  muscle  is  largely  inserted  into  the  fascia  covering  the  triceps. 

The  supraspinatus,  infraspinatus,  and  teres  minor  do  not  differ  materially 
from  those  of  the  horse. 

The  subscapularis  consists  of  three  parts  with  a  common  tendon  of  insertion. 

The  teres  major  and  coraco-brachialis  resemble  those  of  the  horse. 

The  capsularis  is  absent. 

m.  MUSCLES  OF  THE  ARM 

The  biceps  is  smaller  and  less  tendinous,  and  is  situated  more  medially  than 
in  the  horse.  The  tendon  of  origin  is  flat,  and  is  bound  down  in  the  intertuberal  or 
bicipital  groove  by  a  fibrous  band.  The  tendon  to  the  extensor  carpi  radialis  is 
less  distinct  than  in  the  horse.  (In  the  sheep  the  tendon  of  origin  is  round  and  is 
invested  by  the  synovial  membrane  of  the  shoulder  joint.  The  tendon  of  inser- 
tion bifurcates;  one  branch  ends  on  the  tuberosity  of  the  radius,  the  other  on  the 
ulna.) 

1  According  to  Meckel  and  Lesbre,  this  is  the  homologue  of  the  subclavius  of  man. 


352 


THE   MUSCLES    OF   THE    OX 


The  medial  head  of  the  triceps  is  more  developed  than  in  the  horse,  and  ex- 
tends up  to  the  neck  of  the  humerus. 

The  tensor  fasciae  antibrachii  is  a  slender  muscle  which  lies  along  the  posterior 

border  of  the  triceps  and  is  not 
';j  connected  with  the  latissimus 

I  dorsi. 

IV.  MUSCLES  OF  THE  FOREARM 

AND  MANUS 

A.  Extensor  Division 
The  extensor  carpi  radialis 

is  like  that  of  the  horse.  There 
is  sometimes  a  small  muscle 
lying  along  its  medial  border, 
which  may  represent  the  exten- 
sores  pollicis. 

There  are  three  digital  ex- 
tensors: 1.  The  common  digital 
extensor  (M.  extensor  digitalis 
communis)  arises  by  two  heads 
from  the  lateral  epicondyle  of 
the  humerus  and  from  the  ulna. 
The  heads  fuse  about  the  middle 
of  the  forearm,  and  terminate 
soon  on  a  tendon  which  passes 
over  the  carpus  and  metacarpus, 
gradually  inclining  forward.  At 
the  fetlock  joint  it  divides  into 
two  branches,  each  of  which  is 
inserted  into  the  extensor  pro- 
cess of  the  corresponding  third 
phalanx.  2.  The  medial  digital 
extensor  (M.  extensor  digiti  ter- 
tii  proprius)  arises  on  the  lateral 
epicondyle,  and  is  inserted  by 
two  branches  into  the  second 
and  third  phalanges  of  the  me- 
dial digit.  The  tendon  receives 
two  reinforcing  slips  from  the 
suspensory  ligament.  3.  The 
lateral  digital  extensor  (M. 
extensor  digitalis  lateralis  s. 
digiti  quarti  proprius)  is  stronger 
than  that  of  the  horse;  it  arises 
from  the  lateral  ligament  of  the 
elbow  joint,  the  lateral  tuber- 
osity of  the  radius,  and  the 
ulna.  The  tendon  terminates 
like  that  of  the  preceding 
muscle.  "^ 
the  horse. 

^  It  may  be  remarked  that,  in  addition  to  the  extension  action,  the  common  extensor  approxi- 
mates the  digits,  while  the  others  tend  to  abduct  them. 


Fig.  305. — Muscles  of  Antibr.\- 

CHIUM    AND     MaNUS    OF    Ox; 

Lateral  View. 

o.  Extensor  carpi  radialis;  b, 
extensor  digiti  tertii;  c,  extensor 
digitalis  communis;  d,  extensor 
digiti  quarti;  e,  ulnaris  lateralis; 
/,  extensor  carpi  obliquus;  /',  ul- 
nar head  of  flexor  carpi  ulnaris;  g, 
brachialis;  h,  interosseus  mediug 
or  suspensory  ligament;  i,  flexor 
tendons;  i',  branch  of  h,  to  super- 
ficial flexor  tendon;  8,  olecranon; 
11,  accessory  carpal  bone;  12', 
metacarpal  tuberosity.  (After 
EUenberger-Baum,  Anat.  fur 
Kiinstler.) 


Fig.  306. — Muscles  of  Anti- 

BRACHIUM    AND   MaNUS    OF 

Ox;  Medial  View. 

a.  Extensor  carpi  radialis; 
b,  tendon  of  extensor  digiti  ter- 
tii; /,  tendon  of  extensor  carpi 
obliquus;  s,  brachiaUs;  A,  inter- 
osseus medius  or  suspensory 
ligament;  i,  flexor  tendons;  i', 
branch  of  h;  k,  flexor  carpi  radi- 
alis; /,  flexor  carpi  ulnaris;  m, 
superficial  digital  flexor.  (After 
Ellenberger-Baum,  Anat.  fur 
Kiinstler.) 


The  extensor  carpi  obliquus  resembles  that  of 


MUSCLES  OF  THE  FOREARM  AND  MANUS 


353 


The  extensor  tendons  are  bound  down  at  the  carpus  by  an  annular  ligament, 
and  are  furnished  with  synovial  sheaths  (Figs,  307,  308). 

B.  Flexor  Division 

The  three  flexors  of  the  carpus  are  like  those  of  the  horse,  but  the  long  tendon 
of  the  lateral  flexor  ends  on  the  large  metacarpal  bone,  not  on  the  small  one.  The 
tendon  of  the  medial  flexor  naturally  ends  on  the  medial  part  of  the  large  meta- 
carpal bone. 

The  superficial  digital  flexor  is  somewhat  blended  at  its  origin  with  the  middle 
flexor  of  the  carpus.     It  divides  into  two  bellies,  superficial  and  deep,  terminating 


Fig.  307. — Right  Cahpus  or  Ox  with  Burs^  and  Fig.  308. — Right  Carpus  of  Ox  with  Burs^  and 

Synovial  Sheaths  Injected;  Lateral  View.  Synovial  Sheaths  Injected;  Medial  View. 

1,  Extensor  carpi  radialis,  with  synovial  sheath  (/')  and  bursa  (/");  ^.  extensor  carpi  obliquus,  with  synovial 
sheath  (2')  and  bursa  {2");  3,  extensor  digiti  tertii  proprius;  4<  extensor  digitalis  communis;  S',  common  synovial 
sheath  of  3  and  4;  5,  extensor  digiti  quarti  proprius,  with  synovial  sheath  (5') ;  6,  6',  ulnaris  lateralis,  with  bursa 
(6");  7,  flexor  carpi  radialis,  with  synovial  sheath;  S,  deep  digital  flexor,  with  synovial  sheath  {8');  9,  flexor  carpi 
ulnaris;  10,  superficial  digital  flexor,  with  synovial  sheath,  10';  a,  radius;  6,  carpus;  c,  metacarpus;  d,  cut  edge  of 
annular  ligament.     (After  Schmidtchen.) 


on  tendons  at  the  distal  part  of  the  forearm.  The  superficial  tendon  passes  over 
the  posterior  annular  ligament  (Lig.  carpi  transversum),  perforates  the  metacarpal 
fascia,  and  joins  the  deep  tendon  about  the  middle  of  the  metacarpus.  The  deep 
belly  is  connected  with  the  deep  flexor  by  a  strong  fibrous  band.  Its  tendon  passes 
under  the  annular  ligament  of  the  carpus  in  a  groove  on  the  deep  flexor,  from  which 
it  receives  fibers.  The  conjoined  tendon  soon  bifurcates,  each  branch  receiving  a 
reinforcing  band  from  the  suspensory  ligament,  and  forming  near  the  fetlock  a 
ring  for  the  corresponding  branch  of  the  deep  flexor  tendon.  Passing  under  two 
digital  annular  ligaments,  they  are  inserted  into  the  volar  surfaces  of  the  second 
phalanges  by  three  slips, 
23 


354  THE   MUSCLES    OF   THE    OX 

The  deep  digital  flexor  has  the  same  heads  as  in  the  horse,  the  humeral  head, 
as  before  mentioned,  being  connected  ^\^tll  the  deep  part  of  the  superficial  flexor. 
The  tendon,  which  is  not  reinforced  by  a  check  ligament  as  in  the  horse,  divides 
near  the  distal  end  of  the  metacarpus  into  two  branches  which  are  inserted  into  the 
volar  surfaces  of  the  third  phalanges. 

The  synovial  sheaths  at  the  carpus  present  the  following  special  features: 
One  is  found  in  connection  with  the  tendon  of  the  superficial  part  of  the  superficial 
flexor  of  the  digits.  There  is  a  common  sheath  for  the  tendons  of  the  common  ex- 
tensor and  the  medial  extensor. 

Bursse  may  occur  under  the  tendons  of  the  proper  extensors  of  the  digits  at  the 
fetlock;  they  are  constant  only  in  old  animals  (Schmidtchen).  The  branches  of 
the  tendon  of  the  common  extensor  are  provided  with  synovial  sheaths  from  their 
origin  to  the  middle  of  the  second  phalanx.  There  are  two  digital  synovial  sheaths 
for  the  flexor  tendons;  they  may  communicate  at  their  upper  part,  and  they  ex- 
tend from  the  distal  third  of  the  metacarpus  nearly  to  the  distal  sesamoids.  Bursse 
occur  between  the  latter  and  the  branches  of  the  deep  flexor  tendon. 

A  feeble  pronator  teres  is  present  on  the  medial  surface  of  the  elbow  along  the 
medial  collateral  ligament. 

The  fascia  on  the  volar  face  of  the  metacarpus  and  digit  is  very  thick.  It  is 
continuous  above  with  the  ligamentum  carpi  transversum,  and  is  attached  on  either 
side  to  the  metacarpal  bone.  At  the  fetlock  it  forms  the  fibrous  basis  for  the  small 
claws,  and  below  this  it  detaches  two  strong  bands  which  diverge  to  be  inserted  into 
the  second  and  third  phalanges,  blending  with  the  collateral  ligaments. 

The  lumbricales  are  absent,  unless  we  regard  as  such  the  muscular  bundles 
which  arise  on  the  deep  flexor  and  are  inserted  into  the  superficial  flexor  tendon  at 
the  carpus. 

The  interosseus  medius,  or  suspensory  ligament,  is  somewhat  more  muscular 
than  in  the  horse;  indeed,  in  the  young  subject  it  may  be  almost  entirely  fleshy. 
Its  arrangement  is  somewhat  complex.  Single  at  its  origin,  it  detaches  about  the 
middle  of  the  metacarpus  a  band  which  joins  the  tendon  of  the  superficial  flexor 
and  concurs  near  the  fetlock  in  the  formation  of  the  ring  for  the  deep  flexor  tendon.  ^ 
A  little  lower  down  it  divides  into  three  and  then  into  five  branches.  The  abaxial 
branches  (two  pairs)  are  attached  to  the  corresponding  sesamoids  and  tendons  of 
the  proper  extensors,  while  the  middle  branch  passes  through  the  sulcus  at  the  distal 
end  of  the  metacarpus  and  bifurcates,  each  division  fusing  with  the  tendon  of  the 
corresponding  proper  extensor. 


The  Muscles  of  the  Pelvic  Limb 
l  the  sublumbar  muscles 

The  psoas  minor  begins  at  the  disc  between  the  twelfth  and  thirteenth  thoracic 
vertebrae. 

The  psoas  major  has  a  fleshy  origin  on  the  posterior  border  of  the  last  rib,  and 
a  thin  tendon  attached  to  the  twelfth  rib;  it  is  relatively  narrower  than  in  the  horse 
and  does  not  entirely  cover  the  quadratus  lumborum. 

The  iliacus  begins  under  the  body  of  the  sixth  lumbar  vertebra,  and  is  more 
closely  united  with  the  psoas  major  than  in  the  horse. 

The  quadratus  lumborum  extends  as  far  forward  as  the  body  of  the  tenth  or 
eleventh  thoracic  vertebra.  It  is  wider  than  in  the  horse  and  extends  beyond  the 
lateral  border  of  the  psoas  major. 

'  Lesbre  regards  this  band  as  the  subcarpal  check  ligament,  which  on  this  basis  is  blended 
with  the  suspensory  hgament  above. 


LATERAL    MUSCLES    OF   THE   HIP    AND    THIGH 


355 


II.  LATERAL  MUSCLES  OF  THE  HIP  AND  THIGH  (Figs.  303,  309) 

The  tensor  fasciae  latae  is  large,  and  the  fleshy  part  extends  further  down  than 
in  the  horse. 

Tlie  gluteus  superficialis  is  not  present  as  such;    apparently  its  anterior  part 
has  fused  with  the  tensor  fascise  latae  and  its  posterior  part  with  the  biceps  femoris. 

The  gluteus  medius  is  small,  the  lumbar  part  being  insignificant  and  extend- 
ing forward  only  to  the  fourth  lumbar  vertebra.     Its  deep  portion  (gluteus  ac- 
cessorius)  is  easily  separable,  and  its  strong  tendon  is  inserted  into  the  femur  below 
the  trochanter  major,  under  cover  of  the  upper 
part  of  the  vastus  lateralis. 

The  gluteus  profundus  is  thin,  but  exten- 
sive, arising  as  far  forward  as  the  tuber  coxae, 
and  from  the  lower  part  of  the  sacro-sciatic  liga- 
ment. The  fibers  converge  on  a  broad,  strong 
tendon  which  passes  under  the  upper  part  of 
the  vastus  lateralis,  and  is  inserted  into  a  tu- 
bercle a  short  distance  below  the  great  tro- 
chanter. 

The  biceps  femoris  is  very  wide  at  its 
upper  part,  having  apparently  absorbed  the 
posterior  part  of  the  superficial  gluteus.  It 
arises  from  the  sacral  spines,  sacro-sciatic  liga- 
ment, and  tuber  ischii.  It  is  divided  by  a 
fi])ro-elastic  septum  in  the  thigh  into  two  por- 
tions, which  end  in  front  and  below  on  a  wide 
aponeurosis;  the  latter  is  attached  to  the  patella 
and  its  lateral  ligament  and  blends  with  the  fas- 
cia cruris  and  fascia  lata.  There  is  no  femoral 
attachment.  A  large  bursa  occurs  between  the 
muscle  and  the  great  trochanter  in  the  adult. 
The  part  of  the  tendon  which  fuses  with  the 
lateral  patellar  ligament  presents  a  fibro-cartil- 
aginous  thickening,  and  an  extensive  bursa  is 
interposed  between  it  and  the  lateral  condyle 
of  the  femur. 


A  layer  derived  from  the  fascia  lata  is  intimately 
adherent  to  the  deep  face  of  the  muscle,  and  cases  occur 
in  which  this  fascials  ruptured  by  the  trochanter  major, 
thus  fixing  the  muscle  behind  the  trochanter. 


Fig.  309. — Gluteal,  Femor.\l,  and  Crural 
Regions  of  Ox,  After  Removal  op 
Superficial  Muscles. 
p.  Gluteus  medius;  r,  semitendinosus;  u, 
coccygeus;  28,  vastus  lateralis;  28',  rectus  fe- 
moris; 29,  semimembranosus;  30,  gastrocnemi- 
us; 31,  sacro-sciatic  ligament:  16,  tuber  coxae; 
17,  tuber  ischii;  19,  trochanter  major;  20,  patel- 
la; 21',  lateral  condyle  of  tibia.  (After  Ellen- 
berger-Baum,  Anat.  fiir  Kiinstler.) 


The  semitendinosus  and  semimembrano- 
sus arise  on  the  ischium  only.     The  latter  is  very  large  and  has  a  branch  attached 
to  the  medial  condyle  of  the  tibia. 


III.  ANTERIOR  MUSCLES  OF  THE  THIGH 

The  quadriceps  femoris  reseml)les  that  of  the  horse;  but  the  vasti  (and  es- 
pecially the  medial  one)  are  not  so  thick,  and  the  vastus  intermedins  is  more  clearly 
separable,  and  consists  of  two  parts.  Bursae  occur  under  the  insertions  of  the 
medial  and  lateral  vasti,  and  often  under  the  end  of  the  rectus  in  the  adult. 

The  articularis  genu  is  a  small  muscle  which  lies  under  the  distal  part  of  the 
vastus  intermedins,  and  is  partly  inserted  on  the  sui^rapatellar  cul-de-sac  of  the 
synovial  membrane  of  the  stifle  joint. 

The  capsularis  is  absent. 


356  THE   MUSCLES    OF  THE    OX 

IV.  MEDIAL  MUSCLES  OF  THE  THIGH 

The  sartorius  arises  by  two  heads,  one  from  the  tendon  of  the  psoas  minor 
and  the  ihac  fascia,  the  other  from  the  shaft  of  the  ihum.  The  femoral  vessels 
pass  between  them. 

The  gracilis  is  more  extensively  united  with  its  fellow  at  its  origin  than  in  the 
horse. 

The  pectineus  is  large,  and  arises  by  a  single  head  from  the  pubis  and  prepubic 
tendon.  It  divides  into  two  branches,  one  of  which  is  inserted  as  in  the  horse, 
while  the  other  extends  to  the  medial  epicondyle  of  the  femur. 

The  adductor  resembles  that  of  the  horse,  but  does  not  reach  to  the  medial 
condyle  of  the  femur. 

The  quadratus  femoris  and  obturator  extemus  resemble  those  of  the  horse. 

The  obturator  intemus  has  no  iliac  head,  and  its  tendon  passes  through  the 
obturator  foramen. 

The  gemellus  is  large;  some  of  its  fibers  of  origin  join  the  obturator  internus 
through  the  lesser  sciatic  foramen. 

V.  MUSCLES  OF  THE  LEG  AND  FOOT 

A.    DORSO-LATERAL    GrOUP 

There  are  four  digital  extensors,  two  of  which  are  fused  with  each  other  and 
the  peroneus  tertius  in  the  upper  third  of  the  leg. 

1.  The  long  digital  extensor  (M.  extensor  digitalis  longus)  arises  in  common 
with  the  peroneus  tertius  and  the  medial  extensor  in  the  extensor  fossa  of  the  femur, 
and  separates  from  the  other  muscles  near  the  middle  of  the  leg.  At  the  distal 
end  of  the  tibia  it  terminates  on  a  tendon  which  passes  down  over  the  hock  (bound 
down  by  two  annular  ligaments)  and  ends  like  that  of  the  thoracic  limb. 

2.  The  medial  digital  extensor  (M.  extensor  digiti  tertii  proprius)  arises  in  com- 
mon with  the  preceding  muscle  and  the  peroneus  tertius,  and  is  covered  by  them 
to  the  distal  third  of  the  tibia.  Its  tendon  passes  under  the  annular  ligaments 
between  those  of  its  cogeners  and  ends  on  the  second  phalanx  of  the  medial  digit. 

3.  The  lateral  digital  extensor  (M.  extensor  digitahs  lateralis  s.  digiti  quarti 
proprius)^  arises  on  the  lateral  ligament  of  the  stifle  joint  and  the  lateral  condyle  of 
the  tibia.  Its  tendon  passes  over  the  lateral  surface  of  the  hock,  and  terminates 
on  the  dorsal  surface  of  the  second  phalanx  of  the  lateral  digit. 

The  reinforcing  bands  from  the  suspensory  ligament  are  arranged  as  in  the 
forelimb. 

4.  The  short  digital  extensor  (M.  extensor  digitalis  brevis)  resembles  that  of 
the  horse ;  it  is  inserted  on  the  tendon  of  the  long  extensor. 

The  peroneus  longus  (not  present  in  the  horse)  is  situated  in  front  of  the  lateral 
extensor.  It  arises  on  the  lateral  condyle  of  the  tibia  and  the  fibrous  band  which 
represents  the  shaft  of  the  fibula.  Its  tendon  passes  downward  and  backward 
over  the  lateral  surface  of  the  hock,  crosses  over  that  of  the  lateral  extensor  and 
under  the  lateral  ligament,  and  ends  on  the  first  tarsal  bone  and  the  proximal  end 
of  the  large  metatarsal  bone.  It  is  enveloped  by  a  synovial  sheath.  It  would  ap- 
parently act  as  an  inward  rotator  at  the  hock  joint. 

The  peroneus  tertius  is  a  well-developed  muscle  which  arises  on  the  common 
tendon  with  the  long  and  medial  extensors.  It  has  a  large,  fusiform  belly,  which 
is  superficially  situated  on  the  front  of  the  leg.  Close  to  the  tarsus  it  ends  on  a 
flat  tendon,  which  is  perforated  by  that  of  the  tibialis  anterior,  and  ends  on  the 
proximal  end  of  the  large  metatarsal  and  second  and  third  (fused)  tarsal  bones. 

^  Lesbre  regards  this  muscle  as  the  homologue  of  the  peroneus  brevis  of  man  and  other 
pentadactyls. 


MUSCLES  OF  THE  LEG  AND  FOOT 


357 


The  tibialis  anterior  is  smaller,  and  arises  by  two  heads.  The  larger  head 
springs  from  the  lateral  surface  of  the  tuberosity  and  crest  of  the  tibia;  the  lateral, 
smaller  one  (M.  extensor  hallucis  longus),  arises  from  the  upper  part  of  the  lateral 


Fig.  310. — Muscles  of  Left  Leg  and  Foot  of  Ox; 
Antekiok  View. 
o,  Peroneus  tertius;  a',  tibialis  anterior;  6,  long 
digital  extensor;  b',  extensor  digiti  tertii;  c,  peroneus 
longus;  d,  extensor  digiti  quarti;  i,  i,  annular  liga- 
ments; k,  lateral  ligament  of  hock  joint;  I,  branch  of 
suspensory  ligament;  20,  patella;  SI',  lateral  condyle 
of  tibia;  28,  tuberosity  of  tibia.  (After  Ellenberger- 
Baum,  Anat.  fiir  Kunstler.) 


Fig.  311. — Muscles  of  Left  Leg  and  Foot  of  Ox; 
Later.^l  View. 
a,  Peroneus  tertius;  a',  tibialis  anterior;  6,  long 
digital  extensor;  b' ,  tendon  of  6;  c,  peroneus  longus; 
d,  extensor  digiti  quarti;  e,  deep  digital  flexor;  e',  ten- 
don of  e;  e",  branch  of  interosseus  medius  or  suspen- 
sory ligament;  /,  gastrocnemius  (the  soleus  lies  just  in 
front  of  /) ;  /',  tendon  of  superficial  digital  flexor;  h,  in- 
terosseus medius  or  suspensory  ligament;  i,  i,  annular 
ligaments;  20,  patella;  21',  lateral  condyle  of  tibia; 
28,  tuberosity  of  tibia.  (After  Ellenberger-Baum,  Anat. 
fur  Kunstler.) 


l)order  of  the  tibia  and  the  fibrous  band  which  replaces  the  shaft  of  the  fibula.  The 
tendon  perforates  that  of  the  preceding  muscle,  passes  to  the  medial  face  of  the 
hock,  and  ends  on  the  metatarsal  and  second  and  third  tarsal  bones. 


358 


THE    MUSCLES    OF   THE    OX 


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THE   MUSCLES    OF   THE   PIG — MUSCLES   OF  THE    FACE  359 

B.  Plantar  Group 

The  gastrocnemius  and  soleus  resemble  those  of  the  horse. 

The  superficial  flexor  is  more  fleshy  than  in  the  horse.  Its  tendon  termi- 
nates as  in  the  forelimb. 

The  deep  flexor  in  general  resembles  that  of  the  horse,  but  the  tibialis  poste- 
rior (superficial  head)  is  distinct  and  is  larger  than  in  the  horse.  The  flexor  digitahs 
longus  (medial  head)  is  also  larger,  while  the  flexor  hallucis  longus  (deep  head)  is 
smaller.     The  common  tendon  ends  like  that  on  the  forelimb. 

The  synovial  sheaths  and  bursse  of  the  muscles  of  the  leg  and  foot  are  shown  in 
Figs.  312-315. 


THE  MUSCLES  OF  THE  PIG 
Muscles  of  the  Face 

The  facial  cutaneus  is  pale,  thin,  and  difficult  to  separate  from  the  skin. 

The  orbicularis  oris  is  little  developed. 

The  levator  nasolabialis  is  thin  and  pale,  and  is  undivided. 

The  levator  labii  superioris  proprius  may  well  be  termed  the  levator  rostri. 
It  has  a  large  pennate  belly,  which  arises  in  the  preorbital  fossa.  The  tendon  ends 
on  the  anterior  part  of  the  os  rostri.    A  muscular  slip  connects  it  with  the  premaxilla. 

The  zygomaticus  arises  on  the  fascia  over  the  masseter  and  ends  at  the  angle 
of  the  mouth. 

The  depressor  labii  inferioris  separates  from  the  buccinator  only  near  the 
angle  of  the  mouth;    it  ends  by  a  number  of  tendinous  branches  in  the  lower  lip. 

The  dilatator  naris  lateralis  is  well  developed.  It  arises  under  the  levator 
rostri  and  ends  by  a  tendinous  network  around  the  nostril. 

The  transversus  nasi  is  represented  only  by  a  few  fibers  which  cross  over  the 
OS  rostri. 

The  depressor  rostri  arises  on  the  facial  crest.  It  has  a  long  strong  tendon 
which  passes  below  the  nostril  and  turns  dorso-medially  to  meet  the  tendon  of  the 
opposite  side  and  end  in  the  skin  of  the  snout.  It  depresses  the  snout  and  con- 
tracts the  nostril. 

The  malaris  is  absent,  and  the  other  palpebral  muscles  present  no  special 
features. 

MANDIBULAR  MUSCLES 

The  masseter  is  thick. 

The  pterygoideus  medialis  is  wide  at  its  insertion. 

The  pterygoideus  lateralis  is  large  and  distinct. 

The  digastricus  has  only  one  belly  and  has  no  connection  with  the  hyoid  bone. 
It  ends  on  the  medial  and  lower  surface  of  the  mandible,  in  front  of  the  groove  for 
the  facial  vessels. 

HYOID  MUSCLES 

The  mylo-hyoideus  consists  of  two  more  or  less  distinct  layers,  the  superficial 
one  being  the  transversus  mandibulse. 

The  occipito-hyoideus  and  kerato-hyoideus  are  small. 

The  hyoideus  transversus  is  absent. 

The  omo-hyoideus  and  stemo-hyoideus  are  referred  to  in  connection  with  the 
muscles  of  the  neck. 


THE   MUSCLES    OF   THE   PIG 


Muscles  of  the  Neck 


The  cutaneus  consists  of  two  layers  which  cross  each  other  obhquely.  The 
fibers  of  the  superficial  layer  are  directed  nearly  vertically,  those  of  the  deep  layer 
toward  the  face,  on  which  they  are  continued  to  form  the  facial  portion. 

The  brachiocephalicus  is  described  with  the  other  muscles  of  the  shoulder  girdle. 

The  stemo-cephalicus  arises  on  the  sternum  and  is  inserted  by  a  long  round 
tendon  on  the  mastoid  process. 

The  thyroid  part  of  the  stemo-thyro-hyoideus  has  a  peculiar  arrangement. 
It  arises  (separately  from  the  opposite  muscle)  on  the  manubrium  sterni.  About 
the  middle  of  the  neck  it  has  an  oblique  tendinous  intersection,  beyond  which  it 


Fig.  316. — Superficial  Muscles  or  Pig,  After  Removal  op  M.  Cut.vneus. 
a.  Levator  nasolabialis;  6,  levator  labii  superioris  proprius;  h',  fleshy  slip  of  h  which  comes  from  premaxilla;  c, 
dilatator  naris  lateralis;  d,  depressor  rostri;  e,  orbicularis  oris;  /,  depressor  labii  inferioris;  s,  zygomaticus;  /i,  masseter; 
i  i',  i",  brachiocephalicus  (cleido-occipi talis,  cleido-mastoideus,  pars  clavicularis  deltoidei) ;  k,  stemo-cephalicus;  I, 
sterno-hyoideus;  m,  omo-transversarius;  n,  n',  trapezius;  o,  anterior  deep  pectoral;  p,  latissimus  dorsi;  g,  lumbo- 
dorsal  fascia ;  r,  obliquus  abdominis  externus;  r',  aponeurosis  of  r;  s,  serratus  dorsalis;  /,  serratus  ventralis;  m,  posterior 
deep  pectoral;  v,  supraspinatus;  w,  w',  deltoideus;  x,  long  head  of  triceps;  y,  lateral  head  of  triceps;  z,  tensor  fasciae 
antibrachii;  1,  brachialis;  S,  extensor  carpi  radialis;  3,  extensor  digiti  quarti;  4,  extensor  digiti  quinti;  5,  extensor 
carpi  ulnaris;  6,  ulnar  head  of  deep  flexor;  7,  gluteus  medius;  8,  tensor  fasciae  latse;  9,  10,  10',  biceps  femoris;  11, 
semitendinosus;  13,  semimembranosus;  13,  caudal  muscles;  H,  panniculus  adiposus  in  section.  (After  EUenberger, 
in  Leisering's  Atlas.) 


divides  into  two  branches:  one  of  these  is  inserted  in  the  usual  fashion,  the  other 
ends  on  the  laryngeal  prominence.     The  hyoid  part  is  well  developed. 

The  omo-hyoideus  is  thin.  It  arises  as  in  the  horse,  but  has  no  connection 
with  the  brachiocephalicus  nor  with  the  opposite  muscle. 

The  omo-transversarius  arises  on  the  first  or  second  cervical  vertebra  (under 
cover  of  the  brachiocephalicus),  and  is  inserted  into  the  lower  part  of  the  scapular 
spine. 

There  are  two  scaleni.  The  scalenus  ventralis  (s.  primse  costse)  resembles 
that  of  the  ox,  is  attached  to  the  last  four  cervical  vertebrse,  and  is  perforated  by 
the  nerves  of  the  brachial  plexus.  The  scalenus  dorsalis  (s.  supracostalis)  arises 
on  the  transverse  processes  of  the  third  to  the  sixth  cervical  vertebra,  and  ends 
on  the  third  rib. 

The  ventral  muscles  of  the  head  present  no  special  features. 

The  longus  colli  is  separated  from  the  opposite  muscle,  so  that  part  of  the 
bodies  of  the  cervical  vertebrae  is  exposed  as  in  man. 


MUSCLES    OF   THE   THORAX — MUSCLES    OF   THE   BACK   AND    LOINS  361 

The  intertransversales  resemble  those  of  the  ox. 

The  splenius  is  thick  and  extensive.  It  ends  in  three  parts  on  the  occipital, 
the  temporal,  and  the  wing  of  the  atlas  (inconstant) . 

The  longissimus  capitis  et  atlantis  is  small,  and  its  atlantal  part  is  blended 
with  the  longissimus  cervicis. 

The  complexus  is  large,  and  is  clearly  divided  into  two  parts:  the  dorsal  part 
(Biventer  cervicis)  is  marked  by  several  tendinous  intersections;  the  ventral  part 
is  the  complexus  proper. 

The  obliquus  capitis  posterior  is  relatively  thin. 

The  recti  capitis  dorsales  are  thick  and  more  or  less  fused. 

Muscles  of  the  Thorax 

The  levatores  costarum  and  rectus  thoracis  present  no  special  features. 

The  external  intercostal  muscles  are  absent  under  the  serratus  dorsalis  and  the 
digitations  of  the  external  oblique. 

The  internal  intercostals  are  thick  between  the  cartilages  of  the  sternal  ribs. 

The  retractor  costae  and  the  transversus  thoracis  resemble  those  of  the  horse ; 
the  latter  extends  back  to  the  eighth  cartilage  and  fuses  with  the  transversus  ab- 
dominis. 

The  diaphragm  has  seven  costal  digitations  on  each  side,  the  posterior  ones 
being  attached  to  the  ribs  at  some  distance  (ca.  one-third  to  one-fourth  of  rib- 
length)  from  the  costo-chondral  junction.^  The  line  of  attachment  reaches  the 
latter  at  the  tenth  rib,  and  passes  along  the  eighth  cartilage  to  the  xiphoid  process. 
The  tendinous  center  is  more  rounded  than  in  the  horse.  The  crura  are  well 
developed.  The  right  crus  is  very  large,  and  is  perforated  by  the  extensive  slit- 
like hiatus  oesophageus,  which  is  median  in  position,  and  lies  about  two  and  one- 
half  to  three  inches  (ca.  6  to  8  cm.)  below  the  twelfth  thoracic  vertebra.  The  hiatus 
aorticus  is  between  the  crura. 


Abdominal  Muscles 

The  abdominal  tunic  is  little  developed. 

The  obliquus  abdominis  extemus  has  an  extensive  fleshy  portion  and  a  cor- 
respondingly narrow  aponeurosis;  the  latter  does  not  detach  a  femoral  lamina, 
but  is  reflected  in  toto  to  form  the  inguinal  ligament. 

The  obliquus  abdominis  intemus  resembles  that  of  the  ox;  a  small  fusiform 
muscle,  which  crosses  the  inguinal  canal  obliquely  and  is  attached  on  the  abdominal 
surface  of  the  inguinal  ligament,  is  apparently  a  detached  slip  of  the  internal 
oblique. 

The  rectus  abdominis  is  extensive  and  thick.  It  has  seven  to  ten  inscriptions. 
Its  tendon  of  insertion  fuses  largely  with  the  common  tendon  of  the  graciles,  and 
does  not  give  off  an  accessory  band  to  the  head  of  the  femur. 

The  fleshy  part  of  the  transversus  abdominis  is  well  developed.  It  blends 
in  front  with  the  transversus  thoracis. 

The  cremaster  extemus  is  present  in  the  female  as  well  as  in  the  male. 


Muscles  of  the  Back  and  Loins 

The  serratus  dorsalis  anterior  is  inserted  into  the  fifth  to  the  eighth  ribs 
inclusive,  the  serratus  dorsalis  posterior  into  the  last  four  or  five  ribs.  There  are 
usually  no  digitations  attached  to  the  ninth  and  tenth  ribs. 

1  It  is  interesting  to  note  that  the  diaphragm  has  no  attachment  to  the  fifteenth  rib,  which  is 
often  present  and  well  developed. 


362  THE   MUSCLES    OF   THE    PIG 

The  longissimus  costarum  extends  to  the  wing  of  the  atlas. 

The  spinalis  et  semispinalis  can  be  separated  without  much  difficulty  from 
the  longissimus  dorsi,  the  division  from  the  common  mass  of  the  loins  beginning 
about  the  first  lumbar  vertebra. 

The  multifidus  resembles  that  of  the  horse. 

Interspinales  are  present,  as  well  as  distinct  intertransversales  of  the  Imck 
and  loins. 


Muscles  of  the  Tail 

The  dorsal  and  lateral  sacro-coccygei  arise  as  far  forward  as  the  last  lumbar 
vertebra.  Gurlt  explains  the  twist  of  the  tail  as  being  due  to  the  spiral  arrangement 
of  the  insertions  of  the  tendons. 


Muscles  of  the  Thoracic  Limb 
muscles  of  the  shoulder  girdle 

The  trapezius  is  very  wide,  its  line  of  origin  extending  from  the  occipital  bone 
to  the  tenth  thoracic  vertebra.  There  is  no  clear  division  between  its  two  parts, 
which  are  both  inserted  into  the  scapular  spine. 

The  omo-transversarius  resembles  that  of  the  ox. 

The  rhomboideus  consists  of  three  parts.  The  cervical  part  (Rhomboideus 
cervicalis)  is  greatly  developed,  its  origin  extending  from  the  second  cervical  to  the 
sixth  thoracic  vertebra.  The  cephalic  part  (Rhomboideus  capitis)  arises  with  the 
splenius  on  the  occipital  bone,  and  is  inserted  with  the  cervical  part.  The  thoracic 
part  (Rhomboideus  thoracalis)  extends  as  far  back  as  the  ninth  or  tenth  thoracic 
vertebra. 

The  latissimus  dorsi  is  attached  to  the  four  ribs  preceding  the  last.  It  is 
inserted  into  the  medial  tuberosity  of  the  humerus. 

The  brachiocephalicus  divides  into  two  parts,  the  cleido-mastoideus  and 
cleido-occipitalis,  which  arise  on  the  mastoid  process  and  nuchal  crest  respectively, 
and  unite  at  the  fibrous  vestige  of  the  clavicle. 

The  anterior  superficial  pectoral  muscle  is  thin.  The  posterior  superficial  pec- 
toral muscle  is  divided  into  two  parts,  one  of  which  ends  on  the  humerus,  the  other 
on  the  fascia  of  the  forearm.  The  anterior  deep  pectoral  muscle  resembles  that  of 
the  horse,  but  its  origin  does  not  extend  behind  the  first  two  chondro-sternal  joints. 
The  posterior  deep  pectoral  muscle  is  very  long. 

The  cervical  part  of  the  serratus  ventralis  is  greatly  developed,  its  origin  ex- 
tending from  the  wing  of  the  atlas  to  the  upper  part  of  the  fifth  rib,  and  passing 
under  the  thoracic  part;   the  latter  resembles  that  of  the  ox. 

MUSCLES  OF  THE  SHOULDER 

The  deltoid  is  undivided;  it  arises  from  the  aponeurosis  covering  the  infra- 
spinatus, and  it  ends  largely  on  the  deltoid  ridge,  but  partly  on  the  fascia  of  the  arm. 

The  supraspinatus  is  large ;  it  has  a  small  attachment  to  the  medial  tuberosity 
and  ends  chiefly  on  the  lateral  tuberosity  of  the  humerus.  There  is  a  bursa  between 
the  tendon  and  the  anterior  part  of  the  lateral  tuberosity. 

The  infraspinatus  is  wide ;  it  is  inserted  into  a  depression  below  the  posterior 
division  of  the  lateral  tuberosity.  There  is  a  bursa  between  the  tendon  and  the 
tuberosity. 

The  teres  minor  is  large  and  rounded;  it  ends  on  a  tubercle  between  the 
lateral  and  deltoid  tuberosities  of  the  humerus. 


MUSCLES  OF  THE  ARM MUSCLES  OF  THE  FOREARM  AND  MANUS      363 

The  subscapularis  is  very  broad  at  its  upper  part.  It  extends  posteriorly  up 
to  the  dorsal  angle  of  the  scapula,  but  anteriorly  only  about  two-thirds  of  the  way 
up  to  the  vertebral  border. 

The  teres  major  presents  nothing  remarkable. 

The  coraco-brachialis  is  short,  wide,  and  undivided.  There  is  a  bursa  between 
its  broad  tendon  of  origin  and  the  tendon  of  insertion  of  the  subscapularis. 

The  capsularis  is  variable;  it  may  be  half  an  inch  wide  or  very  small  and 
is  frequently  absent. 

MUSCLES  OF  THE  ARM 

The  biceps  brachii  is  fusiform  and  not  greatly  developed.  Its  tendon  of  origin 
is  rounded  and  the  underlying  bursa  communicates  so  freely  with  the  shoulder  joint 
as  to  be  regarded  as  an  evagination  of  the  synovial  membrane  of  the  latter.  A  small 
band  binds  down  the  tendon  in  the  bicipital  groove.  The  tendon  of  insertion  di- 
vides into  two  branches.  One  branch  passes  back  across  the  medial  surface  of  the 
neck  of  the  radius  to  end  on  the  proximal  extremity  of  the  ulna.  The  other  is 
attached  to  the  radius  under  cover  of  the  brachialis  tendon. 

The  brachialis  is  large.  Its  tendon  of  insertion  divides.  The  small  branch  is 
inserted  into  the  medial  border  of  the  radius  distal  to  the  biceps  tendon.  The  large 
branch  crosses  the  medial  border  of  the  radius  and  ends  on  the  medial  surface  of  the 
ulna  distal  to  the  biceps  tendon;   there  is  a  bursa  under  this  tendon. 

The  tensor  fasciae  antibrachii  resembles  that  of  the  horse,  but  is  very  wide  and 
bends  around  the  posterior  border  of  the  triceps. 

The  long  head  of  the  triceps  is  inserted  into  the  summit  of  the  olecranon  by  two 
tendons,  between  which  there  is  a  synovial  bursa.  The  lateral  head  is  inserted  into 
a  crest  on  the  lateral  surface  of  the  olecranon  by  a  thin  tendon,  under  which  there 
is  a  bursa.  The  medial  head  arises  from  the  proximal  third  of  the  medial  surface 
of  the  humerus;  it  is  inserted  into  the  medial  surface  of  the  olecranon  by  a  short 
tendon,  under  which  there  is  a  small  bursa. 

There  are  two  anconei. 


MUSCLES  OF  THE  FOREARM  AND  MANUS 

The  extensor  carpi  radialis  is  a  strong,  fleshy  muscle,  the  tendon  of  which  is 
inserted  into  the  proximal  end  of  the  third  metacarpal  bone.  It  may  be  divided 
into  two  parts  (M.  extensor  carpi  radialis  longus,  brevis). 

The  extensor  carpi  obUquus  is  well  developed ;  it  arises  from  the  distal  two-thirds 
of  the  lateral  surface  of  the  radius  and  ulna  and  ends  on  the  second  metacarpal  bone. 

The  common  digital  extensor  (M.  extensor  digitalis  communis)  arises  on  the 
lateral  epicondyle  of  the  humerus  and  the  lateral  ligament  of  the  elbow,  and  divides 
into  three  parts.  The  tendon  of  the  medial  head  ends  chiefly  on  the  third  digit, 
but  commonly  sends  a  small  branch  to  the  second.  The  tendon  of  the  middle  head 
divides  lower  down  into  two  branches  for  the  third  and  fourth  (chief)  digits;  above 
this  bifurcation  it  detaches  a  small  branch  to  the  second  digit,  which  usually  unites 
with  the  tendon  of  the  extensor  digiti  secundi.  The  tendon  of  the  deep  head  di- 
vides into  two  l)ranches,  the  medial  one  joining  the  tendon  of  the  middle  head,  while 
the  lateral  one  ends  on  the  fifth  digit. 

The  extensor  of  the  second  digit  (M.  extensor  digiti  secundi  proprius)  is  covered 
by  the  preceding  muscle,  with  which  it  is  partially  fused.  It  arises  on  the  ulna. 
Its  delicate  tendon  usually  unites  with  the  tendon  of  the  middle  head  of  the  common 
extensor  which  goes  to  the  second  digit. 

The  lateral  digital  extensor  (M.  extensor  digitalis  lateralis)  consists  of  two  dis- 
tinct parts:  (1)  The  large  dorsal  muscle  is  the  extensor  digiti  quarti  proprius;  it 
has  a  long  tendon  which  ends  on  the  fourth  digit,  and  often  sends  a  slip  to  the  fifth 


364 


THE   MUSCLES    OF   THE    PIG 


digit.     (2)  The  small  volar  muscle  is  the  extensor  digiti  quinti  proprius;   it  ends  by 
a  long  tendon  on  the  lateral  aspect  of  the  fifth  digit. 

The  supinator,  when  present,  is  a  pale,  thin  muscular  slip  which  arises  on  the 

lateral  border  of  the  radius  just  above  the  interosseous  space,  extends  medially  and 

downward  across  the  dorsal  surface  of  the  bone  to  its  medial 

border,  where  it  blends  with  the  radial  head  of  the  deep 

flexor. 

The  pronator  teres  is  a  delicate,  fusiform  muscle  which 
lies  along  the  medial  surface  of  the  elbow  and  proximal  part 
of  the  forearm.  It  arises  from  the  medial  epicondyle  and 
collateral  ligament  of  the  elbow  and  is  inserted  by  a  thin 
tendon  to  the  medial  border  of  the  radius  about  its  middle. 
The  flexor  carpi  radialis  is  well  developed.  It  arises 
on  the  medial  epicondyle  of  the  humerus,  and  is  inserted 
into  the  third  metacarpal  bone. 

The  flexor  carpi  ulnaris  is  narrow  and  has  no  ulnar 
head.  It  runs  obliquely  down  the  back  of  the  forearm  in 
the  furrow  between  the  superficial  and  deep  flexors  of  the 
digit.  It  arises  from  the  medial  epicondyle  of  the  humerus 
and  ends  on  the  accessory  carpal  bone. 

The  ulnaris  lateralis  (M.  extensor  carpi  ulnaris)  is 
covered  by  a  tendinous  band,  which  is  a  thickened  part 
of  the  fascia  of  the  forearm  and  extends  from  the  lateral 
epicondyle  to  the  accessory  carpal  bone  and  lateral  aspect 
of  the  carpus.  The  belly  of  the  muscle  is  round :  its  ten- 
don of  insertion  perforates  this  band  in  the  distal  part  of 
the  forearm  and  ends  on  the  proximal  end  of  the  fifth 
metacarpal  bone. 

The  superficial  digital  flexor  arises  from  the  medial 
epicondyle  of  the  humerus  and  consists  of  two  parts.  The 
tendon  of  the  superficial  head  passes  down  behind  the  pos- 
terior annular  ligament  of  the  carpus  (bound  down  by  a 
special  annular  ligament),  forms  a  ring  at  the  fetlock  for  a 
tendon  of  the  deep  flexor,  and  ends  by  two  branches  on  the 
second  phalanx  of  the  fourth  digit.  It  receives  a  small 
band  from  the  accessory  carpal  bone.  The  tendon  of  the 
deep  head,  after  detaching  a  strong  branch  to  the  tendon 
of  the  deep  flexor,  passes  down  with  the  latter  (for  which 
it  forms  a  ring),  and  ends  on  the  third  digit. 

The  deep  digital  flexor  has  three  heads — humeral, 
ulnar,  and  radial.  The  humeral  head  is  very  large  and 
forms  the  greater  part  of  the  contour  of  the  volar  face  of 
the  forearm.  It  consists  of  two  parts — a  large  superficial 
part,  and  a  much  smaller  deep  part  which  arises  with  the 
superficial  flexor.  Each  ends  at  the  distal  part  of  the  fore- 
arm on  a  short  tendon.  These  unite  and  receive  the  ten- 
dons of  the  radial  and  ulnar  heads  and  a  branch  from  the 
superficial  flexor  tendon.  The  ulnar  head  has  a  short, 
thick,  prismatic  belly  which  arises  from  the  medial  surface  of  the  proximal 
part  of  the  ulna.  Its  long,  thin  tendon  passes  down  on  the  humeral  head  and 
joins  the  tendon  of  the  latter  at  the  level  of  the  accessory  carpal  bone.  The 
radial  head  is  small.  It  arises  from  the  upper  part  of  the  medial  border  of  the 
radius  and  from  the  deep  fascia,  and  its  tendon  joins  that  of  the  humeral  head  at 
the  distal  end  of  the  forearm.     The  common  tendon  divides  into  four  branches, 


Fig.  317. — Muscles  of  Anti- 

BRACHIUM        AND        MaNUS 

OF    Pig;    Dorso- lateral 

View. 

a,  a',  Extensor  carpi 
radialis;  b,  extensor  carpi 
obliquus  (s.  abductor  pollicis 
longus) ;  c,  d,  e,  common  dig- 
ital extensor;  c',  c",  tendons  of 
insertion  of  c;  d',  d",  tendons 
of  d;  e',  e",  tendons  of  e;  f, 
tendon  of  extensor  digiti  se- 
cundi;  ff,  extensor  digiti  quarti ; 
h,  extensor  digiti  quinti;  /(', 
tendon  of  h;  i,  tendinous,  and 
k,  fieshy,  part  of  ulnaris  later- 
alis; k',  tendon  of  k;  I,  ulnar 
head  of  deep  digital  flexor;  m, 
superficial  digital  flexor;  n, 
brachialis.  (After  EUenberger, 
in  Leisering's  Atlas.) 


MUSCLES    OF   THE    HIP   AND    THIGH  365 

the  larger  central  pair  ending  on  the  third  phalanges  of  the  principal  digits,  the 
smaller  abaxial  pair  on  the  accessory  digits.  The  latter  are  bound  down  by  a 
peculiar  spiral  band.  There  is  no  subcarpal  check  ligament.  The  carpal  sheath 
envelops  the  tendon  of  the  deep  flexor  and  that  of  the  deep  part  of  the  superficial 
flexor.  It  extends  from  the  distal  third  of  the  forearm  to  the  distal  third  of  the 
metacarpus.  At  the  proximal  part  of  the  metacarpus  a  small  muscular  band  ex- 
tends from  the  deep  flexor  tendon  to  the  tendon  of  the  deep  part  of  the  superficial 
flexor.  Another  muscular  bundle  passes  from  the  deep  flexor  tendon  to  the  second 
digit. 

The  liimbricales  are  represented  by  bundles  which  extend  from  the  deep  flexor 
tendon  to  the  tendon  of  the  deep  head  of  the  superficial  flexor. 

The  third  and  fourth  interossei  are  present.  Each  sends  two  slips  to  the  cor- 
responding sesamoid  bones  and  extensor  tendon. 

There  are  flexors,  adductors,  and  abductors  of  the  second  and  fifth  digits. 


Muscles  of  the  Pelvic  Limb 
sublumbar  muscles 

The  psoas  minor  is  intimately  united  with  the  psoas  major  in  front,  and  has  a 
long  small  tendon  which  ends  on  the  psoas  tubercle.     It  has  no  thoracic  part. 

The  psoas  major  is  large  and  rounded.     It  begins  at  the  last  rib. 

The  quadratus  lumborum  is  well  developed,  and  extends  to  the  last  three  or 
four  thoracic  vertebrae. 


MUSCLES  OF  THE  HIP  AND  THIGH 

The  tensor  fasciae  latae  is  broad,  and  its  fleshy  part  reaches  almost  to  the  patella. 

The  gluteus  superficialis  has  a  sacral  head  only;  it  blends  with  the  biceps 
femoris. 

The  gluteus  medius  has  a  small  lumbar  part  which  does  not  extend  so  far 
forward  as  in  the  horse.  The  deep  part  (Gluteus  accessorius)  is  pretty  clearly 
marked. 

The  gluteus  profundus  is  extensive,  reaching  nearly  to  the  tuber  coxae. 

The  biceps  femoris  has  a  narrow  origin  from  the  sacro-sciatic  ligament  and 
tuber  ischii.     It  ends  below  like  that  of  the  ox. 

The  semitendinosus  has  two  heads  like  that  of  the  horse. 

The  semimembranosus  arises  from  the  tuber  ischii  and  has  two  insertions  as 
in  the  ox. 

The  sartorius  has  two  heads  of  origin,  between  which  the  external  iliac  vessels 
are  situated.  The  medial  one  arises  from  the  tendon  of  the  psoas  minor,  the  lat- 
eral one  from  the  iliac  fascia. 

The  graciles  are  united  at  their  origin  even  more  than  in  the  ox. 

The  pectineus  is  well  developed  and  is  flattened  from  before  backward. 

The  adductor  shows  no  division  and  is  partially  fused  with  the  gracilis.  It 
ends  on  the  femur  just  above  the  origin  of  the  gastrocnemius. 

The  quadratus  femoris  is  large. 

The  obturator  extemus  resembles  that  of  the  horse. 

The  obturator  intemus  is  extensive  and  strong;  its  tendon  emerges  through 
the  obturator  foramen. 

The  gemellus  is  fused  in  part  ^vith  the  obturator  intemus. 

The  quadriceps  femoris  is  more  clearly  divided  than  in  the  horse,  and  its 
action  is  transmitted  by  a  single  patellar  ligament. 

The  capsularis  is  absent. 


366 


THE   MUSCLES    OF   THE    PIG 


MUSCLES  OF  THE  LEG  AND  FOOT 
The  peroneus  tertius  is  a  well-developed  muscle  which  is  in  great  part  super- 
ficially situated  on  the  front  of  the  leg.     It  covers  the  long  digital  extensor,  with 
which  it  is  united  except  in  the  distal  third  of  the  leg.     It  arises  from  the  extensor 
fossa  of  the  femur  by  a  common  tendon  with  that  muscle, 
a  synovial  pouch  from  the  femoro-til)ial  joint  extending 
down  under  the  origin. 

This  sac  is  an  inch  and  a  half  or  more  (ca.  3  to  4  cm.)  in  length 
in  large  subjects  and  extends  around  the  hiteral  edge  of  the  tendon 
to  its  superficial  face,  so  as  to  make  a  partial  sheath  and  underlie 
the  origin  of  the  peroneus  longus  also. 

The  muscle  is  continued  at  the  distal  end  of  the  leg 
by  a  strong  tendon  which  passes  over  the  flexion  surface  of 
the  hock,  between  the  tendon  of  the  long  extensor  (lateral) 
and  that  of  the  tibialis  anterior  (medial),  all  three  being 
bound  down  by  a  strong  annular  ligament  which  extends 
across  from  one  malleolus  to  the  other.  It  ends  by  two 
or  more  branches  on  the  first  and  second  tarsal  and  third 
metatarsal  bones.  Not  rarely  there  is  a  thin  tendon  in- 
serted into  the  fourth  metatarsal  bone.  The  tendon  usu- 
ally receives  a  small  branch  from  that  of  the  tibialis  an- 
terior at  the  annular  ligament. 

The  tibialis  anterior  is  smaller  than  the  preceding.  It 
arises  from  the  lateral  surface  of  the  tuberosity  and  lateral 
condyle  of  the  tibia.  At  the  distal  end  of  the  leg  the  ten- 
don passes  under  the  annular  ligament  mentioned  above 
(where  it  detaches  a  small  branch  to  the  peroneus  tertius), 
and  ends  on  the  second  tarsal  and  the  proximal  end  of  the 
second  metatarsal  bone.  The  terminal  part  passes  under  a 
superficial  layer  of  the  medial  ligament  of  the  hock,  and  is 
provided  with  a  bursa. 

The  peroneus  longus  descends  in  front  of  the  fibula  and 
the  lateral  extensor.  It  arises  chiefly  from  the  lateral  con- 
dyle of  the  tibia.  The  tendon  of  insertion  descends  through 
a  groove  on  the  lateral  malleolus,  crosses  over  the  tendons 
of  the  lateral  extensor,  then  under  the  lateral  ligament  to 
the  plantar  surface  of  the  hock,  to  end  on  the  first  tarsal 
bone.  There  is  a  bursa  under  the  tendon  where  it  lies  in 
the  groove  on  the  fourth  tarsal.  The  muscle  is  a  flexor  of 
the  hock. 

The  long  digital  extensor  arises  in  common  with  the 
peroneus  tertius,  by  which  it  is  largely  covered  and  with 
which  it  is  united  to  the  distal  third  of  the  leg.  Three  ten- 
dons appear  at  the  proximal  annular  ligament  and  extend 
downward  and  a  little  medially  over  the  flexion  surface  of 
the  hock.  Here  they  are  bound  down  by  an  annular  liga- 
ment given  off  from  the  tendon  of  the  peroneus  tertius  and  attached  laterally 
to  the  distal  end  of  the  fibular  tarsal  bone.  The  tendons  gradually  diverge  as 
they  descend  the  metatarsus.  The  central  one  divides  at  the  distal  end  of  the 
metatarsus  into  two  branches  which  end  on  the  third  phalanges  of  the  chief 
(third  and  fourth)  digits.  This  tendon  is  joined  before  bifurcating  by  the  tendon 
of  the  extensor  digitalis  brevis.  The  medial  tendon  ends  on  the  second  and  third 
phalanges  of  the  medial  chief  (third)  digit.     It  receives  a  branch  from  the  inter- 


FiG.  318. — Muscles  of  Leg 
.\ND  Foot  of  Pig;  Dorso- 
L.\TER,\L  View. 
a.  Tibialis  anterior;  a', 
tendon  of  preceding;  b,  pero- 
neus tertiu.s;  b\  tendon  of  b; 
c,  long  digital  extensor;  d,  e,  f, 
/',  /",  tendons  of  c;  g,  peroneus 
longus;  g',  tendon  of  g;  h, 
extensor  digiti  quarti;  h', 
tendon  of  h,  which  receives  //' 
from  the  interosseus  medius; 
i,  extensor  digiti  quinti;  k,  deep 
digital  flexor;  I,  soleus;  m, 
gastrocnemius;  n,  extensor  dig- 
italis brevis.  (After  Ellenber- 
ger,  in  Leisering's  Atlas.) 


MUSCLES    OF   THE    LEG    AND    FOOT  367 

osseus  at  the  distal  end  of  the  first  phalanx,  and  may  detach  a  tendon  to  the  second 
digit.  The  lateral  tendon  is  smaller.  Its  branches  end  on  the  third  phalanges  of 
the  accessory  (second  and  fifth)  digits  and  on  the  lateral  chief  (fourth  digit) ;  there 
may  be  a  branch  to  the  third  digit,  and  the  branch  for  the  fourth  may  go  to  the 
corresponding  branch  of  the  central  tendon.     Other  variations  occur. 

The  synovial  sheath  for  the  tendons  of  the  extensor  longus  and  peroneus  tertius  at  the  hock 
extends  nearly  half  an  inch  (ca.  1  cm.)  above  the  proximal  annular  ligament  and  an  inch  or  more 
(ca.  2  to  3  cm.)  below  the  distal  annular  ligament  in  a  large  adult. 

The  lateral  digital  extensor  lies  on  the  lateral  face  of  the  leg,  behind  the  per- 
oneus longus.  It  arises  from  the  lateral  surface  of  the  fibula,  the  lateral  femoro- 
tibial  ligament,  and  the  intermuscular  septum  between  this  muscle  and  the  deep 
digital  flexor.  It  consists  of  two  parts.  The  larger  anterior  muscle  (extensor 
digiti  quarti)  has  a  tendon  which  appears  a  little  distal  to  the  middle  of  the  leg,  de- 
scends on  the  grooved  lateral  surface  of  the  fibula,  inclines  forward,  crossing  under 
the  tendon  of  the  peroneus  longus,  and  ends  on  the  extensor  process  of  the  third 
phalanx  of  the  lateral  chief  (fourth)  digit.  It  receives  an  interosseus  tendon  at 
the  first  phalanx.  The  tendon  of  the  posterior  muscle  (extensor  digiti  quinti) 
accompanies  that  of  the  anterior  one  to  the  tarsus  and  descends  to  the  lateral  ac- 
cessory (fifth)  digit. 

The  two  tendons  are  bound  down  at  the  lateral  malleolus  by  an  annular  ligament.  The 
anterior  tendon  may  receive  a  branch  of  the  long  extensor  tendon  and  send  a  tendon  to  the  fifth 
digit.  The  posterior  tendon  may  send  a  reinforcing  branch  to  the  tendon  of  the  long  extensor  for 
the  fifth  digit.  There  may  be  a  third  small  head  which  arises  from  the  middle  of  the  fibula  and 
sends  a  delicate  tendon  to  join  that  of  the  posterior  head. 

The  extensor  hallucis  longus  is  a  small,  fusiform  muscle  which  is  covered  by  the 
extensor  longus  and  peroneus  longus.  It  arises  from  the  proximal  end  of  the  fibula 
and  its  delicate  tendon  descends  at  first  under  that  of  the  peroneus  tertius,  inclines 
medially  at  the  hock,  and  ends  on  the  medial  accessory  (second)  digit. 

The  extensor  digitalis  brevis  is  a  well-developed  muscle  which  lies  on  the  dor- 
sal face  of  the  distal  part  of  the  tarsus  and  on  the  chief  metatarsal  bones.  It  arises 
from  the  neck  of  the  tibial  tarsal  and  the  body  of  the  fibular  tarsal  bone,  and  is 
partially  divided  into  three  parts.  The  tendon  of  the  superficial  part  joins  that  of 
the  long  extensor  for  the  chief  digits.  The  deep  part  has  two  tendons  which  join 
those  of  the  long  extensor  for  the  accessory  digits. 

The  gastrocnemius  has  short  but  wide  and  thick  heads.  The  lateral  one  is 
the  larger  and  is  united  with  the  superficial  digital  flexor  to  the  distal  third  of  the 
leg.  The  tendon  forms  a  groove  for  the  superficial  flexor  tendon  above  the  hock 
and  is  inserted  chiefly  into  the  prominences  on  each  side  of  the  notch  of  the  tuber 
calcis. 

The  soleus  is  thick  and  wide  and  blends  with  the  lateral  head  of  the  gastroc- 
nemius. It  arises  from  the  lateral  epicondyle  of  the  femur  and  the  deep  fascia 
at  the  stifle.     Its  tendon  joins  that  of  the  gastrocnemius. 

The  popliteus  presents  nothing  remarkable. 

The  superficial  digital  flexor  has  a  belly  of  considerable  size.  It  arises  with  the 
lateral  head  of  the  gastrocnemius,  with  which  it  is  fused  to  the  distal  third  of  the 
leg.  The  tendon  is  almost  entirely  enclosed  by  the  twist  of  the  gastrocnemius  in 
the  lower  part  of  the  leg.  At  the  tuber  calcis  it  is  thick  and  largely  cartilaginous, 
and  is  molded  on  the  groove  and  ridges  of  the  bone.  It  is  attached  by  a  strong 
band  to  each  side  of  the  tuber  calcis.  A  large  bursa  under  the  tendon  extends  up- 
ward in  the  groove  formed  by  the  gastrocnemius  almost  to  the  muscular  part  and 
downward  to  the  middle  of  the  fibular  tarsal  bone.  The  tendon  divides  distally 
into  two  branches  which  go  to  the  chief  digits.  It  also  detaches  from  its  plantar 
surface  two  bands  which  join  the  fascia  of  the  accessory  digits. 

The  deep  digital  flexor  presents  three  distinct  heads:     (1)  The  tibialis  pes- 


368  THE   MUSCLES    OF   THE   DOG 

terior  is  the  smallest.  It  has  a  fusiform  belly  in  the  proximal  half  of  the  leg  and 
arises  from  the  grooved  plantar  surface  of  the  fibula.  The  tendon  joins  that  of  the 
flexor  hallucis  at  the  distal  end  of  the  leg.  (2)  The  flexor  digitalis  longus  is  much 
larger  and  has  a  fusiform,  pennate  belly  which  extends  obliquely  across  the  prox- 
imal two-thirds  of  the  leg.  It  arises  from  the  proximal  end  of  the  fibula,  the  pop- 
liteal line,  the  middle  third  of  the  medial  part  of  the  plantar  surface  of  the  tibia,  and 
the  intermuscular  septum  between  this  muscle  and  the  flexor  hallucis.  The  ten- 
don (which  has  a  synovial  sheath)  descends  in  a  groove  behind  the  medial  malleolus, 
bound  down  by  an  annular  ligament,  inclines  laterally  on  the  joint  capsule,  and 
joins  the  tendon  of  the  flexor  hallucis.  (3)  The  flexor  hallucis  has  a  large  fusiform 
belly  which  extends  almost  to  the  distal  end  of  the  leg.  It  arises  from  the  greater 
part  of  the  plantar  surface  of  the  tibia,  the  medial  surface  and  plantar  border  of 
the  fibula,  and  the  interosseous  membrane.  The  tendon  descends  in  the  tarsal 
canal,  receiving  the  tendons  of  the  other  heads,  and  ends  like  the  corresponding 
one  of  the  forelimb.  The  tarsal  synovial  sheath  begins  at  the  distal  end  of  the 
muscular  part  and  extends  to  the  middle  of  the  metatarsus. 

The  lumbricales  are  absent,   but  there  are  four  interossei.     Rudimentary 
adductors  of  the  second  and  fifth  digits  may  be  found. 


THE  MUSCLES  OF  THE  DOG 
Muscles  of  the  Face 

The  cutaneus  of  the  face  is  well  developed.  Most  of  it  is  a  continuation  of  the 
cervical  cutaneus;  the  bundles  extend  forward  over  the  lower  part  of  the  lateral 
surface  of  the  face  to  the  angle  of  the  mouth  and  the  upper  lip.  Other  bundles  ex- 
tend upward;  some  of  these  spread  out  on  the  cheek  and  lateral  nasal  region,  and 
a  thin  la3^er  passes  toward  the  lower  eyelid,  blending  with  the  orbicularis  oculi  and 
constituting  a  malaris  muscle.  Another  stratum  is  attached  to  the  scutiform  carti- 
lage and  spreads  out  on  the  masseter. 

The  orbicularis  oris  is  poorly  developed.  In  the  upper  lip  it  is  divided  cen- 
trally, and  in  the  lower  lip  it  is  distinct  only  near  the  angles  of  the  mouth. 

The  levator  nasolabialis  is  wide  and  undivided.  It  has  an  extensive  origin  on 
the  frontal  and  nasal  bones.  The  fibers  run  downward  and  forward  to  the  lateral 
wing  of  the  nostril  and  the  upper  lip. 

The  levator  labii  superioris  proprius  arises  behind  the  infraorbital  foramen, 
runs  forward  under  the  preceding  muscle,  and  ends  in  numerous  small  tendons 
which  are  in  part  inserted  around  the  nostril,  in  part  blend  with  those  of  the  oppo- 
site side. 

The  zygomaticus  is  narrow  and  very  long;  it  arises  on  the  scutiform  cartilage, 
and  ends  at  the  angle  of  the  mouth. 

The  depressor  labii  inferioris  is  absent. 

There  are  no  special  nasal  muscles.  The  homologue  of  the  lateral  dilator  is 
triangular;  it  is  small  at  its  origin  just  ventral  to  the  levator  labii  superioris  pro- 
prius, and  ends  almost  entirely  in  the  upper  lip. 

The  buccinator  is  wide  and  very  thin,  and  the  two  planes  of  fibers  cross  each 
other. 

The  palpebral  muscles  present  no  very  noteworthy  special  characters.  Two 
small  muscles  act  on  the  upper  eyelid.  One  of  these,  the  corrugator  supercilii, 
arises  from  the  fascia  on  the  frontal  bone  and  ends  near  the  medial  canthus.  The 
other  arises  from  the  zygomatic  arch  and  ends  near  the  lateral  canthus. 


MUSCLES    OF   THE    FACE 


369 


Fig.  319. — Muscles  op  Head  of  Dog. 
o,  Scutularis;  b,  c,  anterior  auricular  muscles;  rf,  helicis;  e,  antitragicus;  /,/,  zygomaticus,  out  of  which  a  portion 
is  cut;  g,  stump  of  cutaneus  attached  to  scutiform  cartilage;  h,  parotido-auricularis;  i,  masseter;  k,  malaris;  I, 
levator  nasolabialis;  m,  levator  labii  superioris  proprius;  ra,  dilatator  naris  lateralis;  o,  p,  buccinator  (buccalis.  molaris) ; 
q,  retractor  angulioris  (from  cutaneus);  r,  occipito-mandibularis;  s,  mylo-hyoideus;  /,  base  of  concha;  S,  parotid 
gland;  2',  parotid  duct;  3,  mandibular  gland;  4.  mandibular  lymph  glands;  S,  buccal  glands;  6,  zygomatic  arch; 
7,  maxilla;   8,  dorsum  nasi;   9,  parotid  lymph  gland.     (Ellenberger-Baum,  Anat.  d.  Hundes.) 


Fig.  320. — Superficial  Muscles  of  Dog,  After  Removal  of  M.  cutaneus. 
Levator  nasolabialis;    2,  levator  labii  superioris  proprius;    3,  dilatator  naris  lateralis;   4,  4'i  buccinator;    5, 


tractor  anguli  oris;  e,  zygomaticus;  7,  malaris;  5,  masseter;  9,  occipito-mandibularis,  /O,  scutularis; /i,  other  auric- 
ular muscles;  12,  parotido-auricularis;  13,  mjlo-hyoideus;  14<  sterno-hyoideus;  IS,  sterno-thyroideus;  16,  spienius; 
17,  lumbo-dorsal  fascia;  18,  rectus  abdominis;  19,  obliquus  abdominis  externus;  19',  aponeurosis  of  preceding;  20, 
intercostal  muscle;  21.  sacro-coccygeus  accessorius;  22,  sacro-coccygeus  dorsalis;  23,  sacro-coccygeus  ventralis;  24i 
great  trochanter;  ^-5,  jugular  vein;  a,  6,  c,  brachiocephalicus;  d,  clavicle;  e, /,  trapezius;  a,  serratus  cervicis;  A,  omo- 
transversarius;  i,  latissimus  dorsi;  k,  posterior  deep  pectoral;  I,  supraspinatus;  to,  to',  deltoid;  re,  infraspinatus;  o, 
triceps,  long  head;  o',  triceps,  lateral  head;  p,  brachialis;  q,  extensor  carpi  radialis;  r,  gluteus  medius;  s,  gluteus 
superficiaUs;  <,«',  tensor  fasciae  latae;  u,  sartorius;  n,  biceps  femoris;  i',  fascia  lata;  t/),  semitendinosus;  z,  semimem- 
branosus; y,  sartorius;  z,  gracilis;  26,  pronator  teres;  27,  flexor  carpi  radialis;  28,  flexor  carpi  ulnaris;  29,  tibialis 
anterior;  30,  popliteus;  5/,  3/',  deep  digital  flexor;  3^,  superficial  digital  flexor;  33,  gastrocnemius;  34,  spine  of  scap- 
ula; a,  parotid  gland,  with  a',  its  duct;  fi,  mandibular  gland;  S,  mandibular  lymph  glands;  rj,  parotid  lymph  gland; 
f,  inferior  buccal  glands.  (After  EUenberger,  in  Leisering's  Atlas.) 
24 


370 


THE   MUSCLES    OF   THE    DOG 


MUSCLES  OF  THE  MANDIBLE 
The  masseter  is  thick  and  its  superficial  face  is  strongly  convex.     It  arises 
from  the  zygomatic  arch,  and  extends  beyond  the  branch  of  the  jaw  below  and  be- 
hind.    Three  partly  separate  strata  may  be  recognized  in  its  structure. 

The  temporalis  is  very  large  and 
strong,  and  contains  much  tendinous 
tissue.  It  arises  from  the  temporal 
fossa  and  the  orbital  ligament  and 
ends  on  the  coronoid  process  of  the 
mandible.  It  blends  in  part  with 
the  masseter. 

The  pterygoideus  lateralis  is 
not  distinct  from  the  medialis. 

The  digastricus  is  absent. 

The  occipito-mandibularis  is  a 
strong,  round,  fleshy  muscle,  which 
arises  on  the  paramastoid  process 
and  is  inserted  into  the  border  and 
medial  surface  of  the  ramus  of  the 
mandible  at  the  level  of  the  last 
molar  teeth;  it  sometimes  has  a 
tendinous  intersection. 


HYOID  MUSCLES 

The  mylo-hyoideus  is  well  de- 
veloped. 

The  stylo-hyoideus  is  very  slen- 
der, and  is  inserted  into  the  body  of 
the  hyoid  bone. 

The  hyoideus  transversus  and 
omo-hyoideus  are  absent. 

The  stemo-thyro-hyoideus  is 
large  and  arises  chiefly  on  the  first 
costal  cartilage.  It  is  clearly  di- 
vided into  stemo-thyroideus  and 
stemo-hyoideus. 


Fig.  321. — Ventral  Muscles  of  Head,  Neck,  and  Thorax 
OF  Dog. 
a,  Mylo-hyoideus;  6,  occipito-mandibularis;  c,  sterno- 
hyoideus;  c',  sterno-thyroideus ;  d,  sterno-cephalicus;  e,  brachio- 
cephalicus;  /,  subscapularis;  g,  superficial  pectoral;  h,  deep  pec- 
toral; i,  rectus  abdominis;  k,  obliquus  abdominis  externus;  I, 
long  head  of  triceps;  m,  medial  head  of  triceps;  n,  biceps 
brachii;  o,  brachialis;  1,  1',  1",  mandibular  lymph  glands;  2, 
thyroid  gland;  3,  external  jugular  vein.  (EUenberger-Baum, 
Anat.  d.  Hundes.) 


Muscles  of  the  Thoracic  Limb 

The  trapezius  is  thin,   and  is 
divided  into   cervical  and  thoracic 
portions  by  a  narrow  aponeurotic 
part.     Its  line  of  origin  extends  from 
about  the  middle  of  the  dorsal  bor- 
der of  the  neck  to  the  ninth  or  tenth  thoracic  spine,  the  right  and  left  muscles 
meeting  (except  at  their  posterior  part)  on  a  median  fibrous  raphe.     It  is  inserted 
into  the  entire  length  of  the  spine  of  the  scapula. 

The  omo-transversarius  arises  by  a  tendon  on  the  lower  part  of  the  spine  of 
the  scapula  (where  it  is  often  partially  blended  with  the  trapezius) ,  and  is  inserted 
into  the  wing  of  the  atlas. 


MUSCLES    OF  THE   THORACIC    LIMB  371 

The  rhomboideus  consists  of  three  parts.  The  rhomboideus  thoracalis  is 
small ;  it  arises  from  the  fourth  to  the  sixth  or  seventh  thoracic  spine,  and  is  inserted 
into  the  medial  surface  (chiefly)  of  the  dorsal  angle  of  the  scapula.  The  rhom- 
boideus cervicalis  arises  from  the  ligamentum  nuchge  as  far  forward  as  the  second 
or  third  cervical  vertebra,  and  is  inserted  into  the  medial  surface  of  the  cervical 
angle  of  the  scapula.  The  rhomboideus  capitis  is  a  narrow  band  which  is  given  off 
laterally  from  the  preceding;  it  is  inserted  into  the  nuchal  crest. 

The  latissimus  dorsi  is  extensive ;  it  has  an  attachment  to  the  last  two  ribs  and 
also  to  the  upper  part  of  the  spine  of  the  scapula  in  addition  to  the  origin  from  the 
lumbo-dorsal  fascia.     Its  lower  edge  blends  near  the  shoulder  with  the  cutaneus. 

The  brachiocephahcus  contains  in  front  of  the  shoulder  a  tendinous  intersec- 
tion and  a  fibrous  mass  in  which  the  clavicle  is  embedded.  Anterior  to  this  it  sepa- 
rates into  two  diverging  parts.  The  dorsal  part  is  the  cleido-cervicaUs,  which 
widens  above  and  is  attached  to  the  median  raphe  of  the  neck  and  to  the  occipital  bone. 
The  ventral  part  is  the  cleido-mastoideus ;  it  is  narrow  and  is  attached  to  the  mas- 
toid process.  The  common  mass  posterior  to  the  clavicle  and  the  fibrous  inter- 
section, which  is  attached  to  the  humerus,  is  homologous  with  the  clavicular  part 
of  the  deltoid  of  man. 

The  superficial  pectoral  muscle  is  small.  It  arises  on  the  sternum  from  the 
manubrium  as  far  back  as  the  third  costal  cartilage,  and  is  inserted  into  the  humerus 
at  the  border  between  the  medial  and  anterior  surfaces.  A  superficial  slip  detached 
from  it  is  inserted  into  the  fascia  of  the  forearm.  The  deep  pectoral  has  no  scapular 
part.  It  arises  on  the  sternum  and  costal  cartilages  from  the  second  costal  to  the 
xiphoid  cartilage,  and  from  the  aponeurosis  of  the  obliquus  abdominis  externus. 
It  is  inserted  chiefly  into  the  medial  tuberosity  of  the  humerus,  but  also  Ijy  small 
slips  into  the  lateral  tuberosity  and  the  fascia  of  the  arm. 

The  serratus  ventralis  shows  no  clear  division  into  cervical  and  thoracic  parts. 
It  arises  from  the  last  five  cervical  vertebrae  and  the  first  eight  ribs,  and  is  inserted 
into  the  upper  part  of  the  costal  surface  of  the  scapula. 

The  deltoid  is  clearly  divided  into  scapular  and  acromial  parts.  The  scapular 
part  is  triangular  and  arises  from  almost  the  entire  length  of  the  spine  of  the  scapula; 
it  is  inserted  largely  into  the  fascia  on  the  lateral  surface  of  the  arm.  The  acromial 
part  is  short,  thick,  and  fusiform;  it  arises  from  the  lower  edge  of  the  acromion, 
and  ends  on  the  deltoid  tuberosity. 

The  supraspinatus  is  large ;  it  ends  chiefly  on  the  lateral  tuberosity  of  the  hu- 
merus, but  has  a  small  attachment  to  the  medial  tuberosity  also. 

The  infraspinatus  is  bipennate.  The  tendon  of  insertion  passes  in  a  groove  on 
the  lateral  tuberosity  of  the  humerus,  to  end  on  a  well-defined  mark  on  the  same;  a 
large  bursa  lies  under  the  tendon. 

The  teres  minor  is  short  and  fusiform ;  it  arises  on  a  tubercle  on  the  posterior 
border  of  the  scapula,  just  above  the  glenoid  cavity,  and  is  inserted  into  a  tubercle 
on  the  upper  part  of  the  deltoid  ridge. 

The  subscapularis  is  wide  and  is  multipennate  in  structure,  being  intersected 
by  fibrous  septa  which  are  attached  to  the  rough  lines  on  the  costal  surface  of  the 
scapula.     It  is  inserted  into  the  medial  tuberosity  of  the  humerus. 

The  teres  major  is  thick.  It  arises  on  the  upper  part  of  the  posterior  border 
of  the  scapula  and  on  the  subscapularis,  and  is  inserted  into  an  eminence  (tuber- 
ositas teres)  on  the  proximal  third  of  the  medial  surface  of  the  humerus  by  a  com- 
mon tendon  with  the  latissimus  dorsi. 

The  coraco-brachialis  has  a  short  and  undivided  belly.  It  arises  from  a  small 
depression  on  the  medial  surface  of  the  tuber  scapulae,  and  ends  on  the  proximal 
third  of  the  humerus,  just  medial  to  the  brachialis.  The  tendon  of  origin  has  a  syno- 
vial sheath. 

The  capsularis  is  absent. 


372 


THE    MUSCLES    OF   THE    DOG 


The  biceps  brachii  lies  almost  entirely  on  the  medial  surface  of  the  humerus. 
It  is  long  and  fusiform.  The  tendon  of  origin  is  round,  and  is  bound  down  in  the 
intertuberal  groove  by  an  annular  ligament.  It  is  enveloped  by  an  extension  of 
the  synovial  membrane  of  the  shoulder  joint.     The  tendon  of  insertion  is  bifid; 


( 

Teres  major  1 

Latissimus  dorsi  -.^^^^K\         ^    'ir'/ 

Lot^g  head  of  triceps _^ ^  '^ 

Tensor  fascice  antibrachii  ...  ||i'|, 

-II  r/    #/^ 

Medial  head  of  triceps —MMLI^^^  /  m// 

Flexor  carpi  ulnar  is -ll|'i  \l  \^ 

Flexor  car  pi  radialis IIL-Vi   \  ' 

Superficial  digital  flexor %-  ^ 

Deep  digital  flexor «»,xM  1^  \\ 

JW 

'I 


~  Subscaj}ularis 
-  Supra spinatus 


Coraco-brachialis 
Accessory  head  of  triceps 


Biceps  brachii 


Humerus 


Extensor  carpi  radialis 
Pronator  teres 


Radius 

Radial  head  of  deep 
digital  flexor 


[uscLEs  OF  Thoracic  Limb  of  Dog;  Medial  View.     CEllenberger-Baum,  Anat.  des  Hundes.) 


one  branch  is  attached  to  a  rough  mark  on  the  lateral  surface  of  the  ulna,  just  below 
the  semilunar  notch;  the  other  branch  ends  on  a  distinct  mark  on  the  postero- 
medial aspect  of  the  proximal  part  of  the  shaft  of  the  radius,  one  to  two  inches  be- 
low the  head. 


MUSCLES    OF   THE    THORACIC    LIMB 


373 


The  brachialis  is  very  little  curved.  Its  tendon  of  insertion  passes  over  the 
medial  ligament  of  the  elbow  and  under  the  ulnar  tendon  of  the  biceps  and  ends 
just  proximal  to  the  latter.  The  tendon  of  the  biceps  forms  a  partial  sheath  for 
that  of  the  brachialis. 

The  tensor  fasciae  antibrachii  is  thin  and  narrow.     It  arises  on  the  tendon  and 
lateral  surface  of  the  latissimus  dorsi,  and  ends  on  the 
olecranon  and  the  fascia  of  the  forearm. 

The  triceps  has  an  additional  deep  head  (Caput 
accessorium),  which  arises  just  below  the  head  of  the 
humerus.  The  medial  head  is  very  long;  it  arises  from 
a  mark  on  the  proximal  fourth  of  the  medial  surface  of 
the  humerus,  just  behind  the  insertion  of  the  teres  major 
and  latissimus  dorsi.  A  bursa  lies  on  the  olecranon  in 
front  of  the  common  tendon  of  insertion. 

The  brachioradialis  is  a  long,  narrow,  delicate  mus- 
cle, situated  superficially  on  the  dorsal  surface  of  the 
forearm.  It  arises  with  the  extensor  carpi  on  the  crest 
above  the  lateral  epicondyle  of  the  humerus,  and  is  in- 
serted into  the  distal  part  of  the  medial  border  of  the 
radius.  It  is  often  much  reduced,  and  is  sometimes  ab- 
sent.    It  rotates  the  forearm  and  paw  outward. 

The  extensor  carpi  radialis  arises  on  the  lateral  con- 
dyloid crest  and  divides  into  two  parts.  The  larger  lat- 
eral part,  the  extensor  carpi  radialis  brevis,  ends  on  the 
proximal  end  of  the  third  metacarpal  bone.  The  medial 
and  more  superficial  part,  the  extensor  carpi  radialis 
longus,  ends  on  the  second  metacarpal  bone.  (A  ten- 
don to  the  fourth  metacarpal  ma}^  occur.) 

The  extensor  carpi  obliquus  or  abductor  pollicis 
longus  arises  from  the  lateral  border  and  dorsal  surface 
of  the  ulna,  the  interosseous  ligament,  and  the  proximal 
part  of  the  lateral  border  of  the  radius.  It  is  inserted 
into  the  first  metacarpal  bone  by  a  tendon  which  con- 
tains a  small  sesamoid  bone.     It  abducts  the  first  digit. 

There  are  three  (or  four)  extensors  of  the  digits. 

1.  The  common  digital  extensor  (M.  extensor  digi- 
talis communis)  arises  on  the  lateral  epicondyle  of  the 
humerus  and  the  lateral  ligament  of  the  elbow  joint. 
It  has  four  bellies,  each  of  which  has  a  tendon  of  inser- 
tion. These  end  on  the  third  phalanges  of  the  second, 
third,  fourth,  and  fifth  digits. 

2.  The  extensor  of  the  first  and  second  digits  (M. 
extensor  pollicis  longus  et  extensor  indicis  proprius)  is 
small,  and  is  covered  by  the  common  and  lateral  ex- 
tensors. It  arises  on  the  proximal  half  of  the  ulna.  Its 
tendon  descends  with  that  of  the  common  extensor  and 
divides  into  two  branches.  The  delicate  medial  branch 
ends  on  the  first  digit,  while  the  larger  lateral  one  ends 
with  the  tendon  of  the  common  extensor  for  the  second 
digit. 

3.  The  lateral  digital  extensor  (M.  extensor  digitalis  lateralis)  consists  of  two 
muscles  which  are  not  rarely  fused.  They  arise  on  the  lateral  epicondyle  of  the 
humerus  and  the  lateral  ligament  of  the  elbow  joint.  The  larger  superficial  muscle 
is  the  extensor  of  the  third  and  fourth  digits  (M.  extensor  digiti  tertii  et  quarti); 


Fig.  323. — Muscles  of  Antibra- 

CHIUM    AND     MaNUS    OF     DoG; 

Lateral  View. 

a,  Triceps  brachii;  6,  brachi- 
alis: c,  extensor  carpi  radialis;  d, 
common  digital  extensor;  d',  d", 
d'",  d"",  tendons  of  preceding;  e, 
lateral  digital  extensor;  e',  /,  ten- 
dons of  preceding;  g,  ulnarid 
lateralis;  h,  ulnar  head,  h',  hu- 
meral head  of  flexor  carpi  ulnaris; 
t,  extensor  carpi  obliquus  (s.  ab- 
ductor pollicis  longus) ;  k,  inter- 
ossei;  I,  branches  from  preceding 
to  extensor  tendons;  1,  olecranon; 
2,  radius;  3,  lateral  epicondyle  of 
humerus.  (After  EUenberger,  in 
Leisering's  Atlas.) 


374 


THE   MUSCLES    OF   THE   DOG 


its  tendon  divides  at  or  near  the  carpus  into  two  branches,  which  are  inserted  into 
the  third  phalanges  of  the  third  and  fourth  digits,  blending  with  the  corresponding 
tendons  of  the  common  extensor.  The  posterior  muscle  is  the  extensor  of  the  fifth 
digit  (M.  extensor  digiti  quinti) ;  its  tendon  fuses  with  that  of  the  common  extensor 
for  the  fifth  digit. 

The  ulnaris  lateralis  or  extensor  carpi  ulnaris  is  a  large  flat  muscle  which  lies 
on  the  lateral  surface  of  the  ulna.  It  arises  on  the  lateral  epicondyle  of  the  humerus, 
and  is  inserted  into  the  proximal  end  of  the  fifth  metacarpal  and  the  accessory  carpal 
bone.     It  is  chiefly  an  abductor  of  the  paw. 

The  flexor  carpi  ulnaris  consists  of  two  quite  distinct  heads.  The  larger 
humeral  head  arises  on  the  medial  epicondyle,  while  the  smaller, 
superficial  ulnar  head  arises  on  the  posterior  border  of  the  ulna. 
The  tendons  of  the  two  end  on  the  accessory  carpal  bone  and 
have  a  bursa  between  them. 

The  flexor  carpi  radiaHs  arises  on  the  medial  epicondyle  of 
the  humerus  and  is  inserted  by  a  bifid  tendon  into  the  second 
and  third  metacarpal  bones. 

The  tendons  of  the  foregoing  eight  muscles  are  provided 
with  synovial  sheaths  at  the  carpus. 

The  pronator  teres  is  a  fusiform  muscle,  which  is  situated 
superficially  on  the  proximal  part  of  the  medial  border  of  the 
radius.  It  arises  on  the  medial  epicondyle  of  the  humerus,  and 
is  inserted  into  the  dorsal  surface  and  medial  border  of  the  radius 
almost  half  way  to  the  carpus.  It  is  related  deeply  to  the  radial 
vessels,  the  median  nerve,  and  the  tendon  of  the  biceps.  Its 
action  is  to  flex  the  elbow  and  rotate  the  forearm  inward  (pro- 
nation). 

The  superficial  digital  flexor  is  situated  superficially  on 
the  medio-volar  surface  of  the  forearm.  It  arises  on  the  medial 
epicondyle  of  the  humerus  and  terminates  near  the  carpus  on  a 
tendon  which  passes  dowTiward  outside  of  the  carpal  canal  and 
receives  below  the  carpus  two  reinforcing  bands,  one  from  the 
accessory  carpal,  the  other  from  the  sesamoid  bone  at  the  medial 
side  of  the  carpus.  It  divides  distally  into  four  branches,  which 
are  inserted  into  the  second  phalanges  of  the  second,  third, 
fourth,  and  fifth  digits. 

The  deep  digital  flexor  has  humeral,  ulnar,   and  radial 

heads;  the  radial  head  arises  from  the  medial  border  of  the 

radius.     They  unite  on  a  common  tendon  which  passes  down 

through  the  carpal  canal,  gives  off  a  branch  to  the  first  digit, 

and  divides  into  four  branches.      These  perforate  the  tendons 

of  the  superficial  flexor  and  are  inserted  into  the  third  phalanges 

of  the  second  to  the  fifth  digits.     The  tendons  are  provided  with 

synovial  sheaths  from  the  middle  of  the  metacarpus  downward, 

and  are  held  in  place  by  three  digital  annular  ligaments. 

The  palmaris  longus^  is  a  small  muscle  which  arises  from  the  deep  digital 

flexor  below  the  middle  of  the  forearm,  and  ends  by  two  tendons  which  unite  with 

those  of  the  superficial  flexor  for  the  third  and  fourth  digits. 

The  supinator  is  a  short,  flat,  fusiform  muscle  which  arises  from  the  front  of 
the  lateral  epicondyle  of  the  humerus  with  the  lateral  ligament,  and  from  the  lateral 
prominence  of  the  head  of  the  radius,  and  is  inserted  into  the  proximal  fourth  of  the 

1  The  homology  here  is  doubtful.  Sussdorf  regards  the  ulnar  head  of  the  deep  digital  flexor 
as  the  homologue  of  the  palmaris  longus  of  man,  while  Alexais  considers  that  the  latter  is  repre- 
sented by  the  superficial  digital  flexor. 


Fig.  324. — Volar  Mus- 
cles OF  Left  Fore- 
Paw  OF  Dog. 
o,  Abductor  pol- 
licis  brevis  et  opponens 
poUicis;  b,  flexor  poUi- 
cis  brevis;  c,  adductor 
poUicis;  d,  adductor 
digiti  secundi;  e,  ad- 
ductor digiti  quinti;  /, 
flexor  digiti  quinti 
brevis;  g,  abductor 
digiti  quinti;  h,  in- 
terossei;  1,  accessory 
carpal  bone;  S,  first 
digit;  3-6,  sesamoids 
of  metacarpo-phalan- 
geal  joints.  (Ellen- 
berger-Baum,  Anat.  d. 
Hundes.) 


MUSCLES    OF   THE   THORACIC    LIMB  375 

dorsal  surface  and  the  medial  border  of  the  radius.  (A  pouch  of  the  capsule  of  the 
elbow  joint  lies  under  the  tendon  of  origin.)  Its  action  is  to  rotate  the  forearm 
outward  (supination) . 

The  pronator  quadratus  consists  of  a  thin  layer  of  fibers  which  cross  the  volar 
surface  of  the  radius  and  the  interosseous  ligament  of  the  forearm,  except  at  the  two 
extremities  of  the  latter.  The  fibers  extend  from  the  medial  border  of  the  radius 
backward  and  outward  to  the  interosseous  border  of  the  ulna.  It  rotates  the  fore- 
arm inward  (pronation). 

The  palmaris  brevis  (?)  is  a  very  small  muscle,  which  arises  on  the  tendon  of 
the  superficial  digital  flexor  at  the  carpus,  and  is  inserted  at  the  fifth  metacarpo- 
phalangeal joint  into  the  sheath  and  annular  ligament  of  the  deep  flexor. 

The  lumbricales  are  three  very  delicate  muscles,  which  arise  on  the  volar  sur- 
face of  the  tendons  of  the  deep  flexor,  and  are  inserted  into  the  first  phalanges  of  the 
third,  fourth,  and  fifth  digits. 

The  abductor  poUicis  brevis  et  opponens  pollicis,  a  very  small  pale  muscle, 
arises  on  the  fibrous  band  which  connects  the  superficial  flexor  tendon  with  the 
medial  carpal  sesamoid,  and  ends  on  the  distal  end  of  the  first  metacarpal  bone  and 
the  first  phalanx  of  the  first  digit.     It  abducts  the  first  digit. ^ 

The  flexor  pollicis  brevis  arises  on  the  volar  carpal  ligament  over  the  second 
metacarpal  bone,  and  ends  on  the  volar  sesamoid  of  the  first  digit. 

The  adductor  pollicis,  situated  lateral  to  the  preceding,  is  the  largest  of  the 
thumb  muscles.  It  arises  between  the  preceding  and  the  second  interosseous 
muscle,  and  is  inserted  into  the  first  phalanx  of  the  first  digit. 

The  adductor  digiti  secundi  is  situated  between  the  second  interosseous 
muscle  and  the  adductor  digiti  quinti.  It  arises  on  the  volar  carpal  ligament,  and 
ends  on  the  first  phalanx  of  the  second  digit. 

The  adductor  digiti  quinti  arises  close  to  the  preceding  muscle,  and  passes 
outward  to  end  on  the  first  phalanx  of  the  fifth  digit. 

The  flexor  digiti  quinti  arises  on  the  ligament  connecting  the  accessory  carpal 
to  the  third  and  fourth  metacarpal  bones,  crosses  the  corresponding  interosseous 
muscle,  and  ends  on  the  fifth  digit  with  the  next  muscle. 

The  abductor  digiti  quinti  is  larger  than  the  two  preceding  muscles;  it  arises 
on  the  accessory  carpal  bone,  and  ends  on  the  lateral  sesamoid  of  the  fifth  digit  and 
on  the  lateral  ligament. 

There  are  four  interossei  which  lie  on  the  volar  surface  of  the  metacarpus. 
They  are  well  developed  and  fleshy.  They  arise  on  the  distal  row  of  the  carpus 
and  on  the  proximal  ends  of  the  metacarpals.  Each  divides  distally  into  two 
branches,  which  are  inserted  by  small  tendons  on  the  corresponcfing  sesamoid 
bones,  and  detach  slips  to  the  extensortendons. 

The  chief  facts  with  regard  to  the  synovial  membranes  in  connection  with  the  muscles  of  the 
forearm  and  manus  are  as  follows:  The  tendons  of  the  extensor  carpi  radiaUs  frequently  have  a 
synovial  sheath  at  the  distal  part  of  the  forearm,  and  there  may  be  one  or  two  bursse  at  the  carpus. 
The  tendons  of  the  extensor  digitalis  communis  have  a  synovial  sheath  which  extends  from  the  distal 
part  of  the  forearm  to  the  carpus  or  to  the  proximal  part  of  the  metacarpus.  The  tendons  of  the 
extensor  digitalis  lateralis  have  in  about  half  of  the  cases  a  synovial  sheath  at  the  distal  part  of  the 
forearm  and  at  the  carpus.  The  tendon  of  insertion  of  the  extensor  carpi  obUquus  has  a  synovial 
sheath.  The  tendon  of  insertion  of  the  ulnaris  lateralis  sometimes  has  a  bursa  between  it  and  the 
styloid  process  of  the  ulna.  The  tendon  of  insertion  of  the  flexor  carpi  radialis  has  a  synovial 
sheath.  There  is  a  bursa  between  the  two  tendons  of  the  flexor  carpi  ulnaris  at  their  insertion; 
it  usually  communicates  with  a  subfascial  bursa  which  lies  on  the  accessory  carpal  bone.  The 
superficial  digital  flexor  has  a  bursa  under  its  origin;  this  communicates  wath  another  bursa  which 
lies  between  the  deep  digital  flexor  and  the  flexor  carpi  ulnaris.  The  tendons  of  the  digital  flexors 
for  the  second  to  the  fifth  digits  have  a  common  sheath  for  each  digit  which  begins  at  the  distal 
part  of  the  metacarpus.     The  tendon  of  the  deep  flexor  for  the  first  digit  has  a  synovial  sheath. 

1  Movements  of  individual  digits  are  specified  with  regard  to  the  axis  of  the  manus  (paw), 
and  not  to  the  median  plane  of  the  body. 


376  THE   MUSCLES    OF   THE    DOG 

Muscles  of  the  Neck 

The  cervical  cutaneus  consists  of  two  strata.  One  of  these  is  composed  of  thin 
bundles  which  curve  across  the  ventral  region  of  the  neck  and  fade  out  laterally. 
The  other  layer  is  thicker  and  rnore  extensive.  Its  bundles  begin  at  the  dorsal 
margin  of  the  neck,  are  directed  obliquely  over  the  sides,  and  are  for  the  most  part 
continued  by  the  facial  part  as  previously  described. 

The  stemo-cephalicus  is  well  developed.  It  arises  on  the  manubrium  sterni, 
diverges  from  its  fellow,  and  ends  on  the  mastoid  process,  blending  with  the  cleido- 
cervicalis.  It  may  be  termed  the  sterno-mastoideus.  It  is  crossed  superficially 
by  the  external  jugular  vein. 

The  scalenus  ventralis  (s.  primse  costae)  arises  on  the  last  four  cervical  trans- 
verse processes,  and  is  inserted  into  the  first  rib. 

The  scalenus  dorsalis  (s.  supracostalis)  is  large.  It  blends  with  the  preceding 
muscle  in  front,  and  divides  into  two  parts  posteriorly.  The  dorsal  part  is  inserted 
on  the  third  and  fourth  ribs,  the  ventral  part  by  a  long,  thin  tendon  on  the  seventh 
or  eighth  rib. 

The  longus  colli  resembles  that  of  the  horse. 

The  rectus  capitis  ventralis  major  arises  on  the  transverse  processes  of  the 
second  to  the  sixth  cervical  vcrtebrse  and  ends  as  in  the  horse.  The  rectus  capitis 
ventralis  minor  and  rectus  capitis  lateralis  resemble  those  of  the  horse. 

The  intertransversales  resemble  those  of  the  ox. 

The  splenius  is  strong  and  extensive.  It  arises  on  the  first  four  or  five  thoracic 
spines  and  the  median  raphe  of  the  neck,  and  is  inserted  into  the  nuchal  crest  and 
mastoid  process. 

The  complexus  is  composed  of  dorsal  and  ventral  parts — the  biventer  cervicis 
and  the  complexus  major.  The  biventer  cervicis  arises  from  the  transverse  proc- 
esses of  the  fifth  and  sixth,  and  the  spines  of  the  second  to  the  fifth  (or  sixth) 
thoracic  vertebrae,  from  the  ligamentum  nuchse,  and  the  median  raphe.  It  has 
four  oblique  tendinous  intersections.  The  complexus  major  arises  on  the  trans- 
verse processes  of  the  first  three  or  four  thoracic  vertebrae  and  the  articular 
processes  of  the  last  five  cervical.  Both  end  on  a  strong  common  tendon  which  is 
inserted  into  the  nuchal  crest  and  the  depression  below  it. 

The  longissimus  capitis  et  atlantis  consists  of  two  unequal  parts.  The  large 
dorsal  part,  the  longissimus  capitis,  arises  from  the  transverse  processes  of  the  first 
four  thoracic  and  the  articular  process  of  the  last  three  or  four  cervical  vertebrae, 
and  ends  with  the  splenius  on  the  mastoid  process  of  the  temporal  bone.  The 
small  ventral  part,  the  longissimus  atlantis,  arises  from  the  articular  processes  of 
the  third,  fourth,  and  fifth  cervical  vertebrae,  and  ends  on  the  wing  of  the  atlas. 

The  other  muscles  present  no  striking  differential  features,  but  it  may  be  noted 
that  distinct  interspinales  are  present.  There  are  also  small  muscular  bundles 
which  lie  beneath  the  multifidus  in  the  back.  These  extend  from  the  transverse 
process  of  one  vertebra  to  the  spine  of  the  preceding  one,  and  are  appropriately 
termed  the  submultifidus. 


Muscles  of  the  Thorax 

There  are  twelve  pairs  of  levatores  costarum. 

The  external  intercostal  muscles  do  not  occupy  the  spaces  between  the  costal 
cartilages. 

The  diaphragm  is  very  strongly  curved,  and  has  a  small  tendinous  center. 
The  hiatus  oesophageus  is  between  the  crura  and  is  ventral  to  the  twelfth  thoracic 
vertebra.     The  costal  part  is  attached  to  the  lower  (horizontal)  part  of  the  ninth 


MUSCLES    OF   THE    ABDOMEN 


377 


costal  cartilage,  to  the  tenth  and  eleventh  cartilages  a  little  (ca.  1  to  2  cm.)  below 
the  junction  with  the  rib,  to  the  twelfth  rib  at  its  ventral  end  and  to  the  last  rib 
below  its  middle.  The  cupola  is  very  unsymmetrical ;  on  the  left  side  it  is  opposite 
the  sixth  rib,  while  on  the  right  it  is  an  intercostal  space  further  back. 


Muscles  of  the  Back  and  Loins 

The  serratus  dorsalis  anterior  arises  from  the  median  raphe  of  the  neck  and  the 
first  six  or  seven  thoracic  spines,  and  is  inserted  into  the  second  to  the  ninth  ribs. 
It  is  well  developed.  The  serratus  dorsalis  posterior — much  weaker — arises  from 
the  lumbo-dorsal  fascia,  and  is  inserted  into  the  last  three  or  four  ribs.  Thus  one 
or  two  ribs  intervene  between  the  two. 

The  longissimus  costarum  is  well  developed,  and  extends  from  the  ilium  to  the 
sixth,  fifth,  or  fourth  cervical  vertebra. 

The  longissimus  dorsi  resembles  that  of  the  other  animals,  but  the  spinalis  et 
semispinalis  separates  clearly  from  the  longissimus  proper  at  the  sixth  or  seventh 
thoracic  vertebra.  It  is  inserted  into  the  articular  and  spinous  processes  of  the 
last   six  cervical   vertebrae. 

It  has  no  depression  in  the  ~\  ^ 

lumbar  region  for  the  glu- 
teus medius. 

The  intertransversales 
are  fleshy,  as  in  the  ox. 

The  interspinales  are 
distinct  and  are  most  devel- 
oped in  the  lumbar  region. 


Muscles  of  the  Tail 

These  present  the 
same  general  arrangement 
as  in  the  horse.  The  sacro- 
coccygei,  however,  arise  on 
the  lumbar  vertebrae  also, 
and  the  coccygeus  on  the 
ischiatic  spine.  There  is  a 
sacro-coccygeus  accessor- 
ius,  which  arises  on  the 
medial  border  of  the  ilium, 
the  edge  of  the  sacrum,  and 
the  transverse  processes  of 
the  first  coccygeal  vertebra,  and  is  inserted  between  the  dorsal  and  lateral  sacro- 
coccygei.     It  is  homologous  with  the  intertransversales. 


Fig.  325. — Muscles  of  Tail,  Anus,  and  Genital  Organs  of  Dog. 
/,  Ilium;  ^,  femur;  3,  tuber  ischii;  4,  sacro-sciatic  ligament;  5,  aacral 
region;  6,  tail;  7,  penis;  8,  anus;  9,  rectum;  a,  sacro-coccygeus  dorsalis; 
h,  sacro-coccygeus  accessorius;  c,  coccygeus;  d,  sacro-coccygeus  ventralis;  e, 
retractor  ani;  /,  /',  sphincter  ani  externus;  g,  retractor  penis;  h,  bulbo- 
cavernosus;  i,  transversus  perinei  (?) ;  k,  m,  ischio-urethrales;  I,  ischio- 
cavernosus;  n,  tendon  of  obturator  internus;  o,  gemellus,  p,  urethral 
muscle.     (After  EUenberger,  in  Leisering's  Atlas.) 


Muscles  of  the  Abdomen 

The  abdominal  tunic  is  practically  absent. 

The  obliquus  abdominis  externus  has  an  extensive  fleshy  part.  It  arises  from 
the  last  eight  or  nine  ribs  and  the  lumbo-dorsal  fascia. 

The  obliquus  abdominis  internus  arises  from  the  tuber  coxae  and  the  lumbo- 
dorsal  fascia.     The  fibers  have  an  almost  vertical  direction,  and  there  is  a  fleshy  at- 


378  THE   MUSCLES    OF   THE    DOG 

tachment  to  the  last  rib.  The  anterior  part  of  the  aponeurosis  divides  into  two 
layers,  which  concur  in  the  formation  of  the  internal  and  external  sheaths  of  the  rec- 
tus. 

The  rectus  abdominis  is  attached  by  a  long  tendon  on  the  first  five  or  six  costal 
cartilages,  and  by  fleshy  fibers  on  the  xiphoid  cartilage.  It  usually  has  five  ten- 
dinous inscriptions.  The  two  recti  diverge  very  gradually  in  front,  so  that  they  are 
about  half  an  inch  (ca.  1  cm.)  apart  in  the  xiphoid  region. 

The  transversus  abdominis  presents  no  special  features  except  that  the  poste- 
rior part  of  its  aponeurosis  splits  into  two  layers  which  include  the  rectus  between 
them. 


Muscles  of  the  Pelvic  Limb 

The  psoas  minor  arises  from  the  bodies  of  the  last  three  or  four  thoracic  and 
first  three  or  four  lumbar  vertebrae,  and  is  inserted  into  the  iliopectineal  line.  Its 
anterior  part  blends  with  the  quadratus  lumborum. 

The  psoas  major  is  relatively  small  and  short;  it  arises  from  the  last  three  or 
four  lumbar  vertebrae. 

The  lateral  head  of  the  iliacus  is  small,  while  the  medial  head  is  large  and  fuses 
with  the  psoas  major  to  constitute  an  ilio-psoas. 

The  quadratus  lumborum  is  well  developed,  and  extends  laterally  beyond  the 
edge  of  the  ilio-psoas.  It  arises  from  the  last  three  or  four  thoracic  vertebrae  in 
common  with  the  psoas  minor,  and  from  the  last  rib  and  the  lumbar  transverse 
processes,  and  ends  on  the  pelvic  surface  of  the  wing  of  the  ilium. 

The  tensor  fasciae  latae  arises  from  the  lateral  border  of  the  ilium  and  the 
gluteus  medius;  it  consists  of  two  parts.  The  anterior  part  is  long  and  rounded; 
the  posterior  is  shorter  and  fan-like. 

The  gluteus  superficialis  is  small.  It  arises  from  the  gluteal  fascia,  the  lateral 
part  of  the  sacrum,  first  coccygeal  vertebra,  and  sacro-sciatic  ligament.  It  is  in- 
serted below  and  behind  the  trochanter  major  of  the  femur,  on  the  lateral  branch  of 
the  linea  aspera.  In  some  cases  there  is  a  bursa  between  the  tendon  and  the  tro- 
chanter major. 

The  gluteus  medius  has  no  lumbar  portion.  It  is  inserted  into  the  trochanter 
major  by  a  strong  tendon.  There  is  a  bursa  under  the  tendon  of  insertion  which 
also  extends  under  the  gluteus  profundus. 

The  gluteus  profimdus  is  broad  and  fan-shaped.  It  arises  on  the  superior 
ischiatic  spine  and  on  the  ilium  as  far  forward  as  the  gluteal  line,  and  is  inserted 
into  the  trochanter  major  below  the  medius.^ 

The  piriformis  is  not  blended  with  the  gluteus  medius.  It  arises  from  the 
border  and  ventral  surface  of  the  sacrum  and  from  the  sacro-sciatic  ligament,  and 
ends  on  the  trochanter  major  with  or  close  to  the  gluteus  medius. 

The  obturators,  gemellus,  and  quadratus  femoris  resemble  in  arrangement 
those  of  the  horse,  and  present  no  notable  special  features.  There  is  a  large  bursa 
under  the  tendon  of  the  obturator  internus. 

The  biceps  femoris  has  two  heads  of  origin  which  soon  fuse.  The  larger  head 
arises  from  the  sacro-sciatic  ligament  and  tuber  ischii,  the  smaller  one  from  the  tuber 
ischii.  The  aponeurosis  of  insertion  ends  on  the  patella,  the  patellar  ligament, 
the  fascia  lata,  and  the  tibial  crest.  There  is  also  a  tendinous  band,  which  comes 
from  the  deep  face  of  the  muscle  and  terminates  at  the  tarsus,  as  in  the  horse. 
There  is  usually  a  bursa  between  the  muscle  and  the  trochanter  major. 

The  abductor  cruris  posterior  may  be  regarded  as  an  accessory  head  of  the 
biceps  femoris.     It  is  a  thin  muscular  band  which  arises  from  the  sacro-sciatic 

^  Lesbre  maintains  that  this  is  the  scansorius,  and  that  the  gluteus  profundus  is  so  intimately 
united  with  the  medius  as  to  have  been  regarded  by  anatomists  as  part  of  the  latter. 


MUSCLES    OF   THE    PELVIC    LIMB 


379 


ligament,  passes  downward  between  the  biceps  and  semimembranosus,  and  ends  by 
blending  with  the  former. 

The  semitendinosus  arises  from  the  tuber  ischii  only.  It  ends  on  the  crest  and 
medial  surface  of  the  tibia. 

The  semimembranosus  is  large  and  arises  from  the  ischium  only.  It  divides 
into  two  parts :  the  anterior  part  ends  on  the  tendon  of  the  pectineus,  on  the  femur 
above  the  medial  condyle,  and  on  the  medial  sesamoid  bone;  the  posterior  part 


Fig.  326. — Muscles  of  Pelvic  Limb  op  Dog;  Medial  View. 
a,  Ilio-psoas;  b,  tendon  of  psoas  minor;  c,  sacro-coccy- 
geus  ventralis  lateralis;  d,  coccygeus;  e,  piriformis;  /,  obtur- 
ator internus;  g,  origin  of  retractor  ani;  h,  h',  sartorius;  i,  rec- 
tus femoris;  k,  vastus  medialis;  I,  pectineus;  m,  adductor; 
n,  gracilis;  o,  semitendinosus;  p,  semimembranosus;  q,  gas- 
trocnemius, medial  head;  q',  tendon  of  gastrocnemius;  r, 
superficial  digital  flexor;  r',  tendon  of  r;  s,  tarsal  tendon 
of  biceps  femoris;  t,  popliteus;  u,  flexor  hallucis  longus;  u', 
long  digital  flexor;  u",  common  tendon  of  u  and  u';  v,  tendon 
of  tibialis  posterior;  w,  tibialis  anterior;  x,  tendon  of  long 
digital  extensor;  1,  pelvic  surface  of  ilium;  S,  section  of  sym- 
physis pelvis;  3,  tuber  ischii;  4.  medial  condyle  of  femur; 
5,  ligamentum  patellae;  6,  7,  medial  surface  of  tibia;  8,  tarsus; 
S',  fibular  tarsal  bone;  9,  metatarsus.  (EUenberger-Baum, 
Anat.  d.  Ilundes.) 


ends  on  the  medial  condyle  of  the  tibia,  the  tendon  passing  under  the  medial  liga- 
ment of  the  stifle  joint. 

It  is  not  possible  clearly  to  separate  the  quadriceps  femoris  into  four  heads. 
The  vastus  lateralis  is  so  much  larger  than  the  vastus  medialis  as  to  indicate  that 
the  vastus  intermedius  is  incorporated  with  the  former.  The  rectus  femoris  has 
only  one  tendon  of  origin.  There  is  a  bursa  under  the  muscle  at  the  distal  third 
of  the  femur.  The  single  patellar  ligament  acts  as  the  tendon  of  insertion  of  the 
quadriceps. 


380  THE   MUSCLES    OF   THE    DOG 

The  capsularis  is  usually  present,  but  is  small  and  pale. 

The  sartorius  consists  of  two  parts.  The  anterior  part  arises  from  the  tuber 
coxee  and  its  flat  tendon  ends  on  the  patella.  The  posterior  part  arises  from  the 
lateral  border  of  the  ilium  and  ends  on  the  medial  surface  of  the  tibia,  its  tendon 
blending  with  that  of  the  gracilis.  The  anterior  part  is  superficial  in  front  of  the 
tensor  fascise  latse  and  forms  here  the  anterior  contour  of  the  thigh. 

The  graciles  are  not  so  much  fused  at  their  origin  as  in  the  other  animals. 
Its  anterior  part  is  thin.  Its  broad  tendon  is  inserted  into  the  tibial  crest,  and 
blends  ^\ath  those  of  the  sartorius  and  semitendinosus. 

The  pectineus  is  long  and  slender.  It  arises  from  the  ilio-pectineal  eminence 
and  ends  on  the  medial  branch  of  the  linea  aspera  above  the  distal  end  of  the  femur. 

The  adductor  femoris  is  a  large  muscle  which  arises  on  the  ventral  surface  of 
the  pubis  and  ischium;  it  ends  on  the  linea  aspera  of  the  femur  and  the  medial 
surface  of  the  stifle.     It  is  commonly  separable  into  two  parts. 

The  peroneus  tertius  is  represented  by  a  tendinous  band  which  arises  on  the 
medial  surface  of  the  tibia  below  the  crest.  It  passes  on  the  medial  surface  of  the 
tibialis  anterior,  blends  with  the  annular  ligament  above  the  tarsus,  and  is  attached 
to  the  joint  capsule  and  the  proximal  end  of  the  third  metatarsal  bone. 

Arloing  and  Lesbre  say:  "The  third  peroneus  is  a  proper  extensor  of  the  fifth  digit;  it 
is  a  very  feeble,  fleshy  band,  situated  behind  the  peroneus  bre^^s,  which  it  partially  covers.  It 
is  attached  to  the  upper  part  of  the  fibula,  and  is  continued  by  a  long,  delicate  tendon  which 
passes  in  the  same  malleolar  groove  with  the  muscle  mentioned;  it  then  crosses  behind  the  tendon 
of  the  peroneus  longus  and  extends  to  the  phalanges  of  the  outer  digit,  where  it  joins  one  of  the 
branches  of  the  common  extensor." 

The  tibialis  anterior  is  large  and  superficial.  It  arises  on  the  lateral  condyle 
and  crest  of  the  tibia,  and  is  inserted  into  the  first  metatarsal  bone,  or  into  the 
first  tarsal  and  second  metatarsal. 

There  are  four  extensors  of  the  digits. 

1.  The  long  digital  extensor  (M.  extensor  digitalis  longus)  is  fusiform,  and  lies 
largely  under  the  preceding  muscle.  It  arises  from  the  extensor  fossa  of  the  femur. 
The  tendon  is  bound  do"\vn  by  two  annular  ligaments:  the  proximal  one,  at  the 
distal  end  of  the  tibia,  encloses  also  the  tendon  of  the  tibialis  anterior;  the  distal 
one  is  at  the  lower  part  of  the  tarsus.  The  tendon  divides  at  the  tarsus  into 
four  branches,  which  end  on  the  distal  phalanges  of  the  digits  (second  to  fifth). 

2.  The  lateral  digital  extensor  {M.  extensor  digitalis  pedis  lateralis  s.  digiti 
quinti)  has  a  small,  unipennate  belly  which  is  covered  by  the  peroneus  longus 
and  the  deep  digital  flexor.  It  arises  on  the  fibula  below  the  head.  The  tendon 
descends  behind  that  of  the  peroneus  longus,  inclines  forward  under  the  lateral 
ligament  of  the  tarsus  and  the  peroneus  tendon,  and  joins  the  branch  of  the 
tendon  of  the  long  extensor  for  the  fifth  digit. 

3.  The  extensor  hallucis  longus  is  a  very  thin  muscle  which  arises  from  the 
fibula  under  the  long  extensor.  Its  delicate  tendon  accompanies  that  of  the  tibialis 
anterior  to  the  first  metatarsal  bone,  or  becomes  lost  in  the  fascia. 

4.  The  extensor  digitalis  brevis  has  three  divisions.  It  arises  on  the  fibular 
tarsal  bone  and  the  adjacent  ligaments.  The  three  tendons  are  inserted  into 
the  second,  third,  and  fourth  digits,  blending  with  the  interossei.  (Sometimes 
there  is  a  tendon  for  the  rudimentary  first  digit,  which  may  represent  the  extensor 
hallucis  brevis.     There  may  be  a  fourth  belly  for  the  tendon  to  the  second  digit.) 

The  peroneus  longus  arises  on  the  lateral  condyle  of  the  tibia,  the  head  of 
the  fibula,  and  the  lateral  ligament.  The  belly  does  not  extend  to  the  middle  of 
the  leg,  and  the  long  tendon  passes  down  the  leg  parallel  to  the  fibula.  It  is  bound 
down  in  the  groove  of  the  lateral  malleolus  by  an  annular  ligament,  crosses  the 
plantar  surface  of  the  tarsus  transversely,  and  ends  on  the  first  metatarsal  bone. 

The  peroneus  brevis  is  unipennate  and  arises  from  the  distal  half  or  more 


MUSCLES    OF    THE    PELVIC    LIMB 


381 


of  the  lateral  face  of  the  tibia  and  the  fibula.  Its  tendon  accompanies  that  of 
the  lateral  extensor  over  the  lateral  malleolus,  and  ends  on  the  proximal  end  of  the 
fifth  metatarsal  bone. 

The  soleus  is  absent.     (It  is  present  and  large  in  the  cat.) 

The  gastrocnemius  arises  from  the  rough  lines  above  the  condyles  of  the 
femur.  The  origin  of  each  head  contains  a  sesamoid 
bone  about  the  size  of  a  pea  (Os  sesamoideum  m.  gas- 
trocnemii),  which  articulates  with  the  corresponding 
condyle  of  the  femur.  The  tendon  comports  itself  as 
in  the  horse. 

The  superficial  digital  flexor  has  a  large  round 
belly.  It  arises  in  common  with  the  lateral  head  of 
the  gastrocnemius  from  the  lateral  rough  line  and  sesa- 
moid bone,  and  from  the  aponeurosis  of  the  vastus 
lateralis.  The  tendon  winds  around  that  of  the  gas- 
trocnemius, passes  over  the  tuber  calcis  (where  it  is 
arranged  as  in  the  horse) ,  and  divides  below  the  tarsus 
into  two  branches.  Each  of  these  divides  into  two 
branches  which  end  as  in  the  forelimb.  The  lateral 
and  medial  branches  detach  slips  to  the  suspensory 
ligaments  of  the  large  digital  pad.  Muscle-fibers 
often  occur  in  the  tendon  in  the  metatarsal  region. 

The  deep  digital  flexor  has  two  heads.  The  large 
lateral  head,  the  flexor  hallucis  longus,  arises  from  the 
posterior  surface  of  the  tibia  and  fibula,  filling  the  in- 
terosseous space.  The  small  medial  head,  flexor  digi- 
talis pedis  longus,  also  arises  from  the  tibia  and  fibula; 
its  tendon  passes  through  the  groove  on  the  medial 
malleolus,  inclines  backward  in  its  descent  over  the 
tarsus,  and  joins  that  of  the  large  head  below  the 
tarsus.  The  common  tendon  detaches  a  branch  to 
the  large  digital  pad  and  terminates  as  in  the  forelimb. 

The  tibialis  posterior  is  a  very  small  but  distinct 
muscle,  which  arises  on  the  proximal  part  of  the  fibula. 
The  deUcate  tendon  accompanies  that  of  the  flexor 
longus  and  ends  on  the  medial  ligament  of  the  tarsus. 

The  tendon  of  origin  of  the  popliteus  contains  a 
small  sesamoid  bone. 

The  adductors  of  the  second  and  fifth  digits,  the 
lumbricales,  and  the  interossei  are  arranged  as  in  the 
thoracic  limb. 

The  quadratus  plantae  arises  on  the  lateral  surface 
of  the  distal  end  of  the  fibular  tarsal  bone  and  on  the 
lateral  tarsal  ligament,  passes  downward  and  inward, 
and  terminates  on  a  thin  tendon  which  fuses  with  that 
of  the  deep  flexor. 

The  abductor  digiti  quinti  is  a  very  small  muscle 
which  consists  of  two  parts.  One  of  these  is  a  tendin- 
ous slip  which  extends  from  the  plantar  surface  of  the 
proximal  part  of  the  fibular  tarsal  bone  to  the  head  of 
the  fifth  metatarsal  bone;  the  other  part  arises  from 

the  medial  surface  of  the  fibular  tarsal  bone  (or  from  the  tendinous  part)  and  ends 
on  the  first  phalanx  of  the  fifth  digit. 

In  case  the  skeleton  of  the  first  digit  is  well  developed,  there  are  three  muscles 


Fig.  327. — Muscles  op  Leg  and 
Foot  of  Dog;  Lateral  View. 
a.  Quadriceps  femoris;  b,  gas- 
trocnemius, lateral  head;  c,  super- 
ficial digital  flexor;  d,  deep  digital 
flexor;  e,  peroneus  longus;  /,  ten- 
don of  lateral  extensor;  g,  peroneus 
brevis;  h,  long  digital  extensor;  h', 
h",  h'",  tendons  of  preceding;  i, 
tibialis  anterior;  k,  extensor  brevis; 
I,  slips  from  interossei  (m);  1,  lateral 
condyle  of  femur;  2,  patella;  3, 
tibia;  4,  tuber  calcis;  5,  6,  annular 
ligaments.  (After  Ellenberger,  in 
Leisering's  Atlas.) 


382  THE   MUSCLES    OF   THE    DOG 

which  are  homologous  with  those  of  the  same  digit  in  the  forehmb.     These  are 
the  abductor  hallucis,  adductor  hallucis,  and  flexor  hallucis  brevis. 

The  principal  bursse  and  synovial  sheaths  of  the  muscles  of  the  leg  and  foot  are  as  follows: 
The  tibialis  anterior  has  a  bursa  under  its  tendon  at  the  tarsus.  A  pouch  of  the  synovaal  membrane 
of  the  stifle  joint  underlies  the  tendon  of  origin  of  the  extensor  digitalis  longus,  and  is  partially 
reflected  upon  the  superficial  face  of  the  tendon;  the  tendons  of  insertion  are  provided  with  a 
sjTiovial  sheath  wliich  begins  at  the  end  of  the  muscular  part  and  extends  to  the  proximal  part  of 
the  metatarsus.  The  tendons  of  the  lateral  digital  extensor  and  peroneus  bre\ns  have  a  common 
syno\'ial  sheath  at  the  distal  end  of  the  leg  and  proximal  part  of  the  tarsus.  The  tendon  of  the 
peroneus  longus  has  a  syno^'ial  sheath  wliich  begins  an  inch  or  more  above  the  lateral  malleolus 
(in  a  good-sized  dog)  and  extends  about  to  the  middle  of  the  tarsus;  another  sheath  envelops  the 
tendon  to  the  point  where  it  bends  round  to  the  plantar  surface  of  the  hock;  a  bursa  lies  between 
the  tendon  and  the  joint  capsule  and  fourth  tarsal  bone,  and  communicates  with  the  joint  ca^'ity. 
A  bursa  underlies  the  terminal  part  of  the  tendon  of  the  peroneus  brev-is.  There  is  a  bursa  in 
front  of  the  distal  part  of  the  tendon  of  the  gastrocnemius;  it  extends  an  inch  or  more  (in  large 
dogs)  above  the  tuber  calcis.  A  bursa  underUes  the  superficial  flexor  tendon  at  the  tarsus;  in  large 
dogs  it  extends  about  an  inch  above  and  below  the  tuber  calcis.  The  tendon  of  the  tibialis  posterior 
has  a  synovial  sheath  at  the  distal  end  of  the  leg.  The  tendon  of  the  flexor  digitalis  longus  has  a 
synovial  sheath  which  begins  a  httlc  above  the  medial  malleolus  and  extends  to  the  junction  -with 
the  tendon  of  the  flexor  hallucis.  The  tarsal  sheath  of  the  flexor  hallucis  begins  (in  large  dogs) 
about  an  inch  and  a  half  above  the  level  of  the  medial  malleolus  and  extends  to  the  distal  end  of 
the  tarsus;  it  communicates  wth  the  tibio-tarsal  joint  cavity.  The  synovial  apparatus  in  the 
distal  part  of  the  hmb  resembles  that  of  the  forelimb. 


SPLANCHNOLOGY 

This  branch  deals  with  the  viscera  of  the  digestive,  respiratory,  and  uro- 
genital systems.^  Each  of  these  systems  consists  fundamentally  of  a  tube  or  tract 
which  is  lined  with  mucous  membrane  (Tunica  mucosa)  and  communicates  with 
the  exterior  at  one  end  or  both.  Thus  the  epithelium  of  the  mucous  membranes 
is  continuous  with  the  epidermis  at  the  various  natural  openings.  In  addition  to 
this  fundamental  part  there  are  to  be  considered  aggregations  of  secreting  cells 
known  as  glands,  muscular  tissue,  fibrous  membranes,  serous  membranes,  vessels 
and  nerves. 

Mucous  Membranes. — These  vary  much  in  thickness,  color,  and  other  char- 
acters. In  many  places  they  form  folds  (Plicae  mucosae)  which  may  be  temporary 
or  permanent.  In  other  places  they  form  ridges  (Rugse).  With  certain  excep- 
tions they  are  moistened  by  a  viscid  secretion,  termed  mucus,  which  is  derived 
from  glands  or  goblet  cells  of  the  epithelium.  The  membrane  consists  of  two  dis- 
tinct parts :  the  epithelium,  which  forms  the  free  surface  and  is  protective  and  secre- 
tory; and  the  lamina  propria,  a  layer  of  connective  tissue  which  contains  and  sup- 
ports the  peripheral  ramifications  of  the  vessels  and  nerves.  The  mucous  mem- 
brane is  connected  with  surrounding  structures  by  areolar  submucous  tissue 
(Tela  submucosa).  In  many  places  there  is  a  layer  of  unstriped  muscle,  the  mus- 
cularis  mucosae,  in  the  deepest  part  of  the  mucous  membrane.  In  many  situa- 
tions the  tunica  propria  presents  numerous  elevations,  known  as  papillae.  When 
small  (microscopic),  the  papillae  do  not  modify  the  surface  of  the  mucous  membrane, 
since  the  epithelium  levels  up  the  depressions  between  them,  but  when  large  (ma- 
croscopic), they  are  conspicuous  surface  features,  and  are  named  according  to  their 
shape  as  conical,  foliate,  etc. 

Glands. — The  term  gland  (Glandula)  is  usually  understood  to  mean  an  aggre- 
gation of  epithelial  cells,  the  secretion  of  which  is  extruded  on  the  free  surface  of  the 
membrane,  or  is  conveyed  away  in  the  blood  or  lymph  stream.^  Glands  are  divided 
according  to  their  form  into  two  chief  classes,  tubular  and  alveolar,  each  of  which 
may  be  simple  or  compound ;  many,  however,  combine  the  characters  of  both  tj'pes 
and  are  termed  tubulo-alveolar  or  alveolo-tubular.  A  simple  tubular  gland  is  a  cylin- 
drical depression  lined  by  epithelium  which  is  continuous  with  that  of  the  surround- 
ing mucous  membrane,  from  which  it  developed  originally  as  an  outgrowth.  The 
deeper  part  of  such  a  gland  is  termed  the  ftmdus,  and  here  the  epithelium  is  differ- 
entiated and  has  taken  on  secretory  function.  The  more  superficial  part  which 
conveys  the  secretion  to  the  surface  is  called  the  duct;  in  it  the  epithelium  resembles 
more  or  less  closely  that  of  the  surrounding  surface.  Many  glands  are  microscopic, 
while  others  are  large  organs.  The  larger  ones  are  composed  of  subdivisions  known 
as  lobules  (Lobuli),  which  are  held  together  by  areolar  interlobular  tissue;  each 
lobule  has  its  duct  and  by  the  union  of  these  ducts  there  is  formed  an  excretory 
duct  (Ductus  excretorius),  through  which  the  secretion  is  conveyed.     Some  glands 

1  The  term  viscus  is  applied  in  general  to  the  organs  which  are  contained  in  the  body  cavities. 
It  is  usual  to  exclude  the  heart,  except  when  considering  the  thoracic  organs  topographically. 
Certain  other  organs  which  do  not  belong  to  these  systems  are  usually  considered  with  them  as  a 
matter  of  convenience. 

2  But  unicellular  glands  are  recognized  in  lower  forms,  and  in  higher  forms  the  goblet-cells 
of  many  mucous  membranes  have  the  same  function.  Other  organs  which  are  not  epithelial  in 
structure  are  commonly  classed  as  glands;  such,  for  example,  are  the  lymph  glands  and  nodules, 
the  thymus,  and  the  spleen.  They  are  usually  termed  ductless  or  vascular  glands,  and  are  des- 
cribed with  the  organs  with  which  they  are  associated  anatomically. 

383 


384  SPLANCHNOLOGY 

consist  of  divisions  of  a  larger  order  which  are  known  as  lobes  (Lobi) ;  these  may  be 
separated  by  layers  of  connective  tissue  (Septa  interlobares)  or  by  fissures  (In- 
cisurse  interlobares). 

There  is  no  correspondence  between  the  size  of  a  gland  and  the  number  of  its  excretory  ducts. 
Thus  the  largest  gland  in  the  body,  the  liver,  has  a  single  excretory  duct,  while  some  small  glands 
have  many. 

Muscular  Tissue.— Most  of  the  hollow  organs  are  provided  with  a  muscular 
coat  (Tunica  muscularis)  outside  of  the  mucous  membrane.  This  is  in  great  part 
composed  of  strata  of  unstriped  muscle,  but  in  certain  places — and  especially  in  the 
vicinity  of  the  natural  apertures- — it  consists  of  striped  muscle.  Some  of  the  solid 
organs  contain  muscular  tissue  in  their  capsule  or  stroma. 

Fibrous  Membranes. — Many  viscera  are  enclosed  by  a  fibrous  coat  (Tunica 
fibrosa).  In  the  case  of  glands  such  an  enveloping  membrane  is  usually  called  the 
capsule.  Other  membranes  of  a  like  character  are  known  as  a  tunica  albuginea 
or  timica  adventitia;  the  former  consist  mainly  of  dense  white  fibrous  tissue,  while 
the  latter  usually  contain  many  elastic  fibers  and  are  looser  in  texture. 

Serous  Membranes. — These  are  thin  membranes  which  line  the  body-cavities 
and  cover  more  or  less  the  external  surface  of  the  viscera  contained  therein.^  They 
include  the  peritoneum  in  the  abdomen,  and  the  pleura  and  the  deep  layer  of  the 
pericardium  in  the  thorax.  Their  free  surface  is  formed  by  a  mesothelium  of 
flat  cells;  it  is  smooth  and  glistening  and  is  moistened  by  a  film  of  serum,  thus  re- 
ducing friction  to  a  minimum.  The  external  surface  is  in  most  places  connected 
with  the  structure  covered  by  areolar  subserous  tissue  (Tela  subserosa)  which 
often  contains  fat.  The  part  which  lines  the  wall  of  a  cavity  is  termed  the  parietal 
layer  (Lamina  parietalis),  while  the  visceral  layer  (Lamina  visceralis)  is  that  which 
forms  the  serous  coat  (Tunica  serosa)  of  the  viscera.  Double  layers  which  connect 
viscera  with  the  wall  or  with  each  other  are  in  general  called  serous  folds  (Phcse 
serosae)  or  serous  ligaments  (Ligamenta  serosa) ,  but  many  special  terms  are  in  use 
and  will  be  referred  to  later. 

1  The  serous  membranes  form  closed  sacs,  except  in  the  female,  in  which  case  the  uterine 
tubes  open  into  the  peritoneal  cavity  and  also  communicate  indirectly  with  the  exterior. 


THE  DIGESTIVE  SYSTEM 

This  apparatus  (Apparatus  digestorius)  consists  of  the  organs  directly  con- 
cerned in  the  reception  and  digestion  of  the  food,  its  passage  through  the  body, 
and  the  expulsion  of  the  unabsorbed  portion.  These  organs  are  conveniently 
grouped  under  two  heads,  viz.:  (1)  the  alimentary  canal;  (2)  the  accessory  organs. 

The  alimentary  canal  (Tractus  alimentarius)  is  a  tube  which  extends  from  the 
lips  to  the  anus.  It  has  a  complete  lining  of  mucous  membrane,  external  to  which 
is  an  almost  continuous  muscular  coat.  The  abdominal  portion  of  the  tube  is 
largely  covered  with  a  serous  membrane — the  visceral  peritoneum.  The  canal 
consists  of  the  following  consecutive  segments:  (1)  The  mouth;  (2)  the  pharynx; 
(3)  the  oesophagus;  (4)  the  stomach;  (5)  the  small  intestine;  (6)  the  large  intestine. 

The  accessory  organs  are  the  teeth,  tongue,  salivary  glands,  liver,  and  pancreas. 


DIGESTIVE  SYSTEM  OF  THE  HORSE 

THE  MOUTH 

The  mouth^  (Cavum  oris)  is  the  first  part  of  the  alimentary  canal.  It  is 
bounded  laterally  by  the  cheeks;  dorsally,  by  the  palate;  ventrally,  by  the  body  of 
the  mandible  and  the  mylo-hyoid  muscles;  behind,  by  the  soft  palate.  In  the 
horse  it  is  a  long,  cylindrical  cavity,  and  when  closed,  it  is  almost  entirely  filled  up 
by  the  contained  structures;  a  small  space  remains  between  the  root  of  the  tongue, 
the  soft  palate,  and  the  epiglottis;  this  may  be  termed  the  glosso-epiglottic  space. 
The  entrance  to  the  mouth  (Rima  oris)  is  closed  by  the  Hps. 

The  cavity  of  the  mouth  is  subdivided  into  two  parts  by  the  teeth  and  alveolar 
processes.  The  space  external  to  these  and  inclosed  by  the  lips  and  cheeks  is 
termed  the  vestibule  of  the  mouth  (Vestibulum  oris).  In  the  resting  state  of  the 
parts  the  walls  of  this  cavity  are  in  contact,  and  the  space  is  practically  obliterated. 
Its  existence  becomes  very  evident  in  facial  paralysis,  when  the  food  tends  to  collect 
in  it  laterally,  pouching  out  the  cheeks.  The  space  within  the  teeth  and  alveolar 
processes  is  termed  the  mouth  cavity  proper  (Cavum  oris  proprium).  When  the 
teeth  are  in  contact,  it  communicates  with  the  vestibule  only  by  the  interdental 
spaces  and  the  intervals  behind  the  last  molar  teeth.  Posteriorly  it  communicates 
with  the  pharynx  through  the  isthmus  faucium. 

The  mucous  membrane  of  the  mouth  (Tunica  mucosa  oris)  is  continuous  at 
the  margin  of  the  lips  with  the  common  integument,  and  behind  with  the  mucous 
lining  of  the  pharynx.  During  life  it  is  chiefly  of  a  pink  color,  but  may  be  more 
or  less  pigmented. 

The  lips  (Labia  oris)  are  two  musculo-membranous  folds  which  surround  the 
orifice  of  the  mouth.  Their  angles  of  union  (Anguli  oris  s.  commissurse  labiorum) 
are  situated  near  the  first  cheek  tooth  and  are  rounded.  Each  lip  presents  two 
surfaces  and  two  borders.  The  external  surface  is  covered  by  the  skin,  which  pre- 
sents long  tactile  hairs  in  addition  to  the  ordinary  fine  hair.  The  upper  lip  has 
a  shallow  median  furrow  (Philtrum),  the  lower  a  rounded  prominence,  the  chin 

^  The  term  "mouth"  is  commonly  used  to  signify  either  the  cavity  (Cavum  oris)  or  the 
entrance  to  it  (Rima  oris). 

25  385 


386 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


THE   MOUTH  387 

(Mentum).  The  internal  surface  is  covered  with  mucous  membrane  which  is  com- 
monly more  or  less  pigmented.  The  small  papilla?  on  the  surface  show  on  their 
summits  the  openings  of  the  ducts  of  the  labial  glands.  Small  folds  of  mucous 
membrane  which  pass  from  the  lip  to  the  gum  form  the  fraenula  labii  (superioris, 
inferioris).  The  free  border  of  the  hp  is  dense  and  bears  short,  very  stiff  hairs. 
The  attached  border  is  continuous  with  the  surrounding  structures. 

Structure. — The  hps  are  covered  externally  by  the  skin,  and  are  lined  by 
mucous  membrane;  between  these  are  muscular  tissue,  glands,  vessels,  and  nerves. 
The  skin  lies  directly  on  the  muscles,  many  fibers  of  which  are  inserted  into  it.  The 
muscles  have  been  described  (p.  255).  The  labial  glands  (Glandula?  labiales) 
form  a  compact  mass  at  the  commissures;  they  are  numerous  in  the  upper  lip, 
fewer  in  the  lower.  The  mucous  membrane  is  often  pigmented,  and  is  reflected 
upon  the  bones  of  the  jaws  to  form  the  gums. 

Vessels  and  Nerves. — The  arteries  are  derived  from  the  superior  and  inferior 
labial  and  palato-labial  arteries.  The  veins  go  chiefly  to  the  external  maxillary 
vein.  The  Ij^mph  vessels  go  to  the  mandibular  lymph  glands.  The  sensory 
nerves  come  from  the  trigeminus,  and  the  motor  nerves  from  the  facial  nerve. 

The  cheeks  (Bucca)  form  the  sides  of  the  mouth,  and  are  continuous  in  front 
with  the  lips.     They  are  attached  to  the  alveolar  borders  of  the  bones  of  the  jaws. 

Structure. — This  comprises:  (1)  The  skin;  (2)  the  muscular  and  glandular 
layer;  (3)  the  mucous  membrane.  The  skin  offers  nothing  in  particular  to  notice. 
The  muscular  tissue  is  formed  mainly  by  the  buccinator,  but  also  by  parts  of  the 
cutaneus,  zygomaticus,  dilatator  naris  lateralis,  levator  nasolabialis,  and  depressor 
labii  inferioris.  The  buccal  glands  (Glandulse  buccales)  are  arranged  in  two  rows. 
The  superior  buccal  glands  lie  on  the  outer  surface  of  the  buccinator  muscle,  near 
its  upper  border.  The  anterior  part  of  the  row  consists  of  scattered  lobules;  the 
posterior  part,  which  lies  under  cover  of  the  masseter  muscle,  is  more  developed  and 
compact.  The  inferior  buccal  glands,  less  voluminous  than  the  upper,  are  situated 
in  the  submucous  tissue  at  the  lower  border  of  the  buccinator  muscle.  The  mucous 
membrane  is  reflected  above  and  below  upon  the  gums,  and  is  continuous  })ehind 
wdth  that  of  the  soft  palate.  It  is  reddish  in  color  and  frequently  shows  pigmented 
areas.  The  parotid  duct  opens  opposite  the  third  upper  cheek  tooth  on  a  papilla 
(Papilla  salivalis).  Linear  series  of  small  papillae  above  and  below  indicate  the 
orifices  of  the  small  ducts  of  the  buccal  glands. 

Vessels  and  Nerves. — The  blood-supply  is  derived  from  the  facial  and  bucci- 
nator arteries,  and  the  blood  is  carried  away  by  veins  of  the  same  name.  The  lymph 
vessels  go  to  the  mandibular  lymph  glands.  The  sensory  nerves  come  from  the 
trigeminus  and  the  motor  nerves  from  the  facial  nerve. 

The  gums  (Gingivae)  are  composed  of  a  dense  fibrous  tissue  which  is  intimately 
united  with  the  periosteum  of  the  alveolar  processes,  and  blends  at  the  edges  of 
the  alveoU  with  the  alveolar  periosteum;  the  latter  fixes  the  teeth  in  their  cavities. 
They  are  covered  by  a  smooth  mucous  membrane,  destitute  of  glands,  and  of  a 
low  degree  of  sensibility. 

The  hard  palate  (Palatum  durum)  is  bounded  in  front  and  on  the. sides  by 
the  alveolar  arches,  and  is  continuous  with  the  soft  palate  behind.  Its  osseous 
basis  is  formed  by  the  premaxilla,  maxilla,  and  palatine  bones.  The  mucous  mem- 
brane is  smooth,  and  is  attached  to  the  bones  by  a  submucosa  which  contains  in 
its  anterior  part  an  exceedingly  rich  venous  plexus,  constituting  an  erectile  tissue. 
A  central  raphe  (Raphe  palati)  divides  the  surface  into  two  equal  portions.  Each 
of  these  presents  about  eighteen  transverse  curved  ridges  (Rugae  palatini)  which 
have  their  concavity  and  their  free  edges  directed  backward.  They  are  further 
apart  and  more  prominent  anteriorly.  The  central  prominence  just  behind  the 
first  pair  of  incisors  is  the  papilla  incisiva ;  it  is  margined  by  a  fissure  on  each  side. 
There  are  no  glands  in  the  submucosa.     The  ductus  incisivus  (s.  ductus  nasopa- 


DIGESTIVE   SYSTEM    OF   THE   HORSE 


latinus)  is  a  small  tube  of  mucous  membrane  which  extends  very  obliquely  through 
the  palatine  fissure.  Its  ventral  or  palatine  end  is  blind  and  lies  in  the  submucous 
tissue  of  the  palate.  The  dorsal  or  nasal  end  communicates  with  the  nasal  cavity 
(in  common  with  the  vomero-nasal  organ)  by  a  slit-like  opening  in  the  anterior 
part  of  the  ventral  nasal  meatus. 

Vessels  and  Nerves. — The  blood-supply  is  derived  chiefly  from  the  palatine 

arteries  and  the  veins  go  to  the  vena  re- 
flexa.  The  nerves  come  from  the  tri- 
geminus. 

The  soft  palate  (Palatum  molle) 
is  a  musculo-membranous  curtain 
which  separates  the  cavity  of  the 
mouth  from  that  of  the  pharynx,  except 
during  swallowing.  It  slopes  down- 
ward and  backward  from  its  junction 
with  the  hard  palate.  The  oral  surface 
faces  ventrally  and  somewhat  forward, 
and  is  covered  with  a  mucous  mem- 
brane continuous  with  that  of  the  hard 
palate.  It  presents  a  rounded,  median 
ridge,  flanked  usually  by  a  sagittal  fold 
on  either  side.  Numerous  small  ducts 
of  the  palatine  glands  open  on  this  sur- 
face. On  each  side  a  short,  thick  fold 
passes  to  the  lateral  border  of  the 
tongue;  this  is  the  anterior  pillar  of 
the  soft  palate  (Arcus  glossopalatinus). 
The  pharjmgeal  surface  faces  dorsally 
and  a  little  backward  and  is  covered  by 
a  mucous  membrane  continuous  with 
that  of  the  nasal  cavity.  The  free  bor- 
der (Arcus  palatinus)  is  concave  and 
thin ;  it  is  in  contact  (except  during  deg- 
lutition) with  the  epiglottis.  It  is  con- 
tinued by  a  fold  of  the  mucous  mem- 
brane, which  passes  on  each  side  along 
the  lower  part  of  the  lateral  wall  of  the 
pharynx  and  unites  with  the  opposite 
fold  over  the  beginning  of  the  oesopha- 
gus; this  fold  is  termed  the  posterior 
pillar  of  the  soft  palate  (Arcus  pharyn- 
gopalatinus).  The  space  between  the 
diverging  anterior  and  posterior  pillars 
(Sinus  tonsillaris)  is  occupied  by  the 
tonsil  (Tonsilla  palatina) .  In  the  horse, 
however,  there  is  not  a  compact  tonsil, 
as  in  man,  dog,  etc.,  but  a  series  of 
masses  of  lymphoid  tissue  and  mucous 
glands  which  extend  backward  from 
the  root  of  the  tongue  on  either  side  a  distance  of  about  four  inches  (ca.  10  cm.). 
These  cause  elevations  of  the  surface,  on  which  there  are  depressions  (crypts)  in 
which  the  gland  ducts  open.  The  soft  palate  is  greatly  developed  in  equidse,  its 
average  length,  measured  medially,  being  about  six  inches  (15  cm.).  Its  length  and 
contact  with  the  epiglottis  may  account  for  the  fact  that  in  these  animals  mouth- 


FiG.  329. — Hard  Palate   and  Adjacent  Part  of  Soft 
Palate  of  Horse, 
1,  Raph6  of  palate;   2,  ridges  of  palate;   3,  soft  palate; 
I.  1,  I.  2,  first   and   second  incisor;   Di.  3,  deciduous  third 
incisor;    P.  1-4,  premolars;    M.  1-3,  molars. 


THE    MOUTH 


389 


breathing  does  not  occur  under  normal  conditions,  and  that  in  vomiting  the  ejected 
matter  escapes  usually  through  the  nasal  cavity.^ 

Structure.— The  soft  palate  consists  of:  (1)  The  oral  mucous  membrane, 
continuous  with  that  of  the  hard  palate,  which  it  resembles;  it  covers  also  a  narrow 
marginal  area  of  the  pharyngeal  surface  along  the  free  border;  (2)  the  palatine 
glands  (Glandular  palatini),  which  form  a  layer  about  half  an  inch  in  thickness; 
(3)  the  aponeurotic  and  muscular  layer;  (4)  the  pharjmgeal  mucous  membrane, 
continuous  with  that  of  the  nasal  cavity,  which  it  resembles. 


Septum  nasi        Dorsal  meatus 


Naso-lacrimal  duct 


Infraorbital  m  rrc 
and  v(  .ss(  Is 

Levator  labii  siipcri- 
oris  proprtus 


Superior  buccal 
nerve 
Facial  artery 

Superior  bucc(d 
glands 

Parotid  duct 


Labial  n 
Inferior  labial  ai 


Mylo-hyoidc 


Dorsal  turbinate 
Common  meatus 

Middle  meatus 

]'r)itral  lurbimite 

Veidral  meatus 

T — i\[(Lrillary  sinus 
J    {anterior  end) 

Palatine  artery 
Facial  artery 

Buccal  mucous 
membrane 

Buccinator 

Hypoglossal 
nerve 
Lingual  artery 

Buccinator  nerve 
Branches  of  lingual  nerve 

Mandibular  duct 
Sublingual  gland 


Digastricus      Sublingual  artery 


Fig.  330. — Cross-section  of  He.\d  op  Horse  .\t  Anterior  End  of  Facial  Crest. 

1,  Cavity  of  dorsal  turbinate;  ^,  cavity  of  ventral  turbinate;  3,  cavum  oris;    4^  4.  genio-glos.si;    o,  -5,  genio-hyoidei;  6, 

hyo-glossus;    7,  upper,  7',  lower,  fourth  cheek  tooth.     Line  to  facial  artery  crosses  zygomaticus. 


The  muscles  proper  to  the  soft  palate  are  the  palatinus,  the  levator  palati, 
and  the  tensor  palati. 

The  palatinus  (M.  palatinus)  consists  of  two  small  muscular  bundles  which 
lie  together  at  the  median  line.  It  is  attached  through  the  medium  of  the  palatine 
aponeurosis  to  the  palatine  bones,  and  terminates  near  the  free  edge  of  the  soft 
palate.  Usually  a  bundle  from  it  is  continued  a  short  distance  into  the  posterior 
pillar.     Its  action  is  to  shorten  the  soft  palate. 

The  levator  palati  (M.  levator  veli  palatini)  arises  from  the  muscular  process 

1  The  epiglottis  may  be  either  in  fi-ont  of  or  behind  the  soft  palate;  most  often  it  is  in  front 
(prevelar),  as  shown  in  Fig.  349. 


390  DIGESTIVE    SYSTEM    OF   THE    HORSE 

of  the  petrous  temporal  bone  and  from  the  lateral  lamina  of  the  Eustachian  tube, 
and  passes  at  first  forward,  lateral  to  the  latter;  it  then  inclines  ventral ly  across 
the  deep  face  of  the  anterior  pharjiigeal  muscles  and  turns  medially  into  the  soft 
palate,  in  which  it  spreads  out  above  the  glandular  layer.  It  raises  the  soft  palate, 
thus  closing  the  posterior  nares  during  deglutition. 

The  tensor  palati  (M.  tensor  veli  palatini)  is  larger  than  the  levator,  and  is 
fusiform  and  flattened.  It  arises  from  the  muscular  process  of  the  petrous  tem- 
poral bone,  the  pterygoid  bone,  and  the  lateral  lamina  of  the  Eustachian  tube, 
and  passes  forward,  lateral  to  the  levator,  across  the  medial  surface  of  the  origin  of 
the  pterygoideus  medialis.  Its  tendon  is  then  reflected  around  the  hamulus  of  the 
pterygoid  bone,  where  it  is  held  in  position  by  a  fibrous  band  and  lubricated  by  a 
bursa,  turns  inward  and  expands  in  the  aponeurosis  of  the  soft  palate.  It  tenses 
the  soft  palate. 

Vessels  and  Nerves. — The  blood-supply  of  the  soft  palate  is  derived  from  the 
internal  and  external  maxillary  arteries  and  the  blood  is  carried  away  by  the  corres- 
ponding veins.  The  lymph  vessels  go  to  the  pharyngeal  lymph  glands.  The  nerves 
come  from  the  trigeminus,  vagus,  and  glosso-pharyngeal  nerves. 

The  floor  of  the  mouth  in  its  anterior  part  is  free  and  is  formed  by  the  body  of 
the  mandible,  covered  by  mucous  membrane.  The  remainder  is  occupied  by  the 
attached  portion  of  the  tongue  in  the  undisturbed  state  of  the  parts.  The  follow- 
ing features  are  exposed  by  raising  the  tongue  and  drawing  it  to  one  side.  About 
opposite  the  canine  tooth  on  each  side  is  a  papilla,  the  canmcula  sublingualis, 
through  which  the  duct  of  the  mandibular  gland  opens.  Just  behind  these  papillae 
is  a  median  fold  of  mucous  membrane  which  passes  to  the  ventral  surface  of  the 
tongue,  constituting  the  frenum  linguae.  On  either  side  is  the  sublingual  fold 
(Plica  sublingualis)  which  extends  from  the  frenum  to  the  level  of  the  fourth  cheek 
tooth.  The  fold  indicates  the  position  of  the  underlying  sublingual  gland,  and 
presents  numerous  small  papillae,  through  which  the  ducts  open.  Behind  the  last 
tooth  a  vertical  fold  of  the  mucous  membrane  passes  from  upper  to  lower  jaw.  This 
is  termed  the  plica  pterygomandibularis ;    it  contains  a  ligament  of  like  name. 

The  isthmus  faucium  is  the  orifice  of  communication  between  the  mouth  and 
the  pharynx.  It  is  bounded  above  by  the  soft  palate,  below  by  the  root  of  the 
tongue,  and  laterally  by  the  anterior  pillars  of  the  soft  palate.  It  is  relatively 
small  and  not  very  dilatable  in  the  horse,  and  is  closed  by  the  soft  palate  under 
normal  conditions,  except  during  deglutition. 


THE  TONGUE 

The  tongue  (Lingua)  is  situated  on  the  floor  of  the  mouth,  between  the  rami  of 
the  mandible,  and  is  supported  mainly  in  a  sort  of  sling  formed  by  the  mylo-hyoid 
muscles.  Its  posterior  part,  the  root  (Radix  linguae),  is  attached  to  the  hyoid  bone, 
soft  palate,  and  pharynx.  Only  the  upper  surface  of  this  part  is  free,  and  slopes 
downward  and  backward.  The  middle  part,  the  body  (Corpus  linguae),  has  three 
free  surfaces.  The  dorsal  surface  is  slightly  rounded.  The  lateral  surfaces  are 
nearly  flat  for  the  most  part,  but  anteriorly  become  rounded  and  narrower.  The 
ventral  surface  is  attached  to  the  mandible.  The  apex  or  tip  (Apex  linguae)  is 
free,  spatula-shaped,  and  presents  upper  and  lower  surfaces  and  a  rounded  border. 
The  term  dorsum  linguae  is  applied  to  the  dorsal  surface;  it  is  free  throughout, 
and  in  the  resting  state  of  the  parts  is  in  contact  with  the  palate  except  at  the  glosso- 
epiglottic  space. 

Structure. — The  tongue  consists  of:  (1)  The  mucous  membrane;  (2)  the 
glands;    (3)  the  muscles;    (4)  vessels  and  nerves. 

The  mucous  membrane  (Tunica  mucosa  linguae)  adheres  intimately  to  the 
subjacent  tissue,  except  on  the  lower  part  of  the  lateral  surfaces  of  the  body  and 


THE    TONGUE 


391 


Thyroid 
gland 


the  ventral  surface  of  the  tip.  It  varies  considerably  in  thickness.  On  the  dorsum 
it  is  very  thick  and  dense ;  underneath  this  part  there  is  a  dense  fibrous  cord,  which 
extends  medially  a  distance  of  five  or  six  inches  forward  from  the  vallate  papillae. 
On  the  sides  and  ventral  surface  of  the  tongue  the  membrane  is  much  thinner  and 
smooth,  and  can  more  readily  be  dissected  off  the  muscular  tissue. ^  From  the 
lower  surface  of  the  free  part  of  the  tongue  a  fold  of  the  mucous  membrane  passes 
to  the  floor  of  the  mouth,  forming  the  frenum  linguae.  Posteriorly  a  fold  passes 
on  each  side  from  the  edge  of  the  dor- 
sum to  join  the  soft  palate,  forming  the 
anterior  pillars  of  the  latter.  A  thick 
central  glosso-epiglottic  fold  (Plica 
glossoepiglottica)  passes  from  the  root 
to  the  base  of  the  epiglottis;  this  en- 
closes the  hyoepiglottic  muscle.  The 
mucous  membrane  presents  numerous 
papillae,  which  are  of  four  kinds — fiH- 
form,  fungiform,  vallate,  and  foliate. 
The  filiform  papillae  (Papillae  filiformes) 
are  fine,  thread-like  projections  which 
stud  the  dorsum  and  the  sides  of  the 
tip;  they  are  absent  on  the  root.  On 
the  anterior  part  they  are  so  small  as 
to  be  scarcely  visible,  but  on  the  pos- 
terior part  they  are  much  larger  and 
give  the  surface  a  distinct  pile.  The 
f imgif orm  papillae  (Papillae  f ungif  ormes) 
are  larger  and  easily  seen;  they  are 
rounded  at  the  free  end,  which  is  sup- 
ported by  a  neck.  They  occur  princi- 
pally on  the  lateral  part  of  the  tongue, 
but  are  also  found  scattered  over  the 
dorsum.  The  vallate  papillae  (Papillae 
vallatae)  are  usually  two  or  three  in 
number.  The  two  constant  ones  are  a 
quarter  of  an  inch  or  more  (ca.  6  to  7 
mm.)  in  diameter,  and  are  found  on 
the  posterior  part  of  the  dorsum,  one 
on  each  side  of  the  median  plane,  about 
an  inch  (ca.  3  cm.)  apart.  The  third, 
when  present,  is  behind  these,  is  cen- 
trally situated,  and  is  always  smaller. 
Rarely  a  fourth  may  be  found.  They 
are  rounded,  broader  at  their  exposed 
than  at  their  attached  surfaces,  and  are 
sunk  in  a  depression  which  is  bounded 
by  an  annular  wall.     Their  free  surface 

is  tuberculate,  i.  e.,  bears  small,  round  secondary  papillae.  The  foliate  papillae 
(Papillae  foliatae)  are  situated  just  in  front  of  the  anterior  pillars  of  the  soft  palate, 
where  they  form  a  rounded  eminence  about  an  inch  (ca.  2  to  3  cm.)  in  length, 
marked  by  transverse  fissures.  The  last  three  varieties  are  covered  with  micro- 
scopic secondary  papillae  and  are  furnished  with  taste-buds.  The  mucous  mem- 
brane of  the  root  of  the  tongue  presents  numerous  folds  and  rounded  elevations. 

1  The  mucous  membrane  is  thick  and  closely  adherent  where  food  naturally  comes  in  contact 
with  the  tongue. 


Trachea 

Crico-arytenoid- 

eus  dorsalis 

muscle 

A  rytenoideus 

muscle 
Arytenoid  carti- 
lages 

Vocal  cord 

Adit  us  laryngis 
Epiglottis 

Tonsil 

Radix  lingucE 

Anterior  pillar  of 
soft  palate  (cut) 


Dorsum  linguae 


Apex  linguae 


ToNGTJE,  Larynx,  and  Part  of  Trachea  of 
Horse;  Dorsal  View. 


392 


DIGESTIVE    SYSTEM    OF   THE   HORSE 


The  latter  are  marked  by  crypts  and  consist  essentially  of  a  mass  of  Ij^mphoid 
tissue;  they  are  knowTi  as  lingual  follicles  (Folliculi  linguales),  and  taken  together 
form  what  is  sometimes  called  the  lingual  tonsil.  The  lingual  glands  (Glandulse 
linguales)  constitute  a  thick  layer  in  the  loose  submucous  tissue  and  also  lie  l^etween 
the  muscle  bundles.  Mucous  glands  are  found  also  in  part  of  the  dorsum  and  sides 
of  the  tongue. 

The  lingual  muscles  (Mm.  linguae)  may  be  divided  into  intrinsic  and  extrinsic. 
The  intrinsic  musculature  consists,  not  of  distinct  muscles,  but  rather  of  systems 
of  fibers  which  run  longitudinally,  vertically,  and  transversely,  blending  with  the 
extrinsic  muscles,  which  are  now  to  be  described.^ 


'■^-  ""^  Kendo-hyoidcus        Hyo-pharyngeus 

Genio-glossus  Thyroid       Trachea 

Depressor  labii  ^^^'^'^ 

inferioris 

Fig.  332. — Muscles  or  Tongue,  Hyoid  Bone,  Pharynx,  etc.,  of  Horse. 
T.  p.,  Tensor  palati;    L.  p.,  levator  palati;    Pt.  p.,  pterygo-pharyngeus;    P.  p.,  palato-pharyngeus;     S.  p.,  stylo- 
pharyngeus;    Th.  p.,  thyro-pharyngeus;    C.  p.,  crico-pharyngeus ;    Th.  h.,  thyro-hyoideus;    Hyo.  gl.,  hyo-glossus;    G.  p., 
guttural  pouch;  F.  p.,  foliate  papilla;  A.  v.,  facial  artery  and  vein.     Most  of  the  left  ramus  of  the  mandible  is  removed. 
The  concealed  parts  of  the  hyoid  bone  are  indicated  by  dotted  lines. 


1.  Stylo-glossus. — This  is  a  long,  thin  muscle,  which  lies  along  the  lateral  part 
of  the  tongue.  It  arises  by  a  thin  tendon  from  the  lateral  surface  of  the  great 
cornu  of  the  hyoid  bone,  near  the  articulation  with  the  small  cornu.  It  terminates 
near  the  tip  of  the  tongue  by  blending  with  its  fellow  of  the  opposite  side  and  with 
the  intrinsic  musculature.  The  action  is  to  retract  the  tongue.  Unilateral  con- 
traction would  also  draw  the  tongue  toward  the  side  of  the  muscle  acting. 

A  small  muscular  band  sometimes  arises  on  the  thyroid  cornu  of  the  hyoid  bone  and  ends 
on  the  tendon  of  origin  of  the  stylo-glossu3.  In  some  cases  a  similar  band  arises  higher  up,  with 
and  on  the  hyo-glossus. 

2.  Hyo-glossus. — This  is  a  wide,  flat  muscle,  somewhat  thicker  than  the  pre- 

1  This  distinction  is  more  or  less  conventional.  It  is  evident  that  much  of  what  may  appear 
on  cross-sections  of  the  tongue  to  be  intrinsic  muscle  is  in  reality  a  part  of  the  extrinsic  musculature. 
The  arrangement  is  further  complicated  by  the  existence  of  bundles  running  in  various  directions, 
intercrossing  of  bundles,  and  the  breaking  up  of  the  systems  by  masses  of  fat. 


THE   TONGUE 


393 


ceding.     It  lies  in  the  lateral  part  of  the  root  and  body  of  the  tongue,  partly  under 
cover  of  the  preceding  muscle.     Its  deep  face  is  related  to  the  genio-glossus.     It 


\     Thyroid 
gland 
Crico-thyroid 
joint 

Foramen  for  anterior 
laryngeal  nerve 


Cenio-hyoideus  (right) 
Gejiio-glossus 
Styh-glossus  (stump) 

Depressor  labii  inferioris  (stump) 


Fig.  333. — Muscles  of  Tongue,  Pharynx,  Larynx,  etc.;  Deep  Dissection. 
T.  p..  Tensor  palati;  L.  p.,  levator  palati,  concealed  part  indicated  by  dotted  line;  Pt.  p.,  pterygo-pharyngeus; 
P.  p.,  palato-pharyngeus;  St.  p.,  stylo-pharyngeus;  C.  a.,  crieo-arytenoideus  dorsalis;  C.  th.,  crico-thyroideus;  Th.  c.^ 
thyroid  cartilage  (lamina) ;  T/i. /i.,  thyro-hyoideus;  X.  A.,  kerato-hyoideus;  T/t.  c,  thyroid  cornu;  .S.  c,  small  cornu; 
L.  p.,  lingual  process;  F.  p.,  foliate  papilla;  Fu.  p.,  fungiform  papillae.  Part  of  great  cornu  is  removed  and  indicated 
by  dotted  lines. 


arises  from  the  lateral  aspect  of  the  hyoid  bone,  from  the  lingual  process  to  the  oral 
extremity  of  the  great  cornu,  and  from  the  thyroid  cornu.     The  fibers  pass  obliquely 


394  DIGESTIVE    SYSTEM    OF   THE    HORSE 

forward  and  upward,  and  for  the  most  part  turn  toward  the  median  plane  of  the 
dorsum  of  the  tongue.     Its  action  is  to  retract  and  depress  the  tongue.^ 

3.  Genio-glossus. — This  is  a  fan-shaped  muscle,  which  lies  parallel  to  the  me- 
dian plane  of  the  tongue.  It  is  separated  from  the  muscle  of  the  opposite  side  by  a 
layer  of  fat  and  areolar  tissue.  It  arises  from  the  medial  surface  of  the  ramus 
of  the  mandible  just  behind  the  symphysis.  From  the  tendon  the  fibers  pass  in 
a  radiating  manner,  some  curving  forward  to  the  tip,  others  pass  toward  the  dorsum, 
and  others  toward  the  root  of  the  tongue;  some  fibers  pass  from  the  posterior  end 
of  the  tendon  to  the  body  and  small  cornu  of  the  hyoid  bone.  '  The  muscle  as  a 
whole  is  a  depressor  of  the  tongue,  and  especially  of  its  middle  portion;  when  both 
muscles  act,  a  median  groove  is  formed  on  the  dorsum.  The  posterior  fibers  pro- 
trude the  tongue,  the  middle  fibers  depress  the  tongue,  and  the  anterior  fibers 
retract  the  tip  of  the  tongue. 

In  some  cases  there  is  a  small  anomalous  muscle  which  arises  by  a  delicate  tendon  with  the 
genio-glossus  and  is  attached  behind  with  the  genio-hyoideus. 

Vessels  and  Nerves. — The  arteries  of  the  tongue  are  the  lingual  and  sub- 
lingual branches  of  the  external  maxillary  artery.  The  veins  go  to  the  internal 
and  external  maxillary  veins.  The  lymph  vessels  go  chiefly  to  the  pharyngeal 
lymph  glands.  The  sensory  nerves  are  the  lingual  and  glosso-pharyngeal,  and  the 
muscles  are  innervated  by  the  hypoglossal  nerve. 


THE  TEETH  IN  GENERAL 
The  teeth  are  hard  white  or  yellowish-white  structures  implanted  in  the  alveoli 
of  the  bones  of  the  jaws.  Morphologically  they  are  large  calcified  papillae.  Func- 
tionally they  are  organs  of  prehension  and  mastication,  and  may  serve  as  weapons. 
The  domesticated  mammals  have  two  sets  of  teeth.  The  teeth  of  the  first  set 
appear  during  early  life  and  are  known  as  deciduous  or  temporary  teeth  (Dentes 
decidui),^  since  they  are  replaced  during  the  period  of  growth  by  the  permanent 
teeth  (Dentes  permanentes) .  They  are  classified  according  to  form  and  position 
as  follows: 

1.  The  incisor  teeth  (Dentes  incisivi)  are  situated  in  front  and  are  implanted 
in  the  premaxilla  and  mandible. 

2.  The  canine  teeth  (Dentes  canini)  are  situated  a  little  further  back,  and 
interrupt  the  interalveolar  space. 

3.  The  premolar  and  molar  teeth  (Dentes  prsemolares  et  molares)  form  the 
sides  of  the  dental  arch.  The  premolars  form  the  anterior  part  of  the  series;  they 
appear  in  both  sets.  The  molars  appear  only  in  the  permanent  dentition.  The 
term  cheek  teeth  is  used  to  include  both  premolars  and  molars. 

The  interval  between  the  incisors  and  premolars  is  the  interalveolar  or  inter- 
dental space. 

As  the  teeth  of  the  two  sides  of  the  jaw  are  alike  in  niunber  and  character 
(in  normal  cases),  the  complete  dentition  may  be  briefly  indicated  by  a  dental 
formula  such  as  the  following : 

2  (  I  -  C  -  P  -  M  -  I  =  32. 


(2        1       2         3\ 
I  -  C  -  P  -  M  -  ) 
2       12         3/ 


In  this  formula  the  letters  indicate  the  kinds  of  teeth,  and  the  figures  above  and 
below  the  lines  give  the  number  of  teeth  of  one  side  in  the  upper  and  lower  jaw 
respectively  in  man. 

^  It  may  be  possible  to  recognize  in  this  muscle  three  parts,  which  would  correspond  to 
the  baseo-,  kerato-,  and  chondro-glossus  of  man. 

^  They  are  also  popularly  spoken  of  as  "milk"  teeth. 


THE    TEETH    IN    GENERAL  395 

The  individual  teeth  of  each  group  are  designated  numerically,  the  starting- 
point  being  the  middle  line ;  thus  the  incisor  on  either  side  of  the  middle  line  is  the 
first  incisor,  and  may  be  conveniently  indicated  by  the  notation  I^  The  deciduous 
teeth  may  be  designated  in  a  similar  manner,  prefixing  D  (for  deciduous)  to  the 
letter  indicating  the  kind  of  tooth.  In  addition  to  the  above  systematic  method  of 
notation  other  terms  have  received  the  sanction  of  popular  usage.  Thus  the  first 
incisors  are  commonly  called  middle  incisors,  ''pinchers,"  or  "nippers";  the  second, 
intermediate;  and  the  third,  corner  teeth.  The  canines,  when  highly  developed, 
may  be  termed  tusks  or  fangs.  The  vestigial  and  inconstant  first  premolar  of  the 
horse  is  popularly  termed  the  "wolf  tooth." 

Each  tooth  presents  for  description  a  part  coated  with  enamel,  termed  the 
crown  (Corona  dentis),  and  a  part  covered  with  cement,  termed  the  root  (Radix 
dentis).  The  line  of  union  of  these  parts  is  the  neck  (Collum  dentis).^  In  many 
teeth  the  neck  is  distinct  and  is  embraced  by  the  gum,  e.  g.,  the  teeth  of  the  dog 
and  the  temporary  incisors  of  the  horse.  In  other  teeth  no  constriction  is  present, 
e.  g.,  the  permanent  incisors  of  the  horse.  Between  these  extremes  are  the  molars 
of  the  horse,  in  which  the  neck  is  seen  only  in  advanced  age. 

The  surface  of  a  tooth  directed  toward  the  lips  is  ternwd  labial ;  that  toward 
the  cheek,  buccal;  and  that  toward  the  tongue,  lingual  (Facies  labiahs, buccalis, 
lingualis).  The  surface  opposed  to  a  neighboring  tooth  of  the  same  dental  arch 
is  termed  the  contact  surface  (Facies  contactus).  The  masticatory  surface  (Facies 
masticatoria)  is  that  which  comes  in  contact  with  a  tooth  or  teeth  of  the  opposite 
jaw.- 

Structure. — Teeth  are  composed  of  four  tissues,  which  are  considered  here 
from  within  outward.  The  pulp  of  the  tooth  (Pulpa  dentis)  is  a  soft,  gelatinous 
tissue,  which  occupies  a  space  in  the  central  part  of  the  tooth  termed  the  pulp 
cavity  (Cavum  dentis).  The  pulp  is  well  supplied  with  blood-vessels  and  nerves. 
It  occupies  a  relatively  large  space  in  young  growing  teeth,  but  later  the  dentine 
deposited  on  its  surface  gradually  encroaches  on  it  until,  in  advanced  age,  the  cavity 
is  much  reduced  or  obliterated.  The  dentine  (Substantia  eburnea)  forms  the  bulk 
of  most  teeth,  covering  the  surface  of  the  pulp.  It  is  hard,  and  is  yellowish-white 
in  color.  The  enamel  (Substantia  adamantina) ,  the  hardest  tissue  of  the  body, 
constitutes  a  layer  of  varying  thickness  covering  the  dentine  of  the  crown  of  the 
tooth.  It  is  easily  distinguished  by  its  clear,  bluish-white  appearance  and  its  ex- 
treme density.  The  cement  (Substantia  ossea)  is  the  outermost  tooth  substance. 
In  simple  teeth  it  forms  usually  a  thin  layer  on  the  surface  of  the  root  only,  but 
in  complex  teeth  it  exists  in  considerable  quantity,  tending  to  fill  in  the  spaces 
between  the  enamel  folds  of  the  crown  also.  Its  structure  is  practically  the  same 
as  that  of  bone  without  Haversian  canals,  and  even  these  occur  where  the  cement 
forms  a  thick  layer.  The  embedded  part  of  the  tooth  is  attached  to  the  alveolus 
by  a  vascular  layer  of  connective  tissue,  the  alveolar  periosteum  (Periosteum 
alveolare);  this  is  the  periosteum  of  the  alveolus  and  performs  a  like  function 
with  regard  to  the  embedded  part  of  the  tooth.  The  name  pericementum  has  also 
been  applied  to  it. 

lit  will  be  noted  that  this  definition  of  crown  and  root  does  not  agree  exactly  with  the 
popular  view  that  the  crown  is  the  free  part  and  the  root  the  embedded  part.  The  objection  to 
the  latter  statement  Ues  in  the  fact  that  it  is  not  capable  of  general  appHcation.  Thus  the  mor- 
phological crown  of  the  permanent  molars  in  the  horse  is  extremely  long,  and  is,  for  the  most 
part,  embedded  in  the  bone  in  the  young  animal.  The  root  proper  begins  to  form  at  four  or  five 
years  of  age,  and  continues  its  growth  for  about  eight  years.  As  the  exposed  part  of  the  crown 
wears  down,  the  embedded  part  erupts,  thus  preventing  deficiency  of  length.  On  the  old  basis 
we  should  have  to  say  that  successive  portions  of  the  root  become  crown,  while  in  point  of  fact  it 
is  only  in  very  extreme  age  that  the  true  root  comes  into  wear.  This  difficulty  does  not  arise  in 
cases  in  which  the  eruption  of  the  teeth  is  completed  rapidly,  e.  g.,  man,  dog.  In  such  brachydont 
forms  the  short  crown  is  clearly  marked  off  from  the  root  or  roots  by  a  neck,  which  is  embraced 
by  the  gum.  The  opposite  extreme  is  seen  in  the  incisors  of  typical  rodents,  which  grow  con- 
tinuously and  have  no  roots. 

2  This  is  popularly  termed  the  grinding  surface  or  "table"  of  the  tooth. 


396 


DIGESTIVE   SYSTEM    OF   THE   HORSE 


The  blood-supply  to  the  pulp  is  derived  from  the  alveolar  branches  of  the  in- 
ternal maxillary  artery;    the  nerve-supply  comes  from  branches  of  the  trigeminus. 


The  Teeth  of  the  Horse  ^ 

The  Permanent  Teeth 
The  formula  of  the  permanent  teeth  of  the  horse  is: 


(3        1        3  or  4         3  \ 
I  _  C  -  P  M  -   I 
3        13  3/ 


40  or  42 


Fig.   334. — Upper   Teeth   of   Horse,   About   Four  and    One-half        Fig.     335 — Lower     Teeth     of     Horse, 


Years  Old. 
2',  /2,  /',  Incisors;    C,  canine;    Pi,  />»,  ps,  P',  premolars;  M',M\ 
M',  molars.     The  eruption  of  the  third  incisor  is  not  complete  and 


Four  Years  of  Age. 
7',    I-,    First    and    second    permanent 


sors;  Di's,  third  deciduous  incisor.     The 
the  tooth  is  unworn.  cheek    teeth    are    numbered    according    to 

popular  usage 

1  Other  figures  illustrating  the  teeth  are  to  be  found  in  the  description  of  the  skull. 


THE    PERMANENT   TEETH 


397 


In  the  mare  the  canines  usually  are  very  small  and  do  not  erupt,  reducing  the  num- 
ber to  36  or  38.  ^ 

Incisor  Teeth. — These  are  twelve  in  number.  The  six  in  each  jaw  are  placed 
close  together,  so  that  their  labial  edges  form  almost  a  semicircle  in  the  young 
horse.  They  have  the  peculiarity  (not  found  in  existing  mammals  other  than  the 
equidse)  of  presenting,  instead  of  the  simple  cap  of  enamel  on  the  crown,  a  deep 
invagination,  the  infundibulum,  which  becomes  partly  filled  up  with  cement. 
Hence  as  the  tooth  wears,  the  masticatory  surface  (or  "table")  has  a  central  ring 
of  enamel  surrounding  this  cavity  in  addition  to  the  peripheral  enamel.  The 
cavity  becomes  darkened  by  deposits  from  the  food,  and  is  commonly  termed 
the  "cup"  or  "mark."     Each  tooth  is  curved  so  that  the  labial  surface  is  convex 


Fig.  3.36. — Upper  Incisor  Teeth  op  Horse.  Fig.  337. — Lower  Incisor  Teeth  of  Horse. 

The  labial  surfaces  ot  the  teeth  have  been  exposed  by  removal  of  the  bone.     Subject  was  five  years  old. 


and  the  embedded  parts  converge.  The  average  total  length  of  an  incisor  at  five 
or  six  years  of  age  is  about  two  and  a  half  to  three  inches  (ca.  7  cm.).  They  taper 
regularly  from  exposed  crown  to  apex,  without  any  constriction,  and  in  such  a 
manner  that  in  young  horses  the  masticatory  surface  is  broad  transversely;  toward 
the  middle  the  two  diameters  of  a  cross-section  are  about  equal;  near  the  apex 
the  antero-posterior  diameter  is  considerably  greater  than  the  transverse. 

This  fact  is  of  value  in  the  determination  of  age  by  the  teeth,  since  the  mas- 
ticatory surfaces  at  different  ages  represent  a  series  of  cross-sections.  As  the  ex- 
posed crown  wears  down,  the  embedded  part  (reserve  crown)  emerges  from  the 

1  Ellenberger  found,  as  the  result  of  extensive  observations  (8000  subjects),  that  about 
2  to  3  per  cent,  of  mares  have  erupted  canines  in  both  jaws;  that  6  to  7  per  cent,  have  them  in 
the  upper  jaw;  while  20  to  30  per  cent,  have  them  in  the  lower  jaw.  The  numerical  variation  in 
the  above  formula  results  from  the  fact  that  the  first  premolar  ("wolf-tooth")  is  often  absent  and 
further  that  it  is  doubtful  to  what  set  it  belongs  when  present.  It  is  commonly  not  included  in 
the  enumeration. 


398 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


Infundibulu 

Central  enamel 
Dentine 
Peripheral 
enamel 

Cemetit 


alveolus,  so  that  the  masticator}^  surfaces  of  the  first  and  second  lower  incisors 

are  at  first  oval,  with  the  long  diameter  transverse; 
later — at  about  fourteen  years  usually  for  the  first 
lower  incisors — they  are  triangular,  with  the  base 
at  the  labial  edge.  At  the  same  time  the  infundib- 
ulum  or  "cup"  becomes  smaller,  approaches  the 
lingual  border,  and  finally  disappears;  it  remains 
longer  on  the  upper  incisors,  as  it  is  deeper  in 
them.  Another  marked  feature  in  old  age  is  the 
progressive  approach  to  a  horizontal  direction  as 
seen  in  profile;  at  the  same  time  the  exposed 
crowns  of  the  teeth  become  parallel  and  finally 
convergent. 

Canine  Teeth. — These  are  four  in  number  in  the 
male ;  in  the  mare  they  are  usually  absent  or  rudi- 
mentary.^ They  interrupt  the  interdental  space, 
dividing  it  into  unequal  parts.     The  upper  canine 

Peripheral  enamel     Cement 
Dentine 
Central  enamel' 
Cement- 


FiG.    338. — Longitudinal    Section    op 

Lower  Incisor  Tooth  of  Horse. 

C,  Pulp  cavity.     Cement  is  shown  in  the 

infundibulum,  but  is  not  marked. 


Fig.  339. — Cross-section  of  Lower  Lx 
/,  Infundibulum 


Tooth  of  Horse. 


is  situated  at  the  junction  of  the  premaxilla  and  the  maxilla;   the  lower  canine  is 
nearer  the  corner  incisor.     The  canines  are  simple  teeth,  smaller  than  the  incisors, 


Fig.  340. — Lower   Incisor  and   Canine   Teeth   of  Fig.   34" 

Horse,  Five  Years  Old. 
The  lingual  border  of  the  third  upper  incisor  is  unworn. 


— Upper   Incisor  and   Canine   Teeth  op 

Horse,  Five  Years  Old. 
/',  /-,  /',   Incisor;   C,   canine. 


and  are  curved  with  the  concavity  directed  backward.     The  exposed  crown  in  the 

^  It  is  interesting  to  notice  that  vestigial  canines  are  not  at  all  uncommon  in  mares,  espe- 
cially in  the  lower  jaw.  They  are  very  small,  and  do  not  usually  erupt;  their  presence  is  indi- 
cated in  the  latter  case  by  a  prominence  of  the  gum.  This  is  in  conformity  with  the  fact  that 
they  were  present  in  both  sexes  in  Eocene  and  Miocene  ancestors  of  existing  equida;. 


THE    PERMANENT   TEETH 


399 


young  subject  is  compressed,  convex  and  smooth  laterally,  concave  with  a  median, 
ridge  medially;  its  edge  is  sharp  in  the  unworn  tooth.  The  embedded  part  (usu- 
ally called  the  root)  is  round  and  the  pulp  cavity  is  large,  persisting  to  advanced 


age.     In  old  subjects,  when  the  compressed  part  of  the  crown  has  worn  away,  the 

exposed  part  is  rounded  and  blunt. 

Cheek  Teeth  (Premolars  and  Molars). i— The  constant  number  of  these  is 
1  It  is  common  in  veterinary  works  to  apply  the  term  "molar"  to  all  the  cheek  teeth,  since, 

in  the  horse  particularly,  the  premolars  are  molariform,  i.  c,  do  not  differ  materially  fron  the  true 

molars  in  size  or  form.     The  term  cheek  teeth  conveniently  mcludes  the  premolars  and  molars. 


400 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


twenty-four — twelve  in  each  jaw.  Quite  commonly,  however,  the  number  is  in- 
creased by  the  presence  in  the  upper  jaw  of  the  so-called  "wolf-tooth."  This 
tooth,  the  first  premolar,  is  usuallj^  situated  just  in  front  of  the  first  well-developed 
tooth;  it  is  a  much-reduced  vestige,  not  often  more  than  one-half  or  three-fourths 
of  an  inch  (ca.  1  to  2  cm.)  in  length.  (It  is  interesting  as  being  the  remnant  of  a 
tooth  which  was  well  developed  in  the  Eocene  ancestors  of  the  horse.)  It  may 
erupt  during  the  first  six  months,  and  is  often  shed  about  the  same  time  as  the 
milk-tooth  behind  it,  but  may  remain  indefinitely.  The  occurrence  of  a  similar 
tooth  in  the  lower  jaw — which  rarely  erupts — increases  the  dental  formula  to  44, 
which  is  considered  the  typical  number  for  mammals.^  The  cheek  teeth  are  very 
large,  prismatic  in  form,  and  quadrilateral  in  cross-section,  except  the  first  and 

last  of  the  series,  which  are  three-sided.     The 
Dentine        Cement  cro^\Ti  is  remarkably  long,  most  of  it  being  em- 

bedded in  the  bone  or  projecting  into  the  max- 
illary sinus  in  the  young  horse.  As  the  exposed 
part  wears  away  the  embedded  part  erupts  to 
replace  it,  so  that  a  functional  crown  of  about 
four-fifths  of  an  inch  (ca.  2  cm.)  is  maintained.^ 
The  root  begins  to  grow  at  about  five  years 
of  age,  and  is  complete  at  twelve  to  fourteen, 
although  the  deposition  of  cement  may  con- 
tinue indefinitely. 

The  maxillary  or   upper    cheek  teeth   are 
embedded  in  the  alveolar  processes  of  the  max- 


Cement 


Enamel 


Cement 


Root  canal 


Fig.  343. — Frontal  Section  of  Upper 

Cheek  Tooth  of  Horse. 

C,  C,  Pulp  cavities.     Infundibulum  filled 

with  cement. 


Fig.  344. — Cross-section  of  Upper  Cheek  Tooth  of  Horse. 
Buccal  (lateral)  surface  to  left.     /.Anterior,   I',  posterior  infundib- 
ulum, both  almost  filled  up  with  cement. 


ilia.  The  exposed  parts  of  the  crowns  are  normally  in  close  contact,  forming  a 
continuous  row  which  is  slightly  curved,  with  the  convexity  toward  the  cheek. 
The  embedded  parts  diverge  in  the  manner  shoAvn  in  the  annexed  figures  (Figs.  342, 
347).  Thus  the  long  axis  of  the  first  is  directed  upward  and  a  little  forward,  that 
of  the  second  is  almost  vertical,  while  in  the  remainder  it  is  curved  backward  in 
an  increasing  degree;  the  last  tooth  in  particular  is  strongly  curved  in  the  adult. 
The  average  length  at  six  years  of  age  is  a  little  more  than  three  inches  (ca.  8  cm.). 
The  buccal  surface  presents  a  central  ridge  running  lengthwise,  and  separating  two 
grooves;  the  first  tooth  has,  in  addition,  a  less  prominent  ridge  in  front  of  the 
primary  one.  The  lingual  surface  is  marked  by  a  wide,  rounded  ridge,  the  acces- 
sory pillar  or  column,  which  separates  two  very  shallow  grooves.     The  masticatory 

1  The  question  to  which  set  these  teeth  belong  is  an  open  one. 

'^  For  teeth  of  this  kind  it  is  convenient  to  employ  the  terms  functional  crowTi  and  reserve 


THE   PERMANENT   TEETH 


401 


surface  presents  two  inf undibula,  anterior  and  posterior.  It  slopes  obliquely  down- 
ward and  outward,  so  that  the  buccal  edge  is  prominent  and  sharp.  Its  average 
width,  except  at  each  end  of  the  series,  is  about  an  inch  (ca.  2.5  cm.).  The  first 
and  last  teeth  have  three  roots,  the  remainder  four  or  three. 

As  may  be  seen  in  Fig.  342,  the  individual  teeth  of  the  series  vary  in  length.  In  the  speci- 
men from  wlaich  the  photograph  was  taken  the  lengths  of  the  upper  teeth  in  centimeters  enumer- 
ated from  before  backward  were:  6.3,  7.7,  8.5,  8.0,  8.8,  8.2.  The  distance  between  the  two  rows 
was  6.6  cm.  at  the  anterior  end  and  8.6  cm.  at  the  posterior  end. 

The  position  of  the  embedded  crowns  and  roots  of  the  last  four  varies  at 

different  ages  and  in  different  subjects.     Two  factors   in   this  variation  may  be 

noted.     All  of  these  teeth  are  developed  in  the  posterior  part  of  the  body  of  the 

maxilla.     As  growth  proceeds  the  teeth  move  forward,  so  that  commonly  only  the 

last  three,  but  sometimes  also  the  third,  project  into 

the  maxillary  sinus.     The  second  cause  of  variation 

is  the  fact  that  the  anterior  limit  of  the  maxillary 

sinus  may  be  at  the  extremity  of  the  facial  crest,  or 

about  an  inch  beyond  it.     In  the  latter  case  the  third 

tooth  projects  into  the  sinus. ^ 

The  mandibular  or  lower  cheek  teeth  are  im- 
planted in  the  rami  of  the  mandible,  forming  two 
straight  rows  which  diverge  behind.  The  space  be- 
tween the  rows  is  considerably  less  than  that  separat- 
ing the  upper  teeth,  especially  in  the  middle  of  the 
series.  The  length  of  the  lower  teeth  is  about  the 
same  as  that  of  the  upper  set.     Their  direction  is 


Cement 


Dentine     Cement 
Enamel 


Cement 


Fig.    345. — Fro.n'tal    Section    op 

Lower  Cheek  Tooth  of  Horse. 

C,  Pulp  cavity.    Infundibulum  filled 

with  cement. 


Fig  346. — Cross-section  of  Lower  Cheek  Tooth  of  Horse. 
Buccal  surface  to  left. 


also  similar,  but  the  embedded  portions  diverge  even  more,  with  the  exception 
of  the  first  and  second.  The  long  axis  of  the  first  is  vertical;  the  remainder 
project  downward  and  backward  in  a  gradually  increasing  obliquity.  The  buc- 
cal surface  has  a  longitudinal  furrow;  the  last  molar  has  a  secondary  shal- 
lower furrow  in  addition.  The  lingual  surface  is  uneven,  but  the  grooves  are 
not  regular;  there  are  usually  three  on  the  first  and  last  tooth.  The  mastic- 
atory surface  is  oblique,  sloping  upward  and  inward  in  correspondence  with  the 
opposing  tooth;  thus  the  lingual  edge  is  prominent.  Its  average  width  (except 
at  each  end  of  the  series)  is  somewhat  less  than  three-fourths  of  an  inch  (ca.  1.8  cm.). 

'  The  student  is  advised  to  amplify  these  very  general  statements  by  the  examination  of 
heads  of  subjects  of  varying  ages.     It  may  also  be  noted  that  the  position  of  the  septum  between 
the  two  divisions  of  the  sinus  varies  much. 
26 


402 


DIGESTIVE   SYSTEM    OF   THE    HORSE 


The  first  five  have  two  roots,  while  the  sixth  commonly  has  three.     The  width  of  the 
lower  molars  is  a  little  more  than  half  that  of  the  upper. 

The  structure  is  quite  complex.     Two  infundibula  run  vertically  through  the 


entire  length  of  the  crown;  these  become  filled  with  cement.  In  the  upper  teeth 
there  are  five  main  divisions  of  the  pulp-cavity  and  five  enamel  folds,  four  of  which 
are  arranged  symmetrically,  while  the  fifth  is  an  outgrowth  from  the  antero-medial 
fold.     In  the  lower  teeth  the  infundibula  are  open  along  the  lingual  surface  until 


THE  DECIDUOUS  TEETH ERUPTION  OF  THE  TEETH  403 

closed  by  deposit  of  cement.  The  pulp-cavity  has  two  main  divisions  (anterior 
and  posterior)  and  three  or  four  secondary  diverticula.  The  enamel  folds  corres- 
pond, forming  a  pattern  even  more  complicated  than  on  the  upper  teeth.  On 
the  exposed  crown  of  the  unworn  tooth  the  enamel  folds  form  rounded  ridges 
covered  with  a  thin  layer  of  cement.  After  the  tooth  comes  into  wear  the  enamel 
on  the  masticatory  surface  stands  out  in  the  form  of  sharp,  prominent  ridges.^ 
Progressive  cementation  of  the  periphery  of  the  tooth  takes  place,  thus  leveling  up 
the  irregularities  of  surface  to  a  considerable  extent. 

The  lengths  of  the  lower  teeth  shown  in  Fig.  342  were  in  centimeters:  5.7,  7.9,  9.0,  8. .5,  S.2 
7.B.  The  distance  between  the  two  rows  was  4.7  cm.  at  the  anterior  end  and  7  cm.  at  the  posterior 
end. 

The  Deciduous  Teeth 
The  deciduous  teeth  are  smaller  and  fewer  than  those  of  the  permanent  set. 
The  formula  is : 


/      3       0       3\ 

2  I  Di  -  Dc  -  Dp  -  I 

V       3        0        3/ 


24 


The  deciduous  incisors  are  much  smaller  than  the  permanent  ones.  They 
have  a  distinct  neck  at  the  junction  of  the  crown  and  root.  The  crown  is  short, 
white  in  color,  and  its  labial  surface  is  smooth.  The  infundibulum  is  shallow. 
The  root  is  flattened;  it  undergoes  absorption  as  the  permanent  tooth  develops 
l^ehind  it. 

The  deciduous  canines  are  quite  vestigial.  They  occur  in  lioth  sexes  as  slender 
spiculse  about  a  quarter  of  an  inch  in  length,  but  do  not  erupt.  The  lower  one 
develops  close  to  the  corner  incisor.  They  are  not  usually  included  in  the  formula, 
as  they  are  never  functional. 

The  deciduous  premolars  differ  from  the  permanent  set  chiefly  in  that  they 
have  much  shorter  cro^vns  than  the  latter.  The  roots  form  early,  so  that  a  distinct 
neck  occurs. 

Vessels  and  Nerves. — The  blood  supply  of  the  teeth  is  derived  from  the 
infraorbital  and  alveolar  branches  of  the  internal  maxillary  artery.  The  lymph 
vessels  go  to  the  mandilmlar  and  pharyngeal  lymph  glands.  The  nerves  come 
from  the  trigeminus. 

Eruption  of  the  Teeth 
The  subjoined  table  indicates  the  average  periods  of  the  erui^tion  of  the  teeth: 

Teeth  Eruption 

A.  Deciduous: 

1st  incisor (Di    1)  Birth  or  first  week. 

2nd       "      (Di  2)  4-6  weeks. 

3rd        "      (Di   3)  6-9  months. 

Canine (Dc     ) 

1st  premolar (Dp  2)  |  ^^^^^  ^^  ^^^^ 

2nd                   (Dp  3)  \  .        wPPk<5 

3rd        "         (Dp  4)  J   ^""^  '^^^^^• 

B.  Permanent: 

1st   incisor (II)  2^  years. 

2nd     "       (12)  31-2  years. 

3rd      " (13)  AXi  years. 

Canine (C)  4-.5  years. 

1st   premolar  (or  wolf-tooth) (PI)  5-6  months. 

2nd        "  (F2)  2H  years. 

3rd        "  (P3)  3  years. 

4th        "  fF4)  4  years. 

1st  molar (Ml)  10-12  months. 

2nd      "      (M2j  2  years. 

,3rd      "      (M3)  3I2-4  years. 

(The  periods  given  for  P  3  and  4  refer  to  the  upper  teeth;  the  lower  ones  may  erupt 
about  six  months  earlier.) 

^  It  is  estimated  that  the  enamel  ridges  of  an  upper  cheek  tooth  of  a  young  adult  horse,  if 
straightened  out,  would  form  a  Une  more  than  a  foot  long.     The  extent  diminishes  with  age. 


404  DIGESTIVE   SYSTEM    OF   THE    HORSE 


THE  SALIVARY  GLANDS 


This  term  is  usually  restricted  to  the  three  pairs  of  large  glands  situated  on  the 
sides  of  the  face  and  the  adjacent  part  of  the  neck — the  parotid,  mandibular,  and 
sublingual.     Their  ducts  open  into  the  mouth. 

The  parotid  gland  (Glandula  parotis)  (Fig.  560) — so  named  from  its  proximity 
to  the  ear — is  the  largest  of  the  salivary  glands  in  the  horse.  It  is  situated  chiefly 
in  the  space  between  the  ramus  of  the  mandible  and  the  wing  of  the  atlas.  It  is 
somewhat  triangular  in  shape,  the  apex  partially  embracing  the  base  of  the  external 
ear.  Its  length  is  about  eight  to  ten  inches  (ca.  20  to  25  cm.),  and  its  average  thick- 
ness nearly  an  inch  (ca.  2  cm.).  Its  average  weight  is  about  seven  ounces  (ca. 
200  to  225  g.).  It  presents  for  description  two  surfaces,  two  borders,  a  base,  and 
an  apex.  The  lateral  (or  superficial)  surface  is  covered  by  the  parotid  fascia  and 
the  cutaneus  and  parotido-auricularis  muscles.  It  is  crossed  obliquely  by  the  j  ugular 
vein,  which  is  largely  embedded  in  the  gland.  It  is  also  related  to  the  great  auricular 
vein,  the  cervical  branch  of  the  facial  nerve,  and  branches  of  the  second  cervical 
nerve.  The  medial  (or  deep)  surface  is  very  uneven,  and  has  numerous  important 
relations.  Some  of  these  are:  the  guttural  pouch  and  the  great  cornu  of  the 
hyoid  bone ;  the  masseter,  occipito-mandibularis,  digastricus,  and  occipito-hyoideus 
muscles;  the  tendons  of  the  brachio-cephalicus  and  sterno-cephalicus  (which 
separate  the  parotid  from  the  underlying  mandibular  gland) ;  the  external  carotid 
artery  and  some  of  its  branches;  the  facial  nerve;  the  pharyngeal  lymph  glands. 
The  anterior  or  facial  border  is  closely  attached  to  the  ramus  of  the  mandilDle  and 
the  masseter  muscle;  it  overlaps  the  latter  to  a  varying  extent.^  The  posterior 
or  cervical  border  is  concave,  and  is  loosely  attached  to  the  underlj^ng  muscles. 
The  base  or  ventral  border  is  related  to  the  external  maxillary  vein.  The  apex 
is  attached  to  the  base  of  the  external  ear,  which  it  partially  embraces.  The  gland 
has  a  yellowish-gray  color  and  is  distinctly  lobulated.  It  is  inclosed  in  a  capsule 
formed  by  the  fascia.  The  parotid  duct  (Ductus  parotideus)^  is  formed  at  the 
ventral  part  of  the  gland,  near  the  facial  edge,  by  the  union  of  three  or  four  radicles. 
It  leaves  the  gland  about  an  inch  (ca.  2  to  3  cm.)  above  the  external  maxillary 
vein,  crosses  the  tendon  of  the  sterno-cephalicus,  and  gains  the  medial  face  of  the 
pterygoideus  medialis.  It  then  runs  forward  in  the  mandibular  space  below  the 
external  maxillary  vein  and  winds  around  the  ventral  border  of  the  mandible  be- 
hind the  vein,  passes  upward  between  the  vein  and  the  masseter  muscle  for  about 
two  inches  (ca.  5  cm.),  turns  forward  underneath  the  facial  vessels,  and  perforates 
the  cheek  obliquely  opposite  the  third  upper  cheek  tooth.  Before  piercing  the 
cheek  it  is  somewhat  dilated,  but  its  termination  is  small,  and  is  surrounded  by  a 
circular  mucous  fold  (Papilla  salivalis).  The  gland  belongs  to  the  compound 
alveolar  glands  of  the  serous  type. 

Blood-supply. — Branches  of  the  carotid  and  maxillary  arteries. 

Nerve-supply. — Trigeminal,  facial,  and  sympathetic  nerves. 

The  mandibular  or  submaxillary  gland  (Glandula  mandibularis  s.  submax- 
illaris)^  is  much  smaller  than  the  parotid.  It  is  long,  narrow,  and  curved,  the 
dorsal  edge  being  concave.  It  extends  from  the  fossa  atlantis  to  the  body  of  the 
hyoid  bone,  so  that  it  is  covered  partly  by  the  parotid  gland,  partly  by  the  lower 
jaw  (Fig.  646).  Its  length  is  eight  to  ten  inches  (ca.  20  to  25  cm.),  its  width  an  inch 
to  an  inch  and  a  half  (ca.  2.5  to  3  cm.),  and  its  thickness  al)out  half  an  inch  (ca. 
1  cm.).     It  weighs  about  one  and  a  half  to  two  ounces  (ca.  45  to  60  g.).     It  is  often 

^  In  some  cases  there  is  a  well-marked  triangular  facial  process,  which  covers  the  temporo- 
mandibular joint,  the  facial  nerve,  and  the  transverse  facial  vessels. 
^  Formerly  known  as  Stenson's  or  Steno's  duct. 
^  The  term  "submaxillary,  "  although  firmly  established  by  usage,  is  a  misnomer. 


THE    PHARYNX  405 

divisible  into  two  parts.  It  presents  for  description  two  surfaces,  two  borders,  and 
two  extremities.  The  lateral  surface  is  covered  by  the  parotid  gland,  the  occipito- 
mandibularis,  digastricus,  and  pterygoideus  medialis  muscles.  The  tendon  of  the 
^temo-cephalicus  crosses  this  surface,  and,  together  with  the  aponeurosis  connect- 
ing it  with  that  of  the  brachiocephalicus,  is  a  useful  guide  in  separating  the  parotid 
gland  from  it.  The  medial  surface  is  related  to  the  rectus  capitis  ventralis  major, 
the  guttural  pouch,  the  larynx,  the  division  of  the  carotid  artery,  and  the  tenth, 
eleventh,  and  sympathetic  nerves.  The  dorsal  border  is  concave  and  thin.  It 
is  related  to  the  guttural  pouch  and  the  duct  of  the  gland.  The  ventral  border 
is  convex  and  thicker.  It  is  related  to  the  external  maxillary  vein  and  often  to 
the  thyroid  gland.  The  posterior  extremity  is  loosely  attached  in  the  fossa  atlantis. 
The  anterior  extremity  lies  at  the  side  of  the  root  of  the  tongue,  and  is  crossed 
laterally  by  the  external  maxillary  artery.  The  mandibular  or  submaxillary  duct 
(Ductus  mandibularis  s.  submaxillaris)  ^  is  formed  by  the  union  of  small  radicles 
which  emerge  along  the  concave  edge.  It  runs  forward  along  this  border,  and,  after 
leaving  the  anterior  extremity,  crosses  the  intermediate  tendon  of  the  digastricus, 
passes  between  the  hyo-glossus  and  mylo-hyoideus,  and  gains  the  medial  surface 
of  the  sublingual  gland.  Its  terminal  part  lies  on  the  body  of  the  mandible,  under 
the  mucous  membrane,  which  it  pierces  opposite  the  canine  tooth.  The  orifice  is 
at  the  end  of  a  flattened  papilla,  the  caruncula  sublingualis.  The  gland  differs 
in  finer  structure  from  the  parotid  in  possessing  serous,  mucous,  and  mixed 
alveoh. 

Blood-supply. — Occipital,  external  carotid,  and  external  maxillary  arteries. 

Nerve-supply. — Chorda  tympani  and  sympathetic  nerves. 

The  sublingual  gland  (Glandula  sublingualis)  (Figs.  330,  561)  is  situated  be- 
neath the  mucous  membrane  of  the  mouth,  between  the  body  of  the  tongue  and  the 
ramus  of  the  mandible.  It  extends  from  the  symphysis  to  the  third  or  fourth 
lower  cheek  tooth.  Its  length  is  about  five  or  six  inches  (ca.  12  to  15  cm.)  and  its 
weight  about  half  an  ounce  (ca.  15  to  16  g.).  It  is  flattened  laterally,  and  has  a 
thin  dorsal  border  which  underlies  the  sublingual  fold  of  the  mucous  membrane 
of  the  floor  of  the  mouth.  The  lateral  surface  is  related  to  the  mylo-hyoideus 
muscle,  and  the  medial  surface  to  the  genio-glossus  and  stylo-glossus,  the  mandib- 
ular duct,  and  branches  of  the  lingual  nerve.  The  ventral  border  is  related  to 
the  geniohyoid  muscle.  The  sublingual  ducts  (Ductus  sublinguales),  about  thirty 
in  number,  are  small,  short,  and  twisted;  they  open  on  small  papillae  on  the  sub- 
lingual fold.     The  gland  has  mixed  alveoli. 

Blood-supply. — Sublingual  artery. 

Nerve-supply. — Trigeminal  and  sympathetic  nerves. 


THE  PHARYNX 

The  pharynx  is  a  musculo-membranous  sac  which  belongs  to  the  digestive  and 
respiratory  tracts  in  common.  It  is  somewhat  funnel-shaped,  the  large  anterior 
part  joining  the  mouth  and  nasal  cavity,  while  the  small  end  is  continued  by  the 
oesophagus.  Its  long  axis  is  directed  obliquely  downward  and  backward,  and  has 
a  length  of  about  six  inches  (ca.  15  cm.).  The  pharynx  is  attached  by  its  muscles 
to  the  palatine,  pterygoid,  and  hyoid  bones,  and  to  the  cricoid  and  thyroid  cartilages 
of  the  larynx. 

Its  principal  relations  are :  dorsally,  the  base  of  the  cranium  and  the  guttural 
pouches;  ventrally,  the  larynx;  laterally,  the  medial  pteryoid  muscle,  the  great 
cornu  of  the  hyoid  bone,  the  external  carotid  and  external  maxillary  arteries,  the 

1  Formerly  known  as  Wharton's  duct. 


406 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


glosso-pharyngeal,   anterior   laryngeal,    and   hypoglossal   nerves,   the   mandibular 
salivary  gland,  and  the  parapharyngeal  Ijonph  glands. 

The  cavity  of  the  pharynx  (Cavum  pharyngis)  presents  seven  openings. 
Through  the  posterior  nares  or  choanae  it  communicates  dorsally  with  the  nasal 
cavity.     The  pharyngeal  orifices  of  the  two  Eustachian  tubes  (Ostia  pharyngea 


Temporal  muscle 


Nerves  III, 
IV,  VI,  and 
ophthalmic 
Internal  max- 
illary artery 
Transverse 
facial  nerve 
Buccinator 

nerve 
Inferior  al- 
veolar nerve 

Inferior  al- 
veolar artery 


Great  cornu  of. 
hyoid  bone 

Lingual  branch. 

of  IX  nerve 
External  max- 
illary artery 
Hypoglossal 
nerve 


Masseteric, 
vessels 


Thyroid  cornu 
of  hyoid  bone 


Lymph  gland 


Coronoid  proce 


Ti  a  nsverse  fa- 
cial vessels 
Ti  a  nsverse  fa^ 

cial  nerve 
Lateral  ptery- 
goid muscle 

internal  maxil- 
lary vein 

Medial  pteryoid 
muscle 

Ramus  of  man- 
dible 

Hyo-pharyngeus 
muscle 

Isthmus  faucium, 

■Tonsil 

igastricus  (in- 
termed,  tendon) 

Anterior  end  of 
mandibular  gland 

Sublingual  vein 

External  maxil- 
lary vein 


Parotid  duct 


Fig.  348. — Cross-section  of  Head  of  Horse. 
The  section  passes  through  the  anterior  part  of  the  temporo-mandibular  articulation,  but  is  slightly  oblique,  passing 
a  few  millimeters  further  forward  on  left  side  than  on  right.  1,  Corpus  callosum;  2,  lateral  ventricle  of  brain;  3, 
caudate  nucleus;  4,  internal  capsule;  5,  lenticular  nucleus;  6,  optic  chiasma;  7,  middle  cerebral  artery;  S,  sphenoidal 
sinuses;  9,  cavernous  sinus;  10,  Eustachian  tube,  medial  lamina;  11,  11,  guttural  pouches;  12,  soft  palate;  IS,  epi- 
glottis; 7.^,  hyo-epiglottic  muscle;  75,  thyro-hyoid  muscle.  The  tensor  palati  (not  marked)  lies  medial  to  the  ptery- 
goideus  lateralis,  and  medial  to  the  tensor  is  the  levator  palati,  which  blends  above  with  the  outer  lamina  of  the  Eustach- 
ian tube. 


tubse  auditivse)  are  situated  on  the  lateral  wall  behind  the  posterior  nares  and  below 
the  level  of  the  ventral  nasal  meatus.  They  are  slit-like  openings,  directed  ob- 
liquely downward  and  backward,  and  are  a  little  more  than  an  inch  (ca.  3  cm.) 
in  length.  They  are  bounded  medially  by  a  fold  which  encloses  the  expanded 
extremity  of  the  cartilaginous  Eustachian  tube.  The  isthmus  fauciimi  is  the  oral 
open  ng;    it  is  closed  by  the  soft  palate  except  during  swallowing.     The  aditus 


THE    PHARYNX  407 

laryngis  occupies  the  greater  part  of  the  ventral  wall  or  floor  of  the  pharynx;  it 
is  open  except  during  deglutition.  Behind  this  is  the  aditus  oesophagi,  the  entrance 
to  the  oesophagus. 

The  wall  of  the  pharynx  comprises,  from  without  inward,  the  muscles,  the 
pharyngeal  aponeurosis,  and  the  mucous  membrane. 

The  muscles  of  the  pharynx  (Mm.  pharyngis)  (Figs.  332,  333)  are  covered 
by  the  pharyngeal  fascia,  which  is  attached  to  the  base  of  the  skull,  the  great  cornu 
of  the  hyoid  bone,  and  the  thyroid  cartilage  of  the  larynx.     They  are  as  follows: 

1.  The  stylo-pharyngeus  arises  from  the  medial  surface  of  the  dorsal  third 
of  the  great  cornu  of  the  hyoid  bone,  passes  ventro-medially,  and  enters  the  wall  of 
the  pharynx  by  passing  between  the  pterygo-pharyngeus  and  palato-pharyngeus. 
Its  fibers  rjldiate,  many  bundles  passing  forward,  others  inward  or  backward  be- 
neath the  hyo-pharyngeus.  It  raises  and  dilates  the  pharynx  to  receive  the  bolus 
in  swallowing. 

2.  The  palato-pharyngeus  arises  chiefly  by  means  of  the  aponeurosis  of  the 
soft  palate  from  the  palatine  and  pterygoid  bones ;  some  fibers  are  attached  to  the 
anterior  wide  part  of  the  Eustachian  tube.  Its  fibers  pass  backward  on  the  lateral 
wall  of  the  pharynx,  and  are  inserted  in  part  into  the  upper  edge  of  the  thyroid 
cartilage,  in  part  turn  inward  to  end  at  the  median  fibrous  raphe.  Its  action  is  to 
shorten  the  pharynx,  and  to  draw  the  larynx  and  cesophagus  toward  the  root  of  the 
tongue  in  swallowing.^ 

3.  The  pterygo-pharyngeus  is  flat  and  triangular.  It  lies  on  the  anterior  part 
of  the  lateral  wall  of  the  i)harynx.  It  arises  from  the  pterygoid  bone  above  the 
preceding  muscle, — from  which  it  is  not  distinctly  separated, — crosses  the  levator 
palati,  and  is  inserted  into  the  median  raphe.     Its  action  is  similar  to  the  preceding, 

4.  The  hyo-pharyngeus  may  consist  of  two  parts : 

(a)  The  kerato-pharyngeus  is  a  small  and  inconstant  muscle  which  arises 
from  the  medial  surface  of  the  great  cornu  of  the  hyoid  bone  near  its  ventral  end. 
It  passes  upward  and  backward  on  the  lateral  face  of  the  palato-pharyngeus, 
turns  toward  the  raphe,  and  spreads  out  under  the  next  muscle. 

(6)  The  chondro-pharyngeus,  broad  and  fleshy,  arises  from  the  thyroid  cornu 
of  the  hyoid  bone  and  by  a  thin  fasciculus  from  the  lamina  of  the  thyroid  cartilage. 
The  bundles  spread  out  and  end  at  the  median  raphe.  The  posterior  part  dips 
under  the  thyro-pharyngeus,  while  the  anterior  part  overlies  the  pterygo-  and 
palato-pharyngeus. 

5.  The  thyro-phar3mgeus  arises  from  the  lateral  surface  of  the  lamina  of  the 
thyroid  cartilage  on  and  behind  its  oblique  line.  Its  fibers  pass  forward  and 
medially  to  the  median  raphe. 

6.  The  crico-pharyngeus  arises  from  the  lateral  part  of  the  arch  of  the  cricoid 
cartilage  and  ends  at  the  raphe.  The  fibers  are  directed  upward,  forward,  and 
inward;   they  blend  behind  with  the  longitudinal  fibers  of  the  oesophagus. 

The  last  three  muscles  are  constrictors  of  the  pharynx. 

The  phar5mgeal  aponeurosis  is  attached  to  the  base  of  the  cranium.  It  is 
well  developed  on  the  medial  face  of  the  palato-pharyngeus  muscle  and  forms  a 
median  raphe  pharyngis  dorsally,  which  is  wide  in  its  posterior  part. 

The  mucous  membrane  of  the  pharynx  is  continuous  with  that  of  the  several 
cavities  which  open  into  it.  It  is  thin  and  closely  adherent  to  the  base  of  the  skull 
in  the  vicinity  of  the  posterior  nares,  where  the  muscular  wall  is  absent.  Behind 
the  Eustachian  openings  there  is  a  median  cul-de-sac,  the  pharyngeal  recess  (Re- 
cessus  pharyngeus) .  The  recess  is  somewhat  variable,  but  is  usually  about  an  inch 
in  depth  and  will  admit  the  end  of  the  finger.  In  the  ass  and  mule  it  is  much  deeper. 
Here  also  the  muscular  wall  is  absent  and  the  mucous  membrane  lies  against  the 

1  Vermeulen  states  that  the  pharyngeal  orifice  of  the  Eustachian  tube  is  opened  by  the 
contraction  of  that  part  of  the  muscle  which  is  attached  to  the  tube. 


408 


DIGESTIVE   SYSTEM    OF   THE    HORSE 


guttural  pouches.  From  the  Eustachian  opening  a  fold  of  the  mucous  membrane 
(Plica  salpingo-pharyngea)  passes  toward  but  does  not  reach  the  aditus  laryngis. 
A  horizontal  fold,  the  posterior  pillar  of  the  soft  palate  (Arcus  pharyngo-palatinus), 
passes  along  the  ventral  part  of  the  lateral  wall  and  unites  with  its  fellow  over  the 
entrance  to  the  oesophagus.  The  dorsal  part  of  the  cavity  (Pars  respiratoria) 
is  lined  with  a  ciliated  epithelium,  while  the  ventral  part  (Pars  digestoria)  has  a 
stratified  squamous  epithelium.     The  communication  between  the  two  is  oval 


Fig.  349. — Posterior  Part  of  a  Sagittal  Section  op  Head  .4nd  Part  of  Neck  of  Horse,  Cut  about  1  cm.  to  the 
Left  of  the  Median  Plane. 
1,  Posterior  nares;  2,  pharyngeal  orifice  of  Eustachian  tube;  3,  aditus  laryngis;  4<  aditus  oesophagi;  a,  posterior 
pillar  of  soft  palate;  S',  junction  of  3  with  its  fellow  over  entrance  to  oesophagus;  6,  epiglottis;  7,  body  of  thyroid 
cartilage;  <S,  arytenoid  cartilage;  5,  S,  cricoid  cartilage;  iO,  true  vocal  cord;  7 /,  false  vocal  cord;  ;;2,  lateral  ventricle 
of  larynx;  13,  crico-arytenoideus  dorsalis;  14,  oesophagus;  15,  external  carotid  arterj';  16,  hypoglossal  nerve;  17, 
glosso-pharyngeal  nerve;  IS,  great  cornu  of  hyoid  bone;  19,  Eustachian  tube;  W,  body  of  hyoid  bone;  21,  hyoideus 
transversus;  32,  ridges  of  hard  palate;  22',  soft  palate;  23,  septum  between  frontal  sinuses;  24,  olfactorj'  mucous 
membrane;  25,  sphenoidal  sinus;  26,  basilar  part  of  occipital  bone;  26',  supra-occipital;  27,  body  of  sphenoid  bone; 
28,  pituitary  body;  29,  chiasma  opticum;  30,  corpora  quadrigemina;  31,  thalamus;  32,  arachnoid;  33,  odontoid 
ligament;   34,  posterior  auricular  muscles. 


and  is  bounded  by  the  free  edge  of  the  soft  palate  and  its  posterior  pillars;  it  is 
termed  the  pharyngeal  isthmus.  On  either  side  of  the  aditus  laryngis  is  a  narrow 
deep  depression,  the  piriform  recess  (Recessus  piriformis). 

The  submucous  tissue  contains  numerous  mucous  glands  (Glandulae  pharyn- 
gese).  In  the  young  subject  the  lymph  follicles  are  numerous  and  form  a  collection 
dorsally  and  between  the  Eustachian  openings,  known  as  the  pharyngeal  tonsil 
(Tonsilla  pharyngea). 


THE    CESOPHAGUS  409 

Vessels  and  Nerves. — The  arteries  are  derived  from  the  common  carotid, 
external  carotid,  and  external  maxillary  arteries.  The  lymph  vessels  pass  to  the 
pharyngeal  and  anterior  cervical  lymph  glands.  The  nerves  are  derived  from  the 
trigeminus,  glosso-pharyngeus,  and  vagus. 


THE  CESOPHAGUS 

The  oesophagus  is  a  musculo-membranous  tube,  about  50  to  60  inches  (ca. 
125  to  150  cm.)  in  length,  which  extends  from  the  pharynx  to  the  stomach.  In 
its  course  it  shows  several  changes  of  direction.  It  begins  in  the  median  plane  above 
the  anterior  border  of  the  cricoid  cartilage  of  the  larynx.  At  the  fourth  cervical 
vertebra  it  has  passed  to  the  left  side  of  the  trachea,  and  continues  this  relation 
as  far  as  the  third  thoracic  vertebra.  Here  it  again  gains  the  dorsal  surface  of  the 
trachea,  and,  passing  backward,  crosses  the  aortic  arch,  by  which  it  is  pushed  over 
to  the  right  of  the  median  plane.  It  continues  in  the  mediastinum  between  the 
lungs,  backward  and  a  little  dorsally,  inclining  gradually  to  the  left,  and  reaches 
the  hiatus  oesophageus  of  the  diaphragm.  Passing  through  this  it  terminates  at 
once  at  the  cardiac  orifice  of  the  stomach,  a  little  to  the  left  of  the  median  plane, 
and  about  four  or  five  inches  (ca.  10  to  12  cm.)  ventral  to  the  vertebral  end  of  the 
fourteenth  rib.^ 

Viewed  with  reference  to  the  horizontal  plane,  its  course  is  downward  and 
backward  till  it  enters  the  thorax  and  passes  upward  to  gain  the  dorsal  face  of 
the  trachea.  Then  for  a  short  distance  (i.  e.,  to  the  root  of  the  lung)  its  direction  is 
almost  horizontal;  behind  this  it  passes  somewhat  upward  to  its  termination. 
The  cervical  part  (Pars  cervicalis)  of  the  tube  is  about  four  to  six  inches  (10  to  15 
cm.)  longer  than  the  thoracic  part  (Pars  thoracalis),  while  the  so-called  abdominal 
part  (Pars  abdominalis)  is  about  an  inch  (2  to  3  cm.)  long.- 

The  principal  relations  of  the  oesophagus  at  its  origin  are:  to  the  cricoid 
cartilage  and  dorsal  crico-arytenoid  muscles  ventrally;  to  the  guttural  pouches 
and  the  ventral  straight  muscles  dorsally;  and  to  the  carotid  arteries  laterally. 
In  the  middle  of  the  neck  the  relations  are:  to  the  left  longus  colli  muscle  dorsally; 
to  the  trachea  medially;  to  the  left  carotid  artery,  vagus,  sympathetic,  and  recurrent 
nerves  laterally.  Near  the  thoracic  inlet  the  oesophagus  is  usually  in  contact 
with  the  left  jugular  vein  for  a  short  distance.  At  its  entrance  into  the  thorax 
it  has  the  trachea  on  its  medial  side;  the  first  rib,  the  roots  of  the  brachial  plexus 
of  nerves,  and  the  left  posterior  cervical  ganglion  laterally.  After  gaining  the 
dorsal  surface  of  the  trachea,  it  has  the  aorta  on  its  left  and  the  vena  azygos  and 
right  vagus  nerve  on  its  right  side.  In  its  course  through  the  posterior  medias- 
tinum the  oesophageal  trunks  of  the  vagus  nerves  he  above  and  below  it,  and  the 
oesophageal  artery  is  dorsal  to  it. 

Structure. — The  wall  is  composed  of  four  coats:  (1)  A  fibrous  sheath  termed 
the  tunica  adventitia;  (2)  the  muscular  coat;  (3)  a  submucous  layer;  (4)  the 
mucous  membrane.  The  muscular  coat  is  of  the  striped  variety  as  far  as  the  base 
of  the  heart,  where  it  rapidly  changes  to  the  unstriped  type.  In  addition  to  this 
change,  the  muscular  coat  becomes  much  thicker  and  firmer,  while  the  lumen  is 
diminished.   Except  at  each  end  of  the  tube  the  muscular  coat  consists  chiefly  of 

^  The  distance  between  the  terminal  part  of  the  oesophagus  and  the  vertebra  varies.  In 
formalin-hardened  subjects  it  is  most  commonly  as  given  above,  but  in  soft  specimens  or  in  those 
which  have  been  frozen  without  previous  fixation  it  is  usually  nearer  the  spine. 

2  Careful  observations  (especially  on  frozen  subjects  and  those  in  which  the  organs  have  been 
hardened  in  situ)  show  that  there  is  no  abdominal  part  of  the  oesophagus  in  the  strict  sense  of  the 
term.  The  stomach  here  lies  directly  on  the  diaphragm,  so  that  the  last  inch  or  so  of  the  oesopha- 
gus is  placed  obliquely  in  the  hiatus  oesophageus,  and  is  covered  on  the  right  and  ventrally  by  the 
pleura,  but  not  by  peritoneum.  In  soft  subjects  the  weight  of  the  stomach,  or  traction  on  it,  draws 
part  of^the  oesophagus  into  the  abdomen,  inclosed  in  a  collar  of  peritoneum. 


410  DIGESTIVE    SYSTEM    OF   THE    HORSE 

two  layers  of  fibers  arranged  spirally  or  elliptically,  which  intercross  dorsally  and 
A-entrally.  At  the  origin  two  bundles  nearly  an  inch  (ca.  2  cm.)  wide  arise  from 
the  wide  posterior  part  of  the  pharyngeal  raphe  and  from  a  tendon  common  to 
the  crico-pharyngeus  and  thyro-pharyngeus.  These  bundles,  which  blend  and 
decussate  at  their  origin,  diverge  and  pass  to  each  side  of  the  oesophagus.  In  the 
angle  between  them  a  deeper  layer  of  circular  fibers  is  visible.  Two  small  ventral 
bundles  emerge  from  the  depression  between  the  lamina  of  the  cricoid  cartilage 
and  the  arytenoid  cartilages.  These  curve  around  to  the  side  of  the  oesophagus 
and  blend  with  the  dorsal  bundles  before  described.  In  the  terminal  part  there 
is  an  external  longitudinal  layer  and  an  internal  circular  layer,  the  latter  being 
extremely  thick.  The  mucous  membrane  is  pale,  and  is  covered  with  squamous 
stratified  epithehum.  It  is  loosely  attached  to  the  muscular  coat  by  an  abundant 
submucosa,  and  lies  in  longitudinal  folds  which  obliterate  the  lumen  except  during 
deglutition.^ 

Blood-supply." — Carotid,  broncho-cesophageal,  and  gastric  arteries. 

Nerve-supply. — Vagus,  glosso-pharyngeal,  and  sympathetic  nerves. 


THE  ABDOMINAL  CAVITY 

The  abdominal  cavity  (Cavum  abdominis)  is  the  largest  of  the  body  cavities. 
It  is  separated  from  the  thoracic  cavity  by  the  diaphragm  and  is  continuous  behind 
with  the  pelvic  cavity.  The  line  of  demarcation  between  the  abdominal  and 
pelvic  cavities  is  known  as  the  terminal  line,  or  brim  of  the  pelvis;  it  is  formed  by 
the  base  of  the  sacrum  dorsally,  the  ileo-pectineal  lines  laterally,  and  the  anterior 
borders  of  the  pubic  bones  ventrally. 

The  cavity  is  ovoid  in  form,  but  is  somewhat  compressed  laterally.  Its  long 
axis  extends  obhquely  from  the  center  of  the  pelvic  inlet  to  the  sternal  part  of  the 
diaphragm.  Its  dorso-ventral  diameter  is  greatest  at  the  first  lumbar  vertebra, 
while  its  greatest  transverse  diameter  is  a  little  nearer  the  pelvis. 

The  dorsal  wall  or  roof  is  formed  by  the  lumbar  vertebrse,  the  lumbar  muscles, 
and  the  lumbar  part  of  the  diaphragm. 

The  lateral  walls  are  formed  by  the  oblique  and  transverse  abdominal  muscles, 
the  abdominal  tunic,  the  anterior  parts  of  the  ilia  with  the  iliacus  muscles,  the 
cartilages  of  the  asternal  ribs,  and  the  parts  of  the  posterior  ribs  which  are  below 
the  attachment  of  the  diaphragm. 

The  ventral  wall  or  floor  consists  of  the  two  recti,  the  aponeuroses  of  the  oblique 
and  transverse  muscles,  the  abdominal  tunic,  and  the  xiphoid  cartilage. 

The  anterior  wall  is  formed  by  the  diaphragm,  which  is  deeply  concave,  thus 
greatly  increasing  the  size  of  the  abdomen  at  the  expense  of  the  thorax. 

It  should  be  noted  that  the  diaphragm  also  concurs  practically  in  the  formation  of  a  con- 
siderable part  of  the  lateral  walls,  since  its  costal  part  even  during  ordinary  inspiration  lies  directly 
on  the  ribs  over  a  width  of  four  or  five  inches  (ca.  10  to  12  cm.) ;  in  expiration  this  area  of  contact 
includes  about  all  of  the  costal  part.  This  fact  is  of  clinical  importance,  with  reference  to  auscul- 
tation and  percussion  and  penetrating  wounds.  The  cupola  of  the  diaphragm  extends  as  far 
forward  as  a  plane  through  the  sixth  rib  to  the  right  of  the  heart. 

The  muscular  walls  are  lined  by  a  layer  of  fascia,  distinguished  in  different 
parts  as:  (1)  The  diaphragmatic  fascia;  (2)  the  transversalis  fascia;  (3)  the  iliac 
fascia;    (4)  the  deep  layer  of  the  lumbo-dorsal  fascia. 

The  subserous  tissue    (Tela  subserosa)   unites  the  fascia  and  peritoneum. 

1  The  potential  lumen  is  difficult  to  determine  at  all  accurately.  When  distended,  its  average 
diameter  (according  to  Rubeli)  is  a  little  more  than  6  cm.  The  thickness  of  the  wall  varies  (in- 
versely as  the  lumen)  from  0.4  to  1.2  cm.  or  more.  The  change  in  type  of  the  muscular  tissue  is 
gradual,  and  begins  in  the  deep  part;  bundles  of  striped  muscle  are  present  even  after  the  apparent 
change  to  unstriped  muscle,  and  may  extend  to  the  stomach.  In  the  posterior  part  of  the  tube 
many  bundles  intercross  in  an  irregular  plexiform  manner. 


THE    PERITONEUM  411 

It  is  areolar  tissue,  and  is  more  or  less  loaded  with  fat  according  to  the  condition 
of  the  subject,  except  over  the  diaphragm.  It  sends  laminae  into  the  various 
peritoneal  folds. 

The  peritoneum,  the  serous  membrane  which  lines  the  cavity,  will  be  described 
later. 

The  abdominal  walls  are  pierced  in  the  adult  by  five  apertures.  These  are 
the  three  foramina  of  the  diaphragm  and  the  inguinal  canals,  which  have  been 
described.  In  the  foetus  there  is  the  umbilical  opening  also.  This  transmits  the 
urachus,  a  tube  which  connects  the  bladder  with  the  allantois;  the  two  umbilical 
arteries,  which  carry  ])lood  from  the  foetus  to  the  placenta;  and  the  umbilical 
vein,  which  returns  blood  from  the  placenta  to  the  liver  of  the  foetus.  After  birth 
the  orifice  is  closed  by  fibrous  tissue,  leaving  a  scar,  the  umbilicus,  which  is  more 
or  less  distinctly  visible  in  the  median  ventral  line  in  a  transverse  plane  about 
tangent  to  the  ventral  end  of  the  last  rib. 

The  cavity  contains  the  greater  part  of  the  digestive  and  urinary  organs,  i^art 
of  the  internal  genital  organs,  numerous  nerves,  blood  vessels,  lymph  vessels  and 
glands,  ductless  glands  (spleen  and  adrenal  bodies),  and  certain  foetal  remains. 

For  topographic  purposes  the  abdomen  is  divided  into  nine  regions  by  imagi- 
nary planes.^  Two  of  these  planes  are  sagittal  and  two  are  transverse.  The 
sagittal  planes  cut  the  middles  of  the  inguinal  ligaments;  the  transverse  planes 
pass  through  the  last  thoracic  and  fifth  luml^ar  vertebrae,  or  the  ventral  end  of  the 
fifteenth  rib  and  the  tuber  coxae  respectively.  The  transverse  planes  divide  the 
abdomen  into  three  zones,  one  behind  the  other,  viz.,  epigastric,  mesogastric, 
and  h)rpogastric :  these  are  subdivided  ]:)y  the  sagittal  planes  as  indicated  in  the 
subjoined  table: 

Left  parachondriac Xiphoid Right  parachondriac 

Left  lumbar Umbilical Right  lumbar 

Left  ihac Prepubic Right  iliac 

Other  useful  regional  terms  are:  sublumbar,  diaphragmatic,  inguinal.  The 
first  two  require  no  explanation.  The  inguinal  regions  (right  and  left)  lie  in  front 
of  the  inguinal  ligament.  The  flank  is  that  part  of  the  lateral  wall  which  is  formed 
only  of  goft  structures.  The  triangular  depression  on  its  upper  part  is  termed 
the  paralumbar  fossa;  this  is  bounded  dorsally  by  the  lateral  border  of  the  lon- 
gissimus,  ventrally  by  the  upper  border  of  the  obliquus  abdominis  internus,  and 
in  front  by  the  last  rib. 

THE  PERITONEUM  = 

The  peritoneum  is  the  thin  serous  membrane  which  lines  the  abdominal  cavity 
and  the  pelvic  cavity  (in  part),  and  covers  to  a  greater  or  less  extent  the  viscera 
contained  therein.  In  the  male  it  is  a  completely  closed  sac,  but  in  the  female 
there  are  two  small  openings  in  it ;  these  are  the  abdominal  orifices  of  the  uterine 
or  Fallopian  tubes,  which  at  their  other  ends  communicate  with  the  uterus,  and  so 
indirectly  with  the  exterior.  The  peritoneal  cavity  (Cavum  peritonsei)  is  only  a 
potential  one,  since  its  opposing  walls  are  normally  separated  only  by  the  thin 
film  of  serous  fluid  (secreted  by  the  membrane)  which  acts  as  a  lubricant.^ 

The  free  surface  of  the  membrane  has  a  glistening  appearance  and  is  very 
smooth.     This  is  due  to  the  fact  that  this  surface  is  formed  by  a  layer  of  flat  mes- 

^  This  method  of  division,  although  long  in  use,  is  practically  valueless  for  accurate  descrip- 
tion. It  is  mentioned  here  chiefly  liecause  agreement  on  a  more  useful  topographic  method  has 
not  been  arrived  at. 

^  Only  a  general  account  of  the  arrangement  of  the  peritoneum  is  given  in  this  section,  since 
a  detailed  description  cannot  be  understood  without  a  knowledge  of  the  viscera  concerned. 

^  It  is  necessary  not  to  confuse  the  peritoneal  cavity  with  the  abdominal  cavity.  The 
organs  are  all  extraperitoneal  and  the  peritoneal  cavity  contains  only  the  serous  fluid. 


412 


DIGESTIVE   SYSTEM    OF  THE   HORSE 


othelial  cells,  and  is  moistened  by  the  peritoneal  fluid.  Friction  is  thus  reduced 
to  a  minimum  during  the  movements  of  the  viscera.  The  outer  surface  of  the  peri- 
toneum is  related  to  the  subserous  tissue,  which  attaches  it  to  the  abdominal  wall 
or  the  viscera. 

In  order  to  understand  the  general  disposition  of  the  peritoneum,  we  may- 
imagine  the  abdominal  cavity  to  be  empty  and  lined  by  a  simple  layer  of  perito- 
neum, termed  the  parietal  layer  (Lamina  parietalis).  We  may  further  imagine 
the  organs  as  beginning  to  develop  in  the  subserous  tissue,  enlarging,  and  migrat- 
ing into  the  abdominal  cavity  to  a  varying  extent.  In  doing  so  they  carry  the  per- 
itoneum before  them,  producing  introversion  of  the  simple  sac,  and  forming  folds 
which  connect  them  with  the  wall  or  with  each  other.  The  viscera  thus  receive 
a  complete  or  partial  covering  of  peritoneum,  termed  the  visceral  layer  (Lamina 
visceraUs).  The  connecting  folds  are  termed  omenta,  mesenteries,  ligaments, 
etc.     They  contain  a  varying  quantity  of  connective  tissue,  fat,  and  lymph  glands, 

and  furnish  a  path  for  the  vessels  and  nerves  of 
the  viscera.  Some  contain  unstriped  muscular 
tissue.  An  omentum  is  a  fold  which  passes  from 
the  stomach  to  other  viscera.  There  are  three  of 
these,  namely :  (1)  Thelesser  omentum  (Omentum 
minus), ^  which  passes  from  the  lesser  curvature  of 
the  stomach  to  the  liver;  (2)  the  gastro-splenic 
omentum  (Ligamentum  gastrohenale),  which  ex- 
tends from  the  greater  curvature  of  the  stomach 
to  the  spleen;  (3)  the  greater  omentum  (Omen- 
tum majus),-  which  passes  from  the  greater  curva- 
ture of  the  stomach  and  from  the  spleen  to  the 
terminal  part  of  the  great  colon  and  the  origin  of 
the  small  colon.  It  does  not  pass  directly  from 
one  organ  to  the  other,  but  forms  an  extensive 
loose  sac  (ligs.  377,  378).  A  mesentery  (Mesen- 
terium)  is  a  fold  which  attaclies  the  intestine  to 
the  dorsal  wall  of  the  abdomen.  There  are  two 
mesenteries  in  the  horse:  (1)  The  great  mes- 
entery connects  the  greater  part  of  the  small 
intestine  with  the  dorsal  abdominal  wall;  (2) 
the  colic  mesentery  attaches  the  small  colon  to 
the  dorsal  abdominal  wall.  Ligaments  are  folds 
which  pass  between  viscera  other  than  parts  of  the 
digestive  tube,  or  connect  them  with  the  abdom- 
inal wall.  The  term  is  also  applied  to  folds  which  attach  parts  of  the  digestive  tract 
to  the  abdominal  wall,  but  do  not  contain  their  blood-vessels  and  nerves.  Some  (e.  g., 
the  lateral  and  coronary  ligaments  of  the  liver)  are  strengthened  by  fibrous  tissue; 
others  (e.  g.,  the  broad  ligaments  of  the  uterus)  contain  also  unstriped  muscular 
tissue. 


Fig.  350. — Diagrammatic  Cross-section 

OF  Abdomen. 

To  show  arrangement   of  peritoneum 

when  reduced  to  its  simplest  form.     The 

external  black  line  indicates  the  body-wall. 

1,  Organ  (e.  g.,  kidney)  in  contact  with  wall; 

2,  organ  (e.  g.,  small  intestine)  at  a  dis- 
tance from  wall;  3,  parietal  peritoneum;  4, 
4,  visceral  peritoneum;  5,  mesentery;  6, 
peritoneal  cavity. 


THE  PELVIC  CAVITY 

The  pelvis  is  the  posterior  part  of  the  trunk.  It  incloses  the  pelvic  cavity 
(Cavum  pelvis),  which  communicates  in  front  with  the  abdominal  cavity,  the  line 
of  demarcation  being  the  terminal  line  or  pelvic  brim. 

The  dorsal  wall  or  roof  is  formed  by  the  sacrum  and  first  three  coccygeal 
vertebrae.     The  lateral  walls  are  formed  by  the  parts  of  the  iha  behind  the  ilio- 

'  Also  known  as  the  gastro-hepatic  omentum. 
^  Also  known  as  the  gastro-colic  omentum. 


THE   PELVIC    CAVITY 


413 


pectineal  lines  and  the  sacro-sciatic  ligaments.     The  ventral  wall  or  floor  is  formed 
by  the  pubic  and  ischial  bones.     The  boundary  of  the  outlet  is  formed  by  the  third 
coccygeal  vertebra  dorsally,  the  ischial  arch  ventrally,  and  the  posterior  edges 
of  the  sacro-sciatic  ligaments  and  the  semi- 
membranosus muscles  laterally.     The  out- 
let is  closed  by  the  perineal  fascia ;  this  con- 
sists of  superficial  and   deep   layers   which 
are  attached  around  the  margin  of  the  outlet 
and  centrally  to  the  organs  at  the  outlet — 
the  anus  and  its  muscles,  the  vulva  (in  the 
female),   and  the  root  of  the  penis  (in  the 
male). 

The  cavity  contains  the  rectum,  parts 
of  the  internal  genital  and  urinary  organs, 
some  foetal  remnants,  muscles,  vessels,  and 
nerves.  It  is  lined  by  the  fascia  pelvis,  and 
in  part  by  the  peritoneum. 

The  pelvic  peritoneum  is  continuous  in 
front  with  that  of  the  abdomen.  It  lines  the 
cavity  for  a  variable  distance  backward,  and 
is  then  reflected  on  to  the  viscera,  and  from 

one  organ  to  another.  We  may  therefore  distinguish  an  anterior,  peritoneal,  and  a 
posterior,  retroperitoneal,  part  of  the  cavity.  Along  the  mid-dorsal  line  it  forms 
a  continuation  of  the  colic  mesentery,  the  mesorectum,  which  attaches  the  first  or 
peritoneal  part  of  the  rectum  to  the  roof.     In  animals  in  fair  condition  a  consider- 


FiG.   351. — Diagram    of    Sagittal   Section    op 
Male     Pelvis     to     show    Disposition    op 
Peritoneum. 
a,  Sacro-rectal  pouch,  continuous  laterally  with 

b,  recto-genital  pouch;    c,  vesico-genital  pouch;    d, 

vesico-pubic  pouch.     The  lateral  Une  of  reflection 

of  the  peritoneum  is  dotted. 


Fig.  352. — Schematic   Cross-section   to   Show  Ar-  Fig.  353. — Schematic   Cross-section   to   Show  Ar- 

rangement of  Pelvic  Peritoneum  in  the  Male.  rangement  of  Pelvic  Peritoneum  in  the  Female. 

o,  b.  Recto-genital  pouch;  c,  c,  vesico-genital  pouch;  d,  d,  vesico-pubic  pouch;  1,  mesorectum;  2,  2,  genital  folds 
in  male,  broad  ligaments  ot  uterus  in  female;  3,  3,  lateral  ligaments  of  bladder;  4,  middle  hgament  of  bladder;  v.d., 
ductus  deferentes;  u.m.,  uterus  masculinus. 


able  quantity  of  subserous  and  retroperitoneal  fat  is  found  on  the  walls  and  in  the 
various  interstices. 

In  the  male  the  general  disposition  of  the  peritoneum  here  is  as  follows.     If 
traced  along  the  dorsal  wall,  it  is  reflected  from  the  sacrum  on  to  the  rectum, 


414 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


forming  the  visceral  peritoneum  for  the  first  part  of  that  tube.^  Laterally  it  is 
reflected  in  a  similar  fashion.  If  the  rectum  be  raised,  it  will  be  seen  that  the 
peritoneum  passes  from  its  ventral  surface  and  forms  a  transverse  fold  which  lies 
on  the  dorsal  surface  of  the  bladder  (Fig.  370).  This  is  the  genital  fold  (Plica 
genitalis).  Its  concave  free  part  passes  on  either  side  into  the  inguinal  canal. 
The  ventral  layer  of  this  fold  is  reflected  on  to  the  dorsal  surface  of  the  bladder. 
Thus  there  is  formed  a  pouch  between  the  rectum  and  bladder — the  recto-vesical 
pouch  (Excavatio  recto- vesicalis),  which  is  partially  subdivided  by  the  genital 
fold  into  recto-genital  and  vesico-genital  cavities.  The  fold  contains  the  ductus 
deferentes,  part  of  the  vesiculae  seminales,  and  the  uterus  masculinus  (a  foetal 
remnant).     If  the  bladder  is  now  raised,  it  is  seen  that  the  peritoneum  passes 


Left  extremity 


Antrum  pyloricum 


Fig.  354. — Stomach  op  Horse;  Parietal  Surface. 

The  organ  was  fixed  in  situ  when  well  tilled.     The  lesser  curvature  has  been  opened  up  slightly  and  the  peritoneum, 

etc.,  in  this  vicinity  removed.     The  larger  branches  of  the  anterior  gastric  artery  and  vein  are  visible. 


from  its  ventral  surface  on  to  the  pelvic  floor,  forming  centrally  the  median  um- 
bilical fold  or  middle  ligament  of  the  bladder  (Plica  umbilicalis  media).  It  also 
passes  from  each  side  of  the  bladder  to  the  lateral  pelvic  wall  and  forms  thus 
the  lateral  umbilical  fold  or  ligament  of  the  bladder  (Plica  umbilicalis  lateralis) ; 
this  contains  in  its  edge  the  so-called  round  ligament  of  the  bladder  (Ligamentum 
teres  vesicse) — the  partially  occluded  umbilical  artery,  which  is  a  large  vessel 
in  the  foetus.^ 

In  the  female  the  arrangement  is  modified  by  the  presence  of  the  uterus; 

^  The  point  at  which  the  reflection  takes  place  is  quite  variable,  and  apparently  depends 
chiefly  on  the  amount  of  feces  in  the  rectum.  When  the  bowel  is  very  full  the  reflection  may  be 
little  behind  the  promontory;  when  it  is  empty,  the  reflection  may  l)e  at  the  posterior  end  of  the 
sacrum. 

^  In  the  foetus  and  new-born  foal  these  three  folds  extend  to  the  umbilicus  in  conformity  with 
the  abdominal  position  of  the  bladder.  When  the  latter  becomes  a  pelvic  organ,  the  lateral  folds 
conform  to  the  change  and  end  at  the  vertex  of  the  bladder.  The  median  fold  may  still  be  trace- 
able to  the  umbilicus. 


THE    STOMACH 


415 


the  genital  fold  is  enlarged,  so  as  to  inclose  the  uterus  and  a  small  part  of  the  vagina. 
It  forms  two  extensive  folds,  the  broad  ligaments  of  the  uterus  (Ligamenta  lata 
uteri),  which  attach  that  organ  to  the  sides  of  the  pelvic  cavity  and  the  lumbar 
part  of  the  abdominal  wall  (Pig.  530).  It  thus  divides  the  recto-vesical  pouch 
completely  into  dorsal  and  ventral  compartments — the  recto-genital  pouch  (Ex- 
cavatio  recto-uterina)  and  the  vesico-genital  pouch  (Excavatio  vesico-uterina). 
Further  details  will  be  given  in  the  description  of  the  pelvic  viscera. 


THE  STOMACH 

The  stomach  (Ventriculus)  is  the  large  dilatation  of  the  alimentary  canal 
behind  the  diaphragm ;  it  intervenes  between  the  oesophagus  and  the  small  intestine. 
It  is  a  sharply  curved,  U-shaped  sac,  the  right  part  being,  however,  much  shorter 


Saccus  cwcus 
{left  extremity) 


Aim  of  attachment  to  dia- 
phragm {non-peritoneal) 


Fig.  355. — Stom.'^ch  op  Horse;  Visceral  Surface,  with  First  Part  of  Duodenum. 
Fixed  in  situ  when  full  but  not  distended.     The  posterior  gastric  artery  and  its  larger  branches  with  two  satellite  veins 


than  the  left  one.  The  convexity  is  directed  ventrally.  When  moderately  dis- 
tended, there  may  be  a  shght  constriction  which  indicates  the  division  into  right 
and  left  sacs.  It  is  relatively  small,  and  is  situated  in  the  dorsal  part  of  the  ab- 
dominal cavity,  behind  the  diaphragm  and  hver,  mainly  to  the  left  of  the  median 
plane. 

It  presents  for  description  two  surfaces,  two  curvatures,  and  two  extremities. 
The  parietal  surface  (Facies  parietalis)  is  convex  and  is  directed  forward,  u]iward, 
and  toward  the  left ;  it  lies  against  the  diaphragm  and  liver.  The  visceral  surface 
(Facies  visceralis),  also  convex,  faces  in  the  opposite  direction;  it  is  related  to  the 
terminal  part  of  the  large  colon,  the  pancreas,  the  small  colon,  the  small  intes- 


416 


DIGESTIVE   SYSTEM    OF   THE   HORSE 


tine,  and  the  greater  omentum.  The  borders  between  these  surfaces  are 
termed  the  curvatures.  The  lesser  curvature  (Curvatura  ventricuh  minor) 
is  very^  short,  extending  from  the  termination  of  the  oesophagus  to  the  junc- 
tion with  the  small  intestine.  When  the  stomach  is  in  situ,  its  walls  are  here  in 
contact,  and  the  cardia  and  pylorus  close  together.^  The  greater  curvature  (Cur- 
vatura ventriculi  major)  is  very  extensive.  From  the  cardia  it  is  first  directed 
dorsally  and  curves  over  the  left  extremity;  it  then  descends,  passes  to  the  right, 
crosses  the  median  plane,  and  curves  upward  to  end  at  the  pylorus.  Its  left  part 
is  related  to  the  spleen,  while  its  ventral  portion  rests  on  the  left  parts 
of  the  great  colon.  The  left  extremity  (Extremitas  sinistra)  has  the  form  of  a 
rounded  cul-de-sac  termed  the  saccus  caecus ;  it  lies  ventral  to  the  left  crus  of  the 
diaphragm,  and  so  beneath  the  dorsal  part  of  the  sixteenth  and  seventeenth  ribs. 
It  is  related  to  the  pancreas  and  the  termination  of  the  great  colon  behind  and  the 
base  of  the  spleen  laterally.     The  right  or  pyloric  extremity  (Extremitas  dextra) 

is  much  smaller  and  is  continuous  w^ith 
the  duodenum,  the  junction  being  in- 
dicated by  a  marked  constriction.  It 
lies  just  to  the  right  of  the  median 
plane,  and  about  two  inches  (ca.  5  cm.) 
lower  than  the  cardia;  it  is  in  contact 
with  the  visceral  surface  of  the  liver. 
About  two  or  three  inches  (ca.  5  to  8 
cm.)  from  the  pylorus  there  is  a  con- 
striction which  marks  off  the  antrum 
pyloricum  from  the  rest  of  the  right 
sac.  The  oesophageal  orifice  is  termed 
the  cardia;  it  is  situated  at  the  left 
end  of  the  lesser  curvature,  but  about 
eight  to  ten  inches  (ca.  20  to  25  cm.) 
from  the  left  extremity.^  The  oesopha- 
gus joins  the  stomach  very  obliquely. 
The  opening  is  closed  by  the  sphincter 
cardiae  and  numerous  folds  of  mucous 
membrane.  The  pylorus  is  the  open- 
ing into  the  intestine.  Its  position  is 
indicated  externally  by  a  distinct  con- 
striction. Internally  it  presents  a  cir- 
cular ridge  caused  by  a  ring  of  mus- 
cular tissue — the  sphincter  pylori. 

The  stomach  is  held  in  position 
mainly  by  the  pressure  of  the  sur- 
The  following  peritoneal  folds  connect 


Fig.  356. — ^Everted  Stomach  of  Horse  from  which 
THE  Mucous  Membrane  has  been  Removed. 
O,  (Esophagus;  D,  duodenum;  6,  circular  layer; 
c',  internal  oblique  fibers;  c",  loop  around  cardia;  c'", 
transition  of  internal  to  external  oblique  fibers;  d,  fibers 
connecting  the  two  branches  of  the  cardiac  loop;  p, 
antral  sphincter;  p',  pyloric  sphincter.  (EUenberger- 
Baum,  Anat.  d.  Haustiere.) 


rounding  viscera  and  by  the  oesophagus, 
it  with  the  adjacent  parts: 

1.  The  gastro-phrenic  ligament  (Lig.  gastrophrenicum)  connects  the  greater 
curvature,  from  the  cardia  to  the  left  extremity,  with  the  crura  of  the  diaphragm. 
This  leaves  a  narrow  area  uncovered  with  peritoneum,  and  here  the  stomach  is 
attached  to  the  diaphragm  by  areolar  tissue. 

1  The  more  expressive  term  "incisiira  angularis"  has  been  suggested  and  is  worthy  of  adop- 
tion. 

2  The  position  of  the  cardia  varies  of  course  vnth  the  excursion  of  the  diaphragm.  It  is 
usually  an  inch  or  more  (ca.  3  cm.)  to  the  left  of  the  median  plane  and  ventral  to  the  vertebral  end 
of  the  fourteenth  rib.  When  the  diaphragm  is  contracted  the  cardia  may  be  six  inches  (ca.  15  cm.) 
below  the  level  of  the  spine;  when  the  diaphragm  is  relaxed,  the  interval  may  be  reduced  to  about 
two  inches  (ca.  5  cm.). 


THE    STOMACH  417 

The  use  of  the  term  ligament  in  regard  to  the  arrangement  here  is  somewhat  misleading, 
since  the  stomach  is  attached  to  the  crus  of  the  diaphragm  by  areolar  tissue;  the  peritoneum 
passes  from  the  diaphragm  to  the  stomach  on  each  side  of  the  area  of  adhesion.  In  soft  material 
there  is  the  appearance  of  a  Ugament  composed  of  two  layers  of  peritoneum,  but  this  is  an  artefact. 

2.  The  lesser  omentum  (Omentum  minus)  connects  the  lesser  curvature  and 
the  first  part  of  the  duodenum  with  the  hver  below  the  oesophageal  notch  and  the 
portal  fissure. 

The  part  of  the  omentum  which  extends  from  the  liver  to  the  stomach  is  designated  the  lig. 
hepato-gastricum,  and  the  remainder  which  goes  to  the  duodenum  as  the  lig.  hepato-duodenale. 

3.  The  gastro-splenic  omentum  (Lig.  gastrolienale)  passes  from  the  left  part 
of  the  greater  curvature  to  the  hilus  of  the  spleen;  it  is  continuous  ventrally  with 
the  greater  omentum. 

4.  The  greater  omenttmi  (Omentum  majus)  connects  the  ventral  part  of  the 
greater  curvature  and  the  first  curve  of  the  duodenum  with  the  terminal  part  of  the 
great  colon  and  the  initial  part  of  the  small  colon.  It  does  not  pass  directly  between 
these  parts  but  forms  a  large  sac,  which  will  be  described  later. 

5.  The  gastro-pancreatic  fold  (Plica  gastropancreatica)  extends  from  the  left 
sac  above  the  cardia  to  the  duodenum.  It  is  attached  dorsally  to  the  liver  and 
vena  cava,  ventrally  to  the  pancreas. 

The  stomach  of  the  equidse  is  relatively  small,  its  capacity  varying  from  two 
to  four  gallons  (ca.  8  to  15  liters). 

The  size,  form,  and  position  of  the  stomach  are  subject  to  considerable  variation.  WTien 
the  stomach  is  nearly  empty,  the  saccus  csecus  contains  only  gas  and  is  strongly  contracted;  the 
middle  part  (physiological  fundus)  contains  the  ingesta  and  preserves  its  rounded  character, 
while  the  pyloric  part  is  contracted.  In  this  state  coils  of  small  intestine  usually  lie  ventral  to  the 
stomach  and  may  separate  it  entirely  from  the  colon.  In  exceptional  cases,  when  the  organ  is 
empty  and  contracted,  even  the  pyloric  end  is  to  the  left  of  the  median  plane.  When  distended, 
the  middle  part  settles  down  some  four  or  five  inches,  pushing  back  coils  of  the  small  intestine 
which  may  lie  between  the  greater  curvature  and  the  large  colon,  and  also  pusliing  to  one  side  the  left 
dorsal  part  of  the  great  colon ;  the  spleen,  small  colon,  and  small  intestine  are  pushed  back  by  the 
disteiltion  of  the  left  sac.  When  the  stomach  is  moderately  full,  its  most  ventral  part  lies  opposite 
to  the  ninth  intercostal  space  and  tenth  rib,  about  a  handbreadth  above  the  level  of  the  left  costal 
arch. 

Structure. — The  wall  is  composed  of  four  coats— serous,  muscular,  submucous, 
and  mucous.  The  serous  coat  (Tunica  serosa)  covers  the  greater  part  of  the  organ 
and  is  closely  adherent  to  the  muscular  coat  except  at  the  curvatures.  It  partially 
bridges  over  the  lesser  curvature,  and  covers  here  elastic  tissue  which  assists  in 
retaining  the  bent  form  of  the  stomach.  The  peritoneal  folds  have  been  described. 
The  muscular  coat  (Tunica  muscularis)  consists  of  three  incomplete  layers,  an 
external  of  longitudinal,  a  middle  of  circular,  and  an  internal  of  oblique  fibers.  The 
layer  of  longitudinal  fibers  (Stratum  longitudinale)  is  very  thin  and  exists  only 
along  the  curvatures  and  at  the  antrum.  It  is  not  present  on  the  saccus  csecus, 
and  about  the  middle  of  the  greater  curvature  it  is  almost  entirely  replaced  by 
elastic  fibers  to  the  antrum  pylori.  At  the  lesser  curvature  it  is  continuous  with  the 
longitudinal  fibers  of  the  oesophagus.  On  the  antrum  pylori  it  forms  a  well-de- 
veloped complete  layer  which  is  separate  from  that  of  the  curvatures.  The  layer 
of  circular  fibers  (Stratum  circulare)  exists  only  on  the  glandular  part.  At  the 
pyloric  orifice  it  forms  a  thick  ring — the  pyloric  sphincter  (Sphincter  pylori). 
Another  ring,  the  antral  sphincter,  is  found  at  the  left  end  of  the  antrum  pylori. 
The  oblique  fibers  (Fibrse  obliquse)  are  arranged  in  coarse  bundles  in  two  layers. 
The  external  stratum  covers  the  left  sac  and  is  largely  a  continuation  of  the  longi- 
tudinal fibers  of  the  oesophagus.  The  internal  stratum  is  found  also  on  the  left 
sac;  it  is  continuous  with  the  circular  fibers  of  the  oesophagus  and  stomach  and 
exchanges  fibers  with  the  external  oblique  layer.  It  forms  a  remarkable  loop 
around  the  cardiac  orifice,  constituting  a  powerful  cardiac  sphincter  (Sphincter 
cardise).  The  submucous  coat  (Tela  submucosa)  is  a  layer  of  loose  connective 
27 


418 


DIGESTIVE   SYSTEM    OF   THE    HORSE 


Saccus  ccEcus 
(left  extremity) 


(Ewphagcal  region 


Diverticulum  duodeni 


Fundus 
gland 
region 


Pylorus 
Pyloric  gland  region 


-Frontal  Section  of  Stomach  and  First  Part  of  Duodenum  op  Horse. 
C,  Cardiac  orifice.     Photograph  of  specimen  fixed  in  situ. 


tissue  which  connects  tlie  muscular  and  mucous  coats;  in  it  the  vessels  and  nerves 
ramify  before  entering  the  mucosa.  The  mucous  coat  (Tunica  mucosa)  is  clearly- 
divided  into  two  parts.  That  which 
lines  the  greater  part  of  the  left  sac  re- 
sembles the  oesophageal  mucous  mem- 
brane, and  is  termed  the  oesophageal 
part  (Pars  oesophagea).  It  is  white  in 
color,  destitute  of  glands,  and  covered 
with  a  thick,  squamous,  stratified  epi- 
thelium. At  the  cardiac  orifice  it  pre- 
sents numerous  folds  which  occlude  the 
opening. '^  It  terminates  abruptly,  form- 
ing an  irregular,  sinuous,  raised  edge, 
termed  the  margo  plicatus  (or  cuticular 
ridge).  Below  and  to  the  right  of  this 
line  the  mucous  membrane  has  a  totally 
different  character,  being  soft  and  vel- 
vety to  the  touch,  and  covered  by  a  mu- 
coid secretion.  It  contains  the  gastric 
glands  (Glandulae  gastricse),  and  is  there- 
fore termed  the  glandular  part  (Pars  glandularis) .  It  is  subdivided  into  three  zones 
according  to  the  types  of  glands  which  it  contains,  but  no  distinct  lines  of  demar- 

1  This  occlusion  is  usually  so  complete  that  distention  of  the  stomach  by  air  or  fluid  forced 
in  through  the  pylorus  may  be  carried  far  enough  to  rupture  the  stomach  without  ligating  the 
oesophagus. 


Fig.  358. 


-Diagram  of  Zones  of  Mucous  Membrane 
OF  Stomach  of  Hohsk. 


THE    SMALL   INTESTINE  419 

cation  exist.  A  narrow  zone  next  to  the  margo  plicatus  has  a  yellowish-gray  color, 
and  contains  short  tubular  cardiac  glands  (cardiac  gland  region) .  Next  to  this  is  a 
large  area  which  has  a  mottled,  reddish-brown  color,  and  contains  fundus  glands 
(fundus  gland  region) ;  these  glands  have  two  distinct  types  of  cells.  This  part  of 
the  mucous  membrane  is  thick  and  very  vascular,  and  corresponds  to  the  fundus 
of  the  stomach  in  man  and  the  dog.  The  remainder  of  the  mucous  membrane  is 
thinner,  has  a  reddish-gray  or  yellowish-gray  color,  and  contains  pyloric  glands, 
which  have  a  single  type  of  cells  corresponding  to  the  chief  cells  of  the  fundus  glands 
(pyloric  gland  region) ;  it  corresponds  to  the  pyloric  portion  of  man  and  the  dog. 
The  folding  of  the  stomach  wall  at  the  lesser  curvature  produces  a  prominent 
ridge  which  projects  into  the  cavity  of  the  stomach.  The  circular  fold  which 
covers  the  pyloric  sphincter  is  termed  the  pyloric  valve  (Valvula  pylori). 

The  oesophageal  part  constitutes  one  third  to  two-fifths  of  the  mucous  membrane.  The 
cardiac  gland  region  is  extremely  narrow  (ca.  0.5  to  1  mm.)  at  the  greater  curvature,  but  becomes  about 
an  inch  wide  toward  the  pyloric  part.  Since  the  majority  of  the  glands  here  are  not  typical 
cardiac  glands,  like  those  of  the  pig  and  other  animals,  but  are  intermediate  in  type  between  these 
and  pyloric  glands,  the  term  intermediate  zone  might  well  be  used. 

Vessels  and  Nerves. — The  stomach  receives  blood  from  all  the  branches  of 
the  cceliac  artery.  The  gastric  veins  drain  into  the  portal  vein.  The  Ijmiph 
vessels  go  chiefly  to  the  gastric  lymph  glands,  thence  to  the  cisterna  chyli.  The 
nerves  are  derived  from  the  vagus  and  sympathetic  nerves. 


THE  SMALL  INTESTINE 

The  small  intestine  (Intestinum  tenue)  is  the  tube  which  connects  the  stomach 
with  the  large  intestine.  It  begins  at  the  pylorus  and  terminates  at  the  lesser 
curvature  of  the  csecum.  Its  average  length  is  about  seventy  feet  (ca.  22  meters), 
and  when  distended  its  diameter  varies  from  three  to  four  inches  (7.5  to  10  cm.). 
Its  capacity  is  about  twelve  gallons  (40  to  50  liters). 

It  is  clearly  divisible  into  a  fixed  and  a  mesenteric  part.  The  fixed  part  is 
termed  the  duodenum,  while  the  mesenteric  part  (Intestinum  tenue  mesenteriale) 
is  arbitrarily  divided  into  parts  termed  the  jejimum  and  ileum. ^ 

The  duodenum  is  about  three  to  four  feet  (ca.  1  m.)  long.  Its  shape  is 
somewhat  like  a  horseshoe,  the  convexity  being  directed  toward  the  right.  The 
first  part  (Pars  prima  duodeni)  is  directed  to  the  right  and  forms  an  po-shaped 
curve.  The  convexity  of  the  first  part  of  the  curve  is  dorsal,  of  the  second,  ventral. 
It  is  in  contact  with  the  middle  and  right  lobes  of  the  liver,  and  presents  two  am- 
pullae with  a  constriction  between  them.  The  duodenal  angle  (or  head)  of  the 
pancreas  is  attached  to  the  concavity  of  the  second  curve,  and  here,  five  to  six 
inches  (ca.  12  to  15  cm.)  from  the  pylorus,  the  pancreatic  duct  and  the  bile  duct 
pierce  the  bowel  Avail.  The  second  part  (Pars  secunda  duodeni)  passes  upward 
and  backward  on  the  right  dorsal  part  of  the  colon  and  ventral  to  the  right  lobe  of 
the  liver,  and,  on  reaching  the  right  kidney  and  the  base  of  the  csecum,  it  curves 
toward  the  median  plane,  opposite  the  last  rib.  The  third  part  (Pars  tertia  duo- 
deni) passes  from  right  to  left  behind  the  attachment  of  the  base  of  the  csecum, 
crosses  the  median  plane  behind  the  root  of  the  great  mesentery,  and  turns  forward 
to  become  continuous  with  the  mesenteric  part  under  the  left  kidney.-  The  sac- 
culations of  the  first  part  have  a  diameter  of  three  to  four  inches  (ca.  7.5  to  10  cm.). 
It  is  attached  by  a  short  peritoneal  fold  termed  the  mesoduodenum.     This  fixes 

^  No  natural  line  of  demarcation  exists,  but  there  is  a  marked  increase  of  the  thickness  of 
the  wall  toward  the  terminal  part.     Other  differences  will  be  noted  in  the  further  description. 

2  The  duodenum  commonly  curves  around  the  periphery  of  the  right  kidney,  from  which  it 
is  separated  by  the  base  of  the  caecum,  but  in  some  cases  it  is  in  contact  with  the  ventral  surface 
of  the  kidney.  It  may  cross  the  median  plane  ventral  to  the  second  lumbar  vertel)ra  or  further 
back,  depending  apparently  on  the  fulness  of  the  csecum. 


420 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


the  first  part  of  the  duodenum  closely  to  the  liver  and  the  right  dorsal  part  of  the 
colon;  the  remainder  is  somewhat  less  closely  attached  by  it  to  the  base  of  the 
caecum  and  right  kidney,  the  sublumbar  muscles,  and  (more  closely)  to  the  terminal 
part  of  the  great  colon  and  the  first  part  of  the  small  colon. ^ 

The  mesenteric  part,  or  jejuno-ileum,  has  been  conventionally  subdivided  into 
the  jejunum  and  ileum,  but  no  distinct  point  exists  at  which  to  make  the  demarca- 
tion. With  the  exception  of  the  origin  and  the  last  two  or  three  feet,  the  mesen- 
teric part  of  the  intestine  varies  so  much  in  position  that  only  a  general  statement 
can  be  made.  It  lies  in  numerous  coils,  mingled  with  those  of  the  small  colon, 
chiefly  in  the  dorsal  part  of  the  left  half  of  the  abdomen,  from  the  visceral  surface 
of  the  stomach  to  the  pelvis.  It  may  insinuate  itself  between  the  left  parts  of  the 
colon  and  the  abdominal  wall ;  also  between  the  ventral  parts  of  the  colon,  reaching 


Fig.  359. — Topography  of  Viscera  of  Mare;  Left  View. 
I.R.,  First  thoracic  vertebra;  I.L.,  first  lumbar  vertebra;  2.K.,  second  sacral  spine;  S.,  scapula;  A.,  humerus; 
St.,  sternum;  B.,  ilium;  O.,  femur;  L.,  lung  in  complete  expiration;  L,  dotted  line  indicating  contour  of  lung  in  in- 
spiration; //..pericardium;  Z.,  costal  part  of  diaphragm;  Z'.,  tendinous  center  of  diaphragm;  i.A'^.,  left  kidney;  l.v.C, 
lelt  ventral  colon;  v.Q.,  sternal  flexure  of  colon;  d.Q.,  diaphragmatic  flexure  of  colon;  D.,  small  intestine;  M.,  small 
colon;  Af'.,  rectum;  o,  coccygeus  muscle;  6,  retractor  ani;  c,  c,  sphincter  ani  externus;  rf,  constrictor  vulvae;  e,  sacro- 
coccygeus  ventralis;  /,  anterior  gluteal  artery;  g,  internal  pudic  artery;  h,  abdominal  wall  in  section.  (After  Ellen- 
berger,  in  Leisering'a  Atlas,  reduced.) 


the  floor  of  the  abdomen.  In  some  cases  coils  of  it  lie  against  the  right  flank  when 
the  caecum  contains  little  material.  The  terminal  part  of  the  intestine  (ileum) 
passes  to  the  medial  (left)  surface  of  the  caecum  and  joins  the  lesser  curvature  of 
its  base.  The  average  diameter  of  the  jejuno-ileum  is  about  two  and  a  half  to  three 
inches  (ca.  6  to  7  cm.).  In  the  cadaver  one  often  finds  much  of  the  tube  presenting 
irregular  constricted  and  dilated  parts  which  are  not  to  be  regarded  as  permanent 
conditions.  The  last  three  or  four  feet  (ca.  1  m.)  are  usually  tightly  contracted, 
resembling  somewhat  the  terminal  part  of  the  oesophagus.  This  part  may  be  termed 
the  ileum. 

The  mesenteric  part  is  connected  with  the  dorsal  abdominal  wall  by  the  great 
mesentery.     This  is  a  wide,  fan-shaped  fold,  consisting  of  two  layers  of  peritoneum, 

1  It  will  be  noticed  that  the  mesoduodenum  is  not  continuous  with  the  great  mesentery,  but 
ends  by  a  free  edge.  The  mesentery  begins  on  the  opposite  surface  of  the  end  of  the  duodenum, 
so  that  the  bowel  is  attached  by  two  peritoneal  folds  at  this  point. 


THE    SMALL    INTESTINE 


421 


between  which  the  vessels  and  nerves  reach  the  bowel ;  it  also  contains  the  mesen- 
teric lymph  glands  and  some  fat.  The  visceral  border  of  the  mesentery  contains 
the  intestine,  while  the  parietal  border  or  root  of  the  mesentery  (Radix  mesenterii) 
is  attached  to  a  small  area  around  the  great  mesenteric  trunk  under  the  first  and 
second  lumbar  vertebrae.  The  root  is  thick,  as  it  contains  a  large  number  of  vessels 
and  nerves  placed  close  together.  The  mesentery  is  short  at  first,  but  soon  reaches 
a  length  of  one  and  a  half  to  two  feet  (ca.  50  cm.) — sufficient  to  allow  coils  of  the 
intestine  to  reach  the  abdominal  floor,  the  pelvic  cavity,  or  even  to  descend  into 
the  scrotum  through  the  inguinal  canal.  Near  its  termination  the  intestine  leaves 
the  border  of  the  mesentery,  so  that  the  latter  has  a  free  edge  which  passes  to  the 
caecum.  Thus  there  is  formed  the  ileo-caecal  fold  (Plica  ileocaecalis),  which  at- 
taches the  ileum  to  the  lesser  curvature  of  the  caecum. 

Structure. — The  wall  consists  of  four  coats — serous,  muscular,  submucous,  and 
mucous.  The  serous  coat  is  complete  except  at  the  mesenteric  edge,  where  the 
vessels  and  nerves  reach  the  bowel.  The  muscular  coat  consists  of  an  external 
longitudinal  and  an  internal  circular  layer,  the  latter  being  the  thicker.  In  the 
last  few  feet  of  the  intestine  the  muscular  coat  is  very  thick,  and  being  usually 
firmly  contracted  in  the  dead  subject,  gives  the  impression  that  this  part  of  the  bowel 
is  of  smaller  caliber;  such,  however,  is 
not  the  case  during  life.  The  sub- 
mucous coat  is  a  layer  of  areolar  tissue 
in  which  the  vessels  and  nerves  ram- 
ify. It  contains  also  the  duodenal 
glands  and  the  bases  of  the  solitary 
and  aggregated  lymph  nodules.  The 
mucous  membrane  is  soft  and  vel- 
vety. It  has  a  grayish  or  yellowish- 
red  color  and  is  very  vascular.  About 
five  or  six  inches  from  the  pylorus  it 
forms  a  pouch,  the  diverticulum  duo- 
deni,  in  which  the  pancreatic  and  he- 
patic ducts  open.  On  a  small  papilla 
nearly  opposite  this  is  the  termina- 
tion of  the  accessory  pancreatic  duct. 
At  the  ileo-caecal  opening  the  mucous 
membrane  projects  slightly  into  the 

cavity  of  the  caecum,  forming  the  ileo-caecal  valve.  The  free  surface  is  thickly 
beset  with  villi,  small  projections  of  the  mucous  membrane  which  can  be  seen  well 
by  placing  a  piece  of  the  membrane  in  water.  They  are  relatively  short  and  thick 
in  the  horse.  Each  contains  a  central  lymph-vessel  (lacteal),  and  around  this  a 
plexus  of  capillaries,  lymphoid  tissue,  and  unstriped  muscle-fibers.  They  are  im- 
portant agents  in  absorption  from  the  contents  of  the  intestine.  The  epithelium 
is  columnar,  with  many  gol^let  cells.  Underneath  the  basement  membrane  is  a 
layer  of  unstriped  muscle-fibers,  the  muscularis  mucosae.  The  glands  of  the  small 
intestine  are  of  two  kinds ;  their  secretion  is  termed  the  succus  entericus. 

1.  The  intestinal  glands  (Glandulae  intestinales)  are  present  throughout.  They 
are  simple  tubular  glands  which  open  between  the  villi. 

2.  The  duodenal  glands  (Glandulae  duodenales)i  are  present  in  the  first 
twenty  feet  or  more  (ca.  6  to  7  m.)  of  the  bowel.  They  are  branched  tubulo- 
alveolar  glands,  and  are  situated  in  the  submucosa,  so  that  their  ducts  perforate 
the  muscularis  mucosae  and  the  mucous  membrane. 

1  These  were  formerly  known  as  Brunner's  glands,  but  in  the  B.  N.  A.  are  termed  glandulse 
duodenales.  On  account  of  their  extension  beyond  the  duodenum  and  their  submucous  position, 
Ellenberger  has  suggested  the  name  glandulse  submucosse. 


Diverticulum 
duodeni 

Fig.   360. — Diagram   of   Section   of   Diverticulum    duo- 
deni OF  Horse. 
Solid  line  indicates  mucous  membrane;  muscular  and  serous 
layers  are  not  shown. 


422 


DIGESTIVE    SYSTEM    OF    THE    HORSE 


Lymphoid  tissue  occurs  in  the  form  of  distinct  nodules  (NoduH  Ijonphatici), 
which  are  either  scattered  or  in  groups.  In  the  former  case  they  are  termed  solitary 
nodules  (NocUiU  lymphatici  soHtarii),  in  the  latter  aggregated  nodules  or  Peyer's 
patches  (Noduli  IjTnphatici  aggregati).  The  solitary  nodules  are  about  the  size  of 
a  millet-seed  or  a  small  sago  grain.  The  patches  are  situated  chiefly  along  the 
surface  opposite  to  the  mesenteric  attachment  and  begin  about  three  or  four  feet 
from  the  pylorus.  They  number  one  to  two  hundred,  and  are  usually  one  to  two 
inches  (2  to  5  cm.)  long  and  a  quarter  of  an  inch  to  one-half  inch  (ca.  2  to  14  mm.) 
wide.  Larger  ones  occur  in  the  terminal  part,  where  one  patch  may  have  a  length 
of  seven  to  fifteen  inches  (ca.  17  to  38  cm.)  and  a  width  of  half  an  inch  to  one  inch 
(ca.  5  to  25  mm.)  in  young  horses  (Ellenberger) .  They  vary  much  in  number, 
size,  and  distribution  in  different  individuals,  and  undergo  atrophy  in  old  subjects. 

Vessels  and  Nerves. — The  arteries  of  the  small  intestine  come  from  the 
coeliac  and  anterior  mesenteric  arteries.  The  veins  go  to  the  portal  vein.  The 
Ijmiph-vessels  are  numerous  and  go  to  the  mesenteric  lymph  glands,  thence  to  the 


Fig.  361. — Large  and  Small  AggrSg.^ted  N 


OR  Peyer's  Patche.s  of  Small  Intestine  of  Horse. 


cisterna  chyli.     The  nerves  are  derived  from  the  A'-agus  and  sympathetic  through 
the  cceliac  plexus. 

THE  LARGE  INTESTINE 
The  large  intestine  (Intestinum  crassum)  extends  from  the  termination  of  the 
ileum  to  the  anus.  It  is  about  twenty-five  feet  (ca.  7.5  to  8  m.)  in  length.  It 
differs  from  the  small  intestine  in  its  greater  size,  in  being  sacculated  for  the  most 
part,  possessing  longitudinal  bands,  and  having  a  more  fixed  position.  It  is  divided 
into  caecum,  great  colon,  small  colon,  and  rectum. 


The  Cecum 

The  caecum  (Intestinum  caecum)  is  a  great  cul-de-sac  intercalated  between  the 

small  intestine  and  the  colon.     It  has  a  remarkable  size,  shape,  and  position  in  the 

horse.     Its  average  length  is  about  four  feet  (ca.  1.25  m.),  and  its  capacity  about 

seven  to  eight  gallons  (ca.  25  to  30  liters).^     It  is  conical  in  form,  and  is  curved 

1  The  length  given  here  is  measured  from  end  to  end  along  the  side  and  midway  between  the 
curvatures. 


THE   C^CUM 


423 


somewhat  like  a  comma.  It  is  situated  chiefly  to  the  right  of  the  median  plane, 
extending  from  the  right  iliac  and  sublumbar  regions  to  the  abdominal  floor  behind 
the  xiphoid  cartilage.  Both  extremities  are  blind,  and  the  two  orifices  are  placed 
close  together  on  the  concave  curvature.  It  presents  for  description  a  base,  a  body, 
and  an  apex.  The  base  (Basis  caeci  s.  Saccus  csecus)  extends  forward  on  the  right 
side  as  far  as  the  fourteenth  or  fifteenth  rib,  about  a  handbreadth  below  its  middle, 
and  backward  to  the  tuber  coxae. ^  It  is  strongly  curved,  the  greater  curvature 
being  dorsal,  the  lesser  ventral;  connected  with  the  latter  are  the  termination  of 
the  ileum  and  the  origin  of  the  colon.  The  rounded  blind  end  is  directed  ventrally. 
The  body  (Corpus  caeci)  extends  downward  and  forward  from  the  base  and  rests 
largely  on  the  ventral  wall  of  the  abdomen.     Its  lesser  curvature  is  about  parallel 


Fig.  362. — Cecum  of  Horse;  Left  View. 
-4.  c,  apex;    I,  ileum;   1,  2,  longitudinal  bands;  3,  ileo-csecal   fold, 
lymph  glands  have  been  removed  to  expose  the  medial  band  (1). 


with  the  costal  arch  and  some  five  to  six  inches  (10  to  15  cm.)  ventral  to  it.  The 
apex  (Apex  caeci)  lies  on  the  abdominal  floor,  usually  to  the  right  of  the  median 
plane,  and  about  a  hand's  length  behind  the  xiphoid  cartilage. 

The  right  or  parietal  surface  of  the  caecum  is  related  chiefly  to  the  right  ab- 
dominal wall,  the  diaphragm,  duodenum,  and  liver.  The  left  or  visceral  surface  lies 
against  the  left  and  terminal  parts  of  the  colon,  the  root  of  the  great  mesentery, 
and  the  small  intestine. 

The  base  is  attached  dorsally  by  connective  tissue  and  peritoneum  on  the 
ventral  surface  of  the  pancreas  and  right  kidney,  and  a  small  area  of  the  abdominal 
wall  behind  these;  it  is  attached  medially  to  the  terminal  part  of  the  great  colon, 
and  ventrally  to  the  origin  of  the  great  colon.     The  body  is  attached  dorso-laterally 


^  The  forward  extent  of  the  base  of  the  caecum  is  subject  to  some  variation, 
noted  that  the  bhnd  end  is  not  the  most  anterior  part. 


It  may  be 


424 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


to  the  first  part  of  the  colon  b}^  the  caeco-colic  fold.     The  apex  is  free,  and  conse- 
quently may  vary  in  position.  — ■ — — 

The  csecmn  has  four  longitudinal  bands  (Taeniae  cseci),  situated  on  the  dorsal, 
ventral,  right,  and  left  surfaces;  these  cause  four  rows  of  sacculations  (Haustra). 

The  ventral  band  is  almost  entirely  exposed  or  free  (Taenia  libera) ;  it  begins  on  the  highest 
part  of  the  base,  extends  along  the  mecUal  side  of  the  greater  curv'ature,  and  joins  the  medial  band 
near  the  apex.  It  is  concealed  only  at  its  origin  where  the  bowel  is  attached  to  the  wall.  The 
dorsaJ  band  extends  along  the  lesser  cur\-ature  from  the  termination  of  the  ileum  to  the  apex. 
The  medial  band  extends  along  the  medial  part  of  the  lesser  curvature  of  the  base,  inchnes 
ventrally  further  fonvard,  and  ends  by  joining  the  ventral  band.  It  is  covered  at  its  origin  by  the 
adhesion  to  the  right  dorsal  part  of  the  great  colon  and  beyond  this  by  the  csecal  vessels  and  lymph 
glands.  Medial  to  the  termination  of  the  ileum  it  projects  from  the  wall  of  the  bowel  as  a  falciform 
band  which  can  be  felt  distinctly  although  covered  by  vessels  and  fat.  The  lateral  band  is 
continuous  with  that  of  the  right  ventral  part  of  the  colon.  It  is  covered  by  vessels,  lymph  glands 
and  fat,  but  can  be  felt  in  its  posterior  part,  where  it  forms  a  concave  projecting  edge.  It  inclines 
ventrally  in  front  and  may  extend  to  the  apex  or  fade  out  without  reaching  it. 


Fig.   303. — Orifices  of  C^cum  of  Horse. 
1,  Ileo-cacal  orifice;    2,  cseco-colic  orifice;    3,  intervening  fold. 


The  ileo-caecal  orifice  (Ostium  ileocsecale)  is  situated  in  the  lesser  curvature  of 
the  base,  about  two  or  three  inches  (ca.  5  to  7.5  cm.)  to  the  right  of  the  median 
plane,  and  in  a  transverse  plane  through  the  first  or  second  lumbar  vertebra.  The 
end  of  the  ileum  is  partially  telescoped  into  the  caecum,  so  that  the  orifice  is  sur- 
rounded by  a  fold  of  mucous  membrane  which  encloses  a  thick  circular  muscular 
layer,  the  sphincter  ilei. 

The  caeco-colic  orifice  (Ostium  caecocolicum)  is  lateral  to  the  preceding  one; 
the  interval  between  them  is  only  about  two  inches  (ca.  5  cm.),  and  they  are  separ- 
ated by  a  large  fold  which  projects  into  the  interior  of  the  caecum.  The  orifice  is 
small  in  relation  to  the  size  of  the  caecum  and  colon.  It  is  slit-like,  or  has  a  narrow 
oval  outline,  and  is  about  two  inches  (ca.  5  cm.)  long.  It  has  a  thick  valvular  fold 
(Valvula  csecocolica)  at  its  ventral  margin  and  is  encircled  by  a  muscular  ring,  the 
sphincter  caeci.^  Large  crescentic  or  semilunar  folds  (Plicae  caeci)  project  into  the 
cavity  of  the  bowel,  and  between  these  are  large  pouches  (Cellulae  caeci). 

^  The  anatomical  arrangement  gives  no  support  to  the  view  which  is  sometimes  expressed 
that  ingesta  may  pass  directly  from  the  ileum  to  the  colon. 


THE   GREAT    COLON 


425 


It  is  somewhat  difficult  to  get  a  correct  idea  of  the  csecal  orifices.  The  csecum  is  sharply- 
curved  here  and  a  large  fold  projects  into  its  interior,  somewhat  like  a  shelf,  and  separates  the  two 
orifices.  The  ileo-cscal  orifice  faces  chiefly  dorsally,  while  the  cseco-colic  orifice  faces  forward 
into  the  csecum. 

The  Great  Colon 
The  great  colon  (Colon  crassum)  begins  at  the  cseco-coUc  orifice,  and  terminates 
by  joining  the  small  colon  behind  the  saccus  csecus  of  the  stomach.  It  is  ten  to 
twelve  feet  (ca.  3  to  3.7  m.)  long,  and  its  average  diameter  (exclusive  of  its  narrowest 
part)  is  about  eight  to  ten  inches  (ca.  20  to  25  cm.).  Its  capacity  is  more  than 
double  that  of  the  csecum.  When  removed  from  the  abdomen,  it  consists  of  two 
parallel  parts,  which  are  connected  by  peritoneum  and  partially  by  areolar  and 
muscular  tissue  also.  In  situ  it  is  folded  so  that  it  consists  of  four  parts,  which  are 
designated  according  to  their  position  or  numerically.  The  three  bent  connecting 
parts  are  termed  the  flexures.  The  first  part,  the  right  ventral  colon  (Colon  ventrale 
dextrum),  begins  at  the  lesser  curvature  of  the  base  of  the  csecum,  about  opposite 
the  ventral  part  of  the  last  rib  or  intercostal  space. "^     It  forms  an  initial  curve,  the 


Origin  of  small  colon 


Diaphragmatic 
flexure 


Ileum 
Fig.  364. — Diagram  of  Cecum  and  Large  Colon  op  Horse. 


convexity  of  which  is  directed  upward  and  backward;  this  part  is  in  contact  with 
the  upper  part  of  the  right  flank.  It  then  passes  downward  and  forward  along  the 
right  costal  arch  and  then  along  the  floor  of  the  abdomen. ^  Over  the  xiphoid 
cartilage  it  bends  sharply  to  the  left  and  backward,  forming  the  sternal  flexure 
(Flexura  sternalis  s.  diaphragmatica  ventralis).  The  second  part,  the  left  ventral 
colon  (Colon  ventrale  sinistrum),  passes  backward  on  the  abdominal  floor,  to  the  left 
of  the  first  part  and  the  csecum  and,  on  reaching  the  pelvic  inlet,  bends  sharply 
dorsally  and  forward,  forming  the  pelvic  flexure  (Flexura  pelvina) .  This  is  continued 
by  the  third  part,  the  left  dorsal  colon  (Colon  dorsale  sinistrum),  which  passes 
forward  dorsal  or  lateral  to  the  left  ventral  part,  and  on  reaching  the  stomach, 
diaphragm,  and  left  lobe  of  the  liver,  turns  to  the  right,  forming  the  diaphragmatic 
flexure  (Flexura  diaphragmatica  dorsalis).  The  fourth  part,  the  right  dorsal  colon 
(Colon  dorsale  dextrum),  passes  backward  dorsal  to  the  first  part,  and  on  reaching 

1  The  position  of  the  origin  of  the  great  colon  is  variable,  and  one  may  easily  get  a  wrong 
impression  on  account  of  the  peculiar  arrangement  of  the  bowel  here.  The  colon  usually  presents 
a  saccular  dilatation  at  the  lesser  curvature  of  the  base  of  the  cajcum,  which  may  be  mistaken  for 
its  origin.  The  real  origin  is  a  constricted  part  or  neck  anterior  to  the  sacculation.  Thus  the 
colon  passes  at  first  backward  and  then  curves  sharply  downward  and  forward.  Schmaltz  has 
proposed  the  name  "vestibulum  coli"  for  this  sacculation. 


426 


DIGESTIVE   SYSTEM    OF   THE   HORSE 


Fig.  365. — Topography  of  Viscera  of  Horse;  Right  View. 
IR.,  First  thoracic  vertebra;  IL.,  first  lumbar  vertebra;  2K.,  second  sacral  spine;  S.,  scapula;  A.,  humerus; 
S<.,  sternum;  B.,  ilium;  O.,  femur;  L.,  right  lung;  77.,  pericardium;  Z.,  diaphragm  (pars  costalis);  r.jj.C,  right  ven- 
tral colon;  V.Q.,  sternal  flexure  of  colon;  d.Q.,  diaphragmatic  flexure  of  colon;  C,  body,  C,  base,  C".,  apex,  of  caecum; 
D.,  small  intestine;  F.,  pelvic  flexure  of  colon;  M.,  rectum;  a.,  abdominal  wall  in  section;  b,  duodenum;  c,  coccygeus 
muscle;  d,  retractor  ani;  e,  e,  sphincter  ani  externus;  /,  anterior  gluteal  artery;  g,  internal  pudic  artery;  h,  xiphoid 
cartilage.  The  origin  of  the  colon  would  be  above  the  blind  end  of  the  base  of  the  caecum  marked  C".  (After  Ellen- 
berger,  in  Leisering's  Atlas.) 


Fig.  366. — Topography  of  Viscera  of  Horse;  Right  Side,  Deeper  View. 
I.R.,  First  thoracic  vertebra;    I.L.,  first  lumbar  vertebra;    2.K.,  second   sacral  spine;    .S.,  scapula;  A.,  humerus; 

B,  ilium;    O.,  femur;    Sc/j.,  pubis;    Si.,  ischium;    St.,  sternum;    L.,  right  lobe  of  liver;    r.N.,  right  kidney;    C,  body, 

C,  base,  C".,  apex  of  caecum;  r.v.C,  right  ventral  colon;  v.Q.,  sternal  flexure  of  colon;  d.Q.,  diaphragmatic  flexure  of 
colon;  r.d.C,  right  dorsal  colon;  F.,  pelvic  flexure  of  colon;  D.,  small  intestine;  H.,  urinary  bladder;  M.,  rectum; 
a,  left  ventricle;  a',  right  ventricle;  6,  6',  right  coronary  artery;  c,  left  atrium;  c',  right  atrium;  d,  left  coronary  artery, 
circumflex  branch;  e,  vena  azygos;  /,  anterior  vena  cava;  g,  posterior  vena  cava;  h,  sinus  venosus;  i,  right  phrenic 
nerve;  ^•,  right  vagus,  with  its  dorsal  (fc')  and  ventral  (fc")  divisions;  Z,  aorta;  m,  cEsophagus;  7i,  trachea;  o,  diaphragm 
(median  section);  p,  right  lateral  ligament  of  liver;  q,  duodenum;  r,  dotted  line  indicating  position  in  median  section 
of  diaphragm  in  inspiratorj'  phase;  s,  recto-coccygeus  muscle;  t,  suspensory  ligament  of  rectum;  u,  sphincter  ani;  v, 
vesicula  seminalis;  m),  prostate;  x,  bulbo-urethral  gland;  j/,  urethra;  s,  abdominal  wall;  z',  xiphoid  cartilage.  (After 
EUenberger,  in  Leisering's  Atlas,  reduced.) 


THE   GREAT   COLON 


427 


the  medial  surface  of  the  base  of  the  caecum  it  turns  dorsally  and  to  the  left  behind 
the  left  sac  of  the  stomach;  here  it  becomes  constricted,  and  joins  the  small  colon 
below  the  left  kidney. 

The  sternal  flexure  extends  forward  to  a  point  opposite  to  the  ventral  part  of  the  seventh  rib, 
and  the  diaphragmatic  flexure  as  far  as  the  sixth  intercostal  space  on  the  right  of  the  median  plane. 


The  caliber  of  the  great  colon 


greatly  at  different  points.     At  its  origin 


Fig.  367. — ^Abdominal  Viscera  of  Horss;  Ventral  View. 
The  ventral  wall  and  part  of  the  lateral  walls  of  the  abdomen  are  removed.  C,  Csecum;  r.v.C,  right  ventral 
part  of  colon;  v.Q.,  sternal  flexure  of  colon;  [l.v.  C,  left  ventral  part  of  colon;  d.Q.,  diaphragmatic  flexure  of  colon; 
D.,  small  intestine;  M.,  small  colon;  a,  ventral  free  band  of  caecum;  6,  medial  band  of  caecum;  c,  lateral  band  of  ventral 
part  of  colon  d,  ventral  band  of  ventral  part  of  colon;  e,  point  of  elbow;  /,  anterior  end  of  sternal  region;  g,  xiphoid 
eartilage;   h,  teats.     (After  Ellenberger-Baum,  Top.  Anat.  d.  Pferdes.) 


it  is  only  about  two  to  three  inches  (ca.  5  to  7.5  cm.)  in  diameter.^  This  soon 
increases  to  about  eight  to  ten  inches  (ca.  20  to  25  cm.)  for  the  ventral  parts. 
Beyond  the  pelvic  flexure  the  diameter  is  reduced  to  about  three  or  four  inches 
(ca.  8  to  9  cm.).  Toward  the  diaphragmatic  flexure  the  caliber  rapidly  increases,  and 
reaches  its  maximum  in  the  last  part,  where  it  forms  a  large  sacculation,  which  may 
1  Usually  there  is  a  sacculation  of  considerable  size  which  succeeds  the  constricted  origin. 


428 


DIGESTIVE   SYSTEM    OF   THE    HORSE 


have  a  diameter  of  about  twent}-  inches  (50  cm.).     This  is  succeeded  bj;  a  funnel- 
shaped  terminal  contraction. 

The  right  ventral  part  of  the  great  colon  is  attached  to  the  lesser  curvature  of 
the  caecum  by  two  layers  of  peritoneum  which  form  the  caeco-colic  fold  (Plica 
csecocolica).  The  right  parts  are  united  by  peritoneum  on  either  sde  and  also  by 
areolar  tissue  and  muscular  fibers,  the  surface  of  contact  being  about  four  or  five 
inches  (ca.  10  to  12  cm.)  -wade;  the  left  parts  are  attached  to  each  other  in  a  similar 
fashion  near  the  anterior  flexures,  but  further  back  the  connection  is  a  peritoneal 
fold  which  gradually  becomes  wide  enough  to  allow  them  to  be  drawn  apart  about 

six  inches  (ca.  15  cm.)  near  the  peMc 
flexure.  The  terminal  part  of  the  colon 
is  attached  by  peritoneum  and  areolar 
tissue  to  the  ventral  surface  of  the  pan- 
creas dorsally  and  to  the  base  of  the 
caecum  laterally.  It  is  connected  in- 
directl}^  with  the  diaphragm  and  hver 
by  means  of  a  fold  derived  from  the 
right  lateral  ligament  of  the  liver. 

The  relations  are  complex,  but  the 
more  important  facts  are  as  follows: 
The  ventral  parts  have  extensive  con- 
tact with  the  abdominal  wall  ventrally 
and  laterally.  On  the  right  side  the 
colon  is  almost  entirely  excluded  from 
contact  with  the  flank  by  the  caecum; 
on  the  left  side  it  has  no  contact  with 
the  upper  part  of  the  flank,  being  ex- 
cluded here  by  coils  of  the  small  colon 
and  small  intestine.  Dorsally  the  chief 
relations  are  to  the  stomach,  duodenum, 
liver,  pancreas,  small  colon,  small  intes- 
tine, aorta,  posterior  vena  cava,  and 
portal  vein.  Since  there  are  no  trans- 
verse attachments  of  the  right  and  left 
parts,  and  the  latter  have  no  attach- 
ment to  the  wall,  they  are  subject  to 
considerable  displacement.^  The  pel- 
vic flexure  is  variable  in  position,  but 
usually  it  is  directed  against  the  poster- 
ior part  of  the  right  flank  or  lies  in  the 
right  inguinal  region.- 

The   longitudinal    bands    (Taeniae 

coli)  vary  in  number  on  the  different 

parts.     The  ventral  parts  have  four  bands.     The  pelvic  flexure  has  a  band  along 

its  lesser  curvature.     The  left  dorsal  colon  has  at  first  only  one  band,  which  is 

a  continuation  of  the  preceding  one;  further  fonvard  two  other  bands  appear,  and 

1  Abnormal  displacement,  e.  g.,  torsion  of  the  left  parts,  is  not  rare,  and  is  liable  to  produce 
death  if  not  promptly  reduced. 

^  The  length  of  the  left  parts  varies  and  this  appears  partly  to  account  for  the  differences  to 
be  found  in  the  arrangement  of  their  posterior  parts  and  the  pehac  flexure.  In  subjects  in  which 
these  parts  of  the  colon  are  relatively  long,  their  posterior  ends  are  usually  bent  to  the  right  across 
the  pelvic  inlet  so  that  the  peh-ic  flexure  lies  to  the  right  of  the  inlet.  In  few  cases  the  'eft  parts 
of  the  colon  seem  relatively  short  and  the  pelvic  flexure  lies  at  the  pehic  inlet.  Other  dispositions 
are  encountered. 


G.  368. — Posterior  Portion  of  I-eft  Parts  of  Colox 

OF  Horse;  Dorsal  View. 
Left  dorsal  part;    2,  left  ventral  part;    3,  pelvic  flexure. 


THE  SMALL  COLON THE  RECTUM  429 

the  three  are  continued  on  the  right  dorsal  part.     The  ventral  parts  have  alternate 
constrictions  and  sacculations  (Haustra  coli). 

On  the  right  ventral  colon  two  bands  are  dorsal,  and  extend  along  the  medial  and  lateral 
sides  of  the  attachment  to  the  right  dorsal  colon.  The  medial  one  is  covered  by  the  colic  vessels, 
etc.,  and  the  lateral  one  is  concealed  entirely  or  almost  entirely  by  the  attachment  to  the  right 
dorsal  part.  A  lateral  band  comes  from  the  lesser  curvature  of  the  caecum  and  becomes  ventral 
at  the  sternal  flexure;  it  is  free.  The  ventral  band  is  also  free.  On  the  left  ventral  colon  also  two 
bands  are  dorsal.  Of  these,  the  medial  one  is  covered  by  the  vessels  and  lymph  glands  and  in  the 
anterior  part  also  by  the  adhesion  to  the  left  dorsal  part.  At  the  pelvic  flexure  it  is  continued 
along  the  concave  face  of  the  bowel  to  the  left  dorsal  part;  it  is  important  clinically  as  being  the 
only  distinct  band  on  the  flexure  and  may  be  felt  per  rectum.  The  dorso-lateral  band  is  largely 
free,  but  is  covered  in  front  by  the  attachment  to  the  left  dorsal  part.  It  fades  out  at  the  pelvic 
flexure.  The  ventro-medial  and  ventro-lateral  bands  are  free  and  fade  out  at  the  pelvic  flexure. 
The  left  dorsal  colon  has  at  first  only  one  band,  which  is  the  continuation  of  the  one  along  the  lesser 
curvature  of  the  pelvic  flexure;  it  extends  along  the  ventral  surface  and  is  continued  on  the  right 
dorsal  colon.  Beyond  the  middle  of  the  left  dorsal  colon  two  dorsal  bands  begin,  diverge  very 
gradually,  and  are  continued  on  the  right  dorsal  colon;  both  are  free  and  broaden  at  the  diaphrag- 
matic flexure.  On  the  right  dorsal  colon  the  ventral  band  is  concealed  by  the  attachment  to  the 
right  ventral  colon  and  by  the  vessels  and  lymph  glands.  The  two  dorsal  bands  are  free  except 
at  the  parietal  attachment  of  the  bowel;  the  lateral  one  is  very  wide  and  somewhat  indistinct; 
the  medial  one  is  narrower  and  more  distinct,  and  is  continued  along  the  mesenteric  border  of  the 
small  colon. 

The  Small  Colon 

The  small  colon  (Colon  tenue)  begins  at  the  termination  of  the  great  colon, 
behind  the  saccus  csecus  of  the  stomach  and  ventral  to  the  left  kidney,  and  is  con- 
tinued by  the  rectum  at  the  pelvic  inlet. ^  Its  length  is  about  ten  to  twelve  feet 
(ca.  3.5  m.),  and  its  diameter  three  to  four  inches  (ca.  7.5  to  10  cm.). 

Its  coils  lie  chiefly  in  the  space  between  the  stomach  and  the  pelvic  inlet, 
dorsal  to  the  left  parts  of  the  great  colon.  They  are  mingled  with  those  of  the 
small  intestine,  from  which  they  are  easily  distinguished  by  the  bands  and  sac- 
culation. 

It  is  attached  to  the  sublumbar  region  by  the  colic  mesentery,  and  to  the 
termination  of  the  duodenum  by  the  narrow  duodeno-colic  fold  of  peritoneum 
(Lig.  duodeno-colicum) .  The  greater  omentum  is  also  attached  to  the  initial 
part  of  the  bowel.  The  colic  mesentery  is  narrow  at  its  origin,  but  soon  reaches 
a  width  of  about  three  feet  (ca.  80  to  90  cm.).  Its  parietal  border  is  attached  along 
a  line  extending  from  the  ventral  surface  of  the  left  kidney  to  the  sacral  promontory; 
it  is  continuous  in  front  with  the  root  of  the  great  mesentery,  and  behind  with  the 
mesorectum. 

There  are  two  longitudinal  bands  and  two  rows  of  sacculations.  One  of  the 
bands  is  free,  the  other  is  concealed  by  the  mesentery.  When  the  bowel  is  hardened 
i7i  situ  its  lumen  between  the  pouches  is  reduced  to  a  narrow  slit. 

The  Rectum 

The  rectum  (Intestinum  rectum)  is  the  terminal  part  of  the  bowel;  it  extends 
from  the  pelvic  inlet  to  the  anus.^  Its  length  is  about  one  foot  (ca.  30  cm.).  Its 
direction  may  be  straight  or  oblique.  The  first  or  peritoneal  part  of  the  rectum  is 
like  the  small  colon,  and  is  attached  by  a  continuation  of  the  colic  mesentery  termed 
the  mesorectum.  The  second  or  retroperitoneal  part  forms  a  flask-shaped  dilata- 
tion termed  the  ampulla  recti ;  it  is  attached  to  the  surrounding  structures  by  con- 
nective tissue  and  muscular  bands. 

The  first  part  of  the  rectum  commonly  lies  along  the  left  wall  of  the  pelvic 
cavity,  but  may  be  about  median  or  (more  rarely)  deflected  to  the  right.  It  is 
related  to  coils  of  the  small  colon  and  (inconstantly)  to  the  left  parts  or  pelvic 

1  The  position  of  the  funnel-shaped  termination  of  the  great  colon  and  the  origin  of  the  small 
colon  is  fixed,  and  this  fact  is  of  clinical  importance  in  regard  to  impaction,  which  is  not  rare  here. 
In  horses  of  medium  size  this  part  of  the  bowel  can  be  palpated  per  rectum  when  distended. 

2  There  is  no  natural  line  of  demarcation  between  the  small  colon  and  rectimi:  the  plane 
•of  the  pelvic  inlet  is  selected  as  the  division  for  convenience  of  description. 


430 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


flexure  of  the  great  colon;  ventrallj^  to  the  bladder  (when  full)  or  to  the  uterus. 
The  second  part  of  the  rectum  is  related  dorsally  and  laterall}^  to  the  pelvic  wall. 
Ventral ly  the  relations  differ  in  the  two  sexes.  In  the  male  they  are  the  bladder, 
the  terminal  parts  of  the  ductus  deferentes,  the  vesiculse  seminales,  the  prostate, 
the  bull)o-urethral  glands  and  the  urethra.  In  the  female  they  are  the  uterus, 
vagina,  and  vulva. ^ 

Structure  of  the  Large  Intestine 
The  serous  coat  covers  the  different  parts  in  varying  degree.     It  does  not 
cover  (a)  the  opposed  surfaces  of  the  caecum  and  colon  which  are  between  the  layers 


Fig.  369. — Topogr.\phy  of  Vis^er.^^  of  M.\.TtE;  Left  Deep  View. 
IR.,  First  thoracic  vertebra;  IL.,  first  lumbar  vertebra;  ^A'.,  second  sacral  spine;  S.,  scapula;  .4.,  humerus; 
B.,  ilium;  F.,  femur;  Sch.,  pubis;  .Si.,  ischium;  L.,  liver  (left  lobe);  Ma.,  stomach,  the  posterior  contour  of  which  is 
indicated  by  dotted  line  x;  Afi.,  spleen;  Z.A'.,  left  kidney,  concealed  part  indicated  by  dotted  line;  j\/.,  small  colon;  D., 
small  intestine,  parts  of  which  have  been  removed;  l.d.C,  left  dorsal  colon;  l.v.C,  left  ventral  colon;  v.Q.,  sternal 
flexure;  d.Q.,  diaphragmatic  flexure;  O.,  left  ovary;  U.,  horn  of  uterus;  L.I.,  broad  ligament  of  uterus;  M'.,  rectum;  V., 
vagina;  H.,  bladder;  a,  left  ventricle;  a',  right  ventricle;  b,  left  coronary  artery  with  descending  (6')  and  circumflex 
(6")  branches;  c,  left  auricle;  d,  pulmonary  artery  (cut) ;  e,  aorta;  /,  ligamentum  arteriosum;  3,  brachiocephalic  trunk 
(anterior  aorta);  A,  trachea;  i,  oesophagus;  A:,  left  phrenic  nerve;  Z,  diaphragm  in  median  section;  m,  uterine  tube; 
n,  bursa  ovarica;  o,  urethra;  p,  cut  edge  of  broad  ligament ;  q,  line  of  reflection  of  pelvic  peritoneum;  r,  recto-coccygeus; 
s,  suspensory  ligament  of  rectum;  t,  sphincter  ani  internus;  u,  sacro-coccygeus  ventralis;  v,  abdominal  wall  in  section; 
w,  xiphoid  cartilage.     (After  Ellenberger,  in  Leisering's  Atlas.) 


of  the  cseco-colic  fold  and  mesocolon;    (h)  the  areas  of  parietal  attachment  of  the 
Cfficum  and  colon ;  (c)  the  retroperitoneal  part  of  the  rectum. 

The  muscular  coat  consists  of  longitudinal  and  circular  fibers.  The  bulk  of 
the  former  is  in  the  bands  of  the  caecum  and  colon.  It  is  to  be  noted,  however, 
that  the  bands  of  the  caecum  and  the  ventral  parts  of  the  great  colon  are  largely 
composed  of  elastic  tissue.  The  bands  of  the  dorsal  parts  of  the  colon  are  largely 
muscular,  and  those  of  the  small  colon  are  almost  entirely  muscular.  Some  of  the 
circular  fibers  pass  from  one  part  of  the  colon  to  another,  where  they  are  attached 
to  each  other,  forming  the  fibrte  transversse  coli.  The  muscular  coat  of  the  ampulla 
of  the  rectum  presents  special  features.     The  longitudinal  layer  of  fibers  is  very 

1  The  anterior  part  of  the  rectum  is  variable  in  position  and  relations.  The  amount  covered 
by  peritoneum  dorsally  and  laterally  is  very  variable,  and  appears  to  be  in  inverse  proportion  to 
the  fulness  of  the  bowel. 


STRUCTURE    OF   THE   LARGE    INTESTINE 


431 


thick  and  consists  of  large  bundles  which  are  rather  loosely  united.  A  large  band, 
the  recto-coccygeus,  is  detached  from  it  on  either  side,  and  passes  upward  and 
backward  to  be  inserted  into  the  fourth  and  fifth  coccygeal  vertebrae. 

The  submucous  tissue  is  abundant  in  the  wall  of  the  rectum,  so  that  the  mucous 
membrane  is  loosely  attached  to  the  muscular  coat,  and  forms  numerous  folds 
when  the  bowel  is  empty. 

The  mucous  membrane  of  the  large  intestine  is  thicker  and  darker  in  color 
than  that  of  the  small  intestine.     It  forms  large  crescentic  or  semilunar  folds 


Fig.  370. — Pelvic  Inlet  and  Posterior  Part  op  Abdominal  Wall  of  Horse,  Viewed  from  the  Front. 
The  left  inguinal  canal  is  partially  opened.  The  peritoneum  is  retained  except  over  a  part  of  the  left  cremaster 
muscle.  The  sublumbar  region  is  greatly  foreshortened  in  this  view,  a,  o',  Kidneys;  a",  adrenal;  6.,  ureter;  c,  renal 
artery;  d,  aorta;  e,  stump  of  cceliac  artery;  /,  stump  of  anterior  mesenteric  artery;  g,  posterior  mesenteric 
artery;  h,  circumflex  ihac  artery;  i,  external  iliac  artery;  k,  internal  iliac  artery;  I,  spermatic  artery  in  peritoneal 
fold  (phca  vasculosa) ,  m;  re,  ductus  deferens,  enclosed  in  genital  fold,  o;  p,  urinary  bladder;  q,  round  ligament  of  blad- 
der; r,  middle  ligament  of  bladder;  s,  rectum;  t,  margin  of  vaginal  ring;  u,  posterior  abdominal  artery;  v,  external 
pudic  artery;  w,  rectus  abdominis  muscle;  x,  transversus  and  obliquus  internus  abdominis;  y,  y',  cremaster  externus; 
z,  posterior  vena  cava  (cut).     (After  EUenberger-Baum,  Top.  Anat.  d.  Pferdes.) 


(Plicae  semilunares) ,  corresponding  to  the  external  constrictions.  It  has  no  villi 
nor  duodenal  glands.  The  intestinal  glands  are  large  and  numerous.  Solitary 
nodules  are  numerous,  and  there  are  aggregated  lymph  nodules  at  the  apex  of  the 
caecum  and  in  the  pelvic  flexure  and  the  adjacent  portion  of  the  left  dorsal  part  of 
the  colon. 

Vessels  and  Nerves. — The  arteries  come  from  the  anterior  and  posterior 
mesenteric  and  internal  pudic  arteries.  The  veins  go  to  the  portal  and  internal 
pudic  veins.  The  lymph  vessels  of  the  caecum  and  colon  go  to  the  caecal  and  colic 
lymph  glands,  thence  to  the  cisterna  chyli.     Those  of  the  rectum  go  to  the  internal. 


432  DIGESTIVE    SYSTEM    OF   THE    HORSE 

iliac  and  lumbar  glands.     The  nerves  are  derived  from  the  mesenteric  and  pelvic 
plexuses  of  the  sympathetic. 

The  Anus 

The  anus  is  the  terminal  part  of  the  alimentary  canal.  It  is  situated  below  the 
root  of  the  tail,  where  it  forms  a  round  projection,  with  a  central  depression  when 
contracted.  It  is  covered  externally  by  an  integument  which  is  thin,  hairless,  and 
provided  with  numerous  sebaceous  and  sweat  glands.  Its  lumen,  the  anal  canal 
(Pars  analis  recti),  is  about  two  inches  (ca.  5  cm.)  long;  except  during  defecation 
it  is  closed  by  the  contraction  of  the  sphincter  muscles  and  folds  of  the  mucous 
lining.  The  mucous  membrane  is  pale,  glandless,  and  covered  with  a  thick,  squa- 
mous, stratified  epithelium. 

There  are  three  muscles  of  the  anus. 

1.  The  sphincter  ani  intemus  is  the  terminal  thickening  of  the  circular  coat 
of  the  bowel. 

2.  The  sphincter  ani  extemus  is  a  broad  ring  of  striped  muscle-fibers  outside 
the  internal  sphincter.  Some  fibers  are  attached  to  the  coccygeal  fascia  above, 
others  to  the  perineal  fascia  below.     Its  action  is  to  close  the  anus. 

3.  The  retractor  ani  is  a  flat  muscle  which  lies  between  the  rectum  and  the 
sacro-sciatic  ligament;  its  fibers  are  directed  backward  and  somewhat  upward. 
It  arises  from  the  superior  ischiatic  spine  and  the  sacro-sciatic  ligament,  and  ends 
under  the  sphincter  ani  externus.  Its  action  is  to  reduce  the  partial  prolapse  which 
the  anus  undergoes  during  defecation. 

The  suspensory  ligament  of  the  anus  (Lig.  suspensorium  ani)  is  a  band  of 
unstriped  muscle  which  arises  from  the  first  coccygeal  vertebra,  passes  downward 
under  cover  of  the  retractor  ani,  and  unites  with  its  fellow  below  the  anus.  In  the 
male  it  is  largely  continued  by  the  retractor  penis  muscle;  in  the  female  it  blends 
with  the  constrictor  vulvae.     It  may  act  as  an  accessory  sphincter  of  the  anus. 

Vessels  and  Nerves. — The  blood-supply  comes  from  the  internal  pudic  arteries, 
and  the  veins  go  to  the  internal  pudic  vein.  The  lymph  vessels  go  to  the  anal 
lymph  glands.     The  nerves  come  from  the  pudic  nerve. 


THE  PANCREAS 

The  pancreas  is  situated  transversely  on  the  dorsal  wall  of  the  abdomen,  the 
greater  part  being  to  the  right  of  the  median  plane.  Its  central  part  lies  under  the 
sixteenth  and  seventeenth  thoracic  vertebrae.  When  fresh,  it  has  a  reddish  cream 
color,  but  if  left  in  the  unpreserved  cadaver,  it  rapidly  decomposes  and  becomes 
dark.  It  resembles  the  salivary  glands  in  appearance,  but  is  softer,  and  its  lobules 
are  more  loosely  united.  Its  average  weight  is  about  twelve  ounces  (ca.  350  g.). 
When  hardened  in  situ  its  shape  is  very  irregular.  It  is  triangular  in  outline,  and 
presents  for  description  two  surfaces,  three  borders,  and  three  angles.^ 

The  dorsal  surface  (Facies  dorsalis)  faces  dorsally  and  forward.  It  is  partially 
covered  by  peritoneum.  It  is  related  chiefly  to  the  ventral  surface  of  the  right 
kidney  and  adrenal,  the  posterior  vena  cava,  the  portal  vein,  the  coeliac  artery  and 
its  divisions,  the  gastro-phrenic  ligament,  and  the  saccus  csecus  of  the  stomach,  the 
right  and  caudate  lobes  of  the  liver,  and  the  gastro-pancreatic  fold.  There  are 
grooves  for  the  divisions  of  the  coeliac  artery  and  a  large  one  for  the  splenic  vein. 

The  ventral  surface  (Facies  ventralis)  faces  ventrally  and  backward ;  it  is  in 
general  concave.  It  presents  two  impressions,  separated  by  an  oblique  ridge.  The 
smaller  of  these  (Impressio  csecalis)  lies  to  the  right,  and  is  caused  by  the  pressure 
of  the  base  of  the  caecum;    the  larger  one  (Impressio  colica)  indicates  the  area  of 

1  A  descriptive  method  based  on  that  in  use  in  human  anatomy  cannot  be  applied  with 
clearness  to  the  organ  in  the  horse. 


THE  PANCKEAS 


433 


contact  with  the  terminal  part  of  the  great  colon  and  its  junction  with  the  small 
colon.  It  has  usually  no  peritoneal  covering  except  over  a  small  area  at  the  anterior 
angle. 

The  right  border  is  nearly  straight;  it  is  related  to  the  second  part  of  the  duo- 
denum. 

The  left  border  is  slightly  concave,  and  is  related  to  the  first  part  of  the  duode- 
num, the  left  sac  of  the  stomach,  and  the  splenic  vessels. 

The  posterior  border  presents  a  deep  notch  (Incisura  pancreatis)  where  the 
root  of  the  great  mesentery  is  in  contact  with  the  gland.  To  the  right  the  portal 
vein  lies  in  the  notch,  and  passes  through  the  gland  very  obliquely;   there  is  a  thin 


Fig.  371. — P.4.ncreas  of  Horse  with  Chief  Hki.atioxs;  \'kxtral  View. 
The  pancreatic  duct  and  its  two  chief  radicles  are  indicated  by  dotted  lines,  since  they  are  in  the  substance  of  the  gland. 


bridge  of  gland  tissue  dorsal  to  the  vein,  thus  forming  the  portal  ring  (Annulus 
portae). 

The  anterior  or  duodenal  angle  (Angulus  cranialis)^  is  the  most  ventral  part 
of  the  gland;  it  is  attached  to  the  concavity  of  the  second  curve  of  the  duodenum 
and  the  adjacent  part  of  the  right  lobe  of  the  liver.  The  ducts  leave  at  this  ex- 
tremity. 

The  left  or  splenic  angle  (Angulus  sinister)-  fits  into  the  space  between  the 
saccus  csecus  of  the  stomach  in  front,  the  left  kidney  behind,  the  base  of  the  spleen 
dorsally,  and  the  termination  of  the  great  colon  ventrally. 

The  right  angle  (Angulus  dexter)  is  rounded,  and  lies  on  the  ventral  surface  of 
the  right  kidney  and  adrenal  body. 

^  This  corresponds  to  the  head  of  the  pancreas  of  man. 
2  This  corresponds  to  the  tail  of  the  pancreas  of  man. 
28 


434  DIGESTIVE    SYSTEM    OF   THE    HORSE 

The  pancreas  is  attached  dorsally  by  connective  tissue  to  the  kidneys  and 
adrenal  bodies,  the  gastro-phrenic  ligament,  the  suspensory  iia;ament  of  the  spleen, 
the  posterior  vena  cava,  the  portal  fissure,  and  the  gastro-pancreatic  fold.  The 
ventral  surface  is  mainly  attached  by  areolar  tissue  to  the  base  of  the  caecum  and 
the  terminal  part  of  the  great  colon. 

There  are  almost  invariably  two  ducts.  The  large  one  is  termed  the  pan- 
creatic duct  (Ductus  pancreaticus).^  It  is  formed  by  the  union  of  two  radicles 
which  come  from  the  right  and  left  extremities,  and  passes  through  the  duodenal 
angle  to  end  at  the  duodenal  diverticulum  alongside  of  the  bile-duct.  The  duct 
is  nearly  half  an  inch  (ca.  1  cm.)  wide,  and  is  very  thin  walled.  It  is  situated  in  the 
substance  of  the  gland  near  its  dorsal  surface;  none  of  it  is  free.  The  accessory 
pancreatic  duct  (Ductus  pancreaticus  accessorius)^  arises  either  from  the  chief 
duct  or  its  left  radicle,  and  ends  on  a  papilla  in  the  duodenum  opposite  the  chief 
duct. 

Structure.^ — The  pancreas  belongs  to  the  class  of  tubulo-alveolar  glands,  the 
alveoli  being  long,  like  those  of  the  duodenal  glands;  in  other  respects  it  resembles 
the  serous  salivary  glands  very  closely.  It  has  no  proper  capsule  and  the  lobules 
are  rather  loosely  united. 

Vessels  and  Nerves. — The  arteries  of  the  pancreas  come  from  the  branches  of 
the  cceliac  and  anterior  mesenteric  arteries.  The  veins  go  to  the  portal  vein.  The 
nerves  are  derived  from  the  cceliac  and  mesenteric  plexuses  of  the  sympathetic. 

THE  LIVER 

The  liver  (Hepar)  is  the  largest  gland  in  the  body.  It  is  situated  obliquely 
on  the  abdominal  surface  of  the  diaphragm.  Its  highest  point  is  at  the  level  of 
the  right  kidney,  its  lowest  on  the  left  side,  usually  about  three  or  four  inches 
(ca.  8  to  10  cm.)  from  the  abdominal  floor,  opposite  the  ventral  end  of  the  seventh 
or  eighth  rib.     The  greater  part  of  it  lies  to  the  right  of  the  median  plane. 

It  is  red-brown  in  color  and  is  rather  friable.  Its  average  weight  is  about  ten 
to  twelve  pounds  (ca.  5  kg.),  but  in  a  large  draft  horse  it  weighs  about  twenty  pounds. 
When  in  the  body,  or  if  hardened  in  situ,  it  is  strongty  curved  and  accurately  adapted 
to  the  abdominal  surface  of  the  diaphragm.  When  removed  in  the  soft  state,  it 
flattens  out  into  a  cake-like  form  quite  different  from  its  natural  configuration. 
It  presents  for  description  two  surfaces,  and  a  circumference  which  may  be  divided 
into  four  borders. 

The  parietal  surface  (Fades  diaphragmatica)  is  strongly  convex,  and  lies 
against  the  diaphragm.  It  faces  chiefly  dorsally  and  forward.  Its  most  anterior 
part  is  opposite  the  ventral  third  of  the  sixth  intercostal  space  or  seventh  rib.  It 
presents,  just  to  the  right  of  the  median  plane,  a  sagittal  groove  for  the  posterior 
vena  cava  (Fossa  venae  cavae),  which  is  partially  embedded  in  the  substance  of  the 
gland. 

The  visceral  surface  (Facies  visceralis)  faces  in  general  ventrally  and  backward; 
it  is  concave  and  irregular,  being  molded  on  the  organs  which  lie  against  it.  It 
presents  the  follo^ving  features:  (1)  The  portal  fissure  (Porta  hepatis)  is  a  depres- 
sion above  the  middle  of  the  surface  and  a  httle  to  the  right  of  the  median  plane; 
through  it  the  portal  vein,  hepatic  artery,  and  hepatic  plexus  of  nerves  enter,  and 
the  hepatic  duct  and  lymph  vessels  leave  the  liver.  The  hepatic  lymph  glands  are 
also  found  here.  The  pancreas  is  attached  at  and  to  the  right  of  the  fissure,  and 
the  lesser  omentum  around  it.  Above  the  fissure  is  the  caudate  lobe  (Lobus  cau- 
datus),  which  is  continued  to  the  right  by  the  pointed  caudate  process  (Processus 
caudatus).     (2)  The  gastric  impression  (Impressio  gastrica)  is  an  extensive  con- 

1  Formerly  termed  the  canal  of  Wirsung. 

2  Formerly  called  the  ductus  pancreaticus  minor  or  duct  of  Santorini. 


THE    LIVER 


435 


cave  area  which  is  the  surface  of  contact  with  the  stomach.  (3)  Leading  from  this 
to  the  right  of  the  portal  fissure  and  dorsally  is  the  duodenal  impression  (Impressio 
duodenahs).  (4)  The  colic  impression  (Impressio  colica)  is  situated  ventrally  and 
to  the  right  of  the  gastric  and  duodenal  impressions,  from  which  it  is  separated  by 
a  rido-e-  it  corresponds  to  the  extensive  contact  of  the  diaphragmatic  flexure  and 
right  dorsal  part  of  the  colon.  (5)  A  caecal  impression  (Impressio  cseciilis)  may 
be  found  dorsal  to  the  preceding;  it  corresponds  to  the  anterior  part  oi  the  base  ol 
the  cgecum.i  Coils  of  the  small  intestine  may  also  lie  on  this  surface,  and  the  apex 
of  the  spleen  mav  reach  to  it  when  the  stomach  is  empty. 

The  dorsal  border  (Margo  dorsalis  s.  obtusus)  is  thick  for  the  most  part.  It 
presents  from  right  to  left:  (1)  The  attachment  of  the  right  lateral  ligament;  (2) 
a  depression  for  the  right  kidney  (Impressio  renalis);    (3)  a  notch,  which  is  the 


Right  lateral  ligament 


h Posterior  vena  cava 


Esophageal         ^^^j lateral  ligament 


Coronary 
ligament 


Falciform  ligament 


■"'iiii^ 


Round 
ligament 

Fig.  372.-LIVER  of  Youmg  Horse.  Hardened  in  situ;  Parietal  Surface. 

dorsal  end  of  the  fossa  ven^  cav^;  (4)  thedeep  oesophageal  notch  (Impressio  oesoph- 
agea),  which  is  occupied  partly  by  the  end  of  the  cesophagus  ^^^  -7  ^  ^y  the 
thick  margin  of  the  hiatus  cesophageus;    (5)  the  attachment  of  the  left  lateral  hga- 

"^'""The  ventral  border  (Margo  ventralis)  is  thin,  and  is  "^^^ked  by  two  deep 
interlobar  fissures  or  incisures  (Incisura.  interlobares) ,  which  partially  divide  the 
^gan  into  three  principal  lobes-right,  middle,  and  left.  The  right  lobe  is  the 
krgest  except  in  old  subjects,  in  which  it  is  frequently  much  atrophied  The 
m  d  Ue  lobe  is  the  smallest.  It  is  marked  by  several  small  fissures  and  by  the 
umbilicarfissure  (Incisura  umbihcalis);  the  latter  contains  the  umbihcal  vein  m 
the  foetus,  which  is  transformed  into  the  round  ligament  after  birth. 

^  These  impressions  are  not  evident  on  the  ^^^^  .-^f^or^.^'^^rL'^dlSe^ 
^^Z^al^"^.  ^^T^JeScireSr^S Zlr^^^L  of&n  happens  in 
old  horses,  the  right  lobe  of  the  liver  is  much  atrophied. 


436 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


The  right  border  (Margo  dexter)  is  thin  and  long;  it  extends  backward  usually 
to  the  sixteenth  rib,  a  little  below  its  middle.^ 

The  left  border  (Margo  sinister)  is  thin  and  convex.  It  begins  at  the  left  side 
of  the  oesophageal  notch,  about  a  handbreadth  ventral  to  the  fourteenth  thoracic 
vertebra.     It  curves  downward,  outward,  and  somewhat  forward  to  a  point  opposite 


Renal  impression 

\ 


Caudate  p7-ocess 


Posterior  vena  cava 


Attachment  of  (/astro- pancreatic  fold 
Portal  vein 


Specii: 


Umbilical  fissure 


Fig.  373. — Liver  of  Horse;  Visceral  Surface. 
from  middle-aged  subject,  hardened  in  situ.     The  fissure  between  the  left  and  middle  lobes  is  shown  but 
not  marked. 


the  ventral  end  of  the  ninth  rib,  and  then  runs  forward  about  parallel  with  the 
costal  arch  as  far  as  the  ventral  end  of  the  seventh  rib.  The  ventral  and  lateral 
borders  together  constitute  the  margo  acutus. 

The  liver  is  held  in  position  largely  by  the  pressure  of  the  other  viscera  and 
by  its  close  application  and  attachment  to  the  diaphragm.     It  has  six  ligaments. 

^  The  right  border  varies  much  in  subjects  in  the  dissecting  room,  since  in  old  subjects  the 
right  lobe  is  often  greatly  atrophied.     Atrophy  of  the  left  lobe  is  extremely  rare. 


THE    LIVER  437 

1 .  The  coronary  ligament  (Lig.  coronarium  hepatis)  attaches  it  closely  to  the 
diaphragm.  It  consists  of  two  strong  laminae.  The  right  one  is  attached  to  the 
right  of  the  fossa  venae  cavse;  the  left  one  begins  to  the  left  of  the  vena  cava  and 
passes  dorsally  and  laterally,  becoming  continuous  mth  the  left  lateral  ligament  at 
the  left  margin  of  the  oesophageal  notch;  it  detaches  a  middle  fold  which  extends 
to  the  oesophageal  notch  and  is  continuous  with  the  lesser  omentum.  The  two 
laminae  unite  below  the  vena  cava  to  form  the  next  ligament. 

2.  The  falciform  ligament  (Lig.  falciforme  hepatis)  is  a  crescentic  fold  which 
attaches  the  middle  lobe  to  the  sternal  part  of  the  diaphragm  and  to  the  abdominal 
floor  for  a  variable  distance. 

3.  The  round  ligament  (Lig.  teres  hepatis)  is  a  fibrous  cord  in  the  concave 


Renal  impression 


Posterior  vena  ca 

Portal  vein 
Hepatic  artery 
Hepatic  duct 
(Esophageal  notch 


Middle  lobe 


Umbilical  vein 


Fig.  374. — Liver  of  New-born  Foal,  Hardened  in  situ;  Visceral  Surface. 
The  differences,  when  compared  with  the  organ  in  the  adult,  are  very  striking. 

edge  of  the  falciform  ligament  which  extends  from  the  umbilical  fissure  to  the 
umbilicus;  it  is  the  vestige  of  the  umbilical  vein,  which  in  the  foetus  carries  the 
blood  from  the  placenta  to  the  liver.' 

4.  The  right  lateral  ligament  (Lig.  triangulare  dextrum)  attaches  the  dorsal 
border  of  the  right  lobe  closely  to  the  costal  part  of  the  diaphragm. 

5.  The  left  lateral  ligament  (Lig.  triangulare  sinistrum)  is  a  triangular  fold 
which  attaches  the  dorsal  edge  of  the  left  lobe  to  the  tendinous  center  of  the  dia- 
phragm, 

6.  The  hepato-renal  or  caudate  ligament  (Lig.  hepatorenale)  attaches  the 
<3audate  process  to  the  right  kidney  and  the  base  of  the  caecum. 

The  lesser  omentum  and  the  first  part  of  the  mesoduodenum  are  formed  by  the 

^  It  is  to  be  noted  that  a  remnant  of  the  lumen  of  the  vein  is  usually  present,  but  has  no 
endothelial  Uning. 


438  DIGESTIVE    SYSTEM    OF   THE    HORSE 

peritoneum  leaving  the  visceral  surface  at  the  portal  fissure  and  along  a  curved 
line  which  extends  from  the  fissure  to  the  oesophageal  notch.  They  pass  to  the 
lesser  curvature  of  the  stomach  and  the  first  part  of  the  duodenum. 

As  stated  above,  the  liver  is  divided  by  fissures  into  three  principal  lobes — 
right,  middle,  and  left.  The  right  lobe  (Lobus  dexter)  is  the  largest  in  the  young 
subject  and  is  irregularly  quadrilateral  in  form.  On  its  dorsal  part  is  the  caudate 
lobe  (Lobus  caudatus),  which  ends  in  a  pointed  caudate  process  directed  outward 
and  assists  in  forming  the  cavity  for  the  right  kidney.  The  central  or  middle  lobe 
(Lobus  centralis)  is  normally  much  the  smallest.  The  left  lobe  (Lobus  sinister)  is 
oval  in  outline  and  thickest  centrally.  In  old  or  middle-aged  subjects  it  commonly 
exceeds  the  right  one  in  size,  and  in  many  cases  constitutes  the  bulk  of  the  gland. 
In  some  cases  the  atrophy  of  the  right  lobe  is  so  extreme  that  the  middle  lobe  may 
exceed  it  in  size.^ 

The  hepatic  duct  (Ductus  hepaticus)  is  formed  at  the  ventral  part  of  the  portal 
fissure  by  the  union  of  right  and  left  chief  lobar  ducts.  It  is  about  two  inches 
(ca.  5  cm.)  long  and  about  half  an  inch  (ca.  1  to  1.5  cm.)  wide.  It  passes  be- 
tween the  two  layers  of  the  mesoduodenum,  and  pierces  the  wall  of  the  duodenum 
five  or  six  inches  (ca.  12  to  15  cm.)  from  the  pylorus,  alongside  of  the  pancreatic 
duct.  The  ducts  pass  obliquely  through  the  wall  of  the  duodenum  for  about 
half  an  inch  (ca.  1  cm.)  before  opening  into  the  diverticulum  duodeni.  The  arrange- 
ment forms  a  valve,  which  prevents  regurgitation  from  the  intestine.  There  is  no 
gall-bladder. 

In  the  new-born  foal  the  liver  presents  striking  differences  when  compared  with  the  gland  of 
the  adult.  It  is  relatively  large  and  weighs  23^  to  3  pounds  (ca.  1.25  kg.).  It  is  thick  and  is  strongly 
curved,  and  a  considerable  part  of  the  parietal  surface  is  in  contact  with  the  floor  of  the  abdomen. 
The  umbilical  fissure  is  large  and  contains  the  umbilical  vein.  The  latter  is  a  very  large  vessel 
which  carries  blood  from  the  placenta  and  joins  the  portal  vein  in  the  substance  of  the  liver;  it  is 
in  the  edge  of  the  falciform  Ugament,  which  at  this  time  extends  to  the  umbiUcus.  The  visceral 
surface  is  deeply  concave  and  is  in  contact  chiefly  with  the  stomach  and  duodenum. 

Structure. — The  liver  is  covered  by  an  external  serous,  and  an  internal  fibrous, 
coat.  The  serous  coat  (Tunica  serosa)  covers  the  gland  except  at  the  attachment 
of  the  pancreas  and  at  the  portal  fissure;  it  is  reflected  from  it  to  form  the  ligaments 
and  the  lesser  omentum.  The  fibrous  capsule  (Capsula  fibrosa)  is  in  general  thin; 
it  sends  laminae  into  the  ligaments,  and  also  trabeculse  into  the  gland.  At  the  portal 
fissure  it  is  abundant  and  surrounds  the  vessels  and  ducts,  which  it  accompanies 
in  the  portal  canals  of  the  gland  substance. 

The  gland  substance  is  composed  of  the  parenchyma  and  the  interstitial 
tissue.  The  parenchyma  is  made  up  of  polygonal  lobules  (Lobuli  hepatis),  about 
1.5  mm.  in  diameter,  which  are  held  together  by  a  small  amount  of  interlobular 
connective  tissue.  On  account  of  the  very  small  amount  of  the  latter,  the 
lobulation  of  the  horse's  liver  is  not  usually  at  all  distinct ;  for  the  same  reason  the 
organ  is  also  quite  friable.  The  lobules  are  composed  of  the  polyhedral  liver  cells, 
a  delicate  reticulum,  the  bile  capillaries,  a  plexus  of  blood  capillaries,  and  a  central 
vein. 

Vessels  and  Nerves. — The  portal  vein  enters  at  the  portal  fissure.  It  conveys 
blood  from  the  digestive  tract  and  the  spleen,  which  contains  various  products  of 
digestion  and  numerous  white  blood-cells.  The  hepatic  artery  also  enters  at  the 
portal  fissure;  it  may  be  termed  the  nutrient  vessel.  All  the  blood  is  returned  from 
the  liver  to  the  posterior  vena  cava  by  the  hepatic  veins.  The  portal  vein  and  the 
hepatic  artery  both  divide  into  interlobular  branches,  which  run  together  in  the 

1  Flower  and  Ruge  describe  the  mammalian  liver  as  being  primarily  divided  by  the  umbiUcal 
fissure  into  two  parts,  the  right  and  left  lobes.  Secondary  fissures  on  either  side  may  subdivide 
each  of  these  primary  lobes.  On  this  basis  we  may  recognize  in  the  liver  of  the  horse  right  lateral, 
right  central,  left  central,  and  left  lateral  lobes.  In  the  young  foal  these  four  lobes  are  distinctly 
recognizable.  The  two  central  lobes  would  correspond  to  the  central  or  middle  lobe  of  the  foregoing 
description,  and  the  right  central  lobe  would  be  the  equivalent  of  the  quadrate  lobe  of  man. 


THE    SPLEEN 


439 


portal  canals  of  the  interlobular  tissue.  The  branches  of  the  portal  vein  (Venae 
interlobulares)  give  off  intralobular  branches  which  form  plexuses  of  capillaries  in 
the  lobules  and  give  rise  to  a  central  vein  (Vena  centralis).  The  interlobular 
branches  of  the  hepatic  artery  (Rami  arteriosi  interlobulares)  are  of  relatively 
small  size.  They  supply  mainly  (if  not  exclusively)  the  interlobular  tissue,  the 
capsule,  and  the  walls  of  the  vessels  and  ducts.  The  hepatic  veins'  (Vena  hepaticse) 
empty  into  the  posterior  vena  cava  as  it  lies  in  the  fossa  of  the  gland.  Their 
ultimate  radicles  are  the  central  lobular  veins  (Venae  centrales),  which  emerge  from 
the  bases  of  the  lobules  and  join 
the  sublobular  veins  (Vena3  sub- 
lobulares) ;  the  latter  unite  to  form 
the  hepatic  veins.  The  largest 
hepatic  veins,  three  or  four  in 
number,  join  the  posterior  vena 
cava  just  before  it  leaves  the  liver 
to  pass  through  the  diaphragm. 

The  nerves  come  from  the 
hepatic  plexus,  which  is  composed 
of  branches  from  the  vagus  and 
sympathetic  nerves. 


THE  SPLEEN 
The  spleen  (Lien)  is  the 
largest  of  the  heterogeneous  group 
of  organs  which  are  usually  desig- 
nated ductless  glands.^  It  is  situ- 
ated chiefly  in  the  left  parachon- 
driac  region,  in  close  relation  to  the 
left  part  of  the  great  curvature  of 
the  stomach,  to  which  its  long  axis 
corresponds.  Its  size  and  weight 
vary  greatly  in  different  subjects, 
and  also  in  the  same  subject  under 
different  conditions,  depending 
chiefly  on  the  great  variability  of 
the  amount  of  blood  contained  in 
it.  The  average  weight  is  about  35 
to  40  ounces  (ca.  1  kg.),  its  length 
about  20  inches  (ca.  50  cm.),  and 
its  greatest  width  about  8  to  10 
inches  (ca.  20  to  25  cm.).  It  is 
usually  bluish-red  or  somewhat  purple  in  color, 
yielding,  but  not  friable. 

The  weight,  which  is  extremely  variable,  appears  to  range  ordinarily  from  about  one  to  eight 
pounds,  although  the  latter  figure  even  may  be  exceeded  without  any  apparent  evidence  of  disease. 

1  The  hepatic  veins  may  be  recognized  on  section  from  the  fact  that  they  remain  open, 
being  connected  closely  with  the  parenchyma. 

2  The  ductless  glands  are  organs  which  elaborate  substances  that  pass  directly  into  the 
veins  or  lymphatics,  instead  of  being  conveyed  away  by  ducts.  This  process  is  termed  internal 
secretion.  The  ductless  glands  include  the  lymph  glands,  which  are  described  with  the  organs 
of  circulation;  the  thyroid  and  thymus  bodies,  described  usually  with  the  respiratory  organs; 
the  adrenal  or  suprarenal  bodies,  described  with  the  urinary  organs;  the  pineal  and  pituitary 
bodies,  described  with  the  brain;  and  the  spleen,  described  w\th  the  digestive  system  as  a  matter 
of  convenience.  The  spleen  is  not,  strictly  speaking,  a  gland  at  all:  it  is  not  epithelial  in  origin 
or  structure,  but  is  mesenchymatous. 


Fig.  375. — Spleen  of  Horse;   Parietal  Surface. 
a,  Dorsal  extremity  or  base;  6,  c,  anterior  and  posterior  basal 
angles;   d,  anterior  border;   e,  ventral  extremity  or  apex;    1,  2,  3, 
impressions  of  last  three  ribs. 

In  the  natural  state  it  is  soft  and 


440 


DIGESTIVE   SYSTEM    OF   THE   HORSE 


The  author  recently  observed  in  a  horse,  which  weighed  about  1200  pounds,  a  spleen  which  weighed 
lOM  pounds,  and  measured  26  inches  in  length  and  11  inches  in  width  at  the  base.  The  ventral 
end  was  situated  opposite  the  lower  part  of  the  seventh  intercostal  space.  In  the  new-born  foal 
the  weight  is  about  10  to  12  ounces  (ca.  300  gm.).  There  does  not  seem  to  be  any  constant  relation 
to  the  body-weight.  For  example,  the  spleen  of  a  colt  of  medium  size  about  ten  months  old 
weighed  three  and  a  half  pounds,  while  it  often  weighs  less  than  two  pounds  in  horses  weighing 
1000  to  1200  pounds.  The  chief  variation  in  outUne  consists  of  increase  of  width,  especially  of  the 
dorsal  part. 

It  extends  obliquely  in  a  curved  direction,  corresponding  to  the  left  part  of  the 
greater  curvature  of  the  stomach,  from  the  left  crus  of  the  diaphragm  to  the  ventral 

third  of  the  tenth  or  eleventh  rib.  It 
presents  for  description  two  surfaces, 
two  borders,  and  two  extremities. 

The  parietal  or  lateral  surface  (Fa- 
des parietalis)  is  convex,  and  lies  chiefly 
against  the  diaphragm,  but  is  in  contact 
with  the  dorsal  parts  of  the  last  two  ribs 
and  usually  to  a  small  extent  with  the 
flank  at  the  lumbo-costal  angle. 

The  visceral  or  medial  surface  (Fa- 
des visceralis)  is  in  general  concave.  It 
is  divided  into  two  unequal  parts  by  a 
longitudinal  ridge;  on  this  is  a  groove, 
the  hilus,  in  which  the  vessels  and  nerves 
are  situated.  The  area  in  front  of  the 
ridge  (Fades  gastrica)  is  molded  on  the 
greater  curvature  of  the  stomach;  it 
is  about  two  inches  (ca.  5  cm.)  wide. 
The  area  behind  the  ridge  (Fades  intes- 
tinalis)  is  much  more  extensive;  it  is 
related  to  the  small  colon,  the  left  parts 
of  the  great  colon,  the  small  intestine, 
and  the  great  omentum.  It  may  be 
marked  by  one  or  two  fissures. 

The  anterior  border  (Margo  crani- 
alis)  is  concave  and  thin,  being  wedged 
in  between  the  diaphragm  and  the 
greater  curvature  of  the  stomach. 

The  posterior  border  (]\Iargo  cau- 
dalis)  is  convex  and  thin. 

The  dorsal  extremity  or  base  (Ex- 
tremitas  dorsalis)  is  beveled,  and  fits  into 
the  interval  l)etween  the  left  crus  of 
the  diaphragm  and  sublumbar  muscles 
above,  and  the  saccus  caecus  of  the  stomach  and  the  left  kidney  below.  When 
hardened  in  situ,  it  shows  an  impression  (Fades  renalis)  where  it  lies  against  the 
kidney.  The  left  extremity  of  the  pancreas  touches  it  also.  The  anterior  basal 
angle  fits  in  between  the  saccus  csecus  of  the  stomach  and  the  left  kidney  at  the 
seventeenth  thoracic  vertebra;  the  posterior  basal  angle  usually  lies  against  the 
upper  part  of  the  left  flank,  just  behind  the  last  rib.^ 

The  ventral  extremity  or  apex  (Extremitas  ventralis)  is  small  and  varies  in 
position.  It  is  commonly  foimd  opposite  the  tenth  or  eleventh  rib,  a  handbreadth 
or  more  above  the  costal  arch,  but  may  be  further  forward  and  higher. 

1  It  is  uncommon  to  find  the  spleen  extending  more  than  two  or  three  inches  behind  the  last 
rib;  on  the  other  hand,  the  posterior  basal  angle  may  lie  just  at  the  last  rib. 


Fig.  .37C. — Spleen  of  Horse,  Hardened 
CERAL  Surface. 
o,  Dorsal  extremity  or  base;  b,  c,  anterior  and  poste- 
rior basal  angles;  d,  anterior  border;  e,  cut  edge  of  sus- 
pensory ligament ;  /,  g,  splenic  artery  and  vein  in  hilus. 
The  area  marked  intestinal  impression  is  related  to  the 
first  coil  of  the  small  colon.  The  area  enclosed  by  the 
suspensorj-  ligament  is  non-peritoneal. 


THE    PERITONEUM  441 

The  position  of  the  ventral  part  depends  largely  upon  two  factors — the  degree  of  fulness  of 
the  stomach  and  the  size  of  the  spleen.  When  the  stomach  is  empty  or  nearly  so  and  the  spleen 
small  (contracted),  the  latter  is  strongly  curved,  and  its  ventral  end  may  be  between  the  left  lobe 
of  the  liver  and  the  left  dorsal  part  of  the  great  colon.  When  the  stomach  is  full,  it  pushes  the 
spleen  backward,  affecting  most  the  ventral  part  of  the  latter.  Of  course  the  spleen  is  affected 
by  the  respiratory  movements,  as  may  be  readily  observed  by  examination  per  rectum  of  the 
Uving  subject. 

The  spleen  is  attached  by  two  peritoneal  folds,  the  suspensory  ligament  and 
the  gastro-splenic  omentum.  The  suspensory  ligament  of  the  spleen  (Lig.  sus- 
pensorium  lienis)  attaches  the  dorsal  end  to  the  left  crus  of  the  diaphragm  and  the 
left  kidney;  it  contains  a  quantity  of  elastic  tissue.  The  dorsal  layer  of  the  liga- 
ment, which  passes  to  the  diaphragm,  is  the  ligamentum  phrenico-lienale,  and  blends 
with  the  gastro-phrenic  ligament;  the  ventral  part,  which  goes  to  the  kidney,  is 
termed  the  ligamentum  renolienale.  The  gastro-splenic  omentum  (Lig.  gastro- 
lienale)  passes  from  the  hilus  to  the  left  part  of  the  greater  curvature  of  the  stomach. 
It  is  narrow  dorsally,  where  it  joins  the  suspensory  ligament;  ventrally  it  becomes 
much  wider  and  is  continuous  with  the  great  omentum. 

Small  globular  or  lenticular  ma.sses  of  splenic  tissue  may  be  found  in  the  gastro-splenic 
omentum.     They  are  termed  accessory  spleens  (Lienes  accessorii). 

Structure. — The  spleen  has  an  almost  complete  serous  coat  (Tunica  serosa). 
Subjacent  to  this  and  intimately  united  with  it  is  a  capsule  of  fibrous  tissue  (Tunica 
albuginea),  which  contains  many  elastic  fibers  and  some  unstriped  muscular  tissue. 
Numerous  trabeculae  (Trabeculse  lienis)  are  given  off  from  the  deep  face  of  the 
capsule  and  ramify  in  the  substance  of  the  organ  to  form  a  supporting  network. 
In  the  interstices  of  this  framework  is  the  spleen  pulp  (Pulpa  lienis),  a  dark  red,  soft, 
grumous  material.  This  is  supported  by  a  delicate  reticulum,  and  contains  numer- 
ous leukocytes,  the  large  splenic  cells,  red  blood-corpuscles,  and  pigment.  The 
pulp  is  richly  supplied  with  blood.  The  branches  of  the  splenic  artery  enter  at 
the  hilus  and  pass  along  the  trabeculse.  The  arteries  which  enter  the  pulp  have  a 
sheath  of  lymphoid  tissue,  which  collects  on  the  vessel  wall  at  certain  points,  form- 
ing small  splenic  lymph  nodules  (Noduli  lymphatici  lienales).^  These  are  visible 
to  the  naked  eye  as  white  spots,  about  as  large  as  the  head  of  a  pin.  The  blood 
passes  into  cavernous  spaces  lined  by  endothelium  which  is  continuous  with  the 
cells  of  the  reticulum  of  the  pulp.  From  these  the  veins  arise.  The  splenic  vein 
runs  in  the  hilus  in  company  with  the  artery  and  nerves,  and  joins  the  posterior 
gastric  vein  to  form  a  large  radicle  of  the  portal  vein. 

Vessels  and  Nerves. — The  arteries  are  derived  from  the  splenic  artery,  which 
is  the  largest  branch  of  the  coeliac  artery.  The  splenic  vein  lies  behind  the  artery 
in  the  hilus;  it  goes  to  the  portal  vein.  The  lymph  vessels  go  to  the  splenic  lymph 
glands.  The  nerves,  derived  from  the  coeliac  plexus  of  the  sympathetic,  accom- 
pany the  vessels. 

THE  PERITONEUM 

The  general  disposition  of  the  peritoneum  has  been  described,  and  other  facts 
in  regard  to  it  were  mentioned  incidentally  in  the  description  of  the  viscera.  It  is 
now  desirable  to  study  it  as  a  continuous  whole-  (Figs.  351,  352,  353,  377,  378). 

We  may  consider  the  peritoneum  as  consisting  of  two  sacs — a  greater  and  a 
lesser.  The  greater  sac  lines  the  greater  part  of  the  abdominal  cavity,  and  covers 
most  of  the  viscera  which  have  a  peritoneal  investment.  The  lesser  sac  is  an 
introversion  or  invagination  of  the  greater  sac,  formed  during  the  development  of 
the  viscera.     The  two  sacs  communicate  by  a  relatively  narrow  passage,  termed 

1  These  are  also  known  as  Malpighian  corpuscles. 

2  The  student  is  strongly  recommended  to  study  the  peritoneum  of  a  foal  or  other  small 
subject  when  the  opportunity  occurs,  as  in  these  the  viscera  are  easily  handled,  and  the  course 
of  the  peritoneum  can  be  followed  without  difficulty. 


442 


DIGESTIVE    SYSTEM    OF   THE   HORSE 


the  epiploic  foramen  (Foramen  epiploicum).^  This  opening  is  situated  on  the 
visceral  surface  of  the  hver  dorsal  to  the  portal  fissure.  It  can  be  entered  by  passing 
the  finger  along  the  caudate  lobe  of  the  liver  toward  its  root.  Its  dorsal  wall  is 
formed  by  the  caudate  lobe  and  the  posterior  vena  cava.  Its  ventral  wall  consists 
of  the  pancreas,  the  gastro-pancreatic  fold,  and  the  portal  vein.  The  walls  are 
normally  in  contact,  and  the  passage  merely  a  potential  one.  It  is  usually  about 
four  inches  (ca.  10  cm.)  in  length.  It  is  narrowest  at  the  lateral  extremity,  where 
it  is  about  an  inch  (ca.  2.5  to  3  cm.)  wide.^  If  the  finger  is  passed  into  the  foramen 
from  right  to  left,  it  enters  the  cavity  of  the  lesser  sac.  If  now  an  opening  is  made 
in  the  great  omentum  and  the  other  hand  introduced  through  it,  the  fingers  of  the 
two  hands  can  touch  each  other  over  the  lesser  curvature  of  the  stomach.  The 
formation  and  boundaries  of  the  lesser  sac  should  now  be  examined  by  spreading 
out  the  great  omentum.  It  will  be  found  that  the  latter  now  encloses  a  considerable 
cavity  behind  the  stomach;  this  is  termed  the  omental  cavity  (Bursa  omentalis). 
Passing  forward  over  the  lesser  curvature  of  the  stomach,  we  enter  another  space, 
the  vestibule  of  the  omental  cavity  (Vestibulum  bursse  omentalis).     This  space  is 


Fig.  377. — Diagram  op  General  Arrangement  of  Peritoneum  (of  Mare)  in  Sagittal  Tracing. 
Sacro-rectal  pouch,  continuous  with  b,  recto-genital  pouch;   c,  vesico-genital  pouch;   d,  pubo-vesical  pouch;  /,  lesser 
omentum;  Int.,  small  intestine.     The  arrow  points  to  the  epiploic  foramen. 


closed  on  the  left  by  the  gastro-phrenic  ligament,  ventrally  and  on  the  right  by 
the  lesser  omentum,  and  dorsally  by  the  gastro-pancreatic  fold,  which  is  attached 
to  the  dorsal  border  of  the  liver  and  to  the  posterior  vena  cava.  Above  the  (Eso- 
phageal notch  there  is  a  recess,  into  which  the  fingers  can  be  passed  around  the 
border  of  the  liver  and  the  vena  cava  till  the  coronary  ligament  is  encountered. 
Thus  the  vestibule  is  closed  except — (1)  on  the  right,  where  it  communicates  with 
the  cavity  of  the  greater  sac  by  the  epiploic  foramen;  and  (2)  behind,  where  it 
communicates  with  the  cavity  of  the  omentum. 

The  general  arrangement  of  the  greater  omenttim  has  already  been  indicated. 
We  may  now  trace  its  line  of  attachment,  which  would  correspond  to  the  mouth  of 
the  sac.  Beginning  at  the  ventral  part  of  the  greater  curvature  of  the  stomach,  it 
passes  to  the  ventral  face  of  the  pylorus,  then  crosses  obhquely  the  first  part  of 
the  duodenum  to  the  point  where  the  pancreas  is  adherent  to  it.  Here  it  passes 
to  the  anterior  face  of  the  terminal  part  of  the  great  colon,  runs  along  this  trans- 
versely (from  right  to  left),  and  continues  for  some  ten  or  twelve  inches  (ca.  25 

^  Also  known  as  the  foramen  of  Winslow. 

^  The  passage  is  subject  to  a  good  deal  of  variation  in  caUber  and  is  sometimes  occluded. 


THE   PERITONEUM 


443 


to  30  cm.)  on  the  small  colon.  It  then  forms  an  acute  angle,  passes  medially  and 
forward  along  the  small  colon  to  the  dorsal  part  of  the  hilus  of  the  spleen,  where  it 
blends  with  the  suspensory  ligament  of  the  latter,  and  forms  a  recess  (Recessus 
lienalis)  behind  the  saccus  caecus  of  the  stomach.  It  now  passes  along  the  hilus 
of  the  spleen,  and  is  continued  to  the  greater  curvature  of  the  stomach  by  the 
gastro-splenic  omentum.  It  is  convenient  to  regard  the  spleen  as  being  interca- 
lated in  the  left  part  of  the  greater  omentum;  on  this  basis  the  gastro-splenic 
omentum  would  be  that  part  of  the  greater  omentum  which  connects  the  hilus  of 
the  spleen  with  the  greater  curvature  of  the  stomach.  The  greater  omentum  is. 
relatively  small  in  the  horse,  and  is 

usually  not  visible  when  the  abdo-  ^     Viaphracrm 

men  is  opened.  It  is  generally  folded 
up  in  the  space  between  the  visceral 
surface  of  the  stomach  and  the  in- 
testine.^ 

The  lesser  sac  furnishes  the  perito- 
neal covering  for:  (1)  the  visceral  surface 
of  the  stomach  and  a  small  area  of  the  first 
curve  of  the  duodenum;  (2)  a  large  part  of 
the  dorsal  surface  of  the  pancreas  and  por- 
tal vein;  (3)  a  small  part  of  the  visceral  sur- 
face of  the  Hver  above  the  attachment  of 
the  lesser  omentum  and  the  portal  fissure ; 
(4)  the  posterior  vena  cava,  from  the  level 
of  the  epiploic  foramen  to  its  passage 
through  the  diaphragm  (in  so  far  as  it  is 
not  embedded);  (5)  the  part  of  the  parie- 
tal surface  of  the  liver  between  the  right 
and  middle  divisions  of  the  coronary  liga- 
ment; (6)  the  corresponding  part  of  the 
diaphragm,  and  the  right  part  of  the  right 
crus  of  the  same;  (7)  part  of  the  anterior 
siirface  of  the  terminal  part  of  the  great 
colon,  and  the  origin  of  the  small  colon; 
(8)  the  left  extremity  of  the  pancreas  (in- 
constant) ;    (9)  the  spleen. 

We  may  now  trace  the  perito- 
neum in  a  longitudinal  direction,  be- 
girming  in  front.  It  is  reflected  from 
the  ventral  abdominal  wall  and  the 
diaphragm  upon  the  liver,  forming 
the  ligaments  and  serous  coat  of  the 
gland.  It  leaves  the  visceral  surface 
of  the  liver  as  lesser  omentum,  and 
the  crura  of  the  diaphragm  as  the 

gastrophrenic  ligament,  reaches  the  saccus  csecus  and  lesser  curvature  of  the  stomach 
and  the  first  curve  of  the  duodenum,  covers  these  organs,  and  is  continued  by  the 
greater  omentum. 

On  the  left  it  passes  from  the  left  crus  of  the  diaphragm  and  the  left  kidney  to 
form  the  suspensory  ligament  of  the  spleen,  clothes  that  organ,  and  leaves  it  to  be 
continued  by  the  greater  and  gastro-splenic  omenta. 

On  the  right  it  passes  from  the  right  crus  of  the  diaphragm  and  the  dorsal 
border  of  the  liver  to  the  concave  border  of  the  duodenum,  forming  the  gastro- 
pancreatic  fold  (second  part  of  the  mesoduodenum) ,  and  covering  part  of  the  dorsal 
surface  of  the  pancreas.  From  the  margin  of  the  pancreas,  the  right  kidney,  and 
a  small  area  of  the  sublumbar  region  behind  the  latter,  it  passes  on  to  the  base  of 

1  In  dissecting-room  subjects  (which  are  usually  aged)  the  omentum  often  exhibits  patho- 
logical changes,  such  as  adhesions,  rents,  tumors,  formation  of  twisted  strands,  etc. 


Fig.  378. — Diagram  op  Abdominal  Peritoneum  in  Frontal 
(OR  Horizontal)  Tracing. 
D,  Duodenum;  1,  falciform  ligament;  2,  le.sser  omentum; 
3,  gastro-splenic  omentum;  4,  greater  omentum;  5,  cavity  of 
omentum;  6,  mesoduodenum;  7,  general  peritoneal  cavity. 
Arrow  indicates  epiploic  foramen.  By  an  oversight  the  pan- 
creas, in  front  of  the  colon,  is  not  marked. 


444 


DIGESTIVE    SYSTEM    OF    THE    OX 


the  csRcum  and  the  terminal  part  of  the  great  colon.  From  these  it  passes  on  the 
right  to  the  duodenum,  forming  the  third  part  of  the  mesoduodenum.  On  the  left 
it  covers  part  of  the  ventral  surface  and  the  lateral  border  of  the  left  kidney,  from 
which  it  passes  to  the  base  of  the  spleen,  forming  the  ventral  layer  of  the  suspen- 
sory ligament  of  the  latter.  Behind  the  terminal  part  of  the  great  colon  it  is  reflected 
from  the  abdominal  wall  around  the  great  mesenteric  artery  to  form  the  great 
mesentery.  Behind  this  it  is  reflected  almost  transversely  from  the  roof  of  the 
cavity  and  from  the  origin  of  the  small  colon  on  to  the  duodenum,  forming  the 
terminal  part  of  the  mesoduodenum.  The  line  of  origin  of  the  colic  mesentery 
begins  on  the  medial  part  of  the  ventral  surface  of  the  left  kidney,  and  extends  to 
the  sacral  promontory,  where  the  mesorectum  begins.  At  the  termination  of  the 
latter  the  peritoneum  is  reflected  from  the  rectum  on  to  the  dorsal  and  lateral  walls 
of  the  pelvic  cavity.  Below  the  rectum  it  forms  the  genital  fold,  and  passes  on  to 
the  dorsal  surface  of  the  bladder,  covers  its  anterior  part,  and  is  reflected  on  to  the 
body-wall  laterally  and  ventrally,  forming  the  lateral  and  middle  ligaments  of  the 
bladder.  In  the  female  the  broad  ligaments  of  the  uterus  replace  the  genital  fold, 
mth  which  they  are  homologous. 

In  the  new-born  foal  certain  folds  are  specially  large.  The  falciform  ligament 
of  the  liver  extends  to  the  umbilical  opening,  and  contains  in  its  free  edge  the  large 
umbilical  vein.  The  bladder — at  this  time  an  abdominal  organ — has  a  ventral 
median  fold  (Plica  umbilicalis  media),  which  connects  it  and  the  urachus  with  the 
alidominal  floor.  This  is  flanked  on  either  side  by  a  fold  (Plica  umbilicalis  lateralis), 
which  also  extends  to  the  umbilicus,  and  contains  the  large  umbilical  artery. 


DIGESTIVE  SYSTEM  OF  THE  OX 

THE  MOUTH 

The  cavity  of  the  mouth  is  shorter  and  wider  than  that  of  the  horse,  and  the 
vestibule  is  more  capacious  (Figs.  381,  386). 

The  lips  are  thick,  wide,  and  comparatively  immobile.     The  middle  part  of 

the  upper  lip  and  the  surface  between  the  nos- 
trils is  bare,  and  is  termed  the  muzzle  (Planum 
nasolabiale).  It  is  smooth,  and  (in  health)  is 
kept  cool  and  moist  by  a  clear  fluid  secreted 
by  the  naso-labial  glands  (Glandulse  nasolabi- 
ales);  they  form  a  subcutaneous  layer  about 
half  an  inch  (ca.  1.5  cm.)  thick.  It  shows  ir- 
regular lines,  mapping  out  small  polygonal  areas 
on  which  the  orifices  of  the  gland  ducts  are  visi- 
ble. There  is  also  a  narrow  bare  strip  along 
the  edge  of  the  lower  lip.  The  remainder  of 
the  integument  is  provided  with  ordinary  and 
tactile  hairs.  The  free  edge  and  the  adjacent 
part  of  the  lining  membrane  bear  short,  blunt, 
horny  papillae ;  toward  the  angles  the  papillae 
become  longer  and  sharp-pointed.  The  labial 
glands  occur  only  near  the  angles,  where  they 
form  compact  masses  (Fig.  385) . 

The  cheeks  are  more  capacious  than  in 
the   horse.     The  mucous   membrane  presents 


Fig.  379. — Lips  axd  Muzzle  of  Ox. 

1,  Muzzle;  2,  nostril;  3,  4,  wings  of  nos- 
tril; 5,  6,  commissures  of  nostril;  7,  8,  upper 
and  lower  lip. 


THE   MOUTH 


445 


large  pointed  conical  papillae  (Papillae  conicae),  which  are  directed  toward  the 
isthmus  faucium  and  are  covered  with  a  horny  epithelium.  The  largest  of  these 
have  a  length  of  about  half  an  inch  (ca.  1  to  1.5  cm.)  and  are  situated  around 
the  angle  of  the  mouth  and  parallel  with  the  cheek  teeth.  The  orifice  of  the  parotid 
duct  is  opposite  the  fifth  upper  cheek  tooth.  The  buccal  glands  (Fig.  385)  are  very 
well  developed,  and  are  arranged 
in  three  parts.  The  dorsal  part 
extends  from  the  angle  of  the 
mouth  to  the  maxillary  tuberos- 
ity; its  lobules  are  of  a  light  j'el- 
low  color.  The  ventral  part  con- 
sists of  a  compact  brownish  mass 
which  reaches  from  the  angle 
of  the  mouth  a  short  distance 
under  the  masseter  muscle.  The 
middle  part  consists  of  loosely 
arranged  yellow  lobules.  The 
small  ducts  of  these  glands  open 
between  the  papillae  of  the  cheek. 

A  linear  series  of  large  pa- 
pillae exists  on  the  floor  of  the 
mouth  on  each  side  of  the  frenum 
linguae.  Near  these  are  found 
the  openings  of  the  small  ducts 
of  the  sublingual  gland.  The 
caruncula  sublingualis,  the  pa- 
pilla on  which  the  sub-maxil- 
lary duct  opens,  is  wide,  hard, 
and  has  a  serrated  edge  (Fig. 
383). 

The  hard  palate  is  wide,  and 
is  usually  more  or  less  pigmented. 
The  body  of  the  premaxilla  is 
covered  with  a  thick  layer  of 
dense  connective  tissue,  which 
has  a  thick,  horny  epithelial  cov- 
ering— forming  the  so-called  den- 
tal plate  or  pad.  The  palatine 
ridges  extend  from  this  back- 
ward about  two-thirds  of  the 
length  of  the  hard  palate;  they 
number  15  to  19.  They  are 
nearly  straight,  and,  with  the 
exception  of  a  few  at  the  poste- 
rior end  of  the  series,  are  serrated  on  the  free  edge.  A  median  raphe  extends 
between  the  ridges.  The  posterior  third  of  the  palate  is  smooth.  Between 
the  dental  plate  and  the  first  ridge  is  the  triangular  papilla  incisiva;  on  either 
side  of  this  is  a  deep  furrow,  in  which  is  the  oral  opening  of  the  ductus  incisivus.^ 
The  duct  is  two  inches  or  more  (ca.  5  to  6  cm.)  in  length  and  opens  on  the  floor 
of  the  nasal  cavity;  it  also  communicates  by  a  slit-like  opening  with  the  vomero- 
nasal organ. 


Fig.  380. — Hard  Palate  of  Ox. 
1,  Dental  pad  or  plate;   2,  placed  on  papilla  incisiva  with  lines 
to  orifices  of  ductus  incisivi;   3,  ridge  of  palate;   4,  raph6  of  palate; 
5,  smooth  part  of  palate  showing  orifices  of  palatine  glands;    6, 
upper  lip;   7,  conical  papillae  of  cheek. 


This  is  also  known  as  the  naso-palatine  canal. 


446 


DIGESTIVE    SYSTEM    OF   THE    OX 


The  soft  palate  is  somewhat  shorter  than  that  of  the  horse,  but  is  long  enough 
to  close  the  isthmus  faucium.  The  posterior  pillars  do  not  extend  to  the  origin  of 
the  oesophagus.  The  palatinus  muscle  is  much  better  developed  than  in  the  horse. 
The  fibrous  aponeurosis  is  for  the  most  part  replaced  by  muscular  tissue. 


Cavity 

Dorsal 

Dorsal 

Septum 

of  dorsal 

Frontal 

turbinate 

meatus 

nasi 

turbinate 

vein 

Middle  meatus- 


Naso-lacrimal 
duct 


Infraorbital 

nerve 


Inferior  labial 
vessels 


Hypoglossal  nerve 


Masseter 


Dorsal 
buccal 
glands 
Facial 
artery 
Facial  vein 


Buccinator 


Ventral  buccal 
glands 


Sublingual  gland 


Digiistricus 


Mandibular  duct        Lingwd  nerve 

Fig.  381. — Cross-section  of  Head  of  Ox. 

The  section  passes  through  the  medial  canthi.     L.  a.,  Lingual  arteries.     The  arrow  indicates  the  communication  be- 
tween the  maxillary  and  palatine  sinuses. 


The  isthmus  faucium  is  wide  and  dilatable.  On  either  side,  behind  the  an- 
terior pillar  of  the  soft  palate,  there  is  a  deep  depression,  the  tonsillar  sinus  (Sinus 
tonsillaris) ;  lateral  to  this  is  the  compact,  bean-shaped  tonsil,  which  is  about  one 
to  one  and  a  half  inches  (ca.  3  to  4  cm.)  in  length.  The  tonsil  does  not  project  into 
the  isthmus  faucium,  but  outward  instead:  hence  it  does  not  occupy  the  tonsillar 
sinus,  and  is  not  visible  internally,  as  is  the  case  in  most  animals. 


THE   TONGUE 


447 


THE  TONGUE 
The  tongue  of  the  ox  is  often  variably  pigmented.  The  root  and  body  are 
wider  than  that  of  the  horse,  but  the  free  part  is  more  pointed.  The  posterior  part 
of  the  dorsum  forms  a  remarkable  elliptical  prominence,  which  is  sharply  defined 
in  front  by  a  transverse  depression.  In  front  of  this  prominence  there  are  large 
and  horny  conical  papillae  (Papilla  conica?),  with  sharp  points  directed  backward; 


Fig.  382. — Tongue  and  Fauces  of  Ox;  Dorsal  View. 
The  pharynx  and  soft  palate  are  cut  dorsally  and  reflected,     a.  Vallate  papillae;   6,  prominence  of  dorsum  with 
broad,  flattened  papillse;  c,  fungiform  papillae;  d,  conical  papillae  of  tip;  1,  glosso-epiglottic  space;  2,  tonsillar  sinus;  3, 
cut  surface  of  soft  palate;  4,  pharynx;  5,  posterior  pillar  of  soft  palate;   6,  epiglottis;   7,  aditus  laryngis. 


they  impart  to  the  tongue  its  rasp-like  roughness.  The  papillae  on  the  prominence 
are  large,  broad,  and  horny;  some  have  a  blunt,  conical  form,  others  are  rounded  or 
flattened  and  are  termed  lenticular  papillae  (Papillae  lenticulares) .  Behind  the 
prominence,  the  papillse  are  long  and  soft,  i.  e.,  not  horny.  The  fungiform  papillse 
are  numerous  and  distinct;  they  are  scattered  over  the  dorsum  and  edges  of  the 
free  part.  The  vallate  papillae  number  8  to  17  on  each  side;  they  are  smaller  than 
those  of  the  horse,  and  form  a  long,  narrow  group  on  either  side  of  the  posterior 
part  of  the  prominence  of  the  dorsum.  The  foliate  papillse  and  the  lingual  fibrous 
<Jord  are  absent.     There  are  lingual  follicles  in  the  posterior  part  of  the  root  and  on 


448  DIGESTIVE    SYSTEM    OF   THE    OX 


each  side  of  the  glosso-epiglottic  fold.  The  muscles  are  well  developed,  and  re- 
semble in  general  those  of  the  horse;  the  hyo-glossus  arises  by  additional  portions 
from  the  great  and  middle  cornua  of  the  hyoid  bone.  The  tongue  is  highly  pro- 
tractile and  is  the  chief  organ  of  prehesion. 

THE  TEETH  1 
The  formula  of  the  permanent  teeth  of  the  ox  is: 


(0     0     3      3\ 
I  -  C  -  P  -  IM  -  I  =  3 
4     0     3       3/ 


The  incisors  are  absent  from  the  upper  jaw.  There  are  eight  incisors  in  the 
lower  jaw,  arranged  in  a  somewhat  fan-like  manner.  They  are  simple  teeth, 
without  infundibulum.  The  croAvn  is  white,  short,  and  shovel-shaped.  The  root 
is  rounded,  and  is  embedded  in  the  jaw  in  such  a  manner  as  to  allow  a  small  amount 
of  movement.  There  is  a  distinct  neck.  In  addition  to  the  simple  numerical 
designation,  the  following  terms  are  commonly  applied  to  the  individual  teeth: 


Fig.  383. — Ixcisor  Teeth  of  Ox;  Lixgual  Aspect. 
C.  s.,  Caruncula  sublingualis. 

central,  first  intermediate,  second  intermediate,  and  corner  incisors.  It  is  probable 
that  the  latter  are  much  modified  canines.  The  incisors  of  the  adult  ox  do  not 
undergo  continued  eruption,  as  is  the  case  in  the  horse;  in  old  age,  however,  the 
gum  retracts  so  that  the  roots  are  partly  exposed  and  may  come  into  wear.-  The 
deciduous  incisors  differ  from  the  permanent  set  chiefly  in  being  much  smaller. 
The  crowais  are  narrower  and  diverge  more. 

The  canines  are  absent  (unless  the  fourth  incisors  be  considered  to  represent 
them  in  the  lower  jaw).^ 

The  cheek  teeth  (Figs.  134,  384)  resemble  those  of  the  horse  in  number  and 
general  arrangement.  They  are,  however,  smaller,  and  also  differ  in  the  fact  that 
they  progressively  increase  in  size  from  before  backward.  This  feature  is  so  marked 
that  the  first  tooth  is  quite  small,  and  the  space  occupied  by  the  first  three  (i.  e., 
the  premolars)  is  only  about  one-half  of  that  required  for  the  posterior  three  (i.  e., 
the  molars).  The  enamel  folds  stand  out  even  more  prominently  in  relief  on  the 
masticatory  surface  than  in  the  horse.     The  occurrence  of  wolf-teeth  is  rare. 

^  Other  figures  which  show  the  teeth  are  to  be  found  in  the  description  of  the  skull. 

2  The  reader  will  note  here  the  difference  between  the  structure  and  behavior  of  the  bracny- 
dont  (short-crowned)  incisors  of  the  ox  and  the  hypsodont  (long-crowned)  type  of  the  horse. 

'  According  to  A.  Hoffman,  the  anlagen  of  the  upper  canines  are  present  in  the  foetus,  but 
soon  disappear. 


THE   TEETH 


449 


29 


450  DIGESTIVE    SYSTEM    OF    THE    OX 

The  formula  of  the  deciduous  teeth  is : 

-  1=  20 


(0      0       3\ 
Di-Dc-Dp-  ) 
4        0        3/ 


TABLE  OF  AVERAGE  FERIOES  OF  EKUFTION  OF  THE  TEETH  IN  THE  OX 

Teeth  Eruption 

A.  Temporary: 

First  incisor  (Di  Ij 1 

Second  incisor  (Di  2) 3j    j^       3  ^^     j. 

Third  incisor  (Di  3) I 

Fourth  incisor  (Di  4) J 

First  cheek  tooth  (Dp  1) Birth  to  3  weeks. 

IS'^SootU^s?:' ::::::::::::::::::::;:::}  «-* ^ '- ^^y- 

B.  Permanent: 

First  incisor  (II)  13^  to  2  years. 

Second  incisor  (12) 2  to  23^  years. 

Third  incisor  (13) 3  years. 

Fourth  incisor  (14) 3J^  to  4  years. 

First  cheek  tooth  (PI) 2  to  2i/^  years. 

Second  cheek  tooth  (P  2j IJ/^  to  23^  years. 

Third  cheek  tooth(P  3) 2J^  to  3  years. 

Fourth  cheek  tooth  (Ml) 5  to  6  months. 

Fifth  cheek  tooth  (M  2) 1  to  13^  years. 

Sixth  cheek  tooth  (M  3) 2  to  23^  years. 

The  eruption  of  the  permanent  teeth  is  sul)ject  to  great  variation.  The  above 
figures  are  the  average  of  observations  of  improved  breeds  under  favorable  condi- 
tions. 


a.  Parotid  gland 
buccinator  nerve;    h,  buccinator  vei 
papillse  of  lip;   5,  buccinator  muscle 


Fig.  385. — Salivary  Glands  of  Ox. 
mandibular  gland;    c,  ventral,  d,  middle,  and   e,  dorsal  buccal   glands;  /,  labial   glands; 


;    1,  masseter  (cut);    2,  ramus  of  mandible; 
(After  EUenberger,  in  Leisering's  Atlas.) 


3,  zygomaticus  muscle;  4,  conical 


THE    SALIVARY    GLANDS THE    (ESOPHAGUS  451 


THE  SALIVARY  GLANDS 

The  parotid  gland  is  smaller  and  denser  in  texture  than  that  of  the  horse,  and 
is  light  red-brown  in  color;  its  average  weight  is  about  four  ounces  (ca.  115  g.). 
It  has  somewhat  the  form  of  a  very  narrow  long  triangle,  and  lies  chiefly  on  the 
posterior  part  of  the  masseter  muscle.  The  dorsal  part  is  wide  and  thick;  its 
anterior  border  partly  covers  a  large  parotid  lymph  gland.  The  small  ventral  end 
is  bent  forward  and  fits  into  the  angle  of  union  of  the  jugular  and  external  maxillary 
veins;  it  lies  on  the  mandibular  gland.  The  parotid  duct  leaves  the  ventral  part 
of  the  deep  face;  in  its  course  it  resembles  that  of  the  horse,  but  it  pierces  the  cheek 
opposite  the  fifth  upper  cheek  tooth. 

The  mandibular  gland  is  larger  than  the  parotid,  and  is  pale  yellow  in  color; 
its  average  weight  is  about  five  ounces  (ca.  140  g.).  It  is  covered  to  a  small  extent 
by  the  parotid.  Its  general  form  resembles  that  of  the  horse,  but  its  ventral  end 
is  large  and  rounded,  and  is  separated  by  a  small  interval  only  from  the  gland  of 
the  other  side  (Fig.  302).  This  part  can  be  distinctly  felt  in  the  living  animal,  and 
is  related  laterally  to  a  large  lymph  gland.  The  duct  leaves  the  middle  of  the 
concave  border  of  the  gland,  crosses  the  stylohyoideus  and  the  intermediate  ten- 
don of  the  digastricus,  and  is  then  disposed  as  in  the  horse. 

The  sublingual  gland  consists  of  two  parts.  The  dorsal  part  (Glandula  sub- 
lingualis parvicanalaris)  is  long,  thin,  and  pale  yellow  in  color.  It  extends  from  the 
anterior  pillar  of  the  soft  palate  about  to  the  symphysis  of  the  mandible.  It  has 
numerous  small  tortuous  ducts  (Ductus  sublinguales  minores),  which  open  between 
the  papillae  under  the  side  of  the  tongue.  The  ventral  part  (Glandula  sublingualis 
grandicanalaris)  is  shorter  and  thicker,  and  lies  ventral  to  the  anterior  portion  of 
the  dorsal  part;  it  is  salmon  pink  in  color.  It  has  a  single  duct  (Ductus  sublin- 
gualis major),  which  either  opens  alongside  of  or  joins  the  mandibular  duct. 


THE  PHARYNX  (Figs.  386,  476,  478) 
The  pharynx  is  short  and  wide.  The  vault  (Fornix  pharyngis)  is  divided  into 
two  culs-de-sac  by  a  median  fold  of  mucous  membrane  (Septum  nasi  membrana- 
ceum),  which  is  a  continuation  of  that  of  the  septum  nasi;  on  the  lateral  wall  of 
each  is  the  relatively  small  opening  of  the  Eustachian  tube,  which  is  covered  by  a 
simple  fold  of  mucous  membrane.  The  posterior  nares  are  small.  The  entrance 
to  the  oesophagus  is  large. 

On  the  dorsal  wall  of  the  pharynx  there  are  two  large  suprapharyngeal  lymph  glands,  which, 
when  enlarged,  cause  difficulty  in  swallowing  and  breathing  (Fig.  386). 


THE  (ESOPHAGUS 

This  is  much  shorter,  wider,  and  more  dilatable  than  that  of  the  horse.  Its 
average  diameter  (when  moderately  inflated)  is  about  two  inches  (ca.  5  cm.),  and 
its  length  in  an  animal  of  medium  size  is  about  three  to  three  and  a  half  feet  (ca. 
90  to  105  cm.).  The  wall  is  relatively  thin,  and  the  muscular  tissue  is  striped 
throughout.  The  latter  consists,  in  the  greater  part  of  the  tube,  of  two  strata  of 
spiral  fibers,  except  near  the  stomach,  where  they  are  longitudinal  and  circular. 
Fibers  are  continued  into  the  wall  of  the  stomach  for  some  distance.  The  mucous 
membrane  forms  a  prominence  at  the  ventral  side  of  the  pharyngeal  end  of  the 
tube  which  contains  glands;  elsewhere  it  is  non-glandular.  There  is  no  terminal 
dilatation,  and  no  part  in  the  abdominal  cavity. 

A  very  large  mediastinal  lymph  gland  lies  above  the  posterior  part  of  the  oesophagus  and 
may,  if  enlarged,  obstruct  it  (Fig.  389). 


452 


DIGESTIVE    SYSTEM    OF   THE    OX 


THE  ABDOMINAL  CAVITY 
The  abdominal  cavity  of  the  ox  is  very  capacious,  both  absolutely  an  1  rela- 
tively, as  compared  with  that  of  the  horse.  This  is  due  to  several  factors.  The 
lumbar  part  of  the  spine  is  about  one-fourth  longer  than  that  of  the  horse.  The 
transverse  diameter  between  the  last  ribs  is  greater.  The  costal  attachment  of  the 
diaphragm  is  almost  vertical  in  direction  from  the  ventral  part  of  the  ninth  rib  to 


Frontal  sinus 


Cavity  of  great  ethmoturbinate 


Cavity  of  dorsal  turbinate 
Cavities  of  ventral  turbinate 


Vesti- 
bule of 
larynx 
Thyroid 
cartilage 


Mylo-hyoideuG 
muscle 


Fig.  386. — Sagittal  Section  of  Head  of  Cow,  Cut  a  Little  to  the  Right  op  the  Median  Plane. 

1,  Cerebral  hemisphere;  2,  corpus  striatum;  3,  hippocampus;  4<  olfactory  bulb;  5,  corpora  quadrigemina;  6, 
optic  nerve;  7,  pons;  <S,  medulla  oblongata;  9,  spinal  cord;  ;0,  pituitary  body;  i 7,  sphenoidal  sinus;  i^,  lateral  n^ass 
of  ethmoid;  13  ventral  straight  muscles;  14,  suprapharyngeal  lymph  gland;  1-5,  longus  colli;  16,  soft  pa'ate;  IT, 
vallate  papillae;  18,  tonsillar  sinus;  19,  conical  papillae  of  cheek;  £0,  hyo-epiglotticus  muscle;  31,  epiglottis;  S£,  h/o- 
glossus  muscle;    CI,  C2,  atlas,  axis.     Subject  was  hardened  with  mouth  open. 


the  dorsal  end  of  the  thirteenth.  Thus  the  abdomen  is  increased  at  the  expense 
of  the  thorax,  and  the  last  three  or  four  ribs  enter  more  largely  into  the  formation 
of  the  abdominal  wall  than  in  the  horse.  The  flank  is  also  much  more  extensive. 
The  ilia,  on  the  other  hand,  do  not  extend  forward  beyond  a  transverse  plane 
through  the  middle  of  the  last  lumbar  vertebra.  The  epigastric  and  mesogastric 
regions  would  be  separated  by  a  plane  through  the  ventral  end  of  the  tenth  pair  of 


THE  PELVIC  CAVITY — THE  STOMACH  453 

ribs,  or  through  the  last  thoracic  vertebra.  The  chief  differential  features  in  the 
arrangement  of  the  peritoneum  will  be  described  with  the  viscera.  The  sub- 
peritoneal tissue  is  more  abundant  than  in  the  horse,  and  in  general  contains  a 
much  larger  amount  of  fat. 

THE  PELVIC  CAVITY 

The  pelvic  cavity  is  relatively  long  and  narrow.  The  inlet  is  more  oblique 
than  that  of  the  horse;  it  is  elliptical  in  outline,  and  the  transverse  diameter  is 
smaller  than  that  of  the  horse.  The  pubic  part  of  the  floor  is  about  horizontal, 
but  the  ischiatic  part  slopes  dorsally  to  a  marked  degree;  this  part  is  also  deeply 
concave  transversely.  The  roof  is  concave  in  both  directions.  The  peritoneum 
extends  backward  as  far  as  the  first  coccygeal  vertebra,  so  that  the  retroperitoneal 
part  of  the  cavity  is  short. 

THE  STOMACH 

General  Arrangement. — The  stomach  of  the  ox  is  very  large,  and  occupies 
nearly  three-fourths  of  the  abdominal  cavity.  It  fills  the  left  half  of  the  cavity 
(with  the  exception  of  the  small  space  occupied  by  the  spleen)  and  extends  con- 
siderably over  the  median  plane  into  the  right  half. 

It  is  compound,  and  consists  of  four  divisions,  viz.,  rumen,  reticulum,  omasum, 
and  abomasum.'^  The  division  is  clearly  indicated  externally  by  furrows  or  con- 
strictions. The  first  three  divisions  are  often  regarded  as  proventriculi  or  oeso- 
phageal sacculations,  the  fourth  being  the  stomach  proper  (in  the  narrower  sense 
of  the  term).  The  oesophagus  opens  into  the  stomach  on  a  sort  of  dome,  the 
atrium  ventricuU,  and  is  continued  through  the  reticulum  by  the  oesophageal 
groove.  From  the  ventral  end  of  the  latter  a  groove  traverses  the  ventral  wall  of 
the  omasum,  thus  giving  a  direct  path  from  the  reticulum  to  the  abomasum  for 
finely  divided  food  or  fluid.     The  abomasum  joins  the  small  intestine. 

Capacity. — The  capacity  of  the  stomach  varies  greatly,  depending  on  the  age 
and  size  of  the  animal.  In  cattle  of  medium  size  it  holds  30  to  40  gallons,  in  large 
animals  40  to  60,  in  small,  25  to  35.  The  relative  sizes  of  the  four  parts  vary  with 
age,  in  correlation  with  the  nature  of  the  food.  In  the  new-born  calf  the  rumen  and 
reticulum  together  are  about  half  as  large  as  the  abomasum;  in  ten  or  twelve  weeks 
this  ratio  is  reversed.  During  this  period  the  omasum  appears  to  be  contracted 
and  functionless.  At  four  months  the  rumen  and  reticulum  together  are  about 
four  times  as  large  as  the  omasum  and  abomasum  together.  At  about  one  and  one- 
half  years  the  omasum  equals  or  approaches  closely  the  abomasum  in  capacity. 
The  four  divisions  have  now  reached  their  definitive  relative  capacities,  the  rumen 
constituting  about  80  per  cent.,  the  reticulum  5  per  cent.,  the  omasum  7  or  8  per 
cent.,  and  the  abomasum  8  or  7  per  cent,  of  the  total  amount. 

Exterior  and  Relations 
The  rumen  occupies  almost  all  of  the  left  half  of  the  abdominal  cavity,  and 
extends  considerably  over  the  median  plane  ventrally  and  in  its  middle.  It  is 
somewhat  compressed  from  side  to  side  and  may  be  described  as  having  two  sur- 
faces, two  curvatures  or  borders,  and  two  extremities.  The  parietal  (or  left) 
surface  (Facies  parietalis  )  is  convex  and  is  related  to  the  diaphragm,  left  wall  of 
the  abdomen,  and  spleen.  It  extends  from  the  ventral  part  of  the  seventh  inter- 
costal space  almost  to  the  pelvis.  The  visceral  (or  right)  surface  (Facies  visceralis) 
is  somewhat  irregular,  and  is  related  chiefly  to  the  omasum  and  abomasum,  the 

1  In  popular  language  these  are  regarded  as  so  many  stomachs,  and  are  often  designated 
numerically.  Other  names  are  in  common  use,  e.  g.,  paunch,  honeycomb,  manifold  or  manyplies, 
and  rennet  or  true  stomach. 


454 


DIGESTIVE    SYSTEM    OF   THE    OX 


intestine,  the  liver,  pancreas,  kidneys,  the  uterus  in  the  female,  and  the  posterior 
aorta  and  vena  cava.  The  dorsal  curvature  (Curvatura  dorsalis)  is  convex,  fol- 
lowing the  curve  formed  by  the  diaphragm  and  sublumbar  muscles.  It  is  firmly 
attached  to  the  left  portion  of  the  crura  of  the  diaphragm  and  the  sul)lumbar 
muscles  by  peritoneum  and  connective  tissue.  The  ventral  curvature  (Curvatura 
ventralis)  is  also  convex  and  lies  on  the  floor  of  the  abdomen.  The  surfaces  are 
marked  by  the  right  and  left  longitudinal  grooves  (Sulcus  longitudinalis  dexter, 
sinister) ,  which  indicate  externally  the  division  of  the  rumen  into  dorsal  and  ventral 
sacs.^  The  reticular  (or  anterior)  extremity  (Extremitas  reticularis)  is  divided 
ventrally  by  a  transverse  anterior  groove  (Sulcus  ruminis  cranialis)  into  two  sacs. 
The  dorsal  sac  is  the  longer  of  the  two,  and  curves  ventrally  over  the  round,  bhnd 


Fig.  387. — Stomach  and  Spleen  of  Ox;  Left  View. 
1,  Left  longitudinal  groove  of  rumen;   2,  rumino-reticular  groove  (not  so  distinct  dorsally  as  shown  here);  3,  an- 
terior groove  of  rumen;   4,  posterior  groove  of  rumen;   5,  6,  coronary  grooves;  7,  8,  anterior,  9,   10,  posterior,  blind 
sacs  of  rumen. 


end  of  the  ventral  sac.  The  former  is  continuous  with  the  reticulum,  the  external 
line  of  demarcation  being  the  rumino-reticular  groove  (Sulcus  rumino-reticularis). 
The  groove  is  deep  ventrally  and  is  distinct  on  part  of  the  lateral  surface,  but  dorsally 
no  natural  separation  exists,  the  rumen  and  reticulum  together  forming  a  dome- 
like vestibule  (Atrium  ventriculi)  on  which  the  oesophagus  terminates.  The  pelvic 
(or  posterior)  extremity  (Extremitas  pelvina),  extends  nearly  to  the  pubis;  it  is 
related  to  the  intestine  and  bladder,  and  to  the  uterus  in  the  cow.  It  is  divided 
into  dorsal  and  ventral  blind  sacs  (Saccus  csecus  caudalis  dorsalis,  ventralis)  by  a 
deep  transverse  posterior  groove  (Sulcus  ruminis  caudalis),  which  connects  the 
longitudinal  grooves.     The  blind  sacs  are  marked  off  from  the  remainder  of  the 

1  It  has  been  customary  to  term  the  sacs  left  and  right  respectively,  but  these  do  not  repre- 
sent the  relations  as  they  exist  in  situ  and  as  they  are  presented  on  frozen  sections.  When  the 
stomach  is  removed  in  the  soft  state,  it  loses  its  shape  and  the  dorsal  and  ventral  sacs  of  the  rumen 
become  left  and  right. 


EXTERIOR   AND    RELATIONS 


455 


rumen  by  the  dorsal  and  ventral  coronary  grooves  (Sulcus  coronarius  dorsalis, 

ventralis) . 

The  left  longitudinal  groove  (Sulcus  longitudinalis  sinister)  begins  at  the  anterior  transverse 
groove,  passes  somewhat  dorsally  and  backward  and  divides  into  two  grooves.  The  ventral 
one  is  the  chief  groove,  and  passes  backward  to  terminate  in  the  angle  of  union  of  the  posterior 
blind  sacs.  The  dorsal  (accessory)  groove  curves  dorsally  and  then  backward  to  terminate  in 
the  dorsal  coronary  sulcus.  On  the  right  surface  there  are  two  longitudinal  grooves.  The  dorsal 
one  is  the  chief  sulcus  (Sulcus  longitudinalis  dexter).  It  extends  in  a  curved  direction  (the  con- 
vexity being  dorsal),  and  is  continuous  with  the  left  longitudinal  groove  by  means  of  the  grooves 
between  the  dorsal  and  ventral  blind  sacs  at  each  end.  The  ventral  groove  (Sulcus  accessorius) 
curves  somewhat  ventrally  and  backward  and  joins  the  chief  sulcus  between  the  posterior  blind 
sacs. 

The  reticulum  is  the  most  anterior  and  the  smallest  of  the  four  divisions;  it 
is  opposite  to  the  ribs  from  the  sixth  to  the  seventh  or  eighth.     It  Hes  against  the 


Fig.  388. — Stomach  of  Ox;  Right  View. 

Oes.,  CEsophagus;    1,  right  longitudinal  groove  of  rumen;  2,  posterior  groove  of  rumen;   .3,  4,  coronary  grooves;   5,  6, 

posterior  blind  sacs  of  rumen;  7,  pylorus. 


diaphragm  and  liver  in  such  a  position  that  the  median  plane  divides  it  into  two 
nearly  equal  portions.  It  is  somewhat  piriform,  but  compressed  from  before 
backward.  The  parietal  or  diaphragmatic  surface  (Facies  diaphragmatica)  faces 
forward;  it  is  convex  and  lies  against  the  diaphragm  and  liver. ^  The  visceral  or 
ruminal  surface  (Facies  ruminalis)  faces  backward;  it  is  flattened  by  the  press- 
ure of  the  other  three  compartments;  it  ends  dorsally  by  joining  the  wall  of 
the  rumen,  the  concave  line  of  junction  corresponding  to  a  ridge  in  the  interior 
of  the  stomach  which  forms  the  lower  margin  of  the  large  rumino-reticular  orifice. 
The  lesser  curvature  faces  to  the  right  and  dorsally,  and  is  connected  with  the 

1  It  is  important  to  notice  that  the  reticulimi  is  separated  from  the  pericardium  by  an  inter- 
val of  only  an  inch  or  less  (ca.  2  cm.j,  since  foreign  bodies  which  are  often  swallowed  by  cattle 
lodge  in  the  reticulum,  and  not  rarely  (if  sharp)  perforate  the  reticulum  and  diaphragm.  When 
the  reticulum  is  full,  its  visceral  surface  is  opposite  to  the  eighth  rib. 


456  DIGESTIVE    SYSTEM    OF    THE    OX 

omasum.  The  greater  curvature  faces  to  the  left  and  ventrally;  it  lies  against  the 
diaphragm,  opposite  the  sixth  and  seventh  ribs.  The  ventral  extremity  forms  a 
rounded  cul-de-sac,  which  is  in  contact  with  the  sternal  part  of  the  diaphragm,  the 
liver,  omasum,  and  abomasum;   it  may  be  termed  the  fimdus  reticuli. 

The  omasum  is  ellipsoidal  in  form  and  somewhat  compressed  laterally.  It  is 
very  clearly  marked  off  from  the  other  divisions.  It  is  situated  almost  entirely 
to  the  right  of  the  median  plane,  opposite  the  seventh  to  the  eleventh  ribs.  The 
parietal  (right)  surface  (Facies  dexter)  lies  against  the  diaphragm,  liver,  and  lateral 
wall  of  the  abdomen.  The  contact  with  the  latter  extends  over  a  small  area  only 
(ventral  part  of  eighth,  ninth,  and  tenth  ribs  usually).  The  visceral  (left)  surface 
(Facies  sinistra)  is  in  contact  with  the  rumen  and  reticulum.  The  greater  curvature 
is  directed  dorsally  and  somewhat  backward;  it  is  convex,  and  is  related  to  the 
diaphragm,  hver,  and  intestine.  The  ventral  (lesser)  curvature  is  concave,  and 
faces  ventrally  and  somewhat  forward;  it  is  in  contact  with  the  abomasum  chiefly, 
the  junction  with  the  latter  appearing  as  a  constriction  near  the  middle  of  the 
curvature;  at  its  anterior  part  there  is  a  neck  (Collum  omasi)  which  is  the  con- 
nection with  the  reticulum.^ 

The  abomasum  is  an  elongated,  piriform  sac,  which  lies  for  the  most  part  on 
the  abdominal  floor,  to  the  right  of  the  reticulum  and  the  ventral  sac  of  the 
rumen.  Its  narrow  posterior  part  is  strongly  curved,  the  concavity  being  dorsal. 
The  parietal  (right)  surface  lies  against  the  abdominal  wall  from  a  point  opposite  to 
the  seventh  or  eighth  rib  as  far  back  as  the  eleventh  or  twelfth  costal  cartilage.  The 
visceral  (left)  surface  is  related  chiefly  to  the  ventral  sac  of  the  rumen.  The  lesser 
curvature  is  dorsal,  and  is  in  contact  with  the  omasum;  the  junction  of  the  two  sacs 
is  indicated  by  a  constriction  about  four  or  five  inches  (ca.  10  to  12  cm.)  from  the 
anterior  extremity  of  the  abomasum.  The  greater  curvature  is  ventral,  and  rests 
on  the  abdominal  wall  from  the  xiphoid  cartilage  to  the  ventral  part  of  the  last 
(right)  intercostal  space;  its  direction  is  approximately  parallel  to  the  right  costal 
arch.2  The  fundus  or  anterior  extremity  forms  a  rounded  blind  sac  which  lies 
against  the  reticulum.  The  pyloric  or  posterior  extremity  is  much  smaller  and  bends 
upward  and  forward  to  join  the  duodenum.  The  intermediate  part  is  sometimes 
termed  the  body.  About  six  to  eight  inches  (ca.  15  to  20  cm.)  from  the  pylorus  there 
is  a  constriction  which  marks  off  the  pyloric  part  from  the  body  and  fundus. 

The  rumen  is  attached  by  peritoneum  and  connective  tissue  to  the  crura  of 
the  diaphragm  and  left  psoas  muscles,  from  the  hiatus  oesophagus  backward  to 
the  fourth  or  fifth  lumbar  vertebra. 

A  small  area  of  the  anterior  part  of  the  right  face  of  the  rumen  is  adherent  to 
the  adjacent  surface  of  the  abomasum.  The  greater  part  of  the  ventral  curvature 
of  the  omasum  is  attached  by  connective  tissue  to  the  dorsal  face  of  the  abomasum.^ 

The  lesser  omentum  attaches  the  right  face  of  the  omasum  and  the  pyloric 
part  of  the  abomasum  to  the  visceral  surface  of  the  liver. 

Interior 
The  cavity  of  the  rumen  is  partially  divided  into  dorsal  and  ventral  sacs  by 
the  pillars  (Pilge  ruminis) ;    these  are  folds  of  the  wall,  strengthened  by  additional 
muscular  fibers,  and  correspond  with  the  grooves  on  the  outside.     The  two  ex- 

1  The  relative  size  of  the  omasum  is  subject  to  considerable  variation.  It  may  extend  back 
to  a  point  opposite  the  ventral  fourth  of  the  twelfth  rib.  The  ventral  curvature  is  usually  opposite 
to  the  ninth,  tenth,  and  eleventh  costal  cartilages,  but  in  some  subjects  it  faces  chiefly  forward  and 
is  opposite  to  the  ventral  third  of  the  eighth  or  ninth  rib. 

2  The  greater  curvature  may  be  in  contact  in  part  with  the  costal  arch,  but  is  chiefly  medial 
and  ventral  to  it.  It  usually  bends  dorsally  near  the  last  costal  cartilage  and  runs  upward  and 
forward  to  the  eleventh  intercostal  space. 

3  Adhesion  of  the  reticulum  to  the  diaphragm  is  frequently  present,  but  is  pathological;  the 
same  is  true  in  regard  to  adhesion  to  the  liver. 


INTERIOR  457 

tensive  chief  pillars  project  like  shelves  into  the  anterior  and  posterior  ends  of  the 
cavity,  forming  the  blind  sacs  at  either  extremity.  The  anterior  pillar  (Pila  cranialis) 
projects  obliquely  backward  and  upward  from  the  ventral  wall,  and  has  a  thick, 
concave  free  edge  which  is  opposite  to  the  tenth  and  eleventh  ribs.  Its  width  from 
the  middle  of  the  free  edge  to  its  attached  border  is  about  eight  to  ten  inches  (ca.  20 
to  25  cm.).  It  is  continued  on  either  side  by  the  relatively  narrow  longitudinal 
pillars  (Pila  dexter,  sinister),  which  connect  it  with  the  posterior  pillar.  The 
posterior  pillar  (Pila  caudalis)  is  more  nearly  horizontal  than  the  anterior  one,  and 
separates  the  large  dorsal  and  ventral  posterior  blind  sacs.  Its  concave  free  border 
is  about  a  hand's  breadth  in  front  of  a  transverse  plane  through  the  tuber  coxge. 
From  it  are  detached  three  accessory  pillars  on  either  side ;  of  these,  two  pass  around 
the  blind  sacs  to  meet  the  corresponding  pillars  of  the  opposite  side.     They  thus 


Fig.  389. — Thoracic  and  Anterior  Abdominal  Viscera  of  Ox;  Deep  Dissection. 
Most  of  the  rumen  has  been  removed  and  the  left  wall  of  the  reticulum  cut  away.     A.,  Left  pulmonary  artery; 
B.,  left  bronchus;    F.  V.  V.,  pulmonary  veins;   6.  b.,  bronchial  lymph  glands;   L.  g.,  posterior  mediastinal  lymph  gland; 
D.,  termination  of  duodenum;    F,  rumino-reticular  fold. 


mark  off  the  posterior  blind  sacs  from  the  general  cavity,  and  are  termed  the 
coronary  pillars  (Pila  coronaria  dorsalis,  ventralis).  It  will  be  noticed  that  the 
ventral  coronary  pillar  is  complete,  while  the  dorsal  one  is  not.  The  other  accessory 
pillars  join  the  right  and  left  longitudinal  pillars.  The  right  longitudinal  pillar  is 
in  part  double ;  its  ventral  division  fades  out  about  the  middle  of  the  surface,  vv^hile 
the  dorsal  one  joins  the  posterior  pillar.  The  distance  between  the  middles  of  the 
anterior  and  posterior  pillars  is  only  about  sixteen  to  eighteen  inches  (ca.  40  to  45 
cm.)  in  a  cow  of  medium  size.  In  this  space  the  dorsal  and  ventral  sacs  communi- 
cate freely. 

The  anterior  end  of  the  dorsal  sac  of  the  rumen  is  separated  ventrally  from  the 
reticulum  by  an  almost  vertical  fold  formed  by  the  apposition  of  the  walls  of  the 
two  compartments.  This  rumino-reticular  fold  (Pila  rumino-reticularis)  is  oppo- 
site to  the  seventh  or  eighth  rib.^     Its  free  dorsal  edge  is  concave  and  forms  the 

1  The  position  of  this  fold  naturally  varies  with  the  degree  of  fulness  of  the  reticulum.  When 
the  latter  is  full,  it  may  extend  back  in  part  to  the  eighth  intercostal  space. 


458 


DIGESTIVE    SYSTEM    OF   THE    OX 


ventral  and  lateral  margin  of  the  large,  oval  rumino-reticular  orifice  (Ostium 
rumino-reticulare).  The  medial  margin  of  the  fold,  if  continued,  would  end  about 
at  the  cardia,  but  there  is  in  this  region  no  demarcation  between  rumen  and  reticu- 
lum;  hence  it  is  termed  the  atrium  ventriculi. 

The  lateral  border  of  the  rumino-reticular  fold  ends  above  the  level  of  and  behind  the  plane 
of  the  cardia,  the  medial  one  just  behind  the  oesophageal  groove  and  about  four  to  five  inches 
lower  down.  Undoubtedly  food  or  water  swallowed  with  even  a  small  degree  of  force  passes  first 
into  the  rumen.  Foreign  bodies  (which  are  commonly  swallowed  by  cattle)  are,  however,  found 
in  the  reticulum. 

The  cardia  is  opposite  the  seventh  intercostal  space  or  eighth  rib,  a  little  to  the 
left  of  the  median  plane,  and  about  a  handbreadth  (ca.  10-12  cm.)  ventral  to  the 
vertebral  column;    it  is  not  funnel-shaped. 

The  mucous  membrane  of  the  rumen  is  brown  in  color,  except  on  the  margins 


Fig.  390. — Reticulum  or  Ox,  rsoM  Photograph. 
The  specimen  was  cut  along  the  greater  curvature  and  laid  open  by  reflecting  the  anterior  wall.      C  is  the  cardia. 
The  arrow  points  to   the  reticulo-omasal  orifice.     The  spiral  twist  of  the  oesophageal  groove  was  of  necessity  partly 
undone  by  reflecting  the  wall ;   its  lips  are  drawn  apart,  showing  some  of  the  peculiar  birdclaw-like  papillae  in  the 
ventral  part. 


of  the  pillars,  where  it  is  pale.  It  is  for  the  most  part  thickly  studded  with  large 
papillse,  many  of  which  are  nearly  half  an  inch  (ca.  1  cm.)  long.  The  edges  of  the 
chief  pillars  and  a  large  part  of  the  wall  of  the  middle  of  the  dorsal  sac  are,  however, 
not  papillated.  The  papillary  arrangement  is  most  developed  in  the  blind  sacs. 
The  papillse  vary  much  in  size  and  form;  the  largest  are  foliate,  many  are  narrow 
or  filiform,  and  others  are  conical  or  club-shaped.  The  mucous  membrane  on  the 
medial  wall  of  the  atrium  is  finely  wrinkled  and  non-papillated,  while  dorsally  and 
laterally  it  is  papillated.  The  papillary  arrangement  also  extends  over  the  edge 
of  the  rumino-reticular  fold  an  inch  or  two  (ca.  2  to  5  cm.). 

The  oesophageal  groove  (Sulcus  oesophagus)  begins  at  the  cardia  and  passes 


INTERIOR  459 

ventrally  on  the  right  wall  of  the  atrium  and  reticulum  to  end  at  the  reticulo- 
omasal  orifice.^  It  is  about  seven  or  eight  inches  (ca.  18-20  cm.)  in  length.  Its 
axial  direction  is  chiefly  dorso-ventral,  but  it  inclines  forward  to  a  variable  extent 
and  somewhat  medially  in  its  ventral  part;  the  ventral  end,  which  is  at  the  reticulo- 
omasal  orifice,  is  about  an  inch  (ca.  2.5  cm.)  in  front  of  the  plane  of  the  cardia  and 
to  the  right  of  the  median  plane.  The  groove  is  twisted  in  a  spiral  fashion,  so  that 
its  thickened  edges  or  lips  project  first  backward,  then  to  the  left,  and  finally  for- 
ward. The  twist  involves  chiefly  the  left  lip,  and  the  relative  position  of  the  lips 
is  reversed  at  the  ventral  end.  The  mucous  membrane  on  the  lips  of  the  oesoph- 
ageal groove  is  brown  and  wrinkled,  like  that  of  the  atrium;   in  the  bottom  of  the 


A  nterior 


Fig.  391. — Omasttm  op  Ox,  Sagittal  Section;  Right  View. 
1,  2,3,4,  Laminae  of  various    orders;   5,  muscular  pillar;   6,  neck  connecting  with    reticulum;    7,  connection    with 


groove  it  is  pale,  like  that  of  the  oesophagus,  marked  by  longitudinal  folds,  and  pre- 
sents pointed,  horny  papillae  on  its  ventral  part. 

In  the  reticulum  the  mucous  membrane  is  raised  into  folds  about  half  an  inch 
high,  which  enclose  four-,  five-,  or  six-sided  spaces  or  cells  (Cellulse  reticuli);  this 
peculiar  arrangement  suggested  the  scientific  name  and  also  the  popular  term 
"honey-comb."  These  cells  are  subdivided  by  smaller  folds,  and  the  bottoms  are 
studded  with  pointed,  horny  papillae.  The  cells  grow  smaller  and  gradually  dis- 
appear near  the  oesophageal  groove  and  the  edge  of  the  rumino-reticular  fold;  an 
inch  or  two  from  the  latter  the  mucous  membrane  has  the  papillary  arrangement 
of  the  rumen.  At  the  reticulo-omasal  orifice  there  are  peculiar  horny  papillae, 
which  are  curved  and  resemble  the  claws  of  a  small  bird;  hence  they  are  termed 
ungulif orm  (Papillae  ungulif ormes) .  The  reticulo-omasal  orifice  (Ostium  reticulo- 
1  It  might  better  be  termed  the  sulcus  reticuli. 


460 


DIGESTIVE    SYSTEM    OF    THE    OX 


omasicum)  is  situated  in  the  medial  wall  of  the  reticulum,  about  five  or  six  inches 
above  the  bottom  of  the  latter.  It  is  rounded,  and  is  limited  below  and  laterally 
by  the  junction  of  the  lips  of  the  oesophageal  groove. 

The  cavity  of  the  omasum  is  occupied  to  a  considerable  extent  by  about  a 
hundred  longitudinal  folds,  the  laminae  omasi,  which  spring  from  the  dorsal  wall 
and  the  sides.  The  largest  of  these — a  dozen  or  more  in  number — have  a  convex 
attached  edge,  and  a  ventral,  concave  free  edge,  which  reaches  to  within  a  short 
distance  of  the  ventral  wall  of  the  sac.  If  these  are  drawn  apart  or  a  cross- 
section  is  made  (Fig.  392),  it  will  be  seen  that  there  is  a  second  order  of  shorter 
laminae,  and  a  third  and  fourth  still  shorter;  finally  there  is  a  series  of  very  low 
folds  or  lines.  The  food  is  pressed  into  thin  layers  in  the  narrow  spaces  between  the 
laminae  (Recessus  interlaminares) ,  and  reduced  to  a  fine  state  of  division  by  being 
ground  do^vn  by  the  numerous  rounded,  horny  papillae  which  stud  the  surfaces  of 
the  folds.     The  ventral  wall  of  the  omasum  forms  a  groove,  the  sulcus  omasi, 

which  connects  the  reticulo- 
omasal  opening  with  the 
omaso-abomasal  opening;  it  is 
about  three  inches  (ca.  7-8 
cm.)  long,  and  is  directed  back- 
ward and  downward.  It  is 
free  from  laminae,  but  presents 
usually  slight  folds  and  small 
papillae;  it  may  function  as  a 
direct  path  from  the  reticulum 
to  the  abomasum  for  fluid  and 
finely  divided  food.  In  the 
neck  of  the  omasum  there  are 
thick  folds,  and  a  number  of 
the  peculiar  papillae  already 
mentioned  as  occurring  in  the 
lower  part  of  the  oesophageal 
groove.  The  omaso-abomasal 
orifice  (Ostium  omaso-abo- 
masicum)  is  oval,  and  is  about 
four  inches  (ca.  10  cm.)  long. 
It  is  bounded  in  front  by  a 
thick  muscular  pillar,  the  fibers 
of  which  spread  out  above  in 
the  sides  of  the  omasum.  The 
mucous  membrane  forms  an 
extensive  fold  on  each  side  of  the  opening;  these  folds  may  act  as  valves  (Valvulae 
terminales),  which  probably  prevent  regurgitation  of  the  contents  of  the  abomasum. 
The  cavity  of  the  abomasum  is  chvided  by  a  constriction  into  two  areas.  The 
first  of  these  (fundus  gland  region)  is  lined  with  a  soft  glandular  mucous  membrane, 
which  forms  a  dozen  or  more  extensive  spiral  folds  (Plicae  spirales).  The  second 
part  (pyloric  region)  is  much  narrower  and  resembles  in  appearance  the  corre- 
sponding region  of  the  horse's  stomach.  A  small  cardiac  gland  zone  surrounds  the 
omaso-abomasal  orifice.     The  pyloric  orifice  is  small  and  round. 

Structure. — The  serous  coat  invests  all  of  the  free  surface  of  the  stomach. 
The  surface  of  the  rumen  which  is  attached  to  the  dorsal  abdominal  wall  is,  of 
course,  uncovered,  as  well  as  the  adjacent  area  to  which  the  spleen  is  attached. 
The  furrows  are  bridged  over  by  the  peritoneum  and  superficial  muscle-fibers, 
and  contain  fat  and  (in  most  cases)  branches  of  the  gastric  arteries. 

The  lesser  omentum  passes  from  the  visceral  surface  of  the  liver  to  the  right 


■^^^ 


Fig.  392. — Cross-section  of  Omasum  of  Ox. 
1-5,   Lamina  of  various  orders;    0,   neck  connecting  with 


INTERIOR  461 

(parietal)  face  of  the  omasum  and  the  pyloric  part  of  the  abomasum  and  the  first 
part  of  the  duodenum.  What  might  be  regarded  as  a  connection  between  the 
omenta  is  a  fold  between  the  ventral  curvature  of  the  omasum  and  the  dorsal 
curvature  of  the  abomasum. 

The  greater  omentum  conceals  the  greater  part  of  the  intestine  on  the  right 
side,  with  the  exception  of  the  duodenum,  and  covers  the  ventral  sac  of  the  rumen 
almost  entirely.  It  is  not  lace-like,  as  in  the  horse,  and  contains  a  large  amount 
of  fat  in  animals  in  good  condition.  It  may  be  described  as  consisting  of  two 
parts,  each  of  which  is  composed  of  two  layers  of  peritoneum;  the  two  serous  layers 
enclose  a  variable  amount  of  fat.  The  superficial  part  extends  from  the  left 
groove  of  the  rumen  ventrally  around  the  ventral  sac  and  ascends  on  the  right 
side,  covering  the  deep  part.  It  ends  along  the  retrograde  part  of  the  duodenum 
and  the  greater  curvature  of  the  abomasum.  The  deep  part  is  attached  along  the 
visceral  (right)  surface  of  the  rumen  ventral  to  the  right  groove,  and  curves  around 
the  intestinal  mass  to  the  right  side,  where  it  is  covered  by  the  superficial  part.     It 


Fig.  393. — I>fTERioR  of  Abomasum  of  Ox. 
F,  Fundus  gland  region  with  large  spiral  folds;   P,  pyloric  region;   D,  duodenum;    1,  pylorus;   2,   torus  pyloricus. 


ends  chiefly  by  blending  with  the  medial  layer  of  the  mesoduodenum,  but  anter- 
iorly is  attached  on  the  first  bend  of  the  colon  and  the  visceral  surface  of  the  liver 
along  the  ventral  border  of  the  pancreas.  The  two  parts  are  continuous  at  the 
posterior  groove  of  the  rumen.  They  also  join  at  the  iliac  flexure  of  the  duodenum 
and  at  the  origin  of  the  colon.  The  epiploic  foramen  is  almost  sagittal  in  direc- 
tion. 

The  muscular  coat  of  the  rumen  consists  of  two  layers.  The  fibers  of  the 
external  layer  are  in  general  longitudinal;  those  of  the  thicker  internal  layer  are 
largely  circular  in  direction.  The  latter  forms  the  bulk  of  the  chief  pillars,  where 
it  is  about  one-half  to  one  inch  (ca.  1  to  2  cm.)  thick.  Scattered  bundles  of  striped 
muscle-fibers  radiate  from  the  cardia  in  the  wall  of  the  atrium  and  extend  also  along 
the  oesophageal  groove. 

The  arrangement  is  in  fact  by  no  means  so  simple  as  might  be  inferred  from  the  above  brief 
statement,  and  much  variation  from  the  typical  disposition  is  present.  Along  the  furrows  the 
fibers  of  the  external  layer  are  disposed  more  or  less  obUquely  or  even  vertically  in  part;  a  super- 
ficial part  of  the  layer  bridges  over  the  furrows  (with  the  fat  and  vessels  contained  therein),  while 
the  deeper  fibers  extend  into  the  pillars.  The  fibers  of  the  inner  layer  on  approaching  the  furrows 
change  to  an  oblique  or  even  horizontal  direction.     On  entering  the  chief  pillars  this  layer  becomes 


462 


DIGESTIVE    SYSTEM    OF   THE    OX 


much  thicker  and  its  fibers  have  the  same  direction  as  the  pillars.  Thus  the  muscular  tissue  of 
the  pillars  is  seen  on  cross-section  to  consist  of  two  thick  layers  of  longitudinal  fibers,  which  are 
separated  (except  at  the  free  margin  of  the  pillar)  by  a  thin  axial  layer  of  fibers  disposed  at  right 
angles  to  the  preceding. 

The  muscular  coat  of  the  reticulum  consists  of  two  chief  layers  which  begin 
and  end  at  the  oesophageal  groove;  they  pass  in  a  circular  or  oblique  fashion  around 
the  sac,  the  fibers  of  the  two  layers  crossing  each  other  at  varying  angles.  The 
walls  of  the  cells  contain  a  central  muscular  layer.  The  lips  of  the  oesophageal 
groove  consist  chiefly  of  a  thick  layer  of  longitudinal  fibers,  which  are  largely  con- 
tinuous at,  or  cross  each  other  below,  the  reticulo-omasal  orifice.  The  bottom  of 
the  groove  has  two  layers  of  oblique,  unstriped  muscle-fibers, 
with  a  variable  outer  layer  of  striped  muscle  continuous  with 
that  of  the  oesophagus. 

The  external  muscular  layer  of  the  oesophagus  is  in  part  continued 
down  along  the  oesophageal  groove  (i.  e.,  along  the  lesser  curvature  of 
the  reticulum),  but  in  greater  part  spreads  out  on  the  wall  of  the  rumen 
and  reticulum.  The  internal  muscular  layer  of  the  oesophagus  forms  a 
loop  over  the  cardia  and  is  largely  continued  in  the  hps  of  the  oesopha- 
geal groove;  part  of  it  is  continuous  with  the  muscular  laj^er  of  the 
bottom  of  the  groove. 

The  muscular  coat  of  the  omasimi  consists  of  a  thin  ex- 
ternal longitudinal  layer  and  a  thick  internal  circular  layer. 
At  the  omasal  groove  there  is  an  incomplete  inner  layer  of 
oblique  fibers.  The  larger  laminae  contain  three  muscular 
strata.  The  fibers  of  the  central  layer  extend  from  the  at- 
FiG.   394.  —  MuscuLA-      tached  edge  toward  the  free  edge,  but  do  not  reach  the  latter ; 

TURE  OF  (Esophageal 
Groove  and  Adjacent 
Part  of  Stomach  of 

Ox,  SEEN  FROM  WITHIN 

after      Removal     of 

Mucous  Membr.vne. 

a,  ffisophagus;  b,  in- 
ner muscular  layer  of  atri- 
um; d,  reticulo-omasal  ori- 
fice; e,  e',  muscle  of  lips  of 
groove;  g,  lower  end  of 
muscle  of  larger  lip,  which 
curves  around  the  reticulo- 
omasal  orifice  in  part  and 
spreads  out  in  the  inner 
muscular  layer  of  the  retic- 
ulum in  part;  h,  lower 
end  of  muscle  of  smaller 
lip,  which  in  part  curves 
around  the  reticulo-omasal 
orifice  and  is  in  part  con- 
tinuous with  the  inner  mus- 
cular layer  of  the  omasal 
groove  and  the  omasum; 
t,  inner  muscular  layer  of 

reticulum.         (Ellenberger-  ^^°-  395- — Stomach  of  New-born  Calf;  Right  View. 

Baum,  Anat.  d.  Haustiere.)  The  rumen  is  raised. 


Oesophagui 


here  there  is  a  marginal  band  of  longitudinal  fibers.  The  central  layer  is  contin- 
uous with  the  inner  circular  layer  of  the  wall.  On  either  side  there  is  a  layer  of 
longitudinal  fibers,  which  are  continuous  at  the  attached  border  with  the  muscu- 
laris  mucosae. 

The  muscular  coat  of  the  abomasum  consists  of  longitudinal  and  circular 
layers;   the  latter  forms  a  well-developed  pyloric  sphincter. 

The  mucous  membrane  of  the  first  three  divisions  is  destitute  of  glands,  and 
is  covered  with  a  thick,  stratified,  squamous  epithelium;    the  superficial  part  of 


THE   INTESTINE 


463 


the  latter  is  horny,  and  is  shed  in  large  patches  in  the  rumen  and  omasum.  The 
tunica  propria  is  papillated.  The  mucous  membrane  of  the  abomasum  is  glandular, 
and  corresponds  to  that  of  the  right  sac  of  the  stomach  of  the  horse.  The  fundus 
glands  (which  are  relatively  short)  occur  in  that  part  which  presents  the  large  folds, 
while  the  long  pyloric  glands  are  found  in  the  remainder,  except  about  the  omaso- 
abomasal  orifice,  where  cardiac  glands  occur.  The  mucosa  of  the  fundus  gland 
region  is  very  thin  as  compared  with  that  of  the 

horse;  toward  the  pylorus  there  is  an  increase  in  f'^?^\^ 

thickness.     There  is  a  round  prominence  (Torus  ^    \  ■      '. ^ 

pyloricus)  on  the  upper  part  of  the  pyloric  valve. 
Vessels  and  Nerves.— The  blood  supply  is 
derived  from  the  coeliac  artery,  and  the  veins 

go  to  the  portal  vein.     The  nerves  come  from  B  *  i'^i^-"' 
the  vagus  and  sympathetic.     Numerous  ganglia 
are  present  in  the  submucous  and  intermuscular 
tissue,    especially  in    the  reticulum    and    oeso- 
phageal groove.                                                             — «■— 


THE  INTESTINE 

The  intestine  of  the  ox  is  about  twenty 
times  the  length  of  the  body.  It  lies  almost 
entirely  to  the  right  of  the  median  plane,  chiefly 
in  contact  with  the  right  face  of  the  rumen.  It 
is  attached  to  the  sublumbar  region  by  a  com- 
mon mesentery. 

The  small  intestine  has  an  average  length 
of  about  130  feet  (ca.  40  m.)  and  a  diameter  of 
about  two  inches  (ca.  5  to  6  cm.).  The  duo- 
denum is  about  three  or  four  feet  (ca.  1  m.)  in 
length.  Beginning  at  the  pylorus  (usually  at  the 
ventral  end  of  the  eleventh  rib  or  intercostal 
space),  it  passes  dorsally  and  forward  to  the 
visceral  surface  of  the  liver;  here  it  forms,  ven- 
tral to  the  right  kidney,  an  S-shaped  curve  (Ansa 
sigmoidea) .  Thence  it  runs  backward  almost  to 
the  tuber  coxae,  where  it  turns  on  itself,  passes 
forward  alongside  of  the  terminal  part  of  the 
colon,  and  joins  the  mesenteric  part  (jejunum) 
under  the  right  kidney.  It  is  attached  to  the 
liver  by  the  lesser  omentum;  the  remainder  of 
the  mesoduodenum  is  a  narrow  fold  which  is 
largely  derived  from  the  right  layer  of  the  com- 
mon mesentery,  but  at  the  iliac  flexure  it  comes 
directly  from  the  sul^lumbar  region.  The  bile 
duct  opens  in  the  ventral  part  of  the  S-shaped  curve 
about  a  foot  (ca.  30  cm.)  further  back. 

The  remainder  of  the  small  intestine  is  arranged  in  numerous  very  close  coils, 
which  form  a  sort  of  festoon  at  the  edge  of  the  mesentery.  It  hes  chiefly  in  the 
space  bounded  medially  by  the  right  face  of  the  ventral  sac  of  the  rumen,  laterally 
and  ventrally  by  the  abdominal  wall,  dorsally  by  the  large  intestine,  and  anteriorly 
by  the  omasum  and  abomasum.  It  is  not  subject  to  much  variation  in  position, 
but  a  few  coils  may  find  their  way  behind  the  blind  sacs  of  the  rumen  to  the  left 
side.     The  terminal  part  leaves  the  edge  of  the  mesentery  and  runs  forward  be- 


FiG.  396. — Large  and  Small  Aggregated 
Follicles  or  Peyer's  Patches  op 
Small  Intestine  of  Ox  (about  M  "."-t- 
ural  size). 


The  pancreatic  duct  opens 


464 


DIGESTIVE    SYSTEM    OF   THE    OX 


tween  the  csecum  and  colon,  to  both  of  which  it  is  adherent.  The  orifices  of  the 
pancreatic  duct  and  the  bile  duct  are  on  papillse  or  thick  folds,  no  diverticulum 
being  present.  There  are  permanent  transverse  folds  of  the  mucous  membrane 
(Plicae  circulares).     Duodenal  glands  occur  in  the  first  twelve  to  fifteen  feet  (4  to  4.5 


Fig.  397, — Projection  of  Viscera  of  Bull  on  Body-wall;  Right  Side. 
P.,  Pylorus;    G.b.,  gall-bladder;    R.K.,  right  kidney;    L.K.,  left  kidney;    P.  (above  duodenum),  pancreas;    Bl., 
urinary  bladder;     V.s.,   vesicula  seminalis;     B.g.,  bulbo-urethral  (Cowper's)  gland.     Costal  attachment  and  median 
line  of  diaphragm  are  indicated  by  dotted  lines. 


Fig.  39S. — Projection  of  Viscera  of  Cow  on  Body-wall;  Left  Side. 
Oes.,  Oesophagus;  Ret.,  reticulum;  b.  s.,  anterior  blind  sac;    b.  s".,  posterior  blind  sacs  of  rumen;   0,  ovary.     The 
left  kidney,  concealed  by  the  dorsal  sac  of  the  rumen,  is  indicated  by  dotted  line.     The  median  line  of  the  diaphragm 
is  dotted. 


m.),  intestinal  glands  throughout.  The  aggregated  follicles  or  Peyer's  patches  are 
larger  and  more  prominent  and  distinct  than  in  the  horse,  and  vary  greatly  in  size 
and  number;  in  adult  cattle  there  are  eighteen  to  forty;  in  calves  twenty  to  fifty- 
eight  have  been  counted.  They  usually  have  the  form  of  narrow  bands.  There 
is  a  patch  close  to  the  ileo-csRcal  ^'alve. 


THE    LIVER  465 

The  large  intestine  is  much  smaller  in  caliber  than  that  of  the  horse,  has  no 
bands,  and  is  not  sacculated.  Most  of  it  is  situated  between  the  layers  of  the 
common  mesentery  in  the  right  dorsal  part  of  the  abdominal  cavity.  It  is  related 
on  the  right  to  the  lateral  abdominal  wall,  from  which,  however,  it  is  almost  com- 
pletely separated  by  the  greater  omentum.  On  the  left  it  is  chiefly  related  to  the 
rumen.  The  average  length  of  the  caecum  is  about  thirty  inches  (ca.  75  cm.),  and 
the  diameter  is  about  five  inches  (ca.  12  cm.).  It  is  directly  continuous  in  front 
with  the  colon,  the  conventional  demarcation  being  the  junction  of  the  ileum  with 
the  large  intestine.^  From  this  junction,  which  is  on  the  medial  side  and  usually 
near  the  ventral  end  of  the  last  rib,  the  caecum  extends  backward  and  upward 
along  the  right  flank  (from  which  it  is  separated  by  the  greater  omentum),  and  its 
rounded  blind  end  commonly  lies  at  the  right  side  of  the  pelvic  inlet.  The  caecum 
is  attached  along  its  medial  side  to  the  mesentery,  except  the  posterior  third,  which 
is  free  and  variable  in  position.  The  terminal  part  of  the  ileum  runs  forward  along 
the  medial  surface  of  the  caecum  and  is  attached  to  the  latter.  The  dorsal  surface 
is  attached  by  areolar  tissue  and  peritoneum  to  the  colon.  The  colon  is  about 
thirty-five  feet  (ca.  10  m.)  in  average  length.  Its  diameter  is  at  first  the  same  as 
that  of  the  caecum,  but  diminishes  to  about  two  inches  (ca.  5  cm.).  The  greater 
part  of  it  is  arranged  in  double  elliptical  coils  between  the  layers  of  the  mesentery; 
the  coils  are  attached  to  each  other  by  areolar  tissue.  It  begins  as  the  direct 
continuation  of  the  caecum,  runs  forward  a  short  distance,  and  turns  dorsally  and 
backward  opposite  to  the  ventral  part  of  the  last  two  ribs.  It  continues  backward, 
in  relation  to  the  right  flank  laterally  and  the  caecum  ventralh^,  to  the  posterior 
part  of  the  sublumbar  region.  Here  it  turns  forward  and  runs  parallel  -with  the 
retrograde  part  as  far  forward  as  the  second  lumbar  vertebra,  turns  backward,  and 
is  continued  by  the  spiral  part  (Ansa  spiralis).  The  coils  of  this  are  alternately 
centripetal  and  centrifugal  (Gyri  centripetales  et  centrif ugales) ;  they  are  best 
seen  from  the  left  side.  The  bowel  gradually  diminishes  in  caliber,  and  the  ter- 
minal part  (Ansa  distalis)  leaves  the  spiral  mass,  passes  forward  to  the  great  mesen- 
teric artery,  and  runs  backward  dorsal  to  the  terminal  part  of  the  duodenum.  It 
inclines  to  the  right  in  relation  to  the  ventral  surface  of  the  right  kidney,  forms  an 
S-shaped  curve  near  the  pelvic  inlet,  and  joins  the  rectum;  this  part  is  attached  to 
the  sublumbar  region  by  a  narrow  mesentery,  and  is  also  attached  to  the  recurrent 
part  of  the  duodenum. 

The  rectum  is  somewhat  shorter  than  that  of  the  horse,  and  is  usually  covered 
with  peritoneum  as  far  back  as  the  first  coccygeal  vertebra.  The  retroperitoneal 
part  is  surrounded  by  a  quantity  of  fat.     The  anus  is  not  prominent. 

The  serous  coat  is  of  course  absent  on  the  adherent  surfaces  of  the  spiral  part 
of  the  colon.  There  is  a  large  amount  of  fat  in  the  mesentery.  The  longitudinal 
fibers  of  the  muscular  coat  are  evenly  distributed,  consequently  there  is  no  saccula- 
tion of  the  bowel.  There  is  a  valvular  mucous  fold  at  the  ileo-caecal  orifice.  A 
Peyer's  patch  occurs  in  the  beginning  of  the  caecum  and  one  in  the  first  part  of  the 
colon. 

THE  LIVER 

The  liver  lies  almost  entirely  to  the  right  of  the  median  plane.  Its  long  axis 
is  directed  obliquely  dowTiward  and  forward,  about  parallel  with  the  median  plane, 
and  corresponds  to  the  curvature  of  the  right  portion  of  the  diaphragm.  It  is  less 
extensive,  but  thicker  than  that  of  the  horse.  Its  average  weight  is  about  10  to 
12  pounds  (ca.  4.5  to  5.5  kg.). 

1  In  formalin-hardened  material  there  is  sometimes  a  constriction  in  front  of  the  termination 
of  the  ileum.  This  might  be  regarded  as  the  demarcation  between  the  csecum  and  colon.  The 
opening  of  the  ileum  is  directly  forward,  so  that  material  from  it  enters  the  origin  of  the  colon. 
The  posterior  free  part  of  the  csecum  is  naturally  variable  in  position;  it  may  be  bent  ventrally, 
so  that  the  blind  end  faces  forward. 
30 


466  DIGESTIVE    SYSTEM    OF   THE    OX 

In  small  subjects  the  weight  (according  to  Schmaltz)  varies  from  6J'2  to  10  pounds  (ca. 
3  to  4.5  kg.),  in  large  subjects  from  11  to  13  pounds  (ca.  5  to  6  kg.).  According  to  Schneider,  the 
average  weight  is  about  13  pounds  (ca.  6  kg.) — a  little  over  1  per  cent,  of  the  live  weight  and 
about  2  per  cent,  of  the  dressed  carcass. 

When  hardened  in  situ,  it  is  seen  to  be  adapted  accurately  to  the  structures 
with  which  it  is  in  contact. 

The  parietal  surface  is  convex  and  is  for  the  most  part  applied  to  the  right 
part  of  the  diaphragm,  but  a  small  part  of  it  is  in  direct  contact  with  the  last  two 
or  three  ribs  and  with  the  flank  at  the  lumbo-costal  angle.  It  faces  dorsally,  for- 
ward, and  to  the  right. 

The  curvature  of  the  parietal  surface  is  not  quite  regular.  It  is  marked,  except  in  its  ventral 
part,  by  a  blunt  oblique  ridge  which  divides  the  surface  into  two  areas.     Of  these,  the  lateral  one 


Caudate  lobe 


Faiciform  ligament  (cut) 


Coronary  ligament  (cut) 

Gall-bladder  ^^^^^^^^mm^  ^as^^^^^^n^m 

Posterior  vena  cava 

Hepatic  veins 
(Esophageal  notch 


FiQ.  399. — Liver  of  Ox,  Parietal  Surface;  Hardened  in  situ. 

Is  directed  outward,  is  only  slightly  convex,  and  often  shows  impro^jsions  of  the  last  three  ribs;  it  is 
in  contact  in  part  directly  with  the  right  abdominal  wall,  in  part  with  the  costal  part  of  the  dia- 
phragm which  is  in  contact  ordinarily  with  the  lateral  wall.  The  medial  area  presents  a  depression 
produced  by  the  right  crus  of  the  diaphragm,  and  otherwise  is  regularly  convex  and  adapted  to 
the  tendinous  center  and  sternal  part  of  the  diaphragm.  The  falciform  ligament  is  attached  to 
the  surface  from  the  oesophageal  notch  to  the  umbilical  fissure.  There  is  a  triangular  area  of 
considerable  size  on  the  dorso-medial  part  of  the  surface  which  is  without  a  peritoneal  covering, 
since  it  is  adherent  to  the  diaphragm. 

The  visceral  surface  is  concave  and  very  irregular;  it  presents  impressions  of 
the  chief  organs  which  are  in  contact  with  it— the  omasum  and  reticulum.  It  is 
also  related  to  the  pancreas  and  duodenum. 

The  following  markings  are  quite  distinct  on  the  visceral  surface  of  well-hardened  speci- 
mens:   (1)  The  omasal  impression  (Impressio  omasica)  is  a  deep  central  cavity  below  the  portal 


THE    LIVER 


467 


fissure.  (2)  The  reticular  impression  (Impressio  reticularis)  is  a  smaller  marginal  depression  below 
the  oesophageal  notch  antl  the  medial  part  of  the  preceding,  from  which  it  is  separated  by  a  rounded 
ridge.     (3)  The  abomasal  impression  (Impressio  abomasica),  present  only  in  the  young  subject 


Renal  impression 


Lesser  omentum  (cut) 
(Esophageal  notch 


I'  till  nlical  fissure 


Fig.  400. — Liver  of  Heifer,  Viscek.4.l  Surface;  Hardened  in  situ. 
The  abomasal  impression  ia  shown  to  the  right  of  the  reticular  impression,  but  by  an  oversight  is  not  marked. 


Area  of  attachment  to 
diaphragm  (noii-pcriloitcal) 


Caudate  lobe 


Coronary  ligameiU 
Posterior  vena  cava 

Hepatic  veins 
(Esophageal  iwtch 
Fig.  40L — Liver  of  Ox,  Left  Marginal  View;  Hardened  in  st 


usually,  corresponds  to  the  fundus  of  the  abomasum.  It  lies  along  the  ventral  part  of  the  surface 
and  is  separated  by  ridges  from  the  preceding  impressions.  It  usually  disappears  as  the  omasum 
and  reticulum  increase  in  size  and  displace  the  abomasum  from  contact  with  the  liver.     (4j  Shallow 


468  DIGESTIVE    SYSTEM    OF  THE    OX 

grooves  for  the  S-sliaped  portion  of  the  duodenum  (Impressio  duodenaUs)  may  be  found  dorsal 
and  lateral  to  the  portal  fissure.  (5)  The  fossa  of  the  gall-bladder  (Fossa  vesicae  fellese)  is  distinct 
when  that  organ  is  full.  In  the  calf  the  omasal  impression  is  small,  and  the  abomasal  one  large  in 
correspondence  with  the  relative  sizes  of  these  two  sacs. 

The  portal  fissure  is  a  well-defined  rounded  depression,  situated  dorsal  to  the 
omasal  impression.  It  contains,  besides  the  vessels  and  duct,  several  large  hepatic 
lymph  glands.     Dorsal  and  lateral  to  it  a  part  of  the  pancreas  is  attached. 

The  dorsal  border  is  short  and  thick;  it  usually  extends  backward  a  short 
distance  beyond  the  upper  part  of  the  last  rib.  It  presents  the  large,  thick,  quad- 
rilateral caudate  lobe,  and  a  deej^  depression  for  the  right  kidney  and  adrenal. 

The  ventral  border  is  short  and  thin  and  has  no  interlobar  incisures. 

The  right  (or  lateral)  border  is  marked  by  the  umbilical  fissure,  in  which  the 
ligamentum  teres  is  attached  in  the  young  subject. 

The  left  border  presents  the  oesophageal  notch  below  its  middle;  the  notch  is 
much  shallower  than  in  the  horse.  Above  this  it  is  practically  median  in  position, 
and  lodges  the  posterior  vena  cava,  which  is  partially  embedded  in  the  gland.  Be- 
low the  notch  the  border  extends  an  inch  or  two  (ca.  2.5  to  5  cm.)  to  the  left  of  the 
median  plane,  opposite  the  ventral  third  of  the  sixth  rib  or  intercostal  space. 

The  right  lateral  ligament  attaches  the  dorsal  border  to  the  anterior  part  of 
the  sublumbar  region.  The  ligament  of  the  caudate  lobe  passes  to  the  ventral 
surface  of  the  right  kidney.  There  is  no  left  lateral  ligament.  The  falciform  liga- 
ment is  generally  present,  but  the  ligamentum  teres  is  usually  found  only  in  young 
subjects.  The  lesser  omentum  leaves  the  liver  along  a  line  extending  from  the 
oesophageal  notch  to  the  portal  fissure.  The  only  distinct  lobes  in  the  adult  are 
the  caudate  and  papillary.  The  latter  is  best  seen  in  the  soft  specimen;  it  is  a 
tongue-like  mass  which  partly  overlaps  the  portal  vein  and  fissure.-^ 

A  gall-bladder  (Vesica  fellea)  is  present.  This  is  a  pear-shaped  sac,  four  to 
six  inches  (ca.  10  to  15  cm.)  long,  which  lies  partly  in  contact  with  the  visceral 
surface  of  the  liver  (to  which  it  is  attached),  but  largely  against  the  abdominal  wall 
at  the  ventral  part  of  the  tenth  or  eleventh  intercostal  space.  It  may  be  regarded 
as  a  diverticulum  of  the  bile-duct,  enlarged  to  form  a  reservoir  for  the  bile.  Its 
neck  is  continued  by  the  cystic  duct  (Ductus  cysticus),  which  joins  the  hepatic 
duct  at  an  acute  angle  just  outside  of  the  portal  fissure,  to  form  with  it  the  bile- 
duct  (Ductus  choledochus) .  The  latter  is  short  and  enters  the  second  bend  of  the 
S-shaped  curve  of  the  duodenum,  i.  e.,  about  two  feet  (ca.  60  cm.)  from  the  pylorus. 
The  opening  of  the  duct  is  at  the  end  of  a  papilla  or  ridge-like  fold.  Several  small 
ducts  (Ductus  hepatocystici)  open  directly  into  the  gall-bladder. 

The  wall  of  the  gall-bladder  consists  of  serous,  muscular,  and  mucous  coats.  The  muscular 
tissue  consists  of  unstriped  fibers  which  run  in  various  directions;  externally  many  are  longitudinal, 
while  internally  (and  especially  at  the  neck)  they  are  chiefly  circular.  The  mucous  membrane  is 
covered  by  a  cylindrical  epithelium  and  contains  numerous  groups  of  branched  tubular  glands. 
The  cystic  and  bile  ducts  have  a  similar  structure. 

In  the  new-born  calf  the  liver  is  relatively  much  larger  than  in  the  adult.  The  visceral 
surface  presents,  below  the  portal  fissure,  a  rounded  eminence,  which  is  caused  by  the  pres- 
ence in  the  underlying  gland  substance  of  a  large  venous  sinus  into  wliich  the  umbilical  and  portal 
veins  empty.  A  large  vessel,  the  ductus  venosus,  leads  from  this  sinus  directly  to  the  posterior 
vena  cava.     The  umbiUcal  fissure  is  deep  and  partially  divides  the  gland  into  two  chief  lobes. 


THE  PANCREAS 

The  pancreas  of  the  ox  is  irregularly  quadrilateral  in  form,  and  lies  almost 

entirely  to  the  right  of  the  median  plane.     Its  weight  is  about  the  same  as  that  of 

the  horse.     Its  dorsal  surface  is  related  to  the  liver,  right  kidney,  crura  of  the 

diaphragm,  posterior  vena  cava,  and  cceliac  and  anterior  mesenteric  arteries;  it  is 

^  The  liver  of  the  ox  might  be  regarded  as  consisting  of  dorsal,  ventral,  caudate,  and  papillary 
lobes.  Pathological  adhesions  of  the  ventral  part  of  the  hver  to  the  diaphragm  and  reticulum 
are  often  present  in  dissecting-room  subjects. 


THE    PANCREAS 


469 


covered  to  a  large  extent  by  peritoneum.  It  is  attached  to  the  hver  at  and  lateral 
to  the  portal  fissure,  and  to  the  crura  of  the  diaphragm.  Between  these  adhesions 
it  is  free  and  forms  the  ventral  wall  of  the  epiploic  foramen.  On  the  right  side  it 
extends  backward  beyond  the  caudate  lobe  of  the  liver  between  the  layers  of  the 
mesoduodenum;  here  it  is  in  contact  with  the  upper  part  of  the  flank  at  the  lumbo- 
costal angle,  and  is  related  dorsally  to  the  right  kidney  and  by  its  ventro-lateral 


Pancreatic  duct  ■ 


Caudate  lobe 
of  liver 


Duodenum 


Gall-bladder 
Round  ligament 
of  liver 


Fig.  402. — Pancreas  and  Related  Strtctt  hks  of  Ox. 
1,  Left  extremity  of  pancreas;    2,  posterior  vena  cava;   3,  portal  vein;   4,  gastro-splenic  vein;    5,  probe  in  epiploic 
foramen;    6,  bile  duct;    7,  cystic  duct;    S,  pancreatico-intestinal  lymph  gland;    9,    cut  edge  of  lesser  omentum;    10, 
omasal  impression  of  liver.      Intraglandular  part  of  pancreatic  duct  and  its  chief  radicles  are  shown  by  dotted  lines. 
Concealed  parts  of  bile  duct,  cystic  duct,  and  neck  of  gall-bladder  are  similarly  indicated. 


border  to  the  retrograde  part  of  the  duodenum.  The  ventral  or  gastro-intestinal 
surface  is  in  contact  with  the  dorsal  curvature  of  the  rumen  and  the  intestine. 
There  is  a  deep  notch  (Incisura  pancreatis)  for  the  portal  vein  and  hepatic  artery, 
and  several  lymph  glands  are  present  here.  The  left  extremity  is  small  and  quad- 
rilateral; it  is  related  dorsally  to  the  crus  of  the  diaphragm,  left  adrenal,  and  the 
cceliac  and  anterior  mesenteric  arteries,  and  is  adherent  ventrally  to  the  rumen. 


470 


DIGESTIVE    SYSTEM    OF   THE    SHEEP 


The  right  or  posterior  part  is  wide  and  thin  and  is  often  divided  into  two  branches. 
The  duct  leaves  the  posterior  part  of  the  ventro-lateral  (or  right)  border  and  enters 
the  duodenum  about  twelve  inches  (ca.  30  cm.)  further  back  than  the  bile-duct. 


Dorsal  extremity 


Splenic  vein 
Splenic  artery 
Hilus 


THE  SPLEEN 

The  spleen  has  an  elongated,  elliptical  outline,  both  extremities  being  thin, 

rounded,  and  similar  in  size. 

Its  average  weight  is  about  two  pounds  (ca.  900  gm.),  or  about  ^  &  per  cent,  of 

the  body-weight.     Its  average  length  is  about  20  inches  (ca.  50  cm.),  its  width 

about  6  inches  (ca.  15  cm.),  and  in  the 
middle  its  thickness  is  about  an  inch  (ca. 
2  to  3  cm.). 

The  dorsal  extremity  lies  under  the 
dorsal  ends  of  the  last  two  ribs,  and  may 
extend  back  as  far  as  the  first  luml^ar 
transverse  process.  The  ventral  extrem- 
ity is  usually  opposite  the  eighth  or  ninth 
rib,  about  a  handbreadth  above  its  junc- 
tion with  the  cartilage.  The  parietal  sur- 
face is  convex,  and  is  related  to  the  dia- 
phragm. The  visceral  surface  is  concave, 
and  is  related  chiefly  to  the  left  face  of  the 
rumen,  but  also  usually  to  a  narrow  ad- 
jacent area  of  the  reticulum.  The  dorsal 
part  is  attached  to  the  left  crus  of  the  dia- 
phragm and  the  left  surface  of  the  rumen 
by  peritoneum  and  connective  tissue ;  the 
ventral  part  is  free.  The  hilus  is  situated 
on  the  dorsal  third  of  the  visceral  surface, 
near  the  anterior  border. 

About  one-half  of  the  visceral  surface  of  the 
spleen  is  attached  directly  to  the  stomach  and  is 
therefore  not  covered  by  peritoneum ;  the  line  of  re- 
flection of  the  latter  crosses  the  surface  obliquely, 
from  the  upper  part  of  the  posterior  border  to 
the  anterior  border  below  its  middle.  Similarly 
there  is  a  narrow  uncovered  area  on  the  upper 
part  of  the  parietal  surface  along  the  anterior 
border.  The  hilus  is  not  a  groove,  but  a  simple 
depression.  When  hardened  in  situ,  the  organ  is 
seen  to  be  somewhat  twisted,  so  that  the  upper 
part  of  the  parietal  surface  faces  dorsally  and 
forward,  while  below  it  is  directed  laterally.  In 
some  cases  the  spleen  is  considerably  longer  than 
IS  stated  aljove.  and  may  extend  to  the  ventral  end  of  the  eighth  rib.  Not  uncommonly  there  are 
pathological  adhesions  of  the  ventral  part  of  the  spleen  to  adjacent  structures. 


Ventral  extremity 


Fig.  403. — Spleen-  of  Ox;  Visceral  Surface. 
1,  Area  of  attachment  to  rumen   (non-peritoneal); 
line  of  peritoneal  reflection. 


posterior  border; 


DIGESTIVE  SYSTEM  OF  THE  SHEEP 

The  lips  are  thin  and  mobile;  the  upper  one  is  marked  by  a  very  distinct 
philtrum,  and  otherwise  is  not  bare. 

The  anterior  part  of  the  hard  palate  is  prominent  and  smooth,  forming  the 
so-called  dental  pad  or  plate.     On  the  posterior  part  of  this  area  there  are  two 


DIGESTIVE    SYSTEM    OF   THE    SHEEP 


471 


narrow  depressions  in  the  form  of  a  V  and  separated  by  the  central  papilla  incisiva, 

at  the  deep  anterior  ends  of  which  the  incisive  or  naso-palatine  ducts  open.     The 

ridges  of  the  palate,  some  fourteen  in  number,  are  irregular  and  their  edges  are 

smooth;    most  of  them    alternate   with  those   of   the 

opposite   side,  from  which  they  are  separated  by  the 

median  raphe  palati.     The  posterior  third   or   rather 

more  is  not  ridged  and  presents  numerous  orifices  of 

ducts  of  the  palatine  glands.     The  mucous  membrane 

is  often  more  or    less    pigmented.     The    soft    palate 

resembles  that  of  the  ox. 

The  mucous  membrane  of  the  cheeks  is  covered 
with  large  papillae,  many  of  which  are  long  and  sharp- 
pointed,  while  others  are  short  and  blunt.  There  is 
also  a  series  of  conical  papillae  on  the  floor  of  the 
mouth,  under  the  lateral  part  of  the  tongue. 

The  tongue  resembles  that  of  the  ox  in  form,  but 
the  tip  is  comparatively  smooth;  the  papillae  here  are 
very  numerous,  but  short  and  blunt.  This  difference 
is  in  conformity  with  the  dissimilarity  in  the  mode  of 
prehension  of  the  two  species.  The  prominence  of 
the  dorsum  is  commonly  not  so  pronounced  nor  so 
sharply  marked  off  in  front  as  in  the  ox.  The  root 
is  smooth.  The  mucous  meml^rane  of  the  dorsum  is 
often  pigmented  in  spots. 

The  dental  formula  is  the  same  as  that  of  the 
ox.^  The  incisor  teeth  form  a  narrow  and  strongly 
curved  arch.  The  crowns  are  long  and  narrow;  their 
labial  surfaces  are  strongly  convex  and  end  at  a  sharp 
edge  which  is  used  in  cropping  the  grass.  The  roots 
are  more  firmly  embedded  than  in  the  ox.     The  cheek  p^^  404.-Palate  of  sheep. 

teeth  resemble  those  of  the  ox,   but  have  a  thinner  i_  Dental  pad;   2,  papiiia  in- 

layer  of  cement,  which  is  often  blackened  by  deposits      cisiva;    3,  3,  openings  of  incisive 
from  the  food.     The   average  periods   of  eruption  of     canals;    <t,  raph^  paiati;    5  phii- 

.  ,  ,   .     .  ,  ,  trum;     G,  conical  papulae  of  cheek; 

the  teeth  are  mdicated  m  the  sulijomed  table:  7,  tonsils;   s,  palatine  arch. 


Temporary 


Permanent 


Ii At  birth  or  first  week 1  to  1  ;^  2  years 

I2 First  or  second  week 1 3^  to  2  years 

I3 Second  or  third  week 23^  to  3  years 

I4 Third  or  fourth  week 33  2  to  4  years 

P2  [    2  to  6  weeks 13^  to  2  years 

P3J 

Ml 3  months  (lower),  5  months  (upper) 

M2 9  to  12  months 

Ms 13^  to  2  years 


The  salivary  glands  resemble  those  of  the  ox  in  general.  The  parotid  gland 
is  darker  in  color  and  more  compact  in  texture  than  the  mandibular.  It  is  rounded 
in  outline,  but  has  a  pointed  cervical  angle  at  which  the  external  jugular  vein 
emerges.  The  duct  leaves  the  lower  part  of  the  anterior  border  of  the  gland  and 
runs  forward  over  the  masseter  muscle,  about  an  inch  and  a  half  (ca.  3.4  cm.) 
above  the  ventral  border  of  the  ramus;  it  opens  opposite  the  third  or  fourth 
cheek  tooth. 

The  tonsil  is  bean-shaped  and  about  half  an  inch  (ca.  12  mm.)  in  length.  Jt 
1  A  lateral  view  of  the  teeth  is  given  in  the  description  of  the  skull. 


472 


DIGESTIVE    SYSTEM    OF    THE    SHEEP 


does  not  project  into  the  isthmus  faucium.  The  mucous  membrane  of  the  latter 
presents  two  deep  and  very  narrow  tonsillar  sinuses  on  either  side. 

The  fornix  of  the  phar3mx  presents  a  median  plicated  fold  which  is  a  continua- 
tion of  the  septum  nasi.  The  pharyngeal  orifice  of  the  Eustachian  tube  has  the 
form  of  a  crescentic  slit,  placed  about  on  a  level  with  the  ventral  nasal  meatus. 
There  are  two  large  lymph  glands  and  a  number  of  hsemolymph  glands  above  the 
pharynx. 

The  oesophagus  has  a  lumen  of  about  an  inch  (ca.  2.5  cm.)  when  moderately 
distended;    otherwise  it  resembles  that  of  the  ox. 

The  stomach  is  like  that  of  the  ox  in  its  general  arrangement.  Its  average 
capacity  is  about  four  gallons  (ca.  15  liters).  The  cardia  is  opposite  the  eighth 
intercostal  space;    it  is  just  to  the  left  of  the  median  plane,  and  about  two  inches 


Dorsal  curvature  of 
rumen 


Fig.  405. — Stomach  of  Shkep;  Left  View, 
From  photograph  of  specimen  hardened  in  situ.     The  reticulum  is 


hat  contracted. 


(ca.  5  cm.)  below  the  vertebral  column.  The  dorsal  sac  of  the  rumen  is  a  little  longer 
than  the  ventral  sac  and  extends  considerably  (ca.  7.8  cm.)  further  forward  than 
the  latter.  The  ventral  sac  is  relatively  larger  and  extends  further  to  the  right  of 
the  median  plane  than  in  the  ox;  its  posterior  blind  sac  extends  further  (ca.  6-8  cm.) 
back  than  that  of  the  dorsal  sac.  The  parietal  attachment  of  the  dorsal  sac 
extends  back  to  the  second  lumbar  vertebra.  The  left  longitudinal  groove  ex- 
tends upward  and  backward  for  a  short  distance  only,  and  therefore  does  not 
connect  with  the  posterior  groove.  There  are  two  longitudinal  grooves  on  the 
right  side  which  join  at  each  end,  thus  enclosing  a  long,  narrow  prominent  area; 
the  dorsal  one  contains  the  right  ruminal  artery,  and  the  ventral  one  corresponds  to 


DIGESTIVE    SYSTEM    OF   THE    SHEEP 


473 


the  pillar.  The  left  coronary  grooves  do  not  extend  to  the  curvatures.  There  is 
no  dorsal  coronary  groove  on  the  right  side,  but  the  ventral  one  is  very  distinct  and 
extends  to  the  curvature.  The  arrangement  of  the  pillars  corresponds  to  these 
external  features.  The  papilla  of  the  rumen  are  relatively  large  and  somewhat 
tongue-like;  the  largest  are  about  a  fourth  of  an  inch  (ca.  6  mm.)  in  length.  The 
dorsal  part  is  papillated,  not  glabrous,  as  in  the  ox.  The  lateral  part  of  the  rumino- 
reticular  fold  ends  half  an  inch  or  more  (ca.  1.5  cm.)  behind  the  cardia.  The 
reticulum  is  relatively  larger  than  in  the  ox.  Its  ventral  part  curves  more  back- 
ward and  less  to  the  right  than  in  the  ox.     The  parietal  surface  extends  forward  as 


Reticulo- 
^       abomasal 
groove 


Fig.  406. — Stomach  of  Sheep;  Right  View. 
From  photograph  of  specimeii  hardened  in  situ.     Dotted  line  indicates  position  of  spleen. 

far  as  the  sixth  rib  or  intercostal  space,  and  is  related  to  the  diaphragm  and  liver. 
The  fundus  lies  on  the  sternal  part  of  the  diaphragm  and  is  in  contact  behind  with 
the  abomasum.  The  oesophageal  groove  is  disposed  in  general  like  that  of  the  ox, 
and  is  about  four  to  five  inches  (ca.  8  to  10  cm.)  long. 

There  are,  however,  several  marked  differences  in  the  arrangement  of  the  groove.  Its  ven- 
tral part  curves  backward,  so  that  the  reticulo-omasal  orifice  is  directed  dorsally  and  lies  in  a  trans- 
verse plane  about  an  inch  (ca.  2-3  cm.)  behind  one  passing  through  the  cardia.  These  differ- 
ences are  correlated  with  the  small  size  of  the  omasum  and  the  large  size  of  the  reticulum. 
Tubulo-alveolar  glands  have  been  found  by  Thanhofer  and  others;  they  occur  chiefly  in  the 
submucous  tissue  at  the  angle  of  junction  of  the  hps  and  bottom  of  the  groove. 


The  folds  surrounding  the  cells  of  the  reticulum  are  only  2-3  mm.  in  height, 


474  DIGESTIVE    SYSTEM    OF   THE    SHEEP 

and  have  serrated  edges.  The  dorsal  part  of  this  sac  has,  in  the  vicinity  of  the 
rumino-reticular  orifice,  a  papillated  mucous  membrane  just  Ul^e  that  of  the 
rumen.  The  omasum  is  much  smaller  than  the  reticulum,  its  capacity  being 
only  about  one  pint.  It  is  oval  and  compressed  laterally.  It  is  situated  almost 
entirely  to  the  right  of  the  median  plane,  opposite  to  the  ninth  and  tenth  ribs, 


Fig.  407. — Cross-section  of  Sheep,  through  Ninth  Thoracic  Vertebra;  Anterior  View. 
1,  Cardia;  2,  oesophageal  groove;  S,  rumino-reticular  orifice;  4>  rumino-reticular  fold;  5,  dorsal  sac  of  rumen; 
6,  body  of  ninth  thoracic  vertebra;  7,  vena  hemiazygos;  S,  aorta;  9,  posterior  mediastinal  lymph  gland;  10,  10,  crura 
of  diaphragm;  77,  posterior  vena  cava;  i^,  portal  vein;  i?./.,  right  lung;  L.Z.,  left  lung;  S,  spleen;  L,  liver;  iJ,  reticu- 
lum (posterior  wall) .  Arrow  points  to  reticulo-omasal  orifice.  The  spleen  is  cut  so  obliquely  as  to  appear  much  thicker 
than  it  really  is. 


higher  than  in  the  ox,  and  has  no  contact  with  the  abdominal  wall.  It  is  related 
on  the  right  to  the  liver  and  gall-bladder,  on  the  left  to  the  rumen,  and  ventrally 
to  the  abomasum.  The  laminae  are  less  numerous  than  in  the  ox;  in  the  neck 
which  connects  the  omasum  with  the  reticulum  they  have  the  form  of  low,  thick 
ridges,    and   bear    long,    pointed,    horny  papillae.     The  abomasum   is  relatively 


DIGESTIVE    SYSTEM    OF   THE    SHEEP 


475 


larger  and  longer  than  in  the  ox.  Its  capacity  is  about  twice  that  of  the 
reticulum  and  averages  about  two  quarts  (ca.  1.75  to  2  liters).  The  blind 
anterior  end  Hes  almost  centrally  in  the  xiphoid  region,  in  relation  to  the  liver  and 
reticulum.  Its  body  extends  backward  a  little  ventral  to  and  almost  parallel 
with  the  right  costal  arch.  The  pylorus  is  usually  opposite  the  ventral  end 
of  the  eleventh  or  twelfth  intercostal  space.  At  the  reticulo-omasal  open- 
ing and  on  the  adjacent  part  of  the  laminae  of  the  omasum  are  large,  pointed, 
horny  papillse. 

The  general  arrangement  of  the  intestine  is  like  that  of  the  ox.     The  small 


Fig.  408.— Abdominal  Viscera  of  Sheep;  Superficial  Ventral  Vii 


intestine  is  about  80  feet  (ca.  24  to  25  m.)  long;  its  average  diameter  is  about  an 
inch  (ca.  2  to  3  cm.) ,  the  caliber  increasing  in  its  terminal  part,  where  a  very  extensive 
Peyer's  patch  is  found.  Duodenal  glands  occur  for  a  distance  of  two  feet  or  more 
(ca.  60-70  cm.)  beyond  the  pylorus.  The  caecum  is  about  10  inches  (ca.  25  cm.) 
long,  2  inches  (ca.  5  cm.)  wide,  and  has  a  capacity  of  about  a  quart  (ca.  1  liter); 
only  about  two  inches  (ca.  5  cm.)  of  it  is  free.  The  colon  is  about  15  feet  (ca.  4  to 
5  m.)  long.  Its  caliber  is  at  first  about  the  same  as  that  of  the  caecum,  but  dimin- 
ishes to  about  the  width  of  the  small  intestine. 

The  liver  weighs  about  20  to  25  ounces  (ca.  550  to  700  gm.).     It  lies  entirely 


476 


DIGESTIVE    SYSTEM    OF   THE   SHEEP 


to  the  right  of  the  median  plane.  The  parietal  surface  is  related  almost  exclusively 
to  the  right  part  of  the  diaphragm.  The  visceral  surface  presents  extensive  reticular 
and  abomasal  impressions,  and  a  small  omasal  impression  medial  to  the  portal 
fissure.  The  umbilical  fissure  is  deep  and  partially  divides  the  gland  into  two 
chief  lobes,  dorsal  and  ventral.  The  caudate  lobe  is  prismatic  and  blunt-pointed. 
The  oesophageal  notch  is  represented  by  a  slight  impression.  The  gall-bladder  is 
long  and  narrow.  The  bile-duct  joins  the  pancreatic  duct  to  form  a  common  bile- 
duct  (Ductus  choledochus  communis),  which  opens  into  the  duodenum  about  one 
foot  (ca.  30  cm.)  from  the  pylorus. 

The  pancreas  is  arranged  as  in  the  ox.  Its  duct  unites  with  the  bile- 
duct. 

The  spleen  (Fig.  405)  is  approximately  triangular,  with  the  angles  rounded  off; 


Renal  impression 


Caudate  lobe 


Posterior  vena 
cava 


Portal  vein 


Hepatic  artery 


Omasal  impres- 
sion 


Lesser  omentum, 


Reticular  imprcs- 


Bile-duct 


Cystic  duct 


Fig.  409 —Liver  of  Sheep,  Visceral  Surface;  Hardened  in  situ. 


the  wider  end  or  base  is  dorsal.  It  weighs  about  three  or  four  ounces  (ca.  100  grams). 
Its  length  is  about  five  to  six  inches  (ca.  12  to  15  cm.),  and  its  greatest  width  three 
to  four  inches  (ca.  7.5-10  cm.).  The  long  axis  is  oblique,  and  corresponds  to  a  line 
drawn  from  the  vertebral  end  of  the  last  rib  to  about  the  middle  of  the  tenth  inter- 
costal space.  The  parietal  surface  is  convex  and  is  related  to  the  diaphragm,  to 
which  rather  more  than  the  anterior  third  is  adherent;  when  hardened  in  situ,  it 
often  shows  impressions  of  the  upper  parts  of  the  last  three  ribs.  The  visceral 
surface  is  concave,  and  its  anterior  half  is  attached  to  the  dorsal  curvature  of  the 
rumen.  The  borders  are  thin,  the  posterior  one  often  being  crenated.  The  dorsal 
end  or  base  is  attached  to  the  left  crus  of  the  diaphragm  under  the  last  two  ribs; 


DIGESTIVE    SYSTEM    OF   THE    PIG THE    MOUTH 


477 


Fig.  410. — Liver  of  Sheep,  Parietal  Surface;    Hardened  in  situ. 
1,  Posterior  vena  cava;  2,  falciform  ligament;  3,  gall-bladder;  4,  umbilical  fissure. 

it  usually  extends  about  an  inch  (ca.  3  cm.)  behind  the  last  rib.  The  hilus  is  on  the 
visceral  surface,  close  to  the  anterior  basal  angle;  it  is  a  round  depression,  not  a 
groove.  The  ventral  end  is  narrower  and  thinner  than  the  base;  it  is  usually 
situated  opposite  the  tenth  intercostal  space  or  eleventh  rib,  a  little  above  its  middle. 


DIGESTIVE  SYSTEM  OF  THE  PIG 
THE  MOUTH 

The  rima  oris  is  extensive,  the  angles  of  the  mouth  being  situated  far  back. 
The  upper  lip  is  thick  and  short,  and  is  blended  with  the  snout;  the  lower  lip  is 
small  and  pointed.     The  labial  glands  are  few  and  small. 

The  mucous  membrane  of  the  cheeks  is  smooth.  The  buccal  glands  are 
compactly  arranged  in  two  rows  opposite  the  cheek  teeth.  The  parotid  duct 
opens  opposite  the  fourth  or  fifth  cheek  tooth. 

The  hard  palate  is  long  and  narrow;  it  is  marked  by  a  median  furrow,  on  each 
side  of  which  are  twenty  or  more  ridges.  On  its  anterior  part  there  is  a  long  narrow 
prominence,  the  incisive  papilla,  at  the  posterior  part  of  which  the  incisive  or  naso- 
palatine ducts  open.  There  is  a  round  prominence  in  front  of  the  first  pair  of 
incisors. 

The  soft  palate  is  wery  thick;  its  length  in  an  animal  of  medium  size  is  about 
two  and  a  half  inches  (ca.  5  cm.).     Its  chrection  almost  continues  that  of  the  hard 


478 


DIGESTIVE    SYSTEM    OF    THE    PIG 


palate,  i.  e.,  it  is  nearly  horizontal.  It  extends  to  the  middle  of  the  oral  surface 
of  the  epiglottis.  It  has  in  many  cases  a  small  median  prolongation  termed  the 
uvula.  The  oral  surface  presents  a  median  furrow,  on  either  side  of  which  is  an 
oval  raised  area,  marked  by  numerous  crypts;  these  elevations  are  the  tonsils. 
Tonsillar  tissue  also  occurs  in  the  lateral  walls  of  the  isthmus  faucium  and  the  root 
of  the  tongue. 

The  tongue  is  long  and  narrow  and  the  apex  is  thin.     Two  or  three  vallate 


Fig.  411. — Hard  Palate  of  Young  Pig. 

1,  Papilla  incisiva;  2,  openings  of  ductus  in- 
cisivi;  3,  raph6  of  palate;  a,  incisor  teeth;  b,  canine 
tooth;    c,    premolar  teeth;    d,  molar  teeth. 


Fig.  412. — Tongue  of  Pig. 
1,  Apex;  2,  dorsum;  3,  root;  a,  orifices  of  ducts  of 
lingual  glands;  b,  papillae  of  root;  c,  vallate  papilla  (not 
really  so  distinct  as  in  figure);  rf,  fohate  papilla;  e,  fungi- 
form papillae;  /,  epiglottis  (pulled  back);  g,  median  glosso- 
epiglottic  fold.     (EUenberger-Baum,  Anat.  d.  Haustiere.) 


papillae  are  present.  The  fungiform  papillse  are  small  and  are  most  numerous 
laterally.  The  filiform  papillae  are  soft  and  very  small.  On  the  root  there  are 
soft,  long,  pointed  papillae,  directed  backward.     Foliate  papillae  are  also  present. 

There  is  a  well-marked  median  glosso-epiglottic  fold,  on  either  side  of  which  is 
a  depression  (Vallecula  epiglottica) .     The  frenum  linguae  is  double. 

The  dental  f ormula^  of  the  pig  is : 


/  3  1  4  3\ 
I  I  -  C  -  P  -  M  -  ) 
V    3      1     4       3/ 


21  I-C-P-M-l  =  44 
V    3      1     4       3/ 

Several  figures  in  the  osteology  also  illustrate  the  teeth. 


THE    MOUTH 


479 


The  formula  for  the  temporary  teeth  is : 

/      3        1        4\ 

2  (  Di-Dc-Dp-  I 

V      3        1        4/ 


32 


The  upper  incisors  are  small;  they  are  separated  from  each  other  by  spaces, 
and  from  the  canines  liy  a  larger  interval.  The  first  incisors  are  the  largest;  they 
are  flattened  and  strongly  curved,  and  the  crowns  are  convergent;    they  have  no 


Fig.  413. — Skull  of  Pig  about  a  Year  and  a  Half  Old,  Sculptured  to  Show  the  Embedded  Parts  of  the  Teeth. 
11-3,  Incisors;    C,  canines;   Pl-4,  premolars;    Ml-3,  molars.     The  third  molar  has  not  erupted  and  its  roots  are  not 

yet  formed. 


Ce77ient  Enamel  Dentine 


distinct  neck.     The  convex  labial  surface  has  an  extensive  covering  of  enamel,  but 
the  latter  covers  only  a  small  marginal  area  on  the  lingual  surface.     The  second  are 
much  shorter  and  are  only  slightly  curved ;  they  have  a  short  flattened  crown  and 
a  rounded  root.     The  third  incisors  are  much  smaller,  are 
flattened  laterally,  and  have  three  small  eminences  on  the 
crown.     The  lower  incisors  are  almost  horizontal  and  are 
convergent  and  close  together.     The  first  and  second  are 
about  equal  in  size,  are  rod-like,  very  slightly  curved,  and 
deeply  implanted  in  the  jaw.     The  labial  surface  is  slightly 
convex,  the  lingual  concave  and  marked  near  its  extremity 
by  a  ridge.     The  third  incisor  is  much  shorter  and  is  some- 
what flattened ;  it  has  a  short  narrow  crown  and  a  distinct 
neck. 

The  canine  teeth  or  tusks  of  the  male  are  greatly  de- 
veloped and  project  out  of  the  mouth.     The  upper  canine  of  the  boar  may  be  three 
or  four  inches  (ca.  8  to  10  cm.)  long.     The  crown  is  conical  and  is  curved  some- 
what backward  and  outward;  the  embedded  part  is  curved  and  has  a  large  pulrt 


Fig.  414. — Cross-section  of 
Lower  Canine  TooTff 
OF  Pig. 

c,  Pulp  cavity. 


480 


DIGESTIVE    SYSTEM    OF    THE    PIG 


cavity.  The  lower  canine  may  reach  a  length  of  eight  inches  or  more  (ca.  20  cm.) ; 
the  crown  is  prismatic  and  is  curved  backward  and  outward  in  front  of  the  upper 
one,  so  that  the  friction  between  the  two  keeps  a  sharp  edge  on  the  lower  tooth. 
In  the  sow  they  are  much  smaller.  ^ 

The  cheek  teeth  increase  in  size  from  before  backward.  They  have  (with 
certain  exceptions  noted  below)  complex  tuberculate  crowns;  the  term  bunodont 
is  applied  to  this  condition,  as  distinguished  from  the  lophodont  and  selenodont 
structure  in  horses  and  cattle,  in  which  there  are  prominent  ridges  of  enamel. 


Fig.  415. — Superfici.\l  Glands  of  Head  of  Pig. 
a,  Parotid  gland;    a',  a",  cervical  and  mandibular  angles  of  a;    b,  c,  ventral  and  dorsal  buccal  glands;   d,  labial 
glands;    e,  masseter  muscle;  /,  /',  lymph  glands;    g,  dotted  line  indicating  outline  of  mandibular  gland,  which  is  con- 
cealed.    (EUenberger-Baum,  Anat.  d.  Haustiere.) 


They  are  short-crowned  teeth  with  a  distinct  neck  and  round,  pointed  roots.  The 
first  tooth  in  each  jaw  is  small,  simple,  and  appears  only  once;  in  the  lower  jaw  it  is 
near  the  canine;  in  the  upper,  near  the  second  cheek  tooth.^  The  next  two  teeth 
are  larger,  laterally  compressed,  and  sectorial.  The  fourth  tooth  below  is  larger, 
but  otherwise  like  the  preceding  ones,  while  the  upper  one  is  much  wider  and  is 
tuberculate.  The  first  premolar  has  two  roots,  the  others  three  or  four.  The 
molars  have  four  roots,  but  the  anterior  pair  may  be  largely  fused. 

1  The  canines  of  the  pig  are  "permanent  pulp"  teeth  and  therefore  capable  of  continued 
growth,  and  are  without  roots  in  the  strict  sense.  The  convex  surface  is  covered  with  enamel,  the 
concave  with  cement. 

2  It  is  often  absent  in  the  lower  jaw. 


THE   MOUTH 


481 


Fig.  416. — Dissection  op  Mouth  and  Pharyngeal  Region  of  Pig. 
1,  Hard  palate;  2,  tongue  showing  distinctly  fungiform  papilla;  3,  foliate  papilla;  4,  lymph  nodules  of  soft  palate; 
5,  stylo-glossus  muscle,  out  of  which  a  portion  has  been  cut;  6,  hyo-glossus;  7,  genio-glossus;  8,  genio-hyoideus;  9, 
mylo-hyoideus  (reflected);  10,  stylo-hyoideus;  11,  great  cornu  of  hyoid  bone;  12,  tensor  palati;  13,  levator  palati; 
i>^,  pterygo- et  palato-pharyngeus;  /5,  stylo-pharyngeus;  i6,  cervico-hyoideus;  ^7,  sterno- et  omo-hyoideus;  18,  a\i- 
prapharyngeal  lymph  glands;   a,  bulla  ossea;   b,  paramastoid  process.     (EUenberger-Baum,  Anat.  d.  Haustiere.) 


The  average  periods  of  eruption  of  the  teeth  are  given  in  the  subjoined  table: 


Tooth 
Ii  .. 
I2    .. 

L  .. 
C  .. 
Pi  .. 
P2.. 

P3.. 

P4.. 

M,.. 

M2.. 

Ms.. 

31 


Eruption  Change 

2  to  4  weeks 12  months 

/  upper  2  to  3  months 

\  lower  1 H  to  2  months 16  to  20  months 

Before  birth 8  to  10  months 

Before  birth 9  to  10  months 

5  months 

5  to  7  weeks 1 

upper  4  to  8  days 

lower  2  to  4  weeks J-  12  to  15  months 

upper  4  to  8  days 

\  lower  2  to  4  weeks 

4  to  6  months 
8  to  12  months 
18  to  20  months 


482  DIGESTIVE    SYSTEM    OF    THE    PIG 

The  parotid  gland  is  large  and  distinct]}^  triangular.  It  extends  very  little  on 
to  the  masseter  muscle,  and  its  upper  angle  does  not  quite  reach  the  base  of  the  ear. 
It  is  pale  in  color,  and  is  embedded  in  fat  in  animals  in  good  condition.  On  its  deep 
face  are  several  large  subparotid  lymph  glands,  some  of  which  are  only  partially 
covered  bj^  the  parotid.  The  parotid  duct  arises  on  the  deep  face,  has  a  course 
similar  to  that  of  the  ox,  and  perforates  the  cheek  opposite  the  fourth  or  fifth  upper 
cheek  tooth.  Small  accessory  parotid  glands  (Glandulae  parotidese  accessorise)  may 
be  found  along  the  course  of  the  duct. 

The  mandibular  or  submaxillary  gland  is  small,  reddish  in  color,  and  oval  in 
outline;  it  is  covered  by  the  parotid.  Its  superficial  face  is  convex,  and  is  marked  by 
rounded  prominences.  From  its  deep  face  a  narrow  process  extends  forward  about 
two  or  three  inches  (ca.  5  to  7.5  cm.)  beneath  the  mylo-hyoideus  muscle  along  with 
the  duct.     The  latter  opens  near  the  frenum  linguae,  but  there  is  no  papilla. 

The  sublingual  gland  has  an  arrangement  similar  to  that  of  the  ox.  The  pos- 
terior part  (Glandula  sublingualis  grand icanalaris)  is  reddish-yellow  in  color,  and 
is  about  two  inches  (ca.  5  cm.)  long  and  half  an  inch  wide;  its  posterior  end  is  in 
relation  to  the  mandibular  gland  and  its  duct.  The  anterior  part  (Gl.  sublingu- 
alis parvicanalaris)  is  much  larger,  being  two  or  three  inches  (ca.  5  to  7  cm.)  long 
and  al)out  twice  the  width  and  thickness  of  the  posterior  part.  All  or  most  of  the 
ducts  from  the  posterior  part  unite  to  form  the  ductus  sublingualis  major,  which 
opens  near  the  ductus  mandibularis.  Eight  or  ten  ductus  sublinguales  minores 
convey  the  secretion  from  the  anterior  part  through  the  floor  of  the  mouth. 


Fig.  417. — Sagittal  Section  of  Pharyngeal  Region  of  Pig,  Partlt  Schematic. 
7,  Palatine  bone;  a^,  sphenoid  bone;  ^',  sphenoidal  sinus;  ^",  occipital  bone;  3,  epiglottis;  4.  arytenoid  cartilage; 
6,  thyroid  cartilage;  6,  root  of  tongue;  7,  mouth  cavity;  S,  isthmus  faucium;  9,  hard  palate;  10,  septum  nasi;  //, 
ventral  muscles  of  head;  a,  soft  palate;  a',  free  edge  of  a;  b,  dorsal  wall  of  pharynx;  c,  fornix  of  pharynx;  d,  cavity  of 
larynx;  e,  3,  naso-pharynx;  /,  oro-pharynx;  A,  posterior  pillar  of  soft  palate;  i,  dotted  line  indicating  lateral  boundary 
between  nasal  cavity  and  pharynx;  A,  aditus  laryngis;  /,  aditus  cesophagi;  ?n,  Eustachian  orifice;  re,  pharyngeal  recess; 
o,  posterior  naris.      (.After  Ellenberger,  in  Lieisering's  Atlas.) 


THE  PHARYNX 
The  pharjmx  presents  in  its  posterior  part  a  median  cul-de-sac  about  an  inch 
and  a  half  (ca.  3  to  4  cm.)  long,  which  is  situated  between  the  ventral  straight 
muscles  of  the  head  and  the  origin  of  the  oesophagus;  this  is  termed  the  diverticu- 
lum pharyngeum.  Its  ventral  margin  is  formed  by  the  junction  of  the  posterior 
pillars  of  the  soft  palate,  which  contain  muscular  tissue  derived  from  the  palatinus 
and  palato-pharyngeus.  The  fornix  of  the  pharynx  is  divitled  by  a  median  fold  of 
mucous  membrane  which  is  a  direct  continuation  of  the  septum  nasi.  On  either 
side  of  this  is  an  infundibulum  in  which  the  Eustachian  tube  opens. 


THE    (ESOPHAGUS THE    STOMACH  483 


THE  (ESOPHAGUS 
The  oesophagus  is  short  and  nearly  straight.  It  has  (according  to  Rubeh)  a 
potential  caliber  in  the  adult  of  nearly  3  inches  (ca.  7  cm.)  at  either  end,  and  about 
1^  inches  (ca.  4.2  cm.)  in  its  middle  part.^  The  muscular  coat  is  striated,  except 
near  the  cardia,  where  the  deep  part  is  unstriped.  There  are  numerous  tubulo- 
alveolar  glands  in  the  anterior  half  of  the  tube;  further  back  they  occur  in  decreas- 
ing numbers.     Many  lymph  nodules  and  much  lymphoid  tissue  are  present. 


THE  STOMACH 
The  stomach  is  large;    its  average   capacity  is  about  l^^  to  2  gallons   (ca. 
5.7  to  8  liters).     When  full,  its  long  axis  is  transverse  and  its  greater  curvature 
extends  backward  on  the  floor  of  the  abdomen  a  little  further  than  a  point  midway 


Durrti- 
culuiiL 


O'Jsophagus 


Pylorus 


Fig.  418. — Stomach  of  Pig;    Parietal  Surface.  Fig.  419. — Stomach  of  Pig;  Visceral  Surface. 

The  organ  contained  a  rather  small  amount  of  ingesta  Organ  was  fixed  in  situ  and  is  somewhat  contracted, 

and  hence  is  somewhat  contracted. 

between  the  xiphoid  cartilage  and  the  umbilicus.  The  left  part  is  large  and  rounded, 
while  the  right  part  (Pars  pylorica)  is  small,  and  bends  sharply  upward  to  join  the 
small  intestine.  The  parietal  surface  faces  chiefly  forward,  and  is  related  to  the 
liver  and  diaphragm.  The  visceral  surface  faces  chiefly  backward,  and  is  related 
to  the  intestine,  greater  omentum,  mesentery,  and  pancreas.  The  greater  cur- 
vature is  related  to  the  diaphragm,  spleen,  liver,  and  abdominal  floor.  The 
pyloric  end  lies  against  the  right  lateral  lobe  of  the  liver,  about  opposite  to  the  middle 
of  the  next  to  the  last  intercostal  space.  The  left  extremity  is  opposite  to  the  last 
intercostal  space  or  preceding  rib,  and  is  related  to  the  dorsal  end  of  the  spleen  and 
the  left  extremity  of  the  pancreas;  it  presents  a  flattened  conical  blind  pouch,  the 
diverticulum  ventricuU,  the  apex  of  which  projects  backward.  The  oesophagus 
joins  the  stomach  very  obliquely,  almost  in  the  median  plane,  and  about  three  or 
four  inches  (ca.  8  to  10  cm.)  ventral  to  the  twelfth  thoracic  vertebra.     The  cardiac 

^  It  is  usually  stated  that  the  cardiac  end  is  funnel-shaped,  but  it  is  not  so  in  formalin-hardened 
cadavers  nor  in  frozen  sections.  The  hiatus  oesophagus  is  a  long  slit  in  the  right  crus  of  the  dia- 
phragm, and  the  terminal  part  of  the  oesophagus,  which  lies  in  it,  is  flattened  transversely. 


484 


DIGESTIVE    SYSTEM    OF    THE    PIG 


opening  is  slit-like  and  is  bounded  above  and  to  the  left  by  a  fold  which  contains  a 
thickening  of  the  internal  oblique  layer  of  the  muscular  coat.  The  opening  into 
the  diverticulum  is  situated  above  and  a  little  to  the  left  of  the  cardia;   it  is  trans- 


FiG.  421. — Everted  Stomach  of  Pig,  from  which  the 
Mucous  Membrane  has  been  Removed. 


Fig.  420. — Visceral  Surface  of  Stomach  of  Pig, 
from  which  the  Serous  Coat  has  been  Re- 
moved. 

O,  (Esophagus;  D,  duodenum;  Di,  diverticulum;  a,  a',  a",  a"  ,  longitudinal  fibers;  b,  circular  fibers;  c,  external 
oblique  fibers;  c',  internal  oblique  fibers;  c",  cardiac  loop;  d,  fibers  which  connect  branches  of  cardiac  loop;  /,  fold  at 
entrance  to  diverticulum;   p,,  pyloric  sphincter;    p',  pyloric  prominence.      (Ellenberger-Baum,  Anat.  d.  Haustiere.) 


versely  oval,  and  is  bounded  (except  laterally)  by  a  thick  fold  which  contains 
spirally  arranged  muscular  fibers.  The  mucous  membrane  may  be  divided  into 
four  regions  (Fig.  422).     Over  a  quadrilateral  area  around  the  cardia  (about  one 


Fig.  422. — Diagram  of  Zones  of  Mucous  Membrane  of  Stomach  of  Pig. 


inch  on  the  right  and  two  or  three  inches  on  the  left  side  of  the  orifice)  it  is  oesopha- 
geal in  character,  and  presents  a  number  of  folds.  A  sharp  line  of  demarcation 
separates  this  from  the  rest  of  the  mucous  membrane,  which  is  soft  and  glandular. 
The  cardiac  gland  region  is  pale  gray  in  color  and  thin  (ca.  0.5  to  1  mm.) ;  it  extends 


THE    STOMACH 


485 


about  to  the  middle  of  the  stomach.  The  fundus  gland  region  is  readily  distin- 
guished by  its  thickness  (ca.  3  mm.)  and  its  brownish-red,  mottled  appearance.^ 
The  fourth  or  pyloric  region  is  pale,  thinner  than  the  preceding,  and  presents  a 
number  of  irregular  folds.^  At  the  pylorus  a  remarkable  prominence  (Torus  pylo- 
ricus)  projects  from  the  wall  of  the  lesser  curvature  and  diminishes  considerably 
the  size  of  the  orifice.     It  is  about  an  inch  and  a  half  (ca.  3  to  4  cm.)  long  and 


The  greater  omenturi 


Fig.  423. — Abdominal  Viscera  of  Pig;  Ventral  View. 
has  been  removed.     B,  urinary  bladder;    G,  gall-bladder;    A',  xiphoid  cartilage.     Arrows  in- 
dicate course  of  coils  of  colon.     The  spleen  was  contracted. 


nearly  half  an  inch  (ca.  1  cm.)  high.  Sometimes  it  is  a  grooved  ridge;  in  other 
cases  it  has  the  form  of  a  rounded  eminence  attached  by  a  pedicle  to  the  wall.  It 
consists  largely  of  fat,  but  fibers  from  the  circular  muscular  coat  extend  into  it. 
The  arrangement  of  the  muscular  coat  is  shown  in  Figs.  420,  421. 

1  It  will  be  noted  that  the  fundus  gland  region  does  not  extend  up  to  the  lesser  curvature; 
here  the  cardiac  gland  region  joins  the  pyloric. 

2  Microscopic  examination  shows  that  these  regions  are  not  sharply  marked  off  from  each 
other;  instead,  there  are  intermediate  zones  in  which  glands  of  both  the  adjacent  regions  are 
present,  and  also  glands  of  intermediate  histological  character. 


486  DIGESTIVE   SYSTEM    OF   THE    PIG 

THE  INTESTINE 

The  intestine  is  about  fifteen  times  the  length  of  the  body. 
The  small  intestine  is  50  to  65  feet  (ca.  15  to  20  m.)  long.     The  mesentery  of 
about  the  first  two  feet  (ca.  60  cm.)  is  two  to  two  and  a  half  inches  (ca.  5  to  6  cm.) 


Fig.  424. — Diagram  of  Caecum  and  Colon  of  Pig. 
Coils  of  colon  have  been  pulled  apart. 


long;  this  part  may  be  termed  duodenum.  The  duodenum  turns  sharply  medially 
on  the  visceral  surface  of  the  liver  to  the  right  of  the  portal  fissure.  It  then  passes 
backward,  in  relation  to  the  medial  part  of  the  right  kidney  dorsally  and  the  colon 
ventrally,  and  about  the  middle  of  the  sublumbar  region  turns  across  the  median 


Fig.  425. — Ileo-c^cal  Opening  of  Pig, 
1,  Ileo-caecal  opening;  2,  2,  frenulum  ilei. 


Fig.  426. — Solitary    Nodules  op  Large  Intestine 
of  Pig.     (EUenberger-Baum,  Anat.  d.  Haustiere.) 


plane  and  runs  forward  to  be  continued  by  the  mesenteric  part.  The  right  end  of 
the  pancreas  is  attached  to  the  first  part,  and  here  the  pancreatic  duct  opens  into 
the  bowel.  The  remainder  of  the  bowel  (Jejuno-ileum)  has  a  mesentery  about  six 
to  eight  inches  (ca.  15  to  20  cm.)  long,  which  is  thick  and  contains  a  quantity  of  fat, 


THE    INTESTINE 


487 


and  numerous  large  lymph  glands  at  its  root;  the  root  is  attached  in  the  sublumbar 
region  behind  the  stomach  and  blends  here  with  the  mesentery  of  the  large  intestine. 
The  mesenteric  part  is  arranged  in  close  coils  and  lies  mainly  above  the  colon  and 
caecum,  from  the  stomach  to  the  pelvis;  many  coils  lie  against  the  right  flank  and 
on  the  posterior  part  of  the  floor  of  the  abdomen.  The  opening  of  the  bile  duct  is 
about  one  or  two  inches  (ca.  2.5  to  5  cm.)  from  the  pylorus,  and  that  of  the  pan- 
creatic duct  about  six  inches  (ca.  15  cm.)  beyond  it.  Aggregated  lymph  nodules 
or  Peyer's  patches  and  solitary  nodules  are  numerous  and  very  distinct.  The 
patches  are  usually  band-like  and  prominent;  their  number  has  been  found  to  vary 
from  16  to  38.  They  begin  8  to  20  inches  (ca.  20-50  cm.)  from  the  pylorus.  The 
last  long  one  is  continued  a  variable  distance  in  the  caecum.     The  solitary  nodules 


Fig.  427. — Cecum  and  Colon  of  Pig;  Left  Ventral  View. 
1,  Apex  of  spiral  coil  of  colon;    2,  apex  of  caecum. 


are  distinct  (except  in  the  duodenum),  but  are  only  about  a  millimeter  high.     The 
duodenal  glands  extend  some  10  to  16  feet  (ca.  3-5  m.)  from  the  pylorus. 

The  large  intestine  is  about  12  to  15  feet  (ca.  4  to  4.5  meters)  in  length,  and  is 
for  the  most  part  much  wider  than  the  small  intestine;  it  is  connected  by  a  mesen- 
tery with  the  dorsal  abdominal  wall  between  the  kidneys.  The  caecum  is  cylin- 
drical, about  8  to  12  inches  (ca.  20  to  30  cm.)  long,  and  3  to  4  inches  (ca.  8  to  10  cm.) 
wide.  It  lies  against  the  upper  and  anterior  part  of  the  left  flank,  and  extends 
ventrally,  backward,  and  medially  behind  the  coiled  part  of  the  colon,  so  that  its 
ventral  blind  end  usually  lies  on  the  floor  of  the  abdomen,  near  the  median  plane, 
and  at  a  variable  point  between  the  umbilicus  and  the  pelvic  inlet  (Fig.  423).  Its 
dorsal  end  is  directly  continued  by  the  colon,  the  line  of  demarcation  being  indi- 
cated by  the  termination  of  the  small  intestine.     The  ileum  joins  the  caecum 


488  DIGESTIVE    SYSTEM    OF    THE    PIG 

obliquely  and  projects  considerably  into  the  latter.  A  fold  of  mucous  membrane 
(Frenulum  ilei)  passes  from  each  side  of  the  ileo-csecal  opening.  The  colon  has  at 
first  about  the  same  caliber  as  the  caecum,  but  becomes  gradually  smaller.  It  lies 
chiefly  to  the  left  of  the  median  plane,  behind  the  stomach.  Most  of  it  is  arranged 
in  three  close,  double  spiral  coils  in  the  mesentery,  in  relation  with  the  floor  of  the 
abdomen  ventralh^,  the  stomach  and  liver  in  front,  the  caecum  and  small  intestine 
behind,  and  the  small  intestine  on  the  right.  On  emerging  from  this  spiral  laby- 
rinth it  passes  at  first  forward  in  the  sublumbar  region  to  the  right  of  the  median 
plane,  and,  on  reaching  the  stomach  and  right  end  of  the  pancreas,  turns  to  the  left. 
It  then  passes  backward,  on  the  ventral  surface  of  the  pancreas,  and  in  relation  to 
the  medial  part  of  the  left  kidney,  inclines  medially,  and  is  continued  at  the  pelvic 
inlet  by  the  rectmn.  This  terminal  part  is  closely  attached  by  a  short  mesentery  to 
the  sublumbar  region.  The  rectum  is  usually  surrounded  by  a  quantity  of  fat. 
The  caecum  has  three  longitudinal  muscular  bands  and  three  rows  of  sacculations, 
which  are  continued  a  short  distance  on  the  colon.  The  spiral  colon  has  two  bands 
and  two  series  of  sacculations,  which,  however,  gradually  disappear  in  the  centrif- 
ugal part.  The  solitary  nodules  are  numerous,  and  appear  as  round  prominences, 
2-3  mm.  in  diameter,  often  %vith  a  crater-like  depression.  The  last  Peyer's  patch 
of  the  small  intestine  is  continued  a  variable  distance  in  the  caecum,  and  there  are 
often  patches  in  the  first  part  of  the  colon. 


THE  LIVER 

The  liver  is  relatively  large,  its  average  weight  in  the  adult  being  about  four 
pounds  (ca.  1.5-2  kg.).  It  is  thick  centrally,  but  the  circumference  is  thin.  It  is 
divided  by  three  deep  interlobar  incisures  into  four  principal  lobes — bright  lateral, 
right  central,  left  central,  left  lateral ;  the  last  of  these  is  usually  considerably  the 
largest.  On  the  upper  part  of  the  right  lateral  lobe,  is  the  caudate  lobe,  which  is 
clearly  marked  off  by  a  fissure  and  is  often  partially  subdivided  by  a  secondary 
fissure.  That  part  of  the  right  central  lobe  which  lies  below  the  portal  fissure  and 
to  the  left  of  the  gall-bladder  and  cystic  duct  is  homologous  with  the  quadrate  lobe 
of  man.  Much  the  greater  part  is  to  the  right  of  the  median  plane.  The  parietal 
surface  is  extremely  convex  in  conformity  with  the  curvature  of  the  diaphragm,  to 
which  it  is  chiefly  related.^  A  small  part  of  the  surface  is  in  contact  with  the 
abdominal  floor  in  the  xiphoid  region  and  ventral  to  the  right  costal  arch.  Its 
most  anterior  part  reaches  to  a  transverse  plane  through  the  ventral  part  of  the 
sixth  rib  or  intercostal  space.  The  visceral  surface  is  deeply  concave;  most  of  it 
is  related  to  the  stomach,  for  which  there  is  a  correspondingly  large  and  deep  gastric 
impression.  There  may  be  a  duodenal  impression  on  the  upper  part  of  the  right 
lateral  lobe,  but  no  renal  impression  exists,  as  the  right  kidney  does  not  touch  the 
liver.  The  fossa  for  the  gall-bladder  (Fossa  vesicae  felleae)  is  mainly  on  the  right 
central  lobe,  but  also  in  part  on  the  adj  acent  surface  of  the  left  central  lobe.  The  pos- 
terior vena  cava  enters  the  dorsal  border  of  the  caudate  lobe  and  soon  becomes  entirely 
embedded  in  the  gland  substance,  emerging  only  at  its  passage  through  the  dia- 
phragm. The  oesophageal  notch  is  large  and  is  occupied  mainly  by  the  large  right 
crus  of  the  diaphragm.  The  right  lateral  border  extends  backward  to  the  upper 
part  of  the  last  intercostal  space.  The  left  lateral  border  is  opposite  the  ninth 
intercostal  space  and  eighth  rib.  The  ventral  border  lies  on  the  abdominal  floor 
a  short  distance  (ca.  3-5  cm.)  behind  the  xiphoid  cartilage. 

The  coronary  ligament  resembles  that  of  the  horse.  The  falciform  ligament  is 
very  short  or  absent  in  the  adult,  and  is  attached  to  the  diaphragm  just  below  the 

^  The  description  here  given  is  based  on  the  appearance  of  the  organ  as  hardened  in  situ, 
which  differs  radically  from  that  of  the  soft  organ.  It  also  differs  much  in  shape  in  young  and 
adult  subjects. 


THE    LIVER 


489 


490 


DIGESTIVE    SYSTEM    OF   THE    PIG 


foramen  vense  cavae.     The  round  ligament  is  present  in  the  young  subject.     Neither 
lateral  nor  caudate  ligaments  are  present. 

The  gall-bladder  is  attached  in  the  fossa  vesicae  felleae;    its  fundus  does  not 


Fig.  430. — Projection  of  Visceba  of  Pig  on  Bodt-wall;  Left  Side. 
D,  Costal  line  of  diaphragm;    U,  ureter;    V.S.,  vesicula  seminalis;   B.g.,  bulbo-urethral  gland;  P,  penis. 

reach  to  the  ventral  border.  The  cystic  duct  joins  the  hepatic  duct  at  an  acute 
angle  immediately  after  the  emergence  of  the  latter  from  the  portal  fissure.  The 
bile  duct  (Ductus  choledochus)  opens  at  the  papilla  duodeni  about  one  or  two  inches 
(ca.  2.5  to  5  cm.)  from  the  pylorus;    an  ampulla  may  be  formed. 


Fig.  431. — Projection  of  Viscera  of  Pig  on  Body-wall;  Right  Side. 

D,  Costal  line  of  diaphragm;  O,  ovary.     The   pancreas  and  duodenum  are  not  in  contact  with  the  flank,  as  would 

naturally  be  inferred  from  this  figure,  but  are  situated  more  medially  and  are  covered  laterally  by  small  intestine. 


Owing  to  the  large  amount  of  interlobular  tissue,  the  lobules  are  mapped  out 
sharply;  they  are  polyhedral  in  form,  and  are  1  to  2.5  mm.  in  diameter.  For  the 
same  reason  the  gland  is  much  less  friable  than  that  of  the  other  animals,  from  which 
it  is  easily  distinguished. 


DIGESTIVE   SYSTEM   OF   THE    DOG — THE   MOUTH 


491 


THE  PANCREAS 
The  pancreas  extends  across  the  dorsal  wall  of  the  abdominal  cavity  behind 
the  stomach.  It  is  triradiate  or  triangular.  The  right  extremitj^  is  attachetl  to  the 
first  curve  (Flexura  portalis)  of  the  duodenum,  and  here  the  duct  passes  to  the 
bowel.  The  left  extremity  is  related  to  the  left  extremity  of  the  stomach,  the 
dorsal  end  of  the  spleen,  and  the  anterior  pole  of  the 
left  kidney.  The  middle  or  posterior  extremity  or 
lobe  is  practically  median  and  is  related  to  the  portal 
vein  and  the  root  of  the  mesentery.  The  pancreatic 
duct  passes  from  the  right  extremity  directly  through 
the  duodenal  wall,  opening  about  four  or  five  inches 
(ca.  10-12  cm.)  from  the  pylorus.  The  interlobular 
tissue  usually  contains  a  good  deal  of  fat. 


THE  SPLEEN 

The  spleen  is  long  and  narrow.  Its  long  axis  is 
nearly  dorso-ventral  in  direction,  and  is  curved  to  con- 
form to  the  left  part  of  the  greater  curvature  of  the 
stomach.  The  dorsal  end  lies  under  the  vertebral 
ends  of  the  last  three  ribs;  it  is  related  to  the 
stomach  in  front,  the  left  kidney  behind,  and  the 
left  extremity  of  the  pancreas  medially.  The  visceral 
surface  has  a  longitudinal  ridge  on  which  the  hilus  is 
situated;  this  divides  the  surface  into  nearly  equal 
gastric  and  intestinal  areas,  which  are  in  contact  with 
the  stomach  and  colon  respectively.  The  parietal 
surface  is  convex  and  is  related  to  the  left  lateral  and 
ventral  wall  of  the  abdomen.  The  ventral  end  is 
smaller  than  the  dorsal  one;  it  lies  on  the  abdom- 
inal floor,  usually  in  the  umbilical  region.  The  spleen 
is  attached  so  loosely  to  the  stomach  that  it  may  be 
regarded  as  being  intercalated  in  the  great  omentum. 
In  large  subjects  it  may  reach  a  length  of  about  25 
inches  (ca.  60  cm.)  and  a  width  of  3  to  4  inches  (ca.  8 
to  10  cm.),  and  a  weight  of  10-15  ounces  (ca.  350  gm.). 


The  position  of  the  spleen  varies  according  to  the  fulness 
of  the  stomach  and  its  own  size.  The  dorsal  end  varies  little. 
But  the  ventral  end  has  a  wide  range,  as  might  be  expected ;  it 
may  be  in  contact  with  the  left  lobe  of  the  liver  or  may  be  cen- 
trally situated  just  in  front  of  the  umbilicus.  As  in  other  ani- 
mals, the  size  of  the  spleen  is  extremely  variable.     Even  in  a 

large  adult  it  may  be  only  a  little  more  than  a  foot  (ca.  35  cm.)  long,  two  and  a  half  inches  wide, 
and  weigh  six  or  seven  ounces  (ca.  200  gm.). 


Fig.  432. — Spleen  of  Pig;  Visceral 
Surface. 
1,  Dorsal  end;  2,  ventral  end;  3, 
stumps  of  splenic  vessels;   4,  gastric 
surface;   5,  hilus  with  vessels. 


DIGESTIVE  SYSTEM  OF  THE  DOG 

THE  MOUTH 

The  size  and  form  of  the  mouth  vary  greatly  in  different  breeds,  the  cavity 

being  in  some  long  and  narrow,  in  others  short  and  wide.     The  rima  oris  is  very 

extensive,  so  that  the  labial  commissure  is  opposite  the  third  or  fourth  cheek  tooth. 

The  lips  are  thin  and  mobile,  and  present  numerous  tactile  hairs.     The  upper  lip 


492 


DIGESTIVE    SYSTEM    OF  THE   DOG 


has  a  small,  central,  bare  area  which  forms  part  of  the  muzzle,  and  is  marked  by  a 
central  groove,  the  philtrum,  or  (as  in  the  bull-dog)  a  fissure,  giving  the  appearance 
of  harelip.  The  lateral  borders  of  the  lower  lip  are  flaccid  and  denticulated.  The 
mucous  membrane  is  usually  pigmented  and  forms  distinct  frena  labiorum.  The 
labial  glands  are  small  and  scanty. 

The  cheeks  are  loose  and  capacious,  and  their  mucous  lining  is  smooth  and 
more  or  less  pigmented.  The  parotid  duct  opens  usually  opposite  the  third  upper 
cheek  tooth.  Near  the  last  tooth  are  the  openings  of  the  four  or  five  ducts  from 
the  zygomatic  gland.     This  gland  may  be  regarded  as  the  homologue  of  the  dorsal 


Fig.  433.- 


-Palate  of  Dog. 

noved  by  sawing  through  the  i 


of  the  mandible  and  cutting 


The  lower  jaw  and  related  structures  have  been 
the  soft  structures  horizontally. 

1,  Raph^  of  palate;  2,  ridges  of  palate;  3,  papilla  incisiva;  4,  soft  palate;  5,  tonsil;  6,  meatus  naso-pharyngeus;  7, 
dorsal  wall  of  pharynx;  8,  parotid  gland;  9,  mandibular  gland;  10,  pharyngeal  lymph  gland;  11,  m.  occipito- 
mandibularis  (cut);  12,  m.  masseter  (cut);  13,  cheek  (cut);  14,  ramus  of  mandible  (section);  15,  parotid  lymph  gland; 
16,  carotid  artery;  I,  incisor  teeth;   C,  canine  tooth;   P,  premolar  teeth;    M,  molar  teeth. 


buccal  glands  of  the  other  animals;  it  will  be  described  later.  The  ventral  buccal 
glands  are  opposite  the  cheek  teeth  and  in  series  with  the  inferior  labial  glands. 

The  hard  palate  is  widest  between  the  fourth  pair  of  cheek  teeth.  It  has 
eight  to  ten  curved  ridges  on  either  side  of  the  median  raphe;  the  latter  may  be 
indistinct  or  scarcely  recognizable.  Behind  the  first  pair  of  incisor  teeth  is  the 
rounded  or  triangular  papilla  incisiva,  at  which  the  incisive  or  naso-palatine  ducts 
open.     The  mucous  membrane  is  usually  pigmented. 

The  soft  palate  (Figs.  433,  488)  is  thick,  except  at  its  margins.  In  the  resting 
state  of  the  parts  it  comes  in  contact  with  the  epiglottis. '^     Between  its  anterior  and 

1  It  is  usually  stated  that  it  is  in  contact  with  the  oral  surface  of  the  epiglottis,  but  the  epi- 
glottis may  be  ventral  to  the  soft  palate  (Fig.  488). 


THE    TEETH 


493 


posterior  pillars  on  either  side  is  a  marked  tonsillar 
fusiform  tonsil  is  situated;  this  is  reddish  in  color, 
about  an  inch  long,  and  is  largely  or  completely 
concealed  between  two  folds  of  mucous  membrane. 
The  posterior  pillar  is  double;  the  upper  fold  passes 
to  the  dorsal  wall  of  the  pharynx,  where  it  subsides; 
the  lower  fold  goes  to  the  side  of  the  epiglottis. 

The  tongue  is  wide  and  thin  in  front,  thicker 
posteriorly;  it  is  very  mobile.  It  is  not  pigmented, 
but  has  a  bright  red  color.  The  dorsum  is  marked 
by  a  median  groove  (Sulcus  medianus  linguae),  and 
is  thickly  beset  with  short,  pointed,  filiform  papillae, 
the  free  ends  of  which  are  directed  backward.  On 
the  root  there  are  long  conical  papillae  which  are 
soft,  and  point  backward;  similar  papillae  occur 
on  the  lateral  walls  of  the  isthmus  faucium.  The 
fungiform  papillae  are  small,  and  are  scattered  over 
the  dorsum  and  sides  of  the  tongue,  but  are  absent 
on  the  posterior  part  of  the  dorsum  and  on  the 
root,  where  the  conical  papillae  occur.  There  are 
usually  two  or  three  vallate  papillae  on  either  side 
on  the  posterior  part  of  the  dorsum,  where  the 
conical  papillae  begin.  Small  foliate  papillae  are 
also  present  just  in  front  of  the  anterior  pillars  of 
the  soft  palate ;  they  are  oval  and  are  crossed  by 
about  half  a  dozen  fine  fissures.  In  the  inferior 
part  of  the  tip  of  the  tongue  is  the  lyssa,  a  fusiform 
cord,  composed  of  fibrous  tissue,  muscular  tissue, 
and  fat.  In  large  dogs  it  is  about  two  inches  (ca. 
4  to  5  cm.)  long.  The  lingual  muscles  present  no 
remarkable  special  characters. 


THE  TEETH 

The  formula  of  the  permanent  teeth  is: 


sinus,  in  which  an  elongated, 


/  3  1  4  2\ 
(  I-C-P-M-  ) 
V    3      1     4      3/ 


42 


All  of  the  teeth  have  short  crowns  and  dis- 
tinct necks;  they  erupt  rapidly.  The  crowns  are 
white,  being  destitute  of  cement.^ 

The  incisors  are  placed  almost  vertically  and 
close  together  in  the  jaw  bones.  They  do  not  cor- 
respond to  an  opposing  tooth,  but  rather  to  parts 
of  two  teeth  of  the  other  jaw.  They  increase  in 
size  from  the  first  to  the  third.  The  crowns  are 
trituberculate,  the  central  projection  being  the 
largest.  The  labial  surface  is  convex;  the  lingual 
surface  is  slightly  concave,  and  is  marked  off  from 
the  neck  by  a  V-shaped  ridge,  the  cingulum.  The 
roots  are  narrow  transversely.  The  lower  incisors 
are  smaller  than  the  upper  ones.     One  or  two  supernumerary  teeth  may  be  present. 

The  canine  teeth  are  large,  conical,  and  curved.     The  upper  canine  is  separated 

1  Other  figures  which  illustrate  the  teeth  are  to  be  found  in  the  description  of  the  skull. 


Fig.  434. — Tongue,  Pharynx,  Larynx, 
ETC.,  OP  Dog;  Dorsal  View. 

The  pharynx  and  soft  palate  have 
been  cut  medially  and  reflected,  and  the 
oesophagus  cut  off. 

1,  Median  groove  of  tongue;  2,  long 
conical  papillae  of  root  of  tongue;  3,  val- 
late papillae;  4,  tonsil  (drawn  out  of  ton- 
sillar sinus;  5,  floor  of  pharynx  (promi- 
nence here  caused  by  cricoid  cartilage 
and  m.  crico-arytenoideus  dorsalis) ;  7, 
vestibule  of  larynx;  8,  epiglottis;  9,  ary- 
tenoid cartilage;  10,  trachea  (membran- 
ous part);  11,  11,  lateral  lobes  of  thyroid 
gland;  12,  12',  anterior  and  posterior  thy- 
roid vessels. 


494 


DIGESTIVE    SYSTEM    OF   THE   DOG 


from  the  corner  incisor  by  an  interval  into  which  the  lower  canine  is  received  when 
the  jaws  are  closed.^  The  lower  canine  is  close  to  the  corner  incisor.  The  root  is 
about  an  inch  (ca.  2  to  3  cm.)  long  and  is  flattened  laterally. 

The  cheek  teeth  are  typically  y,  but  in  brachycephalic  breeds  they  are  com- 
monly reduced  to  f,  and  in  extreme  cases  even  to  f .  The  reduction  occurs  at  either 
end  or  at  both  ends  of  the  series.-  The  first  tooth  appears  only  once.  The  fourth 
tooth  of  the  upper  row  and  the  fifth  of  the  lower  row  are  much  larger  than  the  rest, 
and  are  termed  sectorial  or  camassial  teeth.  From  these  the  teeth  diminish  in  size 
both  forward  and  backward.  The  upper  and  lower  teeth  do  not  correspond,  but 
rather  dovetail.     The  teeth  behind  the  sectorial  ones  are  tuberculate,  i.  e.,  have 


-Skull  of  Adult  St.  Bernard  Dog,  Sculptured  to  Show  the  Embedded  Parts  of  the  Teeth. 
11-3.  Incisors;  C,  canines;   Pi -4,  premolars;  Ml-3,  molars. 


rounded  eminences  on  the  masticatory  surface.  The  others  are  all  sectorial  in 
character,  i.  e.,  have  sharp-edged,  pointed  projections,  the  middle  one  being  the 
most  prominent.  The  premolars  are  laterally  compressed,  and  are  separated  by 
intervals  from  the  canines  and  from  each  other,  except  in  the  brachycephalic 
breeds.  The  upper  molars  have  wide,  somewhat  quadrangular  cro^vns,  and  three 
roots.  The  crown  of  the  upper  fourth  premolar  (Dens  sectorius)  is  divided  into 
two  pointed  lobes  and  has  an  antero-medial  tubercle;    it  has  three  roots.     The 

1  In  the  bull-dog,  which  is  very  prognathic  ("undershot"),  the  lower  canmes  are  opposite 
to  or  slightly  in  front  of  the  plane  of  the  upper  incisors,  and  the  upper  canines  are  about  opposite 
to  the  first  lower  cheek  teeth.  In  the  epignathic  ("overshot")  dachshund  the  lower  canines  are 
under  or  slightly  behind  the  upper  ones. 

-  Increase  in  number  also  occurs,  the  supernumerary  teeth  being  at  either  end  of  the  series. 
The  occurrence  of  a  third  upper  molar  is  not  rare. 


THE   SALIVARY    GLANDS 


495 


crown  of  the  first  lower  molar  (Dens  sectorius)  is  compressed  laterally  and  has  two 
pointed,  sharp-edged  lobes,  behind  which  are  one  or  two  tubercles;  it  has  two  roots. 
The  average  periods  of  eruption  are  given  below. 


Tooth  Eruption 

I, 4  to  5  weeks.  . 

lo 4  to  5  weeks .  . 

I3 4  weeks 

C 3  to  4  weeks .  . 

Pi 4  to  5  months. 

P2 4  to  5  weeks  .  . 

Ps 3  to  4  weeks.  . 

P4 3  to  4  weeks.  . 

M, 4  months 


4  to  5  months 

4  to  5  months 

5  to  6  months 


■jy.^  /  upper  5  to  6  months 

" \  lower  4  J/^  to  5  months 

Ms 6  to  7  months 


Jl-3,  Incisors;    C,  canine;    Pl- 


FiG.  436. — Base  of  Skull  of  Cocker  Spaniel. 

premolars;    Ml-2,  molars.     Note  the  crowding  of  the  canines  and  premolars  on 
account  of  the  shortness  of  the  jaw. 


THE  SALIVARY  GLANDS 
The  parotid  gland  is  small  and  is  irregularly  triangular.  Its  dorsal  end  is  wide 
and  is  divided  into  two  parts  by  a  deep  notch  into  which  the  base  of  the  ear  is 
received.  The  ventral  end  is  small  and  overlaps  the  mandibular  gland.  The 
parotid  duct  leaves  the  gland  at  the  lower  part  of  the  anterior  border,  crosses  the 
masseter  muscle,  and  opens  into  the  mouth  opposite  the  third  upper  cheek  tooth. 


496 


DIGESTIVE    SYSTEM    OF    THE    DOG 


Small  accessory  parotid  glands  (Glandulae  parotidese  accessorise)  are  sometimes 
found  along  the  course  of  the  duct. 

The  mandibular  gland  is  usually  larger  than  the  parotid.  In  large  dogs  it 
is  about  two  inches  (ca.  5  cm.)  long  and  an  inch  or  more  (ca.  3  cm.)  wide.  It  is 
rounded  in  outline,  pale  yellow  in  color,  and  is  enclosed  in  a  fibrous  capsule.  Its 
upper  part  is  covered  by  the  parotid,  but  it  is  otherwise  superficial,  and  is  palpable 
in  the  angle  of  junction  of  the  jugular  and  external  maxillary  veins.  The 
mandibular  duct  leaves  the  deep  face  of  the  gland,  passes  along  the  surface  of 
the  occipito-mandibularis  and  stylo-glossus,  and  opens  into  the  mouth  on  a  very 
indistinct  papilla  near  the  frenum  linguae. 

The  sublingual  gland  is  pink  in  color  and  is  divided  into  two  parts.  The 
posterior  part  (Glandula  sublingualis  grandicanalaris)  lies  on  the  occipito-man- 


FiG.  437. — Dissection  of  Head  of  Dog,  Showing  Salivary  Glands,  etc. 
o,  Ocular  muscles;  6,  pterygoideus  medialis  (cut) ;  c,  stylo-glossus;  d,  occipito-mandibularis  (cut) ;  e,  genio-glossus; 
/,  genio-hyoideus ;  g,  hyo-glossus;  h,  thyro-pharyngeus;  i,  crico-pharyngeus;  k,  thyro-hyoideus ;  I,  zygomatic  process 
of  temporal  (sawn  off) ;  i,  parotid  gland;  ^,  mandibular  gland;  3,  posterior  part  of  sublingual  gland;  S',  anterior  part 
of  same;  4,  mandibular  duct;  5,  ductus  sublingualis  major;  6,  palatine  glands;  7,  zygomatic  gland;  S,  ducts  of  7;  9, 
lacrimal  gland.     (Ducts  colored  red.)      (After  Ellenberger,  in  Leisering's  Atlas.) 


dibularis  muscle  in  intimate  relation  with  the  mandibular  gland,  but  is  clearly  separ- 
able from  it  after  removal  of  the  common  fibrous  capsule.  It  has  a  pointed  anterior 
process.  Its  duct  (Ductus  sublingualis  major)  accompanies  the  mandibular  duct, 
and  either  opens  beside  it  or  joins  it.  The  anterior  part  (Glandula  sublingualis 
parvicanalaris)  is  long  and  narrow;  it  lies  between  the  mucous  membrane  of  the 
mouth  and  the  mylo-hyoideus,  dorsal  to  the  stylo-glossus  muscle.  It  has  a  number 
(8  to  12)  of  small  ducts  (Ductus  sublinguals  minores),  some  of  which  open  directly 
into  the  mouth,  while  others  join  the  large  duct. 

The  zygomatic  gland  (Glandula  zygomatica)i  (Fig.  437)  is  situated  in  the 
anterior  part  of  the  ptery go-palatine  fossa.  It  is  related  superficially  to  the  zygo- 
matic arch  and  the  masseter  and  temporal  muscles.  Its  deep  face  is  in  contact 
with  the  periorbita,  the  pterygoid  muscle,  the  internal  maxillary  artery,  and  the 

^  Also  known  as  the  orbital  gland. 


THE  PHARYNX — THE  CESOPHAGUS — THE  STOMACH  497 

maxillary  nerve.  It  has  four  or  five  ducts  which  open  near  the  last  upper  cheek 
tooth;  one  of  them  (Ductus  glandulse  zygomaticse  major)  is  almost  as  large  as  the 
parotid  duct;    the  others  (Ductus  glandulse  zygomaticse  minores)  are  small. 

THE  PHARYNX  (Fig.  434) 
The  fornix  is  narrow.  The  pharyngeal  orifices  of  the  auditive  or  Eustachian 
tubes  are  small  and  slit-like;  the  end  of  the  tube  causes  a  rounded  projection  of  the 
mucous  membrane  (Torus  tubarius).  The  oesophageal  aditus  is  relatively  small 
and  is  well  defined  by  a  transverse  fold  of  the  mucous  membrane.  The  muscles 
present  no  marked  differential  features,  but  the  hyo-pharyngeus  muscle  is  clearly 
divided  into  a  kerato-pharyngeus  and  a  chondro-pharyngeus. 


THE  (ESOPHAGUS 
The  oesophagus  is  relatively  wide  and  dilatable  except  at  its  origin,  where  there 
is  a  constriction  termed  the  isthmus  oesophagi.  This  initial  narrowness  of  the 
lumen  is  caused  by  a  prominence  of  the  ventral  part  of  the  mucous  membrane, 
underlying  which  is  a  thick  layer  of  mucous  glands  (Fig.  490).  The  cervical  part 
is  at  first  median  and  is  dorsal  to  the  trachea,  but  in  the  posterior  part  of  the  neck 
it  lies  to  the  left  of  the  trachea.  The  thoracic  part  continues  in  this  position  and 
ventral  to  the  left  longus  colli  to  the  base  of  the  heart;  here  it  inclines  medially, 
having  the  aortic  arch  on  its  left,  and  passes  back  over  the  bifurcation  of  the  trachea. 
Continuing  backward  between  the  lungs  it  usually  inclines  slightly  to  the  left, 
passes  through  the  hiatus  cesophageus,  and  joins  the  stomach  just  to  the  left  of  the 
median  plane  and  ventral  to  the  eleventh  or  twelfth  thoracic  vertebra.  The 
muscular  tissue  is  striated  and  consists  mainly  of  two  layers  of  spiral  fibers  which 
cross  each  other;  near  the  cardia,  however,  the  fibers  are  longitudinal  and  circular. 
There  are  tubulo-alveolar  glands  (Gl.  oesophagae)  in  the  submucosa  throughout. 

THE  STOMACH 

The  stomach  is  relatively  large.  Its  capacity  in  a  dog  weighing  about  40 
pounds  is  about  six  to  seven  pints. 

Colin  estimates  the  average  capacity  at  about  3  liters  (ca.  6^  pints),  with  a  range  between 
0.6  and  8  liters  (ca.  l}4  to  173^  pints).  Neumayer  gives  the  capcaity  as  100  to  250  c.c.  per  kilogram 
of  body-weight  (ca.  2.7  ounces  per  pound).  The  average  capacity  of  the  human  stomach  is  esti- 
mated at  1.2  liters  (23/2  pints) — not  much  more  than  a  third  of  that  of  a  dog  of  medium  size. 

When  full,  it  is  irregularly  piriform.  The  left  or  cardiac  part  (Fundus  et  corpus 
ventriculi)  is  large  and  rounded,  while  the  right  or  pyloric  part  (Pars  pylorica)  is 
small  and  cylindrical.  When  empty,  or  nearly  so,  the  left  sac  is  strongly  contracted; 
the  pyloric  part  is  much  less  affected  by  variations  in  the  amount  of  ingesta. 

The  parietal  surface  of  the  full  stomach  is  very  extensive,  strongly  convex, 
and  faces  partly  forward,  but  largely  ventrally  and  to  the  left.  It  is  related  to  the 
liver,  the  left  part  of  the  diaphragm,  and  the  left  and  ventral  abdominal  wall  as  far 
back  as  a  transverse  plane  through  the  second  or  third  lumbar  vertebra.  The 
visceral  surface  is  much  less  extensive  and  is  considerably  flattened ;  it  faces  chiefly 
dorsally  and  to  the  right,  and  is  related  to  the  intestine,  pancreas,  and  left  kidney. 

The  upper  part  of  the  lesser  curvature  is  nearly  straight  and  vertical,  but  the 
lower  part  forms  a  deep,  narrow  angle  (Incisura  angularis),  due  to  the  fact  that  the 
pyloric  part  is  directed  sharply  forward  and  upward.  The  greater  curvature  is 
nearly  four  times  as  long  as  the  lesser  curvature.  In  the  full  stomach  it  extends 
considerably  behind  the  left  costal  arch;  ventrally  it  lies  on  the  abdominal  wall 
about  midway  between  the  xiphoid  cartilage  and  the  pubis. 
32 


498 


DIGESTIVE    SYSTEM    OF    THE    DOG 


(Esophagus 


Pylorus 


The  left  extremity  or  fundus  is  large  and  rounded;    it  is  the  most  dorsal  part 
of  the  organ,  and  lies  under  the  vertebral  ends  of  the  eleventh  and  twelfth  ribs. 

The  pyloric  extremity  is  small 
and  is  directed  forward  and  dor- 
sally;  it  lies  usually  opposite  to 
the  ventral  part  of  the  ninth 
or  tenth  intercostal  space,  and 
about  an  inch  (ca.  2-3  cm.)  to 
the  right  of  the  median  plane. 
It  is  related  to  the  portal  fissure 
of  the  liver  and  to  the  pancreas. 
The  cardia  is  situated  about  two 
to  three  inches  (ca.  5  to  7  cm.) 
from  the  left  extremity,  and  is 
oval;  it  lies  just  to  the  left  of 
the  median  plane,  ventral  to  the 
eleventh  or  twelfth  thoracic  ver- 
tebra. 

When  empty,  or  nearly  so, 
the  stomach  is  separated  from 
the  ventral  abdominal  wall  by 
the  liver  and  intestine,  and  the 
greater  curvature  extends  back 
on  the  left  side  to  the  eleventh 
or  twelfth  rib.  In  this  state  there  is  not  rarely  a  marked  constriction  between  the 
right  and  left  parts. 

The  preceding  topographic  statements  are  based  on  observations  made  on  a  considerable 
number  of  formalin-hardened  subjects,  and  are  to  be  regarded  as  average  findings  in  dogs  of 


18. — Stomach  of  Dog;  Parietal  Surface. 
Organ  fixed  in  situ  when  well  filled. 


Left  extremity 


Duodenum 


Attachment  of 
greater  omentum 

Fig.  439. — Stomach  of  Dog;  Visceral  Surface. 
Organ  fixed  in  situ  when  it  contained  small  amount  of  ingesta. 


medium  size.  The  cardiac  an  1  pyloric  ends  vary  least  in  position,  but  the  former  varies  the 
length  of  one  vertebra  and  the  latter  as  much  as  two  intercostal  spaces.  This  variation  appears 
to  be  due,  not  only  to  the  amount  of  ingesta  in  the  stomach,  but  also  to  the  phase  in  which  the 
diaphragm  is  fixed. 


THE   STOMACH 


499 


The  serous  coat  is  almost  complete.  Along  the  curvatures  it  leaves  the  stom- 
ach to  form  the  omenta.  The  longitudinal  muscular  fibers  are  chiefly  along  the 
curvatures  and  on  the  pyloric  part;  they  are  continuous  with  the  external  layer 
of  the  oesophagus.  The  oblique  fibers  are  arranged  in  two  layers :  the  external  layer 
is  largely  a  continuation  of  the  longitudinal  fibers  of  the  oesophagus  to  the  body 
and  fundus.  The  circular  layer  covers  the  whole  stomach  except  the  fundus,  and 
forms  a  pyloric  sphincter  and  an  antral  sphincter.  The  internal  oblique  layer  is 
arranged  as  in  the  horse,  and  forms  a  similar  loop-like,  cardiac  sphincter.  Three 
regions  of  the  mucous  membrane  exist.  Cardiac  glands  are  found  in  a  very  narrow 
pale  zone  around  the  cardiac  opening,  and  also  scattered  along  the  lesser  curva- 


FiQ.  440. 
1,  Fundus  gland  region;   2,  pyloric  part; 


-Stomach  of  Dog;  Frontal  Section 

,  lesser  curvature;   4,  cardia;   5,  pylorus;   6,  oesophagus;   7,  duodenum. 


ture.  The  fundus  gland  region  has  a  thick,  reddish-bro^^^l  mucous  membrane, 
which  lines  about  two-thirds  of  the  organ.  The  pyloric  mucous  membrane  is 
thinner  and  pale;  in  the  dead  subject  it  is  often  stained  by  regurgitated  bile. 

The  greater  omentum  is  very  extensive,  and  in  well-nourished  subjects  it  con- 
tains much  fat  arranged  in  interlacing  strands.  Viewed  ventrally  it  covers  the 
entire  intestinal  mass,  extending  from  the  greater  curvature  of  the  stomach  to  the 
pelvic  inlet.  It  is  attached  to  the  greater  curvature  of  the  stomach,  the  left  part 
of  the  colon,  the  left  branch  of  the  pancreas,  and  the  hilus  of  the  spleen. 

The  lesser  omentum  extends  from  the  lesser  curvature  of  the  stomach  to  the 
portal  fissure;  to  reach  the  latter  it  passes  in  great  part  between  the  papillary  and 
left  lateral  lobes  of  the  liver. 


500 


DIGESTIVE    SYSTEM    OF   THE    DOG 


THE  INTESTINE 

The  intestine  is  short — only  about  five  times  the  length  of  the  body. 

The  small  intestine  has  an  average  length  of  about  thirteen  feet  (ca.  4  meters). 
It  occupies  most  of  the  abdominal  cavity  behind  the  liver  and  stomach.  The  duo- 
denum begins  at  the  pylorus  and  passes  backward  and  somewhat  dorsally,  at  first 


Fig.  441. — Abdominal  Viscera  of  Dog. 

Ventral  view  after  removal  of  greater  omentum.     The  stomach  is  full. 

a,  Cartilage  of  last  rib;   b,  duodenum;   x,  xiphoid  cartilage. 


on  the  visceral  surface  of  the  liver,  then  in  contact  with  the  right  flank.  Near  the 
pelvis  it  turns  medially  and  passes  forward  along  the  medial  side  of  the  left  part  of 
the  colon  and  the  left  kidney,  bends  ventrally,  and  joins  the  jejunum  to  the  left  of 
the  root  of  the  mesentery. ^    The  mesoduodenum  is  given  off  from  the  right  side  of  the 

1  The  duodenum  might  be  regarded  as  consisting  of  a  right  or  retrograde  part,  an  iliac  flexure, 
and  a  left  or  recurrent  part;   the  terminal  bend  is  the  duodeno-jejunal  flexure. 


THE    INTESTINE 


501 


common  mesentery;  it  is  a  relatively  wide  fold.  The  left  part  of  the  duodenum  is 
connected  with  the  mesocolon  by  a  peritoneal  fold;  this  fold  has  a  free  posterior 
border  which  is  clearly  seen  when  the  posterior  flexure  of  the  duodenum  is  drawn 
away  from  the  sublumbar  region.  The  first  part  of  the  mesoduodenum  contains 
the  right  branch  of  the  pancreas.  Its  root  is  blended  with  the  mesocolon  to  form  a 
common  mesentery.  The  remainder  of  the  small  intestine  forms  numerous  coils, 
and  is  attached  by  a  wide  mesentery  to  the  sublumbar  region.  The  terminal  part 
(ileum)  passes  forward  in  the  sublumbar  region  along  the  medial  surface  of  the 
caecum  and  opens  into  the  beginning  of  the  colon  at  the  ileo-colic  orifice  (Ostium 


Fig.  442. — Deep  Dissection  of  Abdominal  Viscera  of  Dog  (Female). 
Bl.,  Bladder;    B,  body,   C,  C",  cornua  of  uterus;    O,  O',  ovaries;   L.  k.,  left  kidney.     The  concealed  part  of  the  colon 


is  indicated  by  dotted  li 


The  spleen  is  drawn  backward  and  outward. 


ileocolicum).  The  bile  duct  and  smaller  pancreatic  duct  open  into  the  duodenum 
about  two  or  three  inches  (ca.  5  to  8  cm.)  from  the  pylorus;  the  larger  pancreatic 
duct  opens  an  inch  or  two  (ca.  2.5  to  5  cm.)  further  back.  The  mucous  membrane 
has  very  long,  thin  villi.  The  duodenal  glands  occur  only  close  to  the  pylorus. 
Aggregated  lymph  nodules  or  Peyer's  patches  are  numerous  (about  twenty  in 
young  subjects),  and  begin  in  the  duodenum.  They  are  usually  elliptical  in  out- 
line, but  the  last  one  is  band-like,  reaches  to  the  end  of  the  ilemn,  and  is  four  to 
sixteen  inches  (ca.  10  to  40  cm.)  long  in  young  dogs  (Ellenberger) .  There  is  an  ileo- 
colic valve. ^     The  muscular  coat  is  relatively  thick. 

1  The  valve  does  not  seem  always  to  be  efficient,  since  experience  shows  that  rectal  injections 
can  be  made  to  pass  beyond  it.  This  may  be  partly  due  also  to  the  fact  that  the  terminal  part  of 
the  ileum  runs  horizontally  forward,  and  its  orifice  faces  forward  into  the  beginning  of  the  colon. 


502 


DIGESTIVE    SYSTEM    OF    THE    DOG 


The  large  intestine  is  two  to  two  and  a  half  feet  (ca.  60  to  75  cm.)  long  in 
average.  Its  caliber  is  about  the  same  as  that  of  the  small  intestine,  and  it  has 
neither  longitudinal  bands  nor  sacculations. 

The  caecum  averages  about  five  or  six  inches  (ca.  12.5-15  cm.)  in  length,  and 
is  flexuous  (Fig.  442).  The  flexures  are  maintained  by  the  peritoneum,  which 
attaches  it  also  to  the  ileum.  It  is  situated  usually  about  midway  between  the 
right  flank  and  the  median  plane,  ventral  to  the  duodenum  and  the  right  branch  of 
the  pancreas.!  Its  anterior  end  opens  into  the  origin  of  the  colon,  lateral  to  the 
ileo-colic  orifice.     The  other  end  is  pointed  and  blind. 

The  colon  is  attached  to  the  sublumbar  region  by  a  mesentery — the  mesocolon. 
It  presents  three  parts,  which  correspond  to  the  ascending,  transverse,  and  descend- 
ing colon  of  man.  The  first  or  right  part  (Colon 
dextrum  s.  ascendens)  is  very  short.  It  passes  for- 
ward along  the  medial  surface  of  the  first  part  of  the 
duodenum  and  the  right  branch  of  the  pancreas  till 
it  reaches  the  pyloric  part  of  the  stomach;  here  it 
turns  to  the  left  and  crosses  the  median  plane, 
forming  the  transverse  part  (Colon  transversum). 
The  third  or  left  part  (Colon  sinistrum  s.  descen- 
dens)  passes  backward  in  the  sublumbar  region 
along  the  medial  border  or  ventral  surface  of  the 
left  kidney;  it  then  inclines  toward  the  median 
plane  and  is  continued  by  the  rectum.  The  cali- 
ber of  the  colon  is  about  the  same  throughout.  It 
has  no  bands  nor  sacculations.  The  mesen- 
tery of  the  colon  is  termed  the  mesocolon;  it  is 
given  off  from  the  left  side  of  the  common  mesen- 
tery. 2 

The  mucous  membrane  of  the  caecum  con- 
tains numerous  solitary  lymph  nodules  which  are 
circular,  with  a  central  depression;  some  are 
present  also  in  the  first  part  of  the  colon. 

The  rectum  is  almost  completely  covered  with 
peritoneum,  the  line  of  peritoneal  reflection  being 
under  the  second  or  third  coccygeal  vertebra.  At 
the  junction  of  the  rectum  and  anus  the  mucous 
membrane  has  a  stratified  squamous  epithelium, 
and  contains  the  anal  glands.  A  small  opening  on 
cither  side  leads  into  two  lateral  anal  sacs  (Sinus 
paranales) ;  these  are  usually  about  the  size  of  a 
hazel-nut,  and  contain  a  dirty  gray,  fatty  substance, 
which  has  a  peculiar  and  very  unpleasant  odor. 
The  skin  which  lines  these  pouches  contains  coil-glands.  Further  back  the  skin 
contains  large  sebaceous  glands  and  peculiar  circimianal  glands. 

The  retractor  ani  muscle  is  extensive.  It  arises  from  the  shaft  of  the  ilium, 
the  pubis,  and  the  symphysis  pelvis,  and  passes  upward  and  backward  to  end  on  the 


Fig.  443. — Sectional  View   of  Ileum 

C^cuM,  AND  Colon  of  Dog. 

1,  Ileo-colic  orifice;   2,  caeco-colic  orifice 

3,  apex  of  caecum. 


1  In  large  dogs  (e.  g.,  St.  Bernard  or  Great  Dane)  the  csecum  may  reach  a  length  of  45  cm. 
(measured  along  its  curves)  and  a  diameter  of  3  cm.  Its  position  is  somewhat  variable.  It  may 
be  closer  to  the  lateral  wall,  or  more  medial  than  is  stated  above.  Its  anterior  end  is  usually 
in  a  transverse  plane  through  the  ventral  end  of  the  last  rib  if  the  stomach  is  not  very  full. 

2  The  arrangement  of  the  colon  is  variable.  The  transverse  part  may  be  quite  long  and 
extend  across  from  the  angle  of  junction  of  the  two  branches  of  the  pancreas  to  the  dorsal  end  of 
the  spleen.  On  the  other  hand,  a  transverse  part  may  be  absent,  the  colon  forming  instead  an 
acute  angle  or  flexure.  When  the  stomach  is  empty  and  contracted,  the  transverse  part  of  the 
colon  may  be  separated  from  the  ventral  wall  by  the  omentum  only. 


THE    LIVER 


503 


first  coccygeal  vertebrae  and  the  sphincter  ani  externus.     The  retractors,  together 
with  the  coccygei,  form  a  sort  of  pelvic  diaphragm,  analogous  to  that  of  man. 


THE  LIVER 

The  liver  is  relatively  large,  weighing  usually  about  3  per  cent,  of  the  body- 
weight.     It  is  divided  into  five  chief  lobes  by  fissures  which  converge  at  the  portal 
fissure.     When  the  gland  is  ex- 
amined   in   the    soft    condition  post,  l/ena  cai/a 

the  lobes  may  be  spread  out  so 
as  to  be  all  visible  (Fig.  444), 
but  when  the  organ  is  hard- 
ened in  situ  the  lobes  overlap 
to  a  considerable  extent  (Figs. 
445,  446). 

The  left  lateral  lobe  is  the 
largest,  and  is  oval  in  outline. 
The  left  central  lobe  is  smaller 
and  is  prismatic.  The  right 
central  lobe  is  second  in  size, 
and  presents  a  somewhat 
tongue-shaped  quadrate  lobe, 
marked  off  by  the  deep  fossa 
in  which  the  gall-bladder  lies. 
The  right  lateral  lobe  is  third 

in  size,  and  is  oval  in  outline.  On  its  visceral  surface  is  the  large  caudate  lobe; 
this  consists  of  two  parts — on  the  right,  the  caudate  process,  on  the  left,  the  papil- 
lary process,  both  often  being  subdivided  by  secondary  fissures. 


llnihiheni? 


Fig.  444. — Liver  of  Dog. 
Soft  specimen  sketched  with  lobes  drawn  apart. 


Right  lateral  lobe 


Left  central  lobe 


Gall-bladder        Quadrate  lobe 
Fig.  445. — Liver  of  Dog;  Parietal  Surface. 
1,  Hepatic  veins  opening  into  posterior  vena  cava;  2,  coronary  ligament;   3,  falciform  ligament. 


504 


DIGESTIVE    SYSTEM    OF   THE   DOG 


When  hardened  in  situ,  the  gland  presents  the  following  characters:  The 
parietal  surface  is  strongly  convex  in  conformity  with  the  curvature  of  the  dia- 
phragm and  the  adjacent  part  of  the  ventral  wall  of  the  abdomen,  Avith  which  it  is 
in  contact. 

The  visceral  surface  is  in  general  concave,  but  is  irregular  in  adaptation  to  the 
viscera  in  contact  with  it.  The  largest  of  these  is  the  stomach,  and  the  configuration 
of  the  liver  varies  greatly  in  accordance  with  the  degree  of  fulness  of  that  viscus. 
When  the  stomach  is  well  filled,  there  is  a  ridge  on  the  liver  which  corresponds  to 
the  lesser  curvature.  To  the  left  of  this  is  a  large  concavity  adapted  to  the  body 
and  fundus  of  the  stomach ;  and  on  the  right  is  a  smaller  impression  of  the  pyloric 
part  of  the  stomach,  the  first  part  of  the  duodenum,  and  the  anterior  part  of  the 


Left  lateral 
ligament 


(Esophageal  notch 


Posterior  tena  cava 


Right  central  lobe 


Fig.  446. — Liver  of  Dog,  Visceral  Surface;  Hardened  in  situ. 
Left  central  lobe,  gall-bladder,  and  great  part  of  right  central  lobe  not  visible. 


right  branch  of  the  pancreas.  Dorsal  to  the  cavity  for  the  pyloric  part  of  the 
stomach  is  a  deep  depression,  and  at  the  bottom  of  this  is  the  portal  fissure.  To 
see  the  latter  the  papillary  and  caudate  lobes  must  be  drawn  apart.  The  hepatic 
artery  enters  the  liver  at  the  dorsal  part  of  the  fissure,  the  portal  vein  enters  cen- 
trally, and  the  hepatic  duct  emerges  at  the  ventral  part.  The  gall-bladder  is 
usually  not  visible  till  the  right  lateral  and  central  lobes  are  drawn  apart. 

When  the  stomach  is  empty  and  contracted,  the  visceral  surface  of  the  liver  is  strikingly 
different.  There  is  then  a  shallow  impression  for  the  left  part  of  the  stomach  on  the  left  lolie 
and  a  large  convex  area,  related  to  the  small  intestine  and  a  mass  of  omentum.  The  pyloric  and 
duodenal  impressions  are  not  much  changed. 

The  dorsal  l^order  presents  a  deep  renal  impression  on  its  right  part.  The 
posterior  vena  cava  passes  ventrally  and  forward,  at  first  in  a  deep  groove  on  the 
caudate  lobe,  then  largely  embedded  in  the  parietal  surface  of  the  right  lateral  lobe; 
it  receives  two  or  three  large  hepatic  veins  just  before  piercing  the  diaphragm. 


THE    PANCREAS 


505 


Dorsal  end 


The  oesophageal  notch  is  large,  and  is  occupied  on  the  right  by  the  thick  margin  of 
the  hiatus  oesophagus.  The  remainder  of  the  circumference  is  thin,  and  is  cut  into 
by  deep  fissures  which  separate  the  lobes.  The  ventral  border  lies  on  the  abdominal 
wall,  a  variable  distance  behind  the  xiphoid  cartilage.  The  left  border  is  also 
variable,  but  usually  extends  back  ventrally  as  far  as  the  tenth  intercostal  space 
or  eleventh  rib.  The  right  border  corresponds  more  or  less  closely  in  direction 
with  the  costal  arch ;  the  end  of  the  caudate  process  is  ventral  to  the  right  kidney, 
opposite  to,  or  a  little  behind,  the  last  rib. 

The  gall-bladder  lies  in  the  fossa  vesicae  fellese,  between  the  two  parts  of  the 

right  central  lobe;  it  does  not  reach  to  the 
ventral  border  of  the  liver.  The  cystic  duct 
joins  the  hepatic  duct  at  the  ventral  part  of 
the  portal  fissure,  forming  with  it  the  bile 
duct  (Ductus  choledochus) ;  the  latter  passes 
to  the  right  and  opens  into  the  duodenum, 
about  two  or  three  inches  (ca.  5  to  8  cm.) 
from  the  pylorus. 

Of  the  ligaments,  the  coronary  and  right 


Gastric 
surface 


Ventral  end 


Fig.    447. — Splee:^    op    Dog;     Parietal 

Surface. 


Ventral 


Fig.  448. — Spleen  of  Dog;    Visceral  Surface. 


Fig.  447  is  from  subject  in  -nhich  the  stomach  was  full,  -r  hile  the  organ  shown  in  Fig.  448  was  fixed  in  situ  when  the 
stomach  contained  little  food. 

lateral  are  well  developed,  but  the  left  lateral  and  falciform  are  small;   a  ligament 
extends  from  the  caudate  process  to  the  right  kidney. 


THE  PANCREAS 
The  pancreas  is  V-shaped,  consisting  of  two  long  narrow  branches,  which 
meet  at  an  acute  angle  behind  the  pylorus.  The  right  branch  extends  backward 
above  the  first  part  of  the  duodenum,  below  the  caudate  lobe  of  the  liver  and  the 
right  kidney,  and  ends  usually  a  short  distance  behind  the  latter;  it  is  enclosed  by  the 
mesoduodenum.     The  left  branch  passes  to  the  left  and  backward  between  the 


506 


DIGESTIVE    SYSTEM    OF    THE   DOG 


visceral  surface  of  the  stomach  and  the  transverse  colon,  and  ends  at  the  anterior 
pole  of  the  left  kidney.  There  are  usually  two  pancreatic  ducts.  The  smaller  one 
opens  into  the  duodenum  with  the  bile  duct  or  close  to  it;  the  larger  one  opens  into 
the  bowel  an  inch  or  two  (ca.  3-5  cm.)  further  back. 


THE  SPLEEN 
The  spleen  is  bright  red  in  color  in  the  fresh  state.     It  is  somewhat  falciform, 
long,  and  narrow;    the  ventral  part  is  the  widest.     Its  weight  in  a  dog  of  medium 


Fig,  449. — Projection  of  Viscera  of  Dog  (Male)  on  Body  Wall;  Left  Side. 

A,  C,  D,  Apical,  cardiac,  and  diaphragmatic  lobes  of  lung;    P,  pericardium;    Pr,  prostate.     Costal  attachment  and 

median  line  of  diaphragm  are  dotted. 


Fig.  450. — Projection  of  Viscera  of  Dog  (Female)  on  Body  Wall;  Right  Side. 
A,  C,  D,  Apical,  cardiac,  and    diaphragmatic  lobes  of  right  lung;    P,  pericardium;     K,  right  kidney;    Pan.,  right 
branch  of  pancreas;   O,  ovary;    L',  cornu  of  uterus.     Costal  attachment  and  median  line  of  diaphragm  are  dotted;   also 
posterior  contour  of  stomach. 


size  is  13^-2  ounces  (ca.  50  gm.).     It  is  freely  movable,   and,  with  the  exception 
of  its  dorsal  end,  varies  much  in  position  and  shape.     The  dorsal  end  is  ventral  to 


THE    SPLEEN  507 

the  vertebral  end  of  the  last  rib  and  the  first  lumbar  transverse  process;  it  fits  into 
the  interval  between  the  left  crus  of  the  diaphragm,  the  left  end  of  the  stomach, 
and  the  left  kidney.  When  the  stomach  is  full,  the  long  axis  of  the  spleen  corre- 
sponds to  the  direction  of  the  last  rib.  Its  parietal  surface  is  convex  and  lies  largely 
against  the  left  flank.  The  visceral  surface  is  concave  in  its  length,  and  is  marked 
by  a  longitudinal  ridge,  on  which  the  vessels  and  nerves  are  situated,  and  to  which 
the  greater  omentum  is  attached.  The  spleen  is  so  loosely  attached  by  the  omen- 
tum as  to  be  regarded  as  an  appendage  of  the  latter. 

The  dorsal  end  of  the  spleen  does  not  vary  in  position,  but  the  rest  of  the  organ  is  very 
variable.  When  the  stomach  is  full,  the  part  of  the  visceral  surface  of  the  spleen  in  front  of  the 
hilus  is  usually  in  apposition  with  the  left  part  of  the  greater  curvature  of  the  stomach  (as  in  the 
horse).  It  may  have  a  similar  position  when  the  stomach  is  not  full,  and  may  be  in  contact  with 
the  latter  only  to  a  small  extent  dorsally.  It  is  not  rare  to  find  the  spleen  lying  along  the  dorsal 
part  of  the  left  flank,  with  its  long  axis  almost  longitudinal;  this  is  liable  to  be  the  case  when  the 
stomach  is  empty  and  contracted.  In  this  condition  the  spleen  shuts  the  left  kidney  entirely  off 
from  contact  with  the  flank. 


THE  RESPIRATORY  SYSTEM 

The  respiratory  apparatus  (Apparatus  respiratorius)  comprises  the  nasal 
cavity,^  the  pharynx,  the  larynx,  the  trachea,  the  bronchi,  and  the  lungs.  The 
lungs  are  the  central  organs  in  which  the  exchange  of  gases  between  the  blood  and 
the  air  takes  place;  the  other  parts  of  the  system  are  passages  by  which  the  air 
passes  to  and  from  the  lungs.  The  nasal  cavity  opens  externally  at  the  nostrils, 
and  communicates  behind  with  the  pharynx  through  the  choanse  or  posterior  nares; 
it  contains  the  peripheral  part  of  the  olfactory  apparatus,  which  mediates  the  sense 
of  smell.  The  pharynx  is  a  common  passage  for  the  air  and  food — a  remnant  of  the 
primitive  embryonic  arrangement;  it  has  been  described  with  the  digestive  tube. 
The  larynx  is  a  complex  valvular  apparatus  which  regulates  the  volume  of  air  pass- 
ing through  the  tract;  it  is  also  the  chief  organ  of  voice.  The  trachea  and  the 
bronchi  formed  by  its  bifurcation  are  permanently  open  conducting  tubes.  The 
thorax,  the  pleural  sacs  which  it  contains,  and  the  muscles  which  increase  or  di- 
minish the  size  of  the  cavity  are  also  parts  of  the  system.  The  bones,  joints,  and 
muscles  of  the  thorax  have  already  been  described. 

For  topographic  reasons  two  ductless  glands,  the  thyroid  and  the  thymus,  are 
usually  described  in  this  section,  although  they  are  in  no  sense  a  part  of  the  respira- 
tory system. 


RESPIRATORY  SYSTEM  OF  THE  HORSE 

THE  NASAL  CAVITY 

The  nasal  cavity  (Cavum  nasi),  the  first  segment  of  the  respiratory  tract,  is  a 
long,  somewhat  cylindrical  passage,  enclosed  by  all  the  facial  bones  except  the 
mandible  and  hyoid.  It  is  separated  from  the  mouth  ventrally  by  the  palate. 
It  opens  externally  at  the  nostrils,  and  communicates  posteriorly  with  the  pharynx 
through  the  posterior  nares  or  choanse. 

The  nostrils  (Nares)  are  somewhat  oval  in  outline,  and  are  placed  obliquely, 
so  that  they  are  closer  together  below  than  above.  They  are  bounded  by  two  alae  or 
wings  (Alae  nasi),  which  meet  above  and  below,  forming  the  conunissures.  The 
lateral  ala  is  concave;  the  medial  one  is  convex  above,  concave  below.  The 
prominence  of  the  medial  ala  is  caused  by  the  lamina  of  the  alar  cartilage;  this 
prominence,  together  with  the  alar  fold  which  extends  backward  from  it,  partially 
divides  the  nostril  into  a  large  lower  part  and  a  small  upper  part,  which  are  pop- 
ularly distinguished  as  the  ''true"  and  "false"  nostril.-  The  superior  commissure 
is  narrow,  the  inferior  one  ^vide  and  rounded.  If  the  finger  is  passed  into  the  nostril 
at  the  upper  commissure,  it  enters  a  blind  cutaneous  pouch.  This  cul-de-sac,  the 
diverticulum  nasi,  extends  backward  to  the  angle  of  junction  of  the  nasal  bone  and 
the  nasal  process  of  the  premaxilla.  In  order  to  enter  the  nasal  cavity  the  finger 
should  be  introduced  at  the  inferior  commissure  and  directed  toward  the  septum 
nasi.     The  naso-lacrimal  orifice  (Ostium  nasolacrimale),  the  external  opening  of 

^  A  nose  (Nasus  extemus),  such  as  exists  in  man,  forming  a  projection  distinctly  marked 
off  from  the  rest  of  the  face,  does  not  exist  in  the  domesticated  animals. 

2  These  terms  should  be  abandoned,  as  they  tend  unnecessarily  to  complicate  the  description 
as  well  as  to  misconception  with  regard  to  function. 

508 


THE    NASAL    CAVITY 


509 


the  naso-lacrimal  duct,  is  seen  when  the  nostril  is  dilated;  it  is  situated  on  the  floor 
of  the  vestibule,  aoout  two  inches  (ca.  5  cm.)  from  the  lower  commissure,  perforat- 
ing the  skin  close  to  its  junction  with  the  mucous  membrane.  (It  is  not  rare  to  find 
one  or  two  accessory  orifices  further  back.) 

Structure. — The  skin  around  the  nostrils  presents  long  tactile  hairs  as  well  as 
the  ordinary  ones.  It  is  continued  around  the  alee  and  lines  the  vestibule.  The 
skin  of  the  diverticulum  is  thin 
and  usually  black,  and  is  cov- 
ered with  very  fine  hairs;  it  is 
provided  with  numerous  selia- 
ceous  glands.  The  medial  wing 
is  supported  by  the  alar  cartil- 
age (Cartilago  alaris) ,  which  is 


Fig  451. — Cast  of  Left  Nostril,  Nasal 
Diverticulum,  and  Nasal  Vestibule 
OF  Horse;   Dorsal  View. 
N,  Nostril;   D,  diverticulum;   1,  super- 
ior commissure  of  nostril;   2,  inferior  com- 
missure;  3,  space  occupied  by  alar  fold;  4, 
groove  occupied  by  dorsal   turbinate   fold; 
5,  dorsal  meatus. 


Fig.  452. — Cross-section  of  Nasal  Region  of  Horse. 
The  section  is  cut  about  two  inches  (5  cm.)  behind  the  nostrils  and  a 
little  more  than  half  an  inch  behind  the  labial  commissure. 
a.  Dorsal  meatus;  6,  middle  meatus;  c,  ventral  meatus;  d,  diver- 
ticulum nasi;  e,  dorsal  turbinate  fold;  /,  ventral  turbinate  fold;  g, 
prominence  caused  by  venous  plexus  which  extends  back  on  lower  part 
of  ventral  turbinate;  1,  nasal  bone;  2,  cartilage  of  septum  nasi;  3,  4, 
palatine  and  nasal  processes  of  palatine  bones;  5,  maxilla;  6,  tendon  of 
levator  labii  superioris  proprius;  7,  part  of  laterahs  nasi  muscle  which 
goes  to  cartilage  of  ventral  turbinate;  8,  8',  levator  nasolabialis;  9,  dila- 
tor naris  lateralis;  10,  buccinator;  11,  vomero-nasal  organ;  12,  naso- 
lacrimal duct  (wide  part);  13,  lateral  nasal  artery;  14,  14',  branches  of 
superior  labial  artery;  15,  palatine  artery;  16,  labial  branches  of  infra- 
orbital nerve;  17,  external  nasal  nerve;  18,  hard  palate;  19,  cheek;  20, 
superior  labial  vein.  The  veins  (black)  are  filled  by  a  natural  injec- 
tion. 


shaped  somewhat  like  a  com- 
ma, the  convex  margin  being 
medial  (Fig.  453) .  The  cartil- 
ages are  attached  by  fibrous 
tissue  to  the  extremity  of  the 
septal  cartilage.    Each  consists 

of  an  upper,  quadrilateral  curved  plate,  the  lamina,  and  a  narrow  comu  which  curves 
ventro-laterally,  supporting  the  medial  wing  and  the  inferior  commissure,  but  not  en- 
tering into  the  formation  of  the  lateral  ^ving.  The  lamina  causes  the  pro j  ection  of  the 
upper  part  of  the  medial  wing,  from  which  the  thick  alar  fold  (Plica  alaris)  passes 
backward  along  the  lateral  wall  of  the  nasal  cavity  to  join  the  mucous  fold  which 


510 


RESPIRATORY    SYSTEM    OF    THE    HORSE 


encloses  the  cartilaginous  prolongation  of  the  ventral  turbinate  bone.^  The  extrem- 
ity of  the  cornu  usually  causes  a  slight  projection  of  the  skin  a  short  distance  behind 
and  below  the  inferior  commissure. 

The  muscles  of  the  nostrils  have  been  described  (p.  258). 

Vessels  and  Nerves. — The  arteries  are  branches  of  the  palato-labial,  superior 
labial,  and  lateral  nasal  arteries,  and  the  blood  is  conveyed  away  by  corresponding 
veins.  The  lymph  vessels  go  to  the  mandibular  lymph  glands.  The  nerves  are 
derived  from  the  infraorbital  nerve  (sensory)  and  from  the  facial  nerve  (motor) . 

The  nasal  cavity  is  divided  into  two  symmetrical  halves  by  the  median  septum 
nasi  (Figs.  452,  455,  456).  The  osseous  septum  (Septum  nasi  osseum)  is  formed 
behind  by  the  perpendicular  plate  of  the  ethmoid  and  ventrally  by  the  vomer.  A 
few  ridges  on  the  former  correspond  to  the  ethmoidal  meatuses.     The  major  part 

of  it,  however,  is  formed  by  the 
cartilage  of  the  septum  nasi  (Car- 
tilago  septi  nasi).  The  surfaces 
of  the  cartilage  are  marked  by 
faint  grooves  for  the  vessels  and 
nerves  which  course  over  it.  The 
dorsal  border  is  attached  along 
the  frontal  and  nasal  sutures,  and 
extends  beyond  the  apices  of  the 
nasal  bones  about  two  inches  (ca. 
5  cm.).  From  this  border  a  thin, 
narrow  plate,  the  parietal  cartil- 
age (Cartilago  parietalis)  curves 
outward  for  a  short  distance  on 
either  side.  Near  the  nostrils 
these  plates  are  somewhat  wider, 
partially  making  good  the  defect 
(naso-maxillary  notch)  in  the 
bony  wall  of  the  cavity  in  this 
situation.  The  ventral  border  is 
thick  and  rounded;  it  lies  in  the 
groove  of  the  vomer  and  the  pala- 
tine processes  of  the  premaxillse; 
its  anterior  part  occupies  the 
space  between  the  premaxillary 
bones.  A  process  from  it  extends 
into  the  palatine  fissure,  which  it 
almost  completely  fills;  the  pala- 
tine end  of  the  process  lies  in  the 
submucous  tissue  of  the  hard  palate,  and  the  palatine  artery  turns  medially  between 
the  cartilage  and  the  bone.  The  posterior  border  is  continuous  with  the  perpen- 
dicular plate  of  the  ethmoid  bone.^  The  alar  cartilages  are  attached  to  the  anterior 
extremity  l)y  fibrous  tissue  in  such  a  manner  as  to  allow  very  free  movement — in 
fact  an  actual  joint  may  be  present.  The  ventral  part  of  the  cartilage  is  about 
half  an  inch  (ca.  1  cm.),  the  middle  part  about  one-tenth  of  an  inch  (ca.  2.5  mm.), 
and  the  dorsal  part  about  a  quarter  to  a  third  of  an  inch  (ca.  6  to  8  mm.)  in 
thickness. 

1  When  the  nostril  is  fully  dilated  it  is  circular  in  outline,  and  the  so-called  false  nostril  is 
effaced  by  the  lamina  of  the  alar  cartilage  being  brought  in  contact  with  the  superior  commissure. 

2  The  cartilage  is  to  be  regarded  as  an  unossified  part  of  the  mesethmoid.  It  will  be  noted 
that  the  line  of  demarcation  between  the  bone  and  the  cartilage  is  irregular  and  varies  with  age; 
extensive  ossification  (or  calcification)  of  the  cartilage  is  commonly  found  m  old  animals.  The 
process  often  results  in  the  formation  of  calcareous  islands  in  the  cartilage. 


Lfuni/M 
of  alar 
cartilage 

Cornu 
of  alar 
cartilage 


Fig.  453. — Nasal  Cartilages  of  Horse;  Dorsal  View. 

1,  Anterior  extremity  of    cartilage  of  septum   nasi;     2,   foramen 

incisivum. 


THE    NASAL   CAVITY  511 

The  two  turbinate  bones  project  from  the  lateral  wall,  and  divide  the  outer 
part  of  the  cavity  into  three  meatuses— dorsal,  middle,  and  ventral  (Figs.  454, 
455,456). 

The  dorsal  nasal  meatus  (Meatus  nasi  dorsalis)  is  a  narrow  passage,  bounded 
dorsally  by  the  roof  of  the  cavity,  and  ventrally  by  the  dorsal  turbinate  bone ;  its 
posterior  end  is  closed  by  the  junction  of  the  inner  plate  of  the  frontal  bone  with  the 
cribriform  plate  and  lateral  mass  of  the  ethmoid.  It  transmits  air  to  the  olfactory 
region. 

The  middle  nasal  meatus  (Meatus  nasi  medius)  is  between  the  two  turbinate 
bones.  It  is  somewhat  larger  than  the  dorsal  meatus,  and  does  not  extend  back 
so  far;  it  ends  near  the  great  ethmoturbinate  and  the  ethmoidal  meatuses.  In 
its  posterior  part  is  the  extremely  narrow,  slit-like  interval  by  which  the  max- 
illary sinus  communicates  with  the  nasal  cavity — the  naso-maxillary  opening 
(Aditus  naso-maxillaris) .  The  opening,  which  is  normally  a  mere  fissure,  is  not 
visible  from  the  nasal  side,  being  concealed  by  the  overhanging  dorsal  turbinate. 
A  fine  flexible  probe,  passed  outward  and  somewhat  backward  between  the  turbinate 

Dorsal  „  , 

Veyitral  turbinate      r,        ,     7  T"\       Septum  between 

turbinate      Middle  Dorml    turbinates    frontal  sinuses 

Ventral       \  7neatus  ^- - 

meatus 


Fig.  454. — Nasal  Cavitt  of  Horse;  Sagittal  Section  with  Septum  Removed. 
/,  Dorsal  turbinate  fold;  2,  alar  fold,  containing  cartilaginous  prolongation  of  ventral  turbinate;  3,  arrow  pointing- 
to  naso-maxillary  opening,  which  is  concealed  by  dorsal  turbinate  bone;    4,  cranial  cavity;    3,  sphenoidal  sinus;    6, 
hamulus  of  pterygoid  bone.     The  olfactory  mucous  membrane  is  shaded.     Dotted  lines  indicate  anterior  limit  of 
uncoiled  parts  of  turbinate  bones,  which  inclose  parts  of  frontal  and  maxillary  : 


bones,  enters  the  maxillary  sinus;  if  introduced  a  little  further  in  the  same  direction, 
it  usually  passes  through  the  orifice  of  communication  between  the  maxillary 
sinus  and  the  frontal  sinus  and  enters  the  latter.  A  small  part  of  the  fissure  usually 
brings  the  anterior  division  of  the  maxillary  sinus  into  communication  with  the 
nasal  cavity.  The  spaces  enclosed  by  the  coiled  parts  of  the  turbinates  also  open 
into  the  middle  meatus.  This  passage  may  be  characterized  as  the  sinus-meatus, 
but  it  also  conducts  air  to  the  olfactory  region. 

The  ventral  nasal  meatus  (Meatus  nasi  ventralis)  is  situated  between  the 
ventral  turbinate  and  the  floor  of  the  cavity.  It  is  much  larger  than  the  other  two, 
and  is  the  direct  passage  between  the  nostrils  and  the  pharynx.  The  small,  slit- 
like orifice  of  the  vomero-nasal  organ  and  the  incisive  or  naso-palatine  duct  is 
situated  in  the  floor  of  the  anterior  end  of  the  meatus. 

The  common  nasal  meatus  (Meatus  nasi  communis)  is  situated  between  the 
septum  and  the  turbinates,  and  is  continuous  laterally  with  the  other  meatuses. 
It  is  very  narrow  dorsally,  but  widens  ventrally. 

The  lateral  masses  of  the  ethmoid  bone  project  forward  into  the  posterior 
part  (fundus)  of  the  nasal  cavity.     Between  the  ethmoturbinates,  of  which  each 


512  RESPIRATORY   SYSTEM    OF   THE    HORSE 

mass  IS  composed,  there  are  three  principal  and  numerous  small  passages,  the 
ethmoidal  meatuses  (Meatus  ethmoidales). 

The  choanae  or  posterior  nares  are  two  elliptical  orifices  by  which  the  nasal 
cavity  and  pharynx  conununicate.     They  are  in  the  same  plane  as  the  floor  of  the 


Parotid    External  Mandibular 

duct     maxillary  lymph  glands 

vessels 
Fig.  455. — Cross-section  of  He.^d  op  Horse. 
The  section  is  cut  midway  between  the  medial  canthus  and  the  anterior  end  of  the  facial  crest  and  is  a  front  view. 
1,  Septum  nasi;  2,  3,  4,  dorsal,  middle,  and  ventral  meatus  nasi;    5,  common  meatus  nasi;    6,  cavity  of  dorsa.' 
turbinate  bone  (i.  e.,  turbinate  part  of  frontal  sinus) ;  7,  cavity  of  ventral  turbinate  bone  (i.  e.,  turbinate  part  of  maxillajy 
sinus);    8,  maxillary  sinus;  9,  communication  between  7  and  8  over  infraorbital  canal;    10,  naso-lacrimal  duct;    11, 
infraorbital  nerve  and  canal;   12,  m.  levator  labii  superioris  proprius;  13,  mouth  cavity;   14,  palatine  artery;    15,  fifth 
upper  cheek  tooth  (posterior  part);  16,  sixth  lower  cheek  tooth  (anterior  part);  17,  m.  buccinator;   IS,  hard  palate;  19, 
vena  reflexa;  20,  superior  buccal  glands;  21,  buccinator  vessels  and  nerve;   22,  alveolar  vessels  and  nerve  of  mandible; 
23,  lingual  artery;  24,  mm.  gj*nio-glossi ;  25,  m.  hyo-glossus  (number  placed  between  two  radicles  of  lingual  vein);   26, 
m.  stylo-glossus;    27,  m.  m^lo-hyoideus;  28,  m.  genio-hyoideus;    29,  lingual  nerve;     30,  hypoglossal  nerve;     31,  sub- 
lingual artery;  32,  m.  digastricus  (anterior  belly).    The  mandibular  duct  is  shown  in  the  fat  lateral  to  the  genio-hyoideua 
but  is  not  marked. 

nasal  cavity,  and  are  separated  from  each  other  by  the  vomer.  They  are,  taken 
together,  about  two  inches  (ca.  5  cm.)  wide  and  three  to  four  inches  (ca.  8  to  10 
cm.)  long. 

The  nasal  mucous  membrane  (Membrana  mucosa  nasi)  is  thick,  highly  vas- 
cular, and  is,  in  general,  firmly  attached  to  the  underlying  periosteum  and  peri- 


THE    NASAL    CAVITY 


513 


chondrium.  It  is  continuous  in  front  with  the  skin  which  hues  the  nostrils,  and 
behind  with  the  mucous  membrane  of  the  pharynx.  It  is  also  continuous  at  the 
naso-maxillary  opening  with  the  very  thin  and  much  less  vascular  mucous  mem- 
brane which  lines  the  paranasal  sinuses.  In  the  anterior  part  of  the  cavity  it  forms 
prominent  thick  folds  on  the  lateral  wall,  which  extend  from  the  turbinate  bones  to 
the  nostril.     There  are  usually  two  dorsal  turbinate  folds  which  unite  anteriorly. 


Dorsal  meatus 


Septum  nasi  Lacrimal  sac 


Transverse 
facial  vessels 

Palatine  artery 

Vena  reflexa 
Palatine  vein 
Buccinator  and 
Dep.  labii  inf. 
Buccinator 
and 


Lingual  7ierve 
Lingual  artery 
Lingual  vein 

Mandibular 
duct 

Hypoglossal 
nerve 


Digastricus  (ant.  hdly) 


External      t,      .   i   >     ^ 
maxillary     J '^rotul  duct 
vessels 


Fig.  456. — Cross-section  of  Head  of  Horse.     The  Section  Passes  Through  the  Medial  Canthi  and  is  Viewed 

FROM  Behind. 
J,  Mylo-hyoideus;  S,  stylo-glossus ;    3,  hyo-glossus;  .<,  genio-glossus;  .5,  lingual  process  of  hyoid  bone.      An  arrow 
points  to  the  naso-maxillary  opening.      The  projecting  edge  just  above  the  arrow  point  is  the   anterior  margin  of  the 
fronto-maxillary  opening. 


The  upper  one  encloses  a  thin  plate  of  cartilage  which  is  continuous  with  the  dorsal 
turbinate  bone.  The  ventral  turbinate  fold  is  curved,  and  encloses  an  '"N^  shaped 
cartilaginous  plate  which  prolongs  the  ventral  turbinate  bone;  this  fold  is  con- 
tinuous with  the  alar  fold  of  the  nostril,  and  forms  with  it  the  upper  margin  of  the 
entrance  from  the  nostril  to  the  nasal  cavity.  Below  this  there  is  a  rounded  ridge 
produced  by  the  nasal  process  of  the  premaxilla.  The  mucous  membrane  of  the 
33 


514  RESPIRATORY   SYSTEM    OF   THE    HORSE 

greater  part  oi  the  cavity  (Regio  respiratoria)  is  red  in  color,  and  is  covered  with  a 
stratified  cihated  epithelium.  It  contains  numerous  tubulo-alveolar  nasal  glands 
(Glandulae  nasales).  The  submucosa  contains  rich  venous  plexuses  which  form 
in  certain  situations  a  sort  of  cavernous  tissue  (Plexus  cavernosus  nasalis),  composed 
of  several  strata  of  freely  anastomosing  veins,  between  which  there  are  unstriped 
muscle-fibers.  This  arrangement  is  most  marked  in  the  turbinate  folds,  on  the 
lower  part  of  the  ventral  turbinate  bone,  and  the  lower  part  of  the  septum.  The 
mucous  membrane  of  the  vestibule  presents  numerous  small  depressions  (openings 
of  gland  ducts),  and  is  covered  with  stratified  squamous  epithelium.  On  the 
posterior  part  of  the  lateral  masses  of  the  ethmoid  and  the  adjacent  part  of  the 
dorsal  turbinate  and  the  septum  (Regio  olfactoria)  the  mucous  membrane  is  brown- 
ish-yellow in  color  and  thicker;  it  contains  the  olfactory  nerve-endings  in  a  special 
non-ciliated  epithelium.  In  it  are  numerous  olfactory  glands  (Glandulse  olfactorise) ; 
these  are  long,  tubular,  and  often  Ijranched. 

The  vomero-nasal  organ  (Organon  vomeronasale)^  is  situated  on  the  floor  of 
the  nasal  cavity,  on  either  side  of  the  ventral  border  of  the  septum  (Fig.  452). 
It  consists  of  a  tubular  cartilage  (Cartilago  vomeronasal! s)  lined  with  mucous 
membrane  (Ductus  vomeronasalis) ,  to  which  fibers  of  the  olfactory  nerve  may  be 
traced.  Its  anterior  part  communicates  with  the  nasal  cavity  by  a  slit-like  orifice 
in  common  with  the  incisive  or  naso-palatine  duct.  The  posterior  blind  end  is  in  a 
transverse  plane  through  the  second  or  third  cheek  tooth.  The  average  length  of 
the  organ  is  about  five  inches  (ca.  12  cm.). 

The  ductus  incisivus  (or  naso-palatine  duct)  is  a  small  mucous  tube,  an  inch 
or  more  (ca.  2.5-3  cm.)  in  length,  which  extends  obliquely  through  the  palatine 
fissure.  Its  nasal  end  communicates  with  the  nasal  cavity  through  a  slit-like 
opening  in  common  with  the  vomero-nasal  organ.  The  palatine  extremity  ends 
blindly  in  the  submucous  tissue  of  the  hard  palate. 

The  paranasal  sinuses  are  described  in  the  Osteology. 

Vessels  and  Nerves. — The  arteries  are  branches  of  the  ethmoidal,  spheno- 
palatine, palatine,  superior  labial,  and  lateral  nasal  arteries.  The  blood  is  carried 
away  by  corresponding  veins.  The  lymph  vessels  go  to  the  mandibular  and 
pharyngeal  lymph  glands.     The  nerves  come  from  the  olfactory  and  trigeminal 


THE  LARYNX 

The  larynx  is  a  short  tube  which  connects  the  pharynx  and  trachea.  It  is  a 
complex  valvular  apparatus,  which  regulates  the  volume  of  air  in  respiration, 
prevents  aspiration  of  foreign  bodies,  and  is  the  chief  organ  of  voice. 

It  is  situated  partly  between  the  medial  pterygoid  muscles,  partly  in  the  neck 
between  the  parotid  glands.^  Its  long  axis  is  practically  horizontal  in  the  ordinary 
position  of  the  head  and  neck.  It  is  related  dorsally  to  the  pharynx  and  the  origin 
of  the  oesophagus.  Ventrally  it  is  covered  by  the  skin,  fascia,  and  sterno-hyoid 
and  omo-hyoid  muscles.  Laterally  it  is  related  to  the  parotid  and  mandibular 
glands  and  to  the  medial  pterygoid,  occipito-mandibularis,  digastricus,  stylo-hyoid, 
and  pharyngeal  constrictor  muscles.  It  is  attached  to  the  body  and  thyroid  cornua 
of  the  hyoid  bone,  and  thus  indirectly  to  the  base  of  the  cranium.  Its  cavity 
communicates  dorsally  with  the  pharynx,  posteriorly  with  the  trachea.  The 
skeleton  of  the  larynx  consists  of  a  framework  of  cartilages,  which  are  connected  by 
joints  and  ligaments  or  membranes,  and  moved  by  extrinsic  and  intrinsic  muscles. 
It  is  lined  with  mucous  membrane. 

^  Commonly  known  as  the  organ  of  Jacobson. 

2  In  the  ordinary  position  of  the  head  and  neck,  and  while  the  parts  are  at  rest,  about  half 
of  the  larynx  lies  between  the  branches  of  the  mandible;  when  the  head  and  neck  are  extended, 
proportionately  more  of  the  larynx  lies  behind  a  plane  through  the  posterior  borders  of  the  rami. 


CARTILAGES    OF   THE    LARYNX 


515 


Cartilages  of  the  Larynx 

There  are  three  single  cartilages  and  one  pair;  the  single  cartilages  are  the 
cricoid,  thyroid,  and  epiglottic;   the  arytenoid  cartilages  are  paired. 

The  cricoid  cartilage  (Cartilago  cricoidea)  is  shaped  like  a  signet  ring.  The 
dorsal  part  is  a  broad,  thick,  quadrilateral  plate  termed  the  lamina;  the  external 
(dorsal)  surface  of  this  is  marked  by  a  median  ridge  (Crista  mediana)  separating  two 
shallow  cavities,  from  which  the  dorsal  crico-arytenoid  muscles  arise.  On  either 
side  of  these  depressions  are  two  articular  facets.  The  anterior  facet  (Facies  articu- 
laris  arytaenoidea)  is  at  the  anterior  border,  is  oval  and  convex,  and  articulates 
with  the  arytenoid  cartilage.  The  posterior  facet  (Facies  articularis  thyreoidea)  is 
situated  on  the  front  of  a  ridge,  a  short  distance  from  the  posterior  border;  it  is 
concave,  and  articulates  with  the  posterior  cornu  of  the  thyroid  cartilage.  The 
ventral  and  lateral  parts  of  the  ring  are  formed  by  a  curved  band,  called  the  arch 
(Arcus),  which  is  narrowest  ventrally.     The  lateral  surfaces  of  the  arch  are  grooved 


Muscular  process 


pex 


Crico-tracheal  \     Oblique 
membrane  \       line 

Crico-thyroid 
membrane 


Laryngeal  prominence 


Fig.  457. — Laryngeal  Cartilages  and  Part  of  Trachea  or  Horse;  Right  View. 
For  "thyroid  wing"  read  "thyroid  lamina." 


for  the  crico-thyroid  muscle.  The  anterior  l)order  of  the  lamina  is  thick  and 
slightly  concave;  the  posterior  border  is  thin  and  irregular.  The  anterior  border 
of  the  arch  is  concave  ventrally  and  gives  attachment  to  the  crico-thyroid  membrane ; 
laterally  it  is  thicker  and  gives  attachment  to  the  crico-arytenoideus  lateralis 
muscle.  The  posterior  border  of  the  cartilage  is  attached  to  the  first  ring  of  the 
trachea  by  the  crico-tracheal  membrane.  The  internal  surface  is  smooth  and  is 
covered  with  mucous  membrane. 

The  thyroid  cartilage  (Cartilago  thyreoidea)  consists  of  a  median  thickened 
portion,  termed  the  body,  and  two  lateral  laminae.  The  body  forms  ventrally  a 
slight  prominence  (Prominentia  laryngea),  which  can  be  felt,  but  is  not  visible  in 
the  living  subject;  it  is  related  dorsally  to  the  base  of  the  epiglottis,  which  is  at- 
tached to  it  by  an  elastic  ligament.  The  laminae  or  wings  spring  from  the  body 
on  either  side  and  form  a  large  part  of  the  lateral  wall  of  the  larynx.  Each  is  a 
rhomboid  plate,  presenting  a  slightly  convex  lateral  surface,  which  is  divided  into 
two  areas  by  an  oblique  line  (Linea  obliqua),  on  which  the  thyro-hyoid  and  thyro- 
pharyngeus  muscles  meet.  The  dorsal  border  is  nearly  straight;  it  gives  attach- 
ment to  the  pharyngeal  fascia  and  the  palato-pharyngeus  muscle,  and  bears  a  cornu 
at  each  end.     The  anterior  cornu  (Cornu  orale)  articulates  with  the  cartilage  of  the 


516 


RESPIRATORY   SYSTEM    OF   THE    HORSE 


thjToid  cornu  of  the  hyoid  bone;  below  it  is  a  notch  (Fissura  thyreoidea),  which  is 
converted  into  a  foramen  (Foramen  thyreoideum)  by  a  fibrous  band,  and  trans- 
mits the  anterior  lar>Tigeal  nerve  to  the  interior  of  the  larynx.  The  posterior  cornu 
(Cornu  aborale)  articulates  with  the  cricoid  cartilage.  The  ventral  border  joins 
the  body  in  front,  and  behind  diverges 
from   its  fellow  to  inclose   a  triangular  2Joc/;/ 

space,  the  thyroid  notch  (Incisura  thy- 
reoidea  aboralis),  which  is  occupied  by 
the  crico-thyroid  membrane.     The  anter- 


Mediati  ridge        Lamina 


Facet  for 
arytenoid 


Posterior  cornu 
Surface  for 
cricoid 

Fig.  458. — Cricoid  Cartilage  of  Horse;  Left  Antero-       Fig.  459. — Thyroid  Cartilage  of  Horse;  Ventral 

LATERAL  ViEW.  ViEW. 

ior  border  is  slightly  convex,  and  is  attached  to  the  hyoid  bone  by  the  thyro-hyoid 
membrane.     The  posterior  border  overlaps  the  arch  of  the  cricoid  cartilage,  and 


Pharyngeal  surface 


Medial  angle  of  base  Apex 


Cuneiform  process 

Fig.   460. — Epiglottic   Cartilage  of  Horse;  Right 
Lateral  View. 


Vocal  process 


-Left  Arytenoid  Cartilage  of  Horse; 
Medio-ventral  View. 


gives  attachment  to  the  crico-thyroid  muscle.     The  medial   surface  is  concave, 
and  is  partly  covered  })y  mucous  membrane. 

The  epiglottic  cartilage  (Cartilago  epiglottica),  usually  called  the  epiglottis  for 
the  sake  of  brevity,  is  situated  above  the  body  of  the  thyroid  cartilage  and  curves 


JOINTS,    LIGAMENTS,    AND   MEMBRANES    OF   THE    LARYNX  517 

toward  the  root  of  the  tongue.  It  is  shaped  somewhat  like  a  pointed  ovate  leaf, 
and  presents  two  surfaces,  two  borders,  a  base,  and  an  apex.  The  oral  (or  anterior) 
surface  is  concave  in  its  length,  convex  transversely;  the  pharyngeal  (or  posterior) 
surface  has  the  reverse  configuration.  The  borders  are  thin,  irregular,  and  some- 
what everted.  The  base  is  thick,  and  is  attached  to  the  dorsal  surface  of  the  body 
of  the  thyroid  cartilage  by  elastic  tissue.  From  each  side  of  it  a  cartilaginous  bar 
projects  upward  and  backward;  these  are  the  cuneiform  processes  (Processus 
cuneiformes)  and  correspond  to  the  cuneiform  cartilages  of  man.  The  apex  is 
pointed  and  curved  ventrally.  Nearly  all  of  the  epiglottic  cartilage  is  covered  with 
mucous  membrane.  It  usually  projects  into  the  isthmus  faucium,  but  is  often 
on  the  pharyngeal  side  of  the  soft  palate. 

The  arytenoid  cartilages  (Cartilagines  arytenoideae)  are  situated  on  either  side, 
in  front  of  the  cricoid,  and  partly  medial  to  the  laminae  of  the  thyroid  cartilage. 
They  are  somewhat  pyramidal  in  form,  and  may  be  described  as  having  three 
surfaces,  three  borders,  a  base,  and  an  apex.  The  medial  surface  is  concavo- 
convex,  but  very  slightly  curved,  and  is  smooth  and  covered  by  mucous  membrane. 
The  lateral  surface  is  concave  and  is  separated  from  the  lamina  of  the  thyroid 
cartilage  by  the  crico-arytenoideus  lateralis  and  vocalis  muscles,  and  the  laryn- 
geal saccule.  The  dorsal  surface  is  also  concave,  and  is  covered  by  the  aryte- 
noideus  muscle,  which  is  attached  to  it.  The  dorsal  and  lateral  surfaces  are 
separated  (except  in  front)  by  a  ridge  which  increases  in  size  toward  the  lateral 
angle  of  the  base,  where  it  forms  a  rounded  prominence,  the  muscular  process 
(Processus  muscularis).  The  anterior  and  posterior  borders  are  convex;  they 
converge  ventrally  to  a  thin,  wide  angle,  the  vocal  process  (Processus  vocalis). 
The  process  is  so  named  because  it  furnishes  attachment  to  the  vocal  ligament. 
The  dorsal  border  forms  a  deep  notch  with  the  apex.  The  base  is  concave  and 
faces  chiefly  backward;  it  presents  laterally  an  oval  concave  facet  (Facies  artic- 
ularis)  for  articulation  with  the  anterior  border  of  the  lamina  of  the  cricoid  carti- 
lage. The  medial  angle  of  the  base  is  attached  to  its  fellow  by  the  transverse 
arytenoid  ligament.  The  apex  (Cartilago  corniculata)  curves  upward  and  back- 
ward, forming  with  its  fellow  the  pitcher-shaped  lip  from  which  the  cartilages  derive 
their  name. 

The  cricoid  and  thyroid  cartilages  and  the  greater  part  of  the  arytenoid 
cartilages  are  hyaline.  The  apices  and  vocal  processes  of  the  arytenoid  and  the 
epiglottis  (including  the  cuneiform  processes)  consist  of  elastic  cartilage;  they 
show  no  tendency  toward  ossification  at  any  age.  The  thyroid  and  cricoid  carti- 
lages regularly  undergo  considerable  ossification;  the  process  begins  in  the  body  of 
the  thyroid,  and  often  involves  the  greater  part  of  the  cartilage.^ 

Joints,  Ligaments,  and  Membranes  of  the  Larynx 
The  crico-thyroid  joints  (Articulationes  crico-thyreoidese)  are  diarthroses 
formed  by  the  apposition  of  the  convex  facets  on  the  ends  of  the  posterior  cornua 
of  the  thyroid  cartilage  with  corresponding  facets  on  the  sides  of  the  cricoid  car- 
tilage. The  capsule  is  thin,  but  is  strengthened  by  accessory  bands  dorsally, 
laterally,  and  medially.  The  movements  are  chiefly  rotation  around  a  trans- 
verse axis  passing  through  the  centers  of  the  two  joints. 

The  crico-arytenoid  joints  (Articulationes  crico-arytsenoidea)  are  also  diar- 
throdial.  They  are  formed  by  the  apposition  of  the  convex  facets  on  the  anterior 
border  of  the  cricoid  cartilages  with  the  concave  facets  on  the  bases  of  the  arytenoid 
cartilages.     Each  has  a  very  thin,  loose  capsule,  strengthened  by  accessory  bundles 

1  Calcareous  deposits  are  present  in  the  body  of  the  thyroid  cartilage  even  before  adult  age 
is  reached.  Scheier  (by  use  of  X-rays)  found  complete  calcification  of  the  thyroid  in  two  mares 
eight  and  ten  years  of  age;  in  the  former  the  process  also  involved  a  large  part  of  the  lamina  and 
the  adjacent  part  of  the  arch  of  the  cricoid. 


518  RESPIRATORY   SYSTEM    OF   THE    HORSE 

dorsall}'  and  medially.  The  most  important  movement  is  rotation  of  the  arytenoid 
cartilage  about  a  longitudinal  axis  so  that  the  vocal  process  swings  outward  (ab- 
duction) or  inward  (adduction),  carrying  the  vocal  cord  with  it.  Another  move- 
ment here  is  rotation  about  a  transverse  axis,  in  which  the  apical  part  of  the  carti- 
lage is  raised  or  lowered.  The  arytenoid  is  also  capable  of  slight  inward  or  outward 
gliding  movement. 

The  th3rro-hyoid  joints  (Articulationes  hyo-thyreoidese)  are  formed  by  the 
anterior  cornua  of  the  thyroid  cartilage  and  the  cartilaginous  extremities  of  the 
thyroid  cornua  of  the  hyoid  bone.  They  are  diarthroses  and  the  joint  capsule  is 
reinforced  by  a  relatively  strong  thyro-hyoid  ligament.  The  thyroid  cornu  has 
here  a  cartilaginous  prolongation  about  a  quarter  of  an  inch  (ca.  6  mm.)  in  length. 
The  chief  movement  is  rotation  around  a  transverse  axis  passing  through  the  two 
joints. 

The  crico-thyroid  membrane  (Membrana  crico-thyreoidea)  occupies  the  thy- 
roid notch  and  extends  backward  to  the  arch  of  the  cricoid  cartilage.  It  is  tri- 
angular in  form,  and  is  attached  by  its  base  to  the  anterior  border  of  the  arch  of 
the  cricoid  cartilage,  while  its  borders  are  attached  to  the  margins  of  the  thyroid 
notch.  It  is  strong,  tightly  stretched,  and  composed  largely  of  elastic  tissue.  It 
is  reinforced  ventrally  by  longitudinal  fibers,  dorsally  by  fibers  which  stretch  across 
the  thyroid  notch. 

The  thyro-hyoid  membrane  (Membrana  hyo-thyreoidea)  connects  the  body 
and  anterior  borders  of  the  thyroid  cartilage  with  the  body  and  thyroid  cornua  of 
the  hyoid  bone. 

The  hyo-epiglottic  ligament  (Lig.  hyo-epiglotticum)  attaches  the  lower  part 
of  the  oral  surface  of  the  epiglottis  to  the  body  of  the  hyoid  bone.  It  forms  an 
elastic  sheath  for  the  hyo-epiglottic  muscle.  Ventrally  it  blends  with  the  thyro- 
hyoid membrane,  and  dorsally  it  is  not  well  defined. 

The  thyro-epiglottic  ligament  (Lig.  thyreo-epiglotticum)  is  strong  and  thick; 
it  is  composed  chiefly  of  elastic  tissue.  It  connects  the  base  of  the  epiglottis  with 
the  body  and  the  adjacent  medial  surfaces  of  the  laminae  of  the  thyroid  cartilage. 
Other  fibers  attach  the  cuneiform  processes  somewhat  loosely  to  the  thyroid  laminae. 

The  transverse  arytenoid  ligament  (Lig.  arytsenoideum  transversum)  is  a 
slender  band  which  connects  the  medial  angles  of  the  bases  of  the  arytenoid  carti- 
lages. 

The  vocal  (or  posterior  thyro-arytenoid)  ligament  (Lig.  vocale)  underlies  and 
is  intimately  adherent  to  the  mucous  membrane  of  the  true  vocal  cord.  It  is  thin 
and  elastic  and  is  attached  ventrally  to  the  body  of  the  thyroid  cartilage  and  the 
crico-thyroid  membrane  close  to  its  fellow  of  the  opposite  side,  and  ends  dorsally 
on  the  processus  vocalis  of  the  arytenoid  cartilage. 

The  ventricular  (or  anterior  thyro-arytenoid)  ligament  (Lig.  ventriculare)  is 
included  in  the  false  vocal  cord.  It  consists  of  loosely  arranged  bundles  which 
arise  chiefly  from  the  cuneiform  process  and  end  on  the  lateral  surface  of  the  pro- 
cessus vocalis  and  adjacent  part  of  the  arytenoid  cartilage. 

The  crico-tracheal  membrane  (Membrana  crico-trachealis)  connects  the  cri- 
coid cartilage  with  the  first  ring  of  the  trachea. 

Muscles  of  the  Larynx 
A.  Extrinsic  Muscles 
The  stemo-thyro-hyoideus  is  described  on  p.  268. 

The  thyro-hyoideus  (M.  hyo-thyreoideus)  is  a  flat,  quadrilateral  muscle,  which 
lies  on  the  lateral  surface  of  the  thyroid  lamina  and  the  lateral  part  of  the  thyro- 
hyoid membrane.  It  arises  from  the  body  and  thyroid  cornu  of  the  hyoid  bone 
(almost  meeting  the  opposite  muscle),  and  ends  on  the  oblique  line  on  the  lamina 


MUSCLES    OF    THE    LARYNX  519 

of  the  thyroid  cartilage.  Its  action  is  to  draw  the  larynx  toward  the  root  of  the 
tongue.  It  is  related  laterally  to  the  external  maxillary  vein  and  the  anterior  part 
of  the  mandibular  gland. 

The  hyo-epiglotticus  (M.  hyo-epiglotticus)  is  a  feeble  muscle  which  occupies  a 
median  position  above  the  central  part  of  the  thyro-hyoid  membrane,  enclosed  by 
an  elastic  sheath,  the  hyo-epiglottic  ligament.  It  arises  from  the  body  of  the  hyoid 
bone  by  two  branches  which  unite  and  are  inserted  into  the  front  of  the  base  of  the 
epiglottis.     Its  action  is  to  draw  the  epiglottis  toward  the  root  of  the  tongue. 

B.  Intrinsic  Muscles 

The  crico-thyroideus  (M.  crico-thyreoideus)  is  a  short  muscle  which  fills  the 

groove  on  the  lateral  surface  of  the  cricoid  cartilage ;   its  fibers  are  directed  dorsally 

and  somewhat  forward.     It  arises  from  the  ventral  part  of  the  lateral  surface  and 

posterior  edge  of  the  cricoid  cartilage,  and  is  inserted  into  the  posterior  border  and 


Fig.  4G2. — Laryngeal  Muscles  of  Horse,  Seen  from  Left  Side  After  Removal  of  Major  Part  op  Lamina  op 

Thyroid  Cartilage. 
a,  Kerato-hyoideus;  b,  thyro-hyoideus;  c,  crico-thyroideus;  d,  sterno-thyroideus;  e,  ventricularis;  /,  vocalis;  g, 
crico-arytenoideus  lateralis;  h,  crico-arytenoideus  dorsalis;  i,  arytenoideus  transversus;  1,  lingual  process;  2,  small 
cornu,  3,  thyroid  cornu,  of  hyoid  bone;  4<  thyroid  cartilage;  5,  cricoid  cartilage;  6,  epiglottis;  7,  apex  of  arytenoid 
cartilage;  5,  trachea;  S,  muscular  process  of  arytenoid;  ^0,  lateral  lobe  of  thyroid  gland;  iO',  isthmus  of  thyroid  gland; 
11,  laryngeal  saccule.  The  saccule  is  larger  than  it  is  represented  in  this  figure,  and  extends  almost  to  the  vocal 
process.     (Ellenberger-Baum,  Anat.  d.  Haustiere.) 

adjacent  part  of  the  lateral  surface  of  the  lamina  of  the  thyroid  cartilage.  Its 
action  is  to  draw  the  thyroid  cartilage  and  the  ventral  part  of  the  cricoid  cartilage 
together.  In  this  action  the  cricoid  cartilage  is  probably  rotated  about  a  trans- 
verse axis  through  the  crico-thyroid  joints,  carrying  the  bases  of  the  arytenoid 
cartilages  with  it  and  thus  tensing  the  vocal  cords. 

The  crico-arytenoideus  dorsalis  (M.  crico-arytsenoideus  dorsalis)^  is  a  strong, 
somewhat  fan-shaped  muscle,  which,  with  its  fellow,  covers  the  dorsal  surface  of 
the  lamina  of  the  cricoid  cartilage.  It  is  partially  divisible  into  two  layers.  It 
has  a  broad  origin  on  half  of  the  lamina  of  the  cricoid  cartilage,  including  the  me- 
dian ridge,  and  its  fibers  converge  to  be  inserted  into  the  processus  muscularis  of 
the  arytenoid  cartilage.  Its  action  is  to  dilate  the  rima  glottidis  by  rotating  the 
arytenoid  cartilage  so  as  to  carry  the  vocal  process  and  cord  outward  (abduction). 

The  crico-arytenoideus  lateralis  (M.  crico-arytsenoideus  lateralis)  lies  on  the 
medial  face  of  the  thyroid  lamina.  It  arises  from  the  anterior  border  of  the  lateral 
part  of  the  arch  of  the  cricoid  cartilage.  The  fibers  pass  in  a  dorsal  direction  and 
converge  on  the  processus  muscularis  of  the  arytenoid  cartilage.  It  closes  the 
rima  glottidis  by  rotating  the  arytenoid  cartilage  inward  (adduction). 
1  Also  known  as  the  crico-arytenoideus  posterior  s.  posticus. 


520 


RESPIRATORY    SYSTEM    OF    THE    HORSE 


The  arytenoideous  transversus  (M.  arytsenoideus  transversus)  is  an  unpaired 
muscle  which  stretches  across  the  concave  dorsal  surface  of  the  arytenoid  cartilages. 
Its  fibers  are  attached  on  either  side  to  the  processus  muscularis  and  the  ridge  which 
extends  forward  from  it.  The  right  and  left  parts  of  the  muscle  meet  at  a  fibrous 
raphe,  which  is  connected  with  the  transverse  arytenoid  ligament.  Fibers  of  the 
ventricularis  muscle  overlap  its  anterior  part.  It  narrows  the  rima  by  draw- 
ing the  arytenoid  cartilages  together  (adduction). 

The  ventricularis^  lies  in  the  lateral  wall  of  the  larynx,  covered  by  the  lamina  of 
the  thyroid  cartilage.  It  arises  from  the  anterior  part  of  the  crico-thyroid  membrane 
and  the  ventral  border  of  the  thyroid  lamina.     Its  fibers  pass  upward  and  backward 


Salpingo-pharyngeal 
fold 

Epiglottis 

Aryteno-epiglottic 
fold 


Root  of  tongue 
Soft  palate  {cut) 


FiQ.  463." 


Wall  of  pharynx 
Arytenoid  cartilage  (apex) 

Posterior  pillar  of  soft  palate 

Position  of  cricoid 
cartilage  under  oesophagus 

Thyroid  gland 
Trachea 
(Esophagus 


-Aditus  Laryngi8  op  Horse,  Exposed  bt  Opening  Pharynx  and  Beginning  op  Esophagus  Along 
Median  Dorsal  Line. 
1,  False  vocal  cord;  S,  lateral' ventricle;     S,   true  vocal  cords;  4<  rima  glottidis. 


to  end  partly  on  the  processus  muscularis,  partly  on  the  arytenoideus  transversus, 
meeting  its  fellow. 

The  vocalis^  is  also  medial  to  the  lamina  of  the  thyroid  cartilage,  and  is  in  part 
separated  from  the  preceding  muscle  by  the  laryngeal  saccule.  It  has  an  extensive 
origin  on  the  crico-thyroid  membrane.  Its  direction  corresponds  with  that  of  the 
true  vocal  cord.  It  is  inserted  into  the  lateral  surface  of  the  arytenoid  cartilage 
below  the  processus  muscularis. 

The  two  preceding  muscles  close  the  rima  glottidis  and  slacken  the  vocal  cords. 
With  the  arytenoideus  transversus  and  crico-arytenoideus  lateralis  they  form  a 
sphincter  which  closes  the  entrance  to  the  larynx. 

1  These  two  muscles  were  formerly  taken  together  as  parts  of  the  thyro-arytenoideus  muscle. 


CAVITY    OF   THE    LARYNX 


521 


The  ventricularis  rotates  the  arytenoid  so  as  to  bring  the  apical  part  of  the  cartilage  down- 
ward and  forward. 

In  some  cases  there  is  a  small  thyro-ar3rtenoideus  extemus  muscle  which  arises  from  the 
medial  face  of  the  lamina  of  the  thyroid  cartilage  near  the  dorsal  border,  passes  upward  and 
backward,  and  blends  with  the  arytenoideus  trans  versus. 

Cavity  of  the  Larynx 

The  cavity  of  the  larynx  (Cavum  laryngis)  is  smaller  than  one  would  naturally 
expect  from  its  external  appearance.  On  looking  into  it  through  the  pharyngeal 
end  two  folds  are  seen  projecting  from  each  lateral  wall.     These  are  termed  the 


Fig.  464. — Part  of  Sagittal  Section  of  Head  of  Horse. 
Section  is  cut  just  to  left  of  median  plane. 
1,  Epiglottis;  2,  body  of  thyroid  cartilage;  3,  arytenoid  cartilage;  4,  4',  lamina  and  arch  of  cricoid  cartilage;  5, 
ary-epiglottic  fold;  6,  vocal  cord  (laoium  vocale):  7,  ventricular  fold  or  false  vocal  cord  (plica  ventricularis);  8,  lateral 
ventricle  of  larynx;  8',  dotted  line  indicating  contour  of  laryngeal  saccule;  9,  middle  ventricle  of  larynx;  10,  m.  crico- 
arytenoideus  dorsalis;  11,  CEsophagus;  12,  septum  of  areolar  tissue  between  guttural  pouches;  13,  m.  rectus  capitis 
ventralis;  14,  body  of  sphenoid  bone;  15,  pharyngeal  recess;  16,  arrow  points  into  nasal  cavity;  17,  pharyngeal  open- 
ing of  auditive  or  Eustachian  tube;  18,  posterior  pillars  of  soft  palate  united  over  aditus  CEsophagi;  19,  arrow  points 
into  vestibule  of  larynx;  20,  soft  palate;  21,  tonsil;  22,  root  of  tongue;  23,  m.  hyo-epiglotticus;  24,  hyoid  bone;  25, 
mandibular  lymph  glands;  26,  mm.  omo-hyoideus  and  sterno-hyoideus;  A,  vestibule  of  larynx;  B,  glottis;  C,  post- 
glottic  part  of  larynx;   Z),  trachea;   E,  pharynx,  F,  isthmus  faucium. 


vocal  cords,  and  the  narrow  part  of  the  cavity  between  them  is  the  rima  glottidis. 
Thus  it  is  convenient  to  recognize  three  divisions  of  the  cavity. 

The  aditus  laryngis,  or  pharyngeal  aperture,  is  a  large,  oblique,  oval  opening, 
which  faces  into  the  ventral  part  of  the  pharynx.  It  is  bounded  in  front  by  the 
epiglottis,  behind  by  the  arytenoid  cartilages,  and  laterally  by  the  aryteno-epi- 
glottic  folds  of  mucous  membrane  (Plicae  aryepiglotticae) ,  which  stretch  between 
the  edges  of  the  epiglottis  and  the  arytenoid  cartilages. 


522 


RESPIRATORY   SYSTEM    OF   THE    HORSE 


The  vestibule  of  the  larynx  (Vestibulum  laryngis)  is  that  part  of  the  cavity 
which  extends  from  the  aditus  to  the  vocal  cords.  On  its  lateral  walls  are  the  false 
vocal  cords  (Plicae  ventriculares),  each  of  which  consists  of  a  fold  of  mucous  mem- 
brane covering  the  ventricular  ligament  and  the  cuneiform  process.  Between  the 
false  and  true  vocal  cord  there  is  a  pocket-like  depression  termed  the  lateral  ven- 
tricle of  the  larynx  (Ventriculus  lateralis  laryngis).  This  is  the  entrance  to  the 
laryngeal  saccule  (Sacculus  laryngis),  a  cul-de-sac  of  the  mucous  membrane  which 
is  an  inch  or  more  (ca.  2.5  to  3  cm.)  long  and  extends  upward  and  backward  on  the 
medial  surface  of  the  thyroid  lamina.  There  is  a  small  middle  ventricle  (Ventric- 
ulus laryngis  medianus)  at  the  base  of  the  epiglottis. 

The  term  "larjmgeal  saccule"  seems  decidedly  preferable  to  the  "appendix  ventriculi  lar- 
yngis" of  the  B.  N.  A.     The  saccule  is  in  relation  with  the  ventricular  and  vocal  muscles,  and 


Body  of  thyroid 
cartilage 


Crico- 

arytenoideus 
dor  salts 
muscle 


Fig.  466. — Cast    of    Right    Lateral  Ventricle 

AND  Saccule  of  Horse;  Medial  View. 

1,  Ventricle;   2,  saccule.     Figure  is  a  little  less  than 

three-fourths  of  natural  size. 


Fig.  465. — Section  of  Larynx  of  Horse. 
The  section  cut  is  parallel  with  the  vocal  cords. 


Fig.  467. — Cast  of  Left  Lateral  Ventricle  and 

S-4.CCULE  OF  Larynx  of  Horse;  Lateral  View. 

1,  Ventricle;  2,  saccule;  3,  impression  of  ventricu- 

laris  muscle;  4,  impression  of  vocalis  muscle. 


when  the  latter  are  atrophic  (as  in  hemiplegia  laryngis  or  "roaring"),  the  pouch  is  considerably 
larger  on  the  affected  side,  having  occupied  the  space  vacated  by  the  muscles.  The  blind  end  of 
the  saccule  lies  just  below  the  level  of  the  muscular  process  of  the  arytenoid  cartilage.  It  is  loosely 
attached  to  the  contiguous  structures.     The  average  capacity  of  the  saccule  is  about  5  to  6  c.c. 

The  middle,  narrow  part  of  the  cavity  is  termed  the  glottis  or  rima  glottidis. 
It  is  bounded  on  either  side  ])y  the  true  vocal  cord  and  the  medial  surface  of  the  ary- 
tenoid cartilage.  The  true  vocal  cords  (Labia  vocales)  are  situated  behind  the 
false  cords  and  the  lateral  ventricles.  They  extend  from  the  angle  of  junction  of 
the  body  and  laminae  of  the  thyroid  cartilage  to  the  vocal  processes  of  the  arytenoid 
cartilages.  They  are  prisniatic  in  cross-section,  and  their  free  edges  look  forward 
and  somewhat  upward.  The  mucous  membrane  of  the  cord  (Plica  vocalis)  is  very 
thin  and  smooth,  and  is  intimately  attached  to  the  underlying  vocal  ligament.     In 


THE    TRACHEA  523 

ordinary  breathing  the  rima  is  somewhat  lanceolate  in  form  (Fig.  465) ;  when  dilated, 
it  is  diamond-shaped,  the  widest  part  being  between  the  vocal  processes.  The 
narrow  part  of  the  glottis  between  the  vocal  cords  is  termed  the  glottis  vocalis  (Pars 
intermembranacea) ,  while  the  wider  part  between  the  arytenoid  cartilages  is  the 
glottis  respiratoria  (Pars  intercartilaginea) . 

In  the  revised  nomenclature  the  terms  "true"  and  "false"  vocal  cords  have  been  replaced 
by  "labium  vocale"and  "plica  ventricularis."  The  labium  vocale  consists  of  the  plica  vocalis, 
lig.  vocale,  and  m.  vocalis;   the  last  forms  the  bulk  of  the  projection. 

The  posterior  compartment  of  the  laryngeal  cavity  is  directly  continuous  with 
the  trachea.  It  is  enclosed  by  the  cricoid  cartilage  and  the  crico-thyroid  membrane. 
It  is  clearly  marked  off  laterally  by  the  vocal  cord  and  the  projection  caused  by  the 
posterior  iDorder  of  the  arytenoid  cartilage.  It  is  oval  in  form,  the  transverse 
diameter  being  an  inch  and  a  half  to  two  inches  (ca.  4  to  5  cm.),  and  the  dorso- 
ventral  diameter  two  to  two  and  a  half  inches  (ca.  5  to  6  cm.). 

The  mucous  membrane  of  the  larynx  (Tunica  mucosa  laryngis)  is  reflected 
around  the  margin  of  the  aditus  to  become  continuous  with  that  of  the  pharynx, 
and  is  continuous  behind  with  that  which  lines  the  trachea.  It  is  closely  attached 
to  the  epiglottis,  except  at  the  base,  but  elsewhere  in  the  aditus  and  vestibule  it  is 
loosely  attached  by  submucous  tissue  which  contains  many  elastic  fibers.  It  is 
thin  and  very  closely  adherent  over  the  vocal  cords  and  the  medial  surfaces  of  the 
arytenoid  cartilages.  The  epithelium  is  of  the  stratified  squamous  type  from  the 
aditus  to  the  glottis,  beyond  which  it  is  columnar  ciliated  in  character.  There  are 
numerous  mucous  laryngeal  glands  (Glanclulse  laryngese),  except  in  the  glottis  and 
the  pharyngeal  surface  of  the  epiglottis,  in  which  situations  they  are  scanty.  Lymph 
nodules  (Noduli  lymphatic!  laryngei)  are  also  present,  especially  at  the  lateral 
ventricle. 

Vessels  and  Nerves. — The  arteries  are  derived  from  the  laryngeal  and  ascend- 
ing pharyngeal  arteries.  The  veins  correspond  to  the  arteries.  The  lymph- 
vessels  go  to  the  anterior  cervical  and  pharyngeal  lymph  glands.  The  nerves 
come  from  the  vagus.  The  recurrent  or  posterior  laryngeal  is  the  motor  nerve  to 
the  muscles  with  the  exception  of  the  crico-thyroideus.  The  anterior  laryngeal 
is  the  sensory  nerve;   it  commonly  supplies  the  nerve  to  the  crico-thyroideus. 


THE  TRACHEA 

The  trachea  extends  from  the  larynx  to  the  roots  of  the  lungs,  where  it  divides 
into  the  right  and  left  bronchi.  It  is  kept  permanently  open  by  a  series  of  fifty  to 
sixty  incomplete  cartilaginous  rings  embedded  in  its  wall.  It  occupies  a  median 
position,  except  near  its  termination,  where  it  is  pushed  a  little  to  the  right  by  the 
arch  of  the  aorta.  It  is  approximately  cylindrical,  but  its  cervical  part  is  for  the 
most  part  depressed  dorso-ventrally  by  contact  with  the  longus  colli  muscle,  so 
that  the  dorsal  surface  is  flattened.  Its  average  length  is  about  30  to  32  inches  (ca. 
75  to  80  cm.).  The  average  caliber  is  about  two  to  two  and  one-half  inches  (ca.  5  to 
6  cm.),  but  in  the  greater  part  of  the  neck  the  transverse  diameter  is  greater  and  the 
clorso-ventral  smaller.^    It  is  enclosed  by  a  fascia  propria. 

In  its  cervical  part  (Pars  cervicalis)  the  trachea  is  related  dorsally  to  the 
oesophagus  for  a  short  distance,  but  chiefly  to  the  longus  colli  muscles.  It  is  related 
laterally  to  the  lateral  lobes  of  the  thyroid  gland,  the  carotid  artery,  the  jugular 
vein,  the  vagus,  sympathetic,  and  recurrent  laryngeal  nerves,   and  the  tracheal 

1  At  its  origin  the  trachea  is  almost  circular  in  cross-section  and  the  average  diameter  is 
about  two  and  a  quarter  inches  (ca.  5.5  cm.).  It  soon  becomes  flattened  dorso-ventrally,  so  that 
the  transverse  diameter  may  be  nearly  three  inches  (ca.  7  cm.)  and  the  dorso- ventral  about  two 
inches  (ca.  5  cm.).  In  the  thorax  the  diameters  become  more  nearly  equal,  and  sometimes  the 
dorso-ventral  diameter  is  the  greater;   this  is  the  case  where  the  aorta  crosses  the  trachea. 


524 


RESPIRATORY   SYSTEM    OF   THE    HORSE 


Ijonph  ducts  and  cervical  lymph  glands.  The  oesophagus  lies  on  its  left  face  from 
the  third  cervical  vertebra  backward.  The  sterno-cephalicus  muscles  cross  it  very 
obliquely,  passing  from  the  ventral  surface  forward  over  its  sides,  and  diverging  to 
reach  the  angles  of  the  jaw.  The  omo-hyoidei  also  cross  it  very  obliquely,  passing 
over  the  lateral  surfaces  of  the  tube,  and  converging  ventrally  in  the  laryngeal 
region.  The  sterno-thyro-hyoideus  lies  on  the  ventral  surface.^  The  scaleni  lie  on 
either  side  near  the  entrance  to  the  thorax. 

The  thoracic  part  (Pars  thoracalis)  of  the  trachea  (Figs.  553,  554)  passes  back- 


Obliquiis 

capitis 

posterior 

Intertrax.s 

versali. 

Longissirnii 

capitis  et  atlanti 


Rectus  capitis 

ventralis  major 

Brachiocephalic  us 

humeralis 


Vagosympa- 
thetic trunk 
Carotid  artery 

Recurrent  nerve 
Jugular  vein 


Sterno- 
cephalicus 


Omo-hyoideus 


Stemo-thyroideus       Sterno-hyoideus 

Fig.  468. — Cross-section  of  Ventral  Part  of  Neck  of  Horse. 
This  section  is  cut  at  right  angles  to  the  long  axis  of  the  neck,  passing  through  the  junction  of  the  second  and  third 
cervical  vertebrae.     S.c,  Spinal  cord;  S.v.,  spinal  vein;  V.v.,  V.a.,  vertebral  vein  and  artery;   T.p.,  transverse  process 
(tip);  F,  intervertebral  fibro-cartilage;    T,  atlantal  tendon  common  to  brachiocephalicus,  splenius,  and  longissimus 
atlantis;  M,  digitation  of  brachiocephalicus  inserted  by  T. 


ward  between  the  pleural  sacs  and  divides  into  two  bronchi  over  the  left  atrium  of  the 
heart.  It  is  related  dorsally  to  ths  longus  colli  tor  a  short  distance,  and  beyond  this  to 
the  oesophagus.  Its  left  face  is  crossed  by  the  aortic  arch,  the  left  brachial  artery,  and 
the  thoracic  duct.  Its  right  face  is  crossed  by  the  vena  azygos,  the  dorso-cervical 
and  vertebral  vessels,  and  the  right  vagus  nerve.  Ventrally  it  is  related  to  the 
anterior  vena  cava,  the  brachiocephalic  and  common  carotid  trunks,  and  the  car- 
diac and  left  recurrent  nerves. 

1  The  arrangement  of  the  muscles  should  be  noted,  since  the  space  enclosed  by  the  divergence 
of  the  stemo-cephalici  and  the  convergence  of  the  omo-hyoidei  is  the  area  of  election  for  the  opera- 
tion of  tracheotomy. 


THE    BRONCHI THE    THORACIC    CAVITY  525 

The  bifurcation  of  the  trachea  (Bifurcatio  trachese)  is  situated  opposite  to  the 
fifth  rib  or  intercostal  space,  and  about  four  or  five  inches  (ca.  10  to  12  cm.)  ventral 
to  the  vertebral  column. 

The  trachea  is  composed  of — (1)  the  cartilaginous  rings;  (2)  a  fibro-elastic 
membrane  which  encloses  and  connects  the  rings;  (3)  a  muscular  layer;  (4)  the 
mucous  membrane.  The  elastic  membrane  is  intimately  attached  to  the  peri- 
chondrium of  the  rings.  In  the  intervals  between  the  latter  it  constitutes  the 
tracheal  annular  ligaments  (Ligamenta  annularia  trachealia).  The  rings  of  the 
trachea  (Cartilagines  tracheales)  are  composed  of  hyaline  cartilage.  They  are 
incomplete  dorsally,  and  when  their  free  ends  are  drawn  apart,  resemble  somewhat 
the  letter  C.  In  the  cervical  part  the  free  ends  overlap,  while  in  the  thoracic  part 
they  do  not  meet;  here  the  deficiency  is  made  up  by  thin  plates  of  variable  size 
and  form,  embedded  in  a  membrana  transversa.  Ventrally  the  rings  are  about 
one-half  inch  (ca.  1.5  cm.)  wide,  while  dorsally  they  are  wider  and  thinner.  The 
first  ring  is  attached  to  the  cricoid  cartilage  by  the  crico-tracheal  membrane,  and  is 
often  fused  dorsally  with  the  second  ring.  Various  irregularities,  such  as  partial 
bifurcation  or  partial  or  complete  fusion  of  adjacent  rings,  are  common.  The 
arrangement  in  the  terminal  part  is  very  irregular.  The  trachealis  muscle  (M. 
trachealis)  consists  of  unstriped  fibers  which  stretch  across  the  dorsal  part  of  the 
tube.  It  is  separated  from  the  ends  of  the  rings  and  the  membrana  transversa  by 
a  quantity  of  areolar  tissue.  When  it  contracts  the  caliber  of  the  tube  is  diminished. 
The  mucous  membrane  is  pale  normally,  and  presents  numerous  fine  longitudinal 
folds,  in  which  are  bundles  of  elastic  fibers.  The  epithelium  is  stratified  columnar 
ciliated.  Numerous  tracheal  glands  (Glandulae  tracheales)  are  present;  they  are 
tubulo-alveolar  and  mixed  in  type. 

Vessels  and  Nerves. — The  arteries  are  derived  chiefly  from  the  common 
carotid  arteries,  and  the  veins  go  mainly  to  the  jugular  veins.  The  lymph-vessels 
go  to  the  cervical  and  mediastinal  lymph  glands.  The  nerves  come  from  the  vagus 
and  sympathetic. 

THE  BRONCHI 

The  two  bronchi,  right  and  left  (Bronchus  dexter,  sinister),  are  formed  by  the 
bifurcation  of  the  trachea.  Each  passes  backward  and  outward  to  the  hilus  of 
the  corresponding  lung.  The  right  bronchus  is  a  little  larger  and  less  oblique  in 
direction  than  the  left.  They  are  related  ventrally  to  the  divisions  of  the  puhnon- 
ary  artery,  and  dorsally  to  the  branches  of  the  bronchial  artery  and  the  bronchial 
lymph  glands.  Their  structure  is  similar  to  that  of  the  trachea,  but  the  cartilagi- 
nous framework  consists  chiefly  of  plates  instead  of  rings. 


THE  THORACIC  CAVITY 

The  thoracic  cavity  (Cavum  thoracis)  is  the  second  in  point  of  size  of  the  body 
cavities.  In  form  it  is  somewhat  like  a  truncated  cone,  much  compressed  laterally 
in  its  anterior  part,  and  with  the  base  cut  off  very  obliquely.  The  dorsal  wall 
or  roof  is  formed  by  the  thoracic  vertebrae  and  the  ligaments  and  muscles  connected 
with  them.  The  lateral  walls  are  formed  by  the  ribs  and  the  intercostal  muscles. 
The  ventral  wall  or  floor  is  formed  by  the  sternum,  the  cartilages  of  the  sternal 
ribs,  and  the  muscles  in  connection  therewith.  It  is  about  one-half  as  long  as  the 
dorsal  wall.  The  posterior  wall,  formed  by  the  diaphragm,  is  very  oblique  and  is 
strongly  convex.  The  anterior  aperture  or  inlet  (Apertura  thoracis  cranialis)  is 
relatively  small,  and  of  narrow,  oval  form.  It  is  bounded  dorsally  by  the  first 
thoracic  vertebra  and  laterally  by  the  first  pair  of  ribs.  It  is  occupied  by  the  longus 
colli  muscles,  the  trachea,  oesophagus,  vessels,  nerves,  and  lymph  glands. 

A  longitudinal  septum,  termed  the  mediastinima  thoracis  (Septum  medias- 


526  RESPIRATORY    SYSTEM    OF   THE    HORSE 

tinale),  extends  from  the  aorsal  wall  to  the  ventral  and  posterior  walls,  and  divides 
the  cavity  into  two  lateral  chambers.  Each  of  these  chambers  is  lined  by  a  serous 
membrane  called  the  pleura,  and  is  termed  a  pleural  cavity  (Cavum  pleurae) .  The 
mediastinum  is,  for  the  most  part,  not  median  in  position,  as  might  be  inferred 
from  its  name;  this  is  chiefly  due  to  the  fact  that  the  largest  organ  contained  in  it, 
the  heart.,  is  placed  more  on  the  left  side  than  on  the  right;  consequently  the  right 
pleural  cavity  and  lung  are  larger  than  the  left.  Practically  all  of  the  organs  in 
the  thorax  are  in  the  mediastinal  space,  with  the  exception  of  the  lungs,  the  posterior 
vena  cava,  and  the  right  phrenic  nerve.  The  part  in  which  the  heart  and  the  peri- 
cardium are  situated,  together  with  that  dorsal  to  it,  is  usually  called  the  middle 
mediastinal  space  (Cavum  mediastinale  medium);  the  parts  before  and  behind 
this  are  termed  respectively  the  anterior  and  posterior  mediastinal  spaces  (Cavum 
mediastinale  craniale,  caudale). 


THE  PLEURA 

The  pleurae  are  two  serous  membranes,  right  and  left,  which  enclose  on  each 
side  a  pleural  cavity  (Cavum  pleurae) .  They  line  the  walls  of  the  thorax,  form  the 
lateral  laminae  of  the  mediastinum,  and  are  reflected  from  the  latter  upon  the  lungs. 
We  therefore  distinguish  parietal,  mediastinal,  and  pulmonary  or  visceral  parts  of 
the  pleurae. 

The  parietal  pleura  (Pleura  parietalis)  is  attached  to  the  thoracic  wall  bj^  the 
endothoracic  fascia.  On  the  lateral  thoracic  wall  it  is  adherent  to  the  riljs  and 
intercostal  muscles  and  is.  termed  the  costal  pleura  (Pleura  costalis) .  Behind  it  is 
closely  attached  to  the  diaphragm,  forming  the  diaphragmatic  pleura  (Pleura 
diaphragmatica) . 

The  mediastinal  pleura  (Pleura  mediastinalis)  covers  the  organs  in  the  medi- 
astinal space  and  is  in  part  in  apposition  with  the  opposite  sac.  Where  this  layer 
is  adherent  to  the  pericardium,  it  is  distinguished  as  pericardiac  pleura  (Pleura 
pericardiaca).^ 

From  the  mediastinum  each  pleura  is  reflected  upon  the  corresponding  lung, 
which  it  covers,  constituting  the  pulmonary  or  visceral  pleura  (Pleura  pulmonalis). 
The  reflection  occurs  around  and  behind  the  hilus  of  the  lung,  and  is  in  great  part 
direct,  so  that  a  portion  of  the  mediastinal  surface  of  each  lung  has  no  pleural 
covering.  Behind  the  hilus  of  the  lung  a  considerable  triangular  area  is  not  covered 
by  the  pleura,  the  two  lungs  being  attached  to  each  other  by  a  thin  layer  of  con- 
nective tissue  in  this  situation.^  Posteriorly  the  reflection  is  not  direct,  so  that 
there  is  a  fold  formed  by  the  reflection  of  the  pleura  from  the  mediastinum  and  the 
diaphragm  to  the  lung,  behind  the  triangular  area  of  adhesion  just  mentioned;  it 
is  seen  when  the  base  of  the  lung  is  dra^vn  outward.  This  is  the  pulmonary  liga- 
ment (Lig.  pulmonale) ;  it  consists  of  two  layers  of  pleura,  between  which  there  is 
elastic  tissue,  especially  abundant  in  its  posterior  part. 

The  right  pleura  forms  a  special  sagittal  fold  about  a  nandbreaatn  to  the  right 
of  the  median  plane,  which  encloses  the  posterior  vena  cava  in  its  upper  edge;  it  is 
therefore  called  the  fold  of  the  vena  cava  (Plica  venae  cavae).  It  gives  off  a  small 
accessory  fold  for  the  right  phrenic  nerve.  The  fold  arises  from  the  thoracic  floor 
and  from  the  diaphragm  below  the  foramen  venae  cavae,  and  intervenes  between  the 
intermediate  lobe  and  the  body  of  the  right  lung.     It  is  delicate  and  lace-like. 

The  posterior  mediastinum  is  very  delicate  ventral  to  the  oesophagus,  and 

1  The  student  should  bear  in  mind  that  these  terms  are  employed  simply  as  a  matter  of 
convenience  in  description;  all  the  parts  of  each  pleural  sac,  though  differently  named,  form  a 
continuous  whole. 

2  Here  the  mediastinal  pleura  does  not  extend  continuously  from  the  dorsal  to  the  ventral 
wall,  but  consists  of  dorsal  and  ventral  parts. 


THE    PLEURA 


527 


Dorso-scapular  ligament 


Ligamentum  nnchic 


Trapezius 
Rhomhuideus 


Cartilage  of  scapula 


Peciora lis  profit nd u s 
{p.  scapular  is) 


Pectoralis  superficialis 
ip.  transversa] 


Longissimus  dorsi 
Multifidus 
Serratus  veniralis 

Longissimus 
cost  arum 
Levator  costoe 

Suhscapularis 
Lnfraspinatus 

Cutaneiis 


Teres  major 


DeUoideus 
Triceps 
(c.  longum) 


Triceps 
(c.  later-ale) 

Coraco-brachialis 

Brachialis 
Pectoralis  prof, 
{p.  humeralis) 
Extensor  carpi 
radialis 
Biceps  brachii 


Fig.  469. — Section  of  Thorax  of  Horse. 

The  section  is  cut  in  an  oblique  direction  corresponding  with  the  spire  of  the  scapula.  It  passes  through  the  fourth 
thoracic  vertebra  and  a  little  more  than  an  inch  behind  the  shoulder  joint.  The  pleural  cavities,  indicated  by  wide 
black  Unes,  are  exaggerated  for  the  sake  of  clearness. 

1,  Pleural  cavities  (number  is  placed  in  mediastinum);  2,  2',  lungs;  3,  cesophagus;  4,  trachea;  5,  brachiocephalic 
trunk;  6,  anterior  vena  cava;  7,  thoracic  duct;  8,  8',  vagi;  9,  left  recurrent  nerve;  10,  10',  phrenic  nerves;  11,  internal 
thoracic  vessels;  12,  sympathetic  trunk;  13,  subcostal  vessels;  14,  external  thoracic  vessels;  15,  brachial  vein;  16_ 
brachial  artery;  17,  radial  nerve;  IS,  ulnar  nerve;  19,  musculo-cutaneous  nerve;  20,  median  nerve;  21,  subscapular 
vessels;  a,  m.  longus  colli;  6,  m.  rectus  thoracis;  c,  m.  transversus  thoracis;  d,  m.  intercostalis  internus;  S,  sternum; 
H,  humerus.  Ventral  to  the  trachea  there  are  shown,  but  not  marked  on  account  of  lack  of  space,  two  cardiac  nerves- 
and  a  mediastinal  lymph  gland. 


528 


RESPIRATORY    SYSTEM    OF   THE    HORSE 


Trapezius 


Rhomboideus 

Spinalis 

MuUifidus 

Cartilage  of  scapula 

Longissimus  dor  si 

Serratus  dorsalis 
Levator  costce 
et  intercost.  ext. 
Longissimus  costarum 
I  ntercostales 

Serratus  ventralis 

Latissimus  dorsi 

Cidaneus 


Triceps  (c.  longum) 


Pecioralis  prof, 
(p.  humeralis) 

Tensor  fascicB 
uidihrachii 


Pidoralis  superficialis 
{p.  transversa) 

Fig.  470. — Section  of  Thor.a.x  of  Horse. 

The  section  is  cut  in  an  oblique  direction  corresponding  with  the  spine  of  the  scapula.  It  cuts  the  body  of  the 
seventh  thoracic  vertebrae  and  the  .seventh  rib  dorsally  and  the  fourth  rib  and  its  cartilage  ventrally.  The  pleural 
and  pericardiac  cavities,  represented  by  wide  black  lines,  are  exaggerated  for  the  sake  of  clearness. 

L,  L',  lungs;  1,  aorta;  2,  cesophagus;  3,  thoracic  duct;  4,  vena  azygos;  5,  5',  bronchi;  6,  bifurcation  of  pulmonary 
artery;  7,  7',  right  and  left  atria;  8,  right  ventricle;  9,  tricuspid  valve;  10,  origin  of  aorta;  11,  right  coronary  arterj'; 
12,  left  coronary  artery  (circumflex  branch)  and  satellite  vein;  13,  internal  thoracic  vessels;  14,  external  thoracic 
vessels;  S,  sternum;  U,  ulna.  The  following  structures  are  shown,  but  not  marked  on  account  of  lack  of  space:  The 
right  vagus  is  on  the  oesophagus  and  ventral  to  the  vena  azygos.  The  phrenic  nerves  are  on  the  upper  part  of  the  peri- 
cardium on  each  side.  The  sympathetic  trunks  are  on  each  side  of  the  body  of  the  vertebra.  The  number  10  is  placed 
on  the  ventricular  septum.     Bronchial  lymph-glands  are  shown  ventral  to  the  oesophagus  and  the  left  bronchus. 


THE    PLEURA 


529 


Trapezius 


Rhomhoideus 

Longissimus  dor  si 
MuUifidus 
Dorsal  vessels 

Cartilage  of  scapula 

L<mgissimus 

costarum 

Latissimtis 

dorsi 

hdercostalis 

exiernus 


Phrenico-costal 

171118 


Cutaneus 

External 

thoracic  vessels 
Obliquus  abdom- 
inis externus 
Musculo-  phrenic 


Anterior  abdominal 


I     Rectus  abdominis 
Pectoralis  profundus 
{p.  humeralis) 


Transversus  thoracis 


Fig.  471. — Cross-section  of  Body  of  Horse. 

The  section  is  cut  through  the  eighth  thoracic  vertebra  and  the  anterior  part  of  the  xiphoid  cartilage.  It  cuts  the 
vertebral  end  of  the  eighth  rib  and  a  little  more  than  half  of  the  seventh  rib.  The  flexures  of  the  great  colon  and  a  small 
part  of  the  liver,  which  lay  in  the  concavity  of  the  diaphragm,  have  been  removed.  The  dotted  Unes  indicate  the  con- 
tour of  the  bases  of  the  lungs  and  the  apex  of  the  heart,  which  are  concealed  by  the  diaphragm.  The  pleural  cavities, 
indicated  by  wide  black  lines,  are  exaggerated  for  the  sake  of  clearness. 

1,  1',  Lungs;  2,  aorta;  3,  oesophagus;  4,  4'  stem  bronchi;  5,  5',  pulmonary  arteries;  6,  6',  large  pulmonary  veins; 
7,  posterior  vena  cava;  8,  8',  phrenic  nerves;  9,  vena  azygos;  10,  falciform  and  round  ligaments  of  liver;  11,  position 
of  apex  of  heart;  12  (placed  on  cut  surface  of  sternal  part  of  diaphragm),  xiphoid  cartilage.  The  sympathetic  trunks 
(not  marked)  are  shown  on  each  side  of  the  body  of  the  vertebra.  The  oesophageal  trunks  of  the  vagi  (not  marked)  are 
shown  in  relation  to  the  oesophagus.     The  thoracic  duct  is  ventral  to  the  vena  azygos. 


34 


530  RESPIRATORY   SYSTEM    OF   THE    HORSE 

usually  appears  fenestrated;    when  these  apertures  are  present,  tne  two  pleural 
cavities  communicate  with  each  other. ^ 

The  pleural  sacs  contain  a  clear  serous  fluid,  the  liquor  pleurae ;  in  health  there 
is  only  a  sufficient  amount  to  moisten  the  surface,  but  it  accumulates  rapidly  after 
death. 

It  should  be  borne  in  mind  that  the  pleural  cavity  is  normally  a  capillary  space  between  the 
parietal  and  visceral  parts  of  the  pleura,  and  contams  a  film  of  serous  fluid.  In  illustrations  it  is 
necessary,  for  the  sake  of  clearness,  to  exaggerate  the  space. 

The  pleura  resembles  the  peritoneum  in  structure  and  appearance.  It  is 
attached  to  the  structures  which  it  covers  by  subserous  tissue,  which  is  elastic  and 
in  some  situations  contains  fat.  In  the  case  of  the  parietal  pleura  the  subserous 
tissue  is  termed  the  endothoracic  fascia.  This  lines  the  thoracic  walls,  but  is 
practically  absent  over  the  tendinous  center  of  the  diaphragm.  A  strong  layer 
descends  from  it  in  the  mediastinum  and  blends  with  the  fibrous  part  of  the  peri- 
cardium. The  subserous  tissue  of  the  pulmonary  pleura  is  continuous  with  the 
interlobular  tissue  of  the  lung. 

The  pleura  receives  an  abundant  blood  supply  which  is  derived  chiefly  from 
the  intercostal,  internal  thoracic,  and  bronchial  arteries.  Lymph  vessels  are  very 
numerous  in  the  pleura  and  subserous  tissue;  they  go  chiefly  to  the  intercostal  and 
mediastinal  glands. 

The  parietal  pleura  is  reflected  along  three  lines  which  are  known  as  the  lines  of  pleural  re- 
flection; these  may  be  termed  vertebral,  sternal,  and  diaphragmatic.  The  vertebral  line  of 
pleural  reflection  is  that  along  which  the  costal  pleura  turns  ventrally  to  form  the  mediastinal 
pleura;  it  extends  along  the  longus  colli  and  the  bodies  of  the  thoracic  vertebrs  to  the  vertebral 
end  of  the  last  intercostal  space,  where  it  joms  the  line  of  diaphragmatic  reflection.  The 
sternal  line  of  pleural  reflection  is  that  along  which  the  costal  pleura  is  reflected  dorsally 
to  become  the  mediastinal  pleura.  Anteriorly  the  two  lines  are  close  together  along  the  middle  of 
the  floor  of  the  thorax,  but  further  back  they  diverge  to  each  side  of  the  sternal  attachment  of  the 
pericardium.  The  reflection  is  at  an  acute  angle  and  the  narrow  angular  recess  of  the  pleural  cav- 
ity here  is  termed  the  costo- mediastinal  sinus  (Sinus  costomediastinalis).  The  diaphragmatic 
line  of  pleural  reflection  is  that  along  which  the  costal  pleura  passes  from  the  lateral  wall 
to  the  diaphragm.  This  line  is  important  clinically,  since  it  is,  from  the  standpoint  of  physical 
diagnosis,  the  demarcation  between  the  thoracic  and  abdominal  cavities.  It  extends  along  the 
eighth  and  ninth  costal  cartilages,  crosses  the  sternal  end  of  the  nmth  rib,  and  passes  backward  and 
upward  in  a  gentle  curve  and  at  a  gradually  increasing  distance  from  the  sternal  ends  of  the  ribs, 
so  that  its  most  posterior  part  is  about  the  middle  of  the  anterior  border  of  the  last  rib ;  this  is  the 
posterior  limit  of  the  pleural  cavity.  Here  it  turns  medially  and  a  little  forward  and  ends  at  the 
vertebral  end  of  the  last  intercostal  space.  This  reflection  is  also  at  an  acute  angle  and  the  costal 
and  diaphragmatic  pleura  are  in  contact  over  an  area  of  variable  width  along  this  line.  The  nar- 
row angular  recess  of  the  pleural  cavity  here  is  termed  the  phrenico-costal  sinus  (Sinus  phren- 
icocostalis). 

The  apex  of  each  pleural  sac  (Cupula  pleurae)  lies  at  the  anterior  aperture  of  the  thorax. 
On  the  right  side  it  forms  two  culs-de-sac;  one  of  these  may  extend  forward  more  than  an  inch 
(ca.  3  cm.)  beyond  the  first  rib  in  contact  with  the  deep  face  of  the  scalenus;  the  other  is  ventral 
to  the  anterior  vena  cava  and  may  extend  about  an  inch  (ca.  2.5  cm.)  beyond  the  first  rib.  The 
apex  of  the  left  pleura  usually  does  not  extend  beyond  the  plane  of  the  first  rib. 


THE  LUNGS 
The  lungs,  right  and  left  (Pulmo  dexter,  sinister),  occupy  much  the  greater 
part  of  the  thoracic  cavity.  They  are  accurately  adapted  to  the  walls  of  the 
cavity  and  the  other  organs  contained  therein.  The  two  lungs  are  not  alike  in 
form  or  size,  the  right  one  being  considerably  larger  than  the  left;  the  differ- 
ence is  chiefly  in  width,  in  conformity  with  the  projection  of  the  heart  to  the 
left.  The  lung  is  soft,  spongy,  and  highly  elastic.  It  crepitates  when  pressed 
between  the  finger  and  thumb,  and  floats  in  water.  When  the  thoracic  cavity  of 
the  unpreserved  subject  is  opened,  the  lung  collapses  immediately  to  about  one- 

'  The  apertures  do  not  exist  in  the  foetus,  and  are  sometimes  absent  in  the  adult  subject. 
Some  of  them  are  doubtless  produced  in  dissection  by  the  necessary  disturbance  of  the  parts.  The 
character  of  the  pleura  here  probably  explains  the  clinical  observation  that  in  the  horse  fluid  exu- 
date resulting  from  unilateral  pleurisy  is  usually  present  in  both  pleural  sacs  in  like  amount. 


THE    LUNGS 


531 


third  of  its  original  size,  and  loses  its  proper  form;  this  is  due  to  its  highly  elastic 
character  and  the  fact  that  the  tension  of  the  lung  tissue  caused  by  the  air  pressure 
in  its  cavities  has  been  relieved  by  the  external  air  pressure.^  The  color  varies 
according  to  the  amount  of  blood  contained  in  the  lung.  During  life  the  lung  has  a 
pink  color,  but  in  subjects  which  have  been  bled  for  dissection  it  is  light  gray  or 
faintly  tinged  with  red.  In  unbled  subjects  it  is  dark  red;  the  depth  of  color  varies, 
and  is  often  locally  accentuated  by  gravitation  of  blood  to  the  most  dependent  parts 
(hypostasis).  The  fcetal  lung,  since  it  contains  no  air  and  has  a  relatively  small 
blood-supply,  differs  from  that  of  an  animal  which  has  breathed  in  the  following 
respects:  (1)  It  is  much  smaller;  (2)  it  is  firmer  and  does  not  crepitate;  (3)  it  sinks 
in  water;  (4)  it  is  pale  gray  in  color.  In  form  the  lungs  are  like  casts  of  the  cavities 
in  which  they  are  situated.     When  well  hardened  in  situ,  their  surfaces  present 

j)ors  al       bo  r  d  e  t- 


c-^ 


^pex 


Fig.  472. — Right  Lung  of  Horse;  Costal  Surface. 
Specimen  hardened  in  situ. 


impressions  and  elevations  corresponding  exactly  to  the  structures  with  which  they 
are  in  contact.     Each  lung  presents  two  surfaces,  two  borders,  a  base,  and  an  apex. 

The  costal  surface  (Facies  costalis)  is  convex,  and  lies  against  the  lateral 
thoracic  wall,  to  which  it  is  accurately  adapted. 

The  mediastinal  surface  (Facies  mediastinalis)  is  much  less  extensive  than  the 
costal  surface.  It  is  molded  on  the  mediastinum  and  its  contents.  It  presents  a 
large  cavity  adapted  to  the  pericardium  and  heart;  this  is  termed  the  cardiac 
impression  (Impressio  cardiaca),  and  is  larger  and  deeper  on  the  left  lung  than  on 
the  right.  Above  and  behind  this  is  the  hilus  of  the  lung  (Hilus  pulmonis),  at  which 
the  bronchus,  vessels,  and  nerves  enter  the  lung;  the  bronchial  lymph  glands  are 
also  found  here.  Behind  this  the  two  lungs  are  adherent  to  each  other  over  a 
triangular  area.  Above  this  there  is  a  groove  for  the  oesophagus,  which  is  deepest 
on  the  left  lung.  A  groove  for  the  aorta  (Sulcus  aortse)  curves  upward  and  back- 
ward over  the  hilus,  and  passes  backward  near  the  dorsal  border  of  the  lung;  the 

^No  idea  of  the  natural  form  and  size  of  the  lung  can  be  obtained  from  a  specimen  in  this 
state,  nor  can  an  accurate  conception  be  gained  by  examination  of  the  soft  inflated  organ.  The 
lungs  should  be  hardened  in  situ  for  this  purpose,  and  if  the  process  has  been  successful  they  con- 
form in  every  detail  to  the  structures  with  which  they  were  in  contact.  ^ 


532 


RESPIRATORY    SYSTEM    OF    THE    HORSE 


curved  part  of  the  groove  for  the  aortic  arch  is  absent  on  the  right  lung,  on  which 
there  is  a  groove  for  the  vena  azygos.  Anteriorly  there  are  grooves  for  the  trachea, 
the  brachiocephalic  trunk,  the  anterior  vena  cava,  and  other  vessels. 


JDorsctl      horder 


Fig.  473. — Left  Lung  of  Horse;  Costal  Surface. 
Specimen  hardened  in  situ. 


Pulmonary 

artery      Brorochus 
c.d.         \        \    Groove  for  vena  azygos 


Ligament  of  lung  (cut) 


Puhnonary 


Line  of  reflection  of  pie 


Fig.  474. — Right  Lung  of  Horse;  Mediastinal  and  Diaphragmatic  Surfaces. 
Organ  hardened  in  situ.     c.  d.  Grooves  for  deep  cervical  and  dorsal   veins.     Arrows  indicate  canal  for  posterior 
vena  cava  between  intermediate  lobe  and  main  part  of  lung.     By  an  oversight  the  impression  of  the  trachea  is  un- 
marked; it  is  dorsal  to  the  groove  for  the  vena  cava. 


The  dorsal  border  (Margo  dorsalis)  is  long,  thick,  and  rounded;   it  lies  in  the 
groove  alongside  of  the  bodies  of  the  thoracic  vertebrjB.i 

1  In  some  cases  this  border  is  cut  into  by  a  fissure  which  partly  marks  off  the  apex  from  the 
body  of  the  lung. 


THE    LUNGS 


533 


The  ventral  border  (Margo  ventralis)  is  thin  and  short ;  it  occupies  tlie  angular 
space  between  the  mediastinum  and  the  ventral  parts  of  the  sternal  ribs  (Recessus 
costo-mediastinalis) .  It  presents,  opposite  to  the  heart,  the  cardiac  notch  (Incisura 
cardiaca) .  On  the  left  lung  this  notch  is  opposite  to  the  ribs  from  the  third  to  the 
sixth,  so  that  a  considerable  area  of  the  pericardium  here  lies  in  direct  contact  with 
the  chest-wall.  On  the  right  lung  the  notch  is  much  smaller,  and  extends  from  the 
third  rib  to  the  fourth  intercostal  space. 

The  left  cardiac  notch  is  usually  quadrilateral;  its  highest  part  is  about  four  to  five  inches 
(ca.  10-12  cm.)  above  the  sternal  ends  of  the  fourth  and  fifth  ribs.  The  right  notch  is  usually 
triangular;  its  apex  is  about  three  inches  (ca.  7-8  cm.)  above  the  level  of  the  sternal  end  of  the 
ribs  at  the  third  intercostal  space.  In  some  cases  a  fissure  partially  marks  off  the  apex  from  the 
body  of  the  lung. 

The  base  of  the  lung  (Basis  pulmonis)  is  oval  in  outline;   its  surface  (Facies 


Ligament  of  lung  {cut) 


Bronchial  artery 
;'  Bronchus 
Pulmnnary     i    i  Pulmonary        Vascular 
veins        I    I   artery  impression 


Line  of  reflection 
of  pleura 


Fig.  475. — Left  Lung  of  Horse;  Mediastixal  and  Diaphragmatic  Surfaces. 
Organ  hardened  in  situ.     Vascular  impression  for  common  dorso-cervico-vertebral  vein. 


diaphragmatica)  is  deeply  concave  in  adaptation  to  the  thoracic  surface  of  the 
diaphragm.  Laterally  and  dorsally  it  is  limited  by  a  thin  convex  basal  border 
(Margo  basalis)  which  fits  into  the  narrow  recess  (Sinus  phrenico-costalis)  between 
the  diaphragm  and  the  lateral  chest-wall.  The  position  of  this  border,  of  course, 
varies  during  respiration.  In  the  deepest  inspiration  it  may  reach  the  bottom  of 
this  recess. 

In  dissecting-room  subjects  the  distance  between  the  border  and  the  diaphrag- 
matic line  of  reflection  of  the  pleura  increases  from  about  two  inches  (ca.  5  cm.)  at 
the  seventh  rib  to  about  six  or  seven  inches  (ca.  16-18  cm.)  at  the  fifteenth,  and 
then  decreases.  The  dorsal  end  of  the  base  is  usually  at  the  vertebral  end  of  the 
sixteenth  intercostal  space  or  seventeenth  rib.^ 

The  apex  of  the  lung  (Apex  pulmonis)  is  prismatic,  narrow,  and  flattened 
transversely.  It  is  partially  marked  off  from  the  rest  of  the  lung  by  the  cardiac 
1  The  ventral  and  basal  borders  may  be  taken  together  under  the  term  margo  acutus. 


534  RESPIRATORY    SYSTEM    OF   THE    HORSE 

notch.  It  curves  downward,  and  is  related  deeply  to  the  anterior  mediastinum  and 
the  anterior  part  of  the  pericardium. 

The  lungs  of  the  horse  are  not  divided  into  lobes  by  deep  fissures,  as  is  the  case 
in  most  mammals.  The  left  lung  may  be  regarded  as  consisting  of  a  chief  part, 
the  body  of  the  lung  (Corpus  pulmonis),  and  the  apex  (Apex  pulmonis).  But 
the  right  lung  has  in  addition  an  intermediate  lobe  (Lobus  intermedins),^  which  is 
separated  from  the  body  of  the  lung  by  a  fissure  which  forms  in  its  dorsal  part  a 
canal  for  the  posterior  vena  cava  and  the  right  phrenic  nerve,  enclosed  in  a  special 
fold  of  the  right  pleura. ^ 

The  root  of  the  lung  (Radix  pulmonis)  is  composed  of  the  structures  which 
enter  or  leave  the  lung  at  the  hilus  on  the  mediastinal  surface.  These  are:  (1) 
The  bronchus ;  (2)  the  pulmonary  artery ;  (3)  the  pulmonary  veins ;  (4)  the  bron- 
chial artery;  (5)  the  pulmonary  nerves;  (6)  the  Ijrmph  vessels,  which  go  to  the 
l)ronchial  lymph  glands.  The  bronchus  is  situated  dorsally,  with  the  bronchial 
artery  on  its  upper  surface  and  the  pulmonary  artery  immediately  below  it.  The 
pulmonary  veins  lie  chiefly  below  and  behind  the  artery. 

The  lobulation  of  the  lungs  is  not  very  evident  on  account  of  the  small  amount 
of  interlobular  tissue.  The  lobules  appear  on  the  surface  or  on  sections  as  irregular 
polygonal  areas  of  different  sizes. ^ 

Bronchial  Branches. — Each  bronchus  at  its  entrance  into  the  lung  gives  off  a 
branch  to  the  apex  of  the  lung  (Bronchus  apicalis) .  It  is  then  continued  backward 
as  the  main  stem  bronchus,  parallel  with  the  dorsal  border  of  the  lung,  giving  oft' 
branches  (Rami  bronchiales)  in  monopodic  fashion;  these  branch  similarly  and 
reach  all  parts  of  the  lung.  The  right  bronchus  gives  off  a  special  branch  to  the 
intermediate  lobe.  The  apical  bronchus  of  the  right  lung  is  larger  than  that  of 
the  left  lung.  A  large  ventral  bronchial  branch  is  given  off  from  each  stem 
bronchus  to  the  part  of  the  lung  which  is  homologous  with  the  cardiac  lobe  of  other 
animals. 

The  structure  of  the  larger  bronchial  tubes  is,  in  general,  similar  to  that  of  the 
trachea.  Their  walls  contain  irregular  plates  of  cartilage  instead  of  rings.  There 
is  a  continuous  layer  of  unstriped  muscle,  composed  of  circularly  arranged  bundles. 
The  mucous  membrane  presents  numerous  longitudinal  folds;  it  contains  many 
elastic  fibers,  mucous  glands,  and  lymph  nodules,  and  is  lined  by  ciliated  columnar 
epithelium.  As  the  tubes  diminish  in  size  the  coats  become  thinner  and  the  car- 
tilages smaller;  in  tubes  about  1  mm.  in  diameter  the  cartilages  and  mucous  glands 
are  absent. 

By  repeated  branching  the  interlobular  bronchi  are  formed,  and  from  these 
arise  the  lobular  bronchioles.  The  latter  enter  a  lobule  and  branch  within  it, 
forming  the  respiratory  bronchioles  (Bronchioli  respiratorii) ;  these  give  off  the 
alveolar  ducts  (Ductuli  alveolares),  the  walls  of  which  are  pouched  out  to  form 
hemispherical  diverticula,  the  alveoli  or  air-cells. 

A  pulmonary  lobule  (Lobulus  pulmonis),  the  unit  of  lung  structure,  is  made  up 
of  a  lobular  bronchiole  with  its  branches,  and  their  air-cells,  blood-  and  lymph- 
vessels,  and  nerves.  Between  the  lobules  is  the  interlobular  tissue,  which  forms 
the  supporting  framework  of  the  lung. 

Vessels  and  Nerves.^The  branches  of  the  pulmonary  artery  carry  venous 
blood  to  the  lungs.     They  accompany  the  bronchi,  and  form  rich  capillary  plexuses 

1  This  is  also  commonly  called  the  mediastinal  lobe. 

2  Some  authors  consider  each  lung  to  be  divided  into  anterior  and  posterior  lobes  by  the 
cardiac  notch,  so  that  the  right  lung  would  have  three  lobes  and  the  left  lung  two  lobes.  Not 
rarely  a  fissure  or  notch  in  the  dorsal  border  partially  marks  off  the  apex  from  the  body  of  the  lung, 
and  in  some  cases  there  is  a  corresponding  fissure  in  the  ventral  border. 

^  In  foetal  lung  the  lobulation  is  much  more  distinct.  Pigmentation  of  the  lung  is  sometimes 
seen  in  horses,  and  in  such  cases  the  pigment  is  deposited  mainly  in  the  interlobular  tissue,  thus 
mapping  out  the  lobules. 


THE    THYROID    GLAND  535 

on  the  walls  of  the  alveoli.  Here  the  blood  is  arterialized,  and  is  returned  to  the 
heart  by  the  pulmonary  veins.  The  bronchial  arteries  are  relatively  small  vessels 
which  carry  arterial  blood  for  the  nutrition  of  the  lungs.  The  branches  of  these 
arteries  accompany  the  bronchial  ramifications  as  far  as  the  alveolar  ducts,  but 
do  not  extend  to  the  alveoli.  The  oesophageal  branches  of  the  broncho-oesophageal 
and  gastric  arteries  also  supply  pulmonary  branches  (in  the  horse)  which  reach  the 
lung  by  way  of  the  ligament  of  the  latter.  These  branches  vary  much  in  size,  and 
ramify  chiefly  in  the  subpleural  tissue  of  the  basal  part  of  the  lungs.^  The  Ijonph 
vessels  are  numerous,  and  are  arranged  in  two  sets.  The  superficial  set  forms 
close  networks  in  and  under  the  pleura,  while  the  deep  set  accompanies  the  bronchi 
and  pulmonary  vessels.  Most  of  them  converge  to  the  root  of  the  lung  and  enter 
the  bronchial  lymph  glands,  but  some  go  to  the  mediastinal  lymph  glands.  The 
pulmonary  nerves  come  from  the  vagus  and  sympathetic  nerves.  They  enter  at 
the  hilus  and  supply  branches  to  the  bronchial  arteries  and  the  air-tubes. 


THE  THYROID  GLAND 

The  thyroid  gland  (Glandula  thyreoidea)  is  situated  on  the  anterior  part  of  the 
trachea,  to  which  it  is  loosely  attached.  It  is  a  very  vascular  ductless  gland,  and 
is  firm  in  texture  and  dark  red-brown  in  color.  It  consists  of  two  lateral  lobes  and 
a  very  narrow  connecting  isthmus  (Figs.  332,  649). 

The  lateral  lobes  (Lobus  dexter,  sinister)  are  situated  on  each  side  of  the  trachea 
near  to  or  in  contact  with  the  larynx.  Their  position  is  indicated  approximately 
by  the  angle  of  junction  of  the  jugular  and  external  maxillary  veins.  Each  is  oval 
in  outline  and  is  about  as  large  as  a  plum  of  medium  size.  The  superficial  surface 
is  convex  and  is  covered  by  the  cervical  angle  of  the  parotid  gland  and  the  sterno- 
cephalicus  and  omo-hyoideus.  The  deep  surface  is  adapted  to  the  trachea.  About 
the  lobe  are  the  anterior  cervical  lymph  glands.  The  anterior  pole  is  large  and 
rounded,  while  the  posterior  is  smaller  and  often  tapers  to  a  tail-hke  process  which 
is  continuous  with  the  isthmus. 

The  isthmus  (Isthmus  gl.  thyreoidese)  extends  across  the  ventral  face  of  the 
trachea,  connecting  the  two  lobes.  It  is  usually  extremely  narrow  in  the  adult 
horse  and  is  often  reduced  in  great  part  to  a  small  strand  of  fibrous  tissue. 

The  lateral  lobes  are  very  variable  in  size  and  position,  and  are  usually  unsymmetrical.  The 
average  length  is  about  two  inches  (ca.  5  cm.).  The  greatest  height  averages  a  little  more  than  an 
inch  (ca.  2.7  cm.),  and  the  greatest  width  a  little  less  than  an  inch  (ca.  1.5-2  cm.).  The  average 
weight  is  about  half  an  ounce  (ca.  15  gm.).  The  right  lobe  is  commonly  in  contact  with  the  crico- 
pharyngeus  or  crico-thyroideus,  but  may  be  about  a  finger's  breadth  from  the  larynx.  The  left 
lobe  may  be  an  inch  or  more  (ca.  4  cm.)  from  the  larynx,  but  in  some  cases  is  in  contact  with  it. 
The  position  varies  considerably  in  the  dorso-ventral  direction  also,  irrespective  of  the  ventral  dis- 
placement noted  in  enlargement  of  the  gland.  The  most  common  forrn  is  oval,  with  a  smaller 
posterior  pole  which  tapers  to  the  isthmus.  But  the  isthmus  is  sometimes  connected  with  the 
middle  of  the  ventral  border  of  one  lobe  or  both,  so  that  the  two  poles  are  about  alike.  Many  ir- 
regularities may  be  observed.  Cases  occur  in  which  a  variable  posterior  process  is  connected  with 
the  body  of  the  gland  by  a  sort  of  neck.  A  complete  glandular  isthmus  is  not  rare,  although  it  is 
usually  very  narrow  and  may  easily  escape  notice;  in  quite  exceptional  cases  it  may  be  6-8  mm. 
in  width.  Its  connection  with  the  lateral  lobes  and  crossing  of  the  trachea  are  quite  variable. 
Most  often  it  is  connected  with  the  posterior  poles  and  passes  almost  directly  between  the  two. 
But  it  may  run  backward  and  cross  much  further  back;  in  one  case  (personal  observation)  the 
crossing  was  at  the  space  between  the  ninth  and  tenth  tracheal  rings.  In  the  foal  the  isthmus  is 
relatively  large  and  entirely  glandular.  In  the  ass  and  mule  there  is  almost  always  a  well-developed 
isthmus.  Extending  from  it  there  is  sometimes  a  narrow  band  of  thyroid  tissue  which  reaches  to 
the  body  of  the  hyoid  bone;   this  is  the  lobus  pyramidalis. 

Structure.— The  gland  is  enveloped  by  a  thin  fibro-elastic  capsule,  from  which 
trabeculse  pass  into  the  substance  of  the  organ.      The  gland  tissue  is  compact  and 

1  It  must  not  be  inferred  from  the  necessarily  brief  accoimt  here  given  that  the  two  sets  of 
vessels  are  quite  distinct.  On  the  contrary,  competent  observers  state  that  numerous  small 
branches  of  the  bronchial  arteries  anastomose  with  pulmonary  vessels. 


536  RESPIRATORY    SYSTEM    OF    THE    HORSE 

consists  of  lobules  (Lobuli  gl.  thyreoidese),  which  are  embedded  in  a  stroma  of 
strands  of  fibrous  tissue.  The  stroma  contains  numerous  vessels.  The  lobules 
consist  of  non-communicating  alveoli  or  follicles  of  varying  form  and  size.  The 
alveoli  are  lined  by  cubical  or  columnar  epithelium,  and  contain  a  viscid  colloid 
substance. 

Vessels  and  Nerves. — The  arteries  are  relatively  very  large ;  there  are  usually 
two  thyroid  arteries,  which  arise  from  the  carotid;  their  branches  enter  the  gland 
chiefly  at  or  near  the  ends  and  the  dorsal  border.  The  veins  are  also  large;  they 
go  to  the  jugular  vein;  the  largest  one  leaves  the  gland  at  its  posterior  pole.  The 
l3nnph  vessels  go  to  the  cervical  lymph  glands.  The  nerves  are  derived  from  the 
sympathetic  system. 

Nodules  of  thyroid  tissue  of  variable  size,  sometimes  as  large  as  a  pea,  may  be 
found  near  the  anterior  extremity  of  the  lateral  lobes,  on  the  course  of  the  anterior 
thyroid  artery  or  on  the  trachea,  even  at  a  considerable  distance  from  the  thyroid 
region.     They  are  termed  accessory  thyroids  (Glandulse  thyreoideae  accessorise) . 

The  parathyroids  are  small  glandular  bodies  found  in  the  thyroid  region. 
They  are  paler  and  not  so  dense  as  the  thyroid  tissue,  but  often  cannot  be  differen- 
tiated by  their  naked-eye  appearance.  In  the  horse  there  is  usually  only  one  on 
each  side  in  the  connective  tissue  over  the  dorsal  border  or  anterior  extremity  of  the 
lateral  lobe  of  the  thyroid.  One  may  be  embedded  in  the  deep  face  of  the  lateral 
lobe  of  the  thyroid.     They  resemble  in  structure  embryonic  thyroid  tissue. 


THE  THYMUS  GLAND 

The  thjnnus  is  a  ductless  gland  which  has  a  close  resemblance  to  the  lymphoid 
tissues.  It  is  well  developed  only  in  late  foetal  life  and  for  a  few  months  after  birth. 
After  this  it  undergoes  rapid  atrophy,  fatty  infiltration,  and  amyloid  degeneration, 
so  that  in  the  adult  it  is  usually  represented  by  a  thin  remnant  in  the  ventral  part 
of  the  anterior  mediastinum  or  has  entirely  disappeared.  In  the  new-bom  foal 
it  is  of  a  grayish-pink  color,  and  consists  of  right  and  left  lobes  (Lobus  dexter, 
sinister).  The  greater  part  of  the  gland  is  situated  in  the  anterior  mediastinum 
ventral  to  the  trachea  and  large  vessels,  but  the  two  lobes  are  contmued  into  the 
neck  by  a  chain  of  lobules  which  lie  on  the  trachea  along  the  course  of  the  carotid 
artery,  extending  sometimes  as  far  as  the  thyroid  gland. ^ 

Structure. — The  thymus  is  enclosed  in  a  thin  and  loose  fibro-elastic  capsule, 
and  consists  of  secondary  lobules  (Lobuli  thymi),  of  varying  shape  and  size,  held  to- 
gether by  areolar  tissue  and  fat,  and  comiected  with  a  strand  of  comiective  tissue 
termed  the  tractus  centralis.  These  lobules  are  subdivided  into  polyhedral  primary 
lobules,  which  are  composed  of  lymphoid  tissue,  and  present  a  dark,  vascular  cor- 
tex, and  a  lighter  medulla  that  contains  small  masses  of  concentrically  arranged, 
flattened  cells;  these  are  known  as  concentric  corpuscles. 

Vessels  and  Nerves. — The  arteries  are  derived  from  the  internal  thoracic  and 
common  carotid.     The  nerves  come  from  the  sympathetic  and  vagus. 

1  The  cervical  part  of  the  gland  is  very  variable.  The  thoracic  lobe  of  one  side  may  have 
no  cervical  continuation ;  the  other  lobe  may  then  give  off  a  single  prolongation  which  bifurcates. 
The  thoracic  part  in  the  new-born  foal  occupies  most  of  the  space  which  is  later  taken  up  by  the 
apices  of  the  lungs.  Its  two  lobes  are  in  contact,  and  its  deep  surface  is  molded  on  the  anterior 
part  of  the  pericardium  and  the  large  vessels.  In  exceptional  cases  a  considerable  remnant  of  the 
thymus  is  present  in  adult  or  even  old  subjects;  this  is  usually  true  only  of  the  thoracic  part,  but 
it  may  extend  into  the  neck  a  short  distance;  but  a  large  lymph  gland  must  not  be  mistaken  for 
thymus. 


RESPIRATORY   SYSTEM    OF   THE    OX — THE   NASAL   CAVITY 


537 


RESPIRATORY  SYSTEM  OF  THE  OX 

THE  NASAL  CAVITY 

The  nostrils  (Fig.  379),  situated  on  either  side  of  the  muzzle,  are  relatively 
small,  and  are  much  less  dilatable  than  those  of  the  horse.  The  alae  are  thick  and 
firm.  The  superior  commissure  is  narrow.  There  is  no  diverticulum  nasi.  The 
skin  is  smooth,  bare,  and  moist,  and  there  is  no  clear  line  of  demarcation  between 
it  and  the  nasal  mucosa.     The  opening  of  the  naso-lacrimal  duct  is  not  visible,  as 


Frontal  eminence 


Great  ethmo-turbinate 


Dorsal  turbinate 


Dorsal  meatus 
Middle  meatus 


Ventral 
turbinate 


Ventral 
meatus 


Genio-    Mijlo-hy-      Genio- 
glossus     oideus      hyoideus 


Fig.  476. — Sagittal  Section  of  Head  of  Cow. 


Thyroid  cartilage 


/,  Cerebral  hemisphere;  ;2,  lateral  ventricle;  -S,  thalamus,  4.  corpora  quadrigemina;  ^,  optic  chiasma;  6,  pituitary 
body;  7,  pons;  8,  medulla  oblongata;  9,  cerebellum;  10,  spinal  cord;  11,  ventral  straight  muscles;  12,  pharyngeal 
lymph  gland;  / 3,  arytenoid  cartilage;  ^4.  epiglottis;  75,  cricoid  cartilage;  i6',  vocal  cord;  i 7,  palatine  sinus;  75,  soft 
palate;  19,  Eustachian  opening;  CI,  C2,  C3,  first,  second,  and  third  cervical  vertebrae;  B.o.,  basioccipital ;  Sp.,  pre- 
sphenoid. 


it  is  on  the  lateral  wall  of  the  nostril,  and  is  concealed  by  the  cartilaginous  pro- 
longation of  the  ventral  turbinate.  There  are  two  parietal  cartilages  on  either 
side,  united  by  fibrous  tissue.  The  dorsal  cartilages  are  thin  laminae  which  curve 
ventro-laterally  from  the  dorsal  margin  of  the  septal  cartilage;  they  are  prolonga- 
tions of  the  nasal  bones,  and  carry  the  alar  cartilages  on  their  anterior  extremities. 
The  ventral  pair  are  lateral  continuations  of  the  basal  lamellse  of  the  ventral  tur- 
binates. They  lie  along  the  nasal  processes  of  the  premaxillae;  anteriorly  they 
become  thicker,  turn  a  little  upward,  and  each  blends  with  the  cartilaginous  pro- 
longation of  the  upper  coil  of  the  ventral  turbinate.     The  alar  cartilages  are  of 


538 


RESPIRATORY    SYSTEM    OF   THE    OX 


peculiar  form.  The  lamina  is  oblong,  and  curves  ventro-laterally  from  the  anterior 
extremity  of  the  dorsal  parietal  cartilage,  with  which  it  is  connected.  The  cornu 
springs  from  the  lateral  part  of  the  lamina  and  curves  dorso-laterally  into  the  outer 
Aving  of  the  nostril ;  it  carries  on  its  extremity  a  small  transverse  bar,  thus  having 
some  resemblance  to  the  fluke  of  an  anchor. 

The  nasal  cavity  is  short,  wide  anteriorly,  narrow  behind.  It  is  not  com- 
pletely divided  by  the  septum,  which  in  its  posterior  third  is  separated  from  the 
floor  of  the  cavity  by  an  interval  that  increases  from  before  backward  (Figs.  140, 
141).  The  middle  meatus  is  very  narrow,  and  divides  posteriorly  into  two  branches; 
the  upper  division  leads  to  the  ethmoidal  meatuses,  and  communicates  wdth  the 
frontal  sinus  and  the  cavity  of  the  dorsal  turbinate.  Anterior  to  the  division  are 
communications  Avith  the  upper  cavity  of  the  ventral  turbinate  and  the  maxillary 
sinus.     The  main  facts  in  regard  to  the  sinuses  were  stated  in  the  Osteology. 


THE  LARYNX 

The  Iar3nix  is  more  compact  than  in  the  horse,  and  presents  numerous  differ- 
ential features.  The  cricoid  cartilage  is  compressed  laterally.  The  lamina  is  not 
distinctly  marked  off  from  the  arch;  it  slopes  downward  and  backward  and  has  a 


Arytenoid     Processus 
cartilage     muscularis 


tl^'TJ....  Lateral  lobe 
of  thyroid 


cricoid  cartilage 


Epiglottis 


Thyroid 
cartilage 


Laryngeal     Arch  of  cricoid     Isthmus  of 
-prominence         cartilage  thyroid 


Fig.  477. — Cartilages  op  Larynx  .'^.nd  Part  of  Trachea  of  Ox;  Left  View. 

Outline  of  thyroid  gland  indicated  by  dotted  line. 

1,  Anterior  cornu  of  thyroid   cartilage;  2,  thyroid  foramen;  3,  ligament  converting  notch  into  foramen;  4,  posterior 

cornu  of  thyroid  cartilage;   5,  capsule  of  thyro-arytenoid  joint. 


large  median  ridge.  The  thyroid  cartilage  is  complete  ventrally,  i.  e.,  the  laminse 
are  united  to  form  a  long  plate  which  is  notched  in  front  and  behind ;  the  laryngeal 
prominence  is  small  and  is  situated  posteriorly.  The  height  and  thickness  of  the 
cartilage  increase  from  before  backward.  The  posterior  cornua  are  curved  and  are 
about  an  inch  long;  they  form  syndesmoses  with  the  cricoid  cartilage.  The  short 
anterior  cornua  unite  similarly  with  the  hyoid  bone ;  near  them  there  is  a  foramen 
or  a  notch  on  each  side  for  the  passage  of  the  anterior  laryngeal  nerve.  The  epi- 
glottis is  short,  oval  in  outline,  and  its  apex  is  rounded;  its  base  rests  on  the  thyro- 
hyoid membrane,  to  which  it  is  rather  loosely  attached.  The  cuneiform  cartilages 
are  absent.     The  arytenoid  cartilages  present  only  slight  differences.     The  muscular 


THE    LARYNX 


539 


process  is  well  developed,  and  the  vocal  process  is  narrow  and  long.  The  vocal 
cords  are  short  and  project  very  little  from  the  wall,  so  that  the  rima  glottidis  is 
wide;  the  vocal  ligament  is  attached  ventrally  to  the  crico-thyroid  membrane,  it 
has  the  form  of  a  half  tube,  open  behind.  The  lateral  ventricle  is  represented  by  a 
very  shallow  depression,  and  the  saccule  is  absent.     The  thyro-arytenoideus  muscle 


Fig.  478. — Aditus  Laryngis  and  Adjacent  Structures  of  Ox. 
The  pharynx,  soft  palate,  and  origin  of  oesophagus  have  been  cut  along  the  dorsal  median  line  and  refiected. 
1,  Epiglottis;  2,  aditus  laryngis;   3,  3',  apices  of  arytenoid  cartilages;  4,  posterior  pillar  of  soft  palate;   5,  cut  sur- 
face of  soft  palate;   6,  pharynx;   7,  litnen  oesophagi;   8,  oesophagus;   9,  trachea;    10,  glosso-epiglottic  space;   11,  tonsil- 
lar sinus;    12,  root  of  tongue;   13,  vallate  papillae;    14,  dorsum  linguse. 


is  equivalent  to  the  vocalis  and  ventricularis  of  the  horse;  it  is  fan -shaped,  thick, 
and  narrow  dorsally;  it  is  attached  ventrally  to  the  base  of  the  epiglottis,  the  angle 
of  the  union  of  the  thyroid  laminae,  and  the  crico-thyroid  membrane.  The  hyo- 
epiglotticus  muscle  is  large  and  bifid;  it  arises  from  the  small  cornua  and  at  their 
articulation  with  the  body  of  the  hyoid  bone,  and  thus  may  take  the  place  of  the 
hyoideus  transversus  in  its  action  on  the  small  cornua. 


540  RESPIRATORY    SYSTEM    OF   THE    OX 


THE  TRACHEA 


The  trachea  is  shorter  than  that  of  the  horse,  the  average  length  being  about 
26  inches  (ca.  65  cm.).  Its  cahber  is  relatively  small,  the  width  being  about  an 
inch  and  a  half  (ca.  4  cm.)  and  the  height  about  two  inches  (ca.  5  cm.).  The  rings 
are  smaller,  and  number  about  fifty.  At  the  begimiing  of  the  tube  their  free  ends 
are  separated  by  a  varying  interval,  so  that  the  tube  is  flattened  and  membranous 
dorsally;  but  further  back  the  ends  are  in  apposition,  so  that  they  fonn  a  ridge 
dorsally.  The  trachea  is  adherent  to  the  right  lung  from  the  second  rib  backward. 
The  bifurcation  is  opposite  the  fifth  rib,  about  the  junction  of  its  middle  and  ventral 
thirds. 

In  the  sheep  the  average  length  of  the  trachea  is  about  nine  or  ten  inches  (ca. 
25  cm.)  and  its  caliber  a  little  less  than  an  inch  (ca.  2  cm.). 


THE  BRONCHI 

There  are  three  chief  bronchi.  The  bronchus  for  the  apical  lobe  of  the  right 
lung  (Bronchus  apicalis)  is  detached  from  the  trachea  opposite  to  the  third  rib, 
i.  e.,  at  a  considerable  distance  anterior  to  the  bifurcation. 


THE  THORACIC  CAVITY  AND  PLEURA 

The  thoracic  cavity  is  relatively  small;  it  is  especially  short  dorsally,  and  is 
diminished  laterally  by  the  mode  of  attachment  of  the  diaphragm  to  the  ribs  {vide 
Myology).  The  endothoracic  fascia  is  better  developed  than  in  the  horse,  and  is 
distinctly  elastic.  The  pleura  is  also  thick,  and  there  are  no  perforations  of  the 
mediastinum.  The  pleural  sacs  are  even  more  unequal  in  extent  than  in  the  horse, 
and  the  ventral  part  of  the  mediastinum  is  further  to  the  left ;  m  front  of  the  peri- 
cardium it  is  for  the  most  part  in  contact  with  the  left  wall  of  the  chest. 

The  diaplxragmatic  line  of  pleural  reflection  differs  considerably  from  that  of  the  horse  in 
conformity  with  the  diiTerence  in  the  costal  attachment  of  the  diaphragm.  It  begins  over  the 
space  between  the  seventh  and  eighth  costal  cartilages,  crosses  the  ventral  end  of  the  eighth  rib, 
and  extends  in  a  very  slight  curve  upward  and  backward,  so  that  it  crosses  the  twelfth  rib  a  little 
above  its  middle  and  reaches  to  the  last  rib  a  short  distance  from  its  vertebral  end. 

The  pleura  forms  a  cul-de-sac  alongside  of  the  body  of  the  last  thoracic  vertebra.  The  right 
pleural  sac  extends  forward  on  the  deep  face  of  the  scalenus  a  short  distance  beyond  the  first  rib. 


THE  LUNGS 

The  difference  in  size  between  the  two  lungs  is  greater  than  in  the  horse,  the 
right  lung  weighing  about  half  as  much  again  as  the  left  one.  The  average  weight 
of  the  lungs  is  about  73^  pounds  (ca.  3  to  4  kg.) ;  they  form  about  y~to  of  the  body 
weight.  They  are  divided  into  lobes  by  deep  interlobar  fissures  (Incisurse  inter- 
lobares).  The  left  lung  is  divided  into  three  lobes,  named  from  before  backward 
apical,  cardiac,  and  diaphragmatic  (Lobus  apicalis,  cardiacus,  diaphragmaticus). 
The  right  lung  may  be  regarded  as  having  either  four  or  five  lobes.  The  apical 
lobe  is  much  larger  than  that  of  the  left  lung,  and  occupies  the  space  in  front  of 
the  pericarcUum,  pushing  the  mediastinum  against  the  left  wall ;  it  is  usually  sub- 
divided into  anterior  and  posterior  parts  by  a  deep  fissure.  The  other  lobes  are 
the  cardiac,  diaphragmatic,  and  intermediate,  the  last  resembling  that  of  the  horse.^ 

1  It  has  been  customary  to  consider  the  cardiac  lobe  to  consist  of  two  parts,  as  showTi  in  Fig. 
479.  But  the  apical  bronchus  divides  into  two  branches,  the  posterior  of  which  goes  to  that 
division  of  the  lung  which  has  been  regarded  as  belonging  to  the  cardiac  lobe ;  furthermore,  these 
parts  of  the  lung  are  sometimes  fused.  It  therefore  appears  desirable  to  include  both  as  apical 
lobe. 


THE    LUNGS 


541 


The  apical  lobe  of  the  right  lung  receives  a  special  bronchus  from  the  trachea  oppo- 
site the  third  rib,  and  is  adherent  to  the  trachea  from  the  second  rib  backward. 
The  two  lungs  are  not  adherent  to  each  other  behind  the  root  as  in  the  horse,  but 


horde>- 


Hardened  in  situ.     By 


Fig.  479. — Right  Lung  of  Ox;  Costal  Surface. 
the  inscription  "cardiac  lobe"  extends  forward  upon  what  is  a  division  of  the  apical 


Linear 
rejleclior, 
<f  fiJeufcL 


Fig.  480. — Right  Lung  of  Ox;   Medial  View. 
Hardened  in  situ.     1,  Left  bronchus;  2,  pulmonary  veins;  3,  pulmonary  artery.     Mediastinal  lobe  =  intermediate  lobe. 


are  in  contact  with  the  oesophagus;    above  and  below  the  latter  the  pleura  is  re- 
flected, as  shown  in  Fig.  480. 

The  interlobar  fissures  begin  at  the  ventral  margin  of  the  lung  and  pass  toward  the  root. 
Those  of  the  left  lung  lie  opposite  to  the  fourth  and  sixth  ribs.     The  diaphragmatic  lobe  is  the 


542 


RESPIRATORY    SYSTEM    OF   THE    OX 


largest,  and  has  the  form  of  a  three-sided  pyramid  with  its  base  resting  on  the  diaphragm.  The 
cardiac  lobe  is  prismatic  and  forms  the  posterior  margin  of  the  cardiac  notch;  its  long  axis  corre- 
sponds to  the  fifth  rib.     The  apical  lobe  of  the  left  hmg  is  small  and  pomted;   its  ventral  margin 

Dorsal  border 


DiapJtrag  malic 
lobe 


Cardidc  lube 


Fig.  481. — Left  Lung  of  Ox;   Lateral  ^'IEW. 
Arrows  indicate  interlobar  fissures. 


Dorsal  borda 


Diuphrugmalic  lobe 
and  surface 


Apical  lobe 
Cardiac  impression 


Cardiac  lube 


Fig.  482. — Left  Lung  of  Ox;   Media 
1,  Stem  bronchus;    1',  bronchial  branch  for  apical  and  cardiac  lobes 


i,  groove  for  aorta;  5,  groove  for  CBSophagus. 


View. 

^.pulmonary  artery;  3,  ^,  5,  pulmonary  veins; 
Arrows  indicate  interlobar  fissures. 


lies  on  the  pulmonary  artery  and  the  anterior  aorta;  below  this  the  space  in  front  of  the  heart 
is  occupied  by  the  apical  lobe  of  the  right  lung.  In  some  cases  additional  fissures  partially  sub- 
divide the  apical  lobe,  and  on  the  other  hand  the  apical  lobe  of  the  right  lung  may  be  undivided. 


THE    LUNGS 


543 


Apical  lobe 


, Cardiac  lobe 


1  titermediaie  lobe 


Diaphragmatic  lobe 


Posterior  mediastinal  lymph  gland 


Fig.  48.'5.— TjUnos  and  Heart  of  Sheei';  Ventral  View. 
Specimen  hardened  in  situ.     Space  between  heart  and  king.s  was  occupied  by  pericanUum  and  fat. 


r'S^^^  J^ort^e?- 


(hoove  for 
wsophagus 


"—  Diaphragmatic  surface 


Apex  I  / 

Cardiac  notch 


Fig.  484. — Right  Lung  of  Sheep;  Mediastinal  Aspect. 

Hardened  in  siiu.     B,  Bronchus;    P.a.,  pulmonary  artery:    PjK,  pulmonary  vein;    V.c,  posterior  vena  cava;    Ljj, 

bronchial  lymph  gland.     Mediastinal  lobe  =  intermediate  lobe. 


544  RESPIRATORY    SYSTEM    OF    THE    OX 

On  the  left  side  the  cardiac  notch  leaves  the  greater  part  of  the  pericardium  in  contact  with  the 
chest  wall  as  far  back  as  the  fourth  intercostal  space.  On  the  right  side  the  lung  commonly  covers 
the  pericardium,  so  that  the  latter  has  no  contact  with  the  lateral  wall  of  the  thorax.  But  in  some 
cases  (as  in  the  annexed  figures)  there  is  a  small  cardiac  notch  at  the  ventral  part  of  the  third 
intercostal  space  or  fourth  rib.  In  dissecting-room  subjects  the  basal  border  usually  begins  at 
the  space  between  the  fifth  and  sixth  costal  cartilages,  crosses  the  ventral  part  of  the  sixth  rib, 
and  is  then  about  parallel  with  the  diaphragmatic  line  of  pleural  reflection.  It  crosses  the  ninth 
rib  about  its  middle  and  ends  at  the  vertebral  end  of  the  eleventh  intercostal  space. 

The  lobulation  is  very  distinct  on  account  of  the  extremely  large  amount  of 
interlobular  tissue. 

In  the  sheep  the  lungs  resemble  those  of  the  ox  in  lobation,  but  differ  from 
them  considerably  in  shape.  They  are  relatively  somewhat  longer,  and  the  basal 
border  differs  in  conformity  with  the  diaphragmatic  line  of  pleural  reflection. 
There  is  usually  a  small  triangular  cardiac  notch  on  the  right  lung  opposite  to  the 
^'entral  part  of  the  fourth  and  fifth  ribs;  its  greatest  height  is  about  two  inches 
(ca.  5  cm.).  The  left  lung  leaves  the  greater  part  of  the  pericardium  uncovered  as 
far  back  as  the  fifth  intercostal  space.  The  lobulation  of  the  lung  is  much  less 
distinct  than  in  the  ox.  The  pleural  sacs  form  a  cul-de-sac  on  each  side  of  the  first 
lumbar  vertebra. 

In  the  sheep  the  diaphragmatic  line  of  pleural  reflection  differs  from  that  of  the  ox.  It  ex- 
tends along  the  seventh  and  eighth  costal  cartilages,  crosses  the  ninth  cartilage  close  to  the  rib, 
the  ventral  ends  of  the  tenth  and  eleventh  ribs,  the  twelfth  rib  about  an  inch  (ca.  2-3  cm.)  from 
its  ventral  end,  and  the  thirteenth  rib  about  two  inches  (ca.  5  cm.)  from  its  ventral  end.  It 
reaches  as  far  back  as  the  anterior  border  of  the  first  lumbar  transverse  process. 

THE  THYROID  GLAND 

The  thyroid  gland  is  softer  in  texture  than  in  the  horse  and  is  pale  in  color  in 
the  adult;  in  the  calf  it  is  dark  red  in  color.  The  lateral  lobes  are  irregularly 
triangular  in  outline  and  are  more  extensive  and  flatter  than  in  the  horse.  In 
addition  to  their  contact  with  the  trachea  they  are  related  deeply  to  the  oesophagus 
and  the  crico-pharyngeus  muscle  to  a  varying  extent.  The  superficial  face  is 
related  to  the  sterno-thyro-hyoideus,  sterno-cephalicus,  the  carotid  artery,  internal 
jugular  vein,  and  the  vagus  and  sympathetic  nerves.  The  isthmus  is  constantly 
present  and  glandular;  it  is  band-like  and  is  commonly  a  quarter  to  half  an  inch 
(ca.  0.5-1  cm.)  in  width. 

The  lateral  lobes  average  about  three  inches  or  more  (ca.  8  cm.)  in  length  and  about  half  an 
ounce  (ca.  14-15  gm.)  in  weight.  They  are  so  soft  and  loose  in  texture  that  their  true  shape  is 
seen  only  in  specimens  hardened  in  situ.  In  soft  material  they  appear  oval  in  outline.  The 
isthmus  may  be  connected  with  the  ventral  margin  or  the  posterior  end  of  the  lateral  lobes;  it  is 
relatively  large  in  the  calf,  and  is  very  evident  on  account  of  its  dark  color. 

In  the  sheep  the  thyroid  gland  is  dark  red  in  color.  The  lateral  lobes  have  a 
long  elliptical  outline  and  lie  on  each  side  of  the  first  six  or  seA^en  rings  of  the  trachea; 
they  are  two  inches  or  more  (ca.  5-6  cm.)  in  length  antl  half  an  inch  or  more  (ca. 
1.5  cm.)  in  height.  They  are  connected  by  a  flat  glandular  isthmus  a  quarter  of 
an  inch  or  more  (ca.  6-8  mm.)  in  width;  the  isthmus  is  connected  Avith  the  lateral 
lobe  at  or  near  the  posterior  end  of  the  latter,  and  crosses  the  trachea  about  the  fifth 
ring. 

Accessory  thyroids  may  be  found,  and  parathyroids  also  occur  near  the  pos- 
terior extremity  or  on  the  deep  surface  of  the  lateral  lobes  of  the  thyroid. 


THE  THYMUS  GLAND 
The  thymus  is  pale  and  distinctly  lobulated.  It  is  much  larger  in  the  calf 
than  in  the  foal,  weighing  at  five  or  six  weeks  about  15  to  25  ounces  (ca.  425  to  600 
grams).  At  the  period  of  its  greatest  development  it  occupies  the  greater  part  of 
the  anterior  mediastinal  space,  reaching  back  to  the  pericardium,  pulmonary  artery, 
and  aortic  arch.     Its  left  face  (covered  by  the  mediastinal  pleura)  is  in  contact 


RESPIRATORY    SYSTEM   OF   THE    PIG — THE    NASAL   CAVITY 


545 


with  the  chest-wall  and  apical  lobe  of  the  left  lung  as  far  back  as  the  third  rib. 
Its  right  face  is  largely  molded  on  the  great  vessels  in  front  of  the  heart.  The 
cervical  part  forms  the  bulk  of  the  gland;  it  consists  of  right  and  left  lobes  which 
extend  along  the  trachea  and  oesophagus  from  the  thoracic  inlet  to  the  thyroid 
gland.     The  two  lobes  are  large  at  the  root  of  the  neck,  where  they  are  in  apposition 


Fig.  485. — Thymus  of  Young  Calf. 

o,  Thymus  (cervical  part) ;  6,  trachea;  c,  isthmus  of  thyroid  gland ;  d,  laryngeal  prominence;   /,  apical  loDe  of  right  lung; 

^,  heart  (left  ventricle) ;   3,  pulmonary  artery;  4i  aorta;  5,  5',  cesophagus;  6',  m.  longus  colli;  7,  diaphragm. 

and  cover  the  trachea,  oesophagus,  carotid  artery,  and  vago-sympathetic  trunk. 
Further  forward  they  gradually  diminish  in  size  and  diverge  to  the  sides  of  the 
trachea.  They  are  related  superficially  to  the  sterno-cephalicus,  sterno-thyro- 
hyoideus,  and  external  jugular  vein.  It  undergoes  atrophy  slowly  and  remnants 
of  the  thoracic  part  often  remain  even  in  advanced  age. 


RESPIRATORY  SYSTEM  OF  THE  PIG 

THE  NASAL  CAVITY 

The  nostrils  are  small,  and  are  situated  on  the  flat  anterior  surface  of  the 
rostrum  or  snout  (Rostrum  suis).  The  latter  is  a  short  cylindrical  projection, 
Avith  which  the  upper  lip  is  fused,  and  is  circumscribed  by  a  prominent  circular 
margin.  The  skin  on  the  snout  is  thin  and  highly  sensitive;  it  presents  small 
pores,  and  scattered  over  it  are  fine  short  hairs.  In  the  snout  between  the  nostrils 
is  the  OS  rostri,  which  is  to  be  regarded  as  a  special  development  of  the  extremity  of 
the  septum  nasi  in  adaptation  to  the  habit  of  burrowing  or  rooting.  A  plate  of 
cartilage,  representing  the  lamina  of  the  alar  cartilage  of  the  horse,  curves  ventro- 
laterally  from  the  dorsal  part  of  the  os  rostri,  and  a  pointed  bar  of  cartilage  curves 
upward  from  the  lower  part  of  the  bone  in  the  lateral  wing  of  the  nostril.  The 
notch  between  the  nasal  bone  and  the  premaxilla  is  closed  in  by  parietal  cartilages 
which  resemble  those  of  the  ox. 

The  nasal  cavity  (Fig.  180)  is  long  and  narrow.  It  is  divided  behind  by  the 
lamina  transversalis  into  an  upper  olfactory  part,  which  leads  to  the  ethmoidal 
meatuses,  and  a  lower  respiratory  part,  which  is  a  direct  continuation  of  the  ventral 
meatus.  The  posterior  part  of  the  septum  is  membranous.  The  turbinate  bones 
resemble  in  general  those  of  the  ox.  The  dorsal  meatus  is  exceedingly  small.  The 
middle  meatus  is  a  deep  fissure  between  the  two  turbinates:  it  divides  posteriorly 
35 


546  RESPIRATORY    SYSTEM    OF    THE    PIG 

into  two  branches :  one  of  these  extends  upward  and  backward  between  the  lateral 
mass  of  the  ethmoid  bone  and  the  dorsal  turbinate;  the  other  widens  and  joins  the 
ventral  meatus.  The  opening  between  the  maxillary  sinus  and  the  middle  meatus 
lies  in  a  transverse  plane  through  the  last  cheek  teeth.  The  middle  meatus  is 
continuous  with  the  space  enclosed  by  the  dorsal  part  of  the  ventral  turbinate  and 
with  the  cavity  of  the  dorsal  turbinate.  The  dorsal  division  of  the  middle  meatus 
presents  several  openings  into  the  frontal  sinus.  The  ventral  meatus  is  relatively 
roomy;  it  communicates  with  the  space  enclosed  by  the  lower  coil  of  the  ventral 
turbinate.  The  opening  of  the  naso-lacrimal  duct  is  in  the  posterior  part  of  the 
ventral  meatus.  The  incisive  duct  and  the  vomero-nasal  organ  resemble  those  of 
the  ox. 


THE  LARYNX 

The  larynx  is  remarkable  for  its  great  length  and  mobility.  The  cartilages 
are  more  loosely  attached  to  each  other  than  in  the  other  animals.  The  cricoid 
cartilage  is  thick  and  compressed  laterally;  its  lamina  is  long  and  narrow;  its 
arch  is  directed  ol^liquely  downward  and  backward.  The  thyroid  cartilage  is  very 
long;  its  laminae  are  united  ventrally  and  form  a  median  ridge.  The  anterior 
cornua  are  absent,  and  no  joints  are  formed  with  the  hyoid  bone.  The  posterior 
cornua  are  broad,  bent  inward,  and  articulate  with  the  cricoid  cartilage.  The 
epiglottis  is  relatively  very  large,  and  is  more  closely  attached  to  the  hyoid  bone 
than  to  the  rest  of  the  larynx.  The  middle  part  of  its  base  is  turned  forward,  and 
rests  on  the  thyro-hyoid  membrane;  it  is  closely  connected  with  the  body  of  the 
hyoid  bone  by  the  hyo-epiglottic  ligament  and  the  strong  hyo-epiglottic  muscle.^ 
The  apex  of  the  arytenoid  cartilage  is  very  large,  and  is  divided  into  two  parts  at 
its  extremity;  the  medial  part  is  fused  with  that  of  the  opposite  cartilage.  There 
is  a  small  interarytenoid  cartilage  in  the  transverse  ligament.  The  rima  glottidis 
is  very  narrow.  The  vocal  cords  are  directed  obliquely  downward  and  backward; 
and  each  is  pierced  by  a  long,  slit-like  opening,  which  leads  into  the  large  laryngeal 
saccule.  The  vocal  ligament  is  similarly  divided  into  a  larger  anterior  and  a  smaller 
posterior  part.  There  is  a  middle  ventricle  near  the  base  of  the  epiglottis.  The 
thyro-arytenoid  muscle  is  very  strong  and  is  undivided ;  it  is  equivalent  (as  in  the 
ox)  to  the  vocalis  and  ventricularis  muscles  of  the  horse.  The  arj^enoideus  trans- 
versus  is  very  small.  The  crico-thyroid  consists  of  two  strata:  the  superficial 
layer  corresponds  to  the  muscle  of  the  other  animals;  the  deep  part  consists  of 
transverse  fibers. 


TRACHEA  AND  BRONCHI 
The  trachea  is  about  six  to  eight  inches  (ca.  15  20  cm.)  long,  and  contains 
thirty-two  to  thirty-five  rings,  which  overlap  dorsally.  It  is  slightly  depressed 
dorsally,  except  the  terminal  part,  which  is  circular  in  cross-section.  A  special 
bronchus  is  detached  for  the  apical  lobe  of  the  right  lung,  as  in  the  ox.  In  the 
right  lung  the  stem-bronchus  sends  branches  (one  each)  to  the  cardiac  and  inter- 
mediate lobes  and  continues  backward  in  the  diaphragmatic  lobe,  in  which  it 
ramifies.  In  the  left  lung  the  stem-bronchus  gives  off  a  bronchus  which  divides 
into  two  branches  for  the  anterior  part  of  the  lung  (fused  apical  and  cardiac  lobes'), 
and  continues  backward  in  the  diaphragmatic  lobe. 

1  The  arrangement  here  is  one  of  the  most  striking  features  of  the  pig's  larynx.  The  short 
and  thick  middle  hyo-epiglottic  ligament  and  the  anterior  part  of  the  thyro-hyoid  membrane  are 
inelastic,  while  the  posterior  part  of  the  membrane  is  thin  and  elastic  and  allows  the  epiglottis 
to  be  separated  by  a  consideral)le  interval  from  the  thyroid  cartilage.  Moreover,  the  borders  of 
the  epiglottis  are  connected  with  the  thyroid  cornua  of  the  hyoid  bone  by  lateral  hyo-epiglottic 
ligaments. 


THE  THORAX  AND  PLEURA — THE  LUNGS 


547 


THE  THORAX  AND  PLEURAE 
The  ribs  are  in  general  strongly  curved  in  most  of  the  improved  breeds,  so  that 
the  thorax  is  rounded.  The  pleural  sacs  extend  forward  to  the  first  intercostal 
space.  The  diaphragmatic  line  of  pleural  reflection  begins  at  or  a  little  above  the 
sternal  end  of  the  seventh  rib,  and  extends  in  a  gentle  curve  to  about  the  middle  of 
the  last  rib,  along  the  medial  face  of  which  it  continues.  (When  a  fifteenth  rib  is 
present — a  very  common  occurrence — it  does  not  affect  the  arrangement  of  the 
pleura  or  diaphragm). 


Trachea     (Esophagus 


Apical  lobe 


Apical  lobe 


Cardiac  lobe 


Diaphrag- 
matic lobe 


Fig.  486. — Lungs  and  Heart  of  Pig;  Ventral  View. 
L.  %.,  Intermediate  lobe  of  right  lung;  F.  d.,  diaphragmatic  surface  of  lungs;    1,  left  brachial  artery;   2,  brachio- 
cephalic artery ;  3,  apex  of  heart;  4i  pericardium  (cut  edge) ;  5,  plica  venae  cava ;  <?,  posterior  vena  cava;   7,  oesophagus; 
8,  ventral  (Esophageal  nerve  trunk;   9,  aorta. 


THE  LUNGS 


The  right  lung  has  four  lobes — apical,  cardiac,  diaphragmatic,  and  intermedi- 
ate. In  some  cases  the  apical  lobe  is  divided  by  a  fissure  into  two  parts;  sometimes 
it  is  fused  with  the  cardiac  lobe.  The  left  lung  may  be  regarded  as  having  two  or 
three  lobes.    The  diaphragmatic  lobe  is  clearly  marked  off  by  a  fissure.    The  part 


548  RESPIRATORY    SYSTEM    OF   THE    DOG 

anterior  to  the  fissure  represents  the  apical  and  cardiac  lobes,  which  are,  however, 
separated  only  by  the  cardiac  notch,  not  by  an  interlobar  fissure,  as  is  usual  in  the 


Trachea  Dorsal  border 


Diaphragmatic  lobe 

Apical  lobe 

notch 

Cardiac  lobe  Intermediate  lobe 

Fig.  487. — Right  Lung  of  Pig;   Medial  View. 
1,  Left  bronchus  (cut  off) ;  £,  2,  pulmonary  arteries;  3,  3,  3,  pulmonary  veins;  4,  posterior  vena  cava;  5,  groove  for 
anterior  vena  cava;  6,  groove  for  vena  azygos;  7,  groove  for  aorta;  8  (placed  on  groove  for  oesophagus),  lines  of  pleural 
reflection.     Arrows  indicate  interlobar  fissures. 

right  lung.     The  lobulation  is  distinct,  but  the  interlobular  septa  are  thinner  than 
in  the  ox. 

THE  THYROID  GLAND 

The  thjrroid  gland  is  large  and  is  situated  usually  at  a  considerable  distance 
from  the  larynx,  but  may  be  in  contact  with  it.  The  lateral  lobes  are  irregularl}'^ 
triangular  in  outline,  and  are  two  inches  or  more  (ca.  5-6  cm.)  in  length  in  a  large 
adult.  They  are  united  to  a  considerable  extent  ventrally,  so  that  an  isthmus 
cannot  be  distinguished.  The  gland  is  related  deeply  to  the  sides  and  ventral  face 
of  the  trachea,  and  is  in  contact  dorsally  with  the  oesophagus.  The  chief  artery 
enters  at  the  posterior  extremity. 

THE  THYMUS 

The  thymus  in  young  subjects  is  very  large,  extending  to  the  larynx  or  even  to 
the  mandibular  space. 


RESPIRATORY  SYSTEM  OF  THE  DOG 
THE  NASAL  CAVITY 
The  nostrils  are  situated  on  the  muzzle,  with  which  the  upper  lip  blends.  They 
are  shaped  somewhat  like  a  comma,  with  the  broad  part  next  to  the  septum  and 
the  narrow  part  directed  backward  and  outward.  The  skin  around  the  nostrils 
is  bare,  usually  black,  and  in  health  moist  and  cool.  The  muzzle  is  marked  by  a 
median  furrow  (philtrum),  or  a  deep  fissure  in  some  breeds.     The  cartilaginous 


THE    NASAL    CAVITY 


549 


framework  is  formed  essentially  by  the  septal  cartilage  and  the  parietal  cartilages 
which  proceed  from  it.     The  septal  cartilage  projects  beyond  the  premaxilla,  and 


Fig.  488. — Sagittal  Section  of  Head  and  Part  of  Neck  of  Dog. 


porsal  meatus 

%\   /      Middle  meatus 


Fig.  489. — Key  to  Preceding  Figure. 


is  much  thickened  at  its  extremity;    it  gives  off  from  its  margins  the  two  parietal 
cartilages,  which  curve  laterally  and  toward  each  other.     A  grooved  plate  extends 


550 


RESPIRATORY    SYSTEM    OF   THE    DOG 


outward  from  the  septal  cartilage  in  the  floor  of  the  nostril,  and  another  lamina 
supports  the  alar  fold  of  the  ventral  turbinate  bone;  these  may  be  termed  accessory- 
nasal  cartilages  (Cartilagines  nasi  accessorise). 

The  length  of  the  nasal  cavity  varies  greatly  in  different  breeds,  correspond- 
ing, of  course,  to  the  length  of  the  face.  The  cavity  is  roomy,  but  is  very  largely 
occupied  by  the  turbinates  and  the  lateral  masses  of  the  ethmoid  bone.  The 
middle  meatus  is  short  and  narrow,  and  divides  posteriorly  into  two  branches:  the 
upper  branch  leads  to  the  ethmoidal  meatuses;   the  lower  branch  joins  the  ventral 

meatus.  The  ventral  meatus  is  very  small  in 
its  middle  part,  owing  to  the  great  develop- 
ment here  of  the  ventral  turbinate.  The 
posterior  part  of  the  nasal  cavity  is  divided 
by  the  lamina  transversalis  into  an  upper  olfac- 
tory part  and  a  lower  respiratory  part.  The 
sinuses  have  been  described  {vide  Osteology). 


THE  LARYNX 
The  larynx  is  relatively  short.  The  lamina 
of  the  cricoid  cartilage  is  wide;  the  arch  is 
grooved  laterally.  The  laminae  of  the  thyroid 
cartilage  are  high,  but  short;  they  unite  ven- 
trally  to  form  the  body,  on  which  there  is  an- 
teriorly a  marked  prominence,  and  posteriorly 
a  deep  notch.  The  oblique  line  on  the  lateral 
surface  of  the  lamina  is  prominent.  There  is 
a  rounded  notch  (Fissura  thyreoidea)  below  the 
short  anterior  cornu  for  the  passage  of  the  an- 
terior laryngeal  nerve.  The  posterior  cornu  is 
strong,  and  has  a  rounded  surface  for  articula- 
tion with  the  cricoid  cartilage.  The  arytenoid 
cartilages  are  relatively  small,  and  have  between 
them  a  small  interarytenoid  cartilage.  The 
epiglottis  is  quadrilateral;  its  lower  part  or 
stalk  (petiolus)  is  narrow,  and  fits  into  the 
angle  of  the  thyroid  cartilage.  The  cuneiform 
cartilages  (Cartilagines  cuneiformes)  are  large 
and  somewhat  crescent  shaped;  they  are  not 
fused  with  the  epiglottis. 

The  false  vocal  cords  extend  from  the 
cuneiform  cartilages  to  the  thyroid.  The  true 
vocal  cords  are  large  and  prominent.  The 
large  lateral  ventricle  is  a  long  slit  parallel  with 

the  anterior  margin  of  the  true  vocal  cord.     The  lar3mgeal  saccule  is  extensive  and 

lies  lateral  to  both  true  and  false  vocal  cords. 

The  crico-thyroid  muscle  is  thick.     The  hyo-epiglotticus  is  well  developed, 

and  is  double  at  its  hyoid  attachment.     The  ventricularis  or  anterior  part  of  the 

thyro-arytenoideus  arises  on  the  cuneiform  cartilage.     Hence  Lesbre  has  suggested 

the  name  cuneo-arytenoideus  for  it. 


Fig.    490. — Aditus    Laryngis    and    Related 

Structubbs  or  Dog. 
The   pharynx  and   CBsophagus    have   been  cut 

along  the  mid-dorsal  line  and  reflected. 

/,  Epiglottis;  2,  2,  corniculate  cartilages; 
S,  3,  arytenoid  cartilages;  4,  glottis;  o,  wall  of 
pharynx;  6,  oesophagus;  7,  limen  oesophagi;  8, 
pcsterior  pillar  of  soft  palate;  9,  median  sulcus 
of  tongue;  /O,  vallate  papillae;  11,  conical  pa- 
pillae of  root  of  tongue;  IS,  12,  tonsils  (shown 
by  opening  up  tonsillar  sinus). 


THE  TRACHEA  AND  BRONCHI 

The  trachea  is  practically  circular  in  cross-section  at  its  ends,  but  the  inter- 
vening part  is  very  slightly  flattened  dorsally.     It  contains  about  forty  to  forty- 


THE    LUNGS 


551 


five  U-shaped  rings;  the  ends  of  the  rings  do  not  meet  dorsally,  so  that  here  the 
trachea  has  a  membranous  wall  (Paries  membranacea) ,  and  is  composed  of  a  layer 
of  transverse  smooth  muscle-fibers  outside  of  the  rings,  the  fibrous  membrane,  and 
the  mucous  membrane. 

The  stem-bronchi  diverge  at  an  obtuse  angle,  and  each  divides  into  two 
branches  before  entering  the  lung,  but  the  ramification  differs  in  the  two  lungs. 
In  the  right  lung  the  anterior  bronchus  goes  to  the  apical  lobe,  and  the  stem- 
bronchus  gives  off  a  branch  to  the  cardiac  lobe  and  another  to  the  intermediate  lobe. 
In  the  left  lung  the  anterior  bronchus  divides  into  two  branches  for  the  apical  and 
ardiac  lobes.  The  anterior  branch  of  the  left  bronchus  crosses  under  the  pul- 
monary artery. 

THE  LUNGS 

The  lungs  differ  in  shape  from  those  of  the  horse  and  ox  in  conformity  with 
the  shape  of  the  thorax,  which  is  relatively  very  wide  in  the  dog;  the  lateral  thoracic 
walls  are  strongly  curved,  and  the  costal  surface  of  the  lungs  is  correspondingly 
convex.^ 

The  right  lung  is  much  (ca.  25  per  cent.)  larger  than  the  left.     It  is  divided 

Dorsal  border 


Cardiac  notch 


Fig.  491. — Right  Lung  of  Dog;   Medial  View. 
L.  a.,  Apical  lobe;  L.  c,  cardiac  lobe;  L.  (/.,  diaphragmatic  lobe;  L.  i.,  intermediate  lobe;   /,  stem-bronchus;  S,  S', 
bronchi  of  apical  lobe;   3,  3',  divisions  of  pulmonary  artery;   4-7,  pulmonary  veins;   S,  groove  for  anterior  vena  cava; 
9,  groove  for  vena  azygos;   10,  groove  for  CBSophagus;   11,  groove  for  trunk  of  vertebral,  cervical,  and  dorsal  veins;   IS, 
groove  for  internal  thoracic  vessels. 


into  four  lobes  by  deep  fissures  which  extend  to  the  root.  The  lobes  are  the  apical, 
cardiac,  diaphragmatic,  and  intermediate.  The  apical  lobe  extends  considerably 
over  the  median  plane  in  front  of  the  pericardium.  The  intermediate  lobe  has  the 
form  of  an  irregular,  three-sided  pyramid,  with  its  base  against  the  diaphragm  and 
its  apex  at  the  root;  on  its  lateral  face  there  is  a  deep  groove  which  contains  the 
posterior  vena  cava  and  right  phrenic  nerve,  enclosed  in  a  special  pleural  fold.  The 
cardiac  impression  of  the  right  lung  is  much  deeper  than  that  of  the  left.     The 

^The  costal  attachment  of  the  diaphragm  is  lower  than  in  the  other  animals,  thus  further 
increasmg  the  capacity  of  the  thorax  (vide  diaphragm). 


552 


RESPIRATORY    SYSTEM    OF   THE    DOG 


Dorsal  border 


— L.  d. 

\ 


Apex- 


Apical  lobe 

Cardiac  lobe 

Fig.  492. — Left  Lung  of  Dog;   Costal  Surface. 
L.  d..  Diaphragmatic  lobe.       Arrows  indicate  interlobar  fissures. 


Intermediate  Diaphragmatic  lobe 

lobe 


Diaphragmatic  lobe 


Cardiac  lobe 
Cardiac  lobe     Apex  of  heart 
Fig.  493. — Diaphragmatic  Surface  of  Lungs  and  Heart  of  Dog. 
1,  Aorta;   2,  ojsophagus;   3,  oesophageal  nerve  trunk;  4,  posterior  vena  cava. 


THE    THYROID    GLAND — THE    THYMUS  553 

cardiac  notch  is  triangular  and  allows  the  pericardium  to  come  in  contact  with  the 
lateral  wall  at  the  fourth  and  fifth  interchondral  spaces. 

The  left  lung  is  divided  into  three  lobes — apical,  cardiac,  and  diaphragmatic. 
The  cardiac  impression  is  shallow,  and  a  distinct  cardiac  notch  is  not  present,  but 
the  pericardium  is  in  contact  with  the  lateral  wall  along  a  narrow  area  at  the  ventral 
part  of  the  fifth  and  sixth  interchondral  spaces.  The  apical  lobe  has  a  small,  blunt- 
pointed  apex  which  lies  over  the  manubrium  sterni.  On  account  of  the  small 
amount  of  interlobular  tissue  the  lobulation  is  not  distinct.  Pigmentation  of  the 
interlobular  tissue  is  usual  in  dogs  kept  in  town. 

Accessory  fissures  may  partially  subdivide  some  of  the  lobes;  this  is  most  common  in  re- 
gard to  the  apical  lobe.  When  the  lungs  have  been  successfully  hardened  in  situ,  additional  mark- 
ings are  seen  on  the  mediastinal  surface.  On  the  right  lung  there  are:  (1)  A  groove  for  the  an- 
terior vena  cava  in  front  of  the  root;  (2)  a  groove  for  the  vena  azygos  which  curves  upward  and 
backward  over  the  root;  (3)  a  shallow  groove  for  the  aorta  above  the  posterior  part  of  the  root; 
(4)  a  groove  for  the  a?sophagus  behind  the  root;  (5)  a  groove  for  the  internal  thoracic  vessels  curv- 
ing downward  and  backward  over  the  apex;  (6)  a  groove  for  the  right  phrenic  nerve  in  the  upper 
part  of  the  cardiac  impression;  (7)  grooves  for  the  dorso-cervical  and  vertebral  veins  running  from 
the  dorsal  border  to  the  groove  for  the  vena  cava.  On  the  left  lung  there  are:  (1)  A  well-marked 
groove  for  the  aorta,  which  curves  over  the  root  and  runs  back  just  below  the  dorsal  border;  (2) 
a  shallow  groove  for  the  oesophagus  behind  the  root;  (3)  grooves  on  the  apical  lobe  for  the  left 
brachial  and  brachiocephalic  arteries;  (4)  grooves  near  the  apex  for  the  internal  thoracic  ves- 
sels; (5)  a  groove  for  the  left  phrenic  nerve  is  more  or  less  evident;  it  passes  downward  and  back- 
ward over  the  middle  of  the  apical  lobe,  then  runs  backward  over  the  cardiac  and  diaphragmatic 
lobes. 

The  diaphragmatic  line  of  pleural  reflection  extends  along  the  lower  part  of  the  ninth  costal 
cartilage,  crosses  the  tenth  cartilage  a  little  (ca.  1-2  cm.)  below  the  costo-chondral  junction,  and 
the  eleventh  rib  at  the  costo-chondral  junction;  it  then  curves  up  to  the  last  rib,  just  above  its 
middle,  and  passes  medially  and  backward  to  the  second  lumbar  transverse  process.  In  a  good- 
sized  dog  (e.  g.,  bull-terrier)  the  apex  of  the  pleural  sac  extends  about  an  inch  (ca.  2.5  cm.)  anterior 
to  the  plane  of  the  first  rib. 

THE  THYROID  GLAND 

The  lateral  lobes  of  the  thyroid  gland  are  long  and  narrow,  and  have  a  flat- 
tened, ellipsoidal  form;  they  are  situated  on  the  lateral  surfaces  of  the  trachea  near 
the  larynx,  extending  along  the  first  six  or  seven  rings  (Fig.  434).  The  extremities, 
are  small,  the  posterior  one  often  being  pointed.  The  isthmus  is  inconstant  and 
variable;  in  large  dogs  it  has  the  form  of  a  glandular  band  which  may  be  nearly 
half  an  inch  (ca.  1  cm.)  wide;  in  medium-sized  dogs  it  is  often  absent,  and  in  small 
dogs  it  is  usually  absent.  Accessory  thyroids  are  frequently  present;  three  or  four 
may  be  found  on  either  side,  as  well  as  a  median  one  near  the  hyoid  bone. 

The  parathyroids,  al)out  the  size  of  millet  or  hemp  seed,  are  four  in  number 
usually.  Two  are  situated  on  the  deep  face  of  the  thyroid  lobes,  in  which  they  are 
often  embedded;  the  others  are  placed  laterally  near  the  anterior  extremity  of  the 
thyroid. 

THE  THYMUS 

The  thymus  is  relatively  small,  and  is  situated  almost  entirely  in  the  thorax. 
The  left  lobe  is  much  larger  than  the  right,  and  extends  back  on  the  pericardium  as 
far  as  the  sixth  rib  at  the  time  of  its  greatest  size.  According  to  Baum,  the  gland 
increases  in  size  during  the  first  two  weeks  after  birth,  and  atrophies  rapidly  in  the 
next  two  or  three  months.  Traces  of  it  are  present  at  two  or  three  years  of  age, 
and  may  be  found  even  in  old  subjects. 


THE  UROGENITAL  SYSTEM 


The  urogenital  apparatus   (Apparatus  urogeuitalis)   includes  two  groups  of 
organs,  the  urinary  and  the  genital.     The  urinary  organs  elaborate  and  remove  the 

chief  excretory  fluid,  the  urine.  The  geni- 
tal organs  serve  for  the  formation,  develop- 
ment, and  expulsion  of  the  products  of  the 
reproductive  glands.  In  the  higher  verte- 
brates the  two  apparatus  are  independent 
except  at  the  terminal  part,  which  consti- 
tutes a  urogenital  tract,  and  includes  the 
vulva  in  the  female  and  the  greater  part  of 
the  urethra  in  the  male. 


THE  URINARY  ORGANS 


The  urinary  organs  (Organa  uropoiet- 
ica)  are  the  kidneys,  ureters,  bladder,  and 
urethra.  The  kidneys  are  the  glands  which 
secrete  the  urine;  they  are  red-bro\^^l  in 
color,  and  are  situated  against  the  dorsal 
wall  of  the  abdomen,  being  in  most  ani- 
mals almost  symmetrically  placed  on  either 
side  of  the  spine.  The  ureters  are  tubes 
which  convey  the  urine  to  the  urinary 
bladder.  The  latter  is  an  ovoid  or  piri- 
form sac,  which  is  situated  on  the  pelvic 
floor  when  empty  or  nearly  so;  it  is  a  reser- 
voir for  the  urine.  The  urine  accumulates 
in  the  bladder  and  is  then  expelled  through 
the  urethra. 


Fig.  494. — General  Dorsal  View  of  Urinary 
Organs  of  Horse. 
1,  Right  kidney;  1',  left  kidney;  2,  2',  ad- 
renal bodies;  3,  3',  ureters;  4,  urinary  bladder;  4', 
anterior  end  of  bladder  with  cicatricial  remnant  of 
urachus;  4",  urethra;  3,  aorta;  6,  6,  renal  arteries; 
7,  7,  external  iliac  arteries;  8,  8,  internal  ihac  ar- 
teries; 9,  9,  umbilical  arteries.  (After  Leisering'a 
Atlas.) 


THE  URINARY  ORGANS  OF  THE 
HORSE 

THE  KIDNEYS 
Each   kidney   presents   two    surfaces, 
two  borders,  and  two  extremities  or  poles, 
but  they  differ  so  much  in  form  and  position  as  to  require  a  separate  description 
of  each  in  these  respects. 

The  right  kidney  (Ren  dexter)  in  outline  resembles  the  heart  on  a  playing 
card,  or  an  equilateral  triangle  ^^^th  the  angles  rounded  off.  It  lies  ventral  to  the 
upper  parts  of  the  last  two  or  three  ribs  and  the  first  lumbar  transverse  process. 
The  dorsal  surface  (Facies  dorsalis)  is  strongly  convex;  it  is  related  chiefly  to  the 
diaphragm,  but  also  to  a  small  extent  posteriorly  to  the  iliac  fascia  and  psoas 

554 


THE    KIDNEYS 


555 


muscles.  In  well-hardened  specimens,  especially  those  from  thin  subjects,  impres- 
sions of  the  last  two  ribs  and  the  tip  of  the  first  lumbar  transverse  process  are 
usually  visible.^  The  ventral  surface  (Facies  ventralis)  is  in  general  slightly  con- 
cave, and  is  related  to  the  liver,  pancreas,  cfficum,  and  right  adrenal;  it  either  has 
no  peritoneal  covering,  or  only  a  narrow  peritoneal  area  laterally.^  The  medial 
border  (Margo  medialis)  is  convex  and  rounded;  it  is  related  to  the  right  adrenal 
and  the  posterior  vena  cava.  It  presents  about  its  middle  a  deep  notch,  the  renal 
hilus  (Hilus  renalis) ;  this  is  bounded  by  rounded  margins,  and  leads  into  a  space 
termed  the  renal  sinus  (Sinus  renalis).  The  vessels  and  nerves  reach  the  kidney 
at  the  hilus,  and  the  sinus  contains  the  renal  pelvis  or  dilated  origin  of  the  ureter. 
The  lateral  border  (Margo  lateralis)  is  rounded,  and  is  thinner  than  the  medial  one. 


0 

C   L.n 

0 

^    7 

V 

^""^-^^z.Tzr^ 

Fig.  495. — Di.^gram  of  Pcsition  and  Dors.\l  Relations  op  Kidneys  of  Horse. 

Areas  of  direct  relations  are  enclosed  by  continuous  lines;   parts  of  skeleton  which  overlie  the  kidneys  are  indicated  by 

dotted  lines.     L.I. — L.III,  lumbar  transverse  processes. 


It  consists  of  two  parts,  anterior  and  posterior,  which  meet  at  a  lateral  angle;  the 
anterior  part  fits  into  the  renal  impression  of  the  liver.  The  duodenum  curves 
around  the  lateral  border.  The  anterior  extremity  (Extremitas  cranialis),  thick 
and  rounded,  lies  in  the  renal  impression  of  the  liver.  The  posterior  extremity 
(Extremitas  caudalis)  is  thinner  and  narrower. 

The  left  kidney  (Ren  sinister)  is  bean  shaped.  It  is  considerably  longer  and 
narrower  than  the  right  one,  and  is  situated  nearer  the  median  plane  and  further 
back,  so  that  the  hilus  of  the  left  kidney  is  usually  about  opposite  to  the  posterior 
extremity  of  the  right  one.     It  is  usually  ventral  to  the  last  rib  and  the  first  two 

1  The  dorsal  surface,  being  largely  in  contact  with  the  diaphragm,  slopes  downward  in  front; 
thus  its  anterior  part  is  about  three  inches  (ca.  6-8  cm.)  ventral  to  the  dorsal  part  of  the  seven- 
teenth rib. 

2  In  exceptional  cases  a  considerable  area — as  much  as  the  outer  and  posterior  third — of  the 
surface  may  have  a  peritoneal  covering.  In  the  new-born  foal  a  large  part  is  so  covered;  this  is 
apparently  due  to  the  small  size  of  the  ctECum  and  the  small  area  of  attachment  of  its  base. 


556 


THE    URINARY    ORGANS    OF    THE    HORSE 


or  three  lumbar  transverse  processes.     The  dorsal  surface  is  convex,  and  is  related 
to  the  left  crus  of  the  diaphragm,  the  iliac  fascia  and  psoas  muscles,  and  the  dorsal  end 


Right  adrenal 


Left  adrenal      , 

I 


Left  ureter 

Fig.  496. — Kidneys  and  Adrenals  of  Horse;  Dorsal  View. 
Hardened  in  situ.     Impression  of  seventeenth  rib  on  right  kidney  is  indicated  by  small  cross.     The  left  kidney  W£ 
little  further  forward  in  this  subject  than  is  usual. 


Ureters 


Anterior  mesenteric 
artery  {stump) 


Renal  arteries 


Fig.  497. — Kidneys  and  Adrenals  or  Horse;  Ventral  View. 
Hardened  in  situ.     Left  renal  vein  (not  marked)  is  seen  curving  round  posterior  end  of  left  adrenal. 


of  the  spleen.  The  ventral  surface  is  convex  and  irregular ;  the  greater  part  of  it  is 
covered  by  the  peritoneum.  It  is  in  relation  with  the  origin  of  the  small  colon,  the 
terminal  part  of  the  duodenum,  the  left  adrenal,  and  the  left  extremity  of  the 


THE    KIDNEYS 


557 


pancreas.  The  medial  border  is  longer,  straighter,  and  thicker  than  that  of  the 
right  kidney.  It  is  related  to  the  posterior  aorta,  the  adrenal,  and  the  ureter.  The 
lateral  border  is  related  chiefly  to  the  base  of  the  spleen.  The  anterior  extremity 
extends  almost  to  the  saccus  caecus  of  the  stomach;  it  is  related  to  the  left  end  of 
the  pancreas  and  the  splenic  vessels.  The  posterior  extremity  is  usually  larger 
than  the  anterior  one. 

The  form  of  the  left  kidney  is  variable.  In  some  cases  its  outline  is  similar  to  that  of  the 
right  kidney,  but  its  ventral  surface  is  convex  and  is  often  marked  by  several  furrows  which  diverge 
from  the  hilus.  In  well-hardened  specimens  the  three  areas  of  the  dorsal  surface  are  often  dis- 
tinct. The  psoas  area  (Impressio  muscularis)  is  fiat,  parallel  with  the  medial  border,  and  widens 
behmd.  The  diaphragmatic  area  is  small  and  convex;  it  is  crescentic  and  is  confined  to  the  an- 
terior end.  The  lateral  splenic  area  is  somewhat  flattened  and  is  often  so  extensive  and  distinct 
as  really  to  constitute  a  third  surface  as  in  Fig.  496. 

Fixation. — The  kidneys  are  held  in  position  chiefly  by  the  pressure  of  adjacent 
organs  and  by  the  renal  fascia.     The  latter  is  a  special  development  of  the  sub- 

Renal  crest 

Cortical  substance 


Medullary  substance 


Renal  artery 


Ureter 


Fig.  498. — Frontal  (Horizontal)  Section  of  Kidnet  of  Horse. 

The  renal  vein  ia  removed.     A  large  accessory  renal  artery  entered  the  posterior  pole.     Sections  of  arteries  in  limiting 

layer  between  cortical  and  medullary  substance  are  white  in  figure. 


peritoneal  tissue,  which  splits  into  two  layers  to  enclose  the  kidney,  together  with 
the  perirenal  fat,  which  is  termed  the  capsula  adiposa.^  On  account  of  its  relations 
with  the  liver,  pancreas,  and  base  of  the  caecum,  the  right  kidney  is  much  more 
strongly  attached  than  the  left  one.  It  is,  therefore,  not  surprising  that  the  latter 
varies  somewhat  in  position;  its  posterior  extremity  may  be  ventral  to  the  third  or 
fourth  lumbar  transverse  process.  The  position  of  the  right  kidney,  excluding  its 
movements  during  respiration,  seems  to  be  very  constant. 

Weight  and  Size. — The  right  kidney  is  usually  one  or  two  ounces  heavier  than 
the  left.  The  average  weight  of  the  right  kidney  is  about  23  to  24  ounces  (ca. 
700  gm.);  that  of  the  left,  about  22  to  23  ounces  (ca.  670  gm.).  The  relation  of 
the  weight  of  both  kidneys  to  the  body-weight  is  about  1 :  300-350.  In  the  new- 
born foal  the  kidney  weighs  about  6  ounces  (ca.  170  gm.). 

^  The  amount  of  perirenal  fat  varies ;  in  animals  in  good  condition  it  may  entirely  conceal  the 
kidneys;  in  such  cases  the  impressions  produced  by  contact  of  the  kidney  with  contiguous  struc- 
tures may  be  indistinct. 


558  THE    URINARY    ORGANS    OF   THE    HORSE 

Chauveau  gives  as  an  average  750  grams  for  the  right  kidney  and  710  grams  for  the  left. 
Ellenberger  and  Baum  (24  cases)  give  the  right  kidney  as  varying  between  430  and  840  grams; 
and  the  left  between  425  and  780;  this  is  an  average  of  635  grams  (about  22)  2  omices)  for  the 
right  kidney,  and  602.5  grams  (about  213^2  ounces)  for  the  left.  They  give  the  relation  of  the 
weight  of  both  kidneys  to  the  body-weight  as  1 :  255-344.  In  a  Percheron  mare  weighing  about 
2000  pounds  the  right  kidney  weighed  4  pounds  3  ounces,  and  the  left  one  4  pounds.  In  a  horse 
of  medium  size  the  right  kidney  is  about  six  inches  (ca.  15  cm.)  in  length,  about  the  same  in  width, 
and  about  two  inches  (ca.  5  cm.)  thick.  The  left  kidney  is  about  seven  inches  (ca.  18  cm.)  long, 
four  to  five  inches  (ca.  10  to  12  cm.)  wide,  and  two  to  two  and  a  half  inches  (ca.  5  to  6  cm.)  thick. 

Structure. — The  surface  of  the  kidney  is  covered  by  a  thin  but  strong  fibrous 
capsule  (Tunica  fibrosa),  which  is  in  general  easily  stripped  off  the  healthy  kidney; 
it  is  continued  into  the  renal  sinus,  where  it  is  attached.  Sections  through  the 
kidney  show  it  to  consist  of  an  external  cortical  substance  and  an  internal  medullary 
substance.  The  cortical  substance  (Substantia  corticalis)  is  red  brown  in  color 
and  has  a  granular  appearance.  It  is  dotted  over  with  minute  dark  points;  these 
are  the  renal  corpuscles  (Corpuscula  renis),^  each  consisting  of  the  dilated  origin  of 
a  uriniferous  tubule  (Capsula  glomeruli),  with  an  invaginated  tuft  of  capillaries 
(Glomerulus)  enclosed  by  it.     The  medullary  substance  (Substantia  meduUaris) 


Renal  crest         Pelvis  Renal    Branches       Ureter 

vein  of  renal  artery 

Fig.  499. — Transverse  Section  or  Right  Kidney  op  Horse  Passing  Through  the  Hilus. 
Posterior  portion  of  organ  hardened  in  situ.     Note  curvature  of  dorsal  surface. 

is  more  resistant  and  presents  a  distinct  radial  striation.  Its  central  part  is  pale, 
but  its  periphery,  the  intermediate  zone,  is  of  a  deep  red  color;  in  the  latter  are 
seen,  at  fairly  regular  intervals,  sections  of  the  relatively  large  arciform  vessels, 
which  are  taken  to  represent  the  demarcation  between  the  primitive  lobes.^  Be- 
tween the  vessels  the  medulla  is  prolonged  somewhat  toward  the  periphery,  forming 
the  bases  of  the  renal  p)nraniids  (Pyramides  renales).  These  are  not  very  pro- 
nounced in  the  kidney  of  the  horse,  especially  as  the  gland  is  not  papillated.  Be- 
tween the  bases  of  the  pyramids  processes  of  the  cortex  dip  in  toward  the  sinus, 
forming  the  renal  columns  (Columnse  renales).^  The  inner  central  part  of  the 
medulla  forms  a  concave  ridge  which  projects  into  the  pelvis  of  the  kidney.  This 
projection  is  termed  the  renal  crest;  it  presents  numerous  small  openings  at  which 
renal  tubules  open  into  the  pelvis  of  the  kidney,  and  hence  the  surface  here  is  known 
as  the  area  cribrosa. 

^  Also  known  as  Malpighian  corpuscles. 

^  The  fcetal  kidney  is  divided  by  furrows  into  a  number  of  polygonal  areas,  each  of  which 
is  the  base  of  a  pyramidal  lobe  or  renculus.  These  furrows  usually  disappear  before  or  soon  after 
birth  in  the  foal,  although  traces  of  them  are  sometimes  seen  in  the  adult. 

^  In  the  kidney  of  the  horse  the  renal  columns  dip  in  between  the  pyramids  very  superficially 
as  compared  with  the  arrangement  in  the  human  kidney.  Breuer  states  that  the  pyramids  are 
40  to  64  in  number,  and  are  arranged  in  four  rows.     Only  the  middle  ones  are  distinct. 


THE    KIDNEYS 


559 


Examination  with  a  pocket  lens  shows  that  the  cortex  is  imperfectly  divided 
into  lobules  (Lobuli  corticales).  Each  lobule  consists  of  an  axial  radiate  part  (Pars 
radiata),  surrounded  by  a  convoluted  part  (Pars  convoluta).  The  former  appear 
as  ray-like  prolongations  from  the  bases  of  the  pyramids  (hence  also  termed  medul- 
lary rays) ,  and  consist  largely  of  narrow,  straight  or  slightly  flexuous  tubules  (limbs 
of  the  loops  of  Henle).  The  convoluted  part  is  granular  in  appearance,  and  con- 
sists largely  of  the  renal  corpuscles  and  convoluted  tubules. 

The  renal  pelvis  (Pelvis  renalis)  is  the  dilated  origin  of  the  excretory  duct. 
It  lies  in  the  sinus  of  the  kidney,  and  it  is  funnel-shaped,  but  flattened  dorso-ven- 
trally.  The  renal  crest^  (Crista  renalis)  projects  into  the  outer  part  of  the  pelvis 
in  the  form  of  a  horizontal  ridge  with  a  concave  free  edge.  The  tubules  of  the 
middle  part  of  the  medullary  substance  open  on  this  crest  into  the  pelvis.  The 
tubules  from  each  end  of  the  kidney  do  not  open  into  the  pelvis  proper  (Recessus 
medius),  but  into  two  long,  narrow  diverticula  (Recessus  terminales),  which  pro- 
ceed from  it  toward  the  poles  of  the  kidney.  The  wall  of  the  pelvis  consists  of 
three  layers.  The  external  fibrous  coat  or  adventitia  is  continuous  with  the  sup- 
porting tissue  of  the  kidney.     The  muscular  coat  consists  of  longitudinal  and 


Tig.  500. — Cast  of  Right  Renal  Pelvis  (a),  Re- 
cesses (c,  c'),  AND  Origin  of  Ureter  (b)  of  Horse. 
(After  Dumont.) 


Fig.  501. — Cast  of  Left  Renal  Pelvis  (a),  Recesses 
(c,  c'),  AND  Origin  of  Ureter  (6)  of  Horse. 
(After  Dumont.) 


circular  fibers.  The  mucous  coat  does  not  cover  the  renal  crest  nor  is  it  continued 
into  the  diverticula  of  the  pelvis.  It  has  a  yellowish  tinge,  and  forms  numerous 
folds.  It  contains  compound  tubular  glands  (Glandulae  pelvis  renalis),  which 
secrete  the  thick,  viscid  mucus  always  found  in  the  pelvis.^ 

Renal  Tubules. — The  parenchyma  or  proper  substance  of  the  kidney  is  composed  of  the 
small  renal  or  uriniferous  tubules  (Tubuli  renal es),  which  are  very  close  together  and  have  a 
complicated  course.  Each  tubule  begins  in  a  thin-walled,  spherica,l  dilatation  or  capsule  (Cap- 
sula  glomeruli),  which  is  invaginated  to  receive  a  tuft  of  looped  capillaries  termed  a  glomerulus; 
these  two  structures  constitute  a  renal  corpuscle ;  the  corpuscles  are  visible  as  minute  red  or 
dark  spots  in  the  convoluted  part  of  the  cortex.  Succeeding  this  is  a  short  narrow  neck,  beyond 
which  the  tubule  becomes  wide  and  convoluted,  forming  the  proximal  convoluted  tubule,  and 
enters  the  radiate  portion  of  the  cortex.  It  then  gradually  narrows  and  enters  the  intermediate 
zone;  becoming  very  narrow  and  nearly  straight,  it  descends  for  a  variable  distance  into  the  medul- 
lary substance,  turns  sharply  upon  its(-lf,  and  returns  to  the  cortex,  forming  thus  the  loop  of  Henle, 
with  its  descending  and  asceiiding  limbs.  In  the  convoluted  part  of  the  cortex  it  widens  and 
becomes  tortuous,  constituting  tlic  distal  convoluted  tubule.  The  tubule  then  narrows,  enters  a 
medullary  ray,  and  opens  with  other  tubules  into  a  straight  collecting  tubule;  this  passes  axially 
through  a  pyramid,  and  unites  with  other  collecting  tubules  to  form  the  relatively  large  papillary 
ducts,  which  open  into  the  renal  pelvis. 

Stroma. — The  interstitial  tissue  forms  a  reticulum  throughout  which  supports  the  tubules 

1  The  crest  is  the  result  of  fusion  of  the  papillae  or  apices  of  the  pyramids  in  the  embryo  and 
is  therefore  also  known  as  the  papilla  communis. 

2  There  are  goblet  cells  in  the  epithelium  of  the  pelvis  which  doubtless  concur  in  the  secretion 
of  mucus. 


660 


THE    URINARY    ORGANS    OF   THE    HORSE 


and  blood-vessels.     It  is  very  scanty  in  the  cortex,  much  more  abundant  in  the  medulla,  in  which 
it  increases  in  amoimt  toward  the  pelvis. 

Vessels  and  Nerves. — The  kidneys  receive  a  large  amount  of  blood  through  the 
renal  arteries  which  come  from  the  aorta.^  Branches  of  these  enter  at  the  hilus  and 
on  the  ventral  surface  of  the  gland,  and  reach  the  intermediate  zone,  where  they 
form  anastomotic  arches  (Arterise  arciformes).  From  these  arciform  arteries 
branches  pass  into  the  cortex  and  medulla.  The  cortical  branches  (Arterise  inter- 
lobulares)  have  in  general  a  radial  course  between  the  cortical  lobules,  and  give  off 
short  lateral  branches,  each  of  which  ends  as  the  afferent  vessel  (Vas  afferens)  of  a 
renal  corpuscle.     The  blood  is  carried  from  the  glomerulus  by  a  smaller  efferent 


Arched  collecting 
tubule 
Straight  collect- 
ing tubule 
Distal  convo- 
luted tubule 
Renal  {Malpig- 
hian)  corpuscle 
Proximal  convo- 
luted tubule 
Loop  of  Henle 

Collecting  tubule 


Arteria  arci- 
formis 


Large  collecting 
tubule 


^apillary  duct 


^  Artery  of  capsule 


Interlobular 
artery 


Capillary  net- 
work.    Vas 
-'      afferens 
Arteriola  recta 
spuria 


-  Glomerulus 


^"-^  Vena  arciformis 


Fig.  502. — Diagrammatic  Scheme  of  Uriniferous  Tubules  and  Blood-vesseus  of  Kidnet. 
Drawn  in  part  from  the  descriptions  of  Golubew  (Bohm,  Davidoff,  and  Ruber). 


vessel,  which  breaks  up  immediately  into  capillaries  which  form  networks  around 
the  tubules.  The  medullary  branches  descend  in  the  pyramids,  forming  in  them 
bundles  of  straight  twigs  (Arteriolse  rectse).  The  renal  veins  are  large  and  thin- 
walled;  they  go  to  the  posterior  vena  cava.  In  the  superficial  part  of  the  cortex 
the  veins  form  star-like  figures  (Vense  stellatae)  by  the  convergence  of  several  small 
radicles  to  a  common  trunk.  The  l3nnph-vessels  form  two  networks,  capsular  or 
superficial,  and  parenchymatous  or  deep.  On  leaving  the  hilus  they  go  to  lymph 
glands  in  this  vicinity  which  are  known  as  the  renal  lymph  glands. 

The  nerves  are  derived  from  the  renal  plexus  of  the  sympathetic,  which  en- 
laces the  renal  artery. 

^  The  occurrence  of  accessory  renal  arteries  is  not  at  all  rare.  They  may  come  from  various 
branches  of  the  aorta  (e.  g.,  posterior  mesenteric,  spermatic,  circumflex  iliac)  and  enter  the  posterior 
part  of  the  gland. 


THE   URETERS — THE    URINARY    BLADDER  561 


THE  URETERS 


The  ureter  is  the  narrow  part  of  the  excretory  duct  of  the  kidney.  Each 
begins  at  the  renal  pelvis  and  terminates  at  the  bladder.  It  is  about  3^  to  3^  inch 
(ca.  6  to  8  mm.)  in  diameter,  and  its  average  length  is  about  28  inches  (ca.  70  cm.). 
The  abdominal  part  (Pars  abdominalis)  of  each  ureter  emerges  ventrally  from  the 
hilus  of  the  kidney,  and  curves  backward  and  medially  toward  the  lateral  face  of  the 
posterior  vena  cava  (right  side)  or  the  aorta  (left  side).  They  then  pass  almost 
straight  backward  in  the  subperitoneal  tissue  on  the  surface  of  the  psoas  minor, 
cross  the  external  iliac  vessels,  and  enter  the  pelvic  cavity.  The  pelvic  part  (Pars 
pelvina)  passes  backward  and  a  little  ventrally  on  the  lateral  wall  of  the  pelvic 
cavity,  turns  medially,  and  pierces  the  dorsal  wall  of  the  bladder  near  the  neck. 
In  the  male  the  pelvic  part  enters  the  genital  fold  and  crosses  the  ductus  deferens. 
In  the  female  the  ureter  is  situated  in  most  of  its  course  in  the  dorsal  part  of  the 
broad  ligament  of  the  uterus. 

The  wall  of  the  ureter  is  composed  of  three  coats.  The  external  fibrous  coat 
(Tunica  adventitia)  contains  many  elastic  fibers.  The  muscular  coat  consists  of 
internal  and  external  layers  of  longitudinal  fibers,  with  a  stratum  of  circular  fibers 
between  them.  The  mucous  membrane  is  covered  with  transitional  epithelium; 
glands  (Glandulae  mucosae  ureteris)  resembling  those  of  the  renal  pelvis  occur  in  the 
first  three  or  four  inches  of  the  ureter. 

The  blood-supply  is  derived  from  the  renal  and  umbilical  arteries.  The  nerves 
come  from  the  solar  and  pelvic  plexuses;   many  minute  ganglia  are  present. 


THE  URINARY  BLADDER 

The  urinary  bladder  (Vesica  urinaria)  (Figs.  366,  369,  370)  differs  in  form,  size, 
and  position  according  to  the  amount  of  its  contents.  When  empty  and  contracted, 
it  is  a  dense,  piriform  mass,  about  the  size  of  a  fist,  and  lies  on  the  ventral  wall  of 
the  pelvic  cavity  at  a  variable  distance  behind  the  inlet.  When  moderately  filled, 
it  is  ovoid  in  form,  and  extends  a  variable  distance  along  the  ventral  abdominal  wall. 
Its  physiological  capacity  varies  greatly,  but  may  be  estimated  approximately  at 
about  three  or  four  quarts. 

The  anterior  rounded  blind  end  is  termed  the  vertex  ;^  on  its  middle  is  a  mass 
of  cicatricial  tissue  (Centrum  verticis),  a  vestige  of  the  urachus,  which  in  the  foetus 
forms  a  tubular  connection  between  the  bladder  and  the  allantois.  The  middle 
part  or  body  (Corpus  vesicae)  is  rounded,  and  is  somewhat  flattened  dorso-ventrall}^ 
except  when  distended.  It  presents  two  surfaces,  dorsal  and  ventral,  the  former 
being  the  more  strongly  convex,  especially  in  its  posterior  part  in  front  of  the  en- 
trance of  the  ureters.^  The  posterior  narrow  extremity,  the  neck  (Collum  vesicae), 
joins  the  urethra. 

The  relations  of  the  bladder  vary  according  to  the  degree  of  fulness  of  the 
organ,  and  also  differ  in  important  respects  in  the  two  sexes.  The  ventral  surface 
(Facies  ventralis)  lies  on  the  ventral  wall  of  the  pelvis,  and  extends  forward  on  the 
abdominal  wall  as  the  bladder  fills.  The  dorsal  surface  (Facies  dorsalis)  in  the  male 
is  related  to  the  rectum,  the  genital  fold,  the  terminal  parts  of  the  ductus 
deferentes,  the  vesiculae  seminales,  and  the  prostate;  in  the  female  it  is  in  contact 
instead  with  the  body  of  the  uterus  and  the  vagina.  The  vertex  of  the  full  bladder 
has  variable  relations  with  coils  of  the  small  intestine  and  small  colon,  and  the  pelvic 
flexure  of  the  large  colon. 

Fixation. — Displacement  of  the  bladder  is  limited  chiefly  by  three  peritoneal 

^  This  is  often  termed  the  fundus  by  veterinarians,  but  is  not  the  homologue  of  the  fundus  of 
the  human  bladder. 

2  This  would  correspond  to  the  fundus  vesicae  of  man. 
36 


562  THE    URINARY    ORGANS    OF   THE    HORSE 

folds,  termed  the  middle  and  lateral  ligaments  (Figs.  352,  370).  The  middle  liga- 
ment (Plica  umbilicalis  media)  is  a  median  triangular  fold,  formed  by  the  reflection 
of  the  peritonemn  from  the  ventral  surface  of  the  bladder  on  to  the  ventral  wall  of 
the  pelvis  and  abdomen.  In  the  new-born  animal  it  is  extensive  and  reaches  to  the 
umbilicus;  in  the  adult  it  is  usually  much  reduced  in  length  relatively.  It  contains 
elastic  and  muscular  fibers  in  its  posterior  part.  The  lateral  ligaments  (Plica?  um- 
bilicales  laterales)  stretch  from  the  lateral  aspects  of  the  bladder  to  the  lateral  pelvic 
walls.  Each  contains  in  its  free  edge  a  round,  firm  band,  the  roimd  ligament  (Lig. 
teres  vesicae) ;  this  is  the  remnant  of  the  large  foetal  umbilical  artery,  the  lumen  of 
which  in  the  adult  is  very  small.  The  retroperitoneal  part  of  the  bladder  is  attached 
to  the  surrounding  parts  by  loose  comiective  tissue,  in  which  there  is  a  quantity  of 
fat.  It  is  evident  that  the  posterior  part  of  the  bladder  has  a  definite  fixed  position, 
while  its  anterior  part  is  movable. 

Structure. — The  wall  of  the  bladder  consists  of  a  partial  peritoneal  investment, 
the  muscular  coat,  and  the  mucous  lining.  The  serous  coat  (Tunica  serosa)  covers 
the  greater  part  of  the  dorsal  surface,  from  which  it  is  reflected  in  the  male  to  form 
the  genital  fold;  in  the  female  it  passes  on  to  the  vagina,  forming  the  vesico- 
genital  pouch.  Ventrally  the  peritoneum  covers  only  the  anterior  half  or  less  of 
the  bladder,  and  is  reflected  posteriorly  on  to  the  pelvic  floor.  The  muscular  coat 
(Tunica  muscularis)  is  relatively  thin  when  the  bladder  is  full.  It  is  unstriped,  pale, 
and  not  clearly  divided  into  layers,  but  has  rather  a  plexiform  arrangement.  Longi- 
tudinal fibers  occur  on  the  dorsal  and  ventral  surfaces,  but  laterally  they  become 
oblique  and  decussate  with  each  other.  A  distinctly  circular  arrangement  is  found 
at  the  neck,  where  the  fibers  form  a  sphincter  vesicae.  The  mucous  coat  (Tunica 
mucosa)  is  pale  and  thin.  It  is  in  general  attached  by  a  highly  elastic  submucosa 
to  the  muscular  coat,  and  forms  numerous  folds  when  the  organ  is  empty  and  con- 
tracted. It  is  modified  dorsally  in  the  vicinity  of  the  neck  over  a  triangular  area, 
termed  the  trigonum  vesicae ;  the  angles  of  this  space  lie  at  the  orifices  of  the  two 
ureters  and  the  urethra,  which  are  close  together.  Here  the  mucous  membrane  is 
closely  attached  and  does  not  form  folds.  From  each  ureteral  orifice  (Orificium 
ureteris)  a  fold  of  mucous  membrane  (Plica  ureterica)  passes  backward  and  inward, 
uniting  with  its  fellow  to  form  a  median  crest  (Crista  urethralis)  in  the  first  part  of 
the  urethra.  The  ureteral  orifices  are  a  little  more  than  an  inch  (ca.  3  cm.)  apart. 
The  terminal  part  of  the  ureter,  after  piercing  the  muscular  coat  of  the  bladder, 
passes  for  a  distance  of  about  an  inch  (ca.  2  to  3  cm.)  between  the  muscular  and 
mucous  coats  before  piercing  the  latter;  this  arrangement  constitutes  a  valve  which 
prevents  absolutely  the  return  of  the  urine  from  the  bladder  into  the  ureter.  The 
internal  urethral  orifice  (Orificium  urethrae  internum)  lies  at  the  apex  of  the  tri- 
gonum, and  is  about  an  inch  and  a  half  (ca.  4  cm.)  behind  the  ureteral  orifices.  The 
mucous  membrane  is  covered  with  transitional  epithelium  like  that  of  the  ureter 
and  renal  pelvis.     It  contains  lymph  nodules. 

Vessels  and  Nerves. — The  arteries  are  derived  chiefly  from  the  internal  pudic, 
but  branches  also  come  from  the  obturator  and  umbilical  arteries.  The  veins 
terminate  chiefly  in  the  internal  pudic  veins.  They  form  plexuses  posteriorly. 
The  Isnnph-vessels  form  plexuses  on  both  surfaces  of  the  muscular  coat.  They 
go  to  the  internal  iliac  and  lumbar  glands.  The  nerves  are  derived  from  the  pelvic 
plexus  (sympathetic  and  ventral  branches  of  third  and  fourth  sacral  nerves).  They 
form  a  plexus  in  the  submucosa  which  presents  microscopic  ganglia. 

In  the  foetus  and  new-bom  animal  the  bladder  is  situated  chiefly  in  the  abdomen.  It  is 
long,  narrow,  and  fusiform.  Its  abdommal  end  hes  at  the  umbilicus,  through  which  it  is  con- 
tinued by  the  urachus  to  the  extra-embryonic  part  of  the  allantois.  The  lateral  hgaments  also  ex- 
tend to  the  umbilicus  and  each  contains  in  its  edge  the  large  umbilical  artery.  As  the  pelvis  in- 
creases in  size  and  the  large  intestine  grows,  the  bladder  retracts  into  the  pelvis  and  changes  its 
form. 

The  urethra  will  be  described  with  the  genital  organs. 


THE    ADRENAL    BODIES 


563 


THE  ADRENAL  BODIES 

The  adrenal  bodies  or  glands  (Glandulae  adrenales)^  are  two  small,  flattened 
organs,  which  lie  in  contact  with  the  anterior  part  of  the  medial  border  of  the 
kidneys  (Figs.  496,  497).  They  are  ductless.  In  the  horse  they  are  red-ljrown  in 
color,  about  three  and  a  half  to  four  inches  (ca.  9  to  10  cm.)  long,  one  to  one  and  a 
half  inches  (ca.  3  to  4  cm.)  wide,  and  about  half  an  inch  or  more  (ca.  1.5  cm.)  in 
thickness.     The  weight  varies  from  one  to  two  ounces  (ca.  28  to  56  gm.). 

The  right  adrenal  body  is  related  medially  to  the  posterior  vena  cava,  to  which 
it  is  adherent.  Its  anterior  part  curves  dorsally  around  the  medial  border  of  the 
right  kidney.  Its  posterior  part  is  flattened  and  is  related  ventrally  to  the  pancreas 
and  caecum,  dorsally  to  the  right  renal  vessels.  The  anterior  extremity  is  con- 
cealed in  the  renal  impression  of  the  liver;    the  posterior  is  related  to  the  ureter. 

The  left  adrenal  body  is  a  little  shorter  than  the  right  one,  and  its  extremities 
are  rounded;  it  is  usually  curved,  so  that  its  medial  border  partly  embraces  the 
anterior  mesenteric  artery.  Its  dorsal  surface  is  related 
to  the  kidney,  the  renal  artery,  the  aorta,  and  the  left 
coeliaco-mesenteric  ganglion.  The  ventral  surface  is  in 
relation  with  the  left  extremity  of  the  pancreas  and  the 
root  of  the  great  mesentery.     The  posterior  extremity 

often  curves  inward   behind  the   anterior  mesenteric      -?      -Iff— ill  M^        z 

artery;   it  is  related  behind  to  the  left  renal  vein. 

When  hardened  in  situ  the  adrenals  present  several  features 
not  evident  in  the  soft  organs.  The  anterior  part  of  the  right 
adrenal  is  twisted  dorso-laterally  over  the  medial  margin  of  the 
kidney,  so  that  this  part  is  prismatic  and  has  three  surfaces;  of 
these,  the  concave  lateral  one  is  applied  to  the  kidney,  the  dorsal 
one  is  related  to  the  right  crus  of  the  diaphragm  and  the  liver, 
and  the  medial  one  is  in  contact  with  the  posterior  vena  cava. 
The  anterior  mesenteric  artery  is  nearly  always  more  or  less  en- 
larged as  a  result  of  verminous  arteritis,  and  the  form  and  degree 
of  curvature  of  the  left  adrenal  seem  to  vary  m  conformity  with 
the  condition  of  the  artery. 

Structure. — The  fibrous  capsule  adheres  intimately 
to  the  surface  of  the  organ.  It  contains  elastic  fibers, 
and  in  its  deep  part  unstriped  muscle-fibers.  From  it 
trabeculse  pass  radially  into  the  substance,  blending 
with  the  fine  supporting  reticulum.  The  parenchyma 
consists  of  a  cortical  and  a  medullary  part.  The  cor- 
tical substance  (Substantia  corticalis)  is  red-brown  in 

color,  and  is  clearly  distinguishable  from  the  yellow  medullary  substance  (Substantia 
medullaris).     A  large  central  vein  (Vena  centralis)  is  visible  on  cross-sections. 

The  cells  of  the  cortex  are  arranged  in  chains  of  one  or  two  rows.  In  the  peripheral  portion 
the  cells  are  of  high  cylindrical  shape,  and  the  chains  form  connecting  loops;  Gunther  has  pro- 
posed the  name  zona  arcuata  for  this  part,  instead  of  the  usual  term  zona  glomerularis.  More 
deeply  the  chains  are  distinctly  palisade-like,  and  this  region  is  called  the  zona  fasciculata.  Next 
to  the  medulla  is  the  zona  reticularis,  in  which  the  chains  form  a  network.  The  cells  in  these  two 
zones  are  polygonal  and  contain  a  brown  pigment.  The  cells  of  the  medulla  are  arranged  in 
irregular  groups  or  form  sheaths  around  the  veins.  They  react  to  chromic  salts  by  assuming  a 
yellow  or  yellow-brown  color,  and  are  termed  chromaffin  cells;  they  share  this  peculiarity  with 
certain  cells  of  the  sympathetic  ganglia  and  paraganglia,  with  which  they  are  probably  related 
genetically.     The  alkaloid  adrenalin  appears  to  be  formed  in  the  medullary  cells. 

Vessels  and  Nerves. — The  adrenals  receive  a  relatively  large  blood-supply 
through  the  adrenal  arteries,  which  arise  from  the  renal  arteries  or  from  the  aorta 
directly.     The  veins  terminate  in  the  posterior  vena  cava  and  the  left  renal  vein. 

iFrom  the  standpoint  of  comparative  anatomy  the  term  "adrenal"  is  decidedly  preferable 
to  "suprarenal." 


Fig.      503. — Adrenal     Body     of 
Horse;       Horizontal      Sec- 
tion, Reduced. 
1,     Capsule;      2,     2',     cortical 

substance;   3,  medullary  substance; 

4,   blood-vessel  in  section.      (From 

Leisering's  Atlas,  reduced.) 


564 


URINARY   ORGANS   OF   THE    OX 


The  lymph-vessels  go  to  the  renal  lymph  glands.  The  numerous  nerves  are  derived 
from  the  sympathetic  system  through  the  solar  and  renal  plexuses.  The  fibers 
form  a  rich  interlacement,  especially  in  the  medullary  substance.  Ganglion  cells 
are  found  chiefly  in  the  medulla,  but  also  occur  in  the  deeper  part  of  the  cortex. 


URINARY  ORGANS  OF  THE  OX 

The  kidneys  are  superficially  divided  into  polygonal  lobes  by  fissures  of  vari- 
able depth.  The  lobes  vary  in  size,  and  are  commonly  about  twenty  in  number. 
The  fissures  are  filled  with  fat. 

The  right  kidney  has  an  elongated  elliptical  outline,  and  is  flattened  dorso- 
ventrally.     It  commonly  lies  ventral  to  the  last  rib  and  the  first  two  or  three  lumbar 

Lateral  border 


Anterior  extremity 


Ureter        Renal  artery 


Fig.  504.- 
Organ  hardened  in  siti 


-Right  Kidney  of  Ox;   Ventral  Face. 

.     Fat  has  been  removed  from  fissures  between  lobes. 


\ 


h^^ 


Renal  artery 

Fig.  505. — Frontal  Section  of  Kidney  of  Ox. 
L,  Lobes  of  cortex;  P,  papillae;   C,  calyx  major;   c',  calyces  minores. 


transverse  processes,  but  its  extremities  may  be  ventral  to  the  first  and  fourth 
lumbar  transverse  processes.  The  dorsal  surface  is  rounded,  and  is  in  contact 
chiefly  with  the  sublumbar  muscles.  The  ventral  surface  is  less  convex,  and  is 
related  to  the  liver,  pancreas,  duodenum,  and  colon.  The  hilus  is  situated  on  the 
anterior  part  of  this  surface,  near  the  medial  border.  The  medial  border  is 
nearly  straight,  and  lies  parallel  with  the  posterior  vena  cava.  The  lateral  border 
is  convex.  The  anterior  extremity  occupies  the  renal  impression  of  the  liver,  and 
is  capped  by  the  adrenal  body. 


URINARY    ORGANS    OF   THE    OX  565 

The  left  kidney  occupies  a  remarkable  position,  and  when  hardened  in  situ 
differs  strongly  in  form  from  the  right  one.  When  the  rumen  is  full,  it  pushes  the 
kidney  backward  and  across  the  median  plane,  so  that  it  is  situated  on  the  right 
side,  behind,  and  at  a  lower  level  than,  the  right  kidney.  It  then  lies  usually 
ventral  to  the  third,  fourth,  and  fifth  lumbar  vertebrae.  When  the  rumen  is  not 
full,  the  left  kidney  may  lie  partly  to  the  left  of  the  median  plane.  It  has  three 
surfaces.  The  dorsal  surface  is  convex,  and  presents  on  its  antero-lateral  part  the 
hilus,  which  opens  laterally.  The  ventral  surface  is  related  to  the  intestine.  The 
third  face  is  more  or  less  flattened  by  contact  with  the  rumen,  and  may  be  termed 
the  ruminal  surface.  The  anterior  extremity  is  small,  the  posterior  large  and 
rounded.^ 

The  kidneys  are  embedded  in  a  large  amount  of  perirenal  fat  termed  the 
capsula  adiposa.  The  weight  of  a  kidney  of  an  adult  animal  is  about  20  to  25  ounces 
(ca.  600-700  gm.),  the  left  one  being  usually  an  ounce  or  more  the  heavier.  The 
two  form  about  ^  per  cent,  of  the  body-weight. 

The  right  kidney  measures  about  8  or  9  inches  (ca.  20-22.5  cm.)  in  length,  4  to  5  inches  (ca. 
10-12  cm.)  in  width,  and  23^  to  3  inches  (ca.  5-6  cm.)  in  thickness.  The  left  kidney  is  one  or 
two  inches  (ca.  2  to  5  cm.)  shorter,  but  its  posterior  part  is  much  thicker  than  the  right  one. 

Structure. — The  hilus  is  equivalent  to  the  hilus  and  sinus  of  the  kidney  of  the 


Fig.  506. — Cast  of  Origin  of  Ureter  (a),  Calyces  Majores,  and  Calyces  Minores  (b)  of  Ox.     (After  Dumont.) 

horse;  in  the  right  kidney  it  is  an  extensive  elliptical  cavity;  in  the  left  one  it  is  a 
deep  fissure.  The  pelvis  is  absent.  The  ureter  begins  at  the  junction  of  two  wide, 
thin-walled  tubes,  the  calyces  majores;  the  anterior  calyx  is  usually  the  larger. 
Each  calyx  major  gives  off  a  number  of  branches,  and  these  divide  into  several 
funnel-shaped  calyces  minores,  each  of  which  embraces  a  renal  papilla.  The 
space  not  occupied  by  the  calyces  and  vessels  is  filled  with  fat. 

On  section  through  the  kidney  the  renal  pyramids  are  easily  made  out.  The 
blunt  apex  of  each  pyramid,  the  renal  papilla  (Papilla  renalis),  projects  into  a  calyx 
minor.  On  each  papilla  are  small  orifices  (Foramina  papillaria)  by  which  the 
papillary  ducts  (Ductus  papillares)  open  into  the  calyx.  The  renal  columns  are 
much  more  distinct  than  in  the  horse. 

At  the  hilus  the  renal  artery  is  dorsal,  the  vein  in  the  middle,  and  the  ureter 
ventral;   a  quantity  of  fat  surrounds  these  structures  in  the  hilus. 

iThe  above  statements  refer  to  the  adult  subject,  and  are  based  on  investigations  made  on 
living  subjects,  and  studies  of  frozen  sections  and  material  hardened  in  situ.  In  the  new-bom 
calf  the  kidneys  are  almost  symmetrically  placed,  but  as  the  rumen  grows  it  pushes  the  left  kidney 
to  the  right  and  backward  pari  passu.  It  also  usually  causes  a  rotation  of  the  kidney,  so  that  the 
primary  dorsal  surface  comes  to  lie  almost  in  a  sagittal  plane.  Further,  the  gland  is  bent  so  that 
the  hilus  is  largely  closed  up  and  faces  outward  (to  the  right).  In  very  fat  subjects  the  three- 
sided  appearance  of  the  kidney  may  be  absent,  and  about  one-third  or  more  may  remain  to  the  left 
of  the  median  plane,  even  where  the  rumen  is  pretty  well  filled. 


566 


URINARY   ORGANS    OF   THE    OX 


The  kidneys  of  the  sheep  are  bean-shaped  and  smooth,  without  any  superficial 
lol^ation.  The  soft  organ  is  regularly  elliptical  in  form,  with  convex  dorsal  and 
ventral  surfaces  and  rounded  extremities;  its  length  is  about  3  inches  (ca.  7.5  cm.), 
its  width  about  2  inches  (ca.  5  cm.),  and  its  thickness  a  little  more  than  1  inch  (ca. 
3  cm.).  They  are  embedded  in  fat  normally.  In  position  they  resemble  those  of 
the  ox,  except  that  the  right  one  is  usually  a  little  further  back,  and  lies  under  the 
first  three  lumbar  transverse  processes.^  The  average  weight  of  each  is  about  four 
ounces.  The  hilus  is  in  the  middle  of  the  medial  border.  There  is  a  renal  crest  or 
common  papilla  formed  by  the  fusion  of  twelve  to  sixteen  pyramids. 

The  ureters  are,  in  general,  like  those  of  the  horse,  except  in  regard  to  the 
first  part  of  the  left  one,  which  has  a  peculiar  course,  in  conformity  with  the  remark- 
able position  of  the  kidney.     It  begins  at  the  ventral  part  of  the  hilus  (which  faces 


Fig.  507. — Right  Kidney  of  Sheep;  Ventral  View. 
V.V.,  Branches  of  renal  vein. 


Fig.  .508. — Kidnet  op  Sheep;  Horizontal  Section. 
1,  Cortical  substance;  2,  medullary  substance;  3, 
renal  crest;  4.  renal  pelvis;  5,  ureter.  (From  Leisering's 
Atlas,  reduced.) 


toward  the  right),  curves  over  the  lateral  aspect  of  the  kidney  to  its  dorsal  surface, 
crosses  the  median  plane,  and  runs  backward  on  the  left  side. 

The  bladder  is  longer  and  narrower  than  that  of  the  horse,  and  extends  further 
forward  on  the  abdominal  floor.  The  peritoneal  coat  extends  backward  further 
than  in  the  horse. 


THE  ADRENAL  BODIES 
The  right  adrenal  lies  against  the  medial  part  of  the  anterior  pole  of  the  right 
kidney.  When  hardenetl  in  situ,  it  is  pyramidal  in  form.  Its  medial  surface  is 
flattened  and  is  in  contact  with  the  right  crus  of  the  diaphragm.  The  lateral  sur- 
face is  convex  and  lies  in  the  renal  impression  of  the  liver.  The  ventral  surface  is 
grooved  for  the  posterior  vena  cava;  on  this  surface  a  relatively  large  vein  emerges 
near  the  apex.  The  base  is  concave  and  rests  obliquely  against  the  anterior  pole 
of  the  kidney.     The  apex  fits  into  the  angle  between  the  posterior  vena  cava  and 

1  When  the  rumen  is  full,  the  left  kidney  (which  is  attached  by  a  short  mesentery)  usually 
lies  entirely  to  the  right  of  the  median  plane,  and  is  ventral  to  the  third,  fourth,  and  fifth  luml^ar 
transverse  processes.  The  primitive  dorsal  siuiace  has  become  ventro-medial,  and  is  somewhat 
flattened  by  contact  with  the  rumen. 


URINARY    ORGANS    OF   THE    PIG  567 

the  dorsal  border  of  the  Hver,  The  left  adrenal  Hes  on  the  medial  face  of  the 
posterior  vena  cava,  just  behind  the  anterior  mesenteric  artery,  and  is  therefore 
practically  median  in  position.  It  is  flattened,  and  irregularly  triangular  or  heart- 
shaped  in  outline.  Its  left  face  is  related  to  the  dorsal  sac  of  the  rumen.  Its  right 
face  is  related  to  the  vena  cava,  and  presents  a  large  emergent  vein.  The  posterior 
border  or  base  is  deeply  notched.  The  left  adrenal  does  not  migrate  with  the  kid- 
ney, but  retains  its  primitive  position;  it  lies  usually  two  or  three  inches  (ca.  5-8 
cm.)  in  front  of  a  transverse  plane  through  the  anterior  pole  of  the  left  kidney. 

The  adrenals  of  the  sheep  are  both  bean-shaped.  The  right  one  lies  along 
the  anterior  part  of  the  medial  border  of  the  kidney,  at  the  angle  of  the  junction  of 
the  right  renal  vein  and  the  posterior  vena  cava.     It  is  a  little  over  an  inch  (ca. 

Posterior  pole 

Groove  for  vena  cava 


Anterior  pole 


Anterior  pole 

Fig.    509. — Left  Adrenal  of   Ox;   Ventral  View.  Fig.   510. — Right  Adrenal  or  Ox;  Ventral  View. 

Hardened  in  situ.  Hardened  in  situ. 

3  cm.)  long,  and  about  half  as  wide.  The  left  adrenal  is  usually  longer,  and  is 
flatter  and  somewhat  bent.  It  lies  across  the  left  renal  vein,  to  which  it  is  at- 
tached ;  it  is  not  in  contact  with  the  kidney,  from  which  it  may  be  separated  by  a 
distance  of  nearly  two  inches  (ca.  4  cm.). 


URINARY  ORGANS  OF  THE  PIG 

The  kidneys  are  smooth  and  bean-shaped;  they  are  more  flattened  dorso- 
vent rally,  more  elongated,  and  smaller  at  the  extremities  than  those  of  the  dog. 
The  length  is  about  twice  the  width.  They  are  usually  almost  symmetrically  placed 
ventral  to  the  transverse  processes  of  the  first  four  lumbar  vertebrse,  but  the  left 
kidney  is  often  a  little  further  forward  than  the  right  one.  The  lateral  border  lies 
against  the  flank  parallel  "with  the  edge  of  the  longissimus  muscle.  The  posterior 
extremity  is  usually  about  midway  between  the  last  rib  and  the  tuber  coxae.  The 
anterior  extremity  of  the  right  kidney  has  no  contact  with  the  liver. 

Variations  in  position  are  not  rare,  and  involve  the  left  kidney  oftener  than  the  right;  the 
former  has  been  found  near  the  pelvic  inlet.  When  a  fifteenth  rib  is  present  the  anterior  end  of 
the  kidney  is  usually  ventral  to  it.  The  right  kidney  is  usually  separated  from  the  liver  by  an 
interval  of  an  inch  or  more.     Absence  of  the  left  kidney  has  been  recorded. 


568 


URINARY    ORGANS    OF    THE   PIG 


Fig.  511. — Kidneys  of  Pig  in  silu;  Venthai.  ^'I^;\v. 
C.a.,  Hepatic  artery;   M.a.,  gastro-splenic  artery. 


Calyx  major 
Pelvis 


Ureter 


Cortical  substance 

/ 


Medullary  substance 


PapiUcB 


Calyces  minores 


Fig.  512. — Frontal  Section  of  Kidney  of  Pig. 


URINARY    ORGANS    OF   THE   DOG  569 

The  weight  of  the  kidney  of  an  adult  pig  is  about  seven  to  nine  ounces  (200  to 
250  grams).  The  ratio  of  their  combined  weight  to  that  of  the  body  is  about 
1  :  150-200.  The  length  in  an  adult  of  good  size  is  about  five  inches  (ca.  12.5  cm.) 
and  the  greatest  width  about  two  and  a  half  inches  (ca.  6-6.5  cm.). 

Structure. — The  hilus  is  about  in  the  middle  of  the  medial  border.  The  pelvis 
is  funnel-shaped,  and  divides  into  two  calyces  majores,  which  pass  in  a  curve  for- 
ward and  backward  respectively,  and  give  off  some  eight  to  twelve  short  calyces 
minores;  each  of  the  latter  contains  a  papilla.  Some  papillae  are  narrow  and  coni- 
cal, and  correspond  to  a  single  pyramid;  others  are  wide  and  flattened,  and  result 
from  the  fusion  of  two  or  more  pyramids;  some  project  directly  through  the  wall 
of  the  renal  pelvis  without  the  formation  of  a  calyx.  The  renal  pyramids  are  dis- 
tinct, but  it  is  apparent  that  some  are  compound,  i.  e.,  formed  by  fusion  of  primi- 
tively separate  pyramids.  The  renal  vessels  enter  the  ventral  part  of  the  hilus, 
and  the  ureter  leaves  it  dorsally. 

The  adrenals  are  long  and  narrow.  Each  lies  along  the  medial  border  of  the 
corresponding  kidney  from  the  hilus  forward ;  they  are  in  contact  medially  with  the 
crus  of  the  diaphragm  and  the  posterior  vena  cava. 

The  only  special  features  in  regard  to  the  ureter  are  that  it  is  at  first  relatively 
wide  and  gradually  diminishes  in  caliber,  and  that  it  is  slightly  flexuous. 

The  bladder  is  relatively  very  large;  when  full,  it  lies  chiefly  in  the  abdominal 
cavity.  The  dorsal  surface  is  almost  completely  covered  with  peritoneum,  but 
the  serous  covering  does  not  extend  so  far  back  ventrally. 


URINARY  ORGANS  OF  THE  DOG 

The  kidneys  (Fig.  624)  are  relatively  large,  forming  about  y^-q-  to  2T0"  of  the 
body-weight;  the  weight  of  the  kidney  of  a  medium-sized  dog  is  about  two  ounces 
(ca.  50  to  60  grams).  They  are  both  bean-shaped,  thick  dorso-ventrally,  with  a 
rounded  ventral  surface  and  a  less  convex  dorsal  surface;   the  surfaces  are  smooth. 

The  right  kidney  is  not  subject  to  much  variation  in  position;  it  is  situated 
usually  opposite  to  the  bodies  of  the  first  three  lumbar  vertebrae,  but  may  be  as  far 
forward  as  the  last  thoracic.  Its  anterior  half  or  more  lies  in  the  deep  renal  im- 
pression of  the  liver;  its  posterior  part  is  related  to  the  sublumbar  muscles  dorsally, 
and  the  right  branch  of  the  pancreas  and  duodenum  ventrally. 

The  left  kidney  is  subject  to  some  variation  in  position;  this  is  due  to  the  fact 
that  it  is  loosely  attached  by  the  peritoneum,  and  is  affected  by  the  degree  of  ful- 
ness of  the  stomach.  When  the  stomach  is  nearly  empty,  the  kidney  usually 
corresponds  to  the  bodies  of  the  second,  third,  and  fourth  lumbar  vertebrae,  so  that 
its  anterior  pole  is  opposite  to  the  hilus  of  the  right  kidney;  exceptionally  the 
anterior  pole  may  be  opposite  the  posterior  end  of  the  first  lumbar  vertebra.  When 
the  stomach  is  full,  the  left  kidney  is  usually  the  length  of  one  vertebra  further  back, 
so  that  its  anterior  pole  may  be  opposite  the  posterior  pole  of  the  right  kidney. 
The  dorsal  surface  is  related  to  the  sublumbar  muscles.  The  ventral  surface  is  in 
contact  with  the  left  part  of  the  colon.  The  lateral  border  is  related  to  the  spleen 
and  the  flank.  The  anterior  extremity  touches  the  stomach  and  the  left  extremity 
of  the  pancreas. 

The  lateral  border  of  the  left  kidney  usually  has  considerable  contact  with  the  flank,  and 
hence  it  may  be  palpated  more  or  less  distinctly  in  the  living  animal,  about  half-way  between  the 
last  rib  and  the  crest  of  the  ilium.  But  in  some  cases  the  spleen  assumes  an  almost  longitudmal 
direction,  thus  intervening  between  the  kidney  and  the  flank. 

Structure. — The  hilus  is  in  the  middle  of  the  medial  border  and  is  relatively 


570  URINARY    ORGANS    OF   THE   DOG 

wide.  Cortex,  limiting  zone,  and  medulla  are  clearly  defined.  On  frontal  sections 
it  is  seen  that  the  medullar}^  substance  forms  a  horizontal  renal  crest  like  that  of 
the  horse,  but  -with  the  important  difference  that  curved  ridges  proceed  dorsally 
and  ventrall}^  from  the  crest  somewhat  like  buttresses.  Sections  above  or  below 
the  renal  crest  often  cut  these  ridges  in  such  a  manner  as  to  give  the  appearance 
of  conical  papillse,  and  thus  tend  strongly  to  produce  a  false  impression.  The 
pelvis  is  adapted  to  this  arrangement  of  the  medullary  substance.  It  encloses  a 
central  cavitj^  into  which  the  renal  crest  projects,  and  is  prolonged  outward  be- 
tween the  ridges,  forming  cavities  for  the  latter,  thus  simulating  the  appearance 
of  calyces  which  do  not  exist. 

The  ixreters  present  no  special  features. 

The  bladder,  when  full,  is  abdominal  in  position,  the  neck  lying  at  the  anterior 
border  of  the  pubic  bones.  It  is  relatively  large,  and  when  distended,  the  vertex 
may  reach  to  the  umbilicus.  When  empty  and  contracted,  it  is  usually  entirely  in 
the  pelvic  cavity.     It  has  a  practically  complete  peritoneal  coat. 


THE  ADRENALS 

The  right  adrenal  lies  between  the  anterior  part  of  the  medial  border  of  the  kid- 
ney and  the  posterior  vena  cava.  It  is  somewhat  prismatic,  and  is  pointed  at 
either  end.  The  left  adrenal  lies  along  the  posterior  aorta,  from  the  renal  vein 
forward,  but  is  not  in  contact  with  the  kidney.  It  is  elongated  and  flattened  dorso- 
ventrally.  (There  is  a  furrow  on  the  ventral  surface  for  the  phrenico-abdominal 
vein  which  crosses  it ;  the  part  in  front  of  this  furrow  is  discoid,  and  may  be  taken 
for  the  entire  organ  in  a  fat  subject.)  The  cortex  is  pale  yellow  in  color,  the  me- 
dulla dark  brown. 


THE  MALE  GENITAL  ORGANS 

The  male  genital  organs  (Organa  genitalia  masculina)  are:  (1)  The  two 
testicles,  the  essential  reproductive  glands,  with  their  coverings  and  appendages; 
(2)  the  ductus  deferentes,  the  ducts  of  the  testicles;  (3)  the  vesiculae  seminales; 
(4)  the  prostate,  a  musculo-glandular  organ;  (5)  the  two  bulbo-urethral  (or  Cow- 
per's)  glands;  (6)  the  male  urethra,  a  canal  which  transmits  the  generative  and 
urinary  secretions;  (7)  the  penis,  the  male  copulatory  organ.  The  vesiculae 
seminales,  the  prostate,  and  the  bulbo-urethral  glands  discharge  their  secretions 
into  the  urethra,  where  they  mix  with  the  fluid  secreted  by  the  testicles;  hence  they 
are  often  termed  the  accessorv  sexual  glands. 


GENITAL  ORGANS  OF  THE  STALLION 

THE  TESTICLES 

The  testicles  (Testes)  are  situated  in  the  inguinal  region,  enclosed  in  a  divertic- 
ulum of  the  abdomen  termed  the  scrotum.  Their  long  axes  are  nearly  longitu- 
dinal.^ They  are  ovoid  in  form,  but  considerably  compressed  from  side  to  side. 
Each  presents  two  surfaces,  two  borders,  and  two  extremities.  The  medial  and 
lateral  surfaces  (Facies  meclialis,  lateralis)  are  convex  and  smooth;  the  former  is 
somewhat  flattened  by  contact  with  the  septum  scroti.  The  free  border  (Margo 
liber)  is  ventral  and  is  convex.  The  attached  or  epididymal  border  (Margo  epi- 
didymidis)  is  dorsal;  it  is  nearly  straight,  and  is  the  one  by  which  the  gland  is 
suspended  in  the  scrotum  by  the  spermatic  cord ;  the  epididymis  is  attached  to  this 
border  and  overlies  it  laterally.  The  anterior  and  posterior  extremities  (Extremitas 
capitata,  caudalis)  are  rounded. 

At  the  anterior  extremity  there  is  often  a  sessile  or  pedunculated  sac  which  contains  a  clear 
fluid;  this  is  the  appendix  testis,  from  which  a  thread-hke  process  extends  backward  toward 
the  ductus  deferens.     It  is  regarded  as  a  remnant  of  the  Miillerian  duct  of  the  embryo. 

A  testicle  of  average  size  of  an  adult  stallion  is  about  four  or  five  inches  (ca. 
10  to  12  cm.)  long,  two  and  a  half  to  three  inches  (ca.  6  to  7  cm.)  high,  and  two 
inches  (ca.  5  cm.)  wide;  it  weighs  about  eight  to  ten  ounces  (ca.  225-300  grams). 
They  vary  much  in  size  in  different  subjects,  and  are  commonly  of  unequal  size, 
the  left  one  being  more  often  the  larger. 

The  epididjrmis  is  adherent  to  the  attached  border  of  the  testicle,  and  overlaps 
somewhat  the  lateral  surface.  Its  anterior  enlarged  end  is  termed  the  head  (Caput 
epididymidis) ;  and  its  posterior,  slightly  enlarged  end  is  the  tail  (Cauda  epididy- 
midis);  the  intermediate  narrow  part  is  the  body  (Corpus  epididymidis).  The 
head  is  closely  connected  with  the  testicle  by  the  efferent  ducts  of  the  latter,  by 
connective  tissue,  and  by  the  serous  membrane.  The  body  is  less  closely  attached 
by  the  serous  covering,  which  forms  laterally  a  pocket  beneath  the  epididymis 
termed  the  sinus  epididymidis.  The  tail  is  continued  by  the  ductus  deferens;  it  is 
attached  to  the  posterior  extremity  of  the  testicle  by  a  short  ligament  (Lig.  epididy- 
midis) ,  which  is  formed  by  a  thick  fold  of  the  tunica  vaginalis  and  contains  smooth 
muscle-fibers. 

1  When  the  testicle  is  drawn  up  or  has  not  completed  its  descent  into  the  scrotum,  its  long 
axis  is  almost  vertical. 

571 


572 


GENITAL   ORGANS    OF   THE    STALLION 


Structure  of  the  Testicle  and  Epididjonis. — The  greater  part  of  the  surface 
of  the  testicle  is  covered  by  a  serous  membrane,  the  timica  vaginalis  propria,  which 
is  the  visceral  layer  of  the  serous  envelop  of  the  cord  and  testicle ;  this  is  reflected 
from  the  attached  border  of  the  gland,  leaving  an  uncovered  area  at  which  the 
vessels  and  nerves  in  the  spermatic  cord  reach  the  testicle.^  Beneath  this  serous 
covering  is  the  tunica  albuginea,  a  strong  capsule  composed  of  dense  white  fibrous 
tissue  and  unstriped  muscle-fibers.  When  the  tunic  is  cut,  the  gland  substance, 
which  is  soft  and  reddish  gray  in  color,  protrudes.  From  the  attached  border  and 
from  the  deep  face  of  the  tunica  albuginea  trabecule  and  septa  of  connective  tissue 


Fig.  513. — Inguinal  Region  of  Staluon,  with  Testicles  Exposed. 
o,  a',  Testicles;  b,  scrotum,  opened  and  reflected;  c,  tunica  vaginalis  communis,  opened  and  reflected;  d,  reflection 
of  tunica  vaginalis  enclosing  scrotal  ligament;  e,  tunica  vaginalis  propria  (mesorchium) ;  /,  ductus  deferens;  g,  g',  tail 
of  epididymis;  h,  body  of  same;  i,  head  of  same;  k,  sinus  epididymidis;  I,  spermatic  vessels  showing  through  tunica 
vaginahs  propria;  m,  spermatic  artery;  n,  prepuce;  n',  raph6;  o,  preputial  orifice.  (After  EUenberger-Baum,  Top. 
Anat.  d.  Pferdes.) 


and  unstriped  muscle  (Septula  testis)  pass  into  the  gland  and  subdivide  the 
parenchyma  into  lobules  (Lobuli  testis).  The  larger  trabeculae  radiate  from  the 
attached  border  into  the  central  part  of  the  gland. 

A  distinct  mediastinum  testis,  such  as  is  present  in  man  and  many  animals,  does  not  exist  in 
the  horse.  The  trabeculae  and  interlobular  septa  form  a  network  which  shows  no  special  conden- 
sation in  any  part  of  the  gland.  In  correlation  with  this  is  the  absence  of  a  rete  testis,  formed  by 
the  anastomosis  of  the  seminiferous  tubules  in  the  mediastinum. 

The  spaces  imperfectly  marked  off  by  the  septa  contain  the  parench3mia 
testis,   which   consists  of   seminiferous   tubules    (Tubuli    seminiferi),    supported 

^  In  the  normal  state  the  surface  of  the  testicle  is  quite  smooth  on  account  of  the  serous 
covering.  Frequently,  and  especially  in  old  subjects,  local  inflammation  has  produced  roughen- 
ing of  the  surface  and  thread-like  proliferations. 


THE   TESTICLES 


573 


by  loose  intralobular  connective  tissue.  The  tubules  are  at  first  very  tortuous 
(Tubuli  contorti);  then  they  unite  with  other  tubules,  forming  larger  straight 
tubules  (Tubuli  recti).  The  latter  unite  with  adjacent  tubules  and  converge  to- 
ward the  anterior  part  of  the  attached  border  of  the  gland.  In  this  way  there  are 
formed  more  than  a  dozen  larger  efferent  ducts  (Ductuli  efferentes),  which  pierce 
the  albuginea  at  a  small  area  (about  a  centimeter  in  diameter)  at  the  anterior  part 
of  the  attached  border  and  enter  the  head  of  the  epididymis. 

The  epidid3miis  is  covered  by  the  tunica  vaginalis  propria  and  a  thin  albuginea. 
Its  head  consists  of  a  dozen  or  more  coiled  tubules,  which  are  grouped  into  lobules 
(Lobuli  epididymidis).  The  tubules  of  a  lobule  (four  or  five  in  number)  unite  to 
form  a  single  tube,  and  by  the  union  of  the  latter  with  those  of  the  other  lobules 
there  is  formed  a  single  tube,  the  duct  of  the  epidid3Tnis  (Ductus  epididymidis), 


Fig.  514. — Right  Testicle  and  Spermatic  Cord  op 
Horse,  Enclosed  in  Tunica  Vaginaiis. 
c,  Tunica  vaginalis  communis;  g,  prominence 
caused  by  tail  of  epididymis;  p,  cremaster  externus 
muscle.  (After  EUenberger-Baum,  Top.  Anat.  d. 
Pferdes.) 


Fig.  515. — Right  Testicle  and  Spermatic  Cord  of 
Horse,  Exposed. 
a'.  Lateral  surface  of  testicle;  c,  tunica  vagin- 
alis, cut  and  reflected;  d,  reflection  of  tunica  vaginalis; 
e,  mesorchium;  g,  tail,  h,  body,  i,  head,  of  epididymis; 
k,  sinus  epididymidis;  I,  spermatic  vessels  showing 
through  tunica  vaginalis  propria;  m,  end  of  spermatic 
artery.  Dotted  line  indicates  position  of  ductus 
deferens  on  other  side  of  mesorchium.  (After  EUen- 
berger-Baum, Top.  Anat.  d.  Pferdes.) 


which,  by  its  complex  coils,  forms  the  body  and  tail  of  the  epididymis  and  termin- 
ates in  the  ductus  deferens.  The  tubules  and  the  coils  of  the  duct  of  the  epididymis 
are  held  together  by  connective  tissue  and  unstriped  muscle-fibers.  The  tubules 
and  duct  are  lined  with  ciliated  epithelium,  and  the  duct  has  a  muscular  coat  which 
consists  of  longitudinal  and  circular  fibers. 

Several  foetal  remnants  in  connection  with  the  epididymis  and  adjacent  part  of  the  spermatic 
cord  have  been  described  in  man.  The  appendix  epididymidis  is  a  small,  piriform  body,  3-4 
mm.  long,  which  is  attached  to  the  head  of  the  epididymis.  The  paradidymis  consists  of  a  number 
of  tubules  which  lie  in  the  lower  part  of  the  spermatic  cord  close  to  the  head  of  the  epididymis. 
Most  of  the  tubules  are  blind  and  disappear  in  early  life,  but  one  or  more  may  communicate  with 
the  epididymis  or  rete  testis;  the  latter  may  give  rise  to  cysts.  The  ductuli  aberrantes  are 
tubules  that  extend  upward  from  the  canal  of  the  epididymis  and  end  blindly.  Similar  structures 
have  been  mentioned  as  occurring  m  the  domestic  animals,  but  authentic  data  in  regard  to  them 
are  lacking. 

Vessels  and  Nerves. — The  testicle  is  richly  supplied  with  blood  by  the  sper- 
matic artery,  a  branch  of  the  posterior  aorta.     The  artery  descends  in  the  anterior 


574  GENITAL    ORGANS    OF   THE    STALLION 

part  of  the  spermatic  cord,  and  is  very  tortuous  near  the  testicle;  on  reaching  the 
attached  border  of  the  gland  it  passes  backward  in  a  flexuous  manner,  giving 
branches  to  the  testicle  and  epididymis,  turns  around  the  posterior  extremity,  and 
runs  forward  on  the  free  border  to  the  anterior  extremity.  It  is  partially  embedded 
in  the  tunica  albuginea,  and  detaches  lateral  branches  which  ascend  and  descend  in 
a  tortuous  fashion  on  each  surface  of  the  testicle;  these  give  off  small  branches 
which  enter  the  gland  on  the  trabeculae  and  septa.  The  veins  on  leaving  the 
testicle,  form  a  network,  the  pampiniform  plexus,  around  the  artery  in  the  sper- 
matic cord.  The  spermatic  vein,  which  issues  from  this  plexus,  usually  joins  the 
posterior  vena  cava  on  the  right  side,  the  left  renal  vein  on  the  left  side.  The 
lymph-vessels  follow  in  general  the  course  of  the  veins  and  enter  the  lumbar  lymph 
glands.  The  nerves,  derived  from  the  renal  and  posterior  mesenteric  plexuses, 
form  the  spermatic  plexus  around  the  vessels,  to  which  they  are  chiefly  distributed. 


THE  SCROTUM 

The  scrotum,  in  which  the  testicles  and  the  adjacent  parts  of  the  spermatic 
cords  are  situated,  is  somewhat  globular  in  form,  but  is  commonly  asymmetrical, 
since  one  testicle — more  often  the  left — is  the  larger  and  more  dependent.  It 
varies  in  form  and  appearance  in  the  same  subject,  according  to  the  condition  of  its 
subcutaneous  muscular  tissue.  The  latter  contracts  on  exposure  to  cold,  so  that 
the  scrotum  is  drawn  up  and  becomes  thicker  and  wrinkled;  when  relaxed  under  the 
influence  of  heat  or  fatigue,  or  from  debility,  it  becomes  smooth  and  pendulous, 
with  a  constriction  or  neck  superiorly.  It  consists  of  layers  which  correspond 
with  those  of  the  abdominal  wall;   considered  from  without  inward,  these  are: 

(1)  The  skin,  which  is  thin,  elastic,  usually  dark  or  black  in  color,  and  smooth 
and  oily  to  the  touch.  It  presents  scattered  short  fine  hairs,  and  is  abundantly 
supplied  with  very  large  sebaceous  and  sweat  glands.  It  is  marked  centrally  by  a 
longitudinal  raphe  scroti ;  this  is  continued  forward  on  the  prepuce  and  behind  on 
the  perineum. 

(2)  The  dartos  (Tunica  dartos)  is  reddish  in  color  and  is  closely  adherent  to 
the  skin  except  superiorly.  It  consists  of  fibro-elastic  tissue  and  unstriped  muscle. 
Along  the  raphe  it  forms  a  median  partition,  the  septum  scroti,  which  divides  the 
scrotum  into  two  pouches.  Dorsally  the  septum  divides  into  two  layers  which 
diverge  on  either  side  of  the  penis  to  join  the  abdominal  tunic.  At  the  bottom 
of  the  scrotum  fibers  connect  the  dartos  closely  with  the  tunica  vaginalis  (and  thus 
indirectly  with  the  tail  of  the  epididymis),  constituting  the  scrotal  ligament.^ 
Elsewhere  the  dartos  is  loosely  coimected  with  the  underlying  tunic  by  areolar 
tissue  which  contains  no  fat. 

(3)  The  scrotal  fascia,  which  is  apparently  derived  from  the  oblique  abdom- 
inal muscles. 

It  has  been  customary  to  describe  three  layers  of  fascia,  in  conformity  with  the  accounts 
given  in  text-books  of  human  anatomy.  These  are:  (1)  The  intercolumnar  or  spermatic  fascia, 
derived  from  the  margin  of  the  external  inguinal  ring;  (2)  the  cremasteric  fascia,  derived  from  the 
internal  obhque  muscle;  (3)  the  infundibuliform  fascia,  derived  from  the  fascia  transversahs. 
The  first  two  cannot  be  distinguished  by  dissection  and  the  third  is  (in  the  scrotum)  fused  with 
the  parietal  peritoneum  of  the  tunica  vaginalis. 

(4)  The  parietal  layer  of  the  tunica  vaginalis. — This  is  a  fibro-serous  sac  which 
is  continuous  with  the  parietal  peritoneum  of  the  abdomen  at  the  internal  inguinal 
ring.  It  is  thin  above,  but  is  thick  in  its  scrotal  part,  where  it  is  strengthened  by 
fibrous  tissue  (Lamina  fibrosa)  derived  from  the  transversalis  fascia.  It  will  be 
described  further  under  the  caption  tunica  vaginalis.^ 

1  This  is  a  remnant  of  the  gubernaculum  testis  of  the  foetus. 

2  The  tunica  vaginaUs  is  not  a  part  of  the  scrotum  in  the  strict  or  narrow  sense  of  that  term, 
but  is  included  here  on  practical  grounds. 


THE  DUCTUS  DEFERENS THE  SPERMATIC  CORD  575 

Vessels  and  Nerves. — The  blood  supply'  is  derived  from  the  external  pudic 
artery,  and  the  veins  go  chiefly  to  the  external  pudic  vein.  The  nerves  are  derived 
from  the  ventral  branches  of  the  second  and  third  lumbar  nerves. 

THE  DUCTUS  DEFERENS 
This  tube,  also  commonly  termed  the  vas  deferens,  extends  from  the  tail  of  the 
epididymis  to  the  pelvic  part  of  the  urethra.  It  ascends  in  the  inguinal  canal, 
enclosed  in  a  fold  detached  from  the  medial  surface  of  the  mesorchium,  near  the 
posterior  (attached)  border  of  the  latter.  At  the  vaginal  ring  it  separates  from  the 
other  constituents  of  the  spermatic  cord,  and  turns  backward  and  inward  into  the 
pelvic  cavity  (Fig.  370).  For  some  distance  it  lies  in  the  free  edge  of  the  genital 
fold,  by  which  it  is  attached  to  the  inguinal  part  of  the  abdominal  wall  and  the 
ventral  part  of  the  lateral  wall  of  the  pelvis.  In  its  further  course  (over  the  dorsal 
surface  of  the  bladder)  it  leaves  the  edge  of  the  fold  and  inclines  medially  between 
its  layers,  and  comes  in  contact  with  the  medial  face  of  the  vesicula  seminalis.  Over 
the  neck  of  the  bladder  the  two  ducts  lie  very  close  together,  flanked  laterally  by  the 
necks  of  the  vesiculae  seminales,  and  having  the  uterus  masculinus  between  them. 
They  then  disappear  under  the  isthmus  of  the  prostate,  and  are  continued  through 
the  wall  of  the  urethra  to  open  in  a  small  diverticulum  on  the  colliculus  seminahs 
with  the  excretory  duct  of  the  vesicula  seminalis.  The  common  opening  is  the 
ejaculatory  orifice  (Orificium  ejaculatorium). 

It  has  been  customary  to  describe  a  short  tube,  the  ejaculatory  duct,  as  resulting  from  the 
union  of  the  ductus  deferens  and  the  duct  of  the  corresponding  vesicula  seminahs.  Such  a  duct, 
about  18-20  mm.  (ca.  'ji  in.)  long,  exists  in  man  as  the  morphological  continuation  of  the  ductus 
deferens.  In  the  domestic  animals  it  is  not  present,  since  the  ductus  deferens  and  duct  of  the 
vesicula  seminahs  open  either  in  common  or  alongside  of  each  other  in  a  diverticulum  or  evagina- 
tion  of  the  mucous  membrane  on  the  side  of  the  colhculus  seminahs. 

From  its  origin  until  it  reaches  the  dorsal  surface  of  the  bladder  the  ductus 
deferens  has  a  uniform  diameter  of  about  a  quarter  of  an  inch  (ca.  6  mm.).  It  then 
forms  a  fusiform  enlargement,  the  ampulla  ductus  deferentis  (Fig.  517) ;  this  part 
is  about  six  to  eight  inches  (ca.  15  to  20  cm.)  long,  and  in  its  largest  part  nearly  an 
inch  (ca.  2  cm.)  in  diameter  in  the  stallion;  in  geldings  the  enlargement  is  usually 
not  very  pronounced.     Beyond  the  ampulla  the  duct  abruptly  diminishes  in  size.^ 

Structure. — The  wall  of  the  ductus  deferens  is  thick  and  the  lumen  very  small, 
so  that  the  tube  has  a  firm  and  cord-like  character.  It  is  covered  with  peritoneum, 
except  in  the  last  few  inches  of  its  course.  The  loose  adventitia  contains  numerous 
vessels  and  nerves.  The  thick  muscular  coat  consists  of  longitudinal  and  circular 
fibers.  The  mucous  membrane  has  an  epithelium  of  short  columnar  cells.  In  the 
posterior  part  of  the  tube,  and  especially  in  the  ampulla,  there  are  numerous  glands. 

Vessels  and  Nerves. — The  arteries  are  branches  of  the  spermatic,  umbilical, 
and  internal  pudic  arteries,  and  the  nerves  come  from  the  pelvic  plexus  of  the 
sympathetic. 

THE  SPERMATIC  CORD 

The  spermatic  cord  (Funiculus  spermaticus)  consists  of  the  structures  carried 
down  Ijy  the  testicle  in  its  migration  through  the  inguinal  canal  from  the  abdominal 
cavity  to  the  scrotum.  It  begins  at  the  abdominal  inguinal  ring,  where  its  constitu- 
ent parts  come  together,  extends  obliquely  downward  through  the  inguinal  canal, 
passes  over  the  side  of  the  penis,  and  ends  at  the  attached  border  of  the  testicle. 
It  consists  of  the  following  structures: 

(1)  The  spermatic  artery. 

1  The  term  "ampulla"  is  not  entirely  satisfactory,  smce  it  is  likely  to  be  interpreted  to  mean  a 
dilatation.  There  is  no  increase  here  in  the  lumen  of  the  tube,  and  the  increase  in  size  is  caused 
by  a  thickening  of  the  wall,  due  to  the  presence  of  numerous  branched  tubular  glands.  The  term 
"pars  glandularis,"  suggested  by  Schmaltz,  seems  worthy  of  adoption. 


576 


GENITAL    ORGANS    OF   THE    STALLION 


(2)  The  spermatic  veins,  which  form  the  pampiniform  plexus  around  tho 
artery. 

(3)  The  lymphatics,  which  accompany  the  veins. 

(4)  Syinpathetic  nerves,  which  run  with  the  artery. 

(5)  The  ductus  deferens. 

(6)  The  internal  cremaster  muscle,  which  consists  of  bundles  of  unstriped 
muscular  tissue  about  the  vessels. 

(7)  The  visceral  layer  of  the  tunica  vaginalis. 

The  first  four  of  these  constituents  are  gathered  into  a  rounded  mass  which 
forms  the  anterior  part  of  the  cord;  they  are  united  by  connective  tissue,  inter- 
spersed with  which  are  bundles  of  the  cremaster  internus.  The  ductus  deferens  is 
situated  postero-'medially,  enclosed  in  a  special  fold  detached  from  the  medial  surface 
of  the  tunic ;   hence  it  is  not  visible  laterally. 

The  term  spermatic  cord  is  to  a  certain  extent  misleading  as  applied  to  most  animals,  while 
in  man  the  structure  is  distinctly  cord-like.  In  the  horse,  when  the  tunica  vaginalis  is  slit  open 
and  the  "cord"  stretched  out,  the  latter  is  seen  to  have  the  form  of  a  wide  sheet,  the  mesorchium, 
which  has  a  thick,  rounded  anterior  edge,  the  so-called  "vascular  part"  of  the  cord.  The  posterior 
edge  of  the  mesorchium  is  continuous  with  the  parietal  layer  of  the  tunic;  its  medial  surface  pre- 
sents posteriorly  the  deferential  fold  (Plica  ductus  deferentis).  Between  the  two  layers  of  the 
mesorchium  are  bundles  of  unstriped  muscle  (cremaster  internus)  and  small  vessels. 


THE  TUNICA  VAGINALIS 

The  tunica  vaginalis  is  a  flask-like  serous  sac  which  extends  through  the  in- 
guinal canal  to  the  bottom  of  the  scrotum.     Like  the  abdominal  peritoneum,  of 

which  it  is  an  evagination,  it  con- 


Spermatic  vessels  and  nerves 

("A 


Parietal  layer 
of  tunica 
vaginalis 

Mesorchium 


Ductus 
deferens 


sists  of  two  layers — parietal  and  vis- 
ceral. The  parietal  layer  or  timica 
vaginalis  commimis  lines  the  scrotum 
below;  its  narrow,  tubular  part  lies 
in  the  inguinal  canal,  and  is  directly 
continuous  with  the  parietal  perito- 
neum of  the  abdomen  at  the  abdom- 
inal inguinal  ring.  The  cavity  of  the 
tunica  vaginalis  (Cavum  vaginale)  is 
a  diverticulum  of  the  general  perito- 
neal cavity,  with  which  it  communi- 
cates through  the  vaginal  ring  (An- 
nulus  vaginalis);  it  contains  nor- 
mally a  small  quantity  of  serous  fluid. 
The  parietal  layer  is  reflected  from 
the  posterior  wall  of  the  inguinal 
canal  around  the  structures  of  the 
cord,  forming  the  mesorchiimi,  a 
fold  analogous  to  the  mesentery  of 
the   intestine.       The   visceral    layer 

or  tunica  vaginalis  propria  covers  the  spermatic  cord,  testicle,  and  epididymis. 
The  external  cremaster  muscle  (M.  cremaster  externus)  lies  on  the  lateral  and 

posterior  part  of  the  tunic,  to  the  scrotal  part  of  which  it  is  attached. 

Confusion  has  arisen  from  the  use  of  the  term  abdominal  or  internal  inguinal  ring  in  two 
senses.  The  term  is  used  to  designate  the  abdominal  opening  of  the  inguinal  canal,  but  it  is  also 
often  applied  to  the  opening  of  the  cavity  of  the  tunica  vaginalis.  It  should  not  be  used  in  the 
latter  sense.  The  peritoneal  ring  at  which  the  cavity  of  the  tunica  vaginalis  opens  into  the 
general  peritoneal  sac  is  distinguished  by  the  name  vaginal  ring.  It  is  four  or  five  inches  (ca. 
10  to  12  cm.)  from  the  linea  alba,  and  two  or  three  inches  (ca.  6  to  8  cm.)  in  front  of  the  ilio-pec- 
tineal  eminence.     In  stallions  it  will  usually  admit  the  end  of  the  finger  readily,  but  it  may  be 


Fig.  516. — Diagram  of  Cross-section  of  Spermatic  Cord 
AND  Tunica  Vaginalis;  Latter  Represented  as  Dis- 
tended. 


DESCENT   OF   THE   TESTICLES  577 

abnormally  large  and  allow  a  loop  of  bowel  to  enter  the  cavity  of  the  tunica  vaginalis.  It  is  large 
in  the  young  foal.  In  the  gelding  it  is  smaller  and  sometimes  partially  occluded.  In  man  the 
cavity  is  almost  always  obliterated  early,  except  in  its  scrotal  portion,  thus  abolishing  the  vaginal 
ring  and  the  inguinal  part  of  the  cavity. 


DESCENT  OF  THE  TESTICLES 

During  early  foetal  life  the  testicle  is  situated  against  the  dorsal  wall  of  the 
abdominal  cavity,  in  contact  with  the  ventral  surface  of  the  corresponding  kidney. 
As  growth  proceeds  it  gradually  migrates  from  this  primitive  position,  and  finally 
passes  down  the  inguinal  canal  into  the  scrotum.  Previous  to  its  descent  through 
the  abdominal  wall  the  testicle  is  attached  to  the  sublumbar  region  by  a  fold  of 
peritoneum,  termed  the  mesorchium.  This  fold  contains  the  vessels  and  nerves 
of  the  testicle  in  its  anterior  border.  In  its  posterior  edge  is  the  elongated  tail  of 
the  epididymis,  and  two  cords  of  fibrous  tissue  and  unstriped  muscle.  One  of  these 
cords  is  short  and  connects  the  tail  of  the  epididymis  with  the  testicle;  later  it 
becomes  shorter,  and  is  termed  the  ligament  of  the  epididymis.  The  other  cord, 
the  gubemaculum  testis,  extends  from  the  tail  of  the  epididymis  to  the  subperi- 
toneal tissue  in  the  vicinity  of  the  future  vaginal  ring.  The  deferential  fold  (Plica 
ductus  deferentis)  is  given  off  from  the  medial  face  of  the  mesorchium,  and  joins  the 
genital  fold  posteriorly.  The  body  of  the  epididymis  at  this  time  lies  in  the  edge 
of  an  oblique  fold  formed  by  the  lateral  layer  of  the  mesorchium.  After  the  middle 
of  foetal  life  a  pouch  of  the  peritoneum,  the  processus  vaginalis,  grows  downward 
through  the  inguinal  canal,  carrying  with  it  cremaster  fibers  derived  from  the 
internal  oblique  muscle  and  a  layer  from  the  transversalis  fascia.  It  is  accom- 
panied by  an  inguinal  extension  of  the  gubernaculum  testis.  The  latter  blends 
below  with  the  subcutaneous  tissue  which  later  becomes  the  dartos.  The  tail  of 
the  epididymis  first  enters  the  processus  vaginalis,  followed  by  the  testicle  with  its 
mesorchium,  which  descends  within  this  diverticulum  of  the  peritoneum  until  it 
reaches  the  scrotum.  The  ductus  deferens  and  its  fold  descend  synchronously  with 
the  epididymis  and  testicle.  In  the  foal  the  descent  of  the  testicles  is  often  com- 
plete at  birth,  but  it  frequently  happens  that  one  testicle  or  both  may  be  retained 
in  the  inguinal  canal  or  in  the  abdomen  for  some  months.  In  other  cases  the 
testicle  may  return  into  the  canal  or  abdomen,  since  in  the  young  foal  the  vaginal 
ring  is  large  and  the  testicle  small  and  soft,  and  not  yet  closely  anchored  by  the 
scrotal  ligament.  In  rare  cases  the  descent  may  be  completed  as  late  as  the  fourth 
year. 

The  mechanical  factors  concerned  in  the  migration  of  the  testicle  are  matters  on  which 
much  uncertainty  still  exists.  That  the  gubernaculum  exerts  sufficient  traction  to  guide  the 
epididymis  and  testicle  to  the  inguinal  canal  seems  plausible.  The  abdominal  inguinal  ring  may 
constitute  a  locus  minoris  resistentiae  in  the  abdominal  wall,  especially  after  the  descent  of  the 
processus  vaginalis.  Progressive  shortening  of  the  gubernaculum  was  formerly  considered  to  be 
the  chief  cause  of  the  descent  through  the  abdominal  wall.  Increase  in  the  intra-abdominal 
pressure  is  probably  an  important  factor. 

Indefinite  retention  of  one  testicle  or  both  in  the  abdominal  cavity  or  inguinal  canal  is  not 
rare  in  horses;  this  condition  is  termed  cryptorchism.  Abdominal  retention  is  the  more  usual 
form  of  cryptorchism  in  adult  horses,  inguinal  retention  being  usually  temporary.  The  retained 
testicle  is  usually,  but  not  always,  small,  thin,  soft,  and  flabby,  and  is  non-spermiogenic.  The 
processus  vaginalis  and  the  inguinal  part  of  the  gubernaculum  are  usually  present,  but  may  be 
rudimentary.  The  ligament  of  the  epididymis  and  the  corresponding  part  of  the  mesorchium 
are  often  so  long  that  the  tail  of  the  epididymis  may  be  several  inches  distant  from  the  testicle. 
The  abdominal  part  of  the  gubemaculum  may  be  eight  to  ten  inches  (ca.  20  to  25  cm.)  long,  and  the 
ligament  of  the  epididymis  much  elongated  (10  to  15  cm.  in  length,  according  to  Vennerholm) ; 
thus  the  testicle  may  have  a  wide  range.     The  vaginal  ring  is  sometimes  closed. 

In  many  mammals  the  testicles  normally  remain  in  the  abdominal  cavity;  such  animals  are 
termed  testiconda,  and  include  the  elephant,  some  insectivora,  hyrax,  sloths,  ant-eaters,  armadillos, 
and  cetacea.  In  others  the  testicles  descend  periodically  during  the  period  of  oestrum,  and  then 
return  into  the  abdomen,  or  they  may  be  extruded  and  retracted  voluntarily;  this  is  true  of  most 
rodents,  many  insectivora  (moles,  shrews,  hedgehog),  and  bats. 
37 


578 


GENITAL    ORGANS    OF    THE    STALLION 


.Bladder 


THE  VESICULiE  SEMINALES 

The  vesiculae  seminales  (Fig.  517)  are  two  elongated  and  somewhat  piriform 
sacs,  which  He  on  each  side  of  the  posterior  part  of  the  dorsal  surface  of  the  blad- 
der. They  are  partly  enclosed  in 
^-  ,  the  genital  fold,  and  are  related  to 

the  rectum  dorsally.  Their  long  axes 
are  parallel  with  the  ductus  def- 
erentes  and  converge  posteriorly. 
^  Each   consists  of   a  rounded   blind 

end,  the  fundus;  a  middle,  slightly 
narrower  part,  the  body ;  and  a  pos- 
terior constricted  part,  the  neck  or 
duct. 

In  the  stallion  they  are  about 
six  to  eight  inches  (ca.  15  to  20  cm.) 
long,  and  their  greatest  diameter  is 
about  two  inches  (ca.  5  cm.);  in 
the  gelding  they  are  usually  much 
smaller.^ 

The  vesiculae  are  chiefly  retro- 
peritoneal, but  the  fundus  extends 
forward  into  the  genital  fold  and 
hence  has  a  serous  covering.  The 
excretory  duct  (Ductus  excretorius) 
dips  under  the  prostate,  and  opens 
in  common  with  or  alongside  of  the 
ductus  deferens  in  a  pouch  of  the 
mucous  membrane  on  the  side  of 
the  coUiculus  seminalis. 

Structure. — The  wall,  exclusive 
of  the  partial  serous  coat,  consists 
of  a  fibrous  adventitia,  a  middle 
muscular  coat,  and  a  mucous  lining. 
The  muscular  coat  is  thickest  at  the 
fundus,  and  consists  of  two  planes 
of  longitudinal  fibers  with  a  circular 
layer  between  them.  The  mucous 
membrane  is  thin,  and  is  arranged 
in  numerous  folds  and  projections 
which  form  a  network;  the  spaces 
so  enclosed  present  the  openings  of 
tubulo-alveolar  glands.  The  epithe- 
lium is  columnar.  The  blood-supply 
is  derived  from  the  internal  pudic 
artery. 


Ure^hral 
muscU 


Fig.  517. — I.xter.nal  Genital  Organs  of  Stallion;  Dorsal 
View. 
On  left  side  urethral  muscle  has  been  removed  over  bulbo- 
urethral gland.  Cornua  of  uterus  masculinus  are  indicated  in 
genital  fold.  The  posterior  limit  of  the  peritoneum  is  shown 
but  not  marked.  1,  Round  ligament  of  bladder;  2,  lateral  liga- 
ment of  bladder;    3,  bulbo-urethral  gland. 


THE  PROSTATE 
The  prostate  (Prostata)  is  a  lobulated  gland  which  hes  on  the  neck  of  the 
bladder  and  the  beginning  of  the  urethra,  ventral  to  the  rectum.     It  consists  of 

1  Sometimes  one  or  both  of  the  vesiculae  are  very  large  in  the  gelding.  The  writer  has  seen 
four  cases  in  the  dissecting  room,  three  of  which  were  bilateral,  the  other  unilateral.  The  vesicula 
resembled  the  urinary  bladder  in  appearance  and  contained  about  a  quart  of  thick,  amber-colored 
secretion. 


THE    UTERUS   MASCULINUS — THE    BULBO-URETHRAL   GLANDS  579 

two  lateral  lobes  and  a  connecting  isthmus.  The  lateral  lobes,  right  and  left 
(Lobus  dexter  et  sinister),  are  somewhat  prismatic  in  form,  and  are  directed  forward, 
laterally,  and  somewhat  upward.  The  deep  surface  of  each  lobe  is  concave  and 
partly  embraces  the  corresponding  vesicula  seminalis.  The  dorsal  surface  is  con- 
cave and  is  in  relation  with  the  rectum  The  ventral  surface  is  convex  and  lies 
on  the  obturator  internus  muscle  and  fat.  The  apex  is  pointed  and  lies  near  the 
posterior  end  of  the  superior  ischiatic  spine.  The  isthmus  is  a  thin,  transverse 
band,  about  four-fifths  of  an  inch  (ca.  2  cm.)  wide.  It  lies  over  the  junction  of  the 
bladder  with  the  urethra,  the  uterus  masculinus,  the  terminal  parts  of  the  ductus 
deferentes,  and  the  ducts  of  the  vesiculae  seminales.  Dorsally  it  is  partly  covered 
by  fibers  of  the  urethral  muscle. 

Structure. — The  prostate  is  enclosed  in  a  capsule  of  fibrous  tissue,  with  an 
admixture  of  unstriped  muscle  fibers.  The  gland  substance  is  divided  into  sphe- 
roitlal  or  ovoid  lobules  by  trabeculse  which  consist  to  a  large  extent  of  unstriped 
muscle.  Each  lobule  is  traversed  by  an  axial  duct,  which  gives  off  numerous 
tubular  branches  and  these  ramify  further  in  the  lobule.  The  tubules  are  thickly 
beset  v/ith  saccular  diverticula,  giving  the  gland  a  branched,  tubulo-alveolar  .struc- 
ture. The  ducts  and  tubules  are  lined  with  cubical  or  columnar  epithelium.  The 
prostatic  secretion  (Succus  prostaticus)  is  milky  in  appearance  and  has  a  character- 
istic odor.  There  are  fifteen  to  twenty  prostatic  ducts  (Ductus  prostatici)  on  either 
side,  which  perforate  the  urethra  and  open  lateral  to  the  coUiculus  seminalis  (Fig. 
521).     The  blood-supply  is  derived  from  the  internal  pudic  artery. 

The  surface  of  the  prostate  is  commonly  tuberculate  in  old  subjects,  and  amyloid  bodies 
and  calcareous  concretions  may  be  found  in  it. 

THE  UTERUS  MASCULINUS 
The  uterus  masculinus  or  utriculus  prostaticus  is  a  foetal  remnant  of  variable 
size  and  form,  which  is  situated  centrally  on  the  posterior  part  of  the  dorsal  surface 
of  the  bladder.  When  well  developed,  it  consists  of  a  median  flattened  tube,  some 
three  or  four  inches  (ca.  7.5  to  10  cm.)  long,  and  about  half  an  inch  (ca.  1  to  1.5  cm.) 
wide,  the  anterior  part  of  which  lies  in  the  genital  fold  and  gives  ofT  two  slender 
processes  or  cornua;  the  latter  curve  forward  and  outward  in  the  fold  a  variable 
distance,  being  sometimes  traceable  as  far  as  the  anterior  end  of  the  ampulla  of  the 
ductus  deferens.  The  posterior  extremity  of  the  tube  passes  under  the  isthmus  of  the 
prostate,  and  opens  into  the  urethra  on  the  summit  of  the  colliculus  or  joins  a  duct 
of  a  vesicula  seminalis  or  has  a  blind  end.  It  has  a  muscular  coat  and  a  mucous 
lining.  In  many  cases  it  consists  merely  of  a  very  small  central  tubule  with  a  blind 
anterior  end,  or  a  band,  not  sharply  marked  off  from  the  adjacent  tissue;  in  other 
cases  it  cannot  be  recognized.  It  is  a  remnant  of  the  ducts  of  Miiller  and  the 
homologue  of  the  uterus  and  vagina. 


THE  BULBO-URETHRAL  GLANDS 

The  bulbo-urethral  glands  (Glandulae  bulbourethrales)'  are  two  in  number, 
and  are  situated  on  either  side  of  the  pelvic  part  of  the  urethra  close  to  the  ischial 
arch  (Fig.  577).  They  are  covered  by  the  urethral  muscle,  from  which  bundles 
enter  the  larger  trabeculse  of  the  g'and.  They  are  ovoid  in  form,  somewhat  de- 
pressed dorso-ventrally,  and  their  long  axes  are  directed  obliquely  forward  and 
outward.  In  the  stallion  they  may  measure  nearly  two  inches  (ca.  4  cm.)  in  length, 
and  about  an  inch  (ca.  2.5  cm.)  in  width.  In  the  gelding  they  are  about  the  size  of 
an  average  hazel-nut. 

Structure. — They  resemble  the  prostate  in  general  structure,  but  the  inter- 
1  Also  termed  Cowper's  glands. 


580 


GENITAL    ORGANS    OF   THE   STALLION 


stitial  tissue  is  much  less  abundant,  and  contains  much  less  muscular  tissue ;  hence 
the  lobulation  is  not  very  distinct.  The  parenchyma  consists  of  large  collecting 
tubules,  into  which  numerous  side  branches  open;  these  are  lined  with  cubic 
epithelium.  In  the  larger  septa  there  are  striped  muscle-fibers.  Each  gland  has 
six  to  eight  excretory  ducts  (Ductus  excretorii)  which  open  into  the  urethra  on  a 
series  of  small  papillae  behind  the  prostatic  ducts  and  close  to  the  median  plane 
(Fig.  521).  The  blood-supply  comes  from  the  internal  pudic  artery  which  overlies 
the  gland. 

THE  PENIS 

The  penis,  the  male  organ  of  copulation,  is  composed  essentially  of  erectile 
tissue,  and  encloses  the  extrapelvic  part  of  the  urethra.  It  extends  from  the  ischial 
arch  forward  between  the  thighs  to  the  umbilical  region  of  the  abdominal  wall. 
It  is  supported  by  the  fascia  penis  and  the  skin,  and  its  prescrotal  portion  is  situated 
in  a  cutaneous  pouch,  the  prepuce  or  sheath.  It  is  cylindrical  in  form,  but  much 
compressed  laterally  in  the  greater  part  of  its  extent. 

In  the  quiescent  state  it  is  about  20  inches  (ca.  50  cm.)  long;  of  this,  about  6  to  8  inches 
(ca.  15  to  20  cm.)  is  free  in  the  prepuce.     In  erection  it  increases  50  per  cent,  or  more  in  length. 

Deep  artery  (from  internal  pudic) 


Dorsal  artery  (from  Corona  glandis 

external  pudic)  Collum  glandis 

Proc.  dorsalis  glandis         v. 


BODY 


Retractor  penis  muscle 


Fig.  518.— Pe 


Horse;  Lateral  View. 


It  may  be  divided  into  a  root,  a  body,  and  a  terminal  enlargement,  the  glans. 

The  root  of  the  penis  (Radix  penis)  is  attached  to  the  lateral  parts  of  the  ischial 
arch  by  two  crura,  which  converge  and  unite  below  the  arch  (Fig.  577).  The 
urethra  passes  over  the  ischial  arch  between  the  crura,  and  curves  sharply  forward 
to  become  incorporated  with  the  penis.  The  body  of  the  penis  (Corpus  penis) 
begins  at  the  junction  of  the  crura  and  constitutes  the  bulk  of  the  organ.  At  its 
origin  it  is  attached  to  the  symphysis  ischii  by  two  strong  flat  bands,  the  suspensory 
ligaments  of  the  penis  (Ligamenta  suspensoria  penis),  which  blend  with  the  tendon 
of  origin  of  the  graciles  muscles  (Figs.  518,  576).  This  part  of  the  penis  is  flattened 
laterally  for  the  most  part,  but  becomes  rounded  and  smaller  anteriorly.  It  pre- 
sents four  surfaces.  The  dorsum  penis  is  narrow  and  rounded ;  on  it  are  the  dorsal 
arteries  and  nerves  of  the  penis  and  a  rich  venous  plexus.  The  urethral  surface 
(Facies  urethralis)  is  ventral;  it  is  rounded,  and  along  it  runs  the  urethra,  embedded 
in  the  deep  urethral  groove  of  the  corpus  cavernosum.  The  lateral  surfaces  are 
high  and  flattened,  except  anteriorly,  where  they  are  lower  and  rounded;  they  are 
covered  to  a  large  extent  by  a  plexus  of  veins. 

The  glans  penis  is  the  enlarged  free  end  of  the  organ.  Its  anterior  surface  or 
base  is  surrounded  by  a  prominent,  denticulated  margin,  the  corona  glandis.     The 


THE    PENIS 


581 


surface  is  convex ;  its  lower  part  slopes  backward,  and  presents  a  deep  depression, 
the  fossa  glandis,  in  which  the  urethra  protrudes  for  about  an  inch  (ca.  2.5  cm.)  as  a 
free  tube,  the  urethral  process  (Processus  urethrse),  covered  by  a  thin  integument. 
The  urethra  is  thus  surrounded  by  a  circular  fossa,  which  opens  superiorly  into  the 
urethral  sinus,  a  bilocular  diverticulum  lined  by  thin  skin.  This  diverticulum  is 
filled  sometimes  with  a  caseous  mass  of  sebaceous  matter  and  epithelial  debris. 
Behind  the  corona  glandis  there  is  a  constriction,  the  collum  glandis.  It  is  to  be 
noted,  however,  that  this  does  not  indicate  the  demarcation  between  the  glans  and 
corpus  penis,  since  the  former  extends  backward  above  the  corpus  cavernosum  a 
distance  of  about  four  inches  (ca.  10  cm.),  forming  the  processus  dorsalis  glandis 
(Fig.  518). 

Structure. — The  penis  consists  essentially  of  two  erectile  bodies,  the  corpus 
cavernosum  penis  and  the  corpus  cavernosum  urethrse. 

The  corpus  cavernosum  penis  forms  the  greater  part  of  the  bulk  of  the  penis 
except  at  its  free  extremity.  It  arises  from  each  side  of  the  ischial  arch  by  a  cms 
penis,  M^hich  is  embedded  in  the  ischio-cavernosus  muscle.  Below  the  ischial  arch 
the  crura  unite  to  form  the  laterally  compressed  body  of  the  corpus  cavernosum; 
this    presents    ventrally    the    urethral 


Dorsum  penis 


Corpus 
cavernosum 
penis 


Corpus 
cavernosum 
urethrce 


Trabecules 


Tunica 

albuginea 


Urethra 

Bulbo- 

cavernosus 
muscle 


Retractor  penis  muscle 


Fig.  519. — Cross-section  of  Body  of  Penis  of  Hobsb. 


groove  (Sulcus  urethralis),  which  con- 
tains the  urethra  and  corpus  caverno- 
sum urethrge.  Anteriorly  the  corpus 
cavernosum  penis  divides  into  three 
processes — a  long  central  one,  which  is 
capped  by  the  glans  penis,  and  two 
short  blunt  lateral  ones.  The  corpus 
cavernosum  is  enclosed  by  the  tunica 
albuginea,  a  thick  capsule  of  fibrous 
tissue  which  contains  some  elastic 
fibers.  Externally  the  fibers  are  chiefly 
longitudinal ;  internally  they  are  mainly 
circular  and  are  looser  in  arrangement. 
Numerous  trabeculae  pass  inward  from 
the  tunic  and  form  a  framework  in  the 
interior  of  the  corpus  cavernosum.  En- 
closed by  this  framework  is  the  erectile 
tissue,  which  is  readily  distinguished 
from  the  fibrous  trabeculse  by  its  red- 
dish-gray color  and  softer  texture.  It  is  composed  largely  of  strands  of  unstriped 
muscle,  between  which  there  are  cavernous  spaces  (Cavernse).  These  spaces  may 
be  regarded  as  greatly  enlarged  capillaries;  they  contain  blood,  are  lined  with  flat 
endothelial  cells  resting  upon  a  layer  of  delicate  connective  tissue,  and  are  directly 
continuous  with  the  veins  of  the  penis.  Erection  is  produced  by  distention  of 
these  spaces  with  blood;    at  other  times  the  spaces  are  mere  slits. 

In  man  there  are  two  distinct  corpora  cavernosa,  separated  by  a  median  septum  penis, 
which  is  complete  except  in  the  middle  part  of  the  organ,  where  the  septum  is  composed  of  vertical 
trabeculse,  between  which  are  slit-like  intervals;  through  the  latter  the  blood-spaces  of  the  two 
corpora  cavernosa  commvmicate.  In  the  horse  no  distinct  septum  exists  except  near  the  root,  but 
in  the  proximal  and  distal  parts  of  the  corpus  cavernosum  there  are  vertical  trabeculse,  which 
form  an  arrangement  like  the  septum  pectiniforme  of  man. 

The  corpus  cavernosum  urethrae  (or  corpus  spongiosum)  forms  a  tube  around 
the  urethra,  and  is  continuous  at  its  anterior  end  with  the  glans  penis.  It  forms  a 
slight  enlargement  at  the  root  of  the  penis,  which  is  termed  the  bulb  (Bulbus 
urethrae).  In  the  body  of  the  penis  it  forms  a  thinner  layer  dorsally  than  on  the 
sides  and  ventrally.     The  structure  of  the  corpus  cavernosum  urethrse  is  somewhat 


582  GENITAL    ORGANS    OF   THE    STALLION 

like  that  of  the  corpus  cavernosiim  penis,  but  the  trabeculse  are  much  finer;  they 
consist  of  fibrous  tissue,  much  of  which  is  elastic,  and  of  bundles  of  unstriped  muscle 
which  are  chiefly  longitudinal  in  direction.     The  spaces  are  numerous  and  large. 

In  the  glans  penis  the  trabeculse  are  highly  elastic,  and  the  spaces  are  large  and 
very  distensible;  the  latter  are  specially  wide  in  the  posterior  part  of  the  processus 
dorsalis,  where  they  communicate  with  large  veins  on  the  dorsum  penis.  There  is 
a  partial  septum  glandis.  The  skin  covering  the  glans  is  thin,  destitute  of  glands, 
and  richly  supplied  with  nerves  and  special  nerve-endings. 

Vessels  and  Nerves. — The  penis  is  supplied  with  blood  by  three  arteries,  viz., 
the  internal  jiudic,  ol^turator,  and  external  pudic.  The  terminal  part  of  the  internal 
pudic  artery  enters  the  root  as  the  artery  of  the  Ijulb  and  breaks  up  in  the  bull)  into 
numerous  branches.  The  obturator  artery  gives  off  the  large  arteria  profunda 
penis,  which  enters  the  crus  penis  and  ramifies  in  the  corpus  cavernosum.  The 
external  pudic  artery  gives  off  the  dorsal  arteries  of  the  penis,  branches  from  which 
pass  through  the  tunica  albuginea.  The  veins  form  a  rich  plexus  on  the  dorsum 
and  sides  of  the  penis,  which  is  drained  by  the  external  pudic  and  obturator  veins ; 
from  the  root  the  blood  is  carried  by  the  internal  pudic  veins.^  The  lymph  vessels 
run  with  the  veins  and  go  to  the  superficial  inguinal  glands.  The  nerves  are  derived 
chiefly  from  the  pudic  nerves  and  the  pelvic  plexus  of  the  sympathetic.  The  former 
supply  the  dorsal  nerves  of  the  penis;  special  nerve-endings,  the  end-bulbs  (of 
Krause),  occur  in  the  skin  of  the  glans  penis.  The  sympathetic  fibers  supply  the 
unstriped  muscle  of  the  vessels  and  the  erectile  tissue. 


MUSCLES  OF  THE  PENIS  (Figs.  272,  576,  577,  581) 

1.  The  ischio-cavemosus-  is  a  short  but  strong,  paired  muscle,  which  arises 
from  the  tuber  ischii  and  the  adjacent  part  of  the  sacro-sciatic  ligament,  and  is 
inserted  on  the  crus  and  adjacent  part  of  the  body  of  the  penis.  It  is  somewhat 
fusiform,  encloses  the  crus  as  in  a  sheath,  and  is  situated  in  a  deep  depression  in  the 
semimembranosus  muscle.  It  pulls  the  penis  against  the  pelvis,  and  assists  in 
producing  and  maintaining  erection  by  compressing  the  dorsal  veins  of  the  penis. 
Its  blood-supply  is  derived  from  the  obturator  artery,  and  the  nerve-supply  from 
the  pudic  nerve. 

2.  The  retractor  penis  is  an  unstriped  muscle  which  is  a  continuation  of  the  sus- 
pensory ligaments  of  the  anus.  The  latter  arise  on  the  ventral  surface  of  the  first 
and  second  coccygeal  vertebrse  and  pass  downward  over  the  sides  of  the  rectum  to 
meet  below  the  anus.  Here  there  is  a  decussation  of  fibers,  thus  forming  a  sort  of 
suspensory  apparatus  for  the  posterior  part  of  the  rectum  and  the  anus.  From  the 
decussation  the  muscle  passes  for  a  short  distance  between  superficial  and  deep 
layers  of  the  bulbo-cavernosus,  and  then  along  the  ventral  surface  of  the  penis,  to 
which  it  is  loosely  attached.  Near  the  glans  penis  it  splits  up  into  bundles  which 
pass  through  the  bulbo-cavernosus  and  are  attached  to  the  tunica  albuginea.  Be- 
low the  anus  the  muscle  is  attached  to  the  sphincter  ani  externus.  On  the  penis 
the  two  muscles  are  intimately  united  to  each  other.  Their  action  is  to  withdraw 
the  penis  into  the  sheath  after  erection  or  protrusion. 

THE  PREPUCE 
The  prepuce  (Praeputium),  popularly  called  the  "sheath,"  is  a  double  in- 
vagination of  the  skin  which  contains  and  covers  the  free  or  prescrotal  portion  of 

1  It  has  been  shown  that  the  cavernous  spaces  of  the  glans  penis  receive  blood  exckisively 
from  veins  which  come  from  the  penile  layer  of  the  prepuce.  This  may  account  for  the  fact  that 
the  glans  reaches  its  extreme  size  during  erection  later  than  the  corpus  cavernosum  penis. 

''■  Also  termed  the  erector  penis. 


THE    PREPUCE 


583 


the  penis  when  not  erect.  It  consists  of  two  parts,  external  and  internal.  The 
external  part  or  sheath  extends  from  the  scrotum  to  within  two  or  three  inches  of 
the  umbilicus,  where  the  external  layer  is  reflected  ventrally  and  laterally,  forming 
the  thick  margin  of  the  preputial  orifice  (Ostium  praeputiale) ;  dorsally  it  is  directly 
continuous  with  the  integument  of  the  abdominal  wall.  It  is  marked  by  a  median 
raphe  praeputii,  a  continuation  of  the  scrotal  raphe.  At  the  lower  margin  of  the  pre- 
putial orifice  there  are  often  in  the  stallion  two  papillae,  which  are  regarded  as 
rudimentary  teats.  The  internal  layer  passes  backward  from  the  preputial  orifice 
a  distance  of  about  six  to  eight  inches  (ca.  15  to  20  cm.),  lining  the  cavity  of  the  ex- 
ternal part  of  the  prepuce,  and  is  then  reflected  forward  until  it  approaches  the 
orifice,  where  it  is  again  reflected  backward.  It  thus  forms  within  the  cavity  of  the 
sheath  a  secondary  tubular  invagination,  the  prepuce  proper,  in  which  the  anterior 
part  of  the  penis  lies.  This  tubular  cavity  is  closed  behind  by  the  reflection  of  the 
internal  layer  on  to  the  penis  to  form  the  penile  layer  of  the  prepuce.     Its  orifice  is 

--  **«»-—«■«—        ^i)d,omihal    i<jciH 


Fig.  520. — Sagittal  Section  of  Preptxe  and  Part  of  Pexis  of  House. 

P,  Internal  part  of  prepuce  or  prepuce  proper;    P' ,  external  part  of  prepuce  or  sheath;    C.p.,  preputial  cavity;  F.g., 

fossa  glandis;  D,  diverticulum  of  fossa  glandis;   P.m.,  processus  urethrse. 


surrounded  by  a  thick  margin,  the  preputial  ring  (Annulus  prseputialis),  which  is 
connected  ventrally  with  the  external  part  by  the  preputial  frenum  (Frenulum 
praeputii). 

The  arrangement  differs  from  that  found  in  man  in  the  fact  that  the  imier  part  of  the  pre- 
puce as  described  above  is  equivalent  to  the  entire  human  prepuce.  This  part,  the  prepuce 
proper,  is  well  seen  on  sagittal  sections,  and  can  be  demonstrated  by  pulling  the  penis,  enclosed 
in  this  prepuce,  out  of  the  cavity  of  the  sheath;  the  arrangement  of  the  free  part  of  the  penis  and 
prepuce  is  then  like  that  in  man.  (In  paraphimosis  the  penis  is  strangulated  by  the  preputial 
rmg.)     The  external  part  might  be  distinguished  as  the  sheath  or  vagina  penis. 

Structure. — The  outer  skin  of  the  external  part  resembles  that  of  the  scrotum. 
The  internal  layers  of  skin,  as  far  as  the  preputial  ring,  are  almost  hairless,  variable 
in  color,  and  often  irregularly  pigmented ;  they  form  irregular  folds,  and  are  supplied 
with  numerous  large  sebaceous  glands  and  coil  glands,  which  reach  their  greatest 
size  at  the  ring.  Beyond  this  the  glands  are  absent,  and  the  skin  resembles  a  non- 
glandular  mucous  membrane.  The  secretion  of  the  preputial  glands  (Glandulse 
praeputiales) ,  together  with  desquamated  epithelial  cells,  forms  the  fatty  smegma 
praeputii,  which  has  a  strong,  unpleasant  odor,  and  often  accumulates  in  considerable 


584 


GENITAL    ORGANS    OF   THE   STALLION 


amount.  Beneath  the  skin  there  is  a  large  amount  of  loose  connective  tissue, 
except  over  the  glans  penis,  where  the  skin  is  closely  attached  to  the  tunic  of  the 
erectile  tissue.  The  external  part  of  the  prepuce  is  strengthened  by  a  layer  of 
elastic  tissue,  derived  from  the  abdominal  tunic,  and  termed  the  suspensory  liga- 
ment of  the  prepuce. 

Vessels  and  Nerves. — The  arteries  are  branches  of  the  external  pudic  artery, 
and  the  veins  go  chiefly  to  the  external  pudic  vein.  The  lymph  vessels  go  to  the 
superficial  inguinal  and  lumbar  lymph  glands.  The  nerves  are  derived  from  the 
pudic,  ilio-hypogastric,  and  ilio-inguinal  nerves. 


THE  MALE  URETHRA 
The  male  urethra  (Urethra  masculina)  is  the  long  mucous  tube  which  extends 
from  the  bladder  to  the  glans  penis.     It  passes  backward  on  the  floor  of  the  pelvis. 


Lateral  lobe  of  prostate 


Orifice  of  uterus  masculinus 


Ducts  of  lateral  tirethral 
glands 


Collicidus  seminalis 


Ducts  of  bulbo-urethral 
glands 


Fig.  521. — Pelvic  Urethra  and  Posterior  Part  op  Bladder  op  Horse  Sut  Ventrally  and  Laid  Open. 
e.d.,  openings  of  ductus  deferentes  and  ducts  of  vesiculse  seminales. 


turns  around  the  ischial  arch,  forming  a  sharp  bend,  and  passes  forward  as  a  part  of 
the  penis,  enclosed  in  the  corpus  cavernosum  urethrse.  It  may,  therefore,  be  divided 
into  two  parts,  pelvic  and  extrapelvic. 

The  pelvic  part  (Pars  pelvina)  is  four  or  five  inches  (ca.  10  to  12  cm.)  long. 
At  its  origin  it  is  not  distinguishable  from  the  neck  of  the  bladder  in  size  or  structure; 
in  fact,  no  line  of  demarcation  exists  between  the  two.  Behind  the  prostate  the 
tube  dilates  to  a  potential  width  of  two  inches  or  more  (ca.  5  to  6  cm.).     Near  the 


THE   MALE    URETHRA  585 

ischial  arch,  between  the  bulbo-urethral  glands,  it  contracts  again,  forming  the 
isthmus  urethrae.  It  is  related  dorsally  to  the  rectum  and  the  prostate,  ventrally 
to  the  internal  obturator  muscles,  and  laterally  to  the  bulbo-urethral  glands.  It 
is  enclosed,  except  at  its  origin,  by  the  urethral  muscle.^ 

The  extrapelvic  part  (Pars  externa)  passes  between  the  two  crura  of  the  penis 
and  runs  along  the  groove  on  the  ventral  surface  of  the  corpus  cavernosum  penis, 
enclosed  by  the  corpus  cavernosum  urethrae  and  the  bulbo-cavernosus  muscle.  It 
passes  through  the  glans  penis  and  projects  forward  about  an  inch  in  the  fossa 
glandis  as  a  free  tube,  the  processus  urethrae;  this  part  is  covered  by  a  delicate 
integument,  under  which  there  is  a  thin  layer  of  erectile  tissue. 

The  lumen  of  the  tube  is  largely  obliterated  in  the  inactive  condition  of  the  parts.  WTien 
moderately  distended,  its  dimensions  in  a  horse  of  medium  size  are  as  follows:  At  its  origin  the 
diameter  is  about  half  an  inch  (1  to  1.5  cm.) .  The  pelvic  dilatation  at  its  widest  part  measures  one 
and  a  half  to  two  inches  (ca.  3.5  to  5  cm.)  transversely,  and  about  an  inch  (2  to  3  cm.)  vertically; 
it  is  elliptical  in  cross-section  when  fully  distended.  Ttie  isthmus  at  the  ischial  arch  is  a  little 
smaller  than  the  initial  part.  Beyond  this  the  lumen  is  about  one-half  to  three-fourths  of  an 
inch  (ca.  1.5  cm.)  in  diameter,  and  is  fairly  unifonn  to  the  glans  penis.  Here  there  is  a  slight 
fusiform  dilatation  (Fossa  navicularis),  beyond  which  the  tube  contracts. 

The  opening  from  the  bladder  into  the  urethra  is  termed  the  internal  urethral 
orifice  (Orificium  urethrse  internum);  it  is  closed  except  during  urination.  The 
terminal  opening  is  the  external  urethral  orifice  (Orificium  urethrse  externum)  or 
meatus  urinarius.  The  colliculus  seminalis  is  a  rounded  prominence,  situated 
medially  on  the  dorsal  wall,  about  two  inches  (ca.  5  cm.)  behind  the  internal  ure- 
thral orifice.  On  either  side  of  the  colliculus  there  is  a  small  diverticulum,  in  which 
the  ductus  deferens  and  the  duct  of  the  vesicula  seminalis  open.  The  small  orifice 
of  the  uterus  masculinus  is  placed  centrally  on  the  colliculus;  it  is  inconstant.  The 
orifices  of  the  prostatic  ducts  are  on  two  groups  of  small  papillae,  placed  lateral  to 
the  ejaculatory  openings.  The  ducts  of  the  bulbo-urethral  glands  open  on  two 
lateral  series  of  small  papillae,  about  an  inch  (ca.  2.5  cm.)  further  back  and  close  to 
the  median  line.  The  small  orifices  of  the  lateral  urethral  glands  are  situated 
laterally  in  the  wide  pelvic  portion. 

Structure. — The  mucous  membrane  contains  a  large  amount  of  fine  elastic 
fibers,  and  in  its  pelvic  part  there  are  tubulo-alveolar  urethral  glands  (Glandulae 
urethrales)  .2  The  epithelium  is  at  first  like  that  of  the  bladder,  then  becomes 
cylindrical,  and  in  the  terminal  part  is  stratified  squamous.  In  the  dorsal  wall  the 
membrane  forms  a  median  ridge,  the  urethral  crest  (Crista  urethralis) ;  this  termi- 
nates about  two  inches  from  the  internal  urethral  orifice  in  the  colliculus  seminalis. 

At  the  origin  of  the  urethra  there  is  a  layer  of  circular  unstriped  muscle-fibers 
outside  of  the  mucous  coat.  Beyond  this  the  latter  is  enclosed  by  a  layer  of  erectile 
tissue  (Stratum  cavernosum),  which  contains  plexuses  of  veins  supported  by 
trabeculae  of  elastic  and  unstriped  muscular  tissue ;  in  its  peripheral  part  there  are 
numerous  small  arteries.  There  is  a  slight  thickening  of  the  erectile  tissue  at  the 
ischial  arch,  producing  an  enlargement  known  as  the  bulb  of  the  urethra  (Bulbus 
urethrae).  This  is  continued  by  the  corpus  cavernosum  urethrse.  Outside  of  the 
erectile  tissue  there  is  a  continuation  of  the  intrinsic  unstriped  muscular  coat, 
consisting  of  external  and  internal  longitudinal  strata,  with  a  layer  of  circular 
fibers  between  them. 

^It  has  been  customary  to  divide  the  pelvic  part  of  the  urethra  into  prostatic  and  mem- 
branous parts.  These  terms  apply  well  in  human  anatomy,  but  have  no  special  value  in  com- 
parative anatomy.  In  the  horse  a  prostatic  part  hardly  exists,  unless  we  assume  that  it  and  the 
neck  of  the  bladder  together  are  only  about  an  inch  in  length.  There  is  no  membranous  part  in 
the  sense  in  which  that  term  is  used  in  regard  to  man,  since  the  tube  has  a  continuous  envelop  of 
erectile  tissue. 

^  Two  sets  of  glands  can  be  distinguished  in  the  pelvic  part  of  the  urethra.  Two  rows  of  dor- 
sal glands  occur  close  to  the  median  plane;  their  ducts  open  into  those  of  the  bulbo-urethral  glands. 
A  series  of  lateral  glands  extends  on  either  side  from  a  point  near  the  prostatic  ducts  to  the  end  of 
the  pelvic  urethra;   their  ducts  open  laterally,  as  mentioned  above. 


586  GENITAL  ORGANS  OF  THE  BULL 

Except  at  its  origin  and  termination  the  urethra  is  provided  with  a  continuous 
layer  of  striped  muscle,  placed  outside  of  the  erectile  tissue.  This  is  described  as 
consisting  of  two  jxirts  or  muscles. 

(1)  The  urethral  muscle  (M.  urethralis)^  encloses  the  wide  pelvic  part  of  the 
urethra,  and  covers  the  bulbo-urethral  glands.  It  consists  of  longitudinal  and 
transverse  fibers.  It  is  a  compressor  of  the  pelvic  part  of  the  urethra  and  the  bulbo- 
urethral glands.  By  its  forcible  contraction  it  plaj^s  an  important  role  in  the  ejacula- 
tion of  the  seminal  fluid,  and  also  in  evacuating  the  last  of  the  urine  in  micturition. 

(2)  The  bulbo-cavemosus  muscle  (M.  bulbocavernosus)^  is  the  continuation 
of  the  urethral  muscle  on  the  extrapelvic  part  of  the  urethra;  it  extends  from  the 
ischial  arch  to  the  glans  penis.  At  the  root  of  the  penis  it  is  the  thickest,  and 
forms  a  complete  layer  of  circular  fibers  which  enclose  the  corpus  cavernosum 
urethrse.  Beyond  this  it  diminishes  very  gradually  in  thickness,  and  consists  of 
fibers  which  arise  on  a  median  ventral  raphe  and  curve  around  the  corpus  cavernosum 
urethrse  to  end  on  the  tunica  albuginea  of  the  corpus  cavernosum.  Its  action  is  to 
empty  the  extrapelvic  part  of  the  urethra. 

The  ischio-urethral  muscles  (Fig.  577)  are  small  bands  which  arise  on  the 
ischial  arch  and  crura  of  the  penis  and  pass  forward  to  become  lost  on  the  ventral 
layer  of  the  urethral  muscle.  They  may  assist  in  erection  of  the  penis  by  exerting 
pressure  on  the  dorsal  veins. 


GENITAL  ORGANS  OF  THE  BULL 

The  scrotum  is  situated  somewhat  further  forward  than  in  the  horse.  It  is 
ovoid,  but  compressed  from  before  backward,  is  long  and  pendulous,  and  has  a  well- 
marked  neck  when  not  contracted.  The  skin  here  is  usually  flesh-colored,  but  in 
some  breeds  it  is  more  or  less  pigmented;  it  is  sparsely  covered  with  short  hairs. 
Just  in  front  of  it  are  four  (sometimes  only  two)  rudimentary  teats. 

The  testicles  are  relatively  larger  than  those  of  the  horse,  and  have  an  elon- 
gated, oval  outline.  The  long  axis  is  vertical,  the  attached  border  being  posterior. 
The  medial  surface  is  somewhat  flattened.  A  testicle  of  an  adult  bull  measures  on 
the  average  about  four  or  five  inches  (10  to  12  cm.)  in  length,  exclusive  of  the  epi- 
didymis; with  the  latter  the  length  is  about  six  inches  (15  cm.).  The  width  is 
about  two  and  a  half  to  three  inches  (ca.  6  to  8  cm.),  and  the  anterior-posterior 
diameter  about  the  same.  The  weight  is  about  ten  to  twelve  ounces  (ca.  300  grams) . 
The  tunica  albuginea  is  thin;  it  contains  many  elastic  fibers,  but  no  unstriped 
muscle.  The  parenchyma  is  yellowish  in  color.  The  mediastinum  testis  is  an 
axial  strand  of  connective  tissue  (about  5  mm.  in  thickness),  which  descends  from 
the  upper  part  of  the  attached  border  deeply  into  the  gland.  From  it  the  chief 
trabeculse  radiate,  but  distinct  interlobular  septa  are  not  present.  The  seminif- 
erous tubules  form  in  the  mediastinum  a  network,  the  rete  testis.  The  efferent 
ducts  from  the  rete,  a  dozen  in  number,  leave  at  the  upper  end  of  the  mediastinum. 

The  epididymis  is  very  closely  attached  to  the  testicle  along  the  posterior 
border  of  the  latter.  The  head  is  long;  it  curves  over  the  upper  extremity  and 
about  a  third  of  the  way  down  the  anterior  border  of  the  testicle ;  it  is  covered  by 
an  extension  of  the  tunica  albuginea.  The  body  is  very  narrow,  and  lies  along  the 
lateral  part  of  the  posterior  border  of  the  testicle,  to  which  it  is  attached  bj^  a  narrow 
peritoneal  fold.  The  tail  is  large  and  is  closely  attached  at  the  lower  extremity  of 
the  testicle. 

The  spermatic  cord  antl  the  tunica  vaginalis  are  much  longer  than  in  the  horse; 

1  Formerly  termed  Wilson's  muscle.  ^  Formerly  called  the  accelerator  iirinae. 


GENITAL  ORGANS  OF  THE  BULL 


587 


the  extra-inguinal  part  of  the  cord  is  about  eight  to  ten  inches  (20  to  25  cm.)  in 
length.  The  cremaster  externus  is  well  developed,  and  almost  completely  encloses 
the  tunic  to  the  neck  of  the  scrotum;  it  is  inserted  about  at  the  level  of  the  upper 
pole  of  the  testicle.  The  vaginal  ring  is  relatively  very  small,  and  is  about  four 
inches  (ca.  10  cm.)  from  the  linea  alba.     The  cremaster  internus  is  feeble. 

The  spermatic  cords  emerge  through  the  lateral  angles  of  the  subcutaneous  inguinal  rings,  and 
curve  do\TOward  and  mward  to  the  neck  of  the  scrotum.  The  rings  are  about  four  inches  (ca. 
10  cm.)  long,  and  are  two  and  a  half  to  three  inches  (6  to  S  cm.)  apart.  In  animals  in  good  condi- 
tion there  is  a  large  mass  of  fat  above  the  neck  of  the  .scrotum,  between  the  spermatic  cords.  The 
mesorchium  extends  to  the  bottom  of  the  tunica  vaginalis,  forming  a  narrow  fold  (ca.  1  cm.  wide) 
which  attaches  the  epididymis  to  the  posterior  part  of  the  tunic. 

Vesicula  seminalis 
Body  of  prostate     ^^'^'^■■^'^^ 


Tunica  vaginalis 

(opened) 


External 

urethral  orifice 

Testicle 


Tail 
Fig.  522. — General  View  of  Genital  Organs  op  Bulu 


The  inguinal  canal  presents  several  special  features  in  the  bull.  The  abdominal  ring  is  very 
long.  Its  anterior  border,  formed  by  the  edge  of  the  internal  oblique,  is  decidedly  concave  and 
is  tendinous  in  its  medial  part.  The  long  axis  of  the  subcutaneous  ring  is  directed  outward,  for- 
ward, and  downward.  The  spermatic  cord  lies  in  its  lateral  part,  the  external  pudic  vessels  in  its 
middle.  A  muscular  band  about  an  inch  wide,  detached  from  the  internal  oblique  muscle,  cro.sses 
the  lateral  side  of  the  vaginal  ring. 

The  ductus  deferens  is  small  in  caliber  and  has  a  much  thinner  wall  than  that 
of  the  horse.  At  first  it  pursues  a  flexuous  course  upward  along  the  posterior 
border  of  the  testicle,  then  becomes  straight  and  lies  in  the  posterior  part  of  the 
spermatic  cord.  The  genital  fold  is  narrow,  so  that  the  ducts  are  closer  together 
in  it  than  in  the  horse.  On  reaching  the  posterior  part  of  the  bladder  they  are  in 
apposition  for  a  distance  of  about  four  inches  (10  cm.),  flanked  and  overlapped  by 
the  vesiculse  seminales.  They  form  ampullae  about  four  or  five  inches  (10  to  12  cm.) 
long  and  half  an  inch  (1.2  to  1.5  cm.)  wide,  the  mucous  lining  of  which  is  pHcated. 
They  then  pass  under  the  body  of  the  prostate  and  end,  just  medial  to  the  ducts  of 
the  vesiculse  seminales,  as  slit-like  openings  on  either  side  of  the  colliculus  seminalis. 

The  vesiculae  seminales  are  not  bladder-like  sacs,  as  in  the  horse,  but  are 
compact  glandular  organs  with  a  lobulated  surface.  In  the  adult  they  measure 
about  four  or  five  inches  (ca.  10  to  12  cm.)  in  length,  two  inches  (5  cm.)  in  width  in 


588 


GENITAL  ORGANS  OF  THE  BULL 


their  largest  part,  and  an  inch  or  more  (ca.  3  cm.)  in  thickness.  The  dorsal  surface 
of  each  faces  upward  and  medially  and  is  partially  covered  with  peritoneum.  The 
ventral  surface  faces  in  the  opposite  direction  and  is  non-peritoneal.  Each  may  be 
regarded  as  consisting  of  a  very  thick-walled,  sacculated  tube,  bent  on  itself  in  a 
tortuous  manner.     This  tube,  if  straightened  out,  would  be  about  ten  inches  (25 


Galea 
glandis 


Raphe 
glandis 


Raphe 

prceputii 
Prepuce 


-Antkrior  Extremity  of  Penis  of  Bull;  Left 
View.      (After  Bohm.) 


Fig. 


Bull; 


523. — Internal    Genital    Organs 

Dorsal  View. 

The   right  vesicula  is   sectioned    frontally.      The 

dotted   hne   indicates  the   backward  extension   of   the 

peritoneum.   1,  Ureter;  2,  body  of  prostate;  3,  vesicula 

seminaUs;  4,  urethral  muscle;  5,  bulbo-urethral  gland. 


Fig.  525. — Cross-section  of  Pelvic  Urethra  of  Bull, 
1,  Prostate  gland  (pars  disseminata);  3,  urethra;  S, 
urethral  muscle;  4,  aponeurosis.  The  lumen  of  the  urethra 
is  black  and  the  shaded  area  around  the  urethral  lumen  ir 
the  stratum  eavernosum. 


em.)  in  length.  They  are  commonly  unsymmetrical  in  size  and  shape.  Short 
branches  are  often  given  off  from  the  chief  tube.  The  excretory  duct  opens  at  the 
coUiculus  seminalis,  just  lateral  to  the  ductus  deferens. 

The  structure  of  the  vesicula  is  masked  by  a  thick  capsule  of  fibrous  tissue  and  unstriped 
muscle,  which  mamtains  it  in  its  bent  condition  and  also  sends  trabeculse  between  the  alveoU. 
There  is  a  central  canal  into  which  the  secretion  formed  in  the  alveoli  passes.  The  cavities  (central 
canal  and  alveoli)  are  lined  with  colunmar  epithelium.  On  account  of  this  structure  the  term 
glandulse  vesiculares  is  preferred  by  some  anatomists. 


GENITAL  ORGANS  OF  THE  BULL  589 

The  prostate  is  pale  yellow  in  color,  and  consists  of  two  parts,  which  are,  how- 
ever, continuous  with  each  other.  The  body  (Corpus  prostatas)  is  a  small  mass 
which  stretches  across  the  dorsal  surface  of  the  neck  of  the  bladder  and  the  origin 
of  the  urethra.  It  measures  about  an  inch  and  a  half  (ca.  3.5  to  4  cm.)  transversely, 
and  about  half  an  inch  (ca.  1  to  1.5  cm.)  in  width  and  thickness.  The  pars  dis- 
seminata surrounds  the  pelvic  part  of  the  urethra;  dorsally  it  forms  a  layer  about 
half  an  inch  (ca.  10  to  12  mm.)  thick,  but  ventrally  it  is  quite  thin  (ca.  2  mm.). 
It  is  concealed  by  the  urethral  muscle  and  its  aponeurosis;  hence  it  often  escapes 
notice,  but  is  very  evident  on  cross-section  (Fig.  525).  It  has  a  branched  tubular 
structure,  and  the  interlobular  tissue  contains  a  large  amount  of  unstriped  muscle. 
The  prostatic  ducts  open  into  the  urethra  in  rows,  two  of  which  are  between  two 
folds  of  the  mucous  membrane  that  proceed  backward  from  the  colliculus  seminalis; 
two  other  series  occur  on  either  side,  lateral  to  the  folds. 

The  uterus  masculinus  appears  to  be  absent  usually.  Ellenberger  states  that 
it  opens  between  the  ejaculatory  orifices,  while  Martin  says  that  it  usually  has  two 
orifices  at  the  colliculus,  but  that  it  often  unites  with  the  ductus  deferens. 

The  bulbo-urethral  glands  are  somewhat  smaller  than  in  the  stallion.  They 
are  liable  to  escape  notice,  since  they  are  covered  by  a  thick  layer  of  dense  fibrous 
tissue  and  also  partially  by  the  bulbo-cavernosus  muscle.  Each  has  a  single  duct 
which  opens  into  the  urethra  under  cover  of  a  fold  of  the  mucous  membrane. 

The  penis  is  cylindrical,  and  is  longer  and  of  very  much  smaller  diameter  than 
in  the  horse.  Just  behind  the  scrotum  it  forms  an  S-shaped  curve,  the  sigmoid 
flexure;  thus  about  one  foot  of  the  penis  is  folded  up  when  it  is  fully  retracted. 
The  flexure  is  effaced  during  erection.  The  glans  penis  is  about  three  inches  (ca. 
8  cm.)  in  length.  It  is  flattened  dorso-ventrally,  and  its  extremity  is  pointed  and 
twisted.  The  external  urethral  orifice  is  situated  at  the  end  of  a  groove  formed 
by  this  twist;  it  is  only  large  enough  to  admit  a  probe  of  medium  size.  Even  in 
the  non-erect  state  the  penis  is  remarkably  dense  and  firm.  The  tunica  albuginea 
is  very  thick,  and  encloses  the  urethra;  it  is  composed  of  dense  white  fibrous  tissue. 
In  the  first  part,  as  far  as  the  first  curve,  there  is  a  thick  median  septtun  penis. 
Beyond  this  there  is  a  central  axial  band  of  dense  fibrous  tissue  from  which  numerous 
strong  trabecules  radiate.  The  erectile  tissue  is  small  in  amount,  except  in  the  root, 
so  that  the  organ  undergoes  very  little  enlargement  in  erection,  the  chief  effect 
being  increased  rigidity.  The  walls  of  the  cavernous  spaces  are  fibro-elastic,  not 
muscular. 

The  length  of  the  penis  in  the  adult  is  about  three  feet  (ca.  90  cm.).  The  crura  are  flattened 
laterally;  they  contain  a  well-developed  corpus  cavernosum  and  numerous  helicine  arteries,  some 
of  which  open  directly  into  the  cavernous  spaces.  The  suspensory  ligaments  are  attached  to  the 
ventral  ridge  on  the  symphysis  pelvis.  The  body  is  somewhat  flattened  dorso-ventrally  beyond 
the  first  curve.  The  extremity  of  the  glans  is  unsymmetrical,  the  urethral  orifice  being  situated 
ventro-laterafly.  The  glans  contains  only  a  thin  superficial  stratum  of  erectile  tissue^  and  hence 
undergoes  little  enlargement  in  erection.  In  the  body  of  the  penis  there  is  a  longitudinal  vein  on 
either  side  in  the  ventral  part  of  the  corpus  cavernosum. 

The  bulbo-cavernosus  muscle  presents  several  remarkable  features.  It  is  for 
the  greater  part  an  inch  or  more  (ca.  3  cm.)  in  thickness,  but  its  length  is  only 
six  to  eight  inches  (15  to  20  cm.).  It  is  covered  by  a  strong  aponeurosis,  and  is 
divided  by  a  median  raphe  into  two  lateral  halves,  except  at  its  origin.  It 
diminishes  in  size  from  behind  forward,  and  its  anterior  extremity  is  pointed.^ 

The  ischio-cavemosus  muscle  resembles  in  general  that  of  the  horse,  but  is 
flattened  laterally.     It  is  covered  by  a  tight  aponeurosis. 

The  retractor  penis  muscle  resembles  that  of  the  horse  in  origin.     Its  two  parts 

iJn  the  sheep  and  sometimes  in  the  ox  there  is  a  m.  ischio-bulbosus  which  consists  of  fibers 
that  extend  across  the  initial  part  of  the  bulbo-cavernosus.  Fibers  which  extend  from  the  ischial 
arch  over  the  bulbourethral  gland  form  the  m.  ischio-glandularis.  A  urethro-cayernosus  muscle 
is  sometimes  present;  it  consists  of  fibers  which  arise  on  the  urethra  near  the  origin  of  the  bulbo- 
cavernosus  and  end  on  the  latter  and  the  ischio-cavemosus. 


590 


GENITAL  ORGANS  OF  THE  BULL 


are  about  an  inch  (ca.  2  to  5  cm.)  apart  on  the  root  of  the  penis,  where  they  He 
in  a  groove  on  either  side  of  the  bulbo-cavernosus.  They  then  come  close  together 
and  pass  on  either  side  of  the  ventral  curve  of  the  sigmoid  flexure.  Further  for- 
ward they  are  on  the  ventral  surface  of  the  penis,  and  end  about  five  or  six  inches 
(ca.  12  to  15  cm.)  behind  the  glans. 

The  prepuce  is  very  long  and  narrow.  Its  orifice  is  about  two  inches  (ca. 
5  cm.)  behind  the  umbilicus;  it  is  only  large  enough  to  admit  a  finger  readily,  and 
is  surrounded  by  long  hairs.  The  preputial  cavity  is  about  fifteen  inches  (35  to  40 
cm.)  long  and  a  little  over  an  inch  (ca.  3  cm.)  in  diameter.  The  lining  membrane 
forms  longitudinal  folds;  it  is  covered  with  squamous  stratified  epithelium,  and 
has  coiled  tubular  glands.  The  penile  layer  is  glandless,  and  is  reddish  in  color. 
It  presents  lymph  nodules  in  its  posterior  part. 

There  are  two  pairs  of  preputial  muscles  which  are  derivatives  of  the  cutaneus 
muscle.  The  anterior  preputial  muscles  or  protractors  of  the  prepuce  (Mm. 
prseputiales  craniales)  are  two  flat  bands,  two  inches  or  more  (5  to  6  cm.)  in  ^^ddth, 
which  arise  close  together  in  the  xiphoid  region,  about  eight  inches  (20  cm.)  in 


Processus  urethroe 


Galea  glandis 

Corona  glandis 
Collum  glandis 


Prepuce 


Raphe 
glandis 


Processus  urethrce 
Galea  glandis 
Corona  glandis 

Tuherculum 
Collum  glandis 

Prepuce 
Raphe  pra'putii 


Fig.  526. — Anterior  Part  of  Penis  of  Ram. 
A,  Right  side;    B.  left  side.      (After  Bohm.) 


front  of  the  preputial  orifice.  Traced  backwartl  they  diverge,  leaving  the  umbilicus 
and  an  area  about  one  and  a  half  inches  wide  free,  and  then  unite  behind  the  pre- 
putial orifice.  They  draw  the  prepuce  forward.  The  posterior  preputial  muscles 
or  retractors  of  the  prepuce  (Mm.  prseputiales  caudales)  arise  in  the  inguinal  region 
and  converge  on  the  anterior  part  of  the  prepuce.  They  draw  the  prepuce  back- 
ward.^ 

The  urethra  in  its  pelvic  part  is  about  five  inches  (12  cm.)  long,  and  is  of 
relatively  small  and  uniform  caliber.  The  urethral  muscle  encloses  the  tube 
ventrally  and  laterally;  it  is  very  thick,  crescentic  in  cross-section,  and  is  covered 
by  an  aponeurosis.  Dorsally  the  aponeurosis  is  thick  and  the  muscle  absent. 
Inside  of  these  the  pars  disseminata  of  the  prostate  surrounds  the  urethra  as  far 
back  as  the  bulbo-urethral  glands.  The  coUiculus  semmaUs  is  a  rounded  promi- 
nence about  an  inch  (ca.  2.5  cm.)  in  length.  On  it  there  are  two  slit-like  openings, 
situated  close  together.  These  are  the  ejaculate ry  orifices,  at  which  the  ductus 
deferens  and  the  excretory  duct  of  the  vesicula  seminalis  open.     The  urethral 

^  These  muscles  are  subject  to  a  good  deal  of  variation.  The  retractor  may  be  absent.  Many 
fibers  come  m  from  the  cutaneus  on  either  side,  dip  under  the  protractor,  and  are  inserted  into 
the  skin  just  behind  the  preputial  opening.  The  homologue  of  the  protractor  is  present  in  the 
cow. 


GENITAL  ORGANS  OF  THE  BOAR  591 

crest  extends  forward  from  the  colliculus,  and  two  mucous  folds  pass  backward 
from  it  and  diverge.  The  mucous  membrane  behind  the  colHculus  is  red  in  color. 
The  extrapelvic  part  has  an  enlargement,  the  bulb,  at  its  origin;  it  then  gradually 
diminishes  in  diameter,  and  is  relatively  very  small  at  its  termination.  Other 
features  have  been  mentioned  in  preceding  paragraphs. 

The  bulb  of  the  urethra  has  a  thick  tunica  albuginea,  enclosing  a  highly  developed  erectile 
tissue.  The  cavernous  spaces  are  wide;  their  walls  are  relatively  thin  and  consist  of  fibrous  tis- 
sue and  unstriped  muscle.  On  cross-section  many  arteries  are  visible  laterally.  Further  forward 
the  urethra  is  surrounded  by  a  well-developed  corpus  cavernosum,  wjiich  is  thickest  ventrally; 
here  an  artery  of  considerable  size  occurs  on  each  side. 

In  the  ram  the  genital  organs  resemble  in  general  those  of  the  bull.  But  the 
testicles  are  relatively  much  larger;  a  testicle  of  an  adult  ram  may  be  four  inches 
(ca.  10  cm.)  long  and  weigh  about  nine  to  ten  ounces  (ca.  250-300  gm.).  They  are 
broader  in  proportion  to  their  length.  The  prostate  is  entirely  disseminate.  The 
bulbo-urethral  glands  are  relatively  very  large.  The  peculiar  character  of  the 
terminal  part  of  the  penis  is  shown  in  the  annexed  figure.  The  urethra  lies  in  a 
groove  on  the  ventral  surface  of  the  corpus  cavernosum.  Its  terminal  part  pro- 
jects commonly  about  an  inch  and  a  half  (ca.  3-4  cm.)  beyond  the  glans  penis, 
forming  a  twisted  processus  urethrse. 


GENITAL  ORGANS  OF  THE  BOAR 

The  scrotum  is  situated  a  short  distance  from  the  anus,  and  is  not  so  sharply 
defined  from  the  surrounding  parts  as  in  the  other  animals. 

The  testicles  are  very  large  and  are  regularly  elliptical  in  contour.  They  are 
placed  so  that  the  long  axis  is  directed  upward  and  backward,  the  free  border  being 
superficial  and  the  tail  of  the  epididymis  highest.  They  are  comparatively  soft  in 
texture.  The  tunica  albuginea  contains  much  elastic  tissue,  but  no  muscular  fibers. 
The  mediastinum  testis  is  an  axial  strand  of  fibro-elastic  tissue,  from  which  inter- 
lobular septa  radiate.  Other  septa  are  given  off  from  the  deep  face  of  the  tunica 
albuginea.  The  interlobular  tissue  is  abundant,  and  the  lobulation  correspond- 
ingly distinct.  The  parenchyma  is  gray  and  often  dark  in  fat  animals.  There  is  a 
rete  testis  from  which  seven  or  eight  efferent  ducts  proceed  to  the  epididymis. 
The  epididymis  is  closely  attached  to  the  testicle;  its  tail  is  very  large  and  forms  a 
blunt  conical  projection  at  the  posterior  end  of  the  testicle. 

The  spermatic  cord  is  necessarily  very  long  (20  to  25  cm.  in  a  boar  of  medium 
size).  The  ductus  deferens  in  its  testicular  part  is  flexuous,  and  is  closely  attached 
by  the  tunica  vaginalis;  it  forms  no  distinct  ampulla.  The  cremaster  extemus  is 
well  developed,  and  extends  to  about  the  middle  of  the  scrotal  part  of  the  tunic. 

The  vesiculae  seminales  are  exceedingly  large,  and  extend  into  the  abdominal 
cavity.  They  are  three-sided  pyramidal  masses,  are  in  apposition  with  each  other 
medially,  and  cover  the  posterior  part  of  the  bladder  and  the  ureters,  the  ductus 
deferentes,  the  body  of  the  prostate,  and  the  anterior  part  of  the  urethra  and  bulbo- 
urethral glands.  They  are  pale  pink  in  color,  distinctly  lobate  and  glandular  in 
structure,  and  are  enclosed  in  a  thin  fibrous  capsule.  Half  a  dozen  or  more  large, 
thin-walled  ducts  emerge  from  the  medial  surface  of  each  and  converge  to  a  much 
smaller  excretory  duct.  The  latter  passes  back  lateral  to  the  ductus  deferens,  and 
terminates  at  a  slit-like  opening  on  the  colliculus  seminalis.  The  two  ducts  may 
unite. 

In  the  adult  boar  the  vesiculse  are  about  five  to  six  inches  (ca.  12  to  15  cm.)  long,  two  to 
three  inches  (ca.  5  to  8  cm.)  wide,  and  one  and  a  half  to  two  inches  (ca.  4  to  5  cm.)  thick;  they 
weigh  al)out  6  to  8  ounces  each.     They  have  a  branched  tubular  structure  and  are  distinctly  di- 


592 


GENITAL  ORGANS  OF  THE  BOAR 


vided  into  lobules.  Many  of  the  tubules  are  extremely  wide  (as  much  as  2  mm.  in  diameter),  and 
are  lieset  with  bay-like  extensions  and  short,  wide  branches.  These  axial  spaces  of  the  lobules  are 
succeeded  by  the  efferent  ducts.  The  cavities  are  lined  by  a  single  layer  of  columnar  cells.  The 
secretion  is  thick  and  turbid,  and  has  an  acid  reaction. 

The  prostate  consists  of  two  parts,  as  in  the  ox.  The  body  is  about  an  inch 
(2.5  cm.)  wide,  and  overHes  the  neck  of  the  bladder  and  the  urethra  at  their  junc- 
tion. It  is  concealed  by  the  vesiculae  seminales.  The  pars  disseminata  forms  a 
layer  which  surrounds  the  pelvic  part  of  the  urethra,  and  is  covered  by  the  urethral 
muscle,  except  dorsally. 

The  uterus  masculinus  is  small,  and  appears  to  be  inconstant. 
The  bulbo-urethral  glands  are  very  large  and  dense.     They  are  somewhat 

cylindrical,  and  lie  on  either 
side  of  and  upon  the  posterior 
two-thirds  of  the  pelvic  ure- 
thra.^ In  a  large  boar  they 
are  about  five  inches  (ca.  12 
cm.)  in  length  and  an  inch  or 
more  (ca.  2.5  to  3  cm.)  in 
width.  They  are  partially 
covered  with  a  layer  of  stri- 
ated muscle  (M.  bulbo-glan- 
dularis),  and  have  a  lobulated 
surface.  Each  gland  has  a 
large  excretory  duct  which 
leaves  at  the  deep  face  of  the 
posterior  part,  perforates  the 
dorsal  wall  of  the  urethra  at 
the  ischial  arch,  and  opens  in 
a  cul-de-sac  covered  by  a  fold 
of  mucous  membrane. 

It  is  to  be  noted  that  these 
accessory  glands  are  very  small  in 
animals  which  have  been  castrated 
early;  the  bulbo-urethral  glands  may 
be  only  about  an  inch  long  in  such 
subjects. 

The  penis  resembles  in 
general  that  of  the  ox.  The 
sigmoid  flexure  is,  however, 
prescrotal.  The  anterior  part 
has  no  glans,  and  is  spirally 
twisted,  especially  in  erection. 
The  external  urethral  orifice  is 
slit-like  and  is  situated  ventro- 
laterally,  close  to  the  pointed 
extremity.  The  penis  in  the 
adult  boar  measures  about  18 
to  20  inches  (ca.  45  to  50  cm.)  in  length.  Its  muscles  resemble  those  of  the  bull. 
The  bulbo-cavernosus  is  very  strong  but  short.  The  retractor  penis  arises  from 
the  third  and  fourth  sacral  segments;  its  two  parts  run  backward  and  a  little 
ventrally  on  each  side  of  the  rectum  to  the  perineum,  where  they  reach  the  urethral 
surface  of  the  penis;  they  end  on  the  ventral  curve  of  the  sigmoid  flexure  of  the  penis. 

1  When  hardened  in  situ,  they  are  in  great  part  three  sided,  with  rounded  edges.  They  are  in 
contact  with  each  other  to  a  considerable  extent  and  cover  the  urethra  dorsally  and  laterally.  The 
urethral  muscle  partly  covers  their  lateral  surfaces. 


Fig.  527.— Genital  Organs  of  Boar. 
a,  Testicle;  b,  epididymis;  c,  ductus  deferens;  d,  spermatic  artery; 
e,  vesicula  seminalis;  e',  excretory  ducts  of  vesiculae;  /,  body  of  prostate; 
g,  bulbo-urethral  gland;  h,  urinary  bladder;  i,  urethral  muscle;  k, 
bulbo-cavernosus  muscle;  /,  penis;  I',  sigmoid  flexure  of  penis;  I", 
spiral  anterior  part  of  penis,  exposed  by  slitting  open  prepuce;  m,  ori- 
fice of  preputial  pouch;  re,  retractor  penis  muscle.  The  vesiculae  sem- 
inales are  drawn  outward  to  show  the  structures  which,  in  the  natural 
position,  are  covered  by  them.   (Ellenberger-Baum,  Anat.  d.  Haustiere.) 


MALE  GENITAL  ORGANS  OF  THE  DOG  593 

The  prepuce  has  a  narrow  orifice,  around  which  there  are  stiff  hairs.  The 
cavity  is  very  long,  and  is  partially  divided  by  a  circular  fold  into  a  posterior  narrow 
part  and  a  much  wider  anterior  part.  The  lining  membrane  of  the  posterior  part  is 
papillated,  and  is  in  close  contact  with  the  penis;  it  contains  numerous  lymph 
nodules,  the  largest  of  which  occur  in  the  fundus.  In  the  dorsal  wall  of  the  wide 
part  there  is  a  circular  opening  which  leads  into  a  cul-de-sac,  the  preputial  diver- 
ticulum. This  pouch  is  ovoid  in  form  (when  distended),  and  varies  greatly  in  size 
in  different  subjects.  It  extends  for  the  most  part  backward  over  the  narrow  part 
of  the  prepuce.  Its  cavity  is  partially  divided  by  a  narrow  septum.  It  contains 
usually  decomposing  urine  and  macerated  epithelium,  which  have  a  characteristic 
and  very  unpleasant  odor.     Concrements  have  been  found  in  it. 

Oehmke  found  that  a  cast  of  the  pouch  in  a  Yorkshire  boar  weighing  about  500  pounds 
measured  9  cm.  in  length,  12J^  cm.  in  breadth,  and  6  cm.  in  height.  The  opening  into  the  pre- 
puce will  admit  two  fingers  in  the  adult,  but  is  ordinarily  closed  by  folds  of  the  lining  membrane. 
The  sac  is  much  smaller  in  animals  which  were  castrated  young,  and  the  opening  is  vertical  and 
further  back ;  in  them  it  is  often  empty  or  contains  only  a  Httle  clear  urine.  The  pouch  is  gland- 
less,  but  contains  many  small  lymph  nodules;  it  is  covered  by  a  layer  of  striped  muscle  which  is 
mainly  derived  from  the  homologue  of  the  protractor  of  the  prepuce  of  ruminants. 

The  urethra  has  a  very  long  pelvic  part  (ca.  15  to  20  cm.  long  in  the  adult); 
it  is  covered  (with  the  pars  disseminata  of  the  prostate)  by  a  thick  urethral  muscle, 
except  dorsally,  where  there  is  a  dense  fibrous  layer.  Surrounding  the  mucous 
membrane  there  is  a  rich  venous  plexus,  which  is  regarded  as  a  stratum  cavernosum. 
Outside  of  this  the  pars  disseminata  of  the  prostate  is  easily  distinguished  on  cross- 
section  by  its  yellow  color.  The  prostatic  ducts  are  numerous  and  small.  The 
ductus  deferentes  and  the  excretory  ducts  of  the  vesiculae  seminales  have  slit-like 
openings  close  together  in  small  diverticula  on  either  side  of  the  colliculus  seminalis. 
The  latter  has  the  form  of  a  round  prominence.  A  small  uterus  masculinus  may 
occur  in  the  colliculus  between  the  ducts,  but  it  is  often  absent.  There  is  a  distinct 
bulb  at  the  root  of  the  penis.  It  has  a  dense  covering,  which  in  part  resembles 
fibro-cartilage.  The  erectile  tissue  here  is  highly  developed.  The  cavernous 
spaces  are  large,  and  the  trabeculse  contain  much  unstriped  muscle;  between  the 
spaces  there  are  numerous  arteries.  The  penile  part  is  of  small  caliber,  and  is 
surrounded  by  erectile  tissue  which,  however,  does  not  extend  to  the  extremity  of 
the  penis. 


MALE  GENITAL  ORGANS  OF  THE  DOG 

The  scrotum  is  situated  about  half  way  between  the  inguinal  region  and  the 
anus.  The  skin  covering  it  is  pigmented  and  is  covered  sparsely  with  fine  hairs. 
The  raphe  is  not  very  distinct. 

The  testicles  are  relatively  small,  and  have  a  round-oval  form.  The  long 
axis  is  oblique,  and  is  directed  upward  and  backward.  The  mediastinum  testis 
is  central  and  is  well  developed.  The  epididymis  is  large,  and  is  closely  attached 
along  the  dorsal  part  of  the  lateral  surface  of  the  testicle. 

The  spermatic  cord  and  the  tunica  vaginalis  are  long;  they  cross  the  side  of 
the  penis  verj^  obliquely.  The  upper  end  of  the  tunic  is  sometimes  closed,  so  that 
there  is  then  no  vaginal  ring.     The  ductus  deferentes  have  narrow  ampullae. 

The  vesiculae  seminales  are  absent. 

The  prostate  is  relatively  large;  it  is  yellowish  in  color,  dense  in  structure, 
and  lies  at  or  near  the  anterior  border  of  the  pubis.  It  is  globular,  and  surrounds 
the  neck  of  the  bladder  and  the  urethra  at  their  junction.  A  median  furrow  indi- 
cates a  division  into  two  lateral  lobes.  The  capsule  and  stroma  contain  a  large 
amount  of  unstriped  muscle.  The  ducts  are  numerous.  Lobules  of  prostatic 
38 


594 


MALE  GENITAL  ORGANS  OF  THE  DOG 


tissue  (pars  disseminata)  are  also  found  in  the  wall  of  the  urethra  for  a  short  distance 
further  back.  The  gland  is  subject  to  much  variation  in  size,  and  is  often  enlarged, 
especially  in  old  subjects. 

The  position  of  the  prostate  varies.  When  the  bladder  is  empty  and  contracted,  the  gland 
is  entirely  in  the  pelvic  cavity  and  may  be  an  inch  or  more  behind  the  anterior  border  of  the 
pubis.     When  the  bladder  is  full,  the  prostate  is  often  largely  or  entirely  prepubic. 

The  uterus  masculinus  is  a  small  compressed  saccule  in  the  colliculus  seminalis. 

The  bulbo-urethral  glands  are  absent.^ 

The  penis  presents  several  special  features.  In  its  posterior  part  there  are  two 
distinct  corpora  cavernosa,  separated  by  a  median  septum  penis.  In  its  anterior 
part  there  is  a  bone,  the  os  penis,  which  in  large  dogs  reaches  a  length  of  four  inches 
(ca.  10  cm.)  or  more.     It  is  regarded  as  a  part  of  the  corpus  cavernosum  which  has 


Fig.  528. — External  Genital  Organs  of  Male  Dog;  Ventro- 
lateral View  of  Preparation. 
1,  Scrotum;  ?',  tunica  vaginalis;  2,  epididymis;  S,  vascular 
part  of  spermatic  cord ;  4,  ductus  deferens;  5,  prepuce;  5,'pars  longa 
glandis;  6',  corpus  cavernosum  penis;  7,  bulbus  glandis;  7',  con- 
tour of  bulbus  in  erection;  8,  ischio-cavernosus  muscle;  a,  acetab- 
ulum; 6,  obturator  foramen.  (After  Ellenberger,  in  Leisering's 
Atlas.) 


Fig.  529. — Internal  Genital  Organs  of 
Male  Dog;  Dorsal  View. 
1,  Urinary  bladder;  2,  ureter;  3,  ductus 
deferens;  4,  prostate;  5,  urethral  muscle;  6, 
bulb  of  urethra;  a,  abdominal  wall;  b,  ilium; 
c,  ischium.  (After  Ellenberger,  in  Leisering's 
Atlas.) 


ossified.  Ventrally  it  is  grooved  for  the  urethra;  dorsally  it  is  convex,  and  an- 
teriorly it  becomes  smaller  and  has  a  curved  fibrous  prolongation.^  The  glans 
penis  is  very  long,  extending  over  the  entire  length  of  the  os  penis;  its  anterior 
part,  the  pars  longa  glandis,  is  cylindrical,  with  a  pointed  free  end;  behind  this 
there  is  a  rounded  enlargement,  the  bulbus  glandis.  Both  are  composed  of  erectile 
tissue.  The  two  dorsal  veins  arise  from  the  bulbus  glandis,  pass  backward  on  the 
dorsum  penis,  and  unite  at  the  ischial  arch.  A  small  muscle  (M.  compressor  venae 
dorsalis  penis)  arises  from  the  tuber  ischii  on  either  side;  the  two  converge  on  the 
dorsum  penis  near  the  bulbus  glandis.  They  compress  the  dorsal  veins,  and  may 
also  tend  to  elevate  the  penis  and  thus  assist  in  copulation.  The  other  muscles 
offer  no  features  worthj^  of  special  description. 

1  They  are  present  in  the  cat,  and  are  the  size  of  a  pea. 

2  In  the  young  subject  it  has  a  prolongation  composed  of  hyaline  cartilage,  which  becomes 
fibrous  later. 


MALE    GENITAL    ORGANS    OF    THE    DOG  595 

The  cavernous  spaces  of  the  glans  penis  are  venous  in  character.  Von  Frey  has  shown  that 
the  spaces  of  the  pars  longa  are  continuous  with  veins  which  come  from  the  penile  layer  of  the  pre- 
puce, and  have  no  arterial  blood  supply.  The  erectile  tissue  of  the  bulbus  glandis  receives  its 
blood  by  veins  which  come  from  the  pars  longa.  This  arrangement  is  considered  to  account  for 
the  erection  of  the  bulbus  during  copulation,  and  the  slowness  with  which  erection  subsides. 

The  prepuce  forms  a  complete  sheath  around  the  anterior  part  of  the  penis. 
The  outer  layer  is  ordinary  integument.  The  inner  layers  are  thin,  reddish  in 
color,  and  glandless.  The  penile  layer  is  closely  attached  to  the  pars  longa  glandis, 
more  loosely  to  the  bulbus  glandis.  There  are  many  lymph  nodules  in  these  layers, 
which  are  specially  large  and  often  prominent  in  the  fundus  of  the  preputial  cavity. 
The  protractor  muscles  arise  in  the  xiphoid  region  and  decussate  posteriorly  around 
the  extremity  of  the  prepuce. 

The  pelvic  part  of  the  urethra  is  relatively  long.  Its  first  part  is  enclosed  in 
the  prostate.^  At  the  ischial  arch  the  urethra  has  a  well-developed  bulb,  formed 
by  an  enlargement  here  of  the  corpus  cavernosum  urethrse.  It  is  divided  by  a 
median  furrow  and  septum  (Septum  bulbi  urethrse)  into  two  lateral  lobes  or  hemis- 
pheres (Hemispheria  bulbi  urethrse),  and  is  covered  by  the  strong  but  short  bulbo- 
cavemosus  muscle.  The  other  erectile  bodies  have  been  described.  The  urethral 
muscle  is  very  strong;  it  encircles  the  urethra  from  the  prostate  backward  and  has 
a  median  raphe  dorsally.  The  ischio-urethral  muscle  arises  from  the  tuber  ischii 
and  ends  on  a  fibrous  ring  at  the  symphysis  ischii  which  encircles  the  dorsal  veins 
of  the  penis. 

1  This  is  clinically  important,  since  enlargement  of  the  prostate  may  interfere  with  mic- 
turition. 


THE  FEMALE  GENITAL  ORGANS 

The  female  genital  organs  (Organa  genitalia  feminina)  are:  (1)  The  two 
ovaries,  the  essential  reproductive  glands,  in  which  the  ova  are  produced;  (2) 
the  uterine  or  Fallopian  tubes,  which  convey  the  ova  to  the  uterus;  (3)  the  uterus, 
in  which  the  ovum  develops;  (4)  the  vagina,  a  dilatable  passage  through  which  the 
foetus  is  expelled  from  the  uterus;  (5)  the  vulva,  the  terminal  segment  of  the  genital 
tract,  which  serves  also  for  the  expulsion  of  the  urine;  (6)  the  mammary  glands, 
which  are  in  reality  glands  of  the  skin,  but  are  so  closely  associated  functionally 
with  the  generative  organs  proper  that  they  are  usually  described  with  them. 


GENITAL  ORGANS  OF  THE  MARE 

THE  OVARIES 

The  ovaries   (Ovaria)   of  the  mare  are  bean-shaped,   and  are  much  smaller 
than  the  testicles.     Their  size  varies  much  in  different  subjects,  and  they  are 


Fig.  530. — Lateral  View  of  Genital  Organs  and  Adjacent  Structures  of  Mare. 
It  is  to  be  noted  that  the  removal  of  the  other  abdominal  viscera  has  allowed  the  ovaries  and  uterus  to  sink  down; 
this  has,  however,  the  advantage  of  showing  the  broad  ligaments  of  the  uterus.  1,  Left  ovary;  2,  uterine  or  Fallopian 
tube;  3,  left  cornu  uteri;  4,  right  cornu  uteri;  5,  corpus  uteri;  S',  portio  vaginalis  uteri,  and  5",  os  uteri,  seen  through 
window  cut  in  vagina;  6,  broad  ligament  of  uterus;  6",  round  ligament  of  uterus;  7,  vagina;  S,  labia  vulvae;  9,  rima 
vulvae;  9',  dorsal  commissure,  and  9",  ventral  commissure,  of  vulva;  10,  constrictor  vulvae;  11,  position  of  vestibular 
bulb;  13,  ventral  wall  of  abdomen;  13,  left  kidney;  14,  left  ureter;  IS,  urinary  bladder;  16,  urethra;  17,  rectum; 
18,  anus;  19,  19',  unpaired  and  paired  parts  of  sphincter  ani  externus;  20,  retractor  ani  cut  at  disappearance  under 
sphincter  ani  externus;  21,  suspensory  ligament  of  anus;  22,  longitudinal  muscular  layer  of  rectum;  22',  recto-coocygeus; 
23,  constrictor  vaginae;  a,  utero-ovarian  artery,  with  ovarian  (a')  and  uterine  (a")  branches;  6,  uterine  artery;  c,  um- 
bilical artery;   d,  ischium;   e,  pubis;  /,  ihum.     (After  EUenberger,  in  Leisering's  Atlas.) 


normally  larger  in  young  than  in  old  animals;    one  ovary  is  often  larger  than  the 
other.     They  are  about  three  inches  (ca.  7  to  8  cm.)  long  and  an  inch  to  an  inch 

596 


THE    OVARIES 


597 


and  a  half  (ca.  3-4  cm.)  thick.     The  weight  is  about  two  and  a  half  to  three 
ounces  (ca.  70-80  grams). 

Each  presents  for  description  two  surfaces,  two  borders,  and  two  extremities. 
The  surfaces  are  termed  medial  and  lateral  (Facies  medialis,  lateralis);  they  are 
both  smooth  and  rounded. "^  The  attached  or  mesovarial  border  (Margo  mes- 
ovaricus)  is  convex.  It  is  enclosed  in  a  part  of  the  broad  ligament  termed  the  mes- 
ovarium;  the  vessels  and  nerves  reach  the  gland  at  this  border.  The  free  border 
(Margo  liber)  is  marked  by  a  notch  which  leads  into  a  narrow  depression,  the 
ovulation  fossa.  The  tubal  or  anterior  extremity  (Extremitas  tubaria)  is  rounded, 
and  is  related  to  the  fimbriated  end  of  the  uterine 
tube.  The  uterine  or  posterior  extremity  (Extremitas 
uterina)  is  also  round,  and  is  connected  with  the  horn 
of  the  uterus  by  the  ovarian  ligament. 

The  ovaries  are  situated  in  the  sublumbar  region, 
and  are  usually  ventral  to  the  fourth  or  fifth  lumbar 
vertebra.  They  are  usually  in  contact  with  the  lum- 
bar wall  of  the  abdomen.  The  average  distance  from 
the  ovaries  to  the  vulvar  orifice  is  about  twenty  to 
twenty-two  inches  (ca.  50-55  cm.)  in  a  mare  of 
medium  size. 

The  position  of  the  ovaries  is  very  iBconstant,  as  might 
be  expected  from  their  mode  of  attachment.  Either  ovary  or 
both  may  be  deflected  transversely  in  either  direction  to  the 
full  limit  allowed  by  the  mesovarium.  The  so-called  medial 
and  lateral  surfaces  are  usually  dorsal  and  ventral,  or  vice 
versa,  according  to  the  direction  of  the  deflection.  The  range 
of  variation  in  the  longitudinal  direction  is  greater  than  was 
formerly  thought  to  be  the  case.  The  right  ovary  is  often 
about  six  inches  (ca.  15  cm.)  behind  the  corresponding  kid- 
ney, but  the  distance  between  them  may  be  nearly  twice  as 
great  or  may  be  only  about  two  inches  (ca.  5  cm.).  The  left 
ovary  is  usually  a  little  (ca.  2-3  cm.)  further  back  than  the  right 
one,  but  is  usually  nearer  the  corresponding  kidney,  the  average 
distance  between  them  being  about  four  inches  (ca.  10  cm.). 
They  may  be  about  two  inches  (ca.  5  cm.)  from  the  extremity 
of  the  corresponding  cornu  of  the  uterus  or  in  contact  with  it. 
Except  during  pregnancy,  they  are  almost  always  in  contact 
with  the  lumbar  abdominal  wall,  and  do  not  hang  down  among 
the  adjacent  viscera. 


Fig.  531. — Right  Ovart  of  Mare, 
WITH  Adjacent  Structures. 
The  extremity  of  the  cornu  is 
opened.  1,  Ovary;  1',  corpus  luteum; 
2,  uterine  or  Fallopian  tube,  with  its 
ostium  abdominale  (3'),  fimbrise  (2"), 
and  ostium  uterinum  (^'") ;  3,  cornu 
uteri  with  its  mucous  lining  (3')  ex- 
posed; 4,  ligament  of  ovary;  4\  meso- 
salpinx. (After  Ellenberger,  in  Leiser- 
ing's  Atlas,  reduced.) 


The  ovary  is  attached  to  the  sublumbar  region 
by  the  anterior  part  of  the  broad  ligament  of  the 
uterus;  this  part  of  the  ligament,  the  mesovariiun, 
is  about  three  or  four  inches  (ca.  8  to  10  cm.)  wide, 
measured  from  the  ovary  directly  to  the  parietal  at- 
tachment. The  uterine  extremity  of  the  ovary  is 
connected  with  the  extremity  of  the  cornu  of  the 
uterus  by  the  ligament  of  the  ovary  (Lig.  ovarii  pro- 

prium) ;  this  is  a  band  of  unstriped  muscle  enclosed  between  the  layers  of  the  broad 
ligament. 

Structure. — The  greater  part  of  the  surface  of  the  ovary  has  a  covering  of 
peritoneum.  The  peritoneal  investment  is  absent  at  the  attached  border  where 
the  vessels  and  nerves  enter;  this  area  is  termed  the  hilus  of  the  ovary  (Hilus 
ovarii),  although  there  is  no  depression  here.  The  ovulation  fossa  is  covered  by 
a  layer  of  short  polygonal  cells,  a  remnant  of  the  primitive  germinal  epithelium. 

^  These  terms  apply  properly  only  when  the  adjacent  viscera  are  removed  and  the  ovaries 
are  actually  "suspended"  by  the  broad  ligaments.  When  the  ovary  is  in  its  natural  position, 
the  surfaces  are  usually  dorsal  and  ventral,  the  former  corresponding  to  the  "lateral"  surface  if  the 
free  border  is  directed  outward,  to  the  "medial"  if  the  free  edge  is  medial. 


598 


GENITAL  ORGANS  OF  THE  MARE 


The  stroma  of  the  ovary  (Stroma  ovarii)  is  a  network  of  connective  tissue.  In  the 
meshes  of  the  stroma  there  are  (in  young  subjects)  numerous  ovisacs  or  folliculi 
oophori,  containing  ova  (Ovula)  in  various  stages  of  development.  The  immature 
ovum  is  surrounded  by  foUicle  cells;  those  more  advanced  in  development  are 
enclosed  by  several  (5-8)  layers  of  follicle  cells,  forming  the  stratum  granulosum,  and 
by  a  condensation  of  the  stroma  termed  the  theca  folliculi;  ^\^thin  the  theca  is  a 
quantity  of  fluid,  the  liquor  folliculi.  At  one  point  the  follicle  cells  are  heaped  up  as 
a  sort  of  mound  (Cumulus  oophorus),  in  which  the  ovum  is  enclosed.  Such  sacs 
are  termed  folliculi  oophori  vesiculosi;^  they  enlarge  as  they  mature,  becoming 
visible  to  the  naked  eye  as  vesicles  Avith  a  diameter  of  a  centimeter  or  more.  When 
fully  developed,  the  follicles  are  superficially  situated,  and  often  project  slightly 
from  the  surface  of  the  ovary.  At  intervals  follicles  rupture  and  their  contents 
escape.      This    process,   which    sets    free    the    ovum,   is    termed    ovulation ;  it 

takes  place  in  the  mare  only 
at  the  ovulation  fossa,  and 
occurs  during  the  periods  of 
oestrum. 

The  structure  of  the  ovarj'  of 
the  mare  is  peculiar  and  differs  from 
that  of  other  animals  in  the  fact 
that  it  does  not  consist  of  a  cortex 
(zona  parenchymatosa),  in  which 
the  follicles  are  situated,  and  a  me- 
dulla (zona  vasculosa),  which  con- 
tains the  vessels  and  nerves.  This 
arrangement  is  present  in  the  foetus, 
but  later  the  follicles  become  dis- 
tributed throughout  the  interior  of 
the  gland,  and  the  vascular  zone  is 
superficial. 

After  rupture  of  a  follicle,  its 
cavity  is  partly  occupied  by  a  blood- 
clot,    constituting    what     may    be 
termed  a  corpus  rubrum.    By  prolif- 
eration and  enlargement  and  fatty 
changes,  the  follicle  cells  are  trans- 
formed into  lutein  cells,  forming  a 
yellow  mass  knowni  as  a  corpus  lu- 
teum.     If  impregnation  takes  place, 
the  accompanying  increase  in  vas- 
cularity of   the  organs  may  cause 
the  corpus  luteum  to  reach  a  large 
size;    if   impregnation  does  not  oc- 
cur,   it    is    much    smaller,    and    is 
sooner  replaced  by  scar  tissue,  form- 
ing the  corpus  albicans  s.  fibrosiun. 
In  the  new-boni  foal  the  ovaries  are  large  and  oval  in  form.     The  free  l^order  is  convex  and 
is  covered  by  germinal  epithelium,  which  extends  over  a  large  part  of  the  surfaces  also.     This  area 
is  distingiiishable  by  its  dull  gray  appearance  from  the  peritoneal  siu-face,  which  has  the  usual 
smooth  glistening  character.     The  hmit  of  the  peritoneal  epithelium  is  a  distinct  line,  termed  by 
Waldeyer  the  margo  limitans  peritonsei.     As  growth  proceeds  the  ovary  gradually  becomes  bent 
until  it  assumes  its  definitive  curved  shape.     The  germinal  epithelium  is  then  limited  to  the  o\ni- 
lation  fossa.     The  ovary  migrates  somewhat  during  development  from  its  primitive  position, 
which  is  the  same  as  that  of  the  testicle. 


Fig.  5.32. — Schematic  Represent.\tion  of  Changes  in  Ovary  of 
Mare  from  FfETAL  to  Adult  State.  (After  Born.) 
The  changes  affect  chiefly  the  free  border  (upper  in  figure)  and 
the  extent  and  form  of  the  area  covered  by  germinal  epithelium  (4). 
1,  Peritoneum  (broad  ligament);  2,  ligament  of  ovary;  3,  fimbria  of 
uterine  tube;  4.  germinal  epithelium;  o,  vessels,  which  reach  the 
ovarj-  at  the  attached  border  (6).  The  latter  represents  the  hikus, 
while  the  deep  depression  at  the  free  border  is  the  ovulation  fossa. 
(Ellenberger,  in  Leisering's  Atlas.) 


In  old  animals  the  ovaries  commonly  consist  largely  of  fibrous  tissue,  in  which 
there  are  often  cysts  of  various  sizes.  The  ova,  present  in  enormous  number  at 
birth,  have  then  been  extruded,  or  destroyed  by  phagocytic  action  or  degeneration. 

Vessels  and  Nerves. — The  arteries  of  the  ovary  are  derived  from  the  ovarian 
artery.  The  artery  is  relatively  large  and  is  flexuous;  it  reaches  the  attached 
border  of  the  ovary  by  passing  between  the  layers  of  the  mesovarium.  The  veins 
are  large  and  numerous.     They  form  a  plexus  somewhat  like  that  of  the  spermatic 

'■  Also  known  as  Graafian  follicles. 


THE  UTERINE  TUBES THE  UTERUS  599 

cord.  The  lymph  vessels  pass  to  the  lumbar  glands.  The  nerves  are  derived  from 
the  sympathetic  system  through  the  renal  and  aortic  plexuses.  They  accompany 
the  arterial  branches. 

THE  UTERINE  TUBES 

The  uterine  or  Fallopian  tubes  (Tubse  uterinse)  act  as  excretory  ducts  of  the 
ovaries,  since  they  convey  the  ova  from  the  reproductive  glands  to  the  uterus. 
They  are  not,  however,  in  direct  continuity  with  the  glands,  but  rather  partly  in 
contiguity  with,  and  partly  attached  to,  them.^  They  are  two  flexuous  tubes, 
eight  to  twelve  inches  (ca.  30  to  20  cm.)  long,  which  extend  from  the  extremities 
of  the  uterine  cornua  to  the  ovaries.  The  tube  is  very  small  at  its  uterine  end 
(ca.  2-3  mm.  in  diameter),  but  toward  the  ovary  it  widens  considerably  (4-8  mm. 
in  diameter),  forming  the  ampulla  tubae.  Each  is  enclosed  in  a  peritoneal  fold, 
derived  from  the  lateral  layer  of  the  broad  ligament,  and  termed  the  mesosalpinx. 
This  largely  covers  the  lateral  aspect  of  the  ovary,  and  forms  with  it  and  the  broad 
ligament  a  pouch  called  the  bursa  ovarica.  The  uterine  extremity  (Extremitas 
uterina)  of  the  tube  communicates  with  the  cavity  of  the  cornu  by  a  minute  orifice, 
the  ostium  uterinum  tubae.  The  ovarian  extremity  is  expanded  and  somewhat 
funnel  shaped,  and  is  therefore  termed  the  infundibulum  tubae  uterinae.  The 
margin  of  the  latter  is  slit  into  irregular  processes,  the  fimbriae,  some  of  which,  the 
fimbriae  ovaricae,  are  attached  in  the  ovulation  fossa.  About  the  middle  of  the 
infundibulum  is  a  small  opening,  the  ostium  abdominale  tubae,  by  which  the  tube 
communicates  with  the  peritoneal  cavity.  The  ovarian  extremity  of  the  tube 
appears  normally  to  be  applied  to  the  ovary,  so  that  the  extruded  ova  pass  into  it 
and  are  conveyed  to  the  uterus.^ 

Pedunculated  cysts,  the  hydatides  terminales,^  are  often  found  on  one  or  more  of  the 
fimbriae.  In  the  mesosalpinx  are  blind  flexuous  tubules,  which  constitute  the  paroophoron,  a 
remnant  of  the  Wolffian  body.  They  are  most  evident  in  the  young  adult,  and  tend  to  disappear 
with  increasing  age.     Not  uncommonly  they  give  rise  to  cysts. 

Structure. — The  tube  is  covered  externally  by  a  serous  coat  formed  by  the 
mesosalpinx.  The  serous  membrane  is  continued  on  the  fimbriae,  and  meets  the 
mucous  lining  on  them.  The  fibrous  adventitia  is  [continuous  with  the  fibrous 
lamina  of  the  broad  ligament.  The  muscular  coat  consists  chiefly  of  circular 
fibers,  outside  of  which  there  are  longitudinal  fibers  derived  from  the  broad  liga- 
ment; the  thickness  of  the  muscular  coat  diminishes  toward  the  ovarian  extremity. 
The  mucous  coat  is  thin  and  is  much  plicated.  The  folds  (Plicae  tubariae)  are 
chiefly  longitudinal,  but  in  the  wide  part  of  the  tube  (Ampullse  tubae)  they  are  very 
complex,  so  that  on  cross-sections  the  spaces  between  the  folds  may  be  mistaken  for 
branched  tubular  glands.  The  folds  are  continued  on  to  the  fimbriae.  The  epithe- 
lium is  a  single  layer  of  columnar  ciliated  cells,  the  cilia  producing  a  current  directed 
toward  the  uterus.  At  the  ovarian  extremity  this  epithelium  passes  gradually  into 
the  squamous  type  of  the  serous  coat. 

Vessels  and  Nerves. — The  arteries  are  derived  from  the  utero-ovarian  artery. 
The  veins  are  satellites  of  the  arteries.  The  lymph  vessels  pass  with  the  ovarian 
vessels  to  the  lumbar  glands.  The  nerves  have  a  similar  origin  to  those  of  the 
ovary. 

THE  UTERUS 

The  uterus  is  a  hollow  muscular  organ,  which  is  continuous  with  the  uterine 
tubes  anteriorly  and  opens  into  the  vagina  posteriorly.     It  is  situated  chiefly  in  the 

^  The  tubes  may  be  regarded,  both  in  origin  and  structure,  as  prolongations  of  the  uterus. 

^  The  arrangement  is  the  only  exception  to  the  general  rule  that  the  serous  cavities  are 
closed.  In  this  case  the  mucous  membrane  of  the  infundibulum  is  continuous  with  the  adjacent 
peritoneum,  a  persistence  of  the  embryonic  relations  of  the  Miillerian  duct. 

^  Also  kno^\-n  as  hydatids  of  Morgagni. 


600 


GENITAL  ORGANS  OF  THE  MARE 


abdominal  cavity,  but  extends  a  short  distance  into  the  pelvic  cavity.  It  is  at- 
tached to  the  sublumbar  region  and  the  lateral  walls  of  the  pelvic  cavity  by  two 
folds  of  peritoneum  termed  the  broad  ligaments.  It  consists  of  two  horns,  the  body, 
and  the  neck. 

The  horns  or  comua  of  the  uterus  (Cornua  uteri)  are  situated  entireh^  in 
the  abdomen.  They  appear  to  vary  considerably  in  position;  commonly  they 
are  pressed  up  against  the  sublumbar  muscles  by  the  intestine  (caecum,  left  parts  of 


Fig.  533. — Genital  Orgaxs  of  Mare;  Dorsal  View 
The  left  horn  and  adjacent  part  of  the  body  of  the  uterus  and  the  vagina  and  vulva  are  opened  up.  /,  Ovary;  S, 
uterine  tube,  with^',  its  ovarian  end;  3,  cavity  of  body  of  uterus;  4,  cavity  of  left  horn;  5,  right  horn,  with  5',  its  com- 
munication with  the  body;  e,  portio  vaginalis  uteri;  6',  external  orifice  of  uterus;  7,  broad  ligament  of  uterus;  5,  liga- 
ment of  ovarj-;  9,  vagina;  10,  vulva;  10',  orifices  of  ducts  of  glandulae  vestibulares  majores;  10",  orifices  of  ducts  of 
glandute  vestibulares  minores;  11,  transverse  fold;  12,  external  urethral  opening;  13,  13',  labia  vulvse;  14,  glans 
clitoridis;  14',  junction  of  crura  to  form  corpus  chtoridis  indicated  by  dotted  lines;  lo,  urinary  bladder;  a,  utero- 
ovarian  artery  with  ovarian  (a')  and  uterine  (o")  branches;  b,  middle  uterine  artery.  (After  Ellenberger,  in  Leisering's 
Atlas.) 


large  colon,  small  colon,  and  small  intestine).  They  are  cjdindrical  when  moder- 
ately distended,  and  are  about  ten  inches  (ca.  25  cm.)  in  length.  The  anterior 
extremity  of  each  forms  a  blunt  point  which  receives  the  uterine  tube.  Posteriorly 
they  increase  somewhat  in  caliber,  converge,  and  unite  A\dth  the  body.  The  dorsal 
border  (Margo  mesometricus)  is  slightly  concave  and  is  attached  to  the  sublumbar 
region  by  the  broad  ligament.     The  ventral  border  (Margo  liber)  is  convex  and  free. 

When  a  soft  uterus  is  distended,  its  horns  are  strongly  curved,  but  this  does  not  represent 
the  natural  form.    When  fixed  in  situ,  the  horns  are  either  sUghtly  curved  or  nearly  straight. 


THE    UTERUS  601 

The  two  horns  are  commonly  unsymmetrical  in  length  and  diameter  in  mares  which  have  borne 
young. 

The  body  of  the  uterus  (Corpus  uteri)  is  situated  partly  in  the  abdominal, 
partly  in  the  pelvic,  cavity.  It  is  cylindrical,  but  considerably  flattened  dorso- 
ventrally,  so  that  in  cross-section  it  is  elliptical.  Its  average  length  is  seven  or 
eight  inches  (ca.  18-20  cm.),  and  its  diameter,  when  moderately  distended,  about 
four  inches  (10  cm.).  Its  dorsal  surface  (Facies  dorsalis)  is  related  to  the  rectum 
and  other  parts  of  the  intestine.  Its  ventral  surface  (Facies  ventralis)  is  in  contact 
with  the  bladder,  and  has  inconstant  relations  with  various  parts  of  the  intestine. 
The  term  fundus  uteri  is  applied  to  the  wide  anterior  part  from  which  the  cornua 
diverge. 

The  position  of  the  body  of  the  uterus  is  variable,  especially  in  regard  to  its  anterior  part. 
It  is  often  pressed  up  against  the  rectum,  and  may  be  deflected  to  either  side — most  frequently 
to  the  left — by  the  pelvic  flexure  of  the  great  colon  or  coils  of  the  small  colon. 

The  neck  or  cervix  of  the  uterus  (Cervix  uteri)  is  the  constricted  posterior 
part  which  joins  the  vagina.  It  is  about  two  to  three  inches  (5-7.5  cm.)  in  length, 
and  an  inch  and  a  half  (3.5-4  cm.)  in  diameter.  Part  of  it  (Portio  vaginalis  uteri) 
projects  into  the  cavity  of  the  vagina;  it  is  therefore  not  visible  externally,  but 
may  be  felt  through  the  vaginal  wall. 

Attachments. — The  body  and  horns  are  attached  to  the  abdominal  and  pelvic 
walls  by  two  extensive  peritoneal  folds,  the  broad  ligaments  of  the  uterus  (Liga- 
menta  lata  uteri) .  These  extend  on  either  side  from  the  sublumbar  region  and  the 
lateral  pelvic  walls  to  the  dorsal  border  of  the  cornua  and  the  lateral  margins  of  the 
body  of  the  uterus.  They  contain  the  vessels  and  nerves  of  the  uterus  and  ovaries, 
connective  tissue,  and  a  large  amount  of  unstriped  muscular  fibers  which  are  con- 
tinuous with  those  of  the  uterus.  The  ureters  are  situated  along  their  parietal 
margins.  The  lateral  layer  of  each  gives  off  a  fold,  the  round  ligament  of  the  uterus 
(Ligamentum  teres  uteri),  which  blends  with  the  parietal  peritoneum  over  the 
abdominal  inguinal  ring;  its  anterior  extremity  is  situated  above  the  extremity  of 
the  cornu  and  forms  a  long  round  appendix.  It  contains  muscular  tissue,  vessels, 
and  nerves,  and  is  the  homologue  of  the  gubernaculum  testis.  The  anterior  part  of 
the  neck  is  continuous  with  the  vagina,  and  thus  has  a  more  fixed  position  than  the 
rest  of  the  organ. 

The  cavity  of  the  uterus  (Cavum  uteri)  is  largely  obliterated  in  the  non- 
pregnant state  by  the  contraction  of  the  wall  and  by  folds  of  the  mucous  lining. 
At  the  extremity  of  each  cornu  it  communicates  with  the  uterine  tube  by  a  minute 
opening  on  a  small  papilla.  The  cavity  of  the  neck  is  termed  the  cervical  canal 
(Canalis  cervicis);  it  is  closed  ordinarily  by  mucous  folds  and  a  plug  of  mucus. 
It  opens  into  the  vagina  by  the  orificiiun  externum  uteri,^  and  into  the  body  by  the 
orificium  internum  uteri. 

Structure. — The  wall  of  the  uterus  consists  of  three  coats.  The  serous  coat 
(Perimetrium)  is,  for  the  most  part,  closely  adherent  to  the  muscular  coat.  It  is 
continuous  with  the  broad  ligaments.  The  muscular  coat  consists  essentially  of 
two  layers,  a  thin  external  stratum  of  longitudinal  fibers,  and  a  thick  internal  layer 
of  circular  fibers.  Between  these  is  a  very  vascular  layer  (Stratum  vasculare)  of 
connective  tissue  with  circular  and  oblique  muscular  fibers  in  it.  The  circular  coat 
is  very  thick  in  the  neck,  where  it  forms  a  sphincter  half  an  inch  or  more  (ca.  1.5  cm.) 
in  thickness.  The  mucous  membrane  rests  directly  on  the  muscular  coat,  and  is 
brownish-red  in  color,  except  in  the  neck,  where  it  is  pale.  It  is  covered  by  a  single 
layer  of  high  columnar  cells,  and  contains  numerous  long,  branched  tubular  uterine 
glands  (Glandulse  uterinae) ;   these  are  absent  in  the  cervix. 

Vessels  and  Nerves. — The  chief  arteries  are  the  uterine  and  the  uterine 
branch  of  the  utero-ovarian,  which  have  a  flexuous  course  in  the  broad  ligaments; 
^  This  is  frequently  desigiiated  the  os  uteri. 


602  GENITAL  ORGANS  OF  THE  MARE 

there  is  also  a  branch  from  the  internal  pudic  artery.  The  veins  form  pampini- 
form plexuses  and  accompany  the  arteries.  The  lymph  vessels  are  numerous  and 
go  to  the  internal  iliac  and  lumbar  glands.  The  nerves  are  derived  from  the 
sympathetic  through  the  uterine  and  pelvic  plexuses. 

The  foregoing  statements  refer  to  the  non-gravid  uterus.  In  the  pregnant  state  it  under- 
goes important  changes  in  size,  position,  and  structure.  The  increase  in  size  affects  chiefly  the 
gravid  horn  (except  in  the  case  of  twins)  and  the  body.  The  horn  attains  a  length  of  about 
two  and  a  half  to  three  feet  (ca.  80  to  90  cm.),  and  a  corresponding  diameter;  in  this  process  it 
extends  much  beyond  the  ovary  and  the  broad  ligament.  The  gravid  uterus  is  entirely  abdominal 
in  position,  and  extends  along  the  ventral  wall,  chiefly  to  the  left  of  the  median  plane.  It  weighs 
about  nine  pounds  (ca.  4  kg.),  according  to  Ellenberger.  The  broad  ligaments  increase  greatly 
in  size  and  contain  more  muscular  tissue.  The  vessels  are  greatly  enlarged  and  form  new  branches. 
The  muscular  coat,  in  spite  of  the  increase  in  size  and  number  of  the  fibers,  is  somewhat  thinner, 
except  in  the  neck.     The  mucous  membrane  is  thicker  and  more  vascular. 

THE  VAGINA 

The  vagina  is  the  passage  which  extends  horizontally  through  the  pelvic 
cavity  from  the  neck  of  the  uterus  to  the  vulva.  It  is  tubular,  is  about  six  to  eight 
inches  (ca.  15-20  cm.)  in  length,  and,  when  slightly  distended,  about  four  or  five 
inches  (ca.  10-12  cm.)  in  diameter.  Its  dilatability  appears  to  be  limited  only  by 
the  pelvic  wall.  There  is  no  external  line  of  demarcation  between  the  vagina 
and  the  uterus  or  the  vulva. 

It  is  related  dorsally  to  the  rectum,  ventrally  to  the  bladder  and  urethra,  and 
laterally  to  the  pelvic  wall.  The  recto-genital  pouch  of  the  peritoneum  commonly 
extends  between  the  vagina  and  rectum  for  a  distance  of  about  two  inches  (5  cm.), 
and  ventrally  the  vesico-genital  pouch  passes  backward  somewhat  further  between 
the  vagina  and  bladder.  Thus  most  of  the  vagina  is  retroperitoneal  and  is  sur- 
rounded by  a  quantity  of  loose  coimective  tissue,  a  venous  plexus,  and  a  variable 
amount  of  fat.^ 

Structure. — With  the  exception  of  the  short  peritoneal  part,  as  indicated  above, 
the  proper  wall  of  the  vagina  is  composed  of  muscular  and  mucous  coats.  The 
muscular  coat  is  composed  of  a  thin  layer  of  longitudinal  fibers,  and  a  thicker  layer 
of  circular  fibers;  it  is  covered  externally  by  a  fibrous  adventitia,  and  there  is  a 
large  amount  of  intermuscular  connective  tissue.  The  mucous  coat  is  highly 
elastic,  and  is  covered  with  a  stratified — but  not  squamous^ — epithelium.  It  has 
no  glands. 

Under  usual  conditions  the  cavity  is  practically  obliterated  b}^  apposition  of 
the  walls,  so  that  the  lumen  is  a  transverse  slit;  this  condition  is  pronounced  when 
the  rectum  is  full.  The  anterior  end  of  the  vagina  is  largely  occupied  by  the  intra- 
vaginal  part  of  the  neck  of  the  uterus,  so  that  the  cavity  is  here  reduced  to  an  an- 
nular recess  termed  the  fornix  vaginae.  The  posterior  part  is  directly  continuous 
with  the  vulva  without  anj^  line  of  demarcation  except  the  transverse  fold  which 
covers  the  external  urethral  orifice;  in  ver}^  young  sul^jects  this  fold  is  continued 
on  either  side,  forming  the  hymen,  which  narrows  the  entrance  to  the  vagina  (In- 
troit us  vaginae)  .- 

Vessels  and  Nerves. — The  arteries  are  branches  of  the  internal  pudic  arteries. 
The  veins  form  a  rich  plexus  which  is  drained  by  the  internal  pudic  veins.  The 
lymph  vessels  go  to  the  internal  iliac  lymph  glands.  The  nerves  are  derived  from 
the  sympathetic  through  the  pelvic  plexus;  numerous  ganglia  are  present  in  the 
adventitia. 

^The  amount  of  the  vagina  which  is  covered  by  peritoneum  varies,  depending  apparently 
on  the  degree  of  fullness  of  the  rectum  and  bladder.  When  these  organs  are  empty,  the  peritoneum 
may  cover  the  vagina  for  a  distance  of  three  or  four  inches  (ca.  S-10  cm.);  when  they  are  full,  the 
vagina  may  be  completely  retroperitoneal  or  nearly  so. 

2  In  formalin-hardened  subjects  there  is  frequently  a  pronounced  ring-like  constriction  at  the 
junction  of  the  vulva  and  vagina. 


THE   VULVA  603 

THE  VULVA 

The  vulva  or  urogenital  sinus  (Vestibulum  vaginae)  is  the  terminal  part  of  the 
genital  tract. ^  It  is  continuous  in  front  with  the  vagina,  and  opens  externally  at 
the  vulvar  cleft  below  the  anus.  There  is  no  external  line  of  demarcation  between 
the  vagina  and  vulva.  The  tube  is  four  or  five  inches  (ca.  10-12  cm.)  in  length, 
measured  from  the  external  urethral  orifice  to  the  ventral  commissure;  dorsally 
(from  a  point  vertically  opposite  to  the  external  urethral  orifice)  it  is  considerably 
shorter.  It  is  related  dorsally  to  the  rectum  and  anus,  ventrally  to  the  pelvic  floor, 
and  laterally  to  the  sacro-sciatic  ligament,  the  semimembranosus  muscle,  and  the 
internal  pudic  artery.  The  external  orifice,  the  vulvar  cleft  (Rima  vulvae),  has  the 
form  of  a  vertical  slit,  four  or  five  inches  (ca.  10-12  cm.)  high,  and  is  margined 
by  two  prominent  rounded  lips,  the  labia  vulvae.  The  labia  meet  above  at  an  acute 
angle,  forming  the  dorsal  commissure  (Commissura  dorsalis),  which  is  about  two 
inches  (ca.  5  cm.)  below  the  anus.  They  unite  below  to  form  the  thick,  rounded 
ventral  commissure  (Commissura  ventralis),  which  lies  about  two  inches  (ca.  5  cm.) 
behind  and  below  the  ischial  arch.  When  the  labia  are  drawn  apart,  a  rounded 
body,  about  an  inch  (ca.  2.5  cm.)  wide,  is  seen  occupying  a  cavity  in  the  ventral 
commissure;  this  is  the  glans  clitoridis,  the  homologue  of  the  glans  penis,  and  the 
cavity  in  which  it  lies  is  the  fossa  clitoridis.  The  roof  of  the  fossa  is  formed  by  a 
thin  fold,  which  overlies  the  glans  clitoridis  and  is  attached  centrally  to  it.  At 
the  anterior  extremity  of  the  ventral  wall  of  the  vulva,  i.  e.,  four  or  five  inches  (ca. 
10-12  cm.)  from  the  ventral  commissure,  is  the  external  urethral  orifice  (Ori- 
ficium  urethrge  externum).^  It  readily  admits  the  finger  and  is  very  dilatable.  It 
is  covered  by  a  fold  of  mucous  membrane,  the  free  edge  of  which  is  directed  back- 
ward (Fig.  533). 

Structure. — The  labia  are  covered  by  thin,  pigmented,  smooth  skin,  which  is 
richly  supplied  with  sebaceous  and  sweat  glands.  This  is  continuous  at  a  distance 
of  about  half  an  inch  (ca.  1-1.5  cm.)  from  the  free  edge  with  a  thin,  glandless 
mucous  membrane.  Under  the  skin  there  is  a  layer  of  striped  muscle,  the  con- 
strictor vulvae;  this  fuses  above  with  the  sphincter  ani,  and  embraces  the  clitoris 
below,  spreading  out  laterally  at  the  ventral  commissure.  It  constricts  the  vulvar 
orifice  and  elevates  the  clitoris.  The  constrictor  vestibuli  muscle  embraces  the 
vulva  in  front  of  the  preceding;  it  is  deficient  dorsally  and  is  joined  on  either  side 
by  a  band  of  unstriped  muscle,  the  suspensory  ligament  of  the  anus.  It  constricts 
the  vulva.  Within  this  there  is  an  unstriped  muscular  coat,  most  of  the  bundles 
of  which  are  circular.  Chiefly  between  this  coat  and  the  mucous  membrane  there 
is  in  the  lateral  wall,  just  in  front  of  the  labia,  a  flattened,  oval  body,  the  bulbus 
vestibuli  (Fig.  578);  this  is  an  erectile  structure,  homologous  with  the  corpus 
cavernosum  urethrae  of  the  male.  It  is  about  two  and  a  half  to  three  inches  (ca. 
6-8  cm.)  long,  and  an  inch  or  more  (ca.  3  cm.)  wide.  It  is  similar  in  structure  to 
the  bulb  of  the  corpus  cavernosum  urethrae  of  the  male,  and  is  supplied  with  blood 
by  a  large  branch  of  the  internal  pudic  artery.  The  mucous  membrane  of  the 
vulva  is  reddish  in  color,  and  forms  longitudinal  and  transverse  folds.  It  presents 
ventrally  two  linear  series  of  small  papillae  which  converge  toward  the  ventral 
commissure;  these  mark  the  orifices  of  the  ducts  of  the  glandulae  vestibulares 
minores.  On  either  side  of  the  dorsal  wall  is  a  group  of  eight  to  ten  larger  promi- 
nences on  which  the  ducts  of  the  glandulae  vestibulares  majores  open  (Fig.  533). 

Quite  exceptionally  there  may  be  found  on  either  side  of  the  urethral  orifice  the  openings  of 
the  canals  of  Gartner  (Ductus  epoophori  longitudinales) . 

1  The  term  vulva  is  used  here  in  the  sense  in  which  it  is  understood  generally  by  English 
and  French  veterinarians.  In  the  German  works  it  is  applied  only  to  the  labia  and  other  struc- 
tures around  the  external  orifice  of  the  urogenital  sinus,  while  the  sinus  itself  is  termed  the  vestibule 
of  the  vagina  (Vestibulum  vagina*). 

^  Also  termed  the  meatus  urinarius. 


604  GENITAL  ORGANS  OF  THE  MARE 

The  clitoris  is  the  homologue  of  the  penis  and  consists  of  similar  parts  (minus 
the  urethra  and  its  muscle).  The  corpus  clitoridis  is  about  two  inches  (ca.  5  cm.) 
long,  and  its  diameter  about  that  of  one's  little  finger.  It  is  attached  to  the  ischial 
arch  by  two  crura  (Crura  clitoridis).  The  glans  clitoridis  is  the  rounded  and  en- 
larged free  end  of  the  organ  which  was  noted  above  as  occupying  the  fossa  clitoridis 
in  the  ventral  commissure  of  the  vulva.  It  is  covered  by  a  thin  pigmented  integu- 
ment, similar  to  and  continuous  with  that  which  lines  the  fossa;  these  constitute 
the  prepuce  of  the  clitoris  (Praeputium  clitoridis) .  The  organ  is  composed  of  erectile 
tissue  similar  to  the  corpus  cavernosum  penis.  The  ischio-cavemosus  is  the 
homologue  of  the  muscle  of  the  same  name  of  the  male;  it  is  a  very  feeble  muscle. 
The  veins  of  the  clitoris  communicate  by  an  intermediate  plexus  on  either  side  with 
the  bulbus  vestibuli. 

THE  FEMALE  URETHRA 

The  female  urethra  (Urethra  feminina)  represents  only  that  part  of  the  canal 
of  the  male  which  lies  between  the  internal  urethral  orifice  and  the  colliculus  semi- 
nalis.  Its  length  is  two  to  three  inches  (5-7.5  cm.),  and  its  lumen  is  sufficient  to 
allow  easily  the  introduction  of  the  finger;  it  is,  however,  capable  of  remarkable 
dilatation  if  sufficient  care  and  patience  are  exercised  in  the  process.  It  lies  centrally 
on  the  pelvic  floor,  and  is  related  dorsally  to  the  vagina,  to  which  it  is  in  part  at- 
tached.    The  external  orifice  is  at  the  anterior  end  of  the  vulva,  as  described  above. 

Structure.— The  intrinsic  muscular  coat  consists  of  external  longitudinal  and 
internal  circular  fibers;  it  is  absent  where  the  urethra  is  attached  to  the  vagina. 
The  mucous  membrane  is  thrown  into  longitudinal  folds  when  the  canal  is  closed; 
it  is  highly  elastic,  and  is  covered  with  stratified  epithelium.  There  is  a  rich  sub- 
mucous network  of  veins,  forming  a  sort  of  corpus  cavernosum. 

The  urethral  muscle  (M.  compressor  urethrae)  embraces  the  urethra  and  is 
continuous  with  the  constrictor  vestibuli.     It  is  covered  by  a  fibro-elastic  membrane. 


THE  MAMMARY  GLANDS 

The  mammary  glands  (Glandulse  lactiferse)  are  modified  cutaneous  glands 
which  are  so  closely  associated  functionally  with  the  genital  organs  as  to  be  con- 
sidered accessory  to  them. 

In  the  mare  they  are  two  in  number,  and  are  placed  on  either  side  of  the  median 
plane  in  the  inguinal  region.  Each  gland  has  the  form  of  a  very  short,  flattened 
cone,  much  compressed  transversely,  and  having  a  flat  medial  surface.  It  consists 
of  the  glandular  mass  or  body  of  the  gland  (Corpus  mammae)  and  the  papilla  or 
teat  (Papilla  mammae).  The  base  is  related  to  the  abdominal  wall,  to  which  it  is 
attached  by  areolar  tissue,  which  contains  a  venous  plexus,  the  superficial  inguinal 
Ijnnph  glands,  and  a  variable  amount  of  fat.  The  apex  is  constituted  by  the  teat, 
which  is  also  flattened  transversely  and  varies  in  length  from  one  to  two  inches 
(ca.  2.5  to  5  cm.).  Between  the  bases  of  the  teats  is  the  intermammary  groove. 
On  the  apex  of  each  teat  there  are  usually  two  small  orifices  placed  close  together; 
these  are  the  openings  of  the  lactiferous  ducts. 

Structure. — The  skin  covering  the  glands  is  thin,  pigmented,  chiefly  hairless, 
and  supplied  with  numerous  large  sebaceous  and  sweat  glands.  Under  this  are  two 
layers  of  fascia,  except  on  the  teats.  The  superficial  fascia  presents  no  special 
features.  The  deep  fascia  consists  of  elastic  tissue ;  centrally  two  laminae  detached 
from  the  abdominal  tunic  descend  on  either  side  of  the  median  plane,  forming  a 
septum  between  the  two  glands,  and  constituting  their  ligamentum  suspensorium.^ 

The  gland  substance  or  parenchyma  is  pinkish  gray  in  color,  and  of  firmer 

^  These  laminae  are  separated  almost  completely  by  a  layer  of  areolar  tissue,  so  that  it  is  pos- 
sible to  remove  a  diseased  gland  by  careful  dissection  between  the  layers  of  the  septum. 


GENITAL  ORGANS  OF  THE  COW 


605 


consistence  than  the  fat  which  is  found  around  and  within  the  giand.  It  is  enclosed 
by  a  fibro-elastic  capsule  which  sends  inward  numerous  trabeculse;  these  form  the 
interstitial  tissue,  and  divide  the  gland  into  lobes  and  lobules.  In  the  latter  are 
the  secretory  tubules  and  alveoli,  which  unite  to  form  the  larger  ducts.  Each  lobe 
has  a  duct,  which  opens  at  the  base  of  the  teat  into  a  space  called  the  lactiferous 
sinus  (Sinus  lactiferus),  and  from  this  two  (or  three)  lactiferous  ducts  (Ductus 
lactiferi)  pass  through  the  extremity  of  the  teat.  These  ducts  are  lined  with  a  non- 
glandular  mucous  membrane,  which  is  covered  with  stratified  squamous  epithelium. 
They  are  surrounded  by  unstriped  muscular  tissue,  the  bulk  of  the  fibers  being  ar- 
ranged in  a  circular  manner  to  form  a  sphincter. 

The  size  and  form  of  the  mammary  glands  are  subject  to  much  variation.  In  the  young 
subject,  before  pregnancy,  they  are  small  and  contain  little  gland  tissue.  During  the  latter  part 
of  gestation,  and  especially  during  lactation,  they  increase  greatly  in  size,  and  the  gland  tissue  is 
highly  developed.  After  lactation  the  secretory  structures  undergo  marked  involution,  and  the 
gland  is  much  reduced  in  size.  The  relative  amomits  of  gland  substance  and  interstitial  tissue 
vary  greatly;  in  some  cases  a  gland  of  considerable  size  contains  little  parenchyma  and  is  con- 
sequently functionally  deficient. 

Vessels  and  Nerves. — The  arteries  are  derived  from  the  external  pudic  artery, 
which  enters  the  gland  at  the  posterior  part  of  its  base.  The  veins  form  a  plexus 
on  either  side  of  the  base  of  the  gland,  which  is  drained  by  the  external  pudic  vein 
chiefly.  The  lymph  vessels  are  numerous  and  pass  to  the  superficial  inguinal  and 
lumbar  lymph  glands.  The  nerves  are  derived  from  the  inguinal  nerves  and  the 
posterior  mesenteric  plexus  of  the  sympathetic  system. 


GENITAL  ORGANS  OF  THE  COW 

The  ovaries  of  the  cow  are  much  smaller  than  those  of  the  mare ;  they  measure 
usually  about   one  and  a  half  inches  (ca.  3.5-4  cm.)  in  length,   and  an  inch 


Fig.  534. — Ovary  of  Cow. 
1,  Broad  ligament  of  uterus;  2,  ligament  of 
ovary;  3,  fimbria  ovarica;  4,  attachment  of  broad 
ligament;  5,  surface  of  ovary  covered  with  ger- 
minal epithelium;  6,  corpora  lutea;  ~,  Graafian 
follicle.      (From  Leisering's  Atlas.) 


Fig.  535. — Uterits  of  Cow,  Contracted;  Dorsal  View. 
a.  Body  of   uterus;   h,  b',  horn  of  uterus;   c,  ovary;   d,  d, 
triangular  folds  connecting  horns  of  uterus  (Ligg.  intercornu- 
alia).      (After  Zieger.) 


(ca.  2.5  cm.)  in  thickness  in  their   largest   part;   the  weight   is  half   an  ounce 
or  more   (ca.   15-20   gm.).^     They   are   oval   in   form,    pointed   at   the  uterine 

1  Hess  gives  the  following  average  measurements  of  the  ovaries  of  95  cows:  Length  of  right, 
4.3  cm.;  of  left,  3.71  cm.;  width  of  right,  2.8  cm.;  of  left,  2.36  cm.  Zieger  found  that  the  right 
one  was  larger  than  the  left  in  65  out  of  75  cases. 


606 


GENITAL  ORGANS  OF  THE  COW 


-1>^%^.- 


end,   and   have   no   ovulation   fossa.     They  are   situated  usually  a  little   above 

the  middle  of  the  lateral  margin  of  the  pelvic  inlet  in  the  non-pregnant  subject,  but 

may  be  a  little  further  forward.     They  are  thus  about  16  to  18  inches  (ca.  40-45 

cm.)  from  the  vulvar  opening  in  a  cow  of  medium  size.     The  greater  part  of  the 

surface  of  the  gland  is  covered  with  germinal  epithelium,  the  peritoneal  epithelium 

being  limited   to  a  narrow  zone  along  the 

attached  border.     Follicles  of  various  sizes  /'- 

are  often  seen  projecting  from  the  surface, 

as  well  as  corpora  lutea;   a  corpus  luteum 

verum  has  a  pronounced   yellow  color,  and 

may  reach  a  width  of  half  an  inch  or  more 

(ca.  1-1.5  cm.). 

The  uterine  or  Fallopian  tubes  are  long 
(ca.  20-25  cm.)  and  less  flexuous  than  in  the 
mare.  The  junction  with  the  cornu  of  the 
uterus  is  not  so  abrupt  as  in  the  mare,  since 
the  extremities  of  the  horns  are  pointed. 
The  uterine  orifice  of  the  tul^e  is  rather  large 
and  funnel-shaped.  The  fimbrise  are  not  so 
extensive  as  in  the  mare. 

The  uterus  lies  almost  entirely  within 
the  abdominal  cavity  in  the  adult.  The 
body  is  only  about  an  inch  and  a  half  (ca. 
3-4  cm.)   in  length,  although  externally  it 


The  photogra 


aljout  three-fourths  natura 
men  of  medium  size. 


Fig.  537. — Genital  Organs  of  Cow;  Dorsal. 
View. 
The  right  uterine  cornu  and  the  vagina  and 
vulva  are  opened  up:  1,  Labium  vulvae;  2,  ventral 
commissure;  3,  glans  clitoridis;  4.  glandula  vestib- 
ularis major,  exposed  by  slit  in  mucous  mem- 
brane; 5,  pouch  in  which  the  ducts  of  the  pre- 
ceding open;  6,  suburethral  diverticulum;  7,  ex- 
ternal urethral  opening;  8,  openings  of  canals  of 
Gartner;  9,  orificium  uteri  externum;  10,  corpus 
uteri;  11,  cornu  uteri;  12,  cotyledons;  13,  uterine 
tube;  14,  ostium  abdominale  tubse;  15,  ovary. 
(From  Leisering's  Atlas,  reduced.) 


appears  to  be  about  five  or  six  inches  long. 

This  false  impression  is  due  to  the  fact  that 

the  posterior  parts  of  the  cornua  are  united 

by  connective  and  muscular  tissue  and  have 

a  common  peritoneal  covering.     The  cornua 

are,    therefore,  really  more  extensive  than 

they  appear  externally  and  have  an  average 

length  of  about  fifteen  inches  (ca.  35-40  cm.) .    They  taper  gradually  toward  the  free 

end,  so  that  the  junction  with  the  uterine  tubes  is  not  abrupt,  as  in  the  mare.     The 

free  part  of  the  horn  curves  at  first  downward,  forward,  and  outward,  and  then  turns 

backward  and  upward,  forming  a  spiral  coil.     The  cervix  is  about  four  inches  (ca. 

10  cm.)  long;  its  wall  is  remarkably  dense,  and  may  be  more  than  an  inch  (ca.  3  cm.) 


GENITAL  ORGANS  OF  THE  COW  607 

in  thickness.  Its  lumen,  the  cervical  canal,  is  spiral,  and  is  ordinarilj^  tightly  closed 
and  very  difficult  to  dilate.  The  vaginal  part  of  the  uterus  is  fused  ventrally  with 
the  vagina,  so  that  the  fornix  vaginae  is  dorsal,  and  not  an  annular  space  as  in  the 
mare.  The  muscular  coat  of  the  uterus  is  thicker  than  in  the  mare.  It  consists 
of  an  external  .longitudinal  layer  and  two  circular  strata.  The  inner  circular  layer 
is  about  a  fourth  of  an  inch  (ca.  6  mm.)  thick  in  the  cervix.  The  other  layers  are 
continued  in  the  vagina.  The  mucous  membrane  of  the  horns  and  body  presents 
as  a  characteristic  feature  the  uterine  cotyledons  (Cotyledones  uterinse).^  These 
are  oval  prominences,  about  a  hundred  in  number,  which  are  either  irregularly 
scattered  over  the  surface  or  arranged  in  rows  of  about  a  dozen. 

In  the  non-gravid  uterus  they  average  about  half  an  inch  or  more  (ca.  15  mm.)  in  length, 
and  a  Httle  less  in  width  and  thickness.  During  pregnancy  they  become  greatly  enlarged  and 
pedunculated.  The  larger  ones  then  measure  about  four  or  five  inches  (10  to  12  cm.)  in  length, 
an  inch  and  a  half  (3  to  4  cm.)  in  width,  and  an  inch  (2  to  2.5  cm.)  in  thickness.  The  deep  face  has 
a  hilus  at  which  the  vessels  enter.  The  rest  of  the  surface  has  a  spongy  appearance,  due  to  numer- 
ous crypts  which  receive  the  villi  of  the  chorion. 

The  uterine  glands  are  long  and  branched.  The  mucous  membrane  of  the 
cervix  is  pale,  glandless,  and  forms  numerous  folds.  The  latter  are  arranged  in 
several  series  which  obliterate  the  lumen. 
At  the  external  uterine  orifice  the  folds 
(PlicaB  palmatae)  form  rounded  prominences 
arranged  circularly,  which  project  into  the 
cavity  of  the  vagina.  There  are  no  glands 
in  the  cervix,  but  a  thick  mucus  is  secreted 
by  goblet  cells. 

The  broad  ligaments  are  not  attached 
in  the  sublumbar  region  as  in  the  mare,  but 

to    the    upper    part    of    the    flanks,    about  a  Fig.  53S.— Di.a.grammatic  Sagittal  Section  op 

handbreadth     below     the    level   of    the    tuber  P^Rt     of     Urogenital    Tract    of    Cow, 

mi.  X    •  •  J.  Showing  Suburethral  Diverticulum. 

coxse.      1  hey  contam  a  conspicuous  amount 

of  unstriped  muscle.     The  round  ligaments 

are  well  developed,  and  can  be  traced  distinctly  to  the  vicinity  of  the  abdominal 

inguinal  ring. 

The  vagina  is  somewhat  longer  and  more  roomy  than  that  of  the  mare;  its 
wall  is  also  thicker.  Its  length  in  the  non-pregnant  animal  is  about  eight  to  ten 
inches  (ca.  20-25  cm.);  but  in  the  pregnant  cow  the  length  increases  to  twelve 
inches  (30  cm.)  or  more.  The  recto-genital  pouch  of  peritoneum  extends  backward 
about  five  inches  (ca.  12  cm.)  on  the  dorsal  surface,  while  ventrally  the  serous  coat 
only  extends  backward  about  two  inches  (ca.  5  cm.).  In  the  ventral  wall  of  the 
vagina,  between  the  muscular  and  mucous  coats,  there  are  commonly  present  the 
two  canals  of  Gartner  (Ductus  epoophori  longitudinales) .  When  well  developed, 
they  may  attain  the  diameter  of  a  goose  quill,  and  may  be  traced  forward  to  the 
anterior  part  of  the  vagina  or  even  further.  They  open  posteriorly  near  the  ex- 
ternal urethral  orifice." 

The  vulva  has  thick,  wrinkled  labia,  and  both  commissures  are  acute;  the 
ventral  one  is  pointed,  and  has  on  it  a  number  of  long  hairs;  it  lies  about  two  inches 
(5  cm.)  behind,  and  about  the  same  distance  below  the  level  of,  the  ischial  arch. 
The  external  urethral  orifice  is  four  or  five  inches  (10  to  12  cm.)  from  the  ventral 
commissure.     Beneath  it  is  a  blind  pouch,  the  suburethral  diverticulum,  which  is 

^Also  known  as  carimculse  uterinse. 

2  These  tubes  are  remnants  of  the  Wolffian  ducts,  and,  like  other  fcEtal  vestiges,  are  very 
variable.  Roder  states  that  the  right  canal  was  absent  in  over  52  per  cent.,  the  left  in  only  22  per 
cent.,  of  the  cows  examined  by  him.  In  some  cases  they  may  be  traced  in  the  broad  ligaments  for 
a  variable  distance  toward  the  ovary.  They  are  of  clinical  interest  in  that  cysts  frequently  form 
along  their  course. 


608 


GENITAL  ORGANS  OF  THE  COW 


about  an  inch  (ca.  3  cm.)  long,  and  readily  admits  the  end  of  a  finger.^  The  two 
glandulae  vestibulares  majores-  are  situated  in  the  lateral  walls  of  the  vulva,  under 
the  constrictor  vulvae.  They  are  little  over  an  inch  (ca.  3  cm.)  long  and  about  half 
an  inch  (ca.  1.5  cm.)  in  width.  Each  has  two  or  three  ducts  which  open  into  a 
small  pouch  of  the  mucous  membrane;  this  cul-de-sac  opens  on  the  floor  of  the 
vulva,  about  an  inch  and  a  half  (ca.  3-4  cm.)  lateral  to  and  behind  the  external 


Fig.  539. — Cross-section  of  Mammary  Glands  of  Cow. 
■a,  Body  of  gland;    6,  lactiferous  sinus;   c,  cavity  of  teat;   d,  lactiferous  duct;    e,  intermammary  groove;  /,  septum  be- 
tween glands;  g,  supramammary  fat. 


urethral  orifice.  The  gland  consists  of  lobules  separated  by  relatively  thick  trabec- 
ulse  of  connective  tissue  and  unstriped  muscle.  The  glandulae  vestibulares 
minores  occur  along  the  median  ventral  groove.  Numerous  lymph  nodules  are 
present  in  the  mucous  membrane,  especially  in  the  ventral  part;  they  may  be 
large  enough  to  cause  visible  prominences. 

The  clitoris  has  very  short  crura,  but  the  body  is  four  or  five  inches  (ca.  10-12 

1  The  form  and  position  of  this  pouch  should  be  carefully  noted  on  account  of  the  difficulty 
it  causes  in  catheterizing  the  bladder.  If  the  catheter  is  passed  along  the  ventral  wall  of  the 
vulva  (as  in  the  mare),  it  will  always  enter  the  pouch  instead  of  the  urethra. 

2  Also  known  as  the  glands  of  Bartholin. 


GENITAL    ORGANS    OF   THE    EWE  609 

cm.)  long  and  is  flexuous.  Only  the  pointed  end  of  the  glans  is  visible  in  the  ventral 
commissure  of  the  vulva. 

The  urethra  is  about  four  inches  (10  cm.)  in  length;  it  is  narrower  and  much 
less  dilatable  than  that  of  the  mare.  It  is  fused  dorsally  with  the  wall  of  the 
vagina,  while  laterally  and  ventrally  it  is  covered  by  the  constrictor  vaginae  muscle. 

The  mammary  glands,  normally  two  in  number,  are  popularly  termed  the 
udder.  They  are  very  much  larger  than  in  the  mare,  and  the  body  of  each  is 
somewhat  ellipsoidal  in  form,  but  flattened  transversely.  The  base  of  each  gland 
is  slightly  concave  and  slopes  obliquely  downward  and  forward  in  adaptation  to 
the  abdominal  wall,  to  which  it  is  adherent;  it  is  in  relation  posteriorly  to  the  large 
supramammary  lymph-glands  and  a  quantity  of  fat.  The  medial  surface  is  flat, 
and  is  separated  from  the  other  gland  by  a  well-developed  double  septum.  The 
lateral  surface  is  convex.  Four  well-developed  teats  are  present;  they  average 
about  three  inches  (ca.  7-8  cm.)  in  length.  It  is  customary  to  consider  the  udder 
to  consist  of  four  "quarters";  there  is  no  septum  nor  visible  division  between  the 
two  quarters  of  the  same  side,  but,  on  the  other  hand,  injections  of  fluids  of  different 
colors  into  the  two  teats  of  the  gland  demonstrate  that  the  cavities  drained  by  them 
do  not  communicate. 

The  size  and  form  of  the  glands  vary  greatly;  in  the  highly  specialized  dairy  breeds  (e.  g., 
Holsteins)  they  often  attam  enormous  dimensions.  The  size  of  the  udder  is  not  a  certain  index 
of  its  productivity,  since  some  so-called  "fleshy"  udders  contain  a  very  large  amount  of  inter- 
stitial tissue  and  relatively  httle  parenchyma.  Small  accessory  teats  often  occur  posteriorly; 
commonly  these  are  rudimentary  and  imperforate  (polythelia),  but  sometimes  they  drain  a  small 
amount  of  gland  substance  (polymastia).  Sanson  described  a  case  in  which  there  were  seven 
teats,  all  giving  milk. 

Each  teat  has  a  single  duct  which  widens  superiorly  and  opens  freely  into  a 
roomy  lactiferous  sinus  (Sinus  lactiferus),  popularly  known  as  the  milk  cistern. 
The  lactiferous  duct  (Ductus  lactiferus)  or  teat  canal  is  lined  by  a  glandless  mucous 
membrane  which  is  covered  with  stratified  squamous  epithelium;  the  lower  part 
(ca.  1  cm.)  of  the  canal  is  narrow,  and  is  closed  by  a  sphincter  of  unstriped  muscle. 
The  mucous  membrane  of  the  sinus  forms  numerous  folds  which  render  the  cavity 
multilocular. 

Vessels  and  Nerves. — The  arteries  are  derived  from  the  external  pudic  arteries. 
The  veins  form  a  circle  at  the  base  of  the  udder,  from  which  the  blood  is  drained  by 
three  trunks,  viz.,  the  very  large  subcutaneous  abdominal,  the  external  pudic,  and 
the  perineal  vein.  The  lymph  vessels  are  numerous,  and  pass  to  the  supramammary 
glands  chiefly.  The  nerves  are  derived  from  the  inguinal  nerves  and  the  posterior 
mesenteric  plexus  of  the  sympathetic. 


GENITAL  ORGANS  OF  THE  EWE 

The  genital  organs  of  the  ewe  resemble  in  general  those  of  the  cow,  but  a  few 
special  features  may  be  noted. 

The  ovaries  are  almond  shaped  and  are  half  an  inch  or  more  (ca.  1.5  cm.)  in 
length. 

There  is  no  demarcation  between  the  uterine  tube  and  the  horn  of  the  uterus; 
the  tube  is  very  flexuous  near  the  infundil^ulum. 

The  uterus  resembles  that  of  the  cow.  The  horns  are  four  or  five  inches  (ca. 
10-12  cm.)  long  and  taper  in  such  a  manner  to  their  junction  with  the  uterine  tubes 
that  no  clear  distinction  between  the  two  exists.  They  are  coiled  in  a  close  spiral, 
and  an  inch  or  more  of  their  posterior  parts  are  united.  The  body  is  less  than  an 
inch  (ca.  2  cm.)  long.  The  cotyledons  are  much  smaller  than  those  of  the  cow  and 
39 


610  GENITAL  ORGANS  OF  THE  SOW 

have  a  depression  on  the  free  surface.  The  neck  is  about  an  inch  and  a  half  (ca. 
4  cm.)  in  length;  its  lumen  is  closed  by  reciprocal  prominences  and  depressions  of 
the  mucous  membrane.  The  external  uterine  orifice  is  in  the  ventral  part  of  the 
vagina. 

The  vagina  is  three  or  four  inches  (ca.  8  cm.)  long.  Its  ventral  part  contains 
numerous  lymph  follicles. 

The  vulva  is  an  inch  or  more  (ca.  2.5-3  cm.)  in  length.  There  is  a  very  small 
diverticulum  behind  the  urethral  orifice.  The  glandulse  vestibulares  majores  are 
inconstant;  when  present,  they  may  be  about  the  size  of  a  small  bean.  The  labia 
are  thick  and  the  ventral  commissure  is  pointed  and  projects  dowmward. 

The  clitoris  is  short,  and  the  glans  is  concealed  in  the  fossa  clitoridis. 

The  mammary  glands,  two  in  number,  are  relatively  large,  and  are  approxi- 
mately globular,  but  flattened  on  the  septal  side. 


GENITAL  ORGANS  OF  THE  SOW 

The  ovaries  are  concealed  in  the  bursa  ovarii,  owing  to  the  large  extent  of  the 
mesosalpinx.  They  are  more  rounded  than  in  the  bitch,  and  have  a  distinct  hilus. 
They  may  be  situated  at  or  near  the  lateral  margin  of  the  pelvic  inlet,  as  in  the  cow; 
but  their  position  is  quite  variable  in  animals  which  have  borne  young  and  they  may 
be  only  an  inch  or  two  behind  the  kidney.  The  surface  commonly  presents  rounded 
prominences,  so  that  the  gland  usually  has  an  irregular  lobulated  appearance; 
the  projections  are  large  follicles  and  corpora  latea.  Mature  follicles  may  have  a 
diameter  of  about  a  third  of  an  inch  (ca.  7-8  mm.),  and  corpora  lutea  may  be  found 
which  measure  half  an  inch  or  more  (ca.  12-15  mm.). 

The  uterine  or  Fallopian  tubes  are  long  (ca.  15-30  cm.),  and  less  flexuous  than 
in  the  mare.  The  fimbriated  extremity  forms  an  ampulla  and  has  a  large  abdominal 
opening.  The  uterine  end  shades  insensibly  into  the  small  extremity  of  the  cornu 
of  the  uterus. 

The  uterus  presents  several  striking  features.  The  body  is  only  about  two 
inches  (ca.  5  cm.)  long.  The  horns  are  extremely  long  and  flexuous,  and  are  freely 
movable,  on  account  of  the  large  extent  of  the  broad  ligaments.  In  the  non- 
pregnant animal  they  are  arranged  in  numerous  coils  and  appear  somewhat  like 
thick-walled  small  intestine.  They  may  be  four  or  five  feet  (1.2-1.5  m.)  in  length. 
The  extremities  of  the  horns  taper  to  about  the  diameter  of  the  uterine  tubes.  The 
neck  is  remarkable  for  its  length  (ca.  10  cm.)  and  the  fact  that  it  is  directly  con- 
tinued by  the  vagina  without  forming  any  intravaginal  projection.  When  slit  open, 
peculiar  rounded  prominences  are  seen  on  its  interior;  some  of  these  dovetail  and 
occlude  the  cervical  canal.  They  are  continuous  behind  with  folds  of  the  mucous 
membrane  of  the  vagina.  The  broad  ligaments  contain  a  large  amount  of  unstriped 
muscle;  they  also  contain  a  large  lymph  gland  near  the  ovary.^  In  the  upper  part 
of  the  ligament  the  muscular  tissue  forms  a  rounded  band  termed  the  round  liga- 
ment. In  an  adult  sow  of  full  size  it  is  about  six  inches  (ca.  15  cm.)  long;  its 
anterior  end  forms  a  blunt  projection  and  posteriorly  it  ends  in  the  subserous 
tissue  at  the  internal  inguinal  ring.  The  medial  layer  of  the  broad  ligament  is 
continuous  with  the  lateral  ligament  of  the  bladder. 

The  vagina  is  about  four  or  five  inches  (ca.  10-12  cm.)  long  in  a  sow  of  medium 
size.     It  is  small  in  caliber,  and  has  a  thick  muscular  coat  which  consists  of  circular 

1  The  changes  m  form  and  position  of  the  uterus  during  pregnancy  are  similar  to  those  men- 
tioned later  in  the  case  of  the  bitch  (p.  613). 


GENITAL  ORGANS  OF  THE  SOW 


611 


fibers  between  two  layers  of  longitudinal  fibers.     The  mucous  membrane  is  plicated, 
and  is  intimately  united  with  the  muscular  coat. 

The  vulva  is  about  three  inches  (7.5  cm.)  in  length.  The  labia  are  thick  and 
are  covered  with  a  wrinkled  integument.  The  dorsal  commissure  is  rounded,  but 
the  ventral  one  is  produced  to  form  a  long  pointed  projection.  The  fossa  clitoridis 
is  nearly  an  inch  (ca.  2  cm.)  anterior  to  the  ventral  commissure.  Above  it  the 
glans  clitoridis  forms  a  pointed  projection,  from  which  a  mucous  fold  extends 
laterally  and  backward  on  each  side.  There  is  a  deep  central  depression  about 
half  way  between  the  fossa  clitoridis  and  the  external  urethral  orifice.  The  latter 
is  bounded  on  each  side  by  a  thick  fold  which  extends  backward  for  a  variable 


A^.^ 


'  \ 


\ 


Fig.  540. — Genital  Organs  of  Sow;  Dorsal  View.     The  Vulva,  Vagina,  and  Cervix  Uteri  are  Slit  Open. 
/,  Labium  vulvae;   ^,  glans  clitoridis;   S,  vulva;   4<  external  urethral  orifice;   5,  vagina;   .5',  cervix  uteri;  6,  corpus 
uteri;   7,  cornua  uteri,  one  of  which  is  opened  at  7'  to  show  folds  of  mucous  membrane;  8,  uterine  tube;  8',  abdominal 
opening  of  tube ;  9,9,  ovaries;   10,  ovarian  bursa;   11,   11,  broad  ligaments  of  uterus;   13,  urinary  bladder.     (From 
Leisering's  Atlas.) 


distance.     Lateral  to  this  fold  is  a  depression  in  which  the  ducts  of  vestibular  glands 
open. 

On  either  side  of  the  anterior  part  of  the  floor  of  the  vulva  there  is  a  cul-de-sac  and  a  deep 
groove  leading  back  from  it;  these  are  bounded  medially  by  a  longitudinal  fold.  Ductus  epo- 
ophori  (canals  of  Gartner)  may  be  found  openiiig  anterior  to  the  external  urethral  orifice. 

The  clitoris  is  long  and  flexuous;  its  glans  forms  a  pointed  projection  over  the 
fossa  clitoridis. 

The  urethra  is  about  three  inches  (ca.  7-8  cm.)  long.  Its  posterior  part  is  fused 
with  the  vagina  and  produces  a  corresponding  elevation  of  the  floor  of  the  latter. 

The  mammary  glands  are  usually  ten  or  twelve  in  number,  and  are  arranged 
in  two  rows,  as  in  the  bitch.     Each  teat  has  commonly  two  ducts. 


612 


GENITAL    ORGANS    OF   THE    BITCH 


GENITAL  ORGANS  OF  THE  BITCH 

The  ovaries  (Fig.  442)  are  small,  elongated-oval  in  outline,  and  flattened. 
The  average  length  is  a  little  less  than  an  inch  (ca.  2  cm.).  Each  ovar}^  is  commonly 
situated  a  short  distance  (ca.  1-2  cm.)  behind,  or  in  contact  with,  the  posterior  pole 
of  the  corresponding  kidney,  and  thus  lies  opposite  to  the  third  or  fourth  lumbar 
vertebra,  or  about  half  way  between  the  last  rib  and  the  crest  of  the  ilium.     The 

right  one  lies  between  the  right  part  of  the 
duodenum  and  the  lateral  abdominal  wall. 
The  left  one  is  related  laterally  to  the  spleen. 
Each  is  concealed  in  a  peritoneal  pouch,  the 
bursa  ovarii,  which  has  a  slit-like  opening 
ventrally.  The  two  layers  which  form  this 
pouch  contain  a  quantity  of  fat  and  unstriped 
muscle.  They  are  continued  to  the  cornu  of 
the  uterus,  constituting  the  mesosalpinx  and 
the  ligament  of  the  ovary.  The  surface  of 
the  ovary  presents  prominences  caused  by 
projecting  follicles.  Many  follicles  contain 
several  ova.     There  is  no  distinct  hilus. 

The  uterine  or  Fallopian  tubes  are  small 
and  average  two  or  three  inches  (ca.  5-8 
cm.)  in  length.  Each  passes  at  first  forward 
in  the  lateral  part  of  the  bursa  ovarii,  and 
then  runs  backward  in  the  medial  part  of 
the  pouch ;  it  is  only  slightly  flexuous.  The 
pouch  is  thus  a  part  of  the  mesosalpinx.  The 
fimbriated  extremity  lies  chiefly  in  the  bursa 
ovarii,  but  part  of  it  often  protrudes  through 
the  slit-like  opening  of  the  bursa  ovarii;  it 
has  a  rather  large  abdominal  opening.  The 
uterine  orifice  is  very  small. 

The  uterus  has  a  very  short  body  and 
extremely  long  narrow  horns.  In  a  bitch  of 
medium  size  the  body  is  about  an  inch  (ca. 
2-3  cm.)  and  the  cornua  five  or  six  inches 
(ca.  12-15  cm.)  long.  The  horns  are  of 
uniform  diameter,  are  nearlj^  straight,  and  lie 
entirely  within  the  abdomen.  They  diverge 
from  the  body  in  the  form  of  a  V  toward  each 
kidney.  Their  posterior  parts  are  united  by 
the  peritoneum.  The  neck  is  very  short  and 
has  a  thick  muscular  coat.  Dorsally  there 
is  no  line  of  demarcation  between  uterus  and 
vagina,  but  the  cervix  uteri  is  much  thicker 
than  the  vagina.  Ventrally  the  cervix  forms 
a  cylindrical  projection  which  lies  in  a  depression  of  the  vaginal  wall.  The  mucous 
membrane  of  the  uterus  has  long  uterine  glands  and  also  short  tubular  crypts. 

The  broad  ligaments  contain  much  fat  and  some  unstriped  muscle.  They  are 
much  wider  in  the  middle  than  at  either  end.  The  posterior  part  is  attached  to  the 
anterior  part  of  the  vagina.  The  round  ligaments  are  contained  in  the  free  edge  of 
folds  given  olT  from  the  lateral  face  of  the  broad  ligaments.  They  are  bands  of 
unstriped  muscle  and  fat.  Each  passes  through  the  inguinal  canal,  enveloped  by  a 
peritoneal  pouch  (processus  vaginalis).     A  ligamentous  fold  extends  forward  from 


Fig.  541. — Genital  Organs  of  Bitch. 
Vulva,  vagina,  and  uterus  (in  part)  are  slit 
open,  a,  Ovarian  bursa;  6,  same  opened  to  show 
the  right  ovary,  c;  d,  d,  horns  of  uterus;  e,  e',  body 
of  uterus;  /,  neck  of  uterus;  /',  external  uterine 
orifice;  ff,  vagina;  h,  hymen;  i,  vulva;  k,  external 
urethral  orifice;  I,  urinary  bladder;  m,  urethra; 
n,  7t,  labia  vulvse;  o,  fossa  clitoridis;  p,  central 
projection  of  fold  of  mucous  membrane  which  con- 
ceals the  clitoris.  (After  Ellenberger,  in  Leisering's 
Atlas.) 


GENITAL   ORGANS    OF   THE    BITCH  613 

the  bursa  ovarii  lateral  to  the  kidney  and  is  attached  to  the  abdominal  wall  at  the 
middle  of  the  last  rib. 

The  horns  of  the  gravid  uterus  present  dilatations,  the  ampullae,  which  contain  the 
foetuses,  and  are  separated  by  constrictions.  The  gravid  uterus  lies  on  the  ventral  abdominal  wall, 
and  toward  the  end  of  gestation  extends  forward  to  the  stomach  and  liver. 

The  vagina  is  relatively  long.  It  is  narrow  anteriorly,  and  has  no  distinct 
fornix.  The  muscular  coat  is  thick  and  consists  chiefly  of  circular  fibers.  The 
mucous  membrane  forms  longitudinal  folds.  The  canals  of  Gartner  are  usually 
absent. 

The  vulva  has  thick  labia  which  form  a  pointed  inferior  commissure.  The 
mucous  lining  is  smooth  and  red.  It  frequently  presents  small  prominences  caused 
by  lymph  follicles.  On  either  side  of  the  urethral  orifice  there  is  a  small  depression. 
The  glandulse  vestibulares  majores  are  absent,  but  the  smaller  glands  are  often 
present,  and  their  ducts  open  ventrally  on  either  side  of  a  median  ridge.  The 
vestibular  bulbs  are  relatively  large  and  are  commonly  united  ventrally  by  a  sort 
of  isthmus.  The  constrictor  muscle  is  strong  and  divides  into  two  layers  which 
enclose  the  vestibular  bulb.  The  body  of  the  clitoris  is  broad  and  flat,  and  is  about 
an  inch  and  a  half  (ca.  3-4  cm.)  long  in  a  subject  of  medium  size.  It  is  not  erectile 
in  structure,  but  is  infiltrated  with  fat.  It  is  enclosed  by  a  fibrous  albuginea  and 
contains  large  arteries  and  numerous  nerves  in  its  ventral  part.  The  glans  clitoridis 
is  composed  of  erectile  tissue  and  is  situated  in  a  large  fossa  clitoridis.  A  fold  of 
mucous  membrane  extends  backward  over  the  glans  and  fossa;  a  central  projection 
of  this  fold  may  be  mistaken  for  the  glans  clitoridis. 

The  mammary  glands  are  usually  ten  in  number,  and  are  arranged  in  two  series, 
extending  from  the  posterior  part  of  the  pectoral  region  to  the  inguinal  region;  they 
are,  therefore,  designated  according  to  location  as  pectoral,  abdominal,  and  inguinal. 
The  teats  are  short,  and  present  on  their  apices  six  to  twelve  small  orifices  of  the 
excretory  ducts. 


ANGIOLOGY 

Angiology  is  the  description  of  the  organs  of  circulation  of  the  blood  and  lymph 
— the  heart  and  vessels.  The  heart  is  the  central  hollow  muscular  organ  which 
functions  as  a  suction  and  force  pump;  the  differences  in  pressure  caused  by  its 
contraction  and  relaxation  determine  the  circulation  of  the  blood  and  lymph, 
It  is  situated  in  the  middle  mediastinal  space  of  the  thorax  and  is  enclosed  in  a  fibro- 
serous  sac — the  pericardium.  The  vessels  are  tubular  and  run  through  almost  all 
parts  of  the  body.  They  are  designated  according  to  their  contents  as  blood-  and 
lymph-vessels. 

THE  BLOOD-VASCULAR  SYSTEM 

The  blood-vascular  system  consists  of:  (1)  The  arteries,  which  convey  blood 
from  the  heart  to  the  tissues;  (2)  the  capillaries,  microscopic  tubes  in  the  tissues, 
which  permit  of  the  necessary  interchange  between  the  blood  and  the  tissues; 
(3)  the  veins,  which  convey  the  blood  back  to  the  heart. 

The  blood-vessels  are  divided  into  the  pulmonary  and  the  systemic.  The 
pulmonary  artery  conveys  the  blood  from  the  right  ventricle  of  the  heart  to  the 
lungs,  where  it  is  arterialized,  and  is  returned  by  the  pulmonary  veins  to  the  left 
atrium  of  the  heart,  and  passes  into  the  left  ventricle.  The  systemic  arteries 
conve}^  the  blood  from  the  left  ventricle  all  over  the  body,  whence  it  is  returned  by 
the  venae  cavae  to  the  right  atrium,  and  passes  into  the  right  ventricle.^ 

The  term  portal  system  is  often  applied  to  the  portal  vein  and  its  tributaries 
which  come  from  the  stomach,  intestine,  pancreas,  and  spleen.  The  vein  enters 
the  liver,  where  it  branches  like  an  artery,  so  that  the  blood  in  this  subsidiary 
system  passes  through  a  second  set  of  capillaries  before  being  conveyed  to  the  heart 
by  the  hepatic  veins  and  the  posterior  vena  cava. 

The  arteries  (Arteriae),  as  a  rule,  divide  at  an  acute  angle,  giving  off  finer 
and  finer  branches.  In  some  cases  branches  come  off  at  a  right  angle,  and  others 
are  recurrent,  i.  e.,  run  in  a  direction  opposite  to  that  of  the  parent  stem.  The 
intercommunication  of  branches  of  adjacent  arteries  is  termed  anastomosis.  Most 
commonly  the  connections  are  made  by  a  network  of  numerous  fine  branches  which 
constitute  a  vascular  plexus  (Plexus  vasculosus) .  Relatively  large  communicating 
branches  (Rami  communicantes)  occur  in  certain  places;  they  may  be  transverse 
or  in  the  form  of  arches.  Wide-meshed  networks  of  vessels  are  termed  retia  vas- 
culosa.  Terminal  or  end  arteries  are  such  as  form  isolated  networks,  i.  e.,  do  not 
anastomose  with  adjacent  arteries.  A  rete  mirabile  is  a  network  intercalated  in 
the  course  of  an  artery.  A  collateral  vessel  (Vas  collaterale)  is  one  which  pursues 
a  course  near  and  similar  to  that  of  a  larger  vessel. 

The  veins  (Venae)  are  in  general  arranged  like  the  arteries,  but  are  usually  of 
greater  caliber.  When  a  vein  accompanies  an  artery,  it  is  termed  a  vena  comitans 
or  satellite  vein  and  is  usually  homonymous;  in  many  places  two  veins  accompany 
a  single  artery.  The  primitive  venous  trunks  do  not  run  with  the  arteries,  and  most 
of  the  superficial  veins  (Venae  cutaneae)  pursue  independent  courses.  They  anas- 
tomose even  more  freely  than  the  arteries,  and  large  communicating  branches 
are  very  common.  Venous  plexuses  (Plexus  venosi)  occur  in  many  places.  Some 
veins  which  are  enclosed  by  dense  membranes  and  run  usually  in  bony  grooves  are 

^  It  should  be  noted,  however,  that  the  lungs  also  receive  arterial  blood  through  the  systemic 
bronchial  arteries.  This  blood  is  returned  in  part  by  the  bronchial  veins  to  the  right  atrium  (in- 
directly), in  part  by  the  pulmonary  veins  to  the  left  atrium. 

614 


ANGIOLOGY — THE   LYMPHATIC    SYSTEM  615 

termed  (venous)  sinuses;  their  wall  consists  of  endothelium  only;  examples  of 
this  are  the  sinuses  of  the  dura  mater  of  the  brain.  A  vein  which  connects  one  of 
these  sinuses  with  veins  outside  of  the  cranium  is  termed  an  emissarium. 

A  corpus  cavemosum  is  an  erectile  structure  which  consists  essentially  of 
intercommunicating  blood-spaces  enclosed  by  unstriped  muscle  and  fibro-elastic 
tissue.  These  spaces  (Cavernse)  are  lined  with  endothelium  and  contain  blood. 
Some  are  to  be  regarded  as  greatly  enlarged  capillaries,  since  minute  arteries  open 
into  them  and  they  are  drained  by  veins;  others  are  intercalated  in  the  course  of 
veins.  Distention  of  the  cavernse  with  blood  produces  the  enlargement  and  harden- 
ing of  the  corpus  cavernosum  which  is  termed  erection. 

Structure  of  Arteries. — The  wall  consists  of  three  coats.  The  external  coat 
or  adventitia  (Tunica  externa)  consists  chiefly  of  fibrous  connective  tissue.  In  the 
deeper  part  are  some  elastic  fibers,  and  in  some  arteries  there  are  also  longitudinal 
unstriped  muscle-fibers.  The  middle  coat  (Tunica  media)  is  composed  of  unstriped 
muscle  and  elastic  tissue  in  medium-sized  arteries.  In  small  vessels  there  is  chiefly 
muscular  tissue,  and  in  the  largest  trunks  almost  exclusively  elastic  tissue.  The 
internal  coat  or  intima  (Tunica  intima)  consists  of  a  layer  of  endothelial  cells,  resting 
on  an  elastic  membrane.  The  sheath  of  the  vessel  (Vagina  vasis)  is  a  condensation 
of  the  surrounding  connective  tissue,  and  is  attached  more  or  less  closely  to  the 
external  coat. 

Structure  of  Veins. — The  walls  of  veins  are  similar  in  structure  to  those  of 
the  arteries,  but  are  very  much  thinner,  so  that  veins  collapse  more  or  less  com- 
pletely when  empty,  while  arteries  do  not.  The  middle  coat  is  very  thin  and  con- 
sists to  a  large  extent  of  ordinary  fibrous  tissue.  The  internal  coat  is  also  less 
elastic  than  in  the  arteries.  In  many  veins  this  coat  forms  semilunar  valves,  the 
free  edges  of  which  are  directed  toward  the  heart.  They  are  most  numerous  in  the 
veins  of  the  skin  and  of  the  extremities  (except  the  foot),  while  in  most  veins  of  the 
body  cavities  and  viscera  they  are  absent  or  occur  only  where  the  veins  open  into 
larger  ones  or  where  two  veins  join. 

The  walls  of  the  vessels  are  supplied  with  blood  by  numerous  small  arteries, 
called  vasa  vasorum.  These  arise  from  branches  of  the  artery  which  they  supply 
or  from  adjacent  arteries,  ramify  in  the  external  coat,  and  enter  the  middle  coat 
also.  The  nerves  of  the  vessels  (Nervi  vasorum)  consist  of  both  meduUated  and 
non-medullated  fibers.  They  form  plexuses  around  the  vessels,  from  which  fibers 
pass  mainly  to  the  muscular  tissue  of  the  middle  coat. 


The  Lymphatic  System 

The  lymphatic  system  (Systema  lymphaticum)  is  subsidiary  to  the  venous 
part  of  the  circulatory  system,  from  which  it  arises  in  the  embryo.  It  consists  of 
the  lymph  vessels  and  glands. 

The  lymph  vessels  (Vasa  lymphatica)  contain  a  colorless  fluid,  the  lymph, 
which  contains  numerous  lymphocytes. ^  They  resemble  the  veins  in  structure 
but  have  thinner  walls  and  are  provided  with  more  numerous  valves.  The  vessels 
are  sacculated  opposite  the  segments  of  the  valves  and  have  a  characteristic  beaded 
appearance  when  distended.  The  collecting  lymph  vessels  do  not  usually  form  rich 
plexuses,  as  veins  often  do,  their  branching  is  more  limited  and  less  tree-like  than 
that  of  the  blood-vessels,  and  their  caliber  therefore  increases  less  from  the  periphery 
toward  their  termination.  All  of  the  lymph  is  ultimately  carried  into  the  venous 
system  by  two  trunks,  the  thoracic  duct  and  the  right  lymphatic  duct.     Almost  all 

1  The  term  chyle  is  often  applied  to  the  lymph  carried  by  the  efferent  vessels  of  the  intestine 
when  it  contains  products  of  digestion,  and  these  vessels  may  be  designated  accordingly  as  lacteals 
or  chyle 


616  ANGIOLOGY 

of  the  Ijaiiph  passes  through  at  least  one  group  of  lymph  glands  before  entering  the 
blood-vascular  system. 

The  lymph  glands  or  nodes  (Lymphoglandulse)  are  intercalated  in  the  course 
of  the  lymph  vessels.  They  vary  widely  in  size,  some  being  microscopic,  others 
several  inches  in  length.  In  form  they  may  be  globular,  ovoid  and  flattened, 
elongated,  or  irregular.  In  certain  situations  they  are  aggregated  into  groups, 
and  a  knowledge  of  the  position  of  these  and  the  territory  drained  into  them  is  im- 
portant. It  is  convenient,  when  possible,  to  indicate  their  position  with  regard  to 
arteries  on  the  course  of  which  they  are  placed.  In  color  they  are  usually  gray  or 
yellowish-brown  in  the  dead  subject,  pink  or  reddish-brown  during  life,  but  this 
varies  according  to  their  position  and  functional  state.  The  bronchial  glands 
are  often  blackened  by  infiltration  with  carbon.  The  mesenteric  glands  are  creamy 
or  white  while  the  chyle  is  passing  through,  but  pink  at  other  times.  Vessels 
which  carry  lymph  to  a  gland  are  called  afferent;  the  efferent  vessels  which  convey 
it  away  are  larger  and  fewer.  Each  gland  has  a  depression,  the  hilus,  at  which  the 
blood-vessels  enter  and  the  efferent  lymph  vessels  emerge. 

Lymph  nodules  or  follicles  (Noduli  lymphatici)  are  minute  masses  of  lymphoid 
tissue  which  occur  in  certain  mucous  membranes.  They  may  be  solitary,  as  in  the 
solitary  nodules  or  glands  of  the  intestine,  or  aggregated  into  masses  or  patches,  as 
in  the  tonsils  and  the  aggregate  glands  or  so-called  Peyer's  patches. 

The  lymph  nodule  or  follicle  is  the  unit  of  structure  of  the  lymph  gland.  It  consists 
essentially  of  an  artery  surrounded  by  a  reticulum  of  connective  tissue,  the  meshes  of  which 
contain  numerous  lymphocytes.  Surrounding  this  is  a  rich  plexus  of  lymph  vessels,  forming  the 
so-called  sinus,  enclosed  in  some  cases  by  a  fibrous  capsule.  The  gland  consists  of  a  mass  of 
follicles,  enclosed  in  a  fibrous  capsule,  from  which  trabeculae  pass  in  and  unite  the  follicles.  Be- 
neath the  capsule  is  the  peripheral  sinus,  which  consists  of  a  very  rich  plexus  of  lymph  vessels; 
to  this  the  afferent  vessels  pass  at  various  points  of  the  surface.  In  the  cortical  substance  the 
cells  are  in  rounded  masses,  the  cortical  nodules,  while  in  the  medullary  substance  they  lie 
around  the  arteries,  forming  the  so-called  medullary  cords.  The  medulla  is  redder  than  the  cor- 
tex, since  it  is  more  vascular;  it  contains  the  central  Ijrmph  sinuses,  which  have  a  similar  struc- 
ture to  the  peripheral  sinus. 

The  haemolymph  glands  differ  from  the  lymph  glands  in  color  and  structure. 
They  are  of  a  deep  red  color  or  even  black,  which  is  due  to  the  high  vascularity  of 
the  cortical  substance.  The  peripheral  sinuses  especially  are  greatly  developed 
and  contain  numerous  red  blood-cells.  There  is  no  clear  division  into  cortical  and 
medullary  substance,  and  the  trabecule  contain  smooth,  muscle-cells.  Some  have 
afferent  and  efferent  lymph  vessels  and  others  do  not.  They  resemble  the  spleen  in 
some  respects,  but  their  significance  is  not  yet  clear.  They  are  numerous  in  the  ox 
and  sheep,  much  fewer  in  the  dog,  and  apparently  are  absent  in  the  horse.  They 
occur  along  the  course  of  the  aorta,  in  the  perineal  fat,  at  the  portal  fissure,  and  with 
the  gastric  and  mesenteric  lymph  glands.  In  the  ox  they  are  also  found  under  the 
trapezius  muscle,  imder  the  skin  of  the  upper  part  of  the  flank,  and  in  other  places 
less  constantly. 

The  tissue  or  lymph  spaces  are  interstices  of  varying  size  between  cells  or  in 
the  meshes  of  connective  tissue.  They  contain  a  fluid  derived  from  the  blood- 
plasma,  which  is  usually  called  lymph.  They  are  drained  by  the  veins  and  lymph 
vessels.     The  large  serous  sacs  are  often  included  in  this  category. 

The  exact  relationship  between  the  lymphatic  capillaries  and  the  tissue  spaces  is  still  a  matter 
of  controversy.  It  is  held  by  some  that  the  lymph  vessels  are  in  direct  communication  with  the 
tissue  spaces,  while  others  maintain  that  the  lymphatics  are  complete  closed  tubes.  Communi- 
cation between  the  spaces  and  vessels  is  in  general  very  free.  Mall  has  shown  that  granules  in- 
jected into  the  hepatic  artery  are  returned  by  the  lymphatics  as  well  as  by  the  veins,  and  intra- 
muscular injections  will  enter  the  lymph  vessels  of  the  tendon  in  spite  of  the  absence  of  lymphatics 
in  muscle. 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE THE    HEART  617 

BLOOD-VASCULAR  SYSTEM  OF  THE  HORSE 
THE  PERICARDIUM  1 

The  pericardium  is  the  fibro-serous  sac  which  surrounds  the  heart,  and  also 
the  great  vessels  in  connection  with  it  to  a  greater  or  less  extent.  Its  form  is  in 
general  similar  to  that  of  the  heart.  The  fibrous  layer  is  relatively  thm,  but 
strong  and  inelastic.  It  is  attached  dorsally  to  the  large  vessels  at  the  base  of  the 
heart,  and  is  continued  in  part  up  to  the  longus  colli  muscle.  It  is  firmly  attached 
ventrally  to  the  middle  of  the  posterior  half  of  the  thoracic  surface  of  the  sternum. 
The  serous  layer  is  a  closed  sac,  surrounded  by  the  fibrous  pericardium,  and  invag- 
inated  by  the  heart.  It  is  smooth  and  glistening,  and  contains  a  small  amount  of 
clear  serous  fluid,  the  liquor  pericardii.  Like  other  serous  membranes,  it  may  be 
regarded  as  consisting  of  two  parts,  parietal  and  visceral.  The  parietal  part  lines 
the  fibrous  layer,  to  which  it  is  closely  attached.  The  visceral  layer  covers  the 
heart  and  parts  of  the  great  vessels,  and  is  therefore  also  termed  the  epicardium. 
The  serous  pericardium  is  composed  of  a  connective-tissue  membrane,  rich  in 
elastic  fibers,  and  covered  on  its  free  surface  by  a  layer  of  flat  mesothelial  cells. 

The  pericardium  is  covered  by  the  pericardiac  part  of  the  mediastinal  pleura 
(Pleura  pericardia),  and  is  crossed  laterally  by  the  phrenic  nerves.  Its  lateral 
surfaces  are  related  chiefly  to  the  lungs,  but  the  lower  part  is  in  partial  contact  with 
the  chest-wall.  On  the  left  side  the  area  of  contact  is  from  the  third  rib  to  the 
sixth  rib  and  intercostal  space.  On  the  right  side  the  contact  is  smaller  and  is 
chiefly  opposite  the  ventral  part  of  the  third  and  fourth  intercostal  spaces  and  inter- 
vening rib.  The  anterior  end  of  its  base  is  opposite  to  the  second  intercostal  space 
or  third  rib,  and  the  posterior  border  is  opposite  to  the  sixth  rib  and  space.  The 
base  is  related  to  the  great  vessels,  the  trachea  and  its  bifurcation,  the  bronchial 
lymph  glands,  the  oesophagus,  and  the  vagus,  left  recurrent,  and  cardiac  nerves. 

The  extent  of  contact  of  the  pericardium  with  the  lateral  wall  of  the  thorax  is  determined  by 
the  cardiac  notch  of  the  lung.  On  the  left  side  the  anterior  margin  of  the  notch  is  at  the  third 
rib  and  the  posterior  margin  is  at  the  sixth  rib  dorsally  and  sbith  intercostal  space  ventrally.  The 
greatest  height  of  the  notch  is  at  the  fourth  rib  and  intercostal  space,  where  it  is  a  handbreadth 
or  more  (ca.  10-12  cm.)  above  the  sternal  end  of  the  rib.  The  notch  is  quadrilateral,  but  much 
narrower  above  than  below.  On  the  right  side  the  notch  is  usually  triangular  and  is  much  smaller. 
Its  anterior  margin  begins  at  the  third  intercostal  space,  about  three  inches  (ca.  7-8  cm.)  above  the 
sternal  ends  of  the  third  and  fourth  ribs  and  runs  obliquely  to  the  sternal  end  of  the  third  rib.  The 
posterior  margin  begins  at  the  same  point  and  extends  to  the  ventral  end  of  the  fourth  intercostal 
space  or  of  the  anterior  border  of  the  fifth  rib. 

The  two  parts  of  the  serous  pericardium  are,  of  course,  continuous  with  each  other  at  the 
line  of  reflection  on  to  the  great  vessels.  The  latter  are  covered  in  varying  degree  by  the  visceral 
layer.  The  aorta  and  pulmonary  artery  are  enclosed  in  a  complete  common  sheath  as  far  as  the 
bifurcation  of  the  latter.  The  membrane  passes  inward  between  the  pulmonary  artery  and  the 
left  auricle,  and  is  continued  between  the  right  auricle  and  the  aorta,  thus  forming  the  transverse 
sinus  of  the  pericardium  (Sinus  transversus  pericardii).  The  posterior  vena  cava  is  covered 
on  the  right  and  ventrally  for  a  distance  of  an  inch  or  a  little  more  (ca.  3  cm.).  The  pulmonary 
veins  have  practically  no  serous  covering.  The  epicardium  is  closely  adherent  to  the  muscular 
tissue  of  the  heart,  but  is  attached  to  the  vessels  by  areolar  tissue  and  fat,  and  hence  is  easily  dis- 
sected off  them. 

THE  HEART 
The  heart  (Cor)  occupies  the  greater  part  of  the  middle  mediastinal  space. 
Its  shape  is  that  of  an  irregular  and  somewhat  flattened  cone.  It  is  attached  at 
its  base  by  the  great  vessels,  but  is  otherwise  entirely  free  in  the  pericardium.  It 
is  decidedly  asymmetrical  in  position,  about  two-fifths  being  to  the  right  of  the 
median  plane  and  three-fifths  to  the  left.  The  long  axis  (from  the  middle  of  the 
base  to  the  apex)  is  directed  ventrally  and  backward.  The  base  of  the  heart  (Basis 
cordis)  is  directed  dorsally  and  its  highest  part  lies  about  at  the  junction  of  the 

^  The  pericardium  is  described  before  the  heart,  since  it  must  be  examined  first  in  the  labor- 
atory. 


ms 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


dorsal  and  middle  thirds  of  the  dorso-ventral  diameter  of  the  thorax.  It  is  opposite 
to  the  lateral  wall  of  the  thorax,  from  the  second  intercostal  space  or  third  rib  to  the 
sixth  rib  or  intercostal  space. ^  The  apex  (Apex  cordis)  lies  centrally  above  the  last 
segment  of  the  sternum;  it  is  half  an  inch  or  less  (ca.  1  cm.)  above  the  sternum  and 
about  an  inch  (ca.  2-3  cm.)  from  the  sternal  part  of  the  diaphragm.  The  anterior 
border  (Margo  cranialis)  is  strongly  convex  and  curves  ventrally  and  backward; 
the  greater  part  is  parallel  with  the  sternum.  The  posterior  border  (Margo  cau- 
dalis)  is  much  shorter,  is  nearly  vertical,  and  is  opposite  to  the  sixth  rib  and  inter- 
costal space.     The  surfaces,  right  and  left  (Facies  dextra,  sinistra),  are  convex  and 


Lig.  arteriosum        Pulmonary  veins 


Brachiocephalic  trunk 


Left  auricle 


Coronary 
groove 


Left  longitudinal  groove 
Fig.  542. — Heart  op  Horse;  Left  View. 
The  dotted  line  indicates  the  line  of  reflection  of  the  serous  pericardiui 

not  been  removed. 


Hardened  in  situ 
1.     The  epicardium  and  subepicardial  fat  have 


are  marked  by  grooves  which  indicate  the  division  of  the  heart  into  four  chambers, 
the  two  atria  above  and  two  ventricles  below.  The  left  surface  (covered  by  the 
pericardium)  is  related  to  the  lower  third  of  the  chest-wall  from  the  third  to  the 
sixth  rib.  On  the  right  side  the  cardiac  notch  of  the  lung  is  smaller,  so  that  the 
area  of  relation  to  the  chest-wall  extends  from  the  third  to  the  fourth  intercostal 
space.- 

^  The  size  and  form  of  the  heart  vary  according  to  the  degree  of  its  contraction  and  relaxa- 
tion (systole  and  diastole).  In  subjects  which  have  been  bled  and  preserved  by  intravascular 
injection  of  formalin  solution  the  right  side  is  usually  fixed  in  diastole  while  the  left  is  more  or  less 
strongly  contracted.     The  base  may  extend  back  to"  the  seventh  rib. 

2  The  arrangement  in  this  regard  has  been  stated  at  greater  length  in  the  descriptions  of  the 
lungs  and  the  pericardium. 


THE    HEART 


619 


The  coronary  groove  (Sulcus  coronarius)^  indicates  the  division  between  the  atria 
and  the  ventricles.  It  almost  completely  encircles  the  heart,  but  is  interrupted  at 
the  origin  of  the  pulmonary  artery.  The  longitudinal  grooves,^  right  and  left, 
correspond  to  the  septum  between  the  ventricles.  The  left  longitudinal  groove 
(Sulcus  longitudinalis  sinister)  is  left-anterior  in  position.  It  begins  at  the  coronary 
groove,  behind  the  origin  of  the  pulmonary  artery,  and  descends  almost  parallel  to 
the  posterior  border.  The  right  longitudinal  groove  (Sulcus  longitudinalis  dexter) 
is  right-posterior  in  position.     It  begins  at  the  coronary  groove,  below  the  termina- 


Puhnonary  veins 


Pulmonary  artery 


Vena  azygos 


Carunary  groove 


Fig.  543. — Heart  of  Horse;  Right  View.     Hardened  in  situ. 

Line  of  reflection  of  serous  pericardium  dotted.     Epicardium  and  subepicardial  fat  have  not  been  removed  from  heart. 

Left  ventricle  is  considerably  contracted. 


tion  of  the  posterior  vena  cava  and  passes  toward  the  apex,  but  ends  about  an  inch 
and  a  half  (ca.  3-4  cm.)  above  the  latter.  Thus  the  two  grooves  do  not  meet. 
The  grooves  are  occupied  by  the  coronary  vessels  and  a  variable  quantity  of  fat. 

The  left  groove  is  opposite  to  the  fourth  rib,  and  the  right  one  is  opposite  to  the  fifth  inter- 
costal space  above  and  the  sixth  rib  below. 

Size  and  Weight. — The  average  weight  of  the  heart  is  about  nine  pounds 
(ca.  4  kg.)  and  is  about  0.7  per  cent,  of  the  body-weight.  There  is,  however, 
great  range  of  variation  in  apparently  normal  specimens. 

^  Also  termed  the  atrio-ventricular  or  auriculo-ventricular  groove. 
^  Also  termed  the  interventricular  grooves. 


620 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


As  might  be  expected,  race  horses  have  hearts  which  are  larger  than  the  average,  both  abso- 
lutely and  relatively.  In  fat  subjects  the  ratio  to  the  body-weight  may  be  about  0.4  per  cent.,  and, 
on  the  other  hand,  it  is  commonly  1  per  cent,  or  more  in  light  horses  which  are  not  fat. 

The  following  average  measurements  were  obtained  in  medium-sized  hearts: 

Sagittal  diameter  of  base 25  cm. 

Greatest  width  of  base 18  to  20  cm. 

Circumference  at  coronary  groove 65  to  70  cm. 

Distance  between  origin  of  pulmonary  artery  and  apex 25  cm. 

Distance  between  termination  of  posterior  vena  cava  and  apex IS  to  20  cm. 


Pulmonary  vein& 


Pulmonary 
veins 


Posterior  vena  cava 
Left  atrium 


Fig.  544. — Base  of  Heart  of  Horse  with  Large  Vessels:  Dorsal  View.     Specimen  Hardened  in  situ. 


The  Right  Atrium 

The  right  atrium  (Atrium  dextrum)^  forms  the  right-anterior  part  of  the  base 
of  the  heart,  and  lies  above  the  right  ventricle.  It  consists  of  a  sinus  venarum, 
into  which  the  veins  open,  and  an  auricle-  (Auricula  dextra).  The  latter  is  a  conical 
diverticulum  which  curves  around  the  right  and  anterior  surfaces  of  the  aorta,  its 
blind  end  appearing  on  the  left  side  in  front  of  the  origin  of  the  pulmonary  artery;  it 
is  the  most  anterior  part  of  the  heart. 

There  are  five  chief  openings  in  the  right  atrium.  The  opening  of  the  anterior 
vena  cava  (Ostium  venae  cavse  cranialis)  is  in  the  dorsal  part,  and  is  chiefly  opposite 
to  the  fourth  rib.     The  opening  of  the  posterior  vena  cava  (Ostium  vense  cavae 

^  Also  termed  the  right  auricle.  2  ^igQ  termed  the  auricular  appendix. 


THE    RIGHT   ATRIUM 


621 


caudalis)  is  at  the  posterior  part,  opposite  to  the  fifth  intercostal  space.  Between 
the  two  the  wall  pouches  upward  somewhat,  and  here  the  vena  azygos  opens.  The 
coronary  sinus  opens  ventral  to  the  posterior  vena  cava;  the  orifice  is  provided  with 
a  small  semilunar  valve  (V  alvula  sinus  coronarii) .  The  small  coronary  vein  has  a 
separate  opening  in  some  cases  close  to  that  of  the  coronary  sinus.  The  right 
atrio-ventricular  orifice  (Ostium  atrio-ventriculare  dextrum)  is  in  the  ventral  part, 


Orifice  of  vena  azygos 


Anterior  vena  cava 


Posterior  ___^ 

^ 

'^*^Wm^ 

vena  cava 

1^ 

Orifice  of 

J^az^^ 

i 

coronary  -^^ 
sinus 

l^^V^ 

Chordae 
tendinece 

,-- — ""^ 

^"l"^' 

m^ 


^^^ 


Fig.  545. — Right  Side  op  Heart  of  Horse  Opened  up  by  Removal  op  Greater  Part  op  Right  Wall.     Organ 

Hardened  in  situ. 
The  right  ventricle  was  in  diastole,     r,  Intervenous  crest;  V,  V,  tricuspid  valve;  P.  P,  papillary  muscles;  m,  m, 
moderator  bands.     Arrow  points  into  origin  of  pulmonary  artery.     The  crista  supraventricularis,  which  separates  the 
atrio-ventricular  orifice  from  the  conus  arteriosus,  is  shown  but  not  marked.      The  crista  terminalis  (unmarked)  is 
nearly  directly  dorsal  to  the  preceding. 


and  leads  into  the  right  ventricle.  In  addition  to  the  foregoing  there  are  several 
small  orifices  of  the  vense  cordis  parvse;  these  are  concealed  in  the  depressions 
between  the  musculi  pectinati. 

The  atrium  is  lined  with  a  glistening  membrane,  the  endocardium.  Its  walls 
are  smooth  except  on  the  right  and  in  the  auricle,  where  it  is  crossed  in  various 
directions  by  muscular  ridges,  the  musculi  pectinati.  Small  bands  extend  across 
some  of  the  spaces  enclosed  by  the  musculi  pectinati.     The  latter  terminate  above 


622 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


on  a  curved  crest,  the  crista  terminalis,  which  indicates  the  junction  of  the  primi- 
tive sinus  reuniens  of  the  embryo  with  the  atrium  proper,  and  corresponds  with  the 
sulcus  terminalis  externalh'.^  The  openings  of  the  venae  cavae  are  valveless.  A 
ridge,  the  intervenous  crest  (Crista  intervenosa),^  projects  downward  and  forward 
from  the  dorsal  wall  just  in  front  of  the  opening  of  the  posterior  vena  cava;  it 
tends  to  direct  the  flow  of  blood  from  the  anterior  vena  cava  to  the  atrio-ventricular 


Aurta 


Left  pulmonary  artery 
Right  pulmonary  artery 


Pulmonary  vein 

Posterior  vena  cava 


Fig.  546. — Left  Side  of  Heart  of  Hokse,  Opened  up  by  Removal  of  Part  of  Wall. 
A.S.,  Left  atrium;   Au.  s.,  left  auricle;  V,  V,  V,  bicuspid  valve;    V.  s.,  left  ventricle;   M,  M,  moderator  bands;  P, 
P,  papillary  muscles;  1,  2,  great  cardiac  vein  and  circumflex  branches  of  coronary  arteries;  3,  position  of  foramen  ovale 
of  foetus;   .^,  ^,  openings  of  pulmonary  veins  (chiefiy  cut  away) ;   5.  atrio-ventricular  orifice;    6,  arrow  points  toward 
aortic  orifice. 


opening.  The  fossa  ovalis  is  a  diverticulum  in  the  septal  wall,  at  the  point  of 
entrance  of  the  posterior  vena  cava,  bounded  laterally  by  a  concave  margin  (Limbus 
fossa?  ovalis) .  The  fossa  is  the  remnant  of  an  opening  in  the  septum,  the  foramen 
ovale,  through  which  the  two  atria  communicate  in  the  foetus. 

^  The  crista  terminalis  is  showii,  but  not  marked,  in  Fig.  545;  it  is  almost  opposite  (anterior) 
to  the  intervenous  crest.  The  sulcus  terminalis  is  commonly  indistinct  except  near  the  vense 
cavse. 

^  Also  termed  the  tubercle  of  Lower. 


THE    RIGHT   VENTRICLE 


623 


Although  called  a  fossa,  it  is  usually  a  deep  but  narrow  diverticulum  in  the  horse.  The 
interatrial  septum  is  very  thin  here,  and  in  some  cases  the  foramen  ovale  fails  to  close  entirely. 

The  Right  Ventricle 

The  right  ventricle  (Ventriculus  dexter)  constitutes  the  right-anterior  part  of 
the  ventricular  mass.  It  foE;^  almost  all  of  the  anterior  border  of  the  heart,  but 
does  not  reach  the  apex,  which  is  formed  entirely  by  the  left  ventricle.  It  extends 
from  the  third  rib  to  the  fourth  intercostal  space  on  the  left  side,  to  the  fifth  inter- 
costal space  on  the  right  side.  It  is  somewhat  triangular  in  outline,  and  is  crescentic 
in  cross-section.     Its  base  is  connected  largely  with  the  right  atrium,  with  which  it 


Pulmonarij  veins 
Pulmonary  artery  //i  1  \\ 


Anterior 


Right  coronary  ,  \ 
artery 

Tricuspid  cnli,  / 
Chorda!  tendincce 


Great  coronary 
\      ^vein 

«\y   Left  coronary 
'    _,  artery  {circum- 
'  Y  '    flex  branch) 
-&""  Bicuspid  valve 

Chordce  tendinecs 


Musculus 
"'    papillaris 

,-'  Moderator  band 


,,'  Lejt  ventricle 


Moderator  bamt 

Riijht  V,  Ntnde  ■- 

Right  coronary  artery  -'" 
Fig.  547. — Section  of  Heart  of  Horse. 
Specimen  hardened  in  situ  and  cut  nearly  at  right  angles  to  the  ventricular  septum.     The  left  ventricle  is  contracted, 
but  not  ad  maximum.      V.a.,  Segment  of  aortic  valve. 


communicates  through  the  right  atrio-ventricular  orifice;  but  its  left  part  projects 
higher  and  forms  the  conus  arteriosus,  from  which  the  pulmonary  artery  arises. 
Its  apex  is  two  inches  or  more  (ca.  5-6  cm.)  above  the  apex  of  the  heart.  On 
opening  the  cavity  it  is  seen  that  the  atrio-ventricular  orifice  and  the  cavity  of  the 
conus  arteriosus  are  separated  b}^  a  thick  rounded  ridge  (Crista  supraventricularis) . 
The  axis  of  the  cavity,  taken  from  this  ridge  to  the  apex,  forms  a  spiral  curve  down- 
ward and  to  the  right.  The  septal  wall  is  convex  and  faces  obliquely  forward  and 
to  the  right. 

The  right  atrio-ventricular  orifice  (Ostium  atrio-ventriculare  dextrum)  is  oval 
and  is  chiefly  opposite  to  the  fourth  and  fifth  ribs  and  the  intervening  space. ^  The 
plane  of  the  opening  is  oblique,  much  lower  in  front  than  behind. 

1  The  extent  of  the  atrio-ventricular  orifices,  of  course,  varies  with  the  phase  in  which  the  heart 
is  fixed.  In  subjects  which  are  preserved  by  intravascular  injection  of  formalin  solution  the  right 
side  of  the  heart  is  usually  in  diastole,  while  the  left  side  is  more  or  less  contracted. 


624 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


The  anterior  part  of  the  orifice  is  usually  only  about  an  inch  or  two  (ca.  3-5  cm.)  above  the 
level  of  the  ventral  end  of  the  first  rib,  while  the  posterior  part  is  four  or  five  inches  (ca.  10-12  cm), 
higher  than  the  sternal  end  of  the  fifth  rib. 

It  is  guarded  b}^  the  tricuspid  valve  (Valvula  tricuspidalis) ;  of  the  three  large 
cusps  of  this  valve,  one  is  between  the  atrio-ventricular  opening  and  the  conus 
arteriosus,  one  is  septal,  and  the  third  is  on  the  right  margin.  Small  intermediate 
cusps  intervene  between  the  large  ones.  The  peripheral  edges  of  the  cusps  are  at- 
tached to  the  fibrous  ring  at  the  atrio-ventricular  opening.  The  central  edges  are 
irregular  and  hang  down  into  the  ventricle;  they  give  attachment  to  chordae  ten- 
dinese.  The  auricular  surfaces  are  smooth.  The  ventricular  surfaces  are  rough  and 
furnish  attachment  to  interlacing  branches  of  the  chordae  tendineae.  The  valves 
are  folds  of  the  endocardium,  strengthened  by  fibrous  tissue  and  at  the  periphery 


Musculi  pectinati 


Aortic  valve  ^^/ 

Great  coronary 
vein 
Left  coronary 

artery 
Bicusjnd  valve  — 

Chordae  tendincce  ^-  — ' 

Papillary  m usch' - 


Musculi  pectinati 

I 


"•'Right  coronary 
artery 

Tricuspid  valve 
I  pillar  y  muscle 


Trahecul(e  carneoe 


.  Fig.  548. — Section  of  Heart  op  Horse.     Specimen  Hardened  in  situ. 
The  section  is  cut  nearly  at  right  angles  to  the  ventricular  septum,  and  is  viewed  from  the  right  and  posteriorly. 


by  muscular  fillers  also.  The  chordae  tendineae  are  attached  below  to  the  three 
musculi  papillares,  which  project  from  the  ventricular  wall;  superiorly  they 
divide  into  branches  which  are  inserted  into  the  ventricular  surfaces  and  the  free 
edges  of  the  valves.  Each  cusp  of  the  valve  receives  chordae  tendineae  from 
two  papillary  muscles.  Of  the  latter,  two  are  on  the  septum  and  the  third  and 
largest  springs  from  the  anterior  wall. 

The  pulmonary  orifice  (Ostium  pulmonale)  is  circular  and  is  situated  at  the 
summit  of  the  conus  arteriosus,  opposite  to  the  third  rib  and  intercostal  space. 

The  position  of  the  orifice  is  somewhat  variable.     Its  anterior  margin  may  not  be  quite  so 
far  forward  as  the  posterior  border  of  the  third  rib,  and  the  posterior  margin  is  often  opposite  to 


THE    LEFT    ATRIUM THE    LEFT    VENTRICLE  625 

the  fourth  rib.     It  is  commonly  about  three  or  four  inches  (ca.  6-9  cm.)  above  the  sternal  ends 
of  the  ribs. 

It  is  guarded  by  the  pulmonary  valve,  composed  of  three  semilunar  cusps 
(Valvulse  semilunares  arterise  pulmonalis);  of  these,  one  is  medial,  one  lateral, 
and  the  third  posterior.^  The  convex  peripheral  border  of  each  cusp  is  attached 
to  the  fibrous  ring  at  the  junction  of  the  pulmonary  artery  and  the  conus  arteriosus. 
The  central  border  is  free  and  concave.  Each  cusp  consists  of  a  layer  of  endo- 
cardium on  its  ventricular  surface,  a  continuation  of  the  inner  coat  of  the  artery  on 
its  arterial  surface,  and  an  intermediate  layer  of  fibrous  tissue.  The  edge  of  the 
conus  arteriosus  forms  three  arches  with  intermediate  projecting  angles  or  horns, 
to  all  of  which  the  cusps  are  attached;  and  the  artery  forms  opposite  each  cusp  a 
pouch,  the  sinus  of  the  pulmonary  artery.^ 

The  walls  of  the  ventricle  (except  in  the  conus  arteriosus)  bear  muscular  ridges 
and  bands,  termed  trabeculae  cameae.  These  are  of  three  kinds,  viz.,  (1)  ridges  or 
columns  in  relief;  (2)  musculi  papillares,  somewhat  conical  flattened  projections, 
continuous  at  the  base  with  the  wall  and  giving  off  the  chordae  tendineae  to  the 
tricuspid  valve;  (3)  moderator  bands  (Musculi  transversi  cordis)  which  extend 
from  the  septum  to  the  opposite  wall.  The  latter  are  partly  muscular,  partly 
tendinous,  and  vary  in  different  subjects.  The  strongest  one  is  usually  about 
midway  between  the  base  and  apex  and  extends  from  the  septum  to  the  base  of 
the  lateral  musculus  papillaris  (Fig.  547) .  It  is  considered  that  they  tend  to  prevent 
overdistention. 

The  Left  ATRroM 
The  left  atrium  (Atrium  sinistrum)^  forms  the  posterior  part  of  the  base  of  the 
heart.  It  lies  behind  the  pulmonary  artery  and  the  aorta  and  above  the  left 
ventricle.  The  auricle  (Auricula  sinistra)  *  extends  outward  and  forward  on  the  left 
side,  and  its  pointed,  blind  end  is  behind  the  origin  of  the  pulmonary  artery.  The 
pulmonary  veins,  usually  seven  or  eight  in  number,  open  into  the  atrium  behind 
and  on  the  right  side.  The  cavity  of  the  atrium  is  smooth,  with  the  exception  of 
the  auricle,  in  which  the  musculi  pectinati  are  present.  In  some  cases  there  is  a 
depression  on  the  septal  wall  opposite  the  fossa  ovalis,  bounded  above  by  a  fold 
which  is  the  remnant  of  the  valve  of  the  foramen  ovale  of  the  foetus.  The  left 
atrio-ventricular  opening  (Ostium  atrio-ventriculare  sinistrum)  is  situated  below 
and  in  front;  it  usually  appears  smaller  than  the  right  one  on  account  of  the  con- 
traction of  the  left  ventricle  in  the  dead  subject.  The  apertures  of  small  veins  of 
the  heart  are  found  in  the  spaces  enclosed  by  the  musculi  pectinati. 

The  number  and  the  arrangement  of  the  pulmonary  veins  are  variable.  They  may  be 
five  to  nine  in  number.  The  largest  vein  is  posterior;  it  is  formed  by  the  union  of  veins  from  both 
limgs.  Usually  three  veins  of  considerable  size,  which  lie  above  the  posterior  vena  cava,  enter 
close  together  on  the  right,  and  three  or  four  open  close  to  the  ridge  which  projects  from  the  roof 
at  the  base  of  the  auricle. 

The  Left  Ventricle 
The  left  ventricle  (Ventriculus  sinister)  forms  the  left  posterior  part  of  the 
ventricular  mass.  It  is  more  regularly  conical  than  the  right  ventricle,  and  its 
wall  is  much  thicker  except  at  the  apex.  It  forms  all  of  the  posterior  contour  of 
the  ventricular  part  and  the  apex  of  the  heart.  Its  base  is  largely  continuous  with 
the  left  atrium,  with  which  it  communicates  through  the  left  atrio-ventricular 
opening,  but  its  anterior  part  opens  into  the  aorta.  The  cavity  usually  appears 
smaller  than  that  of  the  right  ventricle  in  the  dead  subject,  on  account  of  the  greater 
contraction  of  its  wall.     It  is  almost  circular  in  cross-section. 

^  In  some  cases  there  are  four  cusps,  and  very  rarely  only  two. 
^  These  are  also  known  as  the  sinuses  of  Valsalva. 

^  Also  termed  the  left  auricle.  ■*  Also  termed  the  auricular  appendix. 

40 


626 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


The  left  atrio-ventricular  orifice  (Ostium  atrio-ventriciilare  sinistrum)  is 
chiefly  opposite  to  the  fifth  ril:)  and  intercostal  space. 

The  orifice  frequently  extends  back  opposite  to  the  sixth  rib,  and  its  anterior  margin  may 
be  opposite  to  the  posterior  border  of  the  fifth  rib.  It  is  about  four  inches  (ca.  10  cm.)  above  the 
sternal  end  of  the  fifth  rib.  The  plane  of  the  opening  is  somewhat  obhque,  and  is  higher  behind 
than  in  front. 

It  is  almost  circular  and  is  guarded  by  the  bicuspid  valve  ( Valvula  bicuspidalis)  .^ 
The  two  cusps  of  this  valve  are  larger  and  thicker  than  those  of  the  right  side  of  the 


Fig.  549. — Cross-section  op  Venthicular  Part  of  Heart  op  Horse. 
The  section  is  cut  about  5  cm.  from  the  coronary  groove.  The  ventricles  are  moderately  distended.  V.  d..  Right 
ventricle;  F.  s.,  left  ventricle;  6'.  w.,  ventricular  septum;  1,  1',  papillary  muscles  of  right  ventricle;  2,  large  moderator 
band  of  right  ventricle;  3,  3,  3',  papillary  muscles  of  left  ventricle;  4,  4',  moderator  bands  of  left  ventricle;  5,  descend- 
ing branch  of  left  coronary  artery  and  great  cardiac  vein;  6,  right  coronary  artery  and  small  cardiac  vein.  The  anterior 
septal  papillary  muscle  of  the  right  ventricle  is  not  visible,  and  the  right  one  of  the  left  ventricle  is  double. 


heart.  One  is  placed  in  front  and  separates  the  atrio-ventricular  and  aortic  open- 
ings. The  other  is  placed  behind  and  laterally  and  is  usually  divided  into  two  or 
three  parts. 

The  aortic  orifice  (Ostium  aorticum)  is  directed  upward  and  slightly  forward. 
It  is  chiefly  situated  opposite  to  the  fourth  rib  and  intercostal  space,  but  may  extend 
forward  to  the  third  space  or  backward  to  the  fifth  rib.  It  is  about  five  inches  (ca. 
12-13  cm.)  above  the  sternal  end  of  the  fourth  rib.-  It  is  guarded  by  the  aortic 
valve,  composed  of  three  semilunar  cusps  (Valvulse  semilunares  aortse);  one  cusp  is 

'  Also  termed  the  mitral  valve. 

^  It  may  be  noted  that  the  aortic  opening  is  partly  overlapped  laterally,  so  to  speak,  by  the 
orifice  of  the  pulmonary  artery. 


STRUCTURE    OF   THE    HEART  627 

anterior,  the  others  right  and  left  posterior.  They  are  similar  to  those  of  the  pul- 
monary valve,  but  are  much  stronger.  The  free  edge  of  each  contains  a  central 
nodule  of  fibrous  tissue  (Nodulus  valvulse  semilunaris).^ 

The  chordae  tendineae  are  fewer  but  larger  than  those  of  the  right  ventricle. 
There  are  two  large  musculi  papillares,  one  on  each  side;  they  are  usually  com- 
pound. The  moderator  Ijands  are  variable.  Commonly  two  larger  ones  (which  are 
often  branched)  extend  from  the  musculi  papillares  to  the  septum.  Smaller  ones 
may  be  found  in  various  places,  especially  at  the  apex.  The  other  trabeculse  are 
fewer  and  less  prominent  than  in  the  right  ventricle. 

The  interventricular  septum  (Septum  ventriculorum)  is  the  musculo-membran- 
ous  partition  which  separates  the  cavities  of  the  two  ventricles.  It  is  placed  ob- 
liquely, so  that  one  surface,  which  is  convex,  faces  forward  and  to  the  right,  and 
bulges  into  the  right  ventricle;  the  other  surface,  which  faces  into  the  left  ventricle, 


Origin  of  right  coronary  artery 


Cojius  arteriosus 


Pulmonary  orifice 


Right  atrio-ven- 
tricular  orifice 


Origin  of  left  cor<mary^  -^Mj^    ^^-.^^^^T^HB^  ''^"'^''  '"^^'' 


Left  atrio-ventricular 
orifice 


Fig.  550. — The  Bases  op  the  Ventricles  op  the  Heart  op  the  Horse. 

The  atria  have  been  removed  and  the  aorta  and  pulmonary  artery  cut  off  short.     The  right  ventricle  is  dilated  and  the 

left  ventricle  is  contracted,     p.v.,  Pulmonary  valve;  a.v.,  aortic  valve. 

is  concave  and  looks  backward  and  to  the  left.  The  greater  part  of  the  septum  is 
thick  and  muscular  (Septum  musculare) ,  but  the  upper  part  is  thin  and  membranous 
(Septum  membranaceum).  The  latter  intervenes  between  the  left  ventricle,  on 
the  one  hand,  and  the  right  ventricle  and  atrium,  on  the  other. 

Structure  of  the  Heart 

The  heart-wall  consists  mainly  of  peculiar  striped  muscle,  the  myocardium, 
which  is  covered  externally  by  the  visceral  part  of  the  serous  pericardium  or  epi- 
cardium,  and  is  lined  by  the  endocardium. 

The  epicardium  is  in  general  closely  attached  to  the  muscular  wall,  but  is 
loosely  attached  over  the  coronary  vessels  and  the  associated  subepicardial  fat. 
1  These  nodules  are  also  termed  the  corpora  Arantii. 


628  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

It  consists  of  a  layer  of  flat  polygonal  cells,  resting  on  a  membrane  of  white  and 
elastic  fibers. 

The  myocardium  consists  of  planes  of  fibers  arranged  in  a  somewhat  compli- 
cated manner.  The  muscular  tissue  of  the  atria  is  almost  completely  separated 
from  that  of  the  ventricles  by  the  fibrous  rings  around  the  atrio-ventricular  orifices. 

The  connection  between  the  musculature  of  the  atria  and  that  of  the  ventricles  is  established 
by  the  atrio-ventricxilar  bundle  (Fasciculus  atrio-ventricularis) .  This  begins  as  a  network  of 
fibers  about  the  opening  of  the  coronary  sinus  and  the  adjacent  atrial  wall.  The  fibers  con- 
verge to  a  flat,  irregular  mass  at  the  upper  border  of  the  ventricular  septum.  From  this  two  chief 
divisions  proceed.  One  of  these  descends  on  the  right  side  of  the  ventricular  septum  and  passes 
by  the  moderator  band  to  the  lateral  papillary  muscle.  The  other  branch  descends  on  the  left 
side  of  the  septum  and  ramifies  on  the  wall  of  the  ventricle.  The  left  branch  is  somewhat  diffi- 
cult to  follow,  since  it  is  thin  and  reticulate  and  is  covered  in  great  part  by  a  layer  of  ventricular 
muscle  fibers.  The  right  branch  is  subendocardial.  The  bundle  and  its  divisions  are  enclosed 
in  a  fibrous  sheath.  The  functional  importance  of  the  bundle  in  mediating  the  contraction 
wave  was  shown  by  Erlanger,  who  found  that  clamping  the  bimdle  caused  heart-block. 

In  the  atria  the  muscle  bands  fall  naturally  into  two  groups — superficial  and 
deep.  The  former  are  common  to  both  atria,  the  latter  special  to  each.  The 
superficial  or  common  fibers  for  the  most  part  begin  and  end  at  the  atrio-ventricular 
rings,  but  some  enter  the  interatrial  septum.  The  deep  or  special  bundles  also 
form  two  sets.  Looped  fibers  pass  over  the  atria  from  ring  to  ring,  while  annular 
or  spiral  fibers  surround  the  ends  of  the  veins  which  open  into  the  atria,  the  auricles, 
and  the  fossa  ovalis. 

The  muscular  wall  of  the  ventricles  is  much  stronger  than  that  of  the  atria. 
That  of  the  left  ventricle  is  in  general  about  three  times  as  thick  as  that  of  the  right 
one,  but  is  thin  at  the  apex.  The  superficial  fibers  are  attached  above  to  the  atrio- 
ventricular fibrous  rings  and  pass  in  a  spiral  toward  the  apex.  Here  they  bend 
upon  themselves  and  pass  deeply  upward  to  terminate  in  a  papillary  muscle  of  the 
ventricle  opposite  to  that  in  which  they  arose.  The  loops  so  formed  at  the  apex 
constitute  a  whorl,  the  vortex  cordis.  The  deep  fibers,  although  they  appear  to 
be  proper  to  each  ventricle,  have  been  shown  by  MacCallum  to  be  in  reality  almost 
all  common  to  both.  Their  arrangement  is  scroll-like.  They  begin  on  one  side, 
curve  around  in  the  wall  of  that  ventricle,  then  pass  in  the  septum  to  the  opposite 
side,  and  curve  around  the  other  ventricle.  There  is  a  layer  of  deep  fibers  which  is 
confined  to  the  basal  part  of  the  left  ventricle;  it  is  attached  to  the  left  atrio- 
ventricular ring. 

Four  fibrous  rings  (Annuli  fibrosi)  surround  the  orifices  at  the  bases  of  the 
ventricles.  The  atrio-ventricular  rings  separate  the  musculature  of  the  atria  from 
that  of  the  ventricles.  Those  which  surround  the  origins  of  the  pulmonary  artery 
and  aorta  are  festooned  in  conformity  with  the  attached  borders  of  the  valves. 
The  aortic  ring  contains  on  the  right  side  a  plate  of  cartilage  (Cartilago  cordis), 
which  frequently  becomes  more  or  less  calcified  in  old  animals.  Sometimes  a 
smaller  plate  is  present  on  the  left  side. 

The  endocardium  lines  the  cavities  of  the  heart  and  is  continuous  with  the 
internal  coat  of  the  vessels  which  enter  and  leave  the  organ.  Its  free  surface  is 
smooth  and  glistening  and  is  formed  by  a  layer  of  endothelial  cells.  The  latter 
rest  on  a  thin  layer  of  fibro-elastic  tissue,  which  is  connected  with  the  myocardium 
by  a  subendocardial  elastic  tissue  containing  vessels  and  nerves. 

Vessels  and  Nerves. — The  heart  receives  a  large  blood-supply  through  the  two 
coronary  arteries  which  arise  from  the  aorta  opposite  to  the  anterior  and  left  cusps 
of  the  aortic  valve.  Most  of  the  blood  is  returned  by  the  coronary  veins,  which 
open  into  the  right  atrium  by  the  coronary  sinus.^  A  few  small  veins  open  directly 
into  the  right  atrium,  and  others  are  said  to  open  into  the  left  atrium  and  the 
ventricles.     The  lymph-vessels  form  a  subepicardial  network  which  communicates 

^  These  vessels  will  be  described  later  in  their  systematic  order. 


THE   ARTERIES — THE    PULMONARY   ARTERY — ^THE   SYSTEMIC    ARTERIES         629 

through  stomata  with  the  cavity  of  the  pericardium.  There  is  a  less  distinct 
subendocardial  network.  The  vessels  converge  usually  to  two  trunks,  which  ac- 
company the  blood-vessels  in  the  grooves  and  enter  the  glands  at  the  bifurcation 
of  the  trachea.  The  nerves  are  derived  from  the  vagus  and  sympathetic  through 
the  cardiac  plexus. 


The  Arteries 
the  pulmonary  artery 

The  pulmonary  artery  (A.  pulmonalis)  springs  from  the  conus  arteriosus  at  the 
left  side  of  the  base  of  the  right  ventricle.  It  curves  upward,  backward,  and  medi- 
ally, and  divides  behind  the  arch  of  the  aorta  into  right  and  left  branches.  It  is 
related  in  front  to  the  right  auricle,  behind  to  the  left  auricle,  and  medially  to  the 
aorta.  It  is  enveloped  with  the  latter  in  a  common  sheath  of  the  visceral  laj'er  of 
the  serous  pericardium.  Near  the  bifurcation  it  is  connected  with  the  arch  of  the 
aorta  by  a  fibrous  band  about  half  an  inch  (ca.  1.2  cm.)  in  width;  this  is  the  liga- 
mentum  arteriosum  (Fig.  542),  a  remnant  of  the  large  ductus  arteriosus,  which 
conducts  most  of  the  blood  from  the  pulmonary  artery  to  the  aorta  in  the  foetus.^ 
The  artery  is  bulbous  at  its  origin,  and  forms  three  pouches,  the  sinuses  of  the 
pulmonary  artery,  which  correspond  to  the  cusps  of  the  pulmonary  valve.  Beyond 
this  it  gradually  diminishes  in  caliber. 

In  a  horse  of  medium  size  the  artery  is  about  seven  inches  (ca.  17-18  cm.)  long.  At  the 
origin  it  is  about  two  and  a  half  inches  (ca.  6-6.5  cm.)  in  width;  at  the  bifurcation  its  caliber 
is  about  one  and  a  haK  inches  (ca.  3.5-4  cm.).  The  wall  is  relatively  thin,  especially  at  the 
origin. 

The  right  branch  (Ramus  dexter)  of  the  pulmonary  artery  is  longer  and  a  little 
wider  than  the  left  one.  It  passes  over  the  forepart  of  the  left  atrium  and 
under  the  bifurcation  of  the  trachea  to  the  hilus  of  the  right  lung,  and  enters  the 
latter  below  the  right  bronchus.  In  the  lung  it  passes  to  the  ventro-lateral  side  of 
the  stem-bronchus  and  accompanies  it  to  the  base  of  the  organ.  The  branches 
correspond  to  the  ramification  of  the  bronchi.  The  left  branch  (Ramus  sinister) 
is  very  short.  It  passes  backward  and  enters  the  lung  below  the  left  bronchus.  Its 
branches  within  the  lung  are  arranged  like  that  of  the  right  one 


THE  SYSTEMIC  ARTERIES 

The  aorta  is  the  main  systemic  arterial  trunk.  It  begins  at  the  base  of  the  left 
ventricle  and  is  almost  median  at  its  origin.  Its  first  part,  the  ascending  aorta 
(Aorta  ascendens),  passes  upward  and  forward  between  the  pulmonary  artery  on 
the  left  and  right  atrium  on  the  right.  It  then  curves  sharply  backward  and  dor- 
sally,  inclines  somewhat  to  the  left,  forming  the  arch  of  the  aorta  (Arcus  aortae), 
and  reaches  the  ventral  surface  of  the  spine  at  the  eighth  or  ninth  thoracic  vertebra. 
After  passing  backward  along  the  ventral  aspect  of  the  bodies  of  the  vertebrae  and 
between  the  lungs,  it  traverses  the  hiatus  aorticus  and  enters  the  abdominal  cavity, 
where  it  lies  ventral  to  the  vertebral  bodies  and  the  psoas  minor,  just  to  the  left  of 
the  median  plane.  It  divides  under  the  fifth  lumbar  vertebra  into  the  two  internal 
iliac  arteries. 

From  the  bifurcation  a  small  vessel,  the  middle  sacral  artery  (A.  sacralis  media),  sometimes 
passes  backward  on  the  pelvic  surface  of  the  sacrum.  It  becomes  lost  in  the  periosteum  or  joins 
the  coccygeal  artery,  or  in  exceptional  cases  is  traceable  to  the  sphincter  ani  extemus. 

The  caliber  of  the  aorta  is  greatest  at  its  origin,  which  is  termed  the  bulbus 

1  There  is  a  depression  in  the  interior  of  the  artery  which  corresponds  to  the  attachment  of 
the  lig.  arteriosum,  and  in  some  cases  the  latter  has  a  very  small  lumen. 


630 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


aortae.  Here  is  forms  three  pouch-like  dilatations,  the  sinuses  of  the  aorta.  These 
correspond  to  the  cusps  of  the  aortic  valve,  and  the  coronary  arteries  arise  from  the 
left  posterior  and  anterior  sinuses.  At  the  arch  the  diameter  is  about  two  inches 
(ca.  5  cm.),  and  beyond  this  it  diminishes  rather  rapidly  in  width. 

It  is  convenient  to  divide  the  aorta  into  thoracic  and  abdominal  parts.  The 
thoracic  aorta  (Aorta  thoracica)  (Figs.  553,  554)  lies  within  the  pericardium  to  the 
point  of  attachment  of  the  ligamentum  arteriosum,  and  is  enclosed  with  the  pulmon- 
ary artery  in  a  prolongation  of  the  epicardium.  Beyond  this  it  is  between  the  two 
pleural  sacs.  It  is  crossed  on  the  right  by  the  oesophagus  and  trachea,  on  the  left 
by  the  left  vagus  nerve.     The  left  recurrent  nerve  winds  around  the  concavity  of  the 


Pulmonary  veins 


Right  branch  of 
■pulmonary 


Vena  azygos 


Great  coronary  vein 


Small  coronary  vein 


Bight  coronary  artery 


Veins  are  black,  arteries  white. 


Fig.  551. — Cardiac  Vessels  or  Horse;  Right  Side. 

The  circumflex  branch  of  the  coronary  artery  is  largely  concealed  by  the  great  coronary 
vein. 


arch  from  the  lateral  to  the  medial  side,  and  the  vena  azygos  and  thoracic  duct  lie 
along  the  dorsal  part  of  its  right  face.  The  trachea  causes  it  to  deviate  to  the  left, 
but  beyond  this  it  becomes  median.  The  abdominal  aorta  (Aorta  abdominalis) 
(Fig.  575)  is  related  dorsally  to  the  lumbar  vertebrae,  the  ventral  longitudinal 
ligament,  and  the  left  psoas  minor  muscle;  in  the  hiatus  aorticus  it  is  related  to  the 
cisterna  chyli.  On  its  right  is  the  posterior  vena  cava,  and  on  its  left  the  left  kidney 
and  ureter. 


BRANCHES  OF  THE  THORACIC  AORTA 
I.  CORONARY  ARTERIES 
The  two  coronary  arteries,  right  and  left,  are  distributed  almost  entirely  to 
the  heart,  but  send  some  small  twigs  to  the  origins  of  the  great  vessels. 

The  right  coronary  artery  (A.  coronaria  dextra)  arises  from  the  anterior  sinus 
of  the  aorta.     It  passes  forward  between  the  conus  arteriosus  and  the  right  auricle 


COMMON    BRACHIOCEPHALIC    TRUNK 


631 


to  the  coronary  groove,  in  which  it  curves  around  to  the  right  and  backward.  It 
then  descends  in  the  right  longitudinal  groove  almost  to  the  apex  of  the  heart.  It 
usually  gives  off  a  circiimflex  branch  as  it  turns  downward;  this  branch  (Ramus 
circumflexus)  passes  back  in  the  coronary  groove,  and  anastomoses  with  the  cor- 
responding branch  of  the  left  artery. 

The  left  coronary  artery  (A.  coronaria  sinistra)  arises  from  the  left  posterior 
sinus  of  the  aorta,  emerges  behind  the  origin  of  the  pulmonary  artery,  and  divides 
into  two  branches.     The  descending  branch  (Ramus  descendens)  passes  down  the 


Pulmonary  veins 


Right  coronanj 
artery 


Left  coronary  artery, 
descending  branch 

Great  coronary  vein 


Great  coronary  vein 


Left  coronary  artery, 
circumiiex  branch 


The  dotted  lii 


ARDiAC  Vessels  of  Horse;  Left  Side. 


indicate  part  of  the  left  coronary  artery  which  is  concealed  by  the  left  auricle.     The  ligamentum 
arteriosum  is  shown  but  not  marked. 


left  longitudinal  groove  toward  the  apex.  The  circumflex  branch  (Ramus  circum- 
flexus) runs  backward  in  the  coronary  groove,  in  which  it  winds  around  to  the  right 
side. 


2.  COMMON  BRACHIOCEPHALIC  TRUNK 

The  common  brachiocephalic  trunk  (Truncus  l^rachiocephalicus  communis)^ 
is  a  very  large  vessel  which  arises  from  the  convexity  of  the  arch  of  the  aorta  within 
the  pericardium.  It  is  directed  forward  and  upward.  Its  length  in  horses  of 
medium  size  is  usually  about  two  inches  (ca.  5  cm.),  but  it  is  sometimes  only  half 
an  inch  or  less  (ca.  1  cm.).  It  is  crossed  on  the  left  by  the  left  vagus  and  cardiac 
nerves,  and  the  left  recurrent  nerve  runs  between  it  and  the  trachea.  It  divides 
opposite  to  the  second  intercostal  space  or  third  rib  into  the  brachiocephalic  and 
left  brachial  arteries. 

The  brachiocephalic  artery  (A.  brachiocephalica)  is  directed  forward  and  some- 
what dorsally  in  the  anterior  mediastinum,  beneath  the  trachea.  Opposite  the 
first  rib  it  gives  off  the  bicarotid  trunk  and  is  continued  as  the  right  brachial  artery. 
The  latter  (A.  subclavia  dexter)  turns  ventrally  and  bends  around  the  anterior 
^  Also  known  as  the  anterior  aorta. 


632 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


border  of  the  first  rib  and  the  insertion  of  the  scalenus  muscle  above  the  brachial 
vein.  Its  course  and  branches  beyond  this  point  will  be  described  with  the  vessels 
of  the  thoracic  limb. 

The  left  brachial  artery  (A.  subclavia  sinistra)  is  longer  than  the  right  one  and 
rises  to  a  higher  level.  It  forms  an  almost  semicircular  curve,  the  concavity  being 
ventral.  It  is  related  medially  to  the  oesophagus,  trachea,  and  thoracic  duct; 
and  the  left  vagus,  phrenic,  and  cardiac  nerves  cross  under  its  origin.^  It  emerges 
from  the  thorax  like  the  artery  of  the  right  side.     There  is  thus  a  difference  at  first 


Fig.  553. — Topography  of  Thorax  of  Horse,  Left  Side,  after  Removal  of  Lung,  Pericardium,  and  Greater 
Part  of  Mediastinal  Pleura. 
1,  Right  ventricle;  1',  left  ventricle;  2,  right  auricle;  2',  left  auricle;  3,  pulmonary  artery;  3',  left  branch  of  3; 
4,  aorta;  5,  brachiocephalic  trunk;  6,  left  brachial  vessels;  7,  dorsal  artery;  7',  subcostal  artery;  8,  deep  cervical 
artery;  9,  vertebral  artery;  10,  internal  thoracic  artery;  11,  musculo-phrenic  artery;  12,  inferior  cervical  arterj';  13,  in- 
tercostal artery;  14,  bicarotid  trunk;  15,  common  carotid  arteries;  16,  anterior  vena  cava;  17,  thoracic  duct;  IS,  left 
vagus;  18',  oesophageal  continuations  of  vagi;  19,  left  recurrent  nerve;  20,  left  phrenic  nerve  (part  which  crosses  peri- 
cardium indicated  by  dotted  line) ;  21,  cardiac  nerve;  22,  sympathetic  trunk;  23,  great  splanchnic  nerve;  24,  oesophagus; 
25,  trachea;  26,  left  bronchus;  27,  pulmonary  veins;  28,  apical  lobe  of  right  lung;  29,  basal  border  of  left  lung  indicated 
by  dotted  hne;  30,  diaphragm;  30',  diaphragmatic  Hne  of  pleural  reflection;  31,  32,  external  and  internal  intercostal 
muscles;  33,  longus  colh;  34,  levator  costse;   35,  multifidus  dorsi. 


between  the  trunks  of  opposite  sides,  but  beyond  this  their  course  and  distribution 
are  similar. 

The  left  brachial  and  brachiocephalic  arteries  give  off  within  the  thorax  the 
dorsal,  deep  cervical,  vertebral,  and  internal  thoracic  arteries.  At  the  first  rib  each 
gives  off  the  external  thoracic  and  inferior  cervical  arteries. 

1.  The  dorsal  or  costo-cervical  artery  (A.  costo-cervicalis)  of  the  left  side 
passes  dorsally  across  the  left  face  of  the  trachea  and  oesophagus  toward  the  second 
intercostal  space.  The  right  artery  arises  usually  by  a  common  trunk  with  the 
deep  cervical,  crosses  the  right  face  of  the  trachea,  and  has  no  contact  with  the 
oesophagus.  Both  detach  small  branches  to  the  trachea,  mediastinal  lymph  glands, 
and  pleura,  and  on  reaching  the  longus  colli  divide  into  two  branches.     Of  these,  the 

^  In  some  cases  the  artery  is  too  low  to  touch  the  cesopbagus. 


COMMON    BRACHIOCEPHALIC   TRUNK 


633 


subcostal  artery  (A.  intercostalis  suprema)  is  the  smaller.  It  passes  backward 
along  the  lateral  border  of  the  longus  colli  with  the  sympathetic  trunk.  It  gives 
off  the  second,  third,  and  fourth  intercostal  arteries,  and  ends  at  the  fifth  space, 
where  it  anastomoses  with  the  first  aortic  intercostal  artery,  or  constitutes  the  fifth 
intercostal  artery,  or  dips  into  the  longissimus  muscle.  It  also  gives  off  spinal 
branches  and  twigs  to  the  longus  colli  and  the  pleura.  The  other  branch  (A. 
transversa  colli)  is  the  direct  continuation  of  the  trunk.     It  emerges  through  the 


Fig.  554. — Topography  of  Thorax  of  Horse,  Right  Side,  after  Removal  of  Lung,  Pericardium,  and  Greater 
Part  op  Mediastinal  Pleura. 
1,  Right  ventricle;  1',  left  ventricle;  2,  right  atrium;  2',  left  atrium;  3,  anterior  vena  cava;  4,  posterior  vena  cava 
5,  vena  azygos;  6,  phrenic  vein;  7,  aorta;  8,  right  coronary  artery;  9,  bronchial  artery;  9',  oesophageal  artery  and  vein 
10,  first  aortic  intercostal  artery  and  vein;  11,  right  pulmonary  artery;  12,  pulmonary  veins;  13,  right  brachial  vessels 
14,  dorsal  vessels;  14',  subcostal  vessels;  15,  deep  cervical  vessels;  16,  vertebral  vessels;  17,  inferior  cervical  artery 
18,  internal  thoracic  vessels:  18',  musculo-phrenic  artery;  19,  bicarotid  trunk;  20,  common  carotid  arteries;  21,  jugu- 
lar vein;  22,  thoracic  duct;  23,  right  vagus;  23',  oesophageal  continuations  of  vagi;  24,  right  recurrent  nerve;  25,  right 
phrenic  nerve  (part  which  crosses  pericardium  indicated  by  dotted  line);  26,  sympathetic  trunk;  27,  great  splanchnic 
nerve;  28,  oesophagus;  29,  trachea;  30,  right  bronchus;  31,  left  lung;  32,  basal  border  of  right  lung  indicated  by  dotted 
line;  33,  mediastinal  pleura;  34,  diaphragm;  35,  diaphragmatic  line  of  pleural  reflection;  36,  intercostal  muscle;  37, 
longus  colli;  38,  psoas;  39,  interspinous  ligament;  40,  supraspinous  ligament;  41,  funicular  part,  41',  lamellar  part,  of 
ligamentum  nuchae. 


dorsal  end  of  the  second  intercostal  space,  passes  across  the  longissimus  costarum  and 
longissimus  dorsi  toward  the  withers,  and  divides  into  several  diverging  branches. 
An  anterior  branch  passes  upward  and  forward  between  the  splenius  and  complexus 
and  anastomoses  with  branches  of  the  deep  cervical  artery;  the  others  ascend  on 
the  dorso-scapular  ligament  under  cover  of  the  serratus  ventralis  and  rhomboideus 
to  the  withers,  supplying  the  muscles  and  skin  of  this  region. 

The  left  dorsal  artery  sometimes  arises  with  the  deep  cervical  by  a  common  trunk;  this 
arrangement  is  usual  on  the  right  side,  and  there  may  be  a  common  stem  for  the  dorsal,  deep  cervi- 
cal and  vertebral  arteries.  Occasionally  the  artery  arises  from  the  brachiocephalic  trunk.  Some- 
times it  emerges  through  the  third  space.  The  subcostal  may  arise  independently  behind  the 
dorsal  or  from  the  deep  cervical  artery. 

2.  The  deep  or  superior  cervical  artery  (A.  cervicalis  profunda)  arises  in  front 
of  the  dorsal  or  by  a  common  trunk  with  it.     It  crosses  the  oesophagus  (left  side), 


634  BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 

the  trachea  (right  side),  and  the  longus  colli,  and  emerges  from  the  thoracic  cavity 
by  passing  through  the  space  behind  the  first  costo-transverse  articulation.^  In 
the  thorax  it  gives  off  a  small  mediastinal  branch  (A.  mediastini  cranialis)  to  the 
mediastinum  and  the  pericardium;  also  the  first  intercostal  artery  (A.  intercostalis 
prima),  a  very  small  vessel  which  passes  down  in  the  first  intercostal  space.  After 
leaving  the  thorax  the  artery  passes  upward  and  forward  on  the  spinalis  muscle 
and  the  lamellar  part  of  the  ligamentum  nuchas,  covered  by  the  complexus.  Its 
terminal  branches  anastomose  with  branches  of  the  occipital  and  vertebral  arteries 
in  the  region  of  the  axis.  Numerous  collateral  branches  are  detached  to  the  lateral 
muscles  of  the  neck,  the  ligamentum  nuchse,  and  the  skin,  and  anastomoses  occur 
with  the  dorsal  artery  also. 

3.  The  vertebral  artery  (A.  vertebralis)  arises  from  the  brachial  on  the  left 
side,  the  brachiocephalic  on  the  right;  it  begins  opposite  the  first  intercostal  space 
and  passes  upward  and  forward.  On  the  left  side  it  crosses  the  oesophagus,  on  the 
right,  the  trachea.  Emerging  from  the  thorax  it  passes  between  the  longus  colli 
mediall}^  and  the  scalenus  laterally,  under  the  transverse  process  of  the  seventh 
cervical  vertebra,  and  continues  along  the  neck  through  the  series  of  foramina  trans- 
versaria,  between  which  it  is  covered  by  the  intertransversales  colli. ^  Emerging 

Branches  of 
occipital  artery  ^  Vertebral  artery 


Fig.  55.5. — Vertebral  Artery  of  Horse.     (After  Sohmaltz,  Atlas  d.  Anat.  H.  Pferdes.) 

from  the  foramen  of  the  axis,  it  crosses  the  capsule  of  the  atlanto-axial  joint,  and 
joins  the  recurrent  branch  of  the  occipital  artery  under  cover  of  the  obliquus 
capitis  posterior.  At  each  intervertebral  foramen  a  spinal  branch  (Ramus  spinalis) 
is  given  off  which  enters  the  vertebral  canal  and  reinforces  the  ventral  spinal  artery. 
It  also  gives  off  series  of  dorsal  and  ventral  muscular  branches  (Rami  musculares). 
The  dorsal  branches  are  the  larger;  they  supply  the  deep  extensor  muscles  of  the 
head  and  neck,  and  anastomose  with  the  deep  cervical  and  occipital  arteries.  The 
ventral  branches  supply  chiefly  the  scalenus,  longus  colli,  intertransversales,  and 
rectus  capitis  ventralis  major.  The  artery  is  accompanied  by  the  vertebral  vein 
and  a  sympathetic  nerve  trunk  (Nervus  transversarius). 

4.  The  internal  thoracic  artery  (A.  thoracica  interna)  is  a  large  vessel  which 
arises  from  the  ventral  side  of  the  brachial  opposite  the  first  rib.  It  curves  down- 
ward and  backward,  being  at  first  on  the  medial  surface  of  the  rib,  and  then  crosses 
the  ventral  part  of  the  first  intercostal  space  and  passes  under  the  transversus 
thoracis  muscle.  It  runs  backward  under  cover  of  that  muscle  over  the  chondro- 
sternal  joints  to  the  eighth  costal  cartilage,  where  it  divides  into  musculo-phrenic 
and  anterior  abdominal  branches.  At  each  intercostal  space  two  collateral  branches 
are  detached.  The  intercostal  branches  (Rami  intercostales)  ascend  in  the  inter- 
costal spaces  and  anastomose  with  homonymous  descending  arteries.     The  ventral 

'  The  artery  sometimes  emerges  through  the  second  intercostal  space. 

-  In  some  cases  the  last  cervical  transverse  process  has  a  foramen  transversarium,  through 
which  the  artery  passes. 


THE    COMMON    CAROTID    ARTERY  635 

branches  detach  small  twigs  to  the  transversus  thoracis,  pleura,  and  pericardium, 
and  pass  out  between  the  costal  cartilages  as  perforating  branches  (Rami  perfor- 
antes)  to  supply  the  pectoral  muscles  and  skin,  anastomosing  with  the  external  tho- 
racic artery.  A  very  small  pericardiaco-phrenic  artery  (A.  pericardiaco-phrenica) 
ascends  in  the  mediastinum  on  the  left  side,  in  the  caval  fold  of  pleura  on  the  right 
side;  it  supplies  fine  twigs  to  the  pericardium  and  pleura  and  accompanies  the 
phrenic  nerve  to  the  diaphragm.  In  the  young  subject  it  gives  small  branches, 
the  thymic  arteries  (Aa.  thymicse),  to  the  thymus  gland.  The  musculo-phrenic 
or  asternal  artery  (A.  musculophrenica)  passes  along  the  groove  between  the  eighth 
and  ninth  costal  cartilages  and  continues  along  the  costal  attachment  of  the  trans- 
versus abdominis  (Fig.  275).  It  gives  off  intercostal  branches  which  anastomose 
with  those  descending  from  the  thoracic  aorta,  and  twigs  to  the  diaphragm  and 
transversus  abdominis.  The  anterior  abdominal  artery  (A.  epigastrica  cranialis) 
is  the  direct  continuation  of  the  internal  thoracic.  It  passes  between  the  ninth 
costal  cartilage  and  the  xiphoid  cartilage,  runs  backward  on  the  abdominal  surface 
of  the  rectus  abdominis,  and  then  becomes  embedded  in  the  muscle  (Fig.  590). 
It  supplies  the  ventral  wall  of  the  abdomen  and  anastomoses  with  the  posterior 
abdominal  artery. 

5.  The  external  thoracic  artery  (A.  thoracica  externa)  is  given  off  from  the 
ventral  aspect  of  the  brachial,  usually  at  the  medial  surface  or  anterior  border  of 
the  first  rib.  It  turns  around  the  first  rib  ventral  to  the  brachial  vein  (when  given 
off  within  the  thorax),  and  passes  backward  under  cover  of  the  deep  pectoral  muscle; 
it  is  continued  as  a  small  vessel  in  the  cutaneous  muscle,  where  it  accompanies  the 
external  thoracic  vein.  It  gives  branches  to  the  pectoral  muscles  and  the  axillary 
lymph  glands  and  terminates  in  the  cutaneous  muscle  and  the  skin  of  the  ventral 
wall  of  the  abdomen. 

This  artery  varies  in  origin  and  size.  Not  rarely  it  arises  from  the  internal  thoracic  or 
from  the  brachial  outside  of  the  thorax.  In  other  cases  it  arises  by  a  common  trunk  with  the 
inferior  cervical.  It  may  be  very  small  or  even  absent,  in  which  case  the  perforating  branches 
of  the  internal  thoracic  compensate. 

6.  The  inferior  cervical  artery  (Truncus  omo-cervicalis)  arises  usually  from 
the  dorsal  surface  of  the  brachial  artery  opposite  the  first  rib  or  where  that  vessel 
winds  around  the  rib.  It  is  directed  downward  and  a  little  forward  across  the 
lateral  surface  of  the  terminal  part  of  the  jugular  vein  and  the  deep  face  of  the 
scalenus  among  the  posterior  cervical  lymph  glands,  and  divides  into  ascending  and 
descending  branches.  The  ascending  branch  (A.  cervicalis  ascendens)  passes 
upward  and  forward  along  the  lateral  surface  of  the  jugular  vein,  then  turns  sharply 
backward  and  runs  upward  along  the  anterior  border  of  the  anterior  deep  pectoral 
muscle,  between  the  omo-hyoideus  and  brachiocephalicus  and  in  relation  to  the 
prescapular  lymph  glands;  it  gives  branches  to  these  muscles  and  the  posterior 
cervical  and  prescapular  lymph  glands.  The  descending  branch  (A.  transversa 
scapulae)  passes  ventro-laterally  across  the  surface  of  the  anterior  deep  pectoral  and 
then  runs  in  the  groove  between  the  anterior  superficial  pectoral  muscle  and  the 
brachiocephalicus  in  company  with  the  cephalic  vein.  It  supplies  branches  to  these 
muscles  and  the  skin  of  the  breast.^ 


THE  COMMON  CAROTID  ARTERY 

The  two  common  carotid  arteries  arise  from  the  brachiocephalic  artery  by  a 
common  trunk.  This  stem,  the  truncus  bicaroticus,  is  detached  from  the  medial 
face  of  the  brachiocephalic  opposite  the  first  rib  and  passes  forward  medially  on  the 
ventral  face  of  the  trachea.  It  is  related  ventrally  to  the  posterior  cervical  lymph 
glands,  the  terminal  parts  of  the  jugular  veins,  and  the  anterior  vena  cava,  and 
1  In  rare  cases  the  two  branches  arise  separately. 


636 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


laterally  to  the  vagus  and  recurrent  nerves.  It  is  commonly  two  or  three  inches 
(ca.  5-7  cm.)  in  length,  but  it  may  vary  between  one  and  eight  inches  (ca.  2.5- 
20  cm.).i 

The  right  common  carotid  artery  (A.  carotis  communis  dextra)  passes  obliquely 
from  the  ventral  face  of  the  trachea  to  its  right  side  and  continues  in  this  position, 
but  inclines  toward  the  dorsal  surface  of  the  trachea  near  its  termination.     It 


Fig.  556. — Vessels  and  Nerves  of  Neck  of  Horse. 
a,  Brachiocephalicus;  b,  sterno-cephalicus;  c,  omo-hyoideus;  d,  sterno-thyro-hyoideus;  e,  trachea;  /,  position  of 
cariniform  cartilage;  g,  anterior  superficial  pectoral  muscle;  h,  scalenus;  i,  intertransversales;  k,  insertion  of  serratus 
cervicis;  Z,  remnant  of  trapezius;  m,  rhomboideus;  n,  splenius;  o,  complexus;  p,  g,  longissimus  capitis  et  atlantis;  p',q', 
tendons  of  same;  r,  longissimus;  s,  obliquus  capitis  posterior;  t,  wing  of  atlas;  u,  parotid  gland;  v,  supraspinatus;  w, 
anterior  deep  pectoral ;  x,  spine  of  scapula;  2/,  prescapular  lymph  glands;  1,  external  maxillary  vein;  ^,  S,  jugular  vein; 
4,  carotid  artery,  exposed  by  drawing  jugular  vein  aside;  5,  6,  ascending  and  descending  branches  of  inferior  cervical 
artery;  7,  cephalic  vein;  S,  branches  of  deep  cervical  artery;  9-14,  ventral  branches  of  second  to  seventh  cervical  nerves; 
15,  branches  of  dorsal  divisions  of  cervical  nerves.      (EUenberger-Baum,  Top.  Anat.  d.  Pferdes.) 


divides  at  the  crico-pharyngeus  muscle  and  under  cover  of  the  mandibular  gland 
into  external  carotid,  internal  carotid,  and  occipital  arteries.-  It  is  enclosed  in  a 
fibrous  sheath,  and  is  accompanied  dorsally  by  the  vagus  and  sympathetic  nerves, 
ventrally  by  the  recurrent  nerve.     In  the  posterior  part  of  the  neck  it  is  in  contact 

1  In  very  rare  cases  there  is  no  truncus  bicaroticus.  The  two  carotid  arteries  then  arise 
separately  from  the  brachiocephaUc,  the  left  one  first,  and  the  right  one  an  inch  or  more  further 
forward. 

^  A  small  nodule  is  present  in  the  angle  of  division.  This  is  the  carotid  body  or  glomus  caro- 
ticum. 


THE    COMMON    CAROTID    ARTERY 


637 


superficially  with  the  jugular  vein,  but  further  forward  the  omo-hyoideus  muscle 
intervenes  between  the  arter}^  and  vein.  Near  its  termination  the  artery  becomes 
more  deeply  placed  and  is  related  laterally 
to  the  mandibular  and  parotid  glands,  medi- 
ally to  the  oesophagus.  In  some  cases  it  is  in 
contact  ventrally  with  the  lateral  lobe  of  the 
thyroid  gland,  especially  when  the  latter  is 
more  dorsally  situated  or  larger  than  usual. 
The  left  common  carotid  artery  (A. 
carotis  communis  sinistra)  differs  from  the 
right  one  in  that  it  is  related  deeply  to  the 
oesophagus  also,  which  usually  separates  it 
from  the  trachea  in  part  of  its  course. 

The  left  carotid  is  commonly  in  contact  with 
the  trachea  for  a  short  distance  (ca.  8-10  cm.)  at  the 
root  of  the  neck,  but  this  contact  may  be  even  less 
when  the  a?sophagus  is  more  ventral  than  usual  and 
the  bicarotid  trunk  long.  On  the  other  hand,  the  re- 
lation to  the  trachea  may  be  more  extensive. 

The  collateral  branches  of  the  common 
carotids  are  in  the  main  small.  They  com- 
monly comprise  the  following: 

1.  Muscular  branches  (Rami  muscu- 
lares)  of  variable  size  go  to  the  ventral 
muscles  of  the  neck  and  the  skin. 

2.  (Esophageal  and  tracheal  branches 
(Rami  cesophagei  et  tracheales).  Small 
twigs  go  to  the  cervical  lymph  glands  also. 

3.  The  parotid  artery  (A.  parotidea) 
comes  off  near  the  termination  and  enters 
the  ventral  part  of  the  parotid  gland.  It 
also  sends  twigs  to  the  adjacent  lymph 
glands,  and  sometimes  detaches  a  branch  to 
the  mandibular  gland.     It  is  inconstant. 

4.  The  anterior  thyroid  or  thyro-larjoi- 
geal  artery  (A.  thyreoidea  cranialis),  the 
largest  collateral  branch  of  the  carotid, 
arises  from  the  latter  two  or  three  inches 
before  it  divides.  It  curves  over  the  anterior 
ond  of  the  thyroid  gland,  into  which  it  sends 
several  branches.  It  gives  off  the  lar3mgeal 
artery  (A.  laryngea),  which  sends  branches 
to  the  external  muscles  of  the  larynx  and  the 
constrictors  of  the  pharynx,  passes  between 
the  cricoid  and  thyroid  cartilages,  and  sup- 
plies the  internal  muscles  and  the  mucous 
membrane  of  the  larynx.  A  small  pharyn- 
geal branch  (A.  pharyngea  ascendens)  runs 
upward  and  forward  to  the  crico-pharyn- 
geus,  and  supplies  twigs  to  the  posterior 
part  of  the  pharynx  and  the  origin  of  the 
oesophagus.     Small   innominate   twigs    are 

given  off  to  the  trachea,  the  oesophagus,  and  the  sterno-thyro-hyoideus  and  omo- 
hyoideus  muscles. 


Fig.  557. — Cross-section  of  Neck  op  Hobse, 
Passing  through  Fifth  Cervical  Ver- 
tebra; Anterior  View. 

a,  Branches  of  cervical  nerves;  a',  nuchal  fat; 
b,  intertransversalis  muscle;  c,  longissimus  mus- 
cle; d,  vertebral  artery;  e,  vertebral  vein;  /,  ner- 
vus  transversarius;  g,  spinal  accessory  nerve  (dor- 
sal division);  h,  recurrent  nerve;  i,  vago-sympa- 
thetic  trunk;  k,  tracheal  lymph  duct;  I,  body  of 
fifth  cervical  vertebra;  /',  transverse  process  of 
same;   m,  common  carotid  artery;   n,  jugular  vein; 

0,  deep  cervical  artery;  o',  satellite  vein  of  o; 
p,  spinal  cord;  q,  dura  mater;  r,  spinal  vein;  s, 
ligamentum  nuchse;  t,  rhomboideus  muscle;  u, 
splenius;  v,  complexus;  w,  multifidus;  x,  serratus 
cervicis;  ;/,  brachiocephalicus;  ?,  sterno-cephalicus; 

1,  rectus  capitis  ventralis  major;  $,  omo-hyoideus; 
3,  cutaneus;  4j  sterno-thyro-hyoideus;  5,  longus 
colli;  6,  7,  longissimus  capitis  et  atlantis;  8,  trape- 
zius; 9,  spinalis;  10,  oesophagus;  11,  trachea,  with 
cartilaginous  ring  {11'),  mucous  membrane  {11"), 
and  muscular  layer  {11'").  (After  Ellenberger, 
in  Leisering's  Atlas.) 


638 


BLOOD-YASCULAR    SYSTEM    OF   THE    HORSE 


In  some  cases  the  thyroid  and  h^rJ^lgeal  arteries  arise  from  the  carotid  separately  or  by  a 
short  common  stem.  A  laryngeal  branch  is  often  detached  from  the  carotid  in  front  of  the  thyro- 
larjmgeal  and  enters  the  larynx  with  the  anterior  la^3^lgeal  nerve.  The  pharyngeal  branch  fre- 
quently comes  directlj'  from  the  carotid. 


Fig.  558. — Deep  Dissection  of  Neck  of  Horse. 
a,  a,  Endsof  sterno-cephalicus;  b,  anterior  part  of  omo-hyoideus;  c,  sterno-thyro-hyoideus;  d,  trachea;  e,  oesopha- 
gus; /,  cariniform  cartilage;  g,  rectus  cap.  ventralis  major;  h,  stump  of  longissimus  atlantis;  i,  intertransversales;  k, 
multifidus;  /,  m,  scalenus;  n,  serratus  cervicis;  o,  o,  stumps  of  splenius;  p,  longissimus  cervicis;  g,  complexus  (most  of 
which  is  removed) ;  r,  rhomboideus;  s,  trapezius;  <,  spinalis  et  semispinalis;  m,  lamellar  part  of  lig.  nuchse;  d,  brachio- 
cephalicus;  it',  anterior  deep  pectoral;  i,  supraspinatus;  2/,  anterior  superficial  pectoral ;  z,  tuber  scapulse;  i ,  7 ,  articular 
processes  of  cervical  vertebrae;  2,  2,  transverse  processes  of  same;  3,  atlas;  3',  axis;  4>  4,  jugular  vein  (remainder  re- 
moved) ;  .5,  common  carotid  artery,  from  which  a  piece  is  removed  to  show  the  accompanying  nerves  and  the  CESophagus; 
6,  vago-sympathetic  trunk;  7,  7,  tracheal  and  muscular  branches  of  carotid  artery;  S,  recurrent  nerve;  10,  left  tracheal 
lymph-duct;  11,  12,  ascending  and  descending  branches  of  inferior  cervical  artery  {13) ;  H,  cephalic  vein;  15-20,  ven- 
tral branches  of  second  to  seventh  cervical  nerves;  21,  roots  of  phrenic  nerve;  22,  pectoral  nerves;  22',  nerve  to  ser- 
ratus ventraUs;  .23,  musculo-cutaneous  nerve;  ^4i  median  nerve;  ;25,  ulnar  nerve;  ^6,  radial  nerve;  .27,  axillary  nerve; 
28,  dorsal  branches  of  cervical  nerves;  28',  accessory  nerve  (cut) ;  29,  deep  cervical  artery;  30,  muscular  branch  of  ver- 
tebral arterj"  31,  posterior  branch  of  occipital  artery;  32,  vertebral  artery;  33,  muscular  branches  of  occipital  artery; 
34,  obliquus  capitis  post.;  35,  obi.  cap.  ant.;  36,  twig  from  dorsal  branch  of  third  cervical  nerve.  (After  EUenberger- 
Baum,  Top.  Anat.  des  Pferdes.) 


5.  The  posterior  thyroid  artery  (A.  thyreoidea  caudalis)  is  a  small  and  incon- 
stant vessel  which  arises  from  the  carotid  at  a  variable  distance  behind  the  anterior 
thyroid  or  from  the  latter  or  the  parotid  artery.  It  sends  branches  into  the  pos- 
terior part  of  the  thyroid  gland,  and  detaches  small  tracheal  and  muscular  twigs. 
In  some  cases  it  is  distributed  chiefly  or  entirely  to  the  adjacent  muscles. 


THE    OCCIPITAL    ARTERY 


G39 


THE  OCCIPITAL  ARTERY 

The  occipital  artery  (A.  occipitalis)  is  usually  the  second  in  size  of  the  terminals 
of  the  carotid.  It  arises  commonly  just  in  front  of  the  internal  carotid,  but  in  some 
cases  with  that  artery  by  a  common  trunk  of  variable  length.  It  pursues  a  some- 
what flexuous  course  to  the  fossa  atlantis,  where  it  divides  into  anterior  and  posterior 
branches.  It  is  related  superficially  to  the  mandibular  gland  and  the  brachio- 
cephalicus,  and  deeply  to  the  guttural  pouch  and  the  rectus  capitis  ventralis  major.'- 
The  internal  carotid  artery,  the 
ventral  cerebral  vein,  and  the  ac- 
cessory, vagus,  and  sympathetic 
nerves  cross  its  deep  face.  It 
gives  off  twigs  to  the  mandibular 
gland,  the  ventral  straight  mus- 
cles of  the  head,  the  guttural 
pouch  and  the  adjacent  lymph 
glands,  and  two  named  collateral 
branches.-  The  condyloid  artery 
(A.  condyloidea)  is  a  small  vessel 
which  passes  upward  and  forwartl 
on  the  guttural  pouch,  and  divides 
into  muscular  and  meningeal 
branches.  The  latter  enter  the 
cranium  through  the  foramen 
lacerum  and  hypoglossal  foramen 
and  are  distributed  to  the  dura 
mater.  This  artery  is  very  vari- 
able in  its  origin.^  The  posterior 
meningeal  artery  (A.  meningea 
aboralis)^  is  a  much  larger  vessel 
which  runs  upward  and  forward 
between  the  obliquus  capitis  an- 
terior and  the  paramastoid  proc- 
ess, passes  through  the  mas- 
toid foramen  into  the  temporal 
canal,  enters  the  cranial  cav- 
ity, and  is  distributed  to  the 
dura  mater.  It  gives  collateral 
branches  to  the  atlanto-occipital 
articulation  and  the  adjacent 
muscles. 

The  posterior  or  recurrent 

1  The  relation  to  the  guttural 
pouch  is  not  constant.  In  some  cases — 
especially  when  the  head  and  neck  are 
extended — the  artery  hes  behind  the 
pouch.  The  backward  extension  of  the 
latter  is  variable. 

-  The  branch  to  the  mandibular 
gland  (A.  gland ulaj  mandibularis  dor- 
salis)  may  come  from  the  external  caro- 
tid or  the  posterior  meningeal  artery. 

'  It  is  also  known  as  the  preverte- 
bral ;  it  often  comes  from  the  posterior 
meningeal  artery. 

*  Also  termed  the  mastoid  artery. 


Fig.  559. — Vessels  and  Nerves  of  Base  op^^s^  of  Horse. 
/iJ,  Cerebrospinal  artery;  /4,  ventral  spinal  artery;  ^o,  basilar 
artery;  16,  posterior  cerebellar  artery;  17,  anterior  cerebellar  ar- 
tery; 18,  internal  auditory  artery;  19,  posterior  cerebral  artery; 
'20,  deep  cerebral  artery;  21,  stump  of  internal  carotid  artery;  22, 
anterior  chorioid  artery;  23,  anterior  meningeal  artery;  24,  middle 
cerebral  artery;  25,  artery  of  corpus  callosum;  26,  anterior  com- 
municating artery;  /,  1',  1",  olfactory  striae;  1'",  olfactory 
tract;  2-12,  cranial  nerves;  a,  olfactory  bulb;  6,  trigonum  olfac- 
torium;  c,  lamina  perforata  anterior;  d,  fossa  lateralis;  e,  piri- 
form lobe;  /,  cerebral  peduncle;  g,  tractus  transversus;  h,  corpus 
mammillare;  ?',  tuber  cinereum;  k,  lateral  fissure  (of  Sylvius); 
I,  presylvian  fissure;  m,  pons;  o,  pyramid;  p,  facial  eminence; 
q,  corpus  restiforme;  r,  cerebellum;  s,  middle  peduncle  of  cerebel- 
lum.    (After  EUenberger-Baum,  Top.  Anat.  d.  Pferdes.) 


^40  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

branch  (Ramus  recurrens)^  of  the  occipital  passes  up  through  the  foramen  trans- 
versarium  of  the  atlas  and  joins  the  vertebral  artery.  It  gives  branches  to  the 
obliquus  capitis  posterior,  which  covers  it. 

The  anterior  or  occipital  branch  (Ramus  occipitalis)^  passes  through  the  alar 
foramen  of  the  atlas  and  supplies  the  muscles  and  skin  of  the  poll,  anastomosing 
with  the  deep  cervical  artery  and  its  fellow  of  the  opposite  side.  In  the  alar  furrow 
it  gives  off  the  cerebrospinal  artery  (A.  cerebrospinalis),  which  enters  the  spinal 
canal  through  the  intervertebral  foramen  of  the  atlas,  perforates  the  dura  mater, 
and  divides  into  cerebral  and  spinal  branches.  The  cerebral  branch  (Ramus 
cerebralis)  unites  with  that  of  the  opposite  side  to  form  the  basilar  artery,  and  the 
spinal  branch  (Ramus  spinalis)  similarly  forms  by  union  with  its  fellow  the  ventral 
spinal  artery. 

The  basilar  artery  (A.  basilaris  cerebri)  passes  forward  in  the  median  groove 
on  the  ventral  surface  of  the  medulla  oblongata  and  pons  and  divides  into  the  two 
posterior  cerebral  arteries.     The  collateral  branches  of  the  basilar  are: 

1.  Medullary  branches  (Rami  medullares),  ten  or  twelve  in  number,  dis- 
tributed to  the  medulla  oblongata. 

2.  Posterior  cerebellar  arteries  (Aa.  cerebelli  aborales),  which  pass  outward 
around  the  medulla  behind  the  pons  to  the  cerebellum,  to  which  they  are  distributed 
after  giving  twigs  to  the  medulla  and  pons. 

3.  The  small  auditory  artery  (A.  auditiva  interna)  accompanies  the  eighth 
nerve  to  the  internal  ear.     It  often  arises  from  the  posterior  cerebellar. 

4.  Anterior  cerebellar  arteries  (Aa.  cerebelli  orales).  These  are  very  variable 
in  number  and  origin.  There  are  often  two  or  three  on  either  side,  and  they  fre- 
quently arise  from  the  posterior  cerebral.  They  pass  outward  in  front  of  the  pons 
and  supply  the  anterior  part  of  the  cerebellum. 

The  posterior  cerebral  arteries  (Aa.  cerebri  aborales)  diverge  at  an  acute  angle 
and  join  the  posterior  communicating  branches  of  the  internal  carotid  arteries  on 
the  ventral  surface  of  the  cerebral  peduncles.  They  are  connected  by  a  transverse 
branch  and  by  a  network  of  fine  twigs  which  form  often  a  rete  mirabile. 

The  ventral  spinal  artery  (A.  spinalis  ventralis)  runs  along  the  ventral  median 
fissure  of  the  spinal  cord,  which  it  supplies.  It  is  reinforced  along  its  course  by 
branches  from  the  vertebral,  intercostal,  lumbar,  and  lateral  sacral  arteries,  which 
■enter  the  vertebral  canal  through  the  intervertebral  foramina. 


THE  INTERNAL  CAROTID  ARTERY  (Figs.  559,  561,  562) 

This  artery  (A.  carotis  interna)  is  usually  somewhat  smaller  than  the  occipital. 
It  usually  arises  just  behind  that  artery,  crosses  its  deep  face,  and  runs  upward  and 
forward  on  the  guttural  pouch  to  the  foramen  lacerum.^  It  is  closely  related  to 
the  vagus  nerve  and  the  anterior  cervical  ganglion  of  the  sympathetic  nerve,  fibers 
from  which  accompany  it.  It  is  crossed  laterally  by  the  ninth  and  twelfth  cranial 
nerves  and  the  pharyngeal  branch  of  the  vagus.  It  passes  through  the  ventral 
petrosal  sinus  and  enters  the  cavernous  sinus,  within  which  it  forms  an  S-shaped 
curve.  It  is  connected  mth  the  opposite  artery  by  a  transverse  branch,  the  inter- 
carotid  artery  (A.  intercarotica),  which  lies  in  the  intercavernous  sinus  behind  the 
pituitary  body.  A  branch  (A.  caroticobasilaris)  often  connects  it  with  the  basilar 
artery.  It  then  perforates  the  dura  mater,  gives  ofi  the  posterior  communicating 
artery,  and  passes  forward  and  divides  at  the  side  of  the  optic  chiasma  into  anterior 
and  middle  cerebral  arteries. 

The  posterior  communicating  artery  (A.  communicans  aboralis)  turns  back- 

1  Also  termed  the  retrograde  or  anastomotic  branch. 

2  Also  termed  the  musculo-occipital. 

^  Not  rarely  it  arises  with  the  occipital  artery  from  a  common  trunk  of  variable  length. 


THE  EXTERNAL  CAROTID  ARTERY  641 

ward  and  joins  the  posterior  cerebral  branch  of  the  basilar.  It  gives  off  the  deep 
cerebral  artery  (A.  cerebri  profunda),  which  winds  around  the  cerebral  peduncle 
and  is  distributed  chiefly  to  the  mid-brain;  it  is  often  double.  A  smaller  collateral 
branch  is  the  anterior  chorioid  artery  (A.  chorioidea  oralis),  which  passes  along  the 
optic  tract  and  is  distributed  in  the  chorioid  plexus  of  the  lateral  ventricle. 

The  anterior  cerebral  artery  (A.  cerebri  oralis)  unites  with  the  corresponding 
branch  of  the  opposite  artery  above  the  optic  chiasma.  From  this  junction  pro- 
ceeds the  artery  of  the  corpus  callosum  (A.  corporis  callosi),  which  turns  around  the 
genu  of  the  corpus  callosum,  enters  the  great  longitudinal  fissure,  divides  into  two 
branches,  and  is  distributed  to  the  medial  aspect  of  the  cerebral  hemispheres.  The 
anterior  cerebral  gives  off  the  small  internal  ophthalmic  artery  (A.  ophthalmica 
interna),  which  passes  forward  at  first  lateral  to  the  optic  nerve;  then,  crossing  over 
the  latter  to  its  medial  side,  it  joins  a  branch  of  the  external  ophthalmic.  A  small 
anterior  meningeal  branch  (A.  meningea  oralis)  of  the  anterior  cerebral  is  distributed 
to  the  anterior  part  of  the  dura,  and  assists  in  forming  a  network  in  the  ethmoidal 
fossa  (Rete  ethmoidale),  anastomosing  with  the  ethmoidal  branch  of  the  external 
ophthalmic  artery  and  the  artery  of  the  corpus  callosum. 

The  middle  cerebral  artery  (A.  cerebri  media)  passes  outward  in  the  fossa 
lateralis  in  front  of  the  piriform  lobe,  reaches  the  lateral  fissure,  and  divides  into 
branches  on  the  lateral  surface  of  the  hemisphere. 

The  circulus  arteriosus  (Fig.  559) ^  is  formed  at  the  interpeduncular  space  of 
the  base  of  the  brain  by  the  union  of  the  anterior  cerebral  arteries  in  front,  by  the 
diverging  posterior  cerebral  arteries  behind,  and  is  completed  laterally  by  the  junc- 
tion of  the  latter  with  the  posterior  communicating  arteries  and  by  the  internal 
carotid.  It  is  irregularly  polygonal  in  outline,  and  surrounds  the  optic  chiasma 
and  pituitary  body.- 


THE  EXTERNAL  CAROTID  ARTERY  (Figs.  561,  562) 

This  artery  (A.  carotis  externa),  by  its  size  and  direction,  constitutes  the  con- 
tinuation of  the  common  carotid.  It  passes  forward  on  the  lateral  wall  of  the 
pharynx  at  the  lower  border  of  the  guttural  pouch,  covered  by  the  mandibular 
gland  and  the  occipito-mandibularis,  digastricus,  and  stylo-hyoideus  muscles,  and 
in  relation  to  the  parapharyngeal  lymph  glands.  It  then  emerges  between  the  stylo- 
hyoideus  and  the  great  cornu  of  the  hyoid  bone,  ascends  on  the  latter  parallel  with 
the  posterior  border  of  the  lower  jaw,  and  terminates  about  two  inches  (ca.  5  cm.) 
below  the  temporo-mandibular  articulation  by  dividing  into  superficial  temporal 
and  internal  maxillary  branches.  It  is  crossed  deeply  near  its  origin  by  the  anterior 
laryngeal  and  pharyngeal  branches  of  the  vagus  nerve.  Just  before  its  emergence 
its  superficial  face  is  crossed  by  the  hypoglossal  nerve,  and  the  glosso-pharyngeal 
nerve  passes  over  its  medial  surface  at  the  ventral  border  of  the  great  cornu.  The 
chief  collateral  branches  are  the  masseteric,  external  maxillary,  and  posterior 
auricular.  It  also  furnishes  variable  branches  to  the  mandibular  and  parotid 
glands,  the  guttural  pouch,  and  the  pharyngeal  lymph  glands,  as  well  as  twigs  to 
some  adjacent  muscles. 

1.  The  masseteric  artery  (A.  masseterica)^  is  given  off  from  the  external 
carotid  at  its  emergence  from  beneath  the  stylo-hyoideus.  It  passes  downward 
and  slightly  forward  under  cover  of  the  parotid  gland  and  over  the  tendon  of  in- 
sertion of  the  sterno-cephalicus  to  the  posterior  border  of  the  mandible  and  appears 
on  the  masseter  muscle,  which  it  enters  after  a  short  course  on  its  surface.     It  gives 

1  Also  termed  the  circle  of  Willis. 

"^  The  cerebral  arteries  are  very  variable  in  arrangement,  and  the  foregoing  account  is  a  brief 
statement  of  the  more  usual  disposition  of  the  larger  vessels. 
^  Also  termed  the  maxillo-muscular. 
41 


542  BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 

branches  also  to  the  medial  pterygoid  and  occipito-mandibiilaris  muscles  and  the 
parotid  gland. 

2.  The  external  maxillary  artery  (A.  maxillaris  externa)^  arises  from  the  ex- 
ternal carotid  on  the  deep  surface  of  the  posterior  belly  of  the  digastricus  (Fig.  561). 
It  runs  downward  and  forward  on  the  lateral  wall  of  the  pharynx  across  the  deep  face 
of  the  stylo-hyoideus  toward  the  great  cornu  of  the  hyoid  bone,  accompanied  by 
the  glosso-pharyngeal  nerve  in  front  and  the  hypoglossal  nerve  behind.  After 
giving  off  the  lingual  artery  at  the  posterior  border  of  the  great  cornu,  it  inclines 
more  ventrally  on  the  medial  surface  of  the  medial  pterygoid  muscle,  crosses  over 
the  hyo-glossus  muscle,  the  hypoglossal  nerve,  the  mandibular  duct,  and  the  inter- 
mediate tendon  of  the  digastricus,  and  turns  forward  in  the  mandibular  space. 
Here  it  lies  on  the  lower  part  of  the  medial  pterygoid  muscle,  and  is  related  medially 
to  the  mandibular  lymph  glands,  above  to  the  anterior  belly  of  the  digastricus,  and 
below  to  the  homonymous  vein.  At  the  anterior  border  of  the  masseter  it  turns 
around  the  ventral  border  of  the  jaw  and  ascends  on  the  face  in  front  of  that 
muscle.  At  the  turn  the  artery  is  in  front,  the  vein  in  the  middle,  and  the  parotid 
duct  posterior.^  The  artery  is  conveniently  placed  at  its  inflection  for  taking  the 
pulse,  since  it  is  superficial  and  lies  directly  on  the  bone.  Beyond  this  point  it  is 
commonly  termed  the  facial  artery  (A.  facialis) .  The  artery  and  vein  pass  upward 
along  the  anterior  border  of  the  masseter,  under  cover  of  the  facial  cutaneus  and 
the  zygomaticus,  and  are  crossed  superficially  by  branches  of  the  facial  nerve  and 
deeply  by  the  parotid  duct.  The  artery  terminates  over  the  levator  labii  super- 
ioris  proprius  by  dividing  into  the  dorsal  nasal  and  the  angular  artery  of  the  eye. 
The  chief  branches  of  the  external  maxillary  are  as  follows: 

(1)  The  phar3mgeal  artery  (A.  palatina  ascendens)  arises  usually  behind  the 
stylo-pharyngeus,  passes  between  that  muscle  and  the  great  cornu,  and  runs  for- 
ward on  the  lateral  wall  of  the  pharynx  under  the  elastic  pharyngeal  fascia.  It  is 
distributed  to  the  pharynx,  soft  palate,  and  tonsil. 

(2)  The  lingual  artery  (A.  lingualis)  is  a  large  branch  which  diverges  from  the 
parent  trunk  at  an  acute  angle,  runs  along  the  ventral  border  of  the  great  cornu 
of  the  hyoid  bone,  and  dips  under  the  hyo-glossus  muscle.  It  then  passes  across 
the  kerato-hyoideus,  turns  inward  under  the  intercornual  joint  of  the  hyoid  bone, 
and  runs  forward  in  the  tongue  between  the  hyo-glossus  and  genio-glossus.  This 
part  (A.  profunda  linguie)  is  flexuous  and  is  accompanied  by  branches  of  the  hypo- 
glossal and  lingual  nerves.  It  is  the  chief  artery  of  the  tongue,  and  anastomoses 
with  the  opposite  artery  and  the  sublingual.^ 

(3)  The  sublingual  artery  (A.  sublingualis)  is  a  smaller  vessel  which  arises  at 
the  anterior  extremity  of  the  mandibular  gland  (Fig.  561).  It  passes  forward  on  the 
anterior  belly  of  the  digastricus,  between  the  ramus  of  the  mandible  and  the  mylo- 
hyoideus,  perforates  the  latter,  runs  along  the  lower  border  of  the  sublingual  gland, 
and  ramifies  in  the  mucous  membrane  of  the  anterior  part  of  the  floor  of  the  mouth. 
It  detaches  branches  to  the  muscles  and  skin  in  the  mandibular  space,  the  mandib- 
ular lymph  glands,  and  the  sublingual  gland.  It  also  gives  off  the  small  submental 
artery  (A.  submentalis),  which  runs  forward  superficially  toward  the  lower  lip, 
supplying  twigs  to  the  skin  and  the  mylo-hyoideus. 

In  some  cases  the  sublingual  artery  arises  from  the  lingual  and  the  submental  from  the 
external  maxillary.  Sometimes  the  sublingual  remains  on  the  superficial  face  of  the  mylo-hyoideus 
— thus  resembling  the  submental  of  man — and  the  subhngual  glan  1  is  supplier!  by  a  special 
branch  of  the  lingual. 

'  Also  termed  the  submaxillary  or  facial  artery.  The  term  facial  may  be  applied  to  the  artery 
after  it  reaches  the  lateral  surface  of  the  face. 

-  In  exceptional  cases  the  vein  is  in  front  of  the  artery. 

3  In  some  cases  the  lingual  trunk  runs  on  the  superficial  face  of  the  hyoglossus  instead  of 
passing  beneath  it;  in  such  specimens  a  small  branch  extends  forward  a  variable  distance  under 
the  muscle. 


THE  EXTERNAL  CAROTID  ARTERY 


643 


A  considerable  branch  may  be  given  off  in  the  mandibular  space,  which  turns  around  the 
lower  border  of  the  jaw  and  enters  the  middle  of  the  lower  part  of  the  masseter  muscle.  In  some 
cases  this  artery  is  of  large  size  and  its  pulsation  can  be  felt.     It  is  accompanied  by  a  vein. 

(4)  The  inferior  labial  artery  (A.  labialis  inferior)  arises  from  the  external 
maxillary  a  little  before  it  reaches  the  depressor  labii  inferioris  (Fig.  560).  It 
passes  forward,  dips  under  the  depressor  muscle,  and  continues  to  the  lower  lip. 
It  supplies  branches  to  the  muscles  and  skin  in  this  region,  to  the  inferior  buccal 
glands,  the  mucous  membrane  of  the  cheek,  and  the  lower  lip,  anastomosing  with 
the  mental  artery  and  the  corresponding  vessels  of  the  opposite  side.     It  detaches 


Fig.  560. — Superficial  Dissection  of  Head  op  Horse.  Most  op  the  Cutaneus  is  Removed. 
o,  Lateralis  nasi;  6,  levator  labii  superioris  proprius;  c,  levator  naso-labialis;  d,  dilatator  naris  lateralis;  e,  buc- 
cinator; /,  zygomaticus,  posterior  part  of  which  is  removed;  g,  depressor  labii  inferioris;  h,  stump  of  retractor  anguli 
oris;  i,  masseter;  k,  k,  scutularis;  /,  scutulo-auriculares  superficiales;  m,  zygomatico-auricularis;  n,  parotido-auricu- 
laris;  o,  occipito-mandibularis;  p,  sterno-cephalicus;  p',  tendon  of  p;  g,  omo-hyoideus;  r,  splenius;  s,  tendon  of  sple- 
nius  and  longissimus  capitis;  t,  corrugator  supercilii;  u,  orbicularis  oris;  v,  parotid  gland;  w,  zygomatic  arch;  x,  scuti- 
form  cartilage;  y,  upper  commissure  of  nostril;  /,  facial  nerve;  ^,  superior  buccal  nerve;  3,  inferior  buccal  nerve;  4< 
transverse  facial  nerve;  5,  cervical  branch  of  facial  "nerve ;  6,  posterior  auricular  branch  of  second  cervical  nerve;  7, 
cutaneous  cervical  branch  of  same;  5,  infratrochlear  nerve;  5,  frontal  nerve;  70,  lacrimal  nerve;  70',  end  of  auriculo- 
palpebral  nerve;  11,  masseteric  artery  and  vein;  IS,  transverse  facial  artery  and  vein;  13,  facial  artery;  14,  inferior 
labial  artery;  15,  superior  labial  artery;  16,  lateral  nasal  artery;  17,  dorsal  nasal  artery;  18,  angular  artery  of  the  eye; 
i5,  posterior  auricular  artery;  ;?0,  ^7,  jugular  vein;  ^^,  external  maxillary  vein;  23,  great  auricular  vein;  24,  parotid 
duct;  24',  origin  of  same;  2.5,  superior  buccal  glands;  26,  facial  vein.   (After  EUenberger-Baum,  Top.  Anat.  d.  Pferdes.) 


a  ]:)ranch  (A.  anguli  oris)  to  the  angle  of  the  mouth,  which  anastomoses  with  the 
superior  labial. 

(5)  The  superior  labial  artery  (A.  labialis  superior)  arises  from  the  facial  in 
front  of  the  facial  crest  (Fig.  560) .  It  passes  forward  under  the  dilatator  naris  lat- 
eralis and  levator  nasolabialis  to  the  upper  lip,  gives  twigs  to  the  upper  part  of  the 
cheek  and  the  lateral  nasal  region,  and  ramifies  in  the  upper  lip,  anastomosing  with 
the  opposite  artery  and  the  palato-labial. 

(6)  The  lateral  nasal  artery  (A.  lateralis  nasi)  arises  usually  a  little  above  the 
preceding  one,  and  runs  forward  parallel  with  it  and  under  the  levator  nasolabialis 
to  the  nostril  (Fig.  560).  It  supplies  branches  to  the  lateral  nasal  region  and  the 
nostril. 


644 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


The  vessel  is  often  double.  It  may  arise  from  the  superior  labial  at  the  point  of  bifurcation 
of  the  facial  or  with  the  dorsal  nasal  from  the  infraorbital  artery  (as  in  the  ox).  In  some  cases 
it  gives  off  a  dorsal  nasal  branch. 

(7)  The  dorsal  nasal  artery  (A.  dorsalis  nasi)  arises  on  the  levator  labii  superi- 
oris  proprius  and  passes  forward  under  the  levator  nasolabialis  to  the  dorsum  nasi 
(Fig.  560). 

(8)  The  angular  artery  of  the  eye  (A.  angularis  oculi)  runs  toward  the  medial 


Fig.  561. — Parotid,  Masseteric,  and  Lingual  Regions  of  Horse;  Deep  Dissection,  Third  Layer. 
a,  Mylo-hyoideus,  anterior  part,  reflected;  h,  genio-hyoideus;  c,  genio-glossus;  d,  sublingual  gland;  e,  ramus  of  man- 
dible, greater  part  removed;  e',  stump  of  masseter;  /,  maxillary  tuberosity;  g,  great  cornu  of  hyoid  bone;  h,  wing  of  atlas; 
i,  intermediate  tendon  of  digastricus;  i',  anterior  belly,  i",  posterior  belly,  of  digastricus;  k,  posterior  part  of  mylo- 
hyoideus;  I,  hyo-glossus;  to,  pterygoideus  medialis  (cut);  );,  stylo-hyoideus;  o,  occipito-mandibularis;  p,  crico- 
pharyngeus;  g,  obliquus  capitis  ant. ;  r,  tendon  of  longissimus  atlantis;  s,  rectus  cap.  ventralis;  t,  brachioeephalicus 
(cut) ;  M,  sterno-cephalicus  (cut);  v,  sterno-thyroideus  (cut) ;  tf,  sterno-hyoideus  (cut);  x,  omo-hyoideus;  y.  obliquus 
cap.  post.;  2,  splenius  (cut) ;  1-4^,  upper  cheek  teeth;  4'<  last  cheek  tooth;  5,  stump  of  facial  nerve;  6,  stump  of  bucci- 
nator nerve;  7,  lingual  nerve;  7',  superficial  branch,  7",  deep  branch,  of  hngual  nerve;  8,  stumps  of  inferior  alveolar 
artery,  vein  and  nerve;  9,  mylo-hyoid  nerve  (cut) ;  10,  glosso-pharyngeal  nerve;  11,  hypoglossal  nerve;  12,  anterior  larjTi- 
geal  nerve;  13,  ventral  branch  of  first  cervical  nerve;  14,  vagus  and  sympathetic;  15,  dorsal  branch  of  spinal  accessory 
nerve;  76,  ventral  branch  of  same;  i 7,  ventral  cerebral  vein;  75,  mandibular  duct;  ^S,  common  carotid  artery;  20, 
parotid  branch;  SI,  thyro-laryngeal  artery;  22,  pharyngeal  artery;  23,  laryngeal  artery;  24,  internal  carotid  artery; 
25,  occipital  artery;  26,  external  carotid  artery;  27,  31,  external  maxillary  artery;  28,  pharyngeal  artery;  29,  lingual 
artery;  30,  sublingual  artery;  32,  external  carotid  artery  after  emergence;  33,  internal  maxillary  vein  (origin);  34, 
remnant  of  parotid  gland;  35,  thyroid  gland;  36,  jugular  vein;  37,  parapharyngeal  lymph  glands.  (After  Ellen- 
berger-Baum,  Top.  Anat.  d.  Pferdes.) 


canthus  of  the  eye,  where  it  anastomoses  with  the  oYbital  branch  (Ramus  malaris) 
of  the  infraorbital  artery  (Fig.  560). 

In  addition  to  the  preceding,  unnamed  branches  are  supplied  to  the  mandibu- 
lar salivary  gland  and  lymph  glands.  There  is  commonly  a  branch  of  considerable 
size  which  is  given  off  as  the  external  maxillary  artery  passes  the  anterior  end  of  the 
mandibular  gland ;  it  runs  upward  and  backward  along  the  dorsal  border  of  the 
gland,  which  it  supplies. 

3.  The  posterior  auricular  artery  (A.  auricularis  posterior)  arises  at  an  acute 
angle  from  the  external  carotid  just  above  the  origin  of  the  masseteric.     It 


THE  EXTERNAL  CAROTID  ARTERY  645 

upward  under  cover  of  the  parotid  gland,  to  which  it  gives  branches,  and  divides 
into  several  branches  which  supply  the  skin  and  muscles  of  the  external  ear  (Fig. 
560).  The  posterior  branch  passes  to  the  posterior  part  of  the  base  of  the  ear, 
where  it  divides  into  two  branches;  of  these,  one  (Ramus  intermedins)  passes  up  the 
convex  surface  of  the  external  ear  to  the  apex,  while  the  other  (Ramus  medialis) 
winds  around  to  the  anterior  (medial)  border,  and  forms  an  arch  with  the  inter- 


FiG.  562. — Deep  Dissection  of  Head  of  Horse. 
The  left  ramus  of  the  mandible  and  structures  connected  with  it  have  been  removed,  a,  a.  Stumps  of  styloglossus; 
6,  genio-glossus;  c,  genio-hyoideus;  d,  omo-hyoideus;  e,  kerato-hyoideus;  /,  thyro-hyoideus;  g,  thyro-pharyngeus; 
/i,  crico-thyroideus;  i,  sterno-thyroideus;  A;,  thyroid  gland;  m,  crico-pharyngeus;  «,  palatinus  and  palato-pharyngeus; 
o,  pterygoideus  lateralis;  p,  tensor  palati;  g,  levator  palati;  r,  temporalis;  s,  rectus  cap.  ventralis  major;  t,  obliquus 
cap.  ant.;  u,  guttural  pouch;  v,  great  cornu  of  hyoid  bone,  extremity  of  which  is  removed  and  indicated  by  dotted  line; 
w,  position  of  small  cornu,  dotted  line;  i,  thyroid  cornu;  2/,  tongue;  z,  anterior  pillar  of  soft  palate;  ^ ,  superficial  tem- 
poral nerve;  2,  chorda  tympani;  9,  stump  of  inferior  alveolar  nerve;  4,  4,  lingual  nerve,  intermediate  part  removed;  5, 
deep  temporal  nerve;  6,  masseteric  nerve;  7,  buccinator  nerve;  8,  great  palatine  nerve;  9,  infraorbital  nerve;  10, 
sphenopalatine  and  posterior  nasal  nerves;  11,  spinal  accessory  nerve;  12,  vagus;  13,  pharyngeal  branch  of  vagus; 
14,  anterior  laryngeal  nerve;  lo,  vago-sympathetic  trunk;  16,  sympathetic,  with  anterior  cervical  ganglion  a  little  fur- 
ther back;  17,  glosso-pharyngeal  nerve;  18,  pharyngeal  and  19,  lingual,  branches  of  glosso-pharyngeal ;  20,  hypoglossal 
nerve;  ^/,  left  recurrent  nerve;  .2^,  common  carotid  artery;  ^3,  parotid  branch;  ^-^,  anterior  thyroid  or  thyro-laryngeal 
artery;  ;?4'.  l^^ryngeal  artery;  .25,  occipital  artery;  .25,  internal  carotid  artery;  ^7,  external  carotid  artery;  28,  30,  ex- 
ternal  maxillary  artery;  ^9,  pharyngeal  artery;  Si,  Ungual  artery;  32,  external  carotid  artery;  S3,  stump  of  inferior 
alveolar  artery;  34,  middle  meningeal  artery;  35,  deep  temporal  artery;  36,  buccinator  artery;  37,  palatine  artery; 
S8,  end  of  internal  maxillary  artery;  39,  right  external  maxillary  artery;  40,  satellite  vein  of  39;  41  j  right  parotid  duct; 
42,  mandibular  lymph  glands;  43,  parapharyngeal  lymph  glands;  44 >  trachea;  40,  wing  of  atlas;  46,  dotted  line  indi- 
cating outline  of  mandibular  gland;  4'',  lacrimal  gland.     (After  Ellenberger-Baum,  Top.  Anat.  d.  Pferdes.) 


mediate  branch.  The  lateral  branch  (Ramus  lateralis)  passes  up  the  posterior 
(lateral)  border  of  the  ear  and  forms  an  arch  with  the  intermediate  branch.  The 
deep  branch  (A.  auricularis  profunda)  enters  the  interval  between  the  external 
acoustic  process  and  mastoid  process,  and  passes  through  an  opening  into  the 
interior  of  the  external  ear  and  ramifies  in  the  skin  which  lines  it.  It  gives  off  the 
stylomastoid  artery,  which  passes  through  the  stylomastoid  foramen  into  the  tym- 


646 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


panum,  forms  an  arch  around  the  membrana  tympani,  and  supplies  the  middle  ear 
and  its  muscles. 


THE  SUPERFICIAL  TEMPORAL  ARTERY 

This  artery  (A.  temporalis  superficialis)  is  much  the  smaller  of  the  two  terminal 
branches  of  the  external  carotid,  and  is  usually  less  than  an  inch  (ca.  2  cm.)  in  length. 

It  passes  upward  behind  the  posterior 
border  of  the  ramus  of  the  mandible, 
under  cover  of  the  parotid  gland,  and 
divides  below  the  level  of  the  condyle 
into  the  anterior  auricular  and  trans- 
verse facial  arteries.  It  is  crossed  super- 
ficially by  the  facial  nerve. 

The  anterior  auricular  artery  (A. 
auricularis  anterior)  ascends  behind  the 
temporo-mandibular  articulation  under 
cover  of  the  parotid  gland  and  reaches 
the  temporalis  muscle.  It  is  crossed 
deeply  at  its  origin  by  the  superficial 
temporal  nerve  and  is  accompanied  by 
a  satellite  vein  and  the  auriculo-palpe- 
bral  branch  of  the  facial  nerve.  It  is 
distributed  to  the  skin  and  the  temporal 
and  anterior  auricular  muscles,  and  sends 
a  branch  through  the  concha!  cartilage 
to  the  skin  which  lines  it.  Collateral 
twigs  are  detached  to  the  parotid  gland, 
and  an  anterior  branch  anastomoses  with 
the  supraorbital  artery.  A  branch  some- 
times passes  into  the  temporal  canal  and 
anastomoses  with  the  posterior  meningeal 
artery. 

The  transverse  facial  artery  (A. 
transversa  faciei)  is  larger  than  the  pre- 
ceding. It  turns  around  the  neck  of 
the  mandible  and  emerges  from  beneath 
the  parotid  gland  (Fig.  560).  It  then 
passes  forward  a  short  distance  on  the 
masseter  about  half  an  inch  below  the 
zygomatic  arch,  and  enters  the  muscle, 
in  which  it  commonly  divides  into  two 
chief  branches.  It  is  accompanied  by  a 
vein  and  a  branch  of  the  superficial  tem- 
poral nerve.  It  supplies  the  masseter  and  the  skin  of  this  region,  and  anastomoses 
with  the  external  maxillary  and  posterior  deep  temporal  arteries. 


Fig.  563. — Right  Eye  or  Horse. 

a,  Remnants  of  periorbita;  b,  levator  palpebrae 
auperioris;  c,  obliquus  oculi  inferior;  d,  rectus  oculi 
inferior;  e,  rectus  oculi  lateralis;  /,  rectus  oculi  superior; 
g,  sclera;  g',  cornea;  h,  lacrimal  gland;  i,  frontal  nerve; 
i',  trochlear  nerve;  k,  supraorbital  artery;  i,  branches  of 
lacrimal  nerve  to  gland;  m,  lacrimal  artery;  n,  zygo- 
matic nerve;  o,  branch  of  ophthalmic  artery;  p,  branch  of 
oculomotor  nerve  to  obliquus  oculi  inferior;  q,  maxil- 
lary nerve;  r,  infraorbital  nerve;  s,  posterior  nasal 
nerve;  <,  great  palatine  nerve;  u,  small  palatine  nerve; 
J),  internal  maxillary  artery;  w,  buccinator  artery  (cut) ; 
I,  infraorbital  artery;  x',  malar  artery;  y,  spheno- 
palatine artery;  z,  great  palatine  artery;  z',  small 
palatine  (or  staphyline)  artery;  /,  anterior  deep 
temporal  artery;  S,  stump  of  zygomatic  arch  (sawn 
off) ;  3,  stump  of  supraorbital  process  (sawn  off) ;  4<  fa- 
cial crest;  5,  temporal  fossa;  6,  foramen  orbitale;  7, 
foramen  rotundum  and  anterior  end  of  alar  canal; 
S,  posterior  opening  of  alar  canal.  (After  EUenberger, 
in  Leisering's  Atlas.) 


THE  INTERNAL  MAXILLARY  ARTERY  (Figs.  562,  563,  564) 

This  artery  (A.  maxillaris  interna)  is  much  the  larger  of  the  two  terminal 

branches  of  the  external  carotid.     It  begins  at  the  medial  side  of  the  posterior  border 

of  the  mandible,  about  two  inches  (ca.  5  cm.)  below  the  articulation  of  the  jaw, 

and  ends  in  the  anterior  part  of  the  pterygo-palatine  fossa.     On  account  of  its 


THE    INTERNAL    MAXILLARY    ARTERY  64  T 

complex  course  and  the  large  number  of  branches  given  off  it  is  convenient  to  divide 
it  into  three  parts. 

I.  The  first  part  is  much  the  longest,  forms  an  S-shaped  curve,  and  is  in  great 
part  in  contact  with  the  guttural  pouch.  It  passes  upward  and  forward  on  the 
medial  surface  of  the  mandible  a  distance  of  about  an  inch  (ca.  2-3  cm.),  and  is 
related  here  to  the  vein,  which  is  ventral.  It  then  turns  inward  on  the  ventral 
surface  of  the  lateral  pterygoid  muscle  and  the  mandibular  nerve,  passes  between 
that  muscle  and  the  tensor  palati,  and  runs  forward  to  enter  the  alar  canal. 
This  part  gives  off  the  following  branches: 

1.  The  inferior  alveolar  artery  (A.  alveolaris  mandibulae  s.  inferior) ^  passes 
downward  and  forward  with  the  homonymous  vein  and  nerve,  being  at  first  between 


Fig.  564. — Left  Eye  of  Horse,  Deeper  Dissection. 
The  outer  plate  of  bone  has  been  removed  behind  the  pterygoid  crest  to  expose  the  vessels  and  nerves,  a,  a,  Rem- 
nants of  periorbita;  6,  b,  stumps  of  rectus  oculi  superior;  c,  obliquus  oculi  inferior;  d,  rectus  oculi  inferior;  c,  rectus 
ocuU  lateralis;  e' ,  retractor  oculi;  /,  rectus  ocuh  medialis;  g,  g,  obliquus  ocuU  superior;  h,  eyeball;  i,  trochlear  nerve; 
k,  ophthalmic  nerve;  k',  nasal  nerve;  k",  infratrochlear  nerve;  k'",  ethmoidal  nerve;  I,  optic  nerve;  m,  frontal  nerve; 
71,  lacrimal  nerve;  o,  zygomatic  nerve;  p,  nerve  to  obliquus  inferior  (from  oculomotor);  q,  maxillary  nerve;  r,  infra- 
orbital nerve;  s,  sphenopalatine  nerve;  /,  great  palatine  nerve;  u,  small  palatine  nerve;  v,  internal  maxillary  arteT":.-; 
u\  buccinator  artery  (cut  off);  j,  infraorbital  artery;  x',  malar  artery;  y,  spheno-palatine  artery;  z,  great  palatine 
artery;  2',  small  palatine  artery;  1,  2,  stumps  of  zygomatic  arch;  3,  stump  of  supraorbital  process;  4,  facial  crest; 
S,  temporal  fossa;  6,  external  ophthalmic  artery;  7,  muscular  branch  of  6;  8,  lacrimal  artery  (cut);  9,  supraorbital 
artery;  10,  anterior  deep  temporal  artery;  ii,  ethmoidal  artery.     (After  EUenberger-Baum,  Top.  Anat.  d.  Pferdes.) 

the  lateral  and  medial  pterygoid  muscles,  then  between  the  latter  and  the  ramus  of 
the  mandible.  It  enters  the  mandibular  foramen,  passes  downward  and  forward 
in  the  mandibular  canal,  and  terminates  at  the  mental  foramen  by  dividing  into 
mental  and  incisor  branches.  The  mental  branch  (A.  mentalis)  emerges  throuj  h 
the  mental  foramen  and  anastomoses  in  the  lower  lip  with  the  opposite  artery  and 
the  inferior  labial.  The  incisor  branch  (Ramus  incisivus)  continues  forward  in  the 
bone,  supplies  twigs  to  the  canine  and  incisor  teeth,  and  ana.stomoses  with  its  fellow 
of  the  opposite  side.  Collateral  branches  are  detached  to  the  pterygoid  and  mylo- 
hyoid muscles,  and  within  the  bone  to  the  teeth,  alveolar  periosteum,  the  gums, 
and  the  spongy  substance  of  the  mandible. 

2.  The  pterygoid  arteries,  two  or  three  in  number,  are  distributed  to  the  ptery- 
goid and  tensor  and  levator  palati  muscles. 

1  Also  known  as  the  inferior  dental  artery. 


648 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


3.  The  tympanic  artery  is  a  very  small  vessel  which  passes  along  the  Eusta- 
shian  tube  to  the  petro-tympanic  fissure  and  enters  the  middle  ear. 

4.  The  middle  meningeal  artery  (A.  meningea  media)  arises  beneath  the  buc- 
cinator nerve,  where  the  internal  maxillary  turns  forward.  It  passes  backward 
across  the  temporal  wing  of  the  sphenoid  to  the  antero-lateral  part  (foramen  spino- 
sum)  of  the  foramen  lacerum.  Entering  the  cranium,  it  divides  into  branches  which 
course  in  the  grooves  on  the  temporal  and  parietal  bones  and  supply  the  dura 
mater.     It  anastomoses  with  the  posterior  meningeal. 

The  size  of  this  artery  is  variable,  and  is  in  inverse  ratio  to  that  of  the  posterior  meningeal. 


Fig.  565. — Sagittal  Section  of  Head  of  Horse,  Cut  a  Little  to  the  Right  of  the  Median  Plane. 
i.Skin;  3,  nasal  bone;  3,  frontal  bone ;  4i  parietal  bone;  4',  tentorium  osseum;  5,  occipital  bone;  6,  sphenoid  bone; 
7,  hard  palate;  8,  premaxilla;  9,  mandible;  10,  hyoid  bone;  11,  septum  between  frontal  sinuses;  12,  alar  cartilage; 
IS,  transversus  nasi;  IJf.,  septum  nasi  with  venous  plexuses;  15,  palato-labial  artery;  16,  16',  upper  and  lower 
septal  branches  of  i 5;  i 7,  septal  branch  of  sphenopalatine  artery  and  satellite  vein;  18,  septal  branch  of  ethmoidal 
artery;  19,  sphenoidal  sinus;  20,  guttural  pouch;  21,  pharynx;  22,  pharyngeal  orifice  of  Eustachian  tube;  23,  posterior 
naris;  24,  soft  palate;  25,  palatinus  muscle;  26,  pharyngeal  muscles;  27,  cesophagus;  28,  dotted  line  indicating  posi- 
tion of  posterior  pillar  of  soft  palate;  29,  lamina,  29',  arch  of  cricoid  cartilage;  30,  arytenoideus  transversus  muscle; 
31,  epiglottis;  32,  body  of  thyroid  cartilage;  33,  vocal  process  and  cord;  34,  arytenoid  cartilage;  35,  lateral  ventricle 
of  larynx;  36,  trachea;  37,  ventral  straight  muscles  of  head;  38,  longus  colli;  39,  atlas;  40,  axis;  41,  lig.  nuchse;  42, 
dorsal  spinal  muscles;  43,  muscles  of  external  ear;  4^,  omo- and  sterno-hyoideus;  4<5,  tongue;  4^,  mylo-hyoideus;  47, 
genio-hyoideus;  45.  genio-glossus;  4^,  longitudinalis  inferior;  50,  longitud.  superior;  51,  hypo-epiglotticus;  o^,  chin 
and  mentalis  muscle;  53,  venous  plexus  of  hard  palate;  54,  corpus  callosum;  55,  septum  pellucidum;  56,  fornix;  57, 
thalamus;  58,  pineal  body;  59,  corpora  quadrigemina;  60,  cerebral  peduncle;  61,  corpus  mammillare;  62,  pituitary 
body;  63,  chiasma  opticum;  64,  intercarotid  artery;  65,  medulla  oblongata;  66,  interventricular  foramen;  67,  infun- 
dibulum;  6S,  third  ventricle;  6.9,  cerebral  aqueduct;  70,  anterior  medullary  velum;  7^,  fourth  ventricle;  7^,  posterior 
medullary  velum;  73,  basilar  artery;  74,  spinal  cord;  75,  ethmoidal  nerve;  76,  septal  branch  of  posterior  nasal  nerve; 
76',  branch  of  same  to  vomero-nasal  organ;  77,  olfactory  nerve  to  vomero-nasal  organ;  78,  nasal  branches  of  palatine 
artery.     (After  Ellenberger,  in  Leisering's  Atlas.) 


5.  The  posterior  deep  temporal  artery  (A.  temporalis  profunda  aboralis) 
arises  from  the  internal  maxillary  just  before  the  latter  enters  the  alar  canal.  It 
passes  upward  and  backward  in  the  temporal  fossa  on  the  deep  face  of  the  temporalis 
muscle,  in  which  it  ramifies.  It  sends  a  branch  outward  to  the  masseter,  and 
anastomoses  with  the  superficial  temporal  and  middle  meningeal  arteries. 

In  some  cases  the  tympanic  and  middle  meningeal  arise  from  this  artery. 

II.  The  second  part  lies  in  the  alar  canal,  and  is  about  an  inch  (ca.  2-3  cm.)  in 
length.  It  gives  off  two  branches — the  anterior  deep  temporal  and  the  external 
ophthalmic. 

1.  The  anterior  deep  temporal  artery  (A.  temporalis  profunda  oralis)  emerges 
from  the  canal  through  the  small  alar  or  temporal  foramen,  and  ascends  in  the 


THE   INTERNAL   MAXILLARY   ARTERY  649 

anterior  part  of  the  temporal  fossa  on  the  deep  face  of  the  temporahs  muscle,  in 
which  it  is  chiefly  distributed.  It  gives  twigs  to  the  orbital  fat  and  the  skin  of  the 
frontal  region. 

2.  The  external  ophthalmic  artery  (A.  ophthalmica  externa)  emerges  from  the 
anterior  opening  of  the  alar  canal,  and  enters  the  apex  of  the  periorbita.  Within 
this  it  forms  a  semicircular  bend  under  the  rectus  oculi  superior,  and  is  continued 
by  the  ethmoidal  arter3^     Its  branches  are  as  follows: 

(a)  The  supraorbital  artery  (A.  supraorbitalis)  is  a  small  vessel  which  often 
arises  from  the  anterior  deep  temporal  or  the  internal  maxillary.  It  passes  along 
the  inner  wall  of  the  orbit  in  company  with  the  nerve  of  the  same  name  to  the  supra- 
orbital foramen,  through  which  it  emerges.  It  is  distributed  to  the  orbicularis 
oculi,  the  corrugator  supercilii,  and  the  skin  of  the  supraorbital  region. 

(6)  The  lacrimal  artery  (A.  lacrimalis)  runs  upward  and  forward  within  the 
periorbita  along  the  lateral  edge  of  the  levator  palpebrse  superioris  to  the  lacrimal 
gland,  in  which  it  is  chiefly  distributed.     It  also  sends  twigs  to  the  upper  eyelid. 

(c)  Muscular  branches  (Rami  musculares)  supply  the  orbital  muscles,  the 
periorbita,  the  thirtl  eyelid,  and  the  conjunctiva. 

(rf)  Ciliary  branches  (Aa.  ciliares),  two  sets  of  very  slender  arteries,  arise 
from  the  ophthalmic  direct  and  from  the  muscular  branches.  The  anterior  ciliary 
arteries  (Aa.  ciliares  anteriores)  pierce  the  sclera  in  front  of  the  equator  and  ramify 
chiefly  in  the  ciliary  botly  and  the  iris.  The  posterior  ciliary  arteries  (Aa.  ciliares 
posteriores)  pierce  the  posterior  part  of  the  sclera;  most  of  them  ramify  in  the 
chorioid  coat  as  the  short  ciliary  arteries,  but  two  of  larger  size,  the  long  ciliary 
arteries,  run  forward,  one  on  each  side,  between  the  sclera  and  chorioid  to  the 
periphery  of  the  iris.  Here  they  divide  into  branches  which  anastomose  and  form 
a  circle  (Circulus  iridis  major).  From  this  secondary  branches  are  detached  which 
form  a  second  circle  around  the  pupil  (Circulus  iridis  minor) . 

(e)  The  central  artery  of  the  retina  (A.  centralis  retinae)  is  a  small  vessel  which 
arises  from  the  ophthalmic  or  from  a  posterior  ciliary  artery.  It  pierces  the  optic 
nerve  a  short  distance  behind  the  sclera,  and  runs  in  its  center  to  the  lamina  cribrosa, 
where  it  breaks  up  in  thirty  to  forty  fine  branches.  These  appear  in  the  fundus  of 
the  eye  at  the  margin  of  the  optic  papilla  and  radiate  in  the  posterior  part  of  the 
retina. 

(/)  The  ethmoidal  artery  (A.  ethmoidalis)  is  the  continuation  of  the  oph- 
thalmic. It  enters  the  cranial  cavity  through  the  ethmoidal  foramen,  passes 
inward  on  the  cribriform  plate,  and  divides  into  meningeal  and  nasal  branches. 
The  former  ramify  in  the  anterior  part  of  the  dura  mater  and  anastomose  with 
branches  of  the  artery  of  the  corpus  callosum.  The  nasal  branch  passes  through  the 
cribriform  plate,  gives  branches  to  the  mucous  membrane  of  the  lateral  mass  of  the 
ethmoid  and  the  adjacent  part  of  the  septum  nasi,  and  runs  forward  on  the  dorsal 
turbinate. 

III.  The  third  part  passes  forward  in  the  pterygo-palatine  fossa,  accompanied 
by  branches  of  the  maxillary  nerve.  On  reaching  the  posterior  palatine  foramen  it 
is  continued  by  the  greater  palatine  artery.     Its  branches  are  as  follows: 

(1)  The  buccinator  artery  (A.  buccinatoria)  arises  from  the  ventral  aspect  of 
the  internal  maxillary  shortly  after  its  emergence  (Fig.  562).  It  turns  around  the 
maxillary  tuberosity,  accompanied  by  the  buccinator  nerve,  and  under  the  masseter 
muscle,  enters  the  cheek,  and  runs  forward  in  it.  It  supplies  branches  to  the 
cheek,  the  superior  buccal  glands,  and  the  masseter  and  pterygoid  muscles.  Near 
its  origin  it  gives  off  a  branch  to  the  orbital  fat  behind  the  periorbita. 

(2)  The  infraorbital  artery  (A.  infraorbitalis)^  arises  from  the  upper  aspect  of 
the  internal  maxillary  a  little  in  front  of  the  preceding  vessel.  It  passes  upward 
and  forward  to  the  maxillary  foramen,  runs  in  the  infraorbital  canal  in  company  with 

1  Also  termed  the  superior  dental  artery. 


650  BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 

the  nerve  of  the  same  name,  and  is  continued  forward  within  the  jaw  to  the  incisor 
teeth.  It  gives  branches  to  the  teeth  and  gums,  and  detaches  a  branch  through  the 
infraorbital  foramen  which  anastomoses  with  the  lateral  nasal  and  superior  labial.^ 
About  midway  between  its  origin  and  the  maxillary  foramen  it  gives  off  the  malar 
branch  (Ramus  malaris),  which  passes  along  the  floor  of  the  orbit  to  end  in  the  lower 
lid  and  anastomose  with  the  angularis  oculi.  It  gives  twigs  to  the  inferior  oblique 
muscle  and  the  lacrimal  sac. 

(3)  The  lesser  palatine  artery  (A.  palatina  minor)  is  a  small  vessel  which 
passes  forward  in  the  groove  at  the  medial  side  of  the  maxillary  tuberosity  to  the 
soft  palate.  In  the  groove  it  is  accompanied  by  the  nerve  of  the  same  name  and  the 
palatine  vein. 

(4)  The  sphenopalatine  artery  (A.  sphenopalatina)  arises  in  the  anterior 
part  of  the  pterygo-palatine  fossa,  passes  through  the  sphenopalatine  foramen  into 
the  nasal  cavity,  and  divides  into  two  branches.  The  medial  branch  is  distributed 
to  the  mucous  membrane  of  the  septum  nasi;  the  lateral  one  goes  to  the  ventral 
turbinate,  the  ventral  meatus,  the  posterior  nares,  and  the  maxillary  and  frontal 
sinuses.     It  may  arise  from  the  infraorbital. 

(5)  The  greater  palatine  artery  (A.  palatina  major)  is  the  direct  continuation 
of  the  internal  maxillary.  It  passes  through  the  palatine  canal  to  the  roof  of  the 
mouth,  accompanied  by  the  palatine  nerve,  and  runs  forward  in  the  palatine 
groove,  where  it  is  joined  by  the  vein.  A  little  behind  the  plane  of  the  corner 
incisor  teeth  it  curves  medially  over  a  bar  of  cartilage  to  the  foramen  incisivum, 
where  it  unites  with  its  fellow  of  the  opposite  side.  The  single  artery  thus  formed 
(A.  palato-labialis)  passes  up  through  the  foramen  and  divides  under  the  transversus 
nasi  into  two  branches.  These  ramify  in  the  upper  lip  and  anastomose  with  the 
lateral  nasal  and  superior  labial  arteries.  In  its  course  in  the  palate  the  artery  gives 
off  branches  to  the  hard  and  soft  palate  and  the  gums,  and  others  which  pass  through 
the  accessory  palatine  foramina  to  be  distributed  in  the  mucous  membrane  of  the 
lower  part  of  the  nasal  cavity.  Commonly  two  branches,  right  and  left,  are  de- 
tached from  the  convexity  of  the  arch  formed  by  the  union  of  the  two  arteries; 
these  run  forward  in  the  anterior  part  of  the  hard  palate. 


Arteries  of  the  Thoracic  Limb 
the  brachial  artery 

The  brachial  artery,  after  crossing  the  ventral  border  of  the  scalenus  at  the 
first  rib,  passes  backward  and  downward  across  the  origin  of  the  coraco-brachialis 
and  the  insertion  of  the  subscapularis  muscle  at  the  medial  side  of  the  shoulder 
joint.2  At  the  posterior  border  of  the  subscapularis  it  gives  off  the  subscapular 
artery,  and  turns  distally  on  the  medial  surface  of  the  arm.  In  its  course  in  the 
arm  it  inclines  a  little  forward,  crosses  the  humerus  very  obliquely,  and  is  continued 
by  the  median  artery. 

In  its  course  over  the  chest-wall  the  artery  is  related  medially  to  the  ventral 
border  of  the  serratus  thoracis  and  the  rectus  thoracis.  Opposite  the  ventral  end 
of  the  first  rib  it  is  crossed  medially  by  the  median  nerve  and  laterally  by  the  mus- 
culo-cutaneous  nerve;  the  two  nerves  unite  below  the  artery,  which  is  thus  sus- 
pended in  a  sort  of  loop.  In  the  arm  it  is  related  medially  to  the  posterior  deep 
pectoral  muscle  and  is  covered  by  the  deep  brachial  fascia.  Laterally  it  lies  on  the 
subscapularis,  the  brachialis,  the  insertion  of  the  teres  major  and  latissimus  dorsi, 

1  The  infraorbital  artery  is  usually  small  at  its  emergence  upon  the  face,  but  in  some  cases  it 
is  rather  large  and  may  partially  replace  the  superior  labial  and  lateral  nasal  arteries. 

2  The  term  axillary  is  often  applied  to  the  artery  from  the  first  rib  to  the  point  of  origin  of 
the  subscapular  artery,  and  the  name  brachial  is  given  to  the  artery  beyond  this. 


THE    BRACHIAL   ARTERY  651 

and  the  medial  head  of  the  triceps.  The  coraco-brachialis  muscle  lies  along  the 
front  of  the  artery,  which,  however,  overlaps  the  muscle  distally.  The  vein  crosses 
the  medial  face  of  the  artery  and  runs  down  behind  it,  accompanied  part  way  by  the 
ulnar  and  radial  nerves.     The  chief  branches  are  as  follows: 

1.  The  suprascapular  artery  (A.  thoraco-acromialis)  is  a  small  and  somewhat 
flexuous  vessel,  which  arises  near  the  anterior  border  of  the  subscapularis,  runs 
dorsally,  and  dips  in  between  that  muscle  and  the  supraspinatus.  It  gives  branches 
to  these  muscles,  the  anterior  deep  pectoral,  and  the  brachiocephalicus.  A  branch 
passes  in  front  of  the  coraco-brachialis  to  the  shoulder  joint  and  the  proximal  end 
of  the  humerus.  1 

2.  The  subscapular  artery  (A.  subscapularis)  is  a  very  large  vessel  which  arises 
at  the  posterior  border  of  the  subscapularis  muscle.  It  ascends  in  the  interstice 
between  that  muscle  and  the  teres  major,  on  the  medial  surface  of  the  long  head 
of  the  triceps,  turns  around  the  posterior  border  of  the  scapula  below  the  dorsal 
angle,  and  ends  in  the  infraspinatus  and  deltoid.  Besides  collateral  muscular 
branches  (Rami  musculares)  to  the  subscapularis,  teres  major,  triceps,  and  tensor 
fasciae  antibrachii,  it  gives  off  the  following  named  branches: 

(a)  The  thoraco-dorsal  (A.  thoracodorsalis)  is  a  long  artery  which  is  usually 
given  off  about  an  inch  from  the  origin  of  the  subscapular,  crosses  the  medial  face 
of  the  teres  major,  and  runs  upward  and  backward  on  the  latissimus  dorsi.  It  gives 
branches  to  these  muscles,  the  abdominal  cutaneus  and  the  axillary  lymph  glands. 

(h)  The  posterior  circumflex  artery  of  the  humerus  (A.  circumflexa  humeri 
posterior)  arises  a  little  above  the  preceding  vessel,  and  passes  outward  behind  the 
shoulder  joint  between  the  long  and  lateral  heads  of  the  triceps  with  the  axillary 
nerve.  It  gives  branches  to  these  muscles,  the  joint  capsule,  and  the  muscles  and 
skin  of  the  lateral  side  of  the  shoulder,  anastomosing  with  the  anterior  circumflex 
artery. 

(c)  The  circumflex  artery  of  the  scapula  (A.  circumflexa  scapulae)  arises  about 
two  or  three  inches  (ca.  5-7.5  cm.)  above  the  shoulder  joint,  passes  forward  to 
the  posterior  border  of  the  scapula,  and  divides  into  two  branches.  The  lateral  one 
runs  forward  on  the  lateral  surface  of  the  scapula  below  the  spine,  and  gives  branches 
to  the  supraspinatus,  infraspinatus,  and  teres  minor.  The  medial  branch  passes 
forward  in  a  similar  fashion  on  the  costal  surface  of  the  scapula  and  supphes  branches 
to  the  subscapularis. 

3.  The  anterior  circtraiflex  artery  of  the  humerus  (A.  circumflexa  humeri 
anterior)"  arises  usually  at  the  anterior  border  of  the  teres  major.  It  passes  forward 
between  the  two  parts  of  the  coraco-brachialis  or  between  the  latter  and  the  humerus. 
It  gives  branches  to  the  coraco-brachialis  and  deep  pectoral  and  ends  in  the  upper 
part  of  the  biceps  and  in  the  brachiocephalicus.  It  anastomoses  with  the  posterior 
circumflex  artery. 

Not  rarely  it  is  replaced  largely  by  an  artery  which  arises  from  the  brachial  at  the  distal  end 
of  the  coraco-brachialis,  and  ascends  on  the  front  of  the  humerus.  In  these  cases  a  small  branch 
for  the  coraco-brachialis  is  usually  given  off  at  the  usual  pomt  of  origin  of  the  anterior  circumflex. 

4.  The  deep  brachial  artery  (A.  profunda  brachii)  is  a  large  but  short  trunk 
which  arises  usually  about  the  middle  of  the  humerus.  It  passes  backward  to  the 
interval  between  the  tendon  of  the  teres  major  and  latissimus  dorsi,  and  the  long  and 
medial  heads  of  the  triceps,  where  it  divides  into  several  branches  which  supply  the 
triceps,  tensor  fasciae  antibrachii,  anconeus,  and  brachialis.  A  branch  runs  in  the 
musculo-spiral  groove  with  the  radial  nerve  to  the  front  of  the  elbow  joint  and 
anastomoses  with  the  anterior  radial.     A  slender  branch  descends  along  the  lateral 

1  This  vessel  may  be  double,  or  be  represented  by  one  or  more  branches  of  the  inferior  cervical 
iirtery. 

"  Also  termed  the  prehumeral  artery. 


652 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


A  nterior  deep 
pectoral  muscle 
Suprascapular         / 
artery  ' 


Posterior  deep  pecto- 
ral niukcle 
Tendon  of  cutaru  us 
Nerve  to  bic(  ps 
Anterior  drcumjiix 
arUry 
Anterior  superficial 
pectoral  muscle 


Extensor  carpi  radialis 

Radius 
Accessory  cephalic  vein 


Elbow  joint 
Flexor  carpi 
ulnaris 
Fhxor  carpi 
radialis 
Medial  liga- 
ment of  elbow 
joint 


Fig.  56G. — Dissection  of  Shoulder  and  Arm  of  Horse;  Medial  Surface. 
A,  Brachial  artery,  the  stump  of  which  has  been  turned  backward;  B,  subscapular  artery;  C,  thoraco-dorsal 
artery;  D,  deep  brachial  artery;  E,  ulnar  artery;  F,  anterior  radial  artery;  (7,  median  artery;  //,  stump  of  brachial  vein; 
J,  external  thoracic  vein;  J,  brachial  vein,  part  of  w^hich  has  been  removed  to  expose  deep  brachial  artery;  A',  K,  K, 
median  veins;  L,  cephalic  vein;  L',  communicating  vein;  M,  brachialis  muscle;  A'^,  medial  epicondyle  of  hu- 
merus; O,  prescapular  lymph  glands;  P,  indicating  position  of  axillary  lymph  glands,  should  be  dorsal  to  vein;  Q,  posi- 
tion of  cubital  lymph  glands;  /,  suprascapular  nerve;  S,  subscapular  nerves;  3,  thoraco-dorsal  nerve;  4,  musculo- 
cutaneous nerve;  4',  cutaneous  branch  of  musculo-cutaneous  nerve;  5,  median  nerve;  6,  axillary  nerve;  7,  ulnar  nerve; 
7',  cutaneous  branch  of  ulnar  nerve;  S,  radial  nervt;  9,  thoracic  nerves.  The  vein  at  the  elbow  which  lies  in  front  of  the 
median  artery  should  be  shown  crossing  over  the  median  nerve  and  the  median  and  ulnar  arteries,  as  in  the  next  figure. 
(After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


THE    BRACHIAL   ARTERY 


653 


border  of  the  extensor  carpi  and  supplies  cutaneous  twigs.     Anastomoses  occur 
with  the  ulnar  and  recurrent  interosseous  arteries. 

The  point  of  origin  is  inconstant  and  it  is  not  uncommon  to  find  two  arteries  instead  of  one. 
Often  a  large  branch  for  the  posterior  deep  pectoral  muscle  is  detached  close  to  the  origin  or  arises 
from  the  brachial  directly. 


Brachial 
Median  nerve 
Coraco-brachiahs 


Biceps  brachii 

Cephalic  vein 

Vena  communicans 

Cutaneous  branch  of 
musculo-cutaneous  nerve 

Extensor  carpi  radialis 


Accessory  cephalic  vein 

Cephalic  vein 

Radius 

Flexor  carpi  radialis 


Artery  of  rete  carpi 
dorsale 


Medial  ligament  of 
carpus 

Tendon  of  extensor 
carpi  obliquus 

Common  digital  vein 

Branch  to  deep  volar 
arch 


Dorsal  metacarpal  artery 


Long  head  of  triceps 

Medial  head  of  triceps. 


Tensor  fascim  antibrachii 

Ulnar  head  of  flexor 
carpi  ulnaris 
Humeral  head  of  flexor 
carpi  ulnaris 

Ulnar  head  of  deep  flexor 
Flexor  carpi  radialis 

Common  interosseous 
artery 

Median  artery 

Ulnar  vessels  and  nerve 

Deep  fascia 


Lateral  branch  of  median 

nerve 

Medial  branch  of  median 

nerve 

Flexor  carpi  ulnaris 

Lateral  volar  nerve 

Lateral  volar  met.  artery 
and  vein 

Medial  volar  nerve 

Common  digital  artery 

Medial  volar  met.  artery 

Flexor  tendons 


Fig.  567. — Dissection  or  Right  Forearm  and  Carpus  of  Horse;    Medial  View. 
1,  Ulnar  vessels;   2,  cutaneous  branch  of  musculo-cutaneous  nerve;   3,  3,  satellite  veins  of  median  artery;   4,  posi- 
tion of  cubital  lymph  glands;    5,  anastomosis  of  ulnar  and  lateral  volar  metacarpal  arteries;    6,  brachialis  muscle;   7, 
superficial  digital  flexor;   8,  deep  digital  flexor.     Dotted  lines  indicate  contour  of  flexor  carpi  radialis,  most  of  which  has 
been  removed.     (After  Schmaltz,  Atlas  der  Anatomie  des  Pferdes.) 


654  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

5.  Muscular  branches  (Rami  musculares)  are  distributed  to  the  teres  major, 
deep  pectoral,  coraco-brachialis,  and  biceps.  The  largest  and  least  variable  of 
these  supplies  the  distal  part  of  the  biceps. 

6.  The  ulnar  artery  (A.  collateralis  ulnaris  proximalis)  arises  at  the  distal 
end  of  the  coraco-brachialis  and  passes  downward  and  backward  along  the  ventral 
edge  of  the  medial  head  of  the  triceps  under  cover  of  the  brachial  vein  and  the 
tensor  fasciae  antibrachii.  It  gives  branches  to  these  muscles,  the  posterior  super- 
ficial pectoral,  the  cubital  lymph  glands,  cutaneus,  and  skin.  At  the  elbow  it  lies 
on  the  posterior  part  of  the  medial  epicondyle,  in  relation  in  front  to  the  ulnar 
nerve,  and  largely  covered  by  the  satellite  vein;  it  then  turns  downward  under  the 
ulnar  head  of  the  flexor  carpi  ulnaris.  It  continues  its  descent  with  the  vein  and 
nerve  under  the  deep  fascia  of  the  forearm  between  the  ulnar  and  humeral  heads  of 
the  deep  flexor  of  the  digit,  and  in  the  distal  half  of  the  region  between  the  lateral 
and  middle  flexors  of  the  carpus.  It  unites  just  above  the  carpus  (under  cover  of 
the  flexor  carpi  ulnaris)  with  a  branch  of  the  median  artery,  with  which  it  forms  the 
supracarpal  arch.  It  detaches  small  collaterals  to  the  muscles  along  which  it  passes 
and  terminal  twigs  to  the  lateral  surface  of  the  carpus. 

7.  The  nutrient  artery  of  the  humerus  (A.  nutritia  humeri)  is  a  short  vessel 
which  enters  the  nutrient  foramen  of  the  humerus.     It  often  arises  from  the  ulnar. 

8.  The  anterior  radial  artery  (A.  collateralis  radialis  distalis)i  passes  downward 
and  a  little  outward  on  the  anterior  face  of  the  humerus  under  cover  of  the  biceps 
and  brachialis  to  the  front  of  the  elbow  joint,  where  it  is  in  contact  with  the  radial 
nerve.  It  then  descends  on  the  anterior  surface  of  the  radius,  under  cover  of  the 
common  digital  extensor,  to  the  carpus,  where  it  concurs  in  the  formation  of  the  rete 
carpi  dorsale,  anastomosing  with  the  median  and  dorsal  interosseous  arteries.  It 
supplies  branches  to  the  elbow  joint,  the  biceps,  brachialis,  and  the  extensors  of 
the  carpus  and  digit.  A  cutaneous  branch  emerges  between  the  distal  end  of  the 
biceps  and  the  brachialis. 

THE  MEDIAN  ARTERY 

The  median  or  posterior  radial  artery  (A.  mediana)-  is  the  direct  continuation 
of  the  brachial.  It  descends,  inclining  slightly  backward,  at  first  on  the  medial 
surface  of  the  humerus,  and  then  over  the  capsule  and  medial  ligament  of  the  elbow 
joint,  under  cover  of  the  posterior  superficial  pectoral  muscle.^  At  the  proximal 
third  of  the  forearm  it  dips  under  the  flexor  carpi  radialis  and  passes  down  the  medial 
part  of  the  posterior  surface  of  the  radius.  In  the  distal  part  of  the  forearm  it 
inclines  backward  and  is  separated  from  the  radius  by  the  reinforcing  band  (Caput 
tendineum)  of  the  superficial  flexor  of  the  digit  and  is  continued  by  the  common 
digital  or  large  metacarpal  artery. 

It  is  accompanied  by  the  median  nerve,  which  lies  in  front  of  the  artery  at  its 
origin,  then  usually  crosses  over  it  obliquely  at  the  elbow  joint  and  becomes  posterior. 
At  the  distal  end  of  the  arm  the  artery  is  crossed  by  the  large  anastomotic  vein 
which  connects  the  cephalic  and  brachial  veins,  and  a  radicle  of  the  brachial  vein  lies 
behind  and  partly  upon  the  artery;  lower  down  there  are  usually  two  satellite 
veins,  anterior  and  posterior.     The  chief  collateral  branches  are  as  follows: 

1.  Articular  branches  are  supplied  to  the  elbow  joint. 

2.  Muscular  branches  go  to  the  flexors  of  the  carpus  and  digit ;  the  largest  of 
these  arise  at  the  proximal  third  of  the  forearm. 

3.  The  common  interosseous  artery  (A.  interossea  communis)  is  a  vessel  of 

^  This  vessel  is  apparently  the  A.  transversa  cubiti  of  comparative  anatomy. 

2  Although  the  homology  of  some  arteries  in  this  region  are  still  unsettled,  it  seems  clear  that 
this  vessel  should  be  termed  the  median  artery. 

^  The  pulse  can  be  taken  where  the  artery  lies  on  the  ligament,  since  the  pectoral  muscle  is 
thin  here. 


THE    MEDIAN    ARTERY 


655 


considerable  size  which  arises  at  the  level  of  the  interosseous  space,  through  which 
it  passes  outward.     Before  entering  the  space  it  gives  off  a  small  branch,  the  volar 


Deltoid 

Brachiocephalicus 

Lateral  head  of 

triceps  (cut) 


Cutaneous  hranch  of 

axillary  nerve 

Anterior  radial  arterij 

Common  digital  extensor 

Brachialis 


Extensor  carpi  radialis 


Extensor  carpi  obliquus 

Tendon  of  extensor  carf/i 
radialis 
Lateral  lig.  of  carpus 

Rete  carpi  dor  sale 

Tendon  of  common  extensor 

Branch  to  lateral  extensor 


Tensor  fasdce  antibrachii 
Lung  head  of  triceps 

Brunch  of  radial  nerve  to 
heads  of  triceps  and  anconeus 
Deep  brachial  artery 

Radial  nerve 

Long  head  of  triceps 

Medial  head  of  triceps 

Anconeus 

Lateral  head  of  triceps  (cut  off) 

Olecranon 

Ulnar  head  of  deep  flexor 
Cutaneous  branch  of  ulnar 

nerve 
Lateral  lig.  of  elbow 
Ulnar  is  lateralis  (cut 
and  reflected) 


Common  interosseous  artery 

Ulna 

Ulnar  head  of  common 

digital  extensor 
Deep  digital  flexor 

Lateral  digital  extensor 
Ulnar  nerve  and  vein 


-  Ulnaris  lateralis  (stump) 


Dorsal  interosseous  artery 

Superficial  branch  of  ulnar 
nerve 

Carpal  sheath  (opened) 
Lateral  tendon  of  ulnaris 

lateralis 
Accessory  carpal  bone 

A  ccessorio-metacarpal 
ligaments 

Band  from  accessory  carpal 
to  lateral  extensor  tendon 
Lateral  extensor  tendon 


Fig.  .568.— Dissection  of  Left  Fore.a^rm  of  Hoksk;  Lateral  Surface. 
The  radial  and  ulnar  heads  of  the  anterior  digital  extensor  are  shown  in  front  of  the  lateral  extensor,  but  are  not 
marked.     The  muscular  branches  of  the  radial  nerve  are  shown,  but  not  designated  indi^^dually.     Dotted  lines  indi- 
cate contour  of  parts  of  muscles  which  have  been  removed  (lateral  head  of  triceps,  extensor  carpi  radialis,  lateral  flexor 
of  carpus).     (After  Schmaltz,  Atlas  d.  Anat  d.  Pferdes.) 


interosseous  artery  (A.  interossea  volaris),  which  descends  to  the  radial  head  of  the 
deep  flexor.     In  the  space  it  supplies  the  nutrient  arteries  of  the  radius  and  ulna. 


656 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


Emerging  from  the  space  it  gives  off  branches  to  the  ulnaris  lateralis,  and  the  small 
recurrent  interosseous  artery  (A.  interossea  recurrens),  which  ascends  on  the  lateral 


Artery  of  rete  carpi  volare 


Oblique  ligament 

Medial  lig. 
First  carpal  bone 

Deep  volar  metacarpal  arteries 
Medial  metacarpal  bone 


Radius 


Accessorio-radial  lig. 
Accessorio-ulnar  lig. 

Lateral  lig. 
Check  ligament 

Accessorio-metacarpal  lig. 

Deep  volar  arch 

Suspe7isory  ligament 
Lateral  metacarpal  bone 


Fig.  569. — Deep  Dissection  of  Right  Carpus  of  Horse;  Posterior  View. 
1,  Radial  carpal  bone;   2,  accessory  carpal  bone;   3,  second  carpal  bone.    (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


Joint  capsule 


Tendon  of  lateral 

extensor 

Lateral  ligament 


Long  tendon  of. 
ulnaris  lateralis 

Superficial  branch 
of  ulnar  nerve 


Tf  ndon  of  extensor 
1(11  pi  radialis 


1 1  ndon  of  extensor 
irpi  obliquus 


Midial  ligament 


1 1  ndon  of  flexor 
(  irpi  radialis 
Common  digital  vein 
\[(dial  volar  meta- 
((u  pal  artery 


Common  diqdal  aitiry 
Liiterul  mttuvar pal  vein 

Lateral  volar  metacarpal  artery 
Fig.  570. — Cross-section  of  Proximal  Part  of  Left  Carpus  of  Horse. 
Cr,  Ci,  Cu,  Ca,  radial,  intermediate,  ulnar,  and  accessory  carpal  bones;    1,  superficial  flexor  tendon;   2,  deep  flexor 
tendon;   3  (on  volar  carpal  ligament),  carpal  canal;   4,  oblique  ligament  from  radius  to  radial  carpal  bone;   5,  tendon  of 
common  extensor;   6,  medial  volar  nerve;   7,  lateral  volar  nerve.     Syno\'ial  ca\'ities  are  black. 


surface  of  the  ulna  and  anastomoses  with  the  deep  brachial  and  ulnar  arteries. 
Under  cover  of  the  common  digital  extensor  it  connects  with  the  anterior  radial 
artery  and  gives  off  the  dorsal  interosseous  artery  (Fig.  568).     This  vessel  (A. 


THE   MEDIAN   ARTERY 


657 


interossea  dorsalis)  descends  between  the  common  and  lateral  extensors  of  the  digit 
and  concurs  with  the  anterior  radial  in  forming  a  network  on  the  dorsal  surface  of 
the  carpus,  the  rete  carpi  dorsale.  From  the  latter  arise  two  small  vessels,  the 
medial  and  lateral  dorsal  metacarpal  arteries  (A.  metacarpea  dorsalis  medialis, 
lateralis),  which  run  distally  in  the  grooves  between  the  large  and  small  metacarpal 
bones  and  anastomose  with  the  volar  metacarpal  arteries. 

4.  The  artery  of  the  rete  carpi  volare  (A.  retis  carpi  volaris)  is  a  small  vessel 
which  arises  at  the  distal  third  of  the  forearm  and  descends  on  the  radius  to  the 
posterior  surface  of  the  carpus,  where  it  concurs  with  branches  of  the  volar  meta- 
carpal arteries  in  forming  the  rete  carpi  volare. 

5.  The  lateral  volar  metacarpal  artery  (A.  metacarpea  volaris  lateralis)^  is  a 
small  vessel  which  arises  just  above  the  carpus  under  cover  of  the  flexor  carpi 
ulnaris  and  anastomoses  with  the  ulnar  artery,  forming  the  supracarpal  arch. 
From  the  latter  a  branch  descends  with  the  lateral  branch  of  the  median  nerve, 


Tendon  of  common  extensor 


Skin 
Mc.  Ill 


Mc.  II 


Common  digital  vein 
Common  digital  artery 
Medial  volar  nerve 
Superficial  flexor  tendon 


Tendon  of  lateral  extensor 


_  _      Mc.  IV 

^ Suspensory  ligament 

j  Lateral  volar  metacarpal 

'  vessel 

Lateral  volar  nerve 

Check  ligament 
Deep  flexor  tendon 
Deep  fascia 


Fig.  571. — Cross-section  of  Right  Metacarpus  of  Horse. 

Section  is  cut  a  little  above  middle  of  region. 

1,  1',  Dorsal  metacarpal  arteries;  2,  2',  deep  volar  metacarpal  arteries;  3,  deep  volar  metacarpal  vein;  4,  distal  part  of 

carpal  sheath. 


inclines  outward  toward  the  posterior  border  of  the  accessory  carpal  bone,  and 
arrives  at  the  head  of  the  lateral  metacarpal  bone.  Here  it  is  connected  with  the 
medial  volar  metacarpal  artery,  usually  by  two  transverse  branches,  thus  forming 
the  deep  volar  or  subcarpal  arch  (Arcus  volaris  profundus  proximalis).  One  of 
these  branches  lies  between  the  subcarpal  check  ligament  and  the  suspensory 
ligament ;  the  other  (not  always  present)  lies  beneath  the  latter  on  the  large  meta- 
carpal bone.  A  small  branch  descends  to  the  fetlock  with  the  lateral  volar  nerve. 
Below  the  arch  the  artery  pursues  a  flexuous  course  downward  on  the  volar  face  of 
the  large  metacarpal  bone  alongside  of  the  lateral  small  metacarpal  and  under 
cover  of  the  suspensory  ligament.  At  the  distal  third  of  the  metacarpus  it  com- 
monly unites  with  the  corresponding  vessel  of  the  other  side  to  form  a  short  trunk 
which  passes  backward  through  the  angle  of  divergence  of  the  branches  of  the  sus- 
pensory ligament  and  joins  the  lateral  digital  or  the  common  digital  artery.  This 
junction  forms  the  distal  volar  arch  (Arcus  volaris  distalis). 

6.  The  medial  volar  metacarpal  artery  (A.  metacarpea  volaris  medialis)^  is 

1  Also  termed  the  external  metacarpal  artery. 

2  Also  called  the  internal  or  small  metacarpal  artery. 
42 


658 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


given  off  from  the  median  at  an  acute  angle,  usually  a  little  above  the  lateral 
one  or  by  a  common  trunk  wath  it.  It  passes  clowii  the  medial  side  of  the  carpus 
behind  the  tendon  of  the  flexor  carpi  radialis  and  embedded  in  the  posterior  annular 
ligament.  Arriving  at  the  proximal  end  of  the  medial  metacarpal  bone  it  becomes 
more  deeply  placed  and  is  connected  with  the  lateral  volar  artery  by  one  or  two 
transverse  branches,  as  stated  above.     It  then  pursues  a  flexuous  course  downward 


Medial  ligament  of  carpus 

Tendon  of  extensor  carpi  radialis 
Tendon  of  extensor  carpi  obliquus 


Medial  ligament  of  fetlock  joint 
Common  extensor  tendon 

Extensor  branch  of  suspensory 
ligament 

Dorsal  artery  of  first  phalanx 


Medial  ligament  of  pastern  joint 


-■  Lateral  metacarpal  vein 
Medial  metacarpal  vein 

Postiriur  annulnr  ligament  of 
carpus 


Superficial  flexor  tendon 
Medial  volar  nerve 

Communicating  branch 
Common  digital  artery 
Medial  metacarpal  vein 
Suspensory  ligament 
Lumbricalis  muscle 
Dorsal  digital  nerve 
Volar  digital  nerve 
Digital  artery 
Digital  vein 
Ligament  of  ergot 
Deep  flexor  tendon. 
Cartilage  of  third  phalanx 

Coronary  plexus 


Coronary  corium 
Laminar  corium 


Fig.  572. — Dissection  of  Right  Carpus,  Metacarpus,  and  Digit  op  Horse;  Medial  View.  (After  Schmaltz,  Atlas 

d.  Anat.  d.  Pferues.) 


alongside  of  the  medial  small  metacarpal  bone,  like  the  corresponding  lateral 
artery,  with  which  it  commonly  unites  as  described  above.  It  is  larger  than  the 
lateral  artery,  and  supplies  the  nutrient  artery  to  the  large  metacarpal  bone. 

The  foregoing  account  describes  the  most  common  arrangement  of  the  dorsal  and  volar 
metacarpal  arteries.  Variations  in  their  origin  and  connections  are  common,  but  have  no  great 
surgical  importance.  Collateral  branches  are  omitted  for  the  same  reason.  In  some  cases  the 
medial  volar  metacarpal  is  connected  with  the  common  digital  artery  a  little  below  the  carpus  by 
a  branch  passing  obliquely  across  the  medial  border  of  the  deep  flexor  tendon;  this  forms  a  super- 
ficial volar  arch. 


THE    COMMON    DIGITAL   ARTERY THE    DIGITAL   ARTERIES  659 


THE  COMMON  DIGITAL  ARTERY 
The  common  digital  artery  (A.  digitalis  communis  s.  metacarpea  volaris 
superficialis)^  is  the  direct  continuation  of  the  median.  It  descends  in  the 
carpal  canal  along  the  medial  side  of  the  flexor  tendons  in  company  with  the 
medial  volar  nerve.  Continuing  down  the  limb  it  preserves  this  relation  to  the 
tendons  to  the  distal  third  of  the  Lietacarpus,  where  it  inclines  toward  the  middle 
line  of  the  limb  behind  the  suspensory  ligament,  and  divides  into  the  medial  and 
lateral  digital  arteries.  In  the  metacarpus  the  artery  is  related  to  the  vein  in  front 
and  the  nerve  behind,  and  is  covered  by  the  fascia  and  skin.  It  furnishes  collateral 
branches  to  the  suspensory  ligament,  the  flexor  tendons,  and  the  skin. 


THE  DIGITAL  ARTERIES 
The  digital  arteries,  medial  and  lateral  (A.  digitalis  volaris  propria  medialis, 
lateralis),  are  formed  by  the  bifurcation  of  the  common  digital  at  the  distal  third 
of  the  metacarpus.  They  diverge,  pass  down  over  the  abaxial  surface  of  the  cor- 
responding sesamoid  at  the  fetlock,  and  descend  parallel  with  the  borders  of  the  deep 
flexor  tendon  to  the  volar  grooves  and  foramina  of  the  third  phalanx.  Entering  the 
latter  the  two  arteries  unite  in  the  semilunar  canal  and  form  the  terminal  arch 
(Arcus  terminalis),  from  which  numerous  branches  pass  through  the  bone  to  the 
dorsal  surface  and  ramify  in  the  corium  of  the  wall  and  sole  of  the  hoof .^  A  num- 
ber of  branches  emerge  through  tlie  foramina  at  the  distal  border,  where  they  anas- 
tomose with  each  other  in  arciform  fashion. 

These  branches  were  named  by  Spooner  the  inferior  communicating  arteries,  and  the  anas- 
tomotic arch  formed  by  them  is  termed  the  circumflex  artery  of  the  third  phalanx  (Chauveau) 
or  the  artery  of  the  distal  border  of  the  third  phalanx  (Leisering). 

Each  artery  is  accompanied  by  a  vein  and  by  the  digital  nerves.  Above  the 
fetlock  the  artery  is  most  deeply  placed  and  is  covered  by  the  vein;  the  nerve  is 
beh  nd  the  vein.  At  the  fetlock  the  artery  has  become  superficial  and  is  related 
to  the  vein  in  front  and  the  posterior  branch  of  the  nerve  behind.  The  anterior 
branch  of  the  nerve  crosses  over  the  artery  obliquely  to  the  side  of  the  first  phalanx. 
The  artery  and  nerves  are  crossed  obliquely  by  a  small  band,  the  tendon  or  ligament 
of  the  ergot  {vide  digital  fascia). 

In  addition  to  branches  to  the  joints,  tendons  and  synovial  sheath,  ergot,  and 
skin,  the  digital  arteries  give  off  the  following  named  branches: 

1.  The  artery  of  the  first  phalanx  (A.  phalangis  primse)^  is  a  short  trunk  which 
arises  at  a  right  angle  about  the  middle  of  the  first  phalanx,  and  divides  into 
dorsal  and  volar  branches.  The  dorsal  branch  (Ramus  dorsalis)  passes  between 
the  first  phalanx  and  the  extensor  tendon  and  ramifies  on  the  front  of  the  digit, 
anastomosing  with  its  fellow.  The  volar  branch  (Ramus  volaris)  dips  in  between 
the  flexor  tendons  and  the  first  phalanx  and  anastomoses  with  the  opposite  artery 
between  the  superficial  and  middle  distal  sesamoidean  ligaments. 

2.  The  artery  of  the  digital  cushion  (A.  toricae  phalangis  tertise)  arises  at  the 
proximal  border  of  the  cartilage  of  the  third  phalanx  and  passes  backward  and 
downward  to  ramify  in  the  digital  cushion  and  the  corium  of  the  heels  and  frog. 

3.  The  dorsal  artery  of  the  second  phalanx  (Ramus  dorsalis  phalangis  secundae) 
arises  a  little  above  the  level  of  the  distal  sesamoid  bone,  and  passes  forward  under 
cover  of  the  cartilage  of  the  third  phalanx  and  the  extensor  tendon  to  the  front  of 
the  second  phalanx,  where  it  anastomoses  with  the  opposite  vessel.     It  gives 

^  This  vessel  is  also  termed  the  large  or  palmar  metacarpal  artery. 

2  The  terminal  part  of  the  digital  artery  has  been  termed  the  plantar  artery. 

^  Also  termed  the  perpendicular  artery. 


660  BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 

branches  to  the  skin,  the  tendon,  the  coffin  joint,  and  the  coronary  corium  of  the 
hoof. 

4.  The  volar  artery  of  the  second  phalanx  (Ramus  volaris  phalangis  secundse) 
is  smaller  than  the  preceding,  opposite  to  which  it  arises.  It  passes  above  the 
proximal  border  of  the  distal  sesamoid  and  unites  with  the  opposite  artery. 

The  arteries  of  the  second  phalanx  form  what  is  termed  by  Chauveau  the  coronary  circle. 
The  dorsal  (anterior)  part  of  the  circle  gives  off  commonly  an  artery  (A.  coronal  is  phalangis  tertite) 
near  either  side  of  the  extensor  tendon,  which  divides  into  two  branches.  The  central  branch 
unites  with  that  of  the  opposite  side,  while  the  other  joins  a  branch  of  lli(>  artery  of  the  digital 
cushion.  In  this  way  is  formed  the  circumflex  artery  of  the  coronary  cushion,  an  anastomotic 
arch  which  lies  on  the  extensor  tendon  at  tlie  coronet.  In  some  ca^es  descending  branches  of  the 
arteries  of  the  first  phalanx  concur  in  the  formation  of  the  arch. 

5.  The  dorsal  artery  of  the  third  phalanx  (A.  dorsalis  phalangis  tertise)^  arises 
at  the  deep  face  of  the  angle  of  the  third  phalanx,  passes  through  the  notch  or  fora- 
men there,  and  runs  forward  in  the  groove  on  the  dorsal  surface.  It  gives  off 
ascending  and  descending  branches,  which  ramify  in  the  corium  of  the  wall  of  the 
hoof,  anastomosing  above  "with  the  circumflex  artery  of  the  coronary  cushion  and 
distally  with  the  circumflex  artery  of  the  third  phalanx.  Before  passing  through 
the  wing  it  detaches  a  retrograde  branch  to  the  digital  cushion,  and  after  emerging, 
one  which  ramifies  on  the  convex  surface  of  the  cartilage  of  the  third  phalanx. 

BRANCHES  OF  THE  THORACIC  AORTA 
In  addition  to  the  coronary  arteries  and  the  common  brachiocephalic  trunk 
(which  have  been  described),  the  thoracic  part  of  the  aorta  gives  off  branches  to  the 
thoracic  walls  and  viscera  and  to  the  spinal  cord  and  its  membranes.  The  visceral 
branches  (Rami  viscerales)  are  the  bronchial  and  oesophageal,  which  arise  by  a 
broncho-oesophageal  trunk.  The  parietal  branches  (Rami  parietales)  are  the 
intercostal  and  phrenic  arteries. 

1.  The  broncho-cesophageal  artery  (Truncus  broncho-cesophageus)  is  a  short, 
usually  bulbous,  trunk  which  arises  at  the  sixth  thoracic  vertebra  from  the  aorta  or  in 
common  with  the  first  aortic  intercostal  arteries.  It  descends  (under  cover  of  the 
vena  azygos)  over  the  right  face  of  the  aorta  toward  the  bifurcation  of  the  trachea 
and  divides  into  bronchial  and  oesophageal  branches.  The  bronchial  artery  (A. 
bronchialis)  crosses  the  left  face  of  the  oesophagus  to  the  bifurcation  of  the  trachea, 
where  it  divides  into  right  and  left  branches.  Each  enters  the  hilus  of  the  cor- 
responding lung  above  the  bronchus,  which  it  accompanies  in  its  ramification.  It 
supplies  the  lung  tissue  and  also  detaches  twigs  to  the  bronchial  lymph  glands  and 
the  mediastinum.  The  oesophageal  artery  (A.  oesophagea)  (Fig.  554)  is  a  small 
vessel  which  passes  backward  dorsal  to  the  oesophagus  in  the  posterior  mediastinum 
and  anastomoses  with  the  oesophageal  branch  of  the  gastric  artery.  It  detaches 
twigs  to  the  oesophagus  and  the  mediastinal  lymph  glands  and  pleura,  and  gives  off 
two  branches  which  pass  between  the  layers  of  the  ligaments  of  the  lungs  and  ramify 
in  the  subpleural  tissue.  Very  commonly  there  is  another  artery  which  runs  back- 
ward ventral  to  the  a'sophagus.- 

2.  The  intercostal  arteries  (Aa.  intercostales)  (Figs.  553,  554)  number  eighteen 
pairs.  The  first  arises  from  the  deep  cervical  artery,  the  next  three  from  the 
subcostal  branch  of  the  dorsal  artery,  and  the  remainder  from  the  aorta.  The 
aortic  intercostal  arteries  arise  from  the  dorsal  face  of  the  aorta  in  pairs  close  to- 
gether; the  fifth  and  sixth  usually  spring  from  a  common  stem.  Each  passes  across 
the  body  of  a  vertebra  to  the  corresponding  intercostal  space,  detaches  twigs  to  the 
vertebrae  and  the  pleura,  and  divides  into  dorsal  and  ventral  branches.     The  dorsal 

^  Also  termed  the  preplantar  artery. 

2  In  some  cases  there  is  no  broncho-oesophageal  trunk,  the  bronchial  and  oesophageal  arising 
separately.     In  other  cases  the  second  aortic  intercostal  arises  in  common  with  them  also. 


BRANCHES  OF  THE  ABDOMINAL  AORTA 


661 


branch  (Ramus  dorsalis)  gives  off  a  spinal  branch  (Ramus  spinalis)  which  passes 
through  the  intervertebral  foramen,  gives  twigs  to  the  membranes  of  the  spinal 
cord,  perforates  the  dura,  and  reinforces  the  ventral  spinal  artery.  A  muscular 
branch  passes  to  the  muscles  and  skin  of  the  back.  The  ventral  branch  (Ramus 
ventralis)  is  much  the  larger.  It  descends,  at  first  almost  in  the  middle  of  the 
intercostal  space  between  the  intercostal  muscles,  then  gains  the  posterior  border 
of  the  rib,  and  is  subpleural.  Each  is  accompanied  by  a  vein  and  nerve,  the  artery 
being  in  the  middle  and  the  vein  in  front.  At  the  ventral  part  of  the  space  it  unites 
with  a  ventral  intercostal  branch  of  the  internal  thoracic  or  the  musculo-phrenic 
artery.  It  supplies  the  intercostal  muscles,  the  ribs  and  the  pleura,  and  gives  off 
perforating  branches  which  pass  out  to  the  serratus  ventralis,  the  abdominal 
muscles,  and  the  skin. 

3.  The  phrenic  arteries  (Aa.  phrenicae)  are  two  or  three  small  vessels  which 
arise  at  the  hiatus  aorticus  from  the  ventral  aspect  of  the  aorta,  often  by  a  common 
trunk.  They  supply  the  crura  of  the  diaphragm.  In  some  cases  they  arise  in 
common  with  an  intercostal  artery. 


BRANCHES  OF  THE  ABDOMINAL  AORTA 

The  collateral  branches  of  the  abdominal  part  of  the  aorta  are  distributed 
chiefly  to  the  walls  and  contents  of  the  abdominal  cavity,  but  some  branches  are 


Fig.  673. — Plan  of  Branches  of  Cceliac  Artery  of  Horse. 
1,  Coeliac  artery;   2,  gastric  artery;   3,  hepatic  artery;    4,  splenic  artery;   5,  posterior  gastric  artery;    6,  anterior 
gastric  artery;    7,  oesophageal  branch;    8,  gastro-duodenal  artery;    9,  pancreatico-duodenal  artery;    10,  right  gastro- 
epiploic artery;   11,  pyloric  artery;  12,  left  gastro-epiploic  artery;  13,  short  gastric  branches  of  splenic. 


supplied  to  the  spinal  cord  and  its  membranes,  and  others  extend  into  the  pelvis 
and  to  the  scrotum.     The  visceral  branches  are  the  cceliac,  anterior  mesenteric, 


662  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

renal,  posterior  mesenteric,  and  internal  spermatic  or  utero-ovarian.     The  parietal 
branches  are  the  Imiibar  arteries. 

I,  The  coeliac  artery  (A.  coeliaca)  is  an  unpaired  vessel,  usually  half  an  inch 
or  less  (ca.  1  cm.)  in  length,  which  arises  from  the  ventral  aspect  of  the  aorta  at  its 
emergence  from  the  hiatus  aorticus.  It  divides  on  the  dorsal  surface  of  the  pan- 
creas into  three  branches — the  gastric,  hepatic,  and  splenic. 

1.  The  gastric  artery  (A.  gastrica  sinistra)  passes  downward  and  forward  in 
the  gastro-phrenic  ligament,  gives  off  oesophageal  and  pancreatic  branches, 
and  divides  above  and  behind  the  cardia  into  anterior  and  posterior  branches. 
The  anterior  branch  (Ramus  cranialis)  crosses  the  lesser  curvature  just  to  the  right 
of  the  cardia  and  ramifies  on  the  parietal  surface  of  the  stomach.  The  branches 
pursue  a  fiexuous  course  toward  the  greater  curvature  and  anastomose  with  the 
short  gastric  arteries  and  the  gastric  branch  of  the  hepatic  artery.  The  pos- 
terior branch  (Ramus  caudalis)  is  distributed  in  a  similar  fashion  on  the  visceral 
surface.  The  oesophageal  branch  (Ramus  oesophageus)  passes  through  the  hia- 
tus oesophageus  into  the  thoracic  cavity  above  the  oesophagus  and  anastomoses 
with  the  oesophageal  branch  of  the  broncho-oesophageal  artery. 

The  gastric  artery  often  arises  by  a  common  trunk  with  the  splenic.  The  two  terminal 
branches  may  arise  separately,  or  the  anterior  from  the  splenic  and  the  posterior  from  the  hepatic. 
The  oesophageal  branch  often  arises  from  the  splenic  or  the  posterior  gastric. 

2.  The  hepatic  artery  (A.  hepatica)  is  larger  than  the  gastric.  It  passes  for- 
ward and  to  the  right  and  ventrally  on  the  dorsal  surface  of  the  pancreas,  covered  by 
the  gastro-pancreatic  fold,  crosses  obliquely  under  the  vena  cava,  and  reaches  the 
medial  border  of  the  portal  vein.  It  divides  into  three  or  four  branches  which  enter 
the  portal  fissure  of  the  liver  and  ramify  within  the  gland  with  the  portal  vein  and 
the  hepatic  duct.  It  gives  off  the  following  collateral  branches:  (1)  Pancreatic 
branches  (Aa.  pancreaticse)  are  given  off  as  the  artery  crosses  the  pancreas,  in 
which  it  is  partly  embedded.  (2)  The  pyloric  artery  (A.  gastrica  dextra)  arises 
above  the  first  curve  of  the  duodenum.  It  descends  to  the  pylorus,  sending  branches 
to  the  pylorus  and  the  first  part  of  the  duodenum,  and  anastomoses  with  the  gastric 
and  right  gastro-epiploic  arteries.  It  may  arise  from  the  gastro-duodenal.  (3) 
The  gastro-duodenal  artery  (A.  gastroduodenalis)  passes  to  the  second  curve  of  the 
duodenum  and  divides  into  the  right  gastro-epiploic  and  the  pancreatico-duodenal. 
The  right  gastro-epiploic  artery  (A.  gastroepiploica  dextra)  crosses  over  the  posterior 
surface  of  the  duodenum  and  enters  the  greater  omentum,  in  which  it  runs  to  the 
left,  parallel  with  the  greater  curvature  of  the  stomach.  It  gives  branches  to  the 
latter  and  to  the  omentum  and  forms  an  anastomotic  arch  with  the  left  gastro- 
epiploic artery.  The  pancreatico-duodenal  artery  (A.  pancreaticoduodenalis) 
divides  into  pancreatic  and  duodenal  branches.  The  former  (Ramus  pancreaticus) 
supplies  the  middle  part  of  the  pancreas  and  is  often  replaced  by  a  number  of 
variable  twigs.  The  duodenal  branch  (Ramus  duodenalis)  passes  to  the  right  along 
the  lesser  curvature  of  the  duodenum  and  anastomoses  with  the  first  branch  of  the 
anterior  mesenteric  artery. 

Variations  in  the  branching  of  the  hepatic  artery  are  not  uncommon.  The  pancreatico- 
duodenal may  arise  directly  from  the  trunk,  and  there  may  be  a  common  trunk  for  the  pyloric  and 
right  gastro-epiploic  which  runs  along  the  dorsal  surface  of  the  first  curve  of  the  duodenum  to  the 
pylorus;  here  it  gives  off  the  small  pyloric  branch  and  is  continued  across  the  parietal  surface  of 
the  pylorus  as  the  right  gastro-epiploic,  no  gastro-duodenal  trunk  being  present. 

3.  The  splenic  artery  (A.  lienalis)  is  the  largest  branch  of  the  coeliac.  It  passes 
to  the  left  (with  the  large  satellite  vein)  on  the  left  extremity  of  the  pancreas  and 
across  the  saccus  csecus  of  the  stomach.  Entering  the  suspensory  ligament  of  the 
spleen,  it  runs  in  the  hilus  of  the  spleen  to  the  apex,  beyond  which  it  is  continued 
as  the  left  gastro-epiploic.  It  gives  off  the  following  branches:  (1)  Pancreatic 
branches  (Rami  pancreatici),  which  supply  the  left  extremity  of  the  pancreas. 


BRANCHES  OF  THE  ABDOMINAL  AORTA 


6G3 


(2)  Splenic  branches  (Rami  lienales),  which  plunge  into  the  substance  of  the  spleen. 

3    Short  gastric  branches  (Aa.  gastric^  breves)   which  pass  in  the  g^f  ^^-^Pl^^^^ 

omentum  to  the  greater  curvature  of  the  stomach,  where  they  bifurcate  and  anas- 

tomose^th  the  branches  of  the  gastric  arteries.     (4)  The  left  gastro-epiploic 


Fig  574  —Plan  of  Chiep  Branches  of  Anterior  Mesenteric  Artery  of  Horse. 

2,  stumps  of  arteries  of  small  intestine;   3,  lateral  cscal  artery;    4, 


1,  Stump  of  anterior  mesenteric  artery 
_  1  csecal  artery;  5,  ileal  artery;  6,  venti 
small  colon.     By  an  oversight  the  left  ventral  colon  is  erroneous! 


artery;  8,  middle  colic  or  first  artery  of 
ily  labeled  right  dorsal  (upper  left  part  of  figure). 

artery  (A.  gastroepiploica  sinistra)  is  the  continuation  of  the  splenic  artery  It 
nass^s  to  the  right  in  the  greater  omentum,  parallel  with  the  greater  curvature  of  the 
stomach  and  'anastomoses  with  the  right  gastro-epiploic.  It  gives  off  branches 
to  the  greater  curvature  of  the  stomach  and  twigs  to  the  omentum. 


664 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


E^    ^ 


BRANCHES  OF  THE  ABDOMINAL  AORTA  665 


&.2     I     »-.  ^  s     c  £  o"  t  g  II.  The  anterior  or  great  mesenteric  artery 

S  B     ■%      •„-  §  S     .2. 1  ^  ,°1  =^  (A.  mesenterica  cranialis)  arises  from  the  ventral 

^1     ^     ^"1      ^'^"^^-'^  ^^^6  of  the  aorta  at  the  first  lumbar  vertebra.     It 

:§  §"     "i      S  E  ^      ?  1 1  o  •"  ^^  ^  large  unpaired  trunk,  about  an  inch  (ca.  2-3 

"«'     I     i|«     ■2'1'o-li  cm.)  in  length,  which  passes  ventrally  between  the 

o  ■^      a     -t ::  ^      s  ^  I  ^-  "^  vena  cava  and  the  left  adrenal  into  the  root  of 

^"  i     :l      ^  fi  ^"     ^  ^  I  "  --  ^^^  great  mesentery,  when  it  divides  into  three 

'^-  •-      I     'I  ^  -     t  -  I  I  i  branches — left,  right,  and  anterior.^ 

l|     ■§     -S§;5     l|ft:-|'^  1.  The  left  branch  gives  off  at  once  about 

8  .2  S  1^     §  .s  'o     g  c  a,"  I  c  fifteen  to  twenty  arteries  of  the  small  intestine 

iig-3     |c|     l"aS"||  (Aa.  intestinales)  ."^     These  come  off  close  together 

-||"3     "flig     -slffii^  ^^^d  P^^s  i^  divergent  fashion  between  the  layers 

I  S  §  c|  .g     -^  g  -^   ^  ^.  -3  _!  I  of  the  great  mesentery,  each  dividing  into  two 

§  i"  ^  2  S      i  1 1 1  -^  M  t  if  °  branches  which  anastomose  with  adjacent  branches 

r..  -s  .-  .•=  "^      o  o  I  1 .9  ^  I  °  g  ^Q  form  a  series  of  arches.     In  the  anterior  part  of 

the  series  secondary  arches  are  formed  by  the  union 
of  branches  given  off  from  the  primary  set  of 
arches.  From  the  convex  side  of  these  arches 
terminal  branches  pass  to  the  wall  of  the  small 
intestine,  in  which  they  ramify  and  form  a  vascu- 
lar network.  They  are  accompanied  by  satellite 
i  o  ?.  ^"  s  I  I  I  I  veins  and  by  nerves  and  lymph  vessels.     The  first 

Ifeol      s|^|fl°s|.S  artery  anastomoses  with  the  pancreatico-duodenal, 

^l|§     -^^-lli§^  ^^^  ^^^  l^s*  "^^^^^  ^^^^  ^1^^^  branch  of  the  great 

si.,!--      fi  1 1 1  !•  ^  I  "H  i  mesenteric  artery.     Branches  are  supplied  to  the 

i      M  °  .2  t  o"  I  °  i  ^  mesenteric  lymph  glands. 

^"  ir  I  1 1  I  2.  The    right    branch    (A.    ileo-caeco-colica) 

""  I  la-  ^  ^  ^  might  be  regarded   as  the  continuation  of   the 

'^.  I  "x  S*  -S     1 1  "3  ^  .1  ;;  '^  '^  !^  trunk.     It  runs  downward  and  a  little  forward 

and  to  the  right,  and  gives  off  the  ileal,  the  two 
csecal,  and  the  ventral  colic  arteries.     (1)   The 
I  t  I  ^- 1  5  ^  §  M  ileal  or  ileo-csecal  artery  (A.  ilea)  passes  in  retro- 

ft^l!!§t'.BJ  I  grade  fashion  along  the  terminal  part  of  the  ileum 

■^^  1 1 1)  :§•  I  III  and  unites  with  the  last  branch  of  the  left  division. 

I)l||2s|l3  (2)  The  lateral  caecal  artery  (Ramus  csecalis  later- 

l^i  >  I  a^^Z  alls)  passes  between  the  caecum  and  the  origin  of 

-g  '!°,  ^  S  "^  "o  2  £  a  the  colon  and  runs  on  the  lateral  band  of  the  caecum 

I  ^5)  *"  I  "  I  I  2  S  to  the  apex,  where  it  anastomoses  with  the  medial 

ola^.  3      |ui>g"5°|'p'  artery.  Besides  numerous  collaterals  to  the  caecum, 

I.  « -3  1 1-     g  I  ^  S  "  i  I  Sh  it  gives  off  the  artery  of  the  arch,  which  passes 

6   g  I  a  iT     ;s  g  i  g  I  '^  I  "S   .  along  the  lesser  curvature  of  the  base  of  the  caecum 


a  .E 

^;pg§a_cl5o> 

^  ^  ^"  '^-  ^  ^"  ^"  I  I 
-  o  ^.  ^   o  j,-        -    - 


s 


-^  ._  ^    a 


-tJ     B     O     X     X    *^     •>, 

.d    ^    a  o   «    X    C 
•-   2  _e  o"  ■-   S   ° 


and  runs  on  the  lateral  face  of  the  origin  of  the 
great  colon.     (3)  The  medial  caecal  artery  (Ramus 

■Sli!".  II  l^^l  caecalis  medialis)  passes  along  the  medial  band  to 
1 1  -  "1  I  ^  i"  III  ^  I  "^  -o  "the  apex  of  the  caecum,  where  it  anastomoses  with 
^  I  I  -"^     2  II-  o  s  I  '^^^  ^  S  ii       the  lateral  caecal  artery.     (4)  The  ventral  colic 

°  I  I  "^      e  "S  .2  I  ■§  C  fi  "^  "  "^  1  In  the  great  majority  of  subjects  this  vessel  and  some 

*^.  ft  1 1      ^  c  I  -  "°  t  -^  -2  ^  ^  of  its  branches  are  the  seat  of  more  or  less  extensive  vermin- 

r  95-  ^  »       I  S  ^  a  S  g,  g  I  §  -<  ous  aneurvsm,  produced   by  the  Sclerostomum  vulgare. 

■S  '~'  b- 1      -^  ^  «  -2  "^  ^  .S  *;^  .2  i  In  the  author's  experience  an  entirely  normal  specimen  is 

"'''""  quite  unlikely  to  be  encountered  except  in  very  young  foals. 

i  "I      1  §  '^"  °  M  o"  "-  "S  ri  2  The  left  branch  is  a  descriptive  convention  rather 


§  .2 


-2  =i  ^  a      J  'I  7.  J  ^-  '^-  '^  S  I  ^         than  a  reality,  since  the  arteries  of  the  small  mtestine  spring 
"^  S  fe"^^^  a  5;  c'^  i'3'3:2«        from  the  mesenteric  trunk  either  directly  or  by  short  com- 


o  ^ 


mon  stems  with  an  adjacent  vessel. 


666  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

artery  (A.  colica  ventralis)^  runs  along  the  dorso-medial  bands  of  the  opposed 
surfaces  of  the  ventral  parts  of  the  great  colon  to  the  pelvic  flexure,  where  it  unites 
with  the  dorsal  colic  artery.  It  supplies  the  ventral  parts  of  the  great  colon  and 
sends  a  branch  to  the  base  of  the  caecum. 

3.  The  anterior  branch  divides  after  a  very  short  course  into  the  dorsal  and 
middle  colic  arteries.  (1)  The  dorsal  colic  artery  (A.  colica  dorsalis)^  is  a  large 
vessel  which  passes  along  the  dorsal  parts  of  the  great  colon  to  the  pelvic  flexure, 
where  it  joins  the  ventral  colic  artery.  (2)  The  middle  colic  artery  or  first  artery 
of  the  small  colon  (A.  colica  media)  is  a  much  smaller  vessel  which  passes  to  the 
origin  of  the  small  colon,  enters  the  colic  mesentery,  and  forms  an  arch  by  joining 
the  first  branch  of  the  posterior  mesenteric  artery  close  to  the  lesser  curvature  of 
the  bowel.     It  sends  an  anastomotic  branch  to  the  dorsal  colic  artery. 

III.  The  renal  arteries  (Aa.  renales),  right  and  left,  are  relatively  large  vessels 
which  arise  from  the  aorta  near  the  anterior  mesenteric.  The  right  artery  is  the 
longer  of  the  two.  It  crosses  over  the  dorsal  surface  of  the  vena  cava  to  the  right 
and  somewhat  forward.  At  the  hilus  it  divides  into  several  (five  to  eight)  branches; 
some  of  these  enter  the  gland  at  the  hilus,  while  others  pass  to  the  ventral  surface 
and  enter  there.  The  left  artery  is  short  and  usually  arises  a  little  further  back; 
it  passes  directly  outward  to  the  kidney  and  is  then  disposed  like  the  right  one. 
Small  collateral  branches  are  supplied  to  the  ureters,  the  perirenal  fat,  the  renal 
lymph  glands,  and  the  adrenals.  The  latter  also  receive  small  adrenal  arteries 
directly  from  the  aorta.     The  distribution  within  the  kidney  has  been  described. 

Variations  in  the  renal  arteries  are  frequent.  Two  or  more  arteries  may  occur  on  one  side  or 
both.  Accessory  arteries  are  more  common  on  the  left  side  and  usually  enter  the  posterior  part 
of  the  gland.     They  may  arise  from  the  aorta,  the  external  iliac,  or  the  circumflex  iliac  artery. 

IV.  The  posterior  or  small  mesenteric  artery  (A.  mesenterica  caudalis)  is  an 
unpaired  vessel  which  arises  from  the  ventral  face  of  the  aorta  at  the  fourth  lumbar 
vertebra,  i.  e.,  about  five  or  six  inches  (ca.  12-15  cm.)  behind  the  origin  of  the 
anterior  mesenteric  artery.  It  is  much  smaller  than  the  latter  and  supplies  the 
greater  part  of  the  small  colon  and  rectum.  It  descends  in  the  colic  mesentery 
and,  after  a  short  course,  divides  into  two  branches.  The  anterior  branch  (A.  colica 
sinistra)  gives  off  three  or  four  arteries  which  divide  and  form  anastomotic  arches 
close  to  the  bowel.  The  first  arch  is  formed  by  union  with  the  middle  colic  branch  of 
the  anterior  mesenteric.  The  posterior  branch  or  anterior  haemorrhoidal  artery 
(A.  hsemorrhoidalis  cranialis)  passes  backward  in  the  upper  part  of  the  mesentery 
and  the  mesorectum  and  terminates  near  the  anus  by  anastomosing  with  the 
internal  pudic  artery.  Three  or  four  of  its  anterior  collateral  branches  form, 
arches. 

V.  The  internal  spermatic  arteries  (Aa.  spermaticse  internse),  right  and  left, 
are  long  slender  arteries  which  arise  from  the  aorta  near  the  posterior  mesenteric 
and  supply  the  testicle  and  epididymis.^  Each  passes  backward  in  a  narrow  fold 
of  peritoneum  (Plica  vasculosa)  to  the  internal  inguinal  ring  and  descends  through 
the  inguinal  canal  to  the  scrotum.  In  its  course  in  the  anterior  border  of  the 
spermatic  cord  it  forms  numerous  coils,  surrounded  by  the  pampiniform  plexus 
of  veins,  and  associated  closely  with  the  spermatic  nerves  and  lymphatics  and 
unstriped  muscle-fibers.  It  passes  between  the  epididymis  and  testicle,  runs  in 
flexuous  fashion  along  the  attached  border  of  the  latter,  turns  around  the  posterior 
pole,  and  runs  forward  on  the  free  border  to  the  anterior  pole.  The  largest  branches 
arise  from  its  ventral  part,  pass  tortuously  up  either  side  of  the  gland,  embedded 
in  the  tunica  albuginea,  and  give  off  fine  branches  to  the  gland  substance.     Small 

1  Also  termed  the  right  or  direct  colic  artery. 

2  Also  termed  the  left  or  retrograde  colic  artery. 

'  Variations  in  the  origin  of  the  internal  spermatic  artery  are  common.  It  may  arise  from 
the  posterior  mesenteric,  or  from  the  renal,  or  the  two  may  arise  by  a  short  common  trunk. 


BRANCHES  OF  THE  ABDOMINAL  AORTA 


667 


Internal  iliac  lymph  gland. 

Circumflex  iliac  vessels 

External  iliac  lymph  glands 

Remnant  of  inguvial 
ligament 
Posterior  branch  of  circum- 
flex iliac  artery 
Lateral  cutaneous  nerve 
of  thigh 
External  spermatic  nerve 

Tensor  fascice  latoi 

Femoral  nerve  and  ante- 
rior femoral  vessels 
Femoral  artery 
Prefemoral  lymph  glands 

Deep  inguinal  lymph 
gkijids 

Fascia  lata 


Saphenous  nerves 
Saphenous  vessels 


Medial  pntcllar  ligament 
Middle  patellar  ligament 


Fig.  576.— Dissection  of  Pelvis,  Thigh,  and  Proximal  Part  of  Leg  of  Horsk;  Medial  View. 
L,  Lumbar  vessels;  T'.f.,  posterior  vena  cava;  .4 ,  aorta  (termination) ;  C,  sympathetic  trunk;  ;,  internal  iliae 
artery;  2,  lateral  sacral  artery;  3,  middle  coccygeal  artery;  4,  lateral  coccygeal  artery;  3,  umbilical  artery  (cut  off); 
6,  internal  pudic  artery;  6',  vesico-prostatic  artery;  7,  obturator  artery;  8,  a.  profunda  penis  (from  left  obturator); 
5,  posterior  gluteal  vessels;  70,  external  iliac  artery;  n,  ii',  deep  femoral  artery;  /^,  prepubic  artery;  i 5,  branch  of 
deep  femoral  artery;  14,  great  sciatic  nerve;  IS,  posterior  gluteal  nerve;  16  (above),  pudic  nerve;  16  (below,  near 
pelvic  outlet),  suburethral  venous  plexus;  7  7,  sacro-coccygeus  ventralis;  ;S,  coccygeus;  79,  recto-coccygeus;  ^0,  re- 
tractor ani;  ^/,  ^7 ',  two  heads  of  obturator  internus;  ^^,  symphysis  pelvis;  ^3,  prepubic  tendon;  ^4  suspensory  liga- 
ment of  penis;  2d,  retractor  penis  muscle;  26,  bulbo-cavernosus  muscle;  27,  urethra  (cross-section) ;  ^5,  crus  penis 
(cross-section);  29,  suspensory  ligaments  of  anus;  30,  anal  lymph  glands;  31,  tibial  nerve.  (After  Schmaltz,  Atlas  d. 
Anat.  d.  Pferdes.) 


668 


BLOOD-VASCULAR   SYSTEM    OF   THE   HORSE 


collateral  branches  are  detached  to  the  ureter,  the  epididymis,  and  the  spermatic 

cord. 

V  a.  The  utero-ovarian  arteries  in  the  female  correspond  to  the  precedmg  ves- 
sels, but  are  much  larger  and  shorter.  Each  is  placed  in  the  anterior  part  of  the 
broad  ligament  of  the  uterus  and  divides  into  ovarian  and  uterine  branches.  The 
ovarian  artery  (A.  ovarica)  pursues  a  flexuous  course  to  the  ovary,  which  it  supplies. 
The  anterior  uterine  artery  (A.  uterina  cranialis)  passes  to  the  concave  border  of  the 
cornu  of  the  uterus,  which  it  supplies,  anastomosing  with  the  middle  uterine  artery. 

VI.  The  lumbar  arteries  (Aa.  lumbales)  are  in  series  with  the  intercostal 


Perineal  artery 
Perineal  nerves 
Internal  pudic 

artery 
Dorsal  nerve  of 

penis 


Sacro-coccygeus  ventral  is 
Recto-coccygeus 
Sphincter  ani  externum 
Retractor  ani 


Fig.  577. — Dissection  of  Perineum  of  Horse  (Male). 

/,  Bulbo-urethral  gland;    2,  transversus  perinei  muscle  (?);    3,  ischio-urethral  muscle;    4,  retractor  penis  muscle;    5^ 

bulbo-cavernosus  muscle.     (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


arteries  and  have  a  similar  origin  and  distribution.  There  are  usually  six  pairs  of 
lumbar  arteries,  of  which  five  arise  from  the  aorta  and  the  sixth  from  the  internal 
iliac  or  the  lateral  sacral  at  the  junction  of  the  last  lumbar  vertebra  and  the  sacrum. 
Each  passes  across  the  body  of  a  lumbar  vertebra  to  the  intertransverse  space, 
gives  branches  to  the  sublumbar  muscles,  and  divides  into  dorsal  and  ventral 
branches.  The  dorsal  branch  (Ramus  dorsalis),  the  larger  of  the  two,  passes 
upward  to  ramify  in  the  extensor  muscles  of  the  spine  and  the  skin  of  the  loins; 
it  gives  off  a  spinal  branch  (Ramus  spinalis)  which  comports  itself  like  the  corre- 
sponding branch  of  an  aortic  intercostal  artery.  The  ventral  branch  (Ramus 
ventralis)  runs  outward  in  the  intertransverse  space,  passes  between  the  transversus 


THE    INTERNAL    ILIAC    ARTERY 


669 


and  obliquus  internus  abdominis,  gives  branches  to  these  muscles,  and  ends  in  the 
obliquus  externus,  the  cutaneus,  and  the  skin  of  the  flank. 

THE  INTERNAL  ILIAC  ARTERY 
The  internal  iliac  or  hypogastric  arteries  (Aa.  hypogastrics)  result  from  the 
bifurcation  of  the  aorta  under  the  fifth  or  sixth  lumbar  vertebra.  They  diverge 
at  an  angle  of  about  60  degrees,  and  each  passes  backward  under  the  wing  of  the 
sacrum,  then  inclines  downward  on  the  pelvic  surface  of  the  shaft  of  the  ilium, 
along  the  ventral  border  of  the  iliac  head  of  the  obturator  internus,  and  divides  a 


Coccygeus  muscle 
Anal  lymph  glands 
Branch  of  posterior  gluteal 
arteri) 

Po'^tfnor  hcemorrhoidal 
nerve 

VuUar  branch  of 
pudic  nerve 
Internal  pudic 
artery 

Branch  of  pu- 
dic nerve  to 
clitoris 


Obturator  artery 


Fig.  578. — Dissection  op  Perineum  of  Mare. 
1,  Sacro-coccygeus  dorsalis;    2,  sacro-coccygeus  lateralis;    3,  intertransversales;    4i  sacro-coccygeus  ventralis;    5, 
recto-coccygeus;   6,  sphincter  ani  externus;   6',  branch  connecting  sphincter  ani  with  constrictor  vulvae;    7,  vestibular 
bulb;  5,  tuber  ischii;  9,  sacro-sciatic  Ugament.     (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


little  (ca.  2  cm.)  above  the  psoas  tubercle  into  iliaco-femoral  and  obturator  arteries. 
The  chief  branches  are  as  follows: 

1.  The  last  pair  of  lumbar  arteries  pass  up  through  the  foramina  at  the  junc- 
tion of  the  last  lumbar  vertebra  and  the  sacrum  and  are  distributed  as  already 
described. 

2.  The  internal  pudic  artery  (A.  pudenda  interna)  arises  near  the  origin  of  the 
internal  iliac.  It  passes  backward  and  somewhat  downward,  at  first  along  the 
ventral  border  of  the  iliac  head  of  the  obturator  internus,  then  above  the  superior 
ischiatic  spine  on  the  deep  surface  of  the  sacro-sciatic  ligament,  perforates  the  latter 
and  runs  for  a  variable  distance  in  its  substance  or  on  its  lateral  face.  It  then  re- 
enters the  pelvic  cavity,  passes  backward  on  the  retractor  ani  to  the  ischial  arch, 
and  divides  into  the  perineal  artery  and  the  artery  of  the  bulb  in  the  male,  perineal 
and  artery  of  the  clitoris  in  the  female.  It  is  accompanied  posteriorly  by  the 
pudic  nerve.     Its  chief  branches  are  as  follows: 


670 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


(1)  The  umbilical  artery  is  given  off  from  the  internal  pudic  about  an  inch 
(ca.  2-3  cm.)  from  the  origin  of  that  vessel.  It  is  a  very  large  artery  in  the 
foetus,  in  which  it  curves  downward  and  forward  at  the  side  of  the  bladder  in  the 
edge  of  the  lateral  umbilical  fold  of  peritoneum,  passes  through  the  umbilical  open- 
ing, becomes  a  component  of  the  umbilical  cord,  and  ramifies  in  the  foetal  placenta. 
After  birth  it  extends  only  to  the  vertex  of  the  bladder  and  is  much  reduced.  Its 
lumen  is  almost  obliterated  and  its  wall  is  very  thick,  giving  the  vessel  a  cord-like 
character,  hence  it  is  commonly  termed  the  round  ligament  of  the  bladder. ^  It 
gives  off  small  vesical  branches  (Aa.  vesicales  craniales)  to  the  bladder,  and  twigs 
to  the  prostate  and  ductus  deferens  in  the  male.  In  the  mare  a  small  branch  runs 
forward  along  the  ureter  into  the  broad  ligament  of  the  uterus. 

(2)  The  middle  haemorrhoidal  or  vesico-prostatic  artery  (A.  hsemorrhoidalis 
media)  in  the  male  arises  usually  near  the  prostate  and  runs  backward  lateral  to 
the  rectum.  It  supplies  branches  to  the  rectum,  bladder,  urethra,  and  accessory 
genital  glands.     In  the  female  the  homologous  vessel  is  much  larger  and  gives  off 

the  posterior  uterine  artery  (A. 
uterina  caudalis).  This  runs  for- 
ward on  the  side  of  the  vagina,  to 
which  it  gives  branches,  and  rami- 
fies on  the  body  of  the  uterus,  anas- 
tomosing with  the  anterior  and 
middle  uterine  arteries.  (In  some 
cases  this  artery  arises  from  the 
internal  iliac  or  the  umbilical.) 

(3)  The  perineal  artery  (A. 
perinei)  is  relatively  small  in  the 
male.  It  ascends  at  the  side  of  the 
anus,  which  it  supplies,  and  gives 
twigs  to  the  bulbocavernosus  mus- 
cle and  the  skin  of  the  perineum. 
In  the  female  it  is  large  and  is  dis- 
tributed to  the  anus  and  vulva,  and 
gives  a  large  branch  to  the  vestibu- 
lar bulb. 

(4)  The  artery  of  the  bulb  (A. 
bulbi  urethrse)  may  be  regarded  as 
the  direct  continuation  of  the  in- 
ternal pudic  in  the  male.     It  lies 

at  the  side  of  the  urethra  above  the  ischial  arch,  dips  under  the  bulbo-cavernosus 
muscle,  and  ramifies  in  the  corpus  cavernosum  urethrse.  Before  doing  so  it  gives 
off  a  small  branch  which  turns  around  the  ischial  arch  to  reach  the  dorsum  penis, 
and  anastomoses  with  the  deep  branch  of  the  obturator. 

(4  a)  The  artery  of  the  clitoris  (A.  clitoridis)  is  the  homologue  in  the  female 
of  the  preceding  vessel,  but  is  much  smaller.  It  passes  to  the  ventral  surface  of 
the  vulva  with  a  branch  of  the  pudic  nerve,  supplies  the  clitoris,  and  gives  twigs  to 
the  vulva. 

3.  The  lateral  sacral  artery  (A.  sacralis  lateralis)  arises  at  the  lumbo-sacral 
articulation  (Fig.  576).  It  passes  backward  under  the  wing  of  the  sacrum,  then 
along  the  pelvic  surface  of  the  bone  below  the  ventral  sacral  foramina  and  the 
nerves  emerging  from  them,  and  is  continued  by  the  lateral  coccygeal  artery.  The 
branches  are  as  follows: 

(1)  Spinal  branches  (Rami  spinales)  enter  the  vertebral  canal  through  the 

1  The  obliteration  in  the  adult  extends  a  variable  distance  from  the  vesical  end  toward  the 
origin,  but  usually  involves  completely  only  a  small  part. 


Fig.  579. — Cross-sfxtion  of  Tail  of  Horse. 
1,  Dorso-lateral  coccygeal  vessels  and  nerve;  £,  ventro-lateral 
coccygeal  artery  and  nerve;  3,  middle  coccygeal  artery;  4,  sacro- 
coccygeus  dorsalis;  4',  sacro-coccygeus  lateralis;  5,  5',  intertrana- 
versales;  6,  sacro-coccygeus  ventralis;  7,  recto-coccygeus;  8, 
coccygeal  fascia;  9,  fibro-cartilage  between  fourth  and  fifth 
coccygeal  vertebrae.     The  veins  are  black. 


THE   INTERNAL   ILIAC   ARTERY 


671 


Superficial  peroneal  nerrc 
Deep  peroneal  nerve 


Deep  femoral 


Peroneal  nerve 

Tibial  nerve 
Posterior  femoral 

artery 
A",  cutaneus 

surce^ 
Popliteal  lymph 

glands 
Gastrocneynius 
Recurrent  tarsal 

vessels 


Tarsal  or  acces- 
sory tendon  of 
biceps  femoris 

Deep  flexor  of 
digit 

Gastroc7iemius 
tendon 

Superficial  flexor 
tendon 

Tuber  calcis 


Middle  annular  ligament  ■ 
Lateral  ligament 

Distal  annular  ligament 


Fig.  580. — Dissection  of  Pelvis,  Thigh,  and  Leg  of  Horse;  Lateral  View. 
1.  Dorsal  branches  of  last  thoracic  and  first  three  lumbar  nerves;  ^,  cutaneous  branch  of  fourth  lumbar  nerve;  3, 
ventral  branches  of  last  thoracic  nerve;  4>  branches  of  ilio-hypogastric  nerve;  5,  superficial  branch  of  ilio-inguinal  nerve; 
6,  great  sciatic  nerve;  7,  S,  nerves  to  biceps  femoris  (from  posterior  gluteal  nerve);  9,  nerve  to  semitendinosus  (from 
same);  10,  posterior  cutaneous  nerve  of  thigh;  11,  pudic  nerve;  1£,  anterior  gluteal  vessels  and  nerves;  13,  posterior 
gluteal  vessels;  14,  branches  of  obturator  vessels;  15,  proximal  muscular  branches  of  great  sciatic  nerve  to  biceps  fem- 
oris, semitendinosus,  and  semimembranosus;  16,  nerve  to  tensor  fascise  latae  (from  anterior  gluteal  nerve);  17,  gluteus 
profundus;  ;S,  stump  .of  gluteus  medius;  79,  gemellus;  ^0,  stump  of  quadratus  femoris;  ;2/,  stump  of  biceps  femoris; 
$2,  sacro-coccygeus  dorsalis;  23',  sacro-coccygeus  lateralis;  23,  coccygeus;  24,  sacro-coccygeus  ventraUs;  2.5,  line  of 
fusion  of  aponeuroses  of  internal  and  external  obUque  muscles  of  abdomen;  25',  aponeurosis  of  external  oblique  muscle 
(lamina  iliaca);  26,  branches  of  iliaco-femoral  vessels;  27,  ilio-lumbar  vessels;  2S,  ilio-lumbar  ligament  or  deep  layer 
of  lumbo-dorsal  fascia;  29,  tuber  coxae;  30,  tuber  sacrale;  31,  lateral  sacro-iliac  ligament;  32,  sacro-sciatic  ligament. 
The  ventral  part  of  a  nineteenth  rib  is  shown  in  front  of  3.     (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


672 


BLOOD-VASCULAR   SYSTEM    OF   THE   HORSE 


ventral  sacral  foramina.  They  give  off  branches  to  the  spinal  cord  and  its  mem- 
branes, which  reinforce  the  ventral  spinal  artery-,  and  others  which  emerge  through 
the  dorsal  sacral  foramina  and  supply  the  muscles  and  skin  of  the  croup. 

(2)  The  middle  coccygeal  artery  (A.  coccygea)  is  an  unpaired  vessel  which 
arises  from  the  right  or  left  lateral  sacral  or  from  a  lateral  coccygeal  artery.  It 
passes  backward  on  the  pelvic  surface  of  the  sacrum  to  the  median  line  and  con- 
tinues in  that  position  along  the  tail  between  the  ventral  muscles,  supplying 
these  and  the  skin. 

(3)  The  posterior  gluteal  artery  (A.  glutea  caudalis)^  emerges  through  the 
upper  part  of  the  sacro-sciatic  ligament  and  runs  on  the  latter  toward  the  tuber 
ischii,  under  cover  of  the  Ijiceps  femoris  (Fig.  580).     It  gives  branches  to  that 


Internal  iliac  arterij 

External  iliac  artery 
Circumflex  iliac  artery 
Tuber  c^xce  \ 


Common 
iliac  veins 


Femoral  vessels 


Remnant  of 

inguinal  ligament 

Sartonus 

Femoral  nirve 


Deep  femoral 

vessels 

Trochanter  Urtius 


Obturator 


Biceps  femoris 
Semitendinosus 
Sevnmevihranosus 


Fig.  581. — Deep  Dissection  op  Ventral  Wall  of  Pelvis  of  Hokse  (Male).  ,^. 

/,  External  pudic  artery  and  small  satellite  vein;  Z,  anastomosis  between  external  pudic  vein  and  deep  femoral 
veins;  3,  accessory  ligament;  4,  round  ligament;  5,  transverse  ligament;  6,  head  of  femur;  7,  obturator  externus 
(stumps);  8.  medial  margin  of  obturator  foramen;  9,  origin  of  gracilis;  10,  origin  of  adductor;  11,  bulbocavernosus; 
12,  retractor  penis;  13,  suspensory  ligament  of  penis.     (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.; 


muscle,  the  semitendinosus,  semimembranosus,  superficial  gluteus,  and  coccygeus, 
and  anastomoses  with  the  obturator,  deep  femoral,  and  posterior  femoral  arteries. 
(4)  The  lateral  coccygeal  artery  (A.  caudalis  lateralis  ventralis)  continues  the 
direction  of  the  lateral  sacral,  but  is  much  smaller  than  the  preceding  vessel.  It 
passes  back  between  the  ventral  and  intertransversales  muscles  of  the  tail  and 
divides  into  dorsal  and  ventral  branches  which  supply  twigs  to  the  muscles  and 
skin. 

4.  The  ilio-lumbar  artery  (A.  iliolumbalis)  arises  at  a  right  angle  from  the 
internal  iliac  and  runs  outward  behind  the  sacro-iliac  joint,  crossing  the  ventral 
surface  of  the  ilium  under  cover  of  the  iliacus  muscle.  It  gives  branches  to  the  ilio- 
psoas and  longissimus,  turns  around  the  lateral  border  of  the  ilium  a  little  behind 
the  tuber  coxae,  and  ends  in  the  gluteus  medius  and  tensor  fasciae  latae  (Fig.  580). 

5.  The  anterior  gluteal  artery  (A.  glutea  cranialis)  is  the  largest  branch  of  the 
internal  iliac.     It  arises  usually  opposite  to  the  preceding  vessel,  and  passes  outward 

'  Also  termed  the  ischiatic  artery. 


ARTERIES    OF    THE    PELVIC    LIMB  673 

through  the  greater  sciatic  foramen,  dividing  into  several  branches  as  it  emerges; 
these  enter  the  gluteal  muscles  (Fig.  580). 

6.  The  iliaco-femoral  or  lateral  circumflex  artery  of  the  thigh  (A.  circumflexa 
femoris  lateralis)  passes  ventro-laterally  across  and  beneath  the  shaft  of  the  ilium, 
under  cover  of  the  iliacus  muscle,  and  dips  in  between  the  rectus  femoris  and  vastus 
lateralis.  It  is  accompanied  by  two  satellite  veins.  It  gives  collateral  branches  to 
the  iliopsoas,  the  glutei,  and  the  tensor  fasciae  latse,  supplies  the  nutrient  artery  of 
the  ilium,  and  terminates  in  the  quadriceps  femoris  (Fig.  580) . 

7.  The  obturator  artery  (A.  obturatoria),  the  medial  terminal  branch  of  the 
internal  iliac,  passes  downward  and  backward  on  the  pelvic  surface  of  the  shaft  of 
the  ilium,  along  the  ventral  border  of  the  iliac  head  of  the  obturator  internus,  ac- 
companied by  the  satellite  vein  and  nerve,  which  lie  ventral  to  the  artery  (Fig.  576). 
On  reaching  the  obturator  foramen  it  dips  under  the  obturator  internus  and  passes 
obliquely  through  the  lateral  part  of  the  foramen.  In  this  part  of  its  course  it 
gives  off  a  vesical  branch  and  twigs  to  the  obturator  internus  and  the  hip-joint. 
It  emerges  from  the  obturator  foramen  behind  the  obturator  externus,  passes  be- 
tween the  quadratus  femoris  and  the  adductor,  runs  backward  on  the  ventral  face 
of  the  ischium,  and,  in  the  male,  enters  the  crus  penis,  forming  the  arteria  profunda 
penis.  It  anastomoses  with  the  internal  pudic,  and  usually  with  the  external 
pudic  by  a  branch  (A.  clorsalis  penis  caudalis)  which  runs  forward  on  the  dorsum 
penis.  Collateral  branches  are  detached  to  the  obturator  muscles,  the  adductors 
of  the  thigh,  the  semimembranosus,  biceps  femoris,  and  semitendinosus,  and  anas- 
tomoses are  formed  with  the  deep  femoral  and  posterior  femoral  arteries.  In  the 
female  the  terminal  part  is  small  and  enters  the  root  of  the  clitoris. 


ARTERIES  OF  THE  PELVIC  LIMB 
The  main  arterial  trunk  of  each  pelvic  limb  descends  to  the  proximal  part  of 
the  posterior  surface  of  the  tibia,  where  it  divides  under  cover  of  the  popliteus 
muscle  into  the  anterior  and  posterior  tibial  arteries.  The  different  parts  of  the 
trunk  receive  names  which  correspond  to  the  several  regions  through  which  it 
passes.  In  the  abdomen  it  is  termed  the  external  iliac  artery,  in  the  proximal  two- 
thirds  of  the  thigh  it  is  called  the  femoral  artery,  and  distal  to  this  it  is  termed  the 
popliteal  artery. 

The  External  Iliac  Artery  (Figs.  575,  576) 
The  external  iliac  artery  (A.  iliaca  externa)  arises  from  the  aorta  under  the 
fifth  lumbar  vertebra,  and  usually  just  in  front  of  the  origin  of  the  internal  iliac. 
It  descends  at  the  side  of  the  pelvic  inlet  along  the  tendon  of  the  psoas  minor, 
crosses  the  insertion  of  that  muscle,  and  reaches  the  level  of  the  anterior  border  of 
the  pubis,  beyond  which  it  is  continued  by  the  femoral  artery.  It  is  covered  by  the 
peritoneum  and  fascia,  and  is  related  behind  to  the  corresponding  vein.  Its  chief 
branches  are  as  follows: 

1.  The  circimiflex  iliac  artery  (A.  circumflexa  ilium  profunda)  arises  from  the 
external  iliac  at  its  origin  or  from  the  aorta  directly.  It  passes  across  the  iliac 
fascia  toward  the  tuber  coxae,  and  divides  into  two  branches  at  or  near  the  lateral 
border  of  the  psoas  major.  The  artery  lies  between  the  fascia  and  the  peritoneum 
and  is  accompanied  by  two  veins.  It  furnishes  small  branches  to  the  psoas  muscles 
and  the  external  iliac  lymph  glands.  The  anterior  branch  gives  twigs  to  the  iliacus 
and  psoas  muscles,  and  passes  downward  and  forward  in  the  flank  on  the  trans- 
versus  abdominis,  along,  or  under  cover  of,  the  upper  margin  of  the  obliquus  ab- 
dominis internus.  It  gives  branches  to  these  muscles,  the  obliquus  abdominis 
externus,  and  the  skin  of  the  flank.  The  posterior  branch  perforates  the  abdominal 
wall  close  to  the  tuber  coxse,  and  runs  downward  on  the  medial  face  of  the  tensor 
43 


674 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


fasciae  latae  to  the  fold  of  the  flank,  supplying  branches  to  that  muscle,  the  cutaneus, 
the  prefemoral  hanph  glands,  and  the  skin. 

2.  The  external  spermatic  or  cremasteric  artery  (A.  spermatica  externa)  is  a 
very  small  vessel  which  arises  in  a  variable  manner.  It  springs  most  often  from  the 
external  iliac  near  the  origin  of  the  latter,  but  may  come  from  the  circumflex  iliac, 
the  aorta  between  the  external  and  internal  iliac,  or  the  latter  vessel.  It  accom- 
panies the  cremaster  muscle  to  the  inguinal  canal,  supplies  twigs  to  that  muscle, 
the  tunica  vaginalis,  and  other  constituents  of  the  spermatic  cord  (Fig.  575). 

2  a.  The  middle  uterine  artery  (A.  uterina  media)  of  the  female  is  regarded  as 
the  homologue  of  the  preceding  vessel;  it  has  a  similar  origin,  but  is  a  much  larger 
artery.  It  enters  the  broad  ligament  of  the  uterus,  in  which  it  pursues  a  flexuous 
course  to  the  posterior  part  of  the  horn  of  the  uterus.  Its  branches  are  distributed 
to  the  uterus  and  anastomose  with  those  of  the  other  uterine  arteries. 

The  Femoral  Artery  (Figs.  575,  576) 
The  femoral  artery  is  the  main  arterial  trunk  of  the  thigh.     It  begins  at  the 
level  of  the  anterior  border  of  the  pubis,  from  which  it  is  separated  by  the  femoral 


Fig.  582. — Dissection  of  Inguinal  Region  and  Medial  Surface  of  Thigh  of  Horse. 
1,  External  pudic  artery;  2,  anterior  branches  of  /;  3,  posterior  branches  of  /;  4>  transverse  anastomosis  between 
external  pudio  veins;  4',  venous  plexus  of  dorsum  penis;  5,  femoral  artery;  6,  saphenous  nerve;  7,  anterior  border  of 
external  inguinal  ring;  S,  obliquus  abdominis  internus;  9,  posterior  border  of  external  inguinal  ring;  10,  tunica  vag- 
inalis; //,  ductus  deferens;  /a',  cremaster  muscle;  /3,  prepuce;  74>  glans  penis;  /5,  external  urethral  orifice;  16,  pos- 
terior branches  of  circumflex  iliac  vessels;  / 7,  saphenous  vessels;  J S,  fold  of  flank;  /5,  penis  (cut) ;  .-1,  superficial  ingui- 
nal lymph  glands;  B,  prefemoral  lymph  glands;  C,  deep  inguinal  lymph  glands.  The  testicle  (on  the  right  side)  has 
been  rotated  somewhat  to  show  the  cremaster  muscle.     (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


vein.  It  descends  almost  vertically  in  the  femoral  canal  behind  the  sartorius 
muscle,  covered  at  first  by  the  medial  femoral  fascia  and  lower  down  by  the  gracilis. 
After  passing  over  the  insertion  of  the  pectineus,  it  perforates  the  adductor  muscle, 
crosses  in  the  vascular  groove  of  the  posterior  surface  of  the  femur,  and  is  continued 


THE    FEMORAL   ARTERY  675 

between  the  two  heads  of  the  gastrocnemius  as  the  popliteal  artery.  It  is  related 
at  its  origin  to  the  sartorius  in  front,  the  femoral  vein  behind  (which  separates  it 
from  the  pectineus),  and  the  iliacus  laterally.  Lower  down  it  is  related  super- 
ficially to  the  deep  inguinal  lymph  glands,  and  deeply  to  the  vastus  medialis,  while 
the  saphenous  nerve  is  in  front  of  it,  and  the  vein  passes  to  its  lateral  face.  The 
chief  branches  are  as  follows: 

1.  The  prepubic  artery  (Truncus  pudendo-abdominalis)  arises  usually  by  a 
common  trunk  \\dth  the  deep  femoral,  a  little  below  the  level  of  the  pubis.  It 
passes  forward  across  the  edge  of  the  inguinal  ligament,  inclining  ventro-medially, 
and  then  runs  on  the  abdominal  surface  of  the  ligament  to  the  medial  part  of  the 
internal  inguinal  ring,  where  it  divides  into  the  posterior  abdominal  and  external 
pudic  arteries.  (1)  The  posterior  abdominal  artery  (A.  abdominalis  caudalis) 
(Fig.  370)  passes  along  the  lateral  border  of  the  rectus  abdominis  and  anastomoses 
in  the  umbilical  region  with  the  anterior  abdominal  artery.  It  supplies  branches 
chiefly  to  the  rectus  and  obliquus  internus  muscles.  (2)  The  external  pudic 
artery  (A.  pudenda  externa)  descends  on  the  inguinal  ligament  through  the 
medial  part  of  the  inguinal  canal,  and  emerges  at  the  medial  angle  of  the  ex- 
ternal ring.  In  the  male  it  divides  into  the  subcutaneous  abdominal  artery 
and  the  anterior  dorsal  artery  of  the  penis.  The  former  (A.  abdominalis  sub- 
cutanea)  runs  forward  on  the  abdominal  tunic  a  short  distance  from  the  linea  alba, 
and  gives  branches  to  the  superficial  inguinal  lymph  glands,  the  sheath,  and  the 
scrotum.  The  latter  (A.  dorsalis  penis  cranialis)  passes  to  the  dorsmn  penis  and 
ends  at  the  glans  as  the  arteria  glandis.  It  gives  off  collateral  branches  (Rami 
profundi  penis)  to  the  corpus  cavernosum,  one  of  which  usually  passes  backward 
and  anastomoses  with  a  branch  of  the  obturator  arter3^  Branches  are  also  supplied 
to  the  superficial  inguinal  lymph  glands,  the  prepuce,  and  the  scrotum.  In  the 
female  the  mammary  artery  (A.  mammaria)  takes  the  place  of  the  anterior  dorsal 
artery  of  the  penis ;   it  enters  the  base  of  the  mammary  gland,  in  which  it  ramifies. 

2.  The  deep  femoral  artery  (A.  profunda  femoris)  (Fig.  581)  arises  either  by  a 
common  trunk  with  the  prepubic  or  a  little  distal  to  it.  The  point  of  origin  is 
usually  at  the  level  of  the  anterior  border  of  the  pubis,  but  may  be  as  much  as  an 
inch  lower.  It  passes  backward  and  downward  across  the  medial  face  of  the 
femoral  vein,  then  below  the  pubis  in  the  space  between  the  hip  joint  and  the  pec- 
tineus muscle.  On  reaching  the  obturator  externus  it  inclines  more  ventrally  and 
laterally,  passes  out  between  the  posterior  surface  of  the  femur  and  the  quadratus 
femoris,  and  ramifies  in  the  biceps  femoris  and  semitendinosus.  It  supplies  large 
collateral  branches  to  the  medial  femoral  muscles  and  twigs  to  the  deep  inguinal 
lymph  glands  and  the  hip  joint,  and  anastomoses  with  the  obturator  artery.^ 

3.  The  anterior  femoral  artery  (A.  femoris  cranialis)  (Fig.  575)  arises  a  little 
distal  to  the  preceding  vessel,  from  the  opposite  side  of  the  femoral  trunk.  It 
passes  forward,  outward,  and  a  little  downward  across  the  deep  face  of  the  sartorius, 
dips  in  between  the  rectus  femoris  and  vastus  medialis,  and  ramifies  in  these  muscles 
and  the  vastus  intermedins.  It  is  related  laterally  to  the  ilio-psoas  and  to  the 
femoral  nerve. 

In  some  cases  this  artery  is  replaced  by  a  large  branch  of  the  iliaco-femoral  or  external  cir- 
cumflex, which  passes  between  the  iho-psoas  and  rectus  femoris  and  enters  the  interstice  between 
the  latter  muscle  and  the  vastus  mediahs. 

4.  Innominate  muscular  branches  (Rami  musculares)  of  variable  size  and 
arrangement  are  given  off  to  the  muscles  of  this  vicinity. 

5.  The  saphenous  artery  (A.  saphena)  (Figs.  576,  582)  is  a  small  vessel  which 
arises  from  the  femoral  about  its  middle,  or  from  a  muscular  branch,  and  emerges 
between  the  sartorius  and  gracilis  or  through  the  latter  to  the  medial  surface  of  the 

1  In  the  new  nomenclature  the  term  A.  circumflexa  femoris  medialis  is  applied  to  the  part 
which  turns  outward,  while  the  part  which  runs  backward  is  regarded  as  the  continuing  trunk. 


676  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

thigh.  In  company  with  the  large  saphenous  vein  and  the  saphenous  nerve  it 
descends  superficially  on  the  anterior  part  of  the  gracilis,  continues  on  the  deep 
fascia  of  the  leg,  and  divides  above  the  hock  into  two  branches,  which  accompany 
the  radicles  of  the  vein.  It  gives  off  cutaneous  twigs  and  anastomoses  with  the 
recurrent  tibial  artery. 

In  some  cases  this  anastomosis  does  not  occur.  The  artery  may  be  larger  and  directly  con- 
tinuous with  the  medial  tarsal  artery. 

6.  The  articular  branch  (A.  genu  suprema)  is  a  slender  artery  which  arises 
from  the  femoral  just  before  it  passes  through  the  adductor.  It  descends  along  the 
posterior  border  of  the  vastus  medialis  to  the  medial  surface  of  the  stifle  joint, 
where  it  ramifies. 

7.  The  nutrient  artery  of  the  femur  (A.  nutritia  femoris)  is  given  off  at  the 
middle  of  the  femur  and  enters  the  nutrient  foramen. 

8.  The  posterior  femoral  artery  (A.  femoris  caudalis)i  is  a  large  vessel  which 
arises  from  the  posterior  face  of  the  femoral  just  before  or  as  the  trunk  passes  be- 
tween the  two  heads  of  the  gastrocnemius  (Fig.  584) .  It  is  very  short  and  divides 
into  two  branches.  The  ascending  branch  passes  upward  and  outward  between 
the  adductor  (in  front)  and  the  semimembranosus  (behind),  and  ramifies  in  the 
biceps  femoris,  vastus  lateralis,  adductor,  and  semitendinosus.  The  descending 
branch  passes  downward  and  backward  on  the  lateral  head  of  the  gastrocnemius, 
then  curves  upward  between  the  biceps  femoris  and  semitendinosus  (crossed 
laterally  by  the  tibial  nerve)  and  divides  into  branches  to  these  muscles.  A  branch 
descends  between  the  heads  of  the  gastrocnemius,  gives  branches  to  that  muscle 
and  the  superficial  digital  flexor,  and  is  continued  by  a  slender  artery  which  ac- 
companies the  tibial  nerve  and  unites  with  the  recurrent  tibial  artery.  A  small 
branch  often  ascends  alongside  of  the  sciatic  nerve,  between  the  biceps  and  semi- 
tendinosus and  anastomoses  with  a  descending  branch  of  the  obturator. 

This  branch  is  frequently  absent,  but  the  large  vein  which  it  accompanies  when  present,  is 
constant  and  connects  the  obturator  and  posterior  femoral  veins. 

The  Popliteal  Artery 
This  artery  (A.  poplitea)  is  the  direct  continuation  of  the  femoral.  It  lies 
between  the  two  heads  of  the  gastrocnemius,  at  first  on  the  posterior  face  of  the 
femur,  then  on  the  femoro-tibial  joint  capsule.  It  descends  through  the  popliteal 
notch  under  cover  of  the  popliteus,  inclines  outward,  and  divides  near  the  proximal 
part  of  the  interosseous  space  into  anterior  and  posterior  tibial  arteries.  The 
satellite  vein  lies  along  its  medial  side  at  the  stifle  joint.  Collateral  branches  are 
supplied  to  the  stifle  joint  and  the  gastrocnemius  and  popliteus. 

One  of  the  articular  branches  (A.  genu  media)  runs  directly  forward,  passes  through  the 
posterior  part  of  the  capsule  of  the  femoro-tibial  joint,  and  supplies  the  cruciate  ligaments,  syno- 
vial membrane,  etc.  Another  branch  (A.  genu  lateralis  distalis)  passes  outward  under  the  lateral 
head  of  the  gastrocnemius,  and  concurs  with  the  articular  branch  of  the  femoral  artery  in  forming 
a  plexus  on  the  stifle. 

POSTERIOR  TIBIAL  ARTERY 

The  posterior  tibial  artery  (A.  tibialis  posterior)  is  much  the  smaller  of  the  two 
terminals  of  the  popliteal.  It  lies  at  first  between  the  tibia  and  the  popliteus, 
then  between  that  muscle  and  the  deep  and  medial  heads  of  the  deep  digital  flexor. 
Lower  down  it  descends  along  the  tendon  of  the  flexor  longus,  becomes  superficial 
in  the  distal  third  of  the  leg,  and  divides  into  lateral  and  medial  tarsal  branches. ^ 
The  collateral  branches  include  the  nutrient  artery  of  the  tibia  (A.  nutritia  tibiae) 
and  muscular  branches  (Rami  musculares)  to  the  muscles  on  the  posterior  surface 
of  the  tibia. 

1  Also  termed  the  femoro-popliteal  artery. 

2  Instead  of  dividing  thus,  the  posterior  tibial  may  be  continued  by  the  lateral  tarsal.  The 
medial  tarsal  may  be  a  continuation  of  the  saphenous  artery. 


POSTERIOR   TIBIAL   ARTERY 


677 


The  lateral  tarsal  artery  (A.  tarsea  lateralis)  passes  outward  between  the  tibia 
and  the  deep  flexor  of  the  digit,  and  is  distributed  to  the  outer  surface  of  the  hock. 


Tibial  insertion  of 
semitendinosus 
Saphenous  vein 

Popliteu 

Flexor  dig   long  us 

Posterior  tibial  vessels 
Long  extensor 


Medial  ligament  of  hock 
Peroneus  terlius 


Medial  tendon  of 

tibialis  anterior 

Outline  of  bursa  of  above 


Medial  or  great 
metatarsal  vein 


Tendon  of  semitendinosus 

Gastrocnemius  {medial 
head) 


Tendon  of  gastrocnemius 

Tendon  of  superficial 

flexor 
Tarsal  tendon  of  semi- 
tendinosus 
Tibial  nerve 

Recurrent  tibial  vessels 


\ Deep  flexor  tendon 

Medial  tarsal  artery 


Tendon  of  flexor  dig.  longus 
Lateral  plantar  vein 
Medial  plantar  artery 

Medial  plantar  nerve 
Deep  flexor  tendon 


Medial  superficial  plantar 
metatarsal  vessels 


Fig.  583.— Dissection  of  Right  Leg  and  Hock  of  Horse;  Medial  View.     (After  Schmaltz.  Atlas  d.  Anat.  d.  Pferdes.) 


It  gives  off  the  small  recurrent  tarsal  artery  (A.  tarsea  recurrens),  which  ascends 
along  the  lateral  margin  of  the  gastrocnemius  tendon  with  a  satellite  vein  and  nerve 


678  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

and  anastomoses  with  a  branch  of  the  posterior  femoral  artery.  In  some  cases  an 
arch  is  formed  by  junction  with  the  peroneal  artery  on  the  lateral  surface  of  the  deep 
flexor  at  the  distal  fourth  of  the  leg. 

The  medial  tarsal  artery  (A.  tarsea  medialis)  usually  forms  a  double  curve  in 
front  of  the  tuber  calcis,  then  descends  on  the  deep  flexor  tendon  with  the  plantar 
nerves,  and  divides  into  the  two  plantar  arteries.  From  the  second  part  of  the 
curve  there  arises  a  small  branch,  the  recurrent  tibial  artery  (A.  tibialis  recurrens). 
This  ascends  along  the  medial  border  of  the  superficial  digital  flexor  in  company 
with  a  satellite  vein  and  the  tibial  nerve,  and  anastomoses  with  a  descending  branch 
of  the  posterior  femoral  artery  and  with  the  saphenous  arter3^^ 

6.  The  plantar  arteries,  medial  and  lateral  (A.  plantaris  medialis,  lateralis), 
are  the  small  terminals  of  the  medial  tarsal.  They  descend  along  the  sides  of  the 
tarsal  sheath  of  the  deep  flexor  tendon  with  the  plantar  nerves  to  the  proximal  part 
of  the  metatarsus,  where  they  unite  with  the  perforating  tarsal  artery  to  form  the 
proximal  plantar  arch  (Arcus  plantaris  proximalis).  Four  plantar  metatarsal 
arteries  proceed  from  this  arch.  The  two  slender  superficial  plantar  metatarsal 
arteries  (A.  metatarsea  plantaris  superficialis  medialis,  lateralis)  may  be  regarded 
as  the  continuations  of  the  plantar  arteries;  they  descend  on  either  side  of  the  deep 
flexor  tendon  with  the  plantar  nerves,  and  unite  with  the  corresponding  digital 
artery.  The  medial  one  is  the  smaller;  it  may  give  off  or  connect  with  the  cor- 
responding dorsal  artery.  The  lateral,  larger  one  usually  unites  with  the  lateral 
digital  artery.  Both  may  unite  at  the  distal  part  of  the  metatarsus  to  form  a  short 
trunk  which  joins  one  of  the  digital  arteries.  They  supply  twigs  to  the  flexor 
tendons  and  the  skin.  The  two  deep  plantar  metatarsal  arteries  (A.  metatarsea 
plantaris  profundus  medialis,  lateralis)  descend  on  the  plantar  surface  of  the  large 
metatarsal  bone  alongside  of  the  corresponding  small  metatarsal  bone  and  unite 
near  the  fetlock  with  the  great  metatarsal.  The  medial  artery  is  the  larger  of  the 
two  and  usually  appears  to  be  the  continuation  of  the  perforating  tarsal.  It 
supplies  the  nutrient  artery  of  the  large  metatarsal  bone.  In  other  cases  it  is 
the  direct  continuation  of  the  medial  plantar  artery,  the  lateral  artery  only  uniting 
with  the  perforating  tarsal.  The  connection  of  these  vessels  with  the  great  meta- 
tarsal artery  forms  the  distal  plantar  arch  (Arcus  plantaris  distalis) . 

ANTERIOR  TIBIAL  ARTERY 

The  anterior  tibial  artery  (A.  tibialis  anterior)  is  much  the  larger  of  the  two 
terminal  branches  of  the  popliteal.  It  passes  forward  through  the  proximal  part  of 
the  interosseous  space  and  descends  with  two  satellite  veins  on  the  lateral  part  of 
the  front  of  the  tibia,  under  cover  of  the  tibialis  anterior.  At  the  distal  part  of  the 
leg  it  deviates  to  the  lateral  border  of  the  tendon  of  this  muscle,  passes  on  to  the 
capsule  of  the  hock  joint,  gives  off  the  large  perforating  tarsal  artery,  and  is  con- 
tinued as  the  great  metatarsal  artery.-  It  gives  off  muscular  branches  to  the  dorso- 
lateral group  of  muscles  of  the  leg  and  articular  branches  to  the  hock.  The  per- 
oneal artery  (A.  peronea)  is  a  variable  vessel  which  descends  along  the  fibula  under 
cover  of  the  lateral  extensor;  it  gives  off  muscular  branches  and  one  which  per- 
forates the  fascia  and  divides  into  ascending  and  descending  cutaneous  twigs.^ 

The  perforating  tarsal  artery  (A.  tarsea  perforans)  arises  under  cover  of  the 
lateral  tendon  of  the  peroneus  tertius.  It  passes  backward  through  the  vascular 
canal  of  the  tarsus  with  a  satellite  vein  and  nerve  and  unites  on  the  upper  part  of 

1  The  artery  may  be  double  in  part  or  throughout.  It  may  join  the  popliteal  artery.  The 
S-shaped  curve  may  be  absent  and  the  medial  tarsal  be  the  direct  continuation  of  the  recurrent 
tibial  artery. 

2  The  part  of  the  arterial  trunk  which  is  on  the  dorsal  surface  of  the  tarsus  may  be  distinguished 
by  the  term  A.  dorsalis  pedis. 

^  In  some  cases  the  peroneal  artery  is  larger  than  usual  and  forms  an  anastomotic  arch  with 
the  lateral  tarsal  in  the  distal  part  of  the  leg. 


ANTERIOR   TIBIAL   ARTERY 


679 


the  suspensory  ligament  with  the  plantar  arteries  (or  only  with  the  lateral  plantar) 
to  form  the  proximal  plantar  arch  (Arcus  plantaris  proximalis). 


Vastus  lateralis 

Biceps  femoris 

Gastrocnemius,  lateral  head 

Superficial  digital  flexor 

Lateral  articular  vessels 

Joint  capsule 

Lateral  condyle  of  femur 

Popliteus 

Pouch  of  joint  capsule, 

opened 

Lateral  ligament  of  femoro- 

tibial  joint 

Recurrent  tibial  vessels 


Soleus 
Tibialis  posterioi 


Lateral  extensor  tendon 
Recurrent  tarsal  vein 
Lateral  plantar  vein 

Lateral  tarsal  viin 
Lateral  tarsal  aitti  1/ 

Trochlea  of  tibial  tarsal  bunt 
Lateral  ligament  of  hod  joint    Ji- 

Fibular  tarsal  bont 


Femoral  vessels 
Posterior  femoral  artery 
Popliteal  artery 
Adductor 
Gastrocnemius,  medial  head 
Tibial  nerve 


Flexor  dig.  longus 
Flexor  hallucis  longus 

Posterior  tibial  artery 


Lateral  tarsal  artery 
Medial  tarsal  artery 
Proximal  end  of  tarsal  sheath 
Deep  flexor  tendon 
Long  flexor  tendon 
Plantar  nerves 
Plantar  arteries 
Joint  capsule,  opened 


Fig.  584. — Deep  Dissection  of  Left  Stifle,  Leg,  and  Hock  of  Horse;  Posterior  View. 
The  hock  is  flexed  at  a  right  angle,  and  the  tuber  calcis  is  sawn  off.     The  tibial  nerve  is  drawn  aside  to  show  its 
muscular  branches.     The  capsules  of  the  stifle  and  hock  joints  are  partially  removed.     Branches  of  tibial  nerve;  1,  S, 
to  gastrocnemius;   3,  4,  to  superficial  flexor;   5,  to  popliteus;   6,  to  flexor  longus;    7,  to  deep  flexor.     (After  Schmaltz, 
Atlas  d.  Anat.  d.  Pferdes.) 


BLOOD-VASCULAR   SYSTEM    OF   THE   HORSE 


In  well-injected  specimens  it  is  seen  that  there  is  a  fine  arterial  network  (Rete 
tarsi  dorsale)  on  the  dorsal  surface  of  the  hock,  which  is  formed  by  twigs  from  the 


Patella 


Tendon  of  biceps  femoris 

Lateral  patellar  ligament 
Gastrocnemius,  lateral  head 

Lateral  condyle  of  tibia 

Lateral  ligament  of  femoro- 
tibial  joint 
Common  peroneal  nern 


Superficial  peroneal  nerve 

Lateral  extensor 

Long  extensor 


Peroneus  tertius 


Loop  of  lateral  tendon 
of  peroneus  tertius 


Perforating  tarsal  artery 

Stump  of  extensor 

dig.  brevis 

Great  metatarsal  artery 

Lateral  extensor  tendon 

Long  extensor  tendon 


Vastus  medialis 

Accessory  cartilage  of  patella 

Gracilis 

Sartorius 

Trochlea  of  femur 

(medial  ridge) 

Medial  patellar  ligament 

Middle  patellar  ligament 

Medial  condyle  of  tibia 
Medial  ligament  of  femoro- 
tibial  joint 

Gastrocnemius,  medial  head 

Crest  of  tibia 

Tibial  tendon  of 
semitendinosus 


Tibialis  anterior 
Saphenous  vein 
Deep  fascia  (reflected) 


Anterior  tendon  of  pero- 
neus tertius 

Medial  tendon  of  tibialis 
anterior 


Distal  annular  ligament 
Great  metatarsal  vein 
Deep  peroneal  nerve 


Fig.  585. — Superficial  Dissection-  of  Right  Stifle,  Leg,  and  Hock  of  Horse;   Front  View.     (After  Schmaltz, 

Atlas  d.  Anat.  d.  Pferdes.) 


anterior  tibial  and  lateral  tarsal  arteries.     From  it  proceed  two  very  slender  dorsal 
metatsirsal  arteries  (A.  metatarsea  dorsalis  medialis,  lateralis).     The  medial  one 


THE    VEINS PULMONARY   VEINS— CARDIAC    VEINS  681 

descends  in  the  furrow  between  the  medial  small  and  large  metatarsal  bones,  and 
anastomoses  usually  in  the  proximal  part  of  the  metatarsus  with  the  medial  super- 
ficial plantar  metatarsal,  uniting  sometimes  with  the  medial  deep  plantar  meta- 
tarsal. The  lateral  vessel  passes  down  under  the  periosteum  on  the  dorsal  face  of 
the  large  metatarsal  bone  and  becomes  lost  or  joins  the  great  metatarsal  artery. 

In  rare  cases  the  anterior  tibial  artery  passes  undivided  through  the  tarsus,  gives  off  the 
medial  deep  plantar  metatarsal,  and  is  continued  as  a  very  large  medial  superficial  plantar  meta- 
tarsal along  the  deep  flexor  tendon,  thus  resembling  the  arrangement  in  the  foreUmb. 

In  a  few  cases  the  perforating  tarsal  is  a  large  vessel,  directly  continuing  the  anterior  tibial, 
and  is  continued  by  a  large  medial  deep  plantar  metatarsal.  The  great  metatarsal  is  then  small. 
Other  variations  are  common. 

THE  GREAT  METATARSAL   ARTERY 

This  artery  (A.  metatarsea  dorsalis  lateralis)  is  the  direct  continuation  of  the 
anterior  tibial.  It  descends,  inclining  outward,  under  cover  of  the  extensor  brevis 
and  the  tendon  of  the  lateral  extensor,  at  first  on  the  joint  capsule  and  then  in  the 
oblique  vascular  groove  on  the  proximal  part  of  the  large  metatarsal  bone.  It  then 
descends  superficially  in  the  groove  formed  by  the  apposition  of  the  large  and  lateral 
small  metatarsal  bones,  passes  between  the  two,  and  divides  on  the  distal  part  of 
the  plantar  surface  of  the  large  metatarsal  bone  into  the  medial  and  lateral  digital 
arteries.  It  is  not  usually  accompanied  by  a  vein.  It  is  joined  near  its  termination 
by  two  or  more  of  the  plantar  arteries,  and  beyond  this  the  term  common  digital 
artery  (A.  digitalis  communis)  may  be  applied  to  it.  In  the  digital  region  the 
arterial  arrangement  is  the  same  as  in  the  thoracic  limb;  it  is  only  necessary  in 
reading  the  description  to  substitute  the  word  "plantar"  for  "volar." 


THE  VEINS  1 
PULMONARY  VEINS 
The  pulmonary  veins  (Vv.  pulmonales),  usually  seven  or  eight  in  number, 
return  the  aerated  blood  from  the  lungs  and  open  into  the  left  atrium  of  the  heart. 
They  are  destitute  of  valves.  Their  tributaries  arise  in  the  capillary  plexuses  in 
the  lobules  of  the  lungs,  and  unite  to  form  larger  and  larger  trunks  which  accompany 
the  branches  of  the  bronchi  and  pulmonary  arteries.  A  very  large  vein  is  formed 
by  the  union  at  an  acute  angle  of  a  trunk  from  each  lung,  where  the  latter  are  ad- 
herent to  each  other. 

CARDIAC  VEINS 

The  coronary  sinus  (Sinus  coronarius)  is  a  very  short,  bulbous  trunk  which 
receives  most  of  the  blood  from  the  wall  of  the  heart.  It  is  situated  just  below  the 
termination  of  the  posterior  vena  cava,  and  is  covered  in  part  by  a  thin  layer  of 
atrial  muscle  fibers.  It  opens  into  the  right  atrium  just  below  the  posterior  vena 
cava.  It  is  formed  by  the  union  of  two  tributaries.  The  great  cardiac  or  left 
coronary  vein  (V.  cordis  magna)  ascends  in  the  left  longitudinal  groove  and  turns 
backward  in  the  coronary  groove,  in  which  it  winds  around  the  posterior  border  of 
the  heart  to  the  right  side  and  joins  the  coronary  sinus.  The  middle  cardiac  or 
right  coronary  vein  (V.  cordis  media)  ascends  in  the  right  longitudinal  groove  and 
joins  the  coronary  sinus,  or  opens  separately  into  the  atrium  just  in  front  of  the 

1  Most  of  the  veins  are  depicted  in  the  illustrations  of  the  section  on  the  arteries,  to  which 
reference  is  to  be  made.  Many  satellite  veins  which  are  homonymous  with  the  arteries  which 
they  accompany,  and  present  no  important  special  features,  are  not  described  here. 


682  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

orifice  of  the  great  cardiac  vein,  so  that  a  common  trunk  (coronary  sinus)  does  not 
then  exist. 

The  small  cardiac  veins  (Vv.  cordis  minores),  three  to  five  in  number,  are 
small  vessels  which  return  some  blood  from  the  right  ventricle  and  atrium;  they 
open  into  the  latter  near  the  coronary  groove  in  spaces  between  the  musculi  pec- 
tinati. 

THE  ANTERIOR  VENA  CAVA  (Fig.  554) 
The  anterior  vena  cava  (V.  cava  cranialis)  returns  to  the  heart  the  blood  from 
the  head,  neck,  thoracic  limbs,  and  the  greater  part  of  the  thoracic  wall.  It  is 
formed  at  the  ventral  part  of  the  thoracic  inlet  by  the  confluence  of  the  two  jugu- 
lar and  two  brachial  veins.  It  passes  backward  in  the  anterior  mediastinum,  at 
first  median  and  ventral  to  the  common  carotid  trunk,  then  deviates  to  the  right 
of  the  common  brachiocephalic  trunk,  and  opens  into  the  right  atrium  opposite 
to  the  fourth  rib.  It  is  partly  enclosed  by  the  pericardium.  The  demarcation  be- 
tween vein  and  atrium  is  not  very  distinct.  It  contains  no  valves  except  at  the 
mouths  of  its  radicles.  Its  length  is  about  five  to  six  inches  (ca.  12-15  cm.)  and 
its  caliber  about  two  inches  (ca.  5  cm.)  in  a  subject  of  medium  size.  It  is  related, 
dorsally  to  the  trachea,  the  right  vagus  and  cardiac  nerves,  and  anterior  medias- 
tinal lymph  glands.  Its  right  face  is  crossed  b}^  the  right  phrenic  nerve,  and  on  the 
left  it  is  related  to  the  brachiocephalic  trunk  and  artery.  The  thoracic  duct  opens 
through  the  dorsal  wall  of  the  origin  of  the  vena  cava.  It  receives,  in  addition  to 
small  pericardial  and  mediastinal  veins,  the  following  tributaries : 

1.  The  internal  thoracic  vein  (V.  thoracica  interna)  is  a  satellite  of  the  artery 
of  that  name.  It  opens  into  the  anterior  vena  cava  at  the  first  rib.  The  ventral 
intercostal  veins  (Vv.  intercostales  ventrales)  open  into  the  internal  thoracic  and 
musculo-phrenic  veins. 

2.  The  vertebral  vein  (V.  vertebralis)  corresponds  to  the  homonymous  artery. 
On  the  right  side  it  terminates  either  in  front  of  the  deep  cervical  vein  or  by  a  short 
common  trunk  with  it.  On  the  left  side  it  usually  unites  with  the  deep  cervical 
and  dorsal  veins  to  form  a  common  trunk. 

3.  The  deep  cervical  vein  (V.  cervicalis  profunda)  corresponds  to  the  artery. 
On  the  right  side  it  passes  downward  and  backward  across  the  right  face  of  the 
trachea  and  opens  into  the  vena  cava;  it  may  form  a  common  trunk  "svith  the  dorsal 
or  vertebral.  On  the  left  side  there  is  usually  a  common  trunk  for  all  three.  It 
receives  the  first  intercostal  vein. 

4.  The  dorsal  vein  (V.  costocervicalis)  corresponds  to  the  artery.  On  the 
right  side  it  leaves  the  artery  on  entering  the  thorax,  crosses  the  right  face  of  the 
trachea,  and  opens  into  the  vena  cava  behind  the  deep  cervical  or  by  a  common 
trunk  with  it.  On  the  left  side  it  usually  joins  the  deep  cervical  and  vertebral  to 
form  a  short  common  trunk  which  crosses  the  left  face  of  the  intrathoracic  part  of 
the  brachial  artery  opposite  the  second  rib  and  opens  into  the  anterior  vena  cava. 
It  receives  the  third,  fourth,  and  fifth  intercostal  veins  by  means  of  the  subcostal 
vein  on  the  right  side. 

The  Vena  Azygos 
The  vena  azygos  (Fig.  554)  is  an  unpaired  vessel  which  arises  at  the  level  of 
the  first  lumbar  vertebra  by  radicles  from  the  spinal  and  psoas  muscles  and  the 
crura  of  the  diaphragm.  It  passes  forward  along  the  right  side  of  the  bodies  of  the 
thoracic  vertebrae,  in  contact  usually  with  the  thoracic  duct,  which  separates  the 
vein  from  the  aorta.  At  the  seventh  vertebra  it  leaves  the  spine,  curves  downward 
and  forward  over  the  right  side  of  the  thoracic  duct,  trachea,  and  oesophagus,  and 
opens  into  the  right  atrium  opposite  the  fourth  intercostal  space.     Its  tributaries 


VEINS  OF  THE  HEAD  AND  NECK — JUGULAR  VEINS  683 

1.  The  last  fourteen  dorsal  intercostal  veins  (Vv.  intercostales  dorsales)  of  the 
right  side  go  directly  to  the  vena  azygos;  but  on  the  left  side  a  variable  number 
(four  to  seven  usually)  at  the  end  of  the  series  go  to  the  vena  hemiazygos  when  that 
vessel  is  present. 

2.  The  vena  hemiazygos  arises  from  a  branch  of  the  left  first  lumbar  vein  and 
twigs  from  the  crura  of  the  diaphragm.  It  passes  forward  through  the  hiatus 
aorticus  and  continues  along  the  left  dorsal  face  of  the  aorta,  and  about  the  mid- 
dle of  the  back  joins  the  vena  azygos.  It  receives  the  last  four  to  seven  dorsal 
intercostal  veins  of  the  left  side.  It  is  inconstant  and  variable.  In  its  absence 
its  tributaries  join  the  vena  azygos. 

3.  The  oesophageal  vein  (V.  oesophagea),  satellite  of  the  oesophageal  artery, 
joins  the  vena  azygos  as  it  inclines  downward. 

4.  The  bronchial  vein  (V.  bronchialis)  unites  with  the  preceding  to  form  a 
short  common  trunk,  or,  according  to  Chauveau,  empties  into  the  great  coronary 
vein.  The  author  is  unable  to  find  in  the  horse  any  distinct  bronchial  vein 
emerging  at  the  root  of  the  lung.^ 


VEINS  OF  THE  HEAD  AND  NECK 
Jugular  Veins 

The  jugular  veins  (Vv.  jugulares),  right  and  left  (Fig.  556),  arise  behind  the 
ramus  of  the  mandible,  about  two  and  a  half  inches  (ca.  6-7  cm.)  below  the  tem- 
poro-mandibular  articulation  by  the  union  of  the  superficial  temporal  and  internal 
maxillary  veins.  Each  passes  downward  and  backward,  at  first  embedded  more 
or  less  in  the  parotid  gland,  and  continues  in  the  jugular  furrow  to  the  thoracic 
inlet,  where  it  unites  with  its  fellow  and  the  two  brachial  veins  to  form  the  anterior 
vena  cava.  In  the  neck  it  is  covered  by  the  skin,  fascia,  and  cutaneus  muscle,  and  is 
superficial  to  the  carotid  artery,  from  which  it  is  separated  in  the  anterior  half  of 
the  region  by  the  omo-hyoideus  muscle.^  It  contains  valves  at  the  mouths  of  its 
tributaries,  and  has  several  pairs  of  semilunar  valves  variably  disposed  along  its 
course.     Its  tributaries  are  as  follows: 

1.  The  internal  maxillary  vein  (V.  maxillaris  interna)  is  larger  than  the  external 
maxillary.  It  may  be  considered  to  begin  as  the  continuation  backward  of  the 
buccinator  vein  where  that  vessel  crosses  the  alveolar  border  of  the  mandible, 
about  two  inches  (ca,  5  cm.)  behind  the  last  molar  tooth.  It  runs  backward  on 
the  medial  surface  of  the  ramus  ventral  to  the  lateral  pterygoid  muscle,  and  covered 
by  the  medial  pterygoid  muscle  for  a  distance  of  about  three  inches  (ca.  7-8  cm.), 
then  inclines  a  little  downward  and  runs  ventral  to  the  artery  for  about  an  inch 
(ca.  2-3  cm.).  It  crosses  the  lateral  face  of  the  artery  at  the  posterior  border  of 
the  jaw,  and  is  joined  by  the  superficial  temporal  vein  to  form  the  jugular.  Its 
principal  radicles  are  the  following: 

(1)  The  dorsal  lingual  vein  (V.  dorsalis  linguae)  is  not  a  satellite  on  any  artery, 

1  In  Chauveau-Arloing-Lesbre  the  statement  is  made  that  "the  bronchial  veins,  which  ramify 
on  the  bronchi  like  the  arteries  of  which  they  are  satellites,  open  into  the  great  coronary  vein  very 
near  its  mouth,  after  having  united  to  form  a  single  vessel,  which  sometimes  opens  directly  into 
the  atrium. "  The  arrangement  is  not  illustrated.  Ellenberger  and  Baum  state  that  the  bronchial 
and  a?sophageal  vems  open  into  the  vena  azygos  separately  or  by  a  common  trmik.  Martin  de- 
scribes a  short  broncho-o^sophageal  tnmk,  but  the  vein  which  he  figures  as  the  bronchial  does  not 
come  from  the  Imigs,  but  is  a  small  mediastinal  vessel.  The  author  finds  such  a  vessel  usually 
entering  the  terminal  part  of  the  oesophageal  vem,  but  no  distinct  bronchial  vein  in  the  horse. 
The  statement  and  figure  in  Bossi's  recent  work  agree  substantially  with  those  of  the  German 
authors. 

2  There  is  usually  only  one  jugular  vein  on  each  side  in  the  horse,  but  in  some  cases  there  is  an 
internal  or  deep  jugular  vein  which  accompanies  the  carotid  artery  and  ends  at  the  confluence  of 
the  external  jugulars.  M'Fadyean  records  a  case  in  which  the  vein  lay  on  the  deep  face  of  the 
omo-hyoideus  with  the  carotid  artery.  This  would  appear  to  be  an  instance  of  remarkable  de- 
velopment of  the  internal  jugular  in  place  of  the  usual  external  jugular  vein. 


6g4  BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 

but  is  in  company  witli  the  lingual  nerve.     It  receives  tributaries  from  the  tongue 
and  soft  palate. 

(2)  The  inferior  alveolar  or  dental  vein  (V.  alveolaris  mandibulse)  is  a  satellite 
of  the  corresponding  artery.     It  often  unites  with  the  preceding. 

(3)  The  middle  meningeal  vein  (V.  meningea  media)  emerges  through  the 
foramen  lacerum  anterius. 

(4)  Pterygoid  veins  (Rami  pterygoidei). 

(5)  The  posterior  deep  temporal  vein  (V.  temporalis  profunda  aboralis)  is  a 


Fig.  586. — Veins  op  Head  op  Horse. 
Parts  of  the  superficial  muscles  and  the  ramus  of  the  mandible,  and  all  of  the  masseter  muscle  except 
its  ventral  margin,  have  been  removed.  Veins:  1,  3,  Jugular;  2,  thyroid;  3,  internal  maxillarj';  4<  cranio- 
occipital  trunk;  5,  ventral  cerebral;  6,  occipital;  6',  muscular  branch  of  6;  6",  cerebrospinal  branch  of  6;  6"',  vein 
which  emerges  through  foramen  of  lateral  mass  of  atlas;  6"",  vein  which  emerges  through  intervertebral  foramen  of 
axis;  7,  great  auricular ;  7'-7"",  radicles  of  7;  S,  posterior  auricular;  S,  masseterico-pterygoid;  70,  superficial  temporal; 
11,  deep  auricular;  12,  dorsal  cerebral;  13,  transverse  facial  and  its  anastomosis  with  internal  maxillary;  13",  pal- 
pebral radicle  of  13;  14,  pterygoid;  15,  mandibular  alveolar;  16,  dorsal  lingual;  17,  deep  temporal;  18,  buccinator; 
19,  anastomosis  between  buccinator  and  masseteric;  20,  anastomosis  between  buccinator  and  common  labial  (21);  22, 
;33,  inferior  and  superior  labial;  ;g4.  angular  of  mouth;  ;g5,  ;25',  external  maxillary;  ^fi,  facial;  .27,  lateral  nasal;  .25,  dor- 
sal nasal;  ^9,  angular  of  eye;  SO,  reflexa;  3^,  trunk  of  infraorbital  and  sphenopalatine.  Muscles,  etc.:  a,  Orbicularis  oris; 
h,  levator  nasolabialis;  c,  dilatator  naris  lateralis;  d,  buccalis;  e,  zygomaticus;  /,  levator  labii  superioris  proprius;  g, 
molaris  and  depressor  labii  inferioris;  i,  labial  glands;  k,  m.  temporalis;  I,  m.  masseter;  m,  m.  pterygoideus  medialis; 
n,  m.  parotido-auricularis;  o,  m.  pterygoideus  lateralis;  p,  m.  sterno-cephalicus;  q,  m.  rectus  capitis  ventralis  major; 
T,  m.  omo-hyoideus  and  sterno-hyoideus;  s,  parotid  gland  (dissected  away  from  veins);  t,  dorsal  buccal  glands.  (After 
Mockel.) 

large  vessel  which  receives  tributaries  from  the  temporalis  muscle  and  emissaries 
from  the  temporal  canal.  It  is  connected  with  the  dorsal  cerebral  vein  and  usually 
with  the  meningeal  veins  by  its  frontal  branch.  The  latter  drains  chiefly  the 
lacrimal  gland  and  passes  behind  the  supraorbital  process. 

2.  The  superficial  temporal  vein  (V.  temporalis  superficialis)  is  the  large 
satellite  of  the  corresponding  artery.  It  is  formed  by  the  confluence  of  the  anterior 
auricular  and  transverse  facial  veins.     The  former  is  much  larger  than  the  cor- 


JUGULAR   VEINS  685 

responding  artery.  Its  radicles  come  from  the  posterior  part  of  the  temporalis 
muscle  and  from  the  external  ear.  It  receives  the  dorsal  cerebral  vein  (V.  cere- 
bralis  dorsalis),  which  is  the  emissary  of  the  transverse  sinus  of  the  dura  mater,  and 
emerges  from  the  temporal  canal  behind  the  postglenoid  process.  The  trans- 
verse facial  vein  (V.  transversa  faciei)  runs  at  first  above  the  artery  of  like  name, 
then  plunges  deepl}^  into  the  masseter  and  unites  in  front  with  the  facial  vein.  It 
is  connected  with  the  vena  reflexa  and  with  the  posterior  deep  temporal  vein  by  a 
branch  which  emerges  from  the  temporal  fossa  through  the  mandibular  notch. 

3.  The  masseteric  vein  (V.  masseterica)  joins  the  jugular  at  the  upper  border 
of  the  sterno-cephalicus  tendon.  It  is  a  short  but  large  trunk  which  is  formed 
by  the  confluence  at  the  posterior  border  of  the  jaw  of  masseteric  and  pterygoid 
veins.  The  former  is  commonly  connected  by  an  anastomotic  branch  with  the 
buccinator  vein. 

4.  The  great  auricular  vein  (V.  auricularis  magna)  is  a  satellite  of  the  posterior 
auricular  artery  above,  but  joins  the  jugular  a  variable  distance  below  and  behind 
the  point  of  origin  of  the  artery. 

5.  The  occipital  vein  (V.  occipitalis)  arises  in  the  fossa  atlantis  by  the  union  of 
two  radicles.  It  passes  downward  and  backward  on  the  rectus  capitis  ventralis 
major  and  joins  the  jugular  vein  a  variable  distance  in  front  of  the  termination  of  the 
external  maxillary  vein.  The  anterior  radicle  is  the  ventral  cerebral  vein  (V. 
cerebralis  ventralis).  This  is  an  emissary  of  the  cavernous  sinus  of  the  dura  mater; 
it  emerges  through  the  foramen  lacerum  posterius  and  is  connected  with  a  venous 
plexus  in  the  infratemporal  fossa,  ^t  receives  the  condyloid  vein  (V.  conclyloidea), 
which  is  an  emissary  of  the  basilar  plexus  and  the  petrosal  sinus,  and  emerges 
through  the  hypoglossal  foramen.^  The  posterior  radicle  is  formed  by  the  con- 
fluence of  musciilar  and  cerebro-spinal  branches.  The  former  (Ramus  muscularis) 
comes  through  the  foramen  transversarium  of  the  atlas  from  the  muscles  of  the 
poll;  it  anastomoses  with  the  vertebral  and  deep  cervical  veins.  The  latter  (Ramus 
cerebrospinalis)  receives  emissary  veins  from  the  meningeal  plexus  in  the  atlas, 
which  emerge  through  the  intervertebral  and  alar  foramina  and  the  foramen  of  the 
lateral  mass  of  the  atlas. 

6.  The  external  maxillary  vein  (V.  maxillaris  externa)  arises  by  radicles  which 
correspond  in  general  to  the  branches  of  the  artery  of  like  name.  It  passes  down 
■over  the  cheek  along  the  anterior  border  of  the  masseter  muscle  behind  the  artery, 
crossing  over  the  parotid  duct,  which  lies  behind  the  vein  lower  down.  Thus  on 
the  ramus  and  as  they  turn  around  its  ventral  border  the  artery  is  in  front,  the  vein 
in  the  middle,  and  the  duct  posterior.  In  the  mandibular  space  the  vein  is  ventral 
to  the  artery  for  some  distance,  then  parts  company  with  the  artery,  runs  straight 
backward  along  the  ventral  border  of  the  parotid  gland,  and  opens  into  the  jugular 
vein  at  the  posterior  angle  of  the  gland.-  The  chief  differences  in  the  tributaries 
of  the  vein  as  compared  with  the  branches  of  the  corresponding  artery  are  as  follows : 

The  labial  veins  (Vv.  labiales),  superior  and  inferior,  are  in  the  substance  of  the 
orbicularis  oris  near  the  free  edges  of  the  lips.  The  upper  one  is  the  larger.  They 
anastomose  with  the  opposite  veins.  They  drain  into  a  venous  plexus  which  is 
situated  in  the  submucous  tissue  of  the  cheek  and  the  buccinator  muscle,  and  from 
this  plexus  two  veins  emerge.  The  upper  one  passes  back  and  joins  the  buccinator 
vein.  The  lower  one,  the  common  labial  vein  (V.  labialis  communis),  receives  a 
submental  vein  from  the  chin  and  joins  the  external  maxillary  vein. 

Three  veins  connect  with  the  external  maxillary  at  the  anterior  border  of  the 
masseter. 

^  On  account  of  the  existence  of  this  cranial  affluent  the  term  cranio-occipital  has  been  pro- 
posed for  the  venous  trunk. 

2  The  venous  angle  formed  by  this  junction  indicates  the  position  of  the  thyroid  gland. 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


The  upper  one  is  the  transverse  facial  vein,  which  unites  close  to  the  end  of 
the  facial  crest. 

A  little  lower  is  the  large  valveless  vena  reflexa,  or  alveolar  vein.  This  passes 
back  under  the  upper  part  of  the  masseter  on  the  maxilla,  turns  around  the  tuber 
maxillare,  perforates  the  periorbita,  and  joins  the  ophthalmic  vein.  It  is  relatively 
small  at  each  end,  but  presents  one  or  two  large  fusiform  dilatations.     Its  posterior 

part  is  embedded  in  a  mass  of  fat.  It 
receives  the  following  tributaries :  (a) 
The  great  palatine  vein  (V.  palatina 
major),  separates  from  the  palatine 
artery  at  the  anterior  palatine  fora- 
men, and  passes  in  the  groove  between 
the  tuber  maxillare  and  the  palate 
bone.  The  palatine  veins  form  a  very 
rich  plexus  of  valveless  vessels  in  the 
submucosa  of  the  hard  palate,  which 
consists  of  several  layers  anteriorly, 
(6)  The  sphenopalatine  vein  (V. 
sphenopalatina)  is  the  satellite  of  the 
artery;  it  forms  a  rich  plexus  of  valve- 
less vessels  on  the  turbinate  bones 
and  the  septum  nasi.  The  venous 
plexuses  are  remarkably  developed  in 
certain  parts  of  the  nasal  mucosa. 
On  the  septum  a  little  below  its 
middle  and  on  the  turbinates  the 
veins  are  in  several  layers.  The  ol- 
factory region  does  not  share  in  this 
arrangement,  and  the  veins  here  are 
small  and  join  the  ethmoidal  vein. 
(c)  The  infraorbital  vein  (V.  infra- 
orbitalis)  is  also  a  satellite  of  the  ar- 
terj^;  it  usually  unites  with  the  t  pheno- 
palatine  to  form  a  short  common 
trunk,  (d)  The  ophthalmic  vein  (V. 
ophthalmica)  is  a  short  trunk,  which 
is  connected  in  front  with  the  vena 
reflexa  and  behind  with  the  cavernous 
sinus  through  the  foramen  orbitale. 
It  receives  veins  which  correspond  to 
the  arterial  branches. 

The  buccinator  vein  (V.  buccin- 
atoria)  extends  backward  from  the  ex- 
ternal maxillary  along  the  ventral  bor- 
der of  the  depressor  labii  inf  erioris  and 
buccinator  under  cover  of  the  mas- 
seter, turns  medially  over  the  ramus 
of  the  mandible  about  two  inches  (ca. 
5  cm.)  behind  the  last  molar  tooth,  and  is  continued  as  the  internal  maxillary  vein. 
It  has  a  large  fusiform  dilatation  and  is  valveless.     It  receives  a  large  vein  from 
the  buccal  plexus,  and  is  usually  connected  with  the  masseteric  vein. 

The  lingual  vein  (V.  lingualis)  is  formed  at  the  side  of  the  lingual  process  of  the 
hyoid  bone  by  the  confluence  of  several  veins  which  come  from  the  substance  of  the 
tongue.     One  or  two  considerable  vessels  run  partly  in  the  substance  of  the  hyo- 


iND    Ad- 


Fig.  587. — Dissection-  of  Mandibular  Space 
JACENT  Part  op  Neck  of  Horse. 
a.  Ramus  of  mandible;  b,  sterno-cephalicus  muscle; 
c,  c',  omo-hyoidei  and  sterno-hyoidei  (portion  removed  on 
right  side);  d,  hyoid  bone;  e,  anterior  belly  of  digastricus; 
/,  g,  mylo-hyoideus;  h,  mandibular  lymph  glands  (portion 
removed  on  right  side);  i,  parotid  gland;  k,  mandibular 
salivary  gland;  I,  chin;  m,  occipito-mandibularis;  1,  parotid 
duct;  2,  facial  vein;  3,  facial  artery;  4,  external  maxil- 
lary vein;  5,  lingual  vein;  6,  sublingual  artery;  7,  ventral 
branch  of  first  cervical  nerve;  S,  mylo-hyoid  nerve.  (After 
Ellenberger,  in  Leisering's  Atlas.) 


THE    SINUSES    OF   THE    DURA    MATER 


687 


glossus,  and  another  in  the  genio-hyoideus.  The  vein  is  at  first  covered  by  the 
mylo-hyoideus,  perforates  that  muscle,  runs  back  along  the  omo-hyoideus  in  rela- 
tion to  the  mandibular  lymph  glands,  and  joins  the  external  maxillary  near  the 
posterior  border  of  the  jaw. 

The  sublingual  vein  (V.  sublingualis)  is  smaller  than  the  preceding.  It  re- 
ceives veins  from  the  skin  and  muscles  of  the  mandibular  space,  the  sublingual 
gland,  and  the  gums.  It  opens  into  the  external  maxillary  vein  near  the  lingual  or 
joins  the  latter. 

7.  The  thyroid  vein  (V.  thyreoidea)  is  a  large  vessel  which  joins  the  jugular 
near  the  external  maxillary  vein.  It  receives  anterior  thyroid,  laryngeal,  and 
pharjmgeal  radicles,  and  sometimes  a  posterior  thyroid  vein. 

8.  Muscular,  tracheal,  oesophageal,  and  parotid  veins. 

9.  The  cephalic  vein  (V.  cephalica)  enters  the  jugular  near  its  termination. 
It  will  be  described  with  the  veins  of  the  thoracic  limb. 

10.  The  inferior  cervical  vein  (V.  cervicalis  ascendens)  accompanies  the  as- 
cending branch  of  the  artery.     It  may  open  into  the  brachial  vein. 

The  Sinuses  of  the  Dura  Mater 
These  (Sinus  durae  matris)  are  blood-spaces  between  the  meningeal  and  peri- 
osteal layers  of  the  dura  mater  and  are  lined  with  endothelium.     In  many  places 


Fig.  588. — Median  Section  op  Head  of  Horse,  Upper  Part  with  Septum  Nasi  Removed. 
a.  Lateral  mass  of  ethmoid  bone;  6,  dorsal  turbinate;  c,  ventral  turbinate;  d.  d',  turbinate  folds;  e,  frontal  sinus; 
/,  falx  cerebri;  g,  tentorium  cerebelli;  h,  medial  surface  of  hemisphere;  i,  cerebellum;  k,  occipital  bone;  h',  occipital 
condyle;  /t",  paramastoid  process;  ?,  external  acoustic  meatus;  m,  temporal  condyle;  «,  temporal  canal;  /.branches 
of  ethmoidal  artery;  ;^,  ^',  branches  of  sphenopalatine  artery;  3,  3',  branches  of  sphenopalatine  vein;  4,  branches  of 
ethmoidal  nerve;  .5,  .5',  branches  of  sphenopalatine  nerve;  6,  artery  of  corpus  callosum;  7,  dorsal  longitudinal  sinus;  5, 
straight  sinus;  0,  vena  magna  cerebri;  10,  ventral  longitudinal  sinus;  11,  11',  transverse  sinuses;  U,  dorsal  petrosal  sinus; 
13,  occipital  sinus;   i4,  dorsal  cerebral  vein;  15,  corpus  callosum;  16,  fornix.     (After  Ellenberger,  in  Leisering's  Atlas.) 


the  lumen  is  crossed  by  fibrous  strands.  They  receive  the  cerebral  veins  (Vv. 
cerebri),  meningeal  veins  (Vv.  meningese),  diploic  veins  (Vv.  diploicse),  and  com- 
municate with  veins  outside  of  the  cranium;  their  connections  with  the  latter 
are  by  means  of  emissary  veins  (Emissaria).  They  convey  the  blood  directly  or 
indirectly  to  the  jugular  veins.  Some  are  paired,  others  unpaired.  They  may  be 
divided  into  dorsal  and  basilar  systems. 

The  dorsal  system  comprises  the  following: 

The  dorsal  longitudinal  or  sagittal  sinus  (S.  sagittalis  dorsalis)  is  situated  in 
the  convex  border  of  the  falx  cerebri  along  the  internal  parietal  crest.  It  begins 
at  the  crista  galli  and  ends  near  the  tentorium  osseum  at  the  confluence  of  the 
sinuses  (Confluens  sinuum)  formed  by  the  junction  with  the  straight  sinus.  It 
receives  most  of  the  ascending  cerebral  veins.  Along  each  side  are  small  pouches 
(Lacunge  laterales)  into  which  the  veins  open.  The  lumen  of  the  sinus  is  very 
irregular;  it  is  traversed  by  fibrous  bands  and  is  partially  divided  by  a  longitu- 
dinal septum. 


^88  BLOOD-VASCULAR   SYSTEM    OF    THE    HORSE 

The  ventral  longitudinal  or  sagittal  sinus  (S.  sagittalis  ventralis)  is  much 
smaller  than  the  dorsal  sinus. ^  It  runs  backward  on  the  corpus  callosum  in  the 
concave  edge  of  the  falx  cerebri,  and  joins  the  great  cerebral  vein  to  form  the  straight 
sinus.  It  receives  veins  from  the  medial  surface  of  the  cerebral  hemispheres  and 
from  the  corpus  callosum. 

The  straight  sinus  (S.  rectus)  proceeds  from  the  junction  of  the  ventral  longi- 
tudinal sinus  with  the  great  cerebral  vein  behind  the  corpus  callosum.  It  ascends 
in  the  falx  cerebri,  inclining  backward,  and  joins  the  dorsal  longitudinal  sinus  at 
the  confluens  sinuum. 

The  transverse  sinuses  (Ss.  transversi),  right  and  left,  proceed  laterally  from 
the  confluens  sinuum;  they  pass  outward  in  the  transverse  grooves  of  the  parietal 
bones,  enter  the  temporal  canals,  and  are  continued  by  the  dorsal  cerebral  veins 
to  the  superficial  temporal  veins.  They  receive  the  dorsal  petrosal  sinuses,  veins 
from  the  posterior  part  of  the  cerebrum  and  from  the  corpora  quadrigemina,  and 
the  posterior  meningeal  vein.  The  two  sinuses  are  cormected  by  the  sinus  com- 
municans,  which  extends  across  the  cranial  vault  in  a  channel  in  the  base  of  the 
internal  occipital  protuberance. 

The  dorsal  petrosal  sinuses  (Ss.  petrosi  dorsales)  ascend  in  the  tentorium 
€erebelli  and  join  the  transverse  sinuses  near  the  internal  opening  of  the  temporal 
canal.  Each  is  the  direct  continuation  of  the  vena  rhinalis  posterior  and  receives 
the  vena  basilaris  cerebri.  There  is  sometimes  an  accessory  petrosal  sinus  along- 
side of  the  chief  sinus,  which  is  formed  by  the  confluence  of  veins  from  the  pons 
and  medulla  oblongata. 

The  occipital  sinuses  (Ss.  occipitales)  are  situated  in  the  dura  mater  on  each 
side  of  the  vermis  cerebelli.  They  communicate  in  front  with  the  sinus  communi- 
cans,  and  one  of  them  is  continued  posteriorly  by  the  dorsal  spinal  vein.  Each 
sinus  is  connected  by  a  communicating  branch  with  the  transverse  sinus  and  with 
the  ventral  petrosal  sinus.  The  right  and  left  sinuses  are  connected  by  anasto- 
motic branches,  so  that  the  arrangement  is  more  or  less  plexiform.  They  re- 
ceive veins  from  the  cerebellum,  medulla  oblongata,  and  diploe. 

The  basilar  system  consists  of  the  following: 

The  cavernous  sinuses  (Ss.  cavernosi)  lie  in  the  medial  grooves  of  the  root  of  the 
temporal  wings  of  the  sphenoid  bone  at  either  side  of  the  pituitary  fossa.  The  two 
are  connected  by  a  wide  transverse  branch,  the  intercavernous  sinus  (Sinus  inter- 
cavernosus),  behind  and  below  the  posterior  part  of  the  pituitary  body.^  Each  is 
continuous  in  front  with  the  ophthalmic  vein  and  below  with  the  ventral  petrosal 
sinuses;  it  communicates  also  by  small  anastomotic  veins  with  the  basilar  plexus. 
The  third,  sixth,  and  the  ophthalmic  and  maxillary  divisions  of  the  fifth  nerve  lie 
along  the  lateral  wall  of  the  sinus.  The  internal  carotid  artery  traverses  the  sinus 
and  is  connected  with  its  fellow  by  a  transverse  branch  which  lies  in  the  inter- 
cavernous sinus.  An  oval  opening  in  the  floor  communicates  with  the  ventral 
petrosal  sinus  and  transmits  the  internal  carotid  artery. 

The  sinus  is  not  subdivided  by  strands  of  fibrous  tissue  as  in  man,  but  a  few  delicate  bands 
attach  the  artery  to  its  wall. 

The  ventral  petrosal  sinuses  (Ss.  petrosi  ventrales)^  lie  along  the  borders  of 
the  basilar  part  of  the  occipital  bone,  enclosed  in  the  thick  dura  which  closes  the 
foramen  lacerum.  The  anterior  part  extends  about  half  an  inch  (ca.  12  mm.) 
under  the  temporal  wing  of  the  sphenoid.  Here  communications  exist  with  veins 
in  the  pterygopalatine  fossa.     The  posterior  end  is  bulbous  and  lies  in  the  condy- 

^  It  is  also  termed  the  vena  corporis  callosi  major. 

^  A  small  anterior  intercavernous  sinus  may  connect  the  two  cavernous  sinuses  in  front  of  the 
pituitary  gland.  Mobilio  states  that  he  has  seen  the  cavernous  sinus  having  a  blind  anterior  end, 
the  ophthalmic  vein  passing  laterally  to  the  ventral  petrosal  sinus. 

^  These  are  termed  the  subsphenoidal  confluents  by  Chauveau  and  M'Fadyean. 


THE   VEINS    OF   THE   CRANIUM — VERTEBRAL  AND    SPINAL   VEINS  689 

loid  fossa;  it  communicates  with  the  condyloid  vein  issuing  from  the  hypoglossal 
foramen  and  is  drained  by  the  ventral  cerebral  vein;  it  also  receives  an  emissary 
vein  from  the  temporal  canal.  The  sinus  communicates  with  the  cavernous  sinus 
by  an  oval  opening  at  the  carotid  notch  which  transmits  the  internal  carotid  artery; 
the  latter  forms  the  first  bend  of  its  S-shaped  curve  in  the  petrosal  and  the  second 
in  the  cavernous  sinus. 

The  basilar  plexus  (Plexus  basilaris)  is  situated  on  the  cerebral  surface  of  the 
basilar  part  of  the  occipital  bone,  and  is  directly  continuous  behind  with  the  venous 
plexus  in  the  atlas.  Its  chief  emissary  is  the  condyloid  vein,  which  brings  it  into 
communication  with  the  ventral  petrosal  sinus.  It  is  connected  with  the  cav- 
ernous and  intercavernous  sinuses  by  small  veins. 

The  Veins  of  the  Cranium 

The  cerebral  veins  (Venae  cerebri)  do  not  in  general  accompany  the  cerebral 
arteries.  They  have  very  thin  walls,  no  muscular  coat,  and  no  valves.  They  are 
arranged  in  two  sets,  superficial  or  cortical  and  deep  or  central.  The  superficial 
veins  are  more  numerous  and  larger  than  the  arteries.  They  lie  on  the  surface  of 
the  brain  in  the  pia  mater  and  the  subarachnoid  space. 

The  ascending  cerebral  veins  drain  most  of  the  convex  surface  and  the  medial 
surface  of  the  cerebral  hemispheres.  Most  of  them  open  into  the  dorsal  longitudi- 
nal sinus,  but  some  enter  the  confluens  sinuum  or  the  transverse  sinuses.  Near  the 
termination  they  become  bulbous,  and  open  into  the  sinus  obliquely  and  in  such  a 
manner  as  to  tend  to  prevent  reflux  of  blood  into  them.^  The  descending  cerebral 
veins  which  come  chiefly  from  the  ventral  part  of  the  convex  surface  of  the  cere- 
]jrum  open  into  the  vena  rhinalis  posterior. 

The  basal  cerebral  veins  converge  to  a  large  common  trunk,  the  vena  rhinalis 
posterior ;  this  begins  at  the  anterior  end  of  the  piriform  lobe,  runs  backward  in  a 
groove  on  the  latter,  enters  the  tentorium  cerebelli,  and  opens  into  the  dorsal 
petrosal  sinus. 

The  deep  cerebral  veins  issue  from  the  central  or  ganglionic  parts  of  the  brain 
at  the  transverse  fissure.  The  principal  ones  come  from  the  chorioid  plexuses,  the 
corpus  striatum,  and  the  septum  pellucidum.  These  unite  to  form  the  internal 
cerebral  veins  (Vv.  cerebri  internee),  which  run  backward  in  the  roof  of  the  third 
ventricle  and  unite  to  form  the  great  cerebral  vein  (V.  magna  cerebri).  This 
passes  upward  and  backward  behind  the  splenium  of  the  corpus  callosum  and  is 
continued  as  the  straight  sinus  to  join  the  longitudinal  sinus. 

The  dorsal  cerebellar  veins  ramify  on  the  upper  surface  of  the  cerebellum. 
They  go  chiefly  to  the  occipital  and  dorsal  petrosal  sinuses.  The  ventral  cerebellar 
veins  are  larger  and  go  chiefly  to  the  basilar  plexus.  The  veins  of  the  medulla  and 
pons  end  chiefly  in  the  basilar  plexus  and  the  occipital  and  dorsal  (and  accessory) 
petrosal  sinuses. 

The  meningeal  veins  (Vense  meningese)  arise  in  capillary  plexuses  in  the  su- 
perficial and  deep  faces  of  the  dura  mater.  Some  end  in  the  sinuses  of  the  dura, 
others  accompany  the  meningeal  arteries. 

The  diploic  veins  (Vense  diploicse)  are  anastomosing  channels  in  the  spongy 
substance  of  the  cranial  bones.  Their  walls  are  thin,  consisting  in  many  places 
only  of  the  endothelium,  and  they  have  no  valves.  Some  open  inward  into  venous 
sinuses,  others  into  extracranial  veins. 

Vertebral  and  Spinal  Veins 
Two  venous  trunks,   the  longitudinal  vertebral  sinuses   (Sinus  vertebrales 
l(mgitudinales),  extend  along  the  floor  of  the  vertebral  canal,  one  on  either  side  of 

1  Most  of  these  veins  open  into  the  sinus  in  the  direction  of  the  blood-stream  in  the  sinus,  but 
some  of  the  posterior  ones  open  about  at  a  right  angle,  or  even  contrary  to  the  direction  of  the  cur- 
rent. 

44 


BLOOD-VASCULAR   SYSTEM    OP   THE   HORSE 


the  dorsal  longitudinal  ligament.  They  are  continuous  in  front  with  the  basilar 
plexus.  They  lie  in  the  grooves  on  the  bodies  of  the  vertebrae  and  are  connected 
by  a  series  of  transverse  anastomoses  which  pass  between  the  central  part  of  the 
bodies  of  the  vertebrae  and  the  dorsal  longitudinal  ligament  or  in  channels  in  the 
bone.  They  receive  veins  from  the  spinal  cord,  the  meninges,  and  the  bodies  of  the 
vertebree  (Venae  basis  vertebrae).  Through  the  intervertebral  foramina  efferent 
vessels  connect  with  the  occipital,  vertebral,  intercostal,  lumbar,  and  lateral  sacral 
veins.     The  veins  of  the  spinal  cord  are  drained  by  dorsal  and  ventral  longitudinal 

trunks.     The  ventral  vein,  which  is  the  smaller, 
[y3g^-;Mraf||p!f^M}^  accompanies  the  ventral  spinal  artery. 

If-  If  1  *L. 

VEINS  OF  THE  THORACIC  LIMB 
The  brachial  vein  (V.  brachialis)  (Fig.  566) 
is  the  satellite  of  the  extrathoracic  part  of  the 
brachial  artery.  It  arises  at  the  medial  side  of 
the  distal  end  of  the  shaft  of  the  humerus  and 
ascends  in  the  arm  behind  the  artery  under  cover 
of  a  layer  of  fascia  and  the  posterior  superficial 
pectoral  muscle.  At  the  shoulder  it  is  ventral  to 
the  artery,  crosses  the  anterior  border  of  the  first 
rib,  and  concurs  with  its  fellow  and  the  two  jugu- 
lars in  the  formation  of  the  anterior  vena  cava. 
The  roots  of  the  vein  are  somewhat  variable,  but 
most  often  four  veins  in  addition  to  a  large  ob- 
lique branch  from  the  cephalic  unite  in  its  forma- 
tion; two  or  three  of  these  radicles  are  satellites  of 
the  median  artery.  Its  tributaries  correspond  in 
general  to  the  branches  of  the  artery,  but  a  few 
differences  are  worthy  of  notice.  The  thoraco- 
dorsal vein  (V.  thoracodorsalis)  often  joins  the 
external  thoracic  or  the  deep  brachial  vein.  The 
external  thoracic  vein  (V.  thoracica  externa)^  is  a 
large  vessel  which  arises  in  the  ventral  wall  of  the 
abdomen,  passes  forward  (embedded  partly  in  the  cutaneus  muscle)  along  the  lateral 
border  of  the  posterior  deep  pectoral  muscle,  and  joins  the  brachial  vein  close  to 
the  subscapular  or  in  common  with  it.  It  may  receive  a  vein  which  is  the  satellite 
of  the  external  thoracic  artery. 

The  cephalic  vein  (V.  cephalica)  arises  at  the  medial  side  of  the  carpus  as  the 
continuation  of  the  medial  metacarpal  vein.  It  ascends  on  the  deep  fascia 
of  the  forearm  at  first  in  the  furrow  between  the  flexor  carpi  radialis  and  the 
radius.  Toward  the  middle  of  the  forearm  it  inclines  gradually  forward  on  the 
medial  surface  of  the  radius,  accompanied  by  a  branch  of  the  musculo-cutaneous 
nerve,  and  arrives  at  the  insertion  of  the  biceps.  Here  it  detaches  a  large  com- 
municating branch  (Ramus  communicans),  which  passes  upward  and  backward  over 
the  medial  insertion  of  the  biceps  and  the  median  artery  and  median  nerve, 
and  joins  the  brachial  vein.  The  vein  to  this  point  is  often  termed  the  internal  sub- 
cutaneous vein  of  the  forearm  (V.  cephalica  antebrachii).  It  is  continued  (as  the 
V.  cephalica  humeri)  in  the  furrow  between  the  brachiocephalicus  and  the  anterior 
superficial  pectoral  muscle  with  a  branch  of  the  inferior  cervical  artery,  crosses  the 
deep  face  of  the  cervical  cutaneus,  and  opens  into  the  terminal  part  of  the  jugular 
or  the  brachial  vein.  It  receives  the  accessory  cephalic  vein  (V.  cephalica  accessoria) , 
which  arises  from  the  carpal  network,  runs  upward  on  the  deep  fascia  along  the 
1  Often  termed  the  spur  vein. 


Fig.  589. — Vertebral  Sinuses  op  Horse. 
The  vertebral  canal  has  been  opened 
by  sawing  off  the  arches.  The  nerve-roots 
are  cut  on  one  side  and  the  spinal  cord 
turned  over  to  right.  1,  Ventral  spinal 
artery;  2,  reinforcing  branches  from  verte- 
bral, intercostal,  or  lumbar  arteries  (ac- 
cording to  region);  3,  longitudinal  verte- 
bral sinuses;  a,  ventral  surface  of  spinal 
cord;  b,  dura  mater  (cut);  c,  nerve-roots; 
d,  dorsal  longitudinal  ligament.  (After 
Ellenberger,  in  Leisering's  Atlas.) 


VEINS    OF    THE   THORACIC    LIMB 


691 


medial  border  of  the  extensor  carpi,  and  joins  the  cephalic  vein  at  the  proximal 
end  of  the  forearm. 

The  deep  veins  of  the  forearm  are  variable.     Commonly  two  median  veins 


Fig.  590. — Dissection  of  Pectoral  Region  and  Anterior  Part  of  Abdominal  Wall  of  Horse. 
1,  Jugular  vein;  2,  loose  connective  tissue  of  axillary  space;  3,  ascending  branch  of  inferior  cer^'^caI  artery;  4,  de- 
scending branch  of  same;  5,  cephalic  vein;  5,  median  nerve;  7,  ulnar  nerve ;  5,  brachial  artery;  S,  brachial  vein;  10, 
external  thoracic  vein;  /;,  anterior  abdominal  artery  and  vein;  12,  branches  of  sixth  cervical  nerve;  13,  cutaneous 
branch  of  axillary  nerve;  14,  cutaneous  branch  of  musculo-cutaneous  nerve;  15,  cervical  cutaneus;  16,  sterno-cephahcus ; 
17,  scalenus;  18,  brachiocephalicus;  19,  anterior  superficial  pectoral;  20,  posterior  superficial  pectoral;  21,  anterior 
deep  pectoral;  22,  posterior  deep  pectoral;  23,  abdominal  cutaneus;  24,  obliquus  abdominis  externus;  25,  rectus 
abdominis;  26,  coraco-brachialis;  27,  tensor  fascise  antibrachii;  a,  prescapular  lymph  glands;  h,  prepectoral  lymph 
glands;  c,  axillary  lymph  glands;  d,  cubital  lymph  glands;  c.  x.,  xiphoid  cartilage.  (After  Schmaltz,  Atlas  d.  Anat. 
d.  Pferdes.) 


(Vense  medianae)  accompany  the  artery  of  like  name,  one  in  front  and  one  behind. 
A  third  vein  arises  by  radicles  emerging  from  the  proximal  part  of  the  deep  flexor; 


692  BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 

it  joins  the  posterior  satellite  of  the  median  artery  or  forms  one  of  the  roots  of  the 
brachial  vein.  The  common  interosseous  vein  joins  the  posterior  satellite.  The 
anterior  radial  vein  (V.  collateralis  radialis)  is  a  satellite  of  the  artery.  The  ulnar 
vein  is  usually  double  at  its  proximal  part,  and  communicates  with  the  deep  brachial 
vein. 

There  are  three  chief  metacarpal  veins.  The  medial  metacarpal  or  common 
digital  vein  (V.  metacarpea  volaris  superficialis  medialis)  arises  from  the  volar 
venous  arch  above  the  fetlock.  It  is  the  largest  vein  of  the  region  and  lies  in 
front  of  the  common  digital  artery.  It  separates  from  the  artery  at  the  proximal 
end  of  the  metacarpus,  passes  upward  on  the  medio-volar  surface  of  the  carpus, 
under  cover  of  the  superficial  layer  of  the  volar  annular  ligament,  and  is  con- 
tinued as  the  cephalic  vein.  It  communicates  at  its  proximal  part  with  the  origin 
of  the  median  veins  by  a  short  but  relatively  large  branch.  The  lateral  metacaipal 
vein  (V.  metacarpea  volaris  superficialis  lateralis)  arises  from  the  venous  arch  above 
the  fetlock  and  passes  upward  behind  the  lateral  border  of  the  suspensory  ligament 
in  front  of  the  lateral  volar  nerve  and  accompanied  by  a  small  artery.  At  the 
proximal  end  of  the  metacarpus  it  is  connected  with  the  deep  metacarpal  vein  by 
two  transverse  anastomoses  which  pass  across  the  suspensory  ligament.  It  then 
ascends  as  a  satellite  of  the  lateral  volar  metacarpal  artery  and  concurs  in  the 
origin  of  the  ulnar  and  median  veins.  The  deep  metacarpal  vein  (V.  metacarpea 
volaris  profunda  medialis)  arises  from  the  venous  arch,  passes  forward  between 
the  two  branches  of  the  suspensory  ligament,  and  ascends  on  the  posterior  surface 
of  the  large  metacarpal  bone.  At  the  proximal  end  of  the  latter  it  communicates 
with  the  other  metacarpal  veins,  ascends  with  the  medial  volar  metacarpal  artery, 
and  concurs  in  forming  the  median  veins. 

The  venous  arch  (Arcus  venosus  volaris),  from  which  the  metacarpal  veins 
arise,  is  situated  above  the  sesamoids  of  the  fetlock,  between  the  suspensory  liga- 
ment and  the  deep  flexor  tendon.  It  is  formed  by  the  junction  of  the  two  digital 
veins. 

The  digital  veins,  medial  and  lateral  (V.  digitalis  medialis,  lateralis),  drain  the 
venous  plexuses  of  the  foot.  They  arise  at  the  proximal  edge  of  the  cartilages  of 
the  third  phalanx  and  ascend  in  front  of  the  corresponding  arteries. 

It  is  convenient  to  recognize  the  following  venous  plexuses  of  the  foot,  which, 
however,  communicate  very  freely : 

1.  The  coronary  plexus  encircles  the  upper  part  of  the  foot.  It  covers  the 
terminal  part  of  the  extensor  tendon,  the  cartilages  of  the  third  phalanx,  and  the 
bulbs  of  the  digital  cushion. 

2.  The  dorsal  (or  laminal)  plexus  covers  the  dorsal  surface  of  the  third  phalanx 
in  the  deep  layer  of  the  corium  of  the  wall  of  the  hoof.  It  forms  the  circumflex 
vein  of  the  third  phalanx,  or  vein  of  the  distal  border  of  the  third  phalanx,  which 
corresponds  to  the  artery  of  like  name. 

3.  The  volar  plexus  is  in  the  deep  layer  of  the  corium  of  the  sole  of  the  hoof 
and  on  the  deep  surface  of  the  cartilages  of  the  third  phalanx.  It  communicates 
around  the  distal  border  of  the  third  phalanx  with  the  dorsal  plexus  and  through  the 
cartilages  with  the  coronary  plexus. 

The  deep  vein  of  the  third  phalanx  accompanies  the  terminal  part  of  the 
digital  artery.     It  drains  the  intraosseous  plexus  contained  in  the  third  phalanx. 


THE  POSTERIOR  VENA  CAVA  (Figs.  554.  575) 

The  posterior  vena  cava  (V.  cava  caudalis)  returns  almost  all  of  the  blood  from 
the  abdomen,  pelvis,  and  pelvic  limbs.  It  is  formed  by  the  confluence  of  the  right 
and  left  common  iliac  veins  at  the  fifth  lumbar  vertebra,  above  the  terminal  part 
of  the  aorta,  and  chiefly  to  the  right  of  the  median  plane. 


THE    PORTAL    VEIN  693 

The  mode  of  origin  is  variable.  In  some  cases  there  is  a  common  trunk  formed  by  the 
union  of  the  two  internal  iliac  veins  so  that  the  arrangement  resembles  the  termination  of  the 
aorta.  In  other  cases  the  internal  iliac  vein  does  not  exist.  Exceptionally  there  is  a  small  middle 
sacral  vein  on  the  middle  of  the  pelvic  surface  of  the  sacrum.  It  opens  at  the  angle  of  divergence 
of  the  common  iliac  veins. 

It  passes  forward  on  the  ventral  face  of  the  psoas  minor  to  the  right  of  the 
abdominal  aorta.  At  the  last  thoracic  vertebra  it  separates  from  the  aorta  and 
runs  forward  between  the  right  crus  of  the  diaphragm  and  the  pancreas  till  it 
reaches  the  liver.  Here  it  inclines  ventrally  along  the  medial  border  of  the  right 
lobe  and  on  the  parietal  surface  of  the  liver,  largely  embedded  in  the  gland  sub- 
stance, and  passes  through  the  foramen  venae  cavae  of  the  diaphragm.  It  then  runs 
forward  and  somewhat  ventrally  between  the  intermediate  lobe  and  the  main  mass 
of  the  right  lung  at  the  upper  margin  of  a  special  fold  of  the  right  pleura,  accom- 
panied by  the  right  phrenic  nerve,  and  opens  into  the  posterior  part  of  the  right 
atrium  opposite  the  fifth  intercostal  space.     It  receives  the  following  tributaries: 

1.  The  phrenic  veins  (Vv.  phrenicse),  two  or  three  in  number,  return  the  blood 
from  the  diaphragm.  They  are  very  large  in  comparison  with  the  arteries,  and 
join  the  vena  cava  at  the  foramen  venae  cavae. 

2.  The  lumbar  veins  (Vv.  lumbales)  correspond  to  the  arteries.  Five  pairs 
usually  empty  into  the  posterior  vena  cava.  Sometimes  the  corresponding  veins 
of  opposite  sides  unite  to  form  a  common  trunk.  The  first  communicate  with  the 
vena  azygos  or  hemiazygos,  and  the  last  usually  enters  the  common  iliac  vein. 

3.  The  internal  spermatic  veins  (Vv.  spermaticae  internae)  (Fig.  575)  accompany 
the  arteries  of  like  name.  In  the  spermatic  cord  they  form  a  very  rich  network,  the 
pampiniform  plexus  (Plexus  pampiniformis)  about  the  artery  and  nerves.  Their 
termination  is  variable.  The  right  one  commonly  joins  the  vena  cava  near  the 
renal  vein,  often  by  a  common  trunk  with  the  left  one.  Frequently  the  left  vein 
joins  the  left  renal,  and  sometimes  the  right  one  ends  similarly. 

3  a.  The  utero-ovarian  veins  are  much  larger  than  the  preceding  and  are 
satellites  of  the  arteries  in  the  broad  ligaments.  The  ovarian  branch  is  plexiform 
near  the  ovary.  The  uterine  branches  form  a  rich  plexus  in  the  wall  of  the  uterus. 
The  trunk  is  very  short  and  terminates  like  the  corresponding  vein  of  the  male. 

4.  The  renal  veins  (Vv.  renales),  satellites  of  the  arteries,  are  of  large  caliber 
and  thin  walled.  The  right  vein  passes  medially  and  backward  on  the  ventral  face 
of  the  kidney,  between  the  artery  in  front  and  the  ureter  behind.  It  joins  the  vena 
cava  above  the  right  adrenal.  The  left  vein  is  somewhat  longer.  It  passes  medially 
at  first  like  the  right  one,  then  bends  around  the  posterior  end  of  the  adrenal,  crosses 
the  origin  of  the  renal  artery,  and  opens  into  the  vena  cava  a  little  further  back  than 
the  right  one.  They  receive  veins  from  the  adrenals,  but  some  adrenal  veins  (Vv. 
adrenales)  open  directly  into  the  vena  cava. 

5.  The  hepatic  veins  (Vv.  hepaticae)  return  the  blood  from  the  liver,  and  open 
into  the  vena  cava  as  it  lies  in  the  groove  in  the  liver.  Three  or  four  large  veins 
open  into  the  vena  cava  just  before  it  leaves  the  liver,  and  numerous  small  ones 
discharge  into  its  embedded  part. 

Of  the  foregoing,  the  phrenic  and  lumbar  veins  are  termed  parietal  radicles 
(Radices  parietales),  and  the  remainder  are  visceral  radicles  (Radices  viscerales). 

THE  PORTAL  VEIN 
The  portal  vein  (V.  porta?)  is  a  large  trunk  which  returns  the  blood  carried  to 
the  viscera  by  the  gastric,  splenic,  and  mesenteric  arteries;  its  average  diameter  is 
a  little  more  than  an  inch  (ca.  3  cm.).  Its  peripheral  tributaries  correspond  closely 
with  the  branches  of  the  arteries,  but  the  trunks  do  so  in  part  only.  The  vein  is 
formed  behind  the  pancreas  and  below  the  posterior  vena  cava  by  the  confluence 
of  the  anterior  and  posterior  mesenteric  and  splenic  veins.     It  passes  forward, 


694 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


traverses  the  posterior  part  of  the  pancreas  very  obliquely,  inclines  ventrally  and 
a  little  to  the  right,  and  reaches  the  portal  fissure  of  the  liver.  Here  it  divides  into 
three  branches  which  enter  the  liver  and  ramify  in  the  substance  of  the  gland  like 
an  artery,  terminating  in  the  lobular  capillaries.  From  the  lobules  the  blood  passes 
into  the  hepatic  veins  and  through  these  to  the  posterior  vena  cava.  Thus  the 
blood  Avhich  is  distributed  to  the  stomach,  nearly  the  entire  intestinal  tract,  the 
pancreas,  and  the  spleen,  passes  through  two  sets  of  capillaries  prior  to  its  return 
to  the  heart,  viz.,  the  capillaries  of  these  viscera  and  of  the  liver. 

1.  The  anterior  mesenteric  vein  (V.  mesenterica  cranialis)  is  the  largest  of 
the  portal  radicles.  It  is  situated  to  the  right  of  the  artery  of  like  name,  and  its 
tributaries  correspond  in  general  to  the  branches  of  the  artery.  The  dorsal  colic 
vein  usually  unites  with  the  ventral  one  at  the  pelvic  flexure,  thus  forming  a  single 
trunk  (V.  colica  dextra)  which  runs  between  the  right  parts  of  the  colon.     There  is, 


Fig.  591. — Portal  Vein  of  Horse. 


a,  Intrahepatic  part,  6,  extrahepatic  part,  of  portal  vein;  c,  anterior  gastric  vein;  d,  right  gastro-epiploic  vein; 
e,  pancreatico-duodenal  vein;  /,  splenic  vein;  /',  left  gastro-epiploic  vein;  g,  posterior  gastric  vein;  ?i,  posterior  mesen- 
teric vein;  t,  middle  colic  vein;  i-,  left  colic  vein;  fc',  anterior  haemorrhoidal  vein;  m,  jejunal  trunk;  m',  jejunal  veins; 
o,  right  colic  vein;  o',  ventral  colic  vein;  o",  dorsal  colic  vein;  o'",  small  collateral  vein  connecting  dorsal  colic  and 
posterior  mesenteric  veins;  p,  ileal  vein;  g,  csecal  veins;  J,  liver;  JJ,  spleen;  J7J,  stomach;  7F,  duodenum;  T,  jejunum; 
VI,  csecum;  VII,  ventral  parts  of  great  colon;  VIII,  pelvic  flexure;  IX,  dorsal  parts  of  great  colon;  X,  small  colon; 
XI,  rectum.    (After  Schmitz.) 


however,  a  small  vein  on  the  right  dorsal  colon  which  is  connected  by  numerous 
branches  with  the  right  colic  vein;  it  joins  the  posterior  mesenteric  vein  or  its 
middle  colic  radicle.  The  veins  of  the  small  intestine  (Vv.  intestinales)  unite  to 
form  a  short  trunk. 

2.  The  posterior  mesenteric  vein  (V.  mesenterica  caudalis)  is  the  smallest  of 
the  radicles  of  the  portal  vein.  It  accompanies  the  artery  in  the  colic  mesentery, 
and  its  rectal  branches  (Vv.  haemorrhoidales  craniales)  anastomose  with  those  of 
the  internal  pudic  vein.  It  receives  the  middle  colic  vein  from  the  initial  part  of 
the  small  colon  and  also  the  small  vein  of  the  right  dorsal  colon,  as  mentioned  above, 

3.  The  splenic  vein  (V.  lienalis)  is  the  very  large  satellite  of  the  splenic  artery. 
It  is  formed  by  the  union  of  two  radicles  at  the  base  of  the  spleen.  On  leaving  the 
hilus  of  the  spleen  it  passes  medially  between  the  anterior  pole  of  the  left  kidney  and 
the  saccus  ciecus  of  the  stomach  and  above  the  left  end  of  the  pancreas,  receives 


THE    COMMON    ILIAC    VEINS — THE    VEINS    OF   THE    PELVIC    LIMB  695 

commonly  the  posterior  gastric  vein  (V.  gastrica  caudalis),  and  unites  with  the 
anterior  mesenteric  at  the  posterior  border  of  the  pancreas.     Not  uncommonly  the 
splenic  and  posterior  mesenteric  veins  form  a  short  common  trunk. 
The  collateral  tributaries  of  the  portal  vein  are  as  follows: 

(1)  Pancreatic  veins  (Rami  pancreatici). 

(2)  The  gastro-duodenal  vein  (V.  gastroduodenaHs),  when  present,  corresponds 
mainly  to  the  extrahepatic  branches  of  the  hepatic  artery;  but  in  most  cases  it  does 
not  exist,  and  the  right  gastro-epiploic  vein  (V.  gastroepiploica  dexi^ra)  and  pan- 
creatico-duodenal  vein  (V.  pancreaticoduodenalis)  open  directly  into  the  portal 
vein. 

(3)  The  anterior  gastric  vein  (V.  gastrica  cranialis)  joins  the  portal  vein  at  the 
portal  fissure. 

THE  COMMON  ILIAC  VEINS  (Fig.  581) 
These  (V.  iliacse  communes)  are  two  very  large  but  short  trunks,  which  result 
from  the  union  of  the  internal  and  external  iliac  veins  of  each  side  at  the  sacro-iliac 
articulation.     The  left  one  is  the  longer,  and  crosses  obliquely  over  the  terminal 
part  of  the  aorta.     The  chief  tributaries  of  each  are  as  follows: 

1.  The  last  lumbar  vein. 

2.  The  circumflex  iliac  veins  (Vv.  circumflexae  ilium  profundae)  are  the  two 
satellites  of  the  corresponding  artery,  on  either  side  of  which  they  are  placed. 
They  may  open  directly  into  the  posterior  vena  cava  or  into  the  external  iliac  vein. 

3.  The  ilio-lumbar  vein  (V.  iliolumbalis)  may  open  into  the  common  iliac, 
the  external  iliac,  or  the  internal  iliac  vein. 


THE  INTERNAL  ILL^C  VEINS 
The  internal  iliac  or  hypogastric  veins  (Vv.  iliacae  internee  s.  hypogastricse), 
right  and  left,  are  usually  formed  by  the  confluence  of  lateral  sacral,  gluteal,  and 
internal  pudic  veins.  The  obturator  vein  may  open  into  them  also.  They  are 
short  trunks,  and  are  smaller  than  the  external  iliac  veins.  The  tributaries  corre- 
spond in  general  to  the  branches  of  the  three  arteries  of  like  names.  The  internal 
pudic  veins  receive  affluents  from  the  anus  and  posterior  part  of  the  rectum ;  from 
the  venous  plexuses  of  the  prepuce  and  penis  in  the  male ;  and  from  those  of  the 
mammary  gland,  vulva,  vagina,  and  vestibular  bulb  in  the  female.  A  large  anas- 
tomotic branch  connects  the  internal  pudic  and  obturator  veins  at  the  lesser  sciatic 
notch. 

THE  VEINS  OF  THE  PELVIC  LIMB 
The  external  iliac  vein  (V.  iliaca  externa)  (Figs.  576,  581)  lies  behind  the  cor- 
responding artery  at  the  brim  of  the  pelvis.     It  is  the  upward  continuation  of  the 
femoral  vein,  and  unites  at  the  sacro-iliac  joint  with  the  internal  iliac  to  form  the 
common  iliac  vein.     Its  tributaries  are  as  follows: 

1.  The  obturator  vein  (V.  obturatoria)  is  a  satellite  of  the  artery,  except  in  its 
terminal  part;  it  usually  opens  into  the  external  iliac  at  the  insertion  of  the  psoas 
minor.  Its  radicles  anastomose  with  those  of  the  internal  and  external  pudic  veins 
(Figs.  576,  658). 

2.  The  iliaco-femoral  or  lateral  circumflex  veins  (Vv.  circumflexae  femoris 
laterales)  are  the  two  satellites  of  the  homonymous  artery.  They  open  a  little 
higher  than  the  obturator. 

The  femoral  vein  (V.  femoralis)  (Figs.  575,  582)  lies  behind  the  artery  in  the 
proximal  part  of  the  thigh,  lateral  to  it  lower  down.     Its  chief  tributaries  are: 

1.  A  large  but  short  trunk  is  formed  by  the  union  of  the  deep  femoral  and 
the  external  pudic  vein.     The  deep  femoral  vein  (V.  profunda  femoris)  corresponds 


696  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

otherwise  to  the  artery.  The  external  pudic  vein  (V.  pudenda  externa)  arises 
chief!}'  from  a  rich  plexus  of  large  veins  situated  above  and  along  the  sides  of  the 
penis  and  prepuce  in  the  male,  the  mammary  glands  in  the  female.  It  passes 
through  a  foramen  in  the  anterior  part  of  the  tendon  of  origin  of  the  gracilis  and 
runs  outward  behind  the  pectineus  to  unite  with  the  deep  femoral  vein.  The  right 
and  left  veins  are  connected  by  a  large  transverse  anastomotic  branch  which  lies 
in  the  subpubic  groove,  and  each  has  a  large  connection  with  the  obturator  vein. 
Each  receives  the  posterior  abdominal  vein  (V.  abdominalis  caudalis),  which  ac- 
companies the  artery  of  like  name.  The  subcutaneous  abdominal  vein  (V.  ab- 
dominalis subcutanea)  arises  in  the  skin  and  cutaneous  muscle  of  the  ventral 
abdominal  wall,  anastomoses  with  the  internal  and  external  thoracic  and  deep 
abdominal  veins,  and  joins  the  external  pudic  or  the  posterior  abdominal  vein. 
A  small  vein  may  accompany  the  external  pudic  artery  in  the  inguinal  canal. 

2.  The  anterior  femoral  vein  (V.  femoris  cranialis)  accompanies  the  artery. 

3.  The  saphenous  vein  (V.  saphena)  (Figs.  575,  576,  583)  arises  on  the  dorso- 
medial  surface  of  the  tarsus  as  the  upward  continuation  of  the  medial  metatarsal 
vein.  Its  course  is  distinctly  visible.  It  ascends  on  the  subcutaneous  surface  of 
the  tibia  and  the  popliteus  muscle,  enclosed  between  layers  of  the  deep  fascia,  in- 
clines a  little  backward  to  the  proximal  part  of  the  leg,  then  deviates  slightly  for- 
ward, runs  upward  on  the  gracilis,  passes  between  that  muscle  and  the  sartorius, 
and  joins  the  femoral  or  the  external  pudic  vein.^  On  the  upper  part  of  the  capsule 
of  the  hock  joint  it  forms  an  arch  with  the  anterior  tibial  vein.  The  vein  has 
numerous  valves.  The  satellite  artery  is  relatively  small,  and  lies  in  front  of  the 
vein  as  far  as  the  junction  with  the  recurrent  tibial  vein,  which  it  accompanies  on 
the  leg.  It  receives  the  recurrent  tibial  vein  (V.  recurrens  tibialis)  at  the  proximal 
fourth  of  the  leg.  This  vessel  arises  at  the  distal  third  of  the  leg,  where  it  forms  an 
arch  with  the  posterior  tibial  vein;  here  it  is  a  satellite  of  the  artery  of  like  name. 
It  ascends  in  the  furrow  in  front  of  the  gastrocnemius  tendon,  inclines  forward  at 
the  proximal  third  of  the  leg,  and  joins  the  saphenous  vein  at  an  acute  angle.  It 
gives  off  a  branch  which  ascends  with  the  artery  and  joins  the  posterior  femoral  or 
the  popliteal  vein.^  A  smaller  vein  from  the  anterior  face  of  the  metatarsus  joins 
the  saphenous  at  the  hock. 

4.  Muscular  branches  which  correspond  to  the  arteries. 

5.  The  posterior  femoral  vein  (V.  femoris  caudalis)  is  a  satellite  of  the  artery. 
It  receives  the  recurrent  tarsal  vein  (V.  tarsea  recurrens),  which  arises  at  the  lateral 
side  of  the  hock,  ascends  on  the  deep  fascia  of  the  lateral  surface  of  the  leg  in  front 
of  the  tendo  Achillis,  passes  between  the  biceps  femoris  and  semitendinosus,  and 
joins  the  posterior  femoral  vein.  It  is  connected  with  the  recurrent  tibial  vein  by 
a  large  anastomotic  branch  which  crosses  in  front  of  the  tuber  calcis.  Usually  a 
branch  from  it  ascends  along  the  great  sciatic  nerve  and  anastomoses  with  the  ob- 
turator vein. 

The  popliteal  vein  (V.  poplitea)  lies  along  the  medial  side  of  the  artery  (Fig. 
584).     It  is  formed  by  the  confluence  of  anterior  and  posterior  tibial  veins. 

Two  anterior  tibial  veins  (Vv.  tibiales  anteriores)  usually  accompany  the  artery 
of  like  name;  the  lateral  vein  is  much  the  larger.^     In  other  cases  there  is  a  single 

1  The  place  and  mode  of  termination  are  quite  variable.  It  may  disappear  from  the  surface 
of  the  thigh  at  any  point  above  the  distal  third.  In  some  cases  it  passes  through  the  anterior 
part  of  the  gracihs  instead  of  dipping  in  between  that  muscle  and  the  sartorius,  and  more  rarely 
it  joins  the  external  pudic  vein  at  the  origin  of  the  gracilis. 

2  The  arrangement  here  is  subject  to  variation.  Some  authors  regard  the  ascending  branch 
of  this  description  as  the  trunk,  and  the  connection  with  the  saphenous  as  an  anastomotic  branch. 
The  latter  is  usually,  so  far  as  size  is  concerned,  the  trunk. 

'  The  large  size  of  this  vein,  the  thinness  of  its  wall,  and  the  fact  that  it  is  separated  only  by  a 
thin  layer  of  muscle  (lateral  part  of  tibialis  anterior)  from  the  deep  peroneal  nerve  should  be  noted 
with  reference  to  section  of  that  nerve.  The  vein  is  sometimes  markedly  varicose  in  the  proximal 
part  of  the  leg. 


LYMPHATIC    SYSTEM   OF  THE    HORSE — THE   THORACIC    DUCT  697 

large  vein  in  the  proximal  part  of  the  leg,  two  lower  down.  They  arise  from  a 
number  of  anastomosing  radicles  on  the  front  of  the  capsule  of  the  hock  joint, 
chiefly  as  the  continuation  of  the  perforating  tarsal  vein.  A  large  branch  from  the 
saphenous  vein  concurs  in  the  formation  of  the  somewhat  plexiform  arrangement 
on  the  flexion  surface  of  the  hock. 

The  posterior  tibial  vein  (V.  tibialis  posterior)  is  commonly  double  (Fig.  583). 
It  arises  at  the  level  of  the  tuber  calcis,  where  it  has  a  communication  with  the 
recurrent  tibial  vein.     It  is  a  satellite  of  the  artery. 

The  medial  or  great  metatarsal  vein  (V.  metatarsea  dorsalis  medialis  (Figs. 
583,  585)  arises  from  the  venous  arch  above  the  sesamoids  at  the  fetlock,  but  is 
practically  the  upward  continuation  of  the  medial  digital  vein.  It  ascends  along 
the  medial  border  of  the  suspensory  ligament,  then  in  the  groove  on  the  proximal 
part  of  the  large  metatarsal  bone  to  the  capsule  of  the  hock  joint,  and  is  continued 
by  the  saphenous  vein.  The  small  middle  dorsal  metatarsal  vein  (V.  met.  dorsalis 
media)  joins  this  vein  or  the  saphenous  at  the  hock. 

The  lateral  metatarsal  vein  (V.  metatarsea  dorsalis  lateralis)  is  the  very  small 
satellite  of  the  great  metatarsal  artery.  It  is  inconstant,  but  may  be  double  in  the 
proximal  part  of  the  metatarsus. 

The  medial  plantar  vein  (V.  metatarsea  plantaris  superficialis  medialis)  is  very 
small,  and  is  not  always  present.  It  ascends  along  the  medial  border  of  the  deep 
flexor  tendon  in  front  of  the  corresponding  nerve.  It  is  connected  below  with  the 
medial  digital  vein,  and  above  with  the  deep  metatarsal  or  the  lateral  plantar  vein. 

The  lateral  plantar  vein  (V.  metatarsea  plantaris  superficialis  lateralis)  arises 
from  the  venous  arch  above  the  fetlock,  but  appears  to  be  the  upward  continuation 
of  the  lateral  digital  vein.  It  ascends  along  the  lateral  border  of  the  deep  flexor 
tendon  in  front  of  the  plantar  nerve,  and  is  connected  with  the  deep  metatarsal 
vein  at  the  proximal  part  of  the  metatarsus  by  a  transverse  branch.  It  then  passes 
upward  along  the  deep  flexor  tendon  in  relation  to  the  plantar  nerves  and  the 
medial  tarsal  artery,  and  is  continued  by  the  recurrent  tibial  vein. 

The  deep  metatarsal  vein  (V.  metatarsea  plantaris  profunda  medialis)  arises 
from  the  plantar  venous  arch,  above  the  fetlock,  passes  forward  between  the  branches 
of  the  suspensory  ligament,  and  ascends  on  the  posterior  face  of  the  large  meta- 
tarsal bone.  At  the  proximal  end  of  the  metatarsus  it  is  connected  with  the  lateral 
plantar  vein  by  a  transverse  branch,  thus  forming  the  deep  plantar  arch  (Arcus 
plantaris  profundus).  It  then  passes,  as  the  perforating  tarsal  vein  (V,  tarsea 
perforans),  through  the  vascular  canal  of  the  tarsus  and  forms  the  chief  radicle  of 
the  anterior  tibial  vein. 

The  distal  plantar  venous  arch  (Arcus  venosus  plantaris  distalis)  and  the  digital 
veins  are  arranged  like  those  of  the  thoracic  limb. 


Lymphatic  System  of  the  Horse 

THE  THORACIC  DUCT  (Figs.  553,  554) 
The  thoracic  duct  (Ductus  thoracicus)  is  the  chief  collecting  trunk  of  the  lym- 
phatic system.  It  begins  as  an  elongated  irregular  dilatation,  the  cisterna  chyli, 
which  is  situated  between  the  right  side  of  the  aorta  and  the  right  eras  of  the 
diaphragm  at  the  first  and  second  lumbar  vertebrae.  The  duct  enters  the 
thorax  through  the  hiatus  aorticus  and  runs  forward  on  the  right  of  the  median 
plane,  between  the  vena  azygos  and  the  aorta,  covered  by  the  pleura.  At  the  sixth 
or  seventh  thoracic  vertebra  it  inclines  somewhat  ventrally,  crosses  obliquely  over 
the  left  face  of  the  oesophagus,  and  passes  forward  on  the  left  side  of  the  trachea 
to  the  inlet  of  the  thorax.     The  extrathoracic  terminal  part  passes  downward  and 


^98  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

forward  a  variable  distance  (3-4  cm.)  on  the  deep  face  of  the  left  scalenus  muscle, 
bends  inward  and  backward  under  the  bicarotid  trunk,  and  opens  into  the  dorsal 
part  of  the  origin  of  the  anterior  vena  cava  just  behind  the  angle  of  junction  of  the 
jugular  veins.  The  terminal  bend  is  ampuUate,  and  sometimes  divides  into  two 
very  short  branches  which  open  close  together. 

Since  the  duct  develops  from  a  plexus  of  ducts  in  the  embryo,  considerable  variation  from 
the  more  usual  course  occurs.  There  is  often  a  left  duct  which  arises  at  the  cistema  or  at  a  var- 
iable point  from  the  right  duct,  rims  across  the  left  intercostal  arteries  parallel  to  the  latter,  and 
unites  with  it  over  the  base  of  the  heart  or  further  forward.  The  two  are  connected  by  cross- 
branches.  In  some  cases  the  left  duct  is  the  larger,  and  there  may  indeed  be  none  on  the  right 
side.     Other  variations  are  common. 

The  chief  tributaries  of  the  thoracic  duct  are  as  follows: 

1.  The  two  lumbar  trunks  (Trunci  lumbales)  are  formed  by  the  confluence 
of  the  efferent  ducts  of  the  lumbar  glands,  and  commonly  unite  with  each  other 
and  ^vith  the  posterior  intestinal  trunk  before  opening  into  the  cistern. 

2.  The  intestinal  trunks  (Trunci  intestinales),  two  or  three  in  number,  receive 
the  efferents  of  the  lymph  glands  of  the  intestine,  stomach,  liver,  and  spleen.^ 

In  its  course  through  the  thorax  the  thoracic  duct  receives  efferents  from  the 
intercostal,  mediastinal,  and  bronchial  glands.  At  the  thoracic  inlet  it  is  joined  by 
ducts  from  the  prepectoral  and  right  axillary  glands,  and  by  the  left  tracheal  duct. 
The  duct  is  provided  with  several  pairs  of  valves;  the  best  developed  are  at  its 
termination. 

THE  RIGHT  LYMPHATIC  DUCT 

This  vessel  (Ductus  lymphaticus  dexter) — when  present — collects  the  l>Tnph 
from  the  right  side  of  the  head,  neck,  and  thorax,  and  from  the  right  thoracic  limb. 
It  is  commonly  absent,  being  represented  by  a  number  of  short  ducts  which  termin- 
ate in  the  thoracic  duct,  the  right  jugulo-brachial  junction,  or  the  origin  of  the 
anterior  vena  cava.  When  present  in  its  typical  form,  it  results  from  the  con- 
fluence of  efferent  ducts  from  the  right  axillary  and  posterior  cervical  lymph  glands 
with  the  right  tracheal  duct.  It  lies  on  the  deep  face  of  the  scalenus  muscle,  above 
the  terminal  part  of  the  right  jugular  vein.  It  is  more  or  less  ampullate  and  usually 
opens  into  the  anterior  vena  cava  to  the  right  of  the  thoracic  duct.  It  may  be 
connected  with  the  latter  by  anastomoses  or  may  join  it. 

The  duct  is  very  variable  in  form  and  in  regard  to  its  afferents.  Often  it  is  a  very  short, 
irregular,  and  bulbous  trunk;  in  some  cases  it  is  about  an  inch  and  a  half  (ca.  3-4  cm.)  in  length 
and  receives  the  tracheal  duct  at  its  terminal  bend.  The  lymphatico-venous  connections  here 
have  not  yet  been  satisfactorily  worked  out  by  modern  methods. 


THE  LYMPH  GLANDS  AND  VESSELS  OF  THE  HEAD  AND  NECK 
1.  The  mandibular  or  submaxillary  lymph  glands  (Lgg.  mandibulares  s.  sub- 
maxillares)  (Figs.  265,  587)  are  arranged  in  two  elongated  groups  in  the  mandibular 
space  along  each  side  of  the  omo-hyoid  muscles.  The  two  groups  are  in  apposition 
in  front  of  the  insertion  of  these  muscles,  and  diverge  posteriorly  in  the  form  of  a  V, 
extending  backward  about  four  or  five  inches  (ca.  10-12  cm.).  They  are  covered 
by  the  skin  and  a  thin  layer  of  fascia  and  cutaneus  muscle,  and  are  therefore  pal- 
pable. Anteriorly  they  are  firmly  attached  to  the  mylo-hyoidei,  but  otherwise  they 
are  freely  movable  in  the  normal  state.  Each  group  is  related  laterally  to  the 
external  maxillary  artery  and  the  anterior  belly  of  the  digastricus,  ventrally  to  the 
external  maxillary  vein,  and  dorsally  to  the  lingual  and  sublingual  veins. 

They  receive  afferent  vessels  from  the  lips,  nostrils,  nasal  region,  cheeks,  the 

1  The  lymph  vessels  of  these  organs  appear  to  vary  considerably  in  their  mode  of  termina- 
tion, and  the  arrangement  needs  further  study.  Some  lymph  vessels  from  the  stomach,  liver,  and 
spleen  open  directly  into  the  cistern. 


THE  LYMPH  GLANDS  AND  VESSELS  OF  THE  HEAD  AND  NECK        699 

anterior  part  of  the  tongue,  the  jaws,  the  floor  of  the  mouth,  and  the  greater  part 
of  the  hard  palate  and  nasal  cavity.  The  efferent  vessels  pass  to  the  anterior 
cervical  and  pharyngeal  glands. 

Most  of  the  superficial  lymph  vessels  of  the  face  converge  to  twelve  to  fifteen  trunks  which 
turn  around  the  lower  border  of  the  jaw  with  and  m  front  of  the  facial  vessels.  Those  of  the  lips 
form  plexuses  at  the  commissures.  The  nasal  mucous  membrane  is  richly  supplied  with  lymph 
vessels  which  accompany  the  veins;  posteriorly  they  communicate  with  the  subdural  and  sub- 
araclmoid  spaces  and  send  efferents  to  the  pharyngeal  and  anterior  cervical  glands. 

2.  The  phar3nigeal  lymph  glands  (Figs.  562,  706)  usually  comprise  two 
groups.  One  lies  on  the  upper  part  of  the  lateral  surface  of  the  pharynx,  along  the 
course  of  the  external  carotid  artery.  These  glands  are  related  laterally  to  the 
occipito-mandibularis  and  cligastricus,  and  often  to  the  mandibular  gland  also, 
above  to  the  guttural  pouch;  they  may  properly  be  termed  the  parapharyngeal 
lymph  glands  (Lgg.  parapharyngeales) .  Other  small  glands  are  commonly  found 
on  the  guttural  pouch  along  the  course  of  the  internal  carotid  artery;  they  are  best 
designated  as  the  suprapharjnageal  lymph  glands  (Lgg.  suprapharyngeales).'^  They 
lie  below  the  artery  and  are  covered  by  the  aponeurosis  of  the  brachiocephalicus 
and  the  cervical  end  of  the  mandibular  gland.  In  some  cases  a  number  of  glands 
occur  in  the  angle  of  divergence  of  the  external  and  internal  carotid  arteries. 

They  receive  afferent  vessels  from  the  cranium,  the  posterior  part  of  the  tongue, 
the  soft  palate,  pharynx,  guttural  pouch,  larynx,  posterior  part  of  the  nasal  cavity, 
and  efferents  from  the  mandibular  glands. 

3.  The  anterior  cervical  lymph  glands  (Lgg.  cervicales  craniales)  (Fig.  646)  are 
situated  along  the  course  of  the  common  carotid  artery,  in  the  vicinity  of  the  thyroid 
gland,  under  cover  of  the  cervical  angle  of  the  parotid  gland.  Some  occur  between 
the  thyroid  and  the  mandibular  salivary  gland,  others  above  and  partly  upon  the 
thyroid.  They  are  related  deeply  to  the  posterior  part  of  the  larynx,  the  trachea, 
the  thyroid  gland,  and  the  oesophagus;  below  to  the  external  maxillary  vein  and 
the  lateral  border  of  the  omo-hyoideus.^ 

These  glands  are  variable.  Often  there  are  none  in  front  of  the  thyroid  and  the  group  may 
•extend  back  a  considerable  distance  along  the  course  of  the  carotid  artery. 

Their  afferents  are  deep  lymph  vessels  from  the  head,  the  pharynx,  larynx, 
guttural  pouch,  and  thyroid  gland,  and  efferents  from  the  mandibular  and  pharyn- 
geal glands.     Their-^fferent  vessels  go  to  the  middle  and  posterior  cervical  glands. 

4.  The  middle  cervical  lymph  glands  (Lgg.  cervicales  medise)  form  an  incon- 
stant group  situated  a  little  in  front  of  the  middle  of  the  neck  on  the  trachea  below 
the  caroticl  artery.  The  group  is  usually  small,  and  in  some  cases  is  replaced  by  a 
number  of  glands  occurring  at  intervals  along  the  course  of  the  carotid  artery.  In 
other  subjects  the  group  consists  of  several  glands  of  considerable  size.  They  are 
intercalated  in  the  course  of  the  tracheal  lymph  ducts. 

5.  The  posterior  cervical  or  prepectoral  lymph  glands  (Lgg.  cervicales  caudales) 
form  a  large  group  below  the  trachea  at  the  entrance  to  the  thorax  (Fig.  590). 
They  occupy  the  interstices  between  the  vessels  and  muscles  and  extend  forward  a 
variable  distance  on  the  ventral  aspect  of  the  trachea.  Posteriorly  they  are  con- 
tinuous with  the  anterior  mediastinal  glands.  They  are  covered  by  the  cutaneus 
and  sterno-cephalicus.  Their  afferent  vessels  come  from  the  head,  neck,  thorax, 
and  thoracic  limb.  They  receive  efferent  ducts  of  the  anterior  and  middle  cervical, 
prescapular,  and  axillary  glands.  Their  efferents  go  to  the  thoracic  duct  on  the 
left,  to  the  right  lymphatic  duct  on  the  right,  or  open  directly  into  the  vena  cava. 

6.  The  prescapular   or   superficial   cervical  lymph   glands    (Lgg.    cervicales 

1  Much  confusion  exists  in  the  terminology  used  in  regard  to  these  glands  and  the  next  group. 
'The  terms  here  recommended  appear  to  the  author  to  be  the  best,  all  things  considered.  The 
pharyngeal  and  anterior  cervical  glands  are  all  subparotid  in  the  horse. 

2  Abscess  here  can  be  reached  readily  by  an  incision  between  the  vein  and  the  omo-hyoideus. 


700  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

superficiales)  lie  on  the  anterior  border  of  the  anterior  deep  pectoral  muscle,  in 
relation  to  the  omo-hyoideus  medially  and  the  brachiocephalicus  laterally  (Figs. 
556,  566,  590).  They  are  on  the  course  of  the  ascending  branch  of  the  inferior 
cervical  artery,  and  may  form  an  elongated  series  which  is  continuous  ventrally 
with  the  posterior  cervical  group.  They  receive  afferents  from  the  neck,  breast, 
shoulder,  and  arm.     Their  efferents  pass  to  the  posterior  cervical  glands. 

The  tracheal  ducts,  right  and  left  (Ductus  trachealis  dexter,  sinister),  are  col- 
lecting trunks  for  the  lymph  of  the  head  and  neck.  They  lie  on  the  trachea  in 
relation  to  the  carotid  arteries.  The  right  one  goes  to  the  posterior  cervical  glands 
or  to  the  right  lymphatic  duct,  the  left  one  to  the  terminal  part  of  the  thoracic  duct. 


THE  LYMPH  GLANDS  AND  VESSELS  OF  THE  THORAX 

The  thoracic  lymph  glands  (Lgg.  thoracales)  are  in  general  of  small  size,  Imt 
are  numerous.     They  comprise  the  following: 

1.  The  intercostal  lymph  glands  (Lg.  intercostales)  are  small  and  are  situated 
at  the  sides  of  the  bodies  of  the  thoracic  vertebrae,  in  series  corresponding  to  the 
intercostal  spaces;  others  are  between  the  aorta  and  the  vertebrae.  They  receive 
afferents  from  the  vertebral  canal,  the  spinal  muscles,  the  diaphragm,  intercostal 
muscles,  and  pleura.     The  efferent  vessels  go  to  the  thoracic  duct.^ 

2.  The  anterior  mediastinal  lymph  glands  (Lgg.  mediastinales  craniales) 
are  numerous.  Some  are  situated  on  the  course  of  the  brachial  arteries  and 
their  branches;  on  the  right  side  they  are  related  deeply  to  the  trachea,  on  the  left 
to  the  oesophagus  also.  They  are  variable  in  size  and  disposition  and  are  continuous 
in  front  with  the  posterior  cervical  glands.  Other  glands  lie  along  the  ventral  face  of 
the  trachea  on  the  anterior  vena  cava  and  the  right  atrium  of  the  heart;  these  are 
continuous  behind  with  the  bronchial  glands.  A  few  glands  usually  occur  along  the 
dorsal  surface  of  the  trachea,  and  there  is  often  one  at  the  angle  of  divergence  of 
the  brachiocephalic  trunk.  The  afferent  vessels  come  chiefl}^  from  the  pleura, 
the  pericardium,  the  heart,  the  thymus  or  its  remains,  the  trachea,  the  oesophagus, 
and  the  bronchial  lymph  glands.  Their  efferent  vessels  pass  to  the  posterior 
cervical  glands  and  the  thoracic  duct. 

The  glands  along  the  ventral  face  of  the  trachea  are  frequently  enlarged  and  commonly  pig- 
mented in  dissecting-room  subjects.  The  left  recurrent  nerve  lies  above  them  on  the  ventral 
face  of  the  trachea. 

3.  The  bronchial  lymph  glands  (Lgg.  bronchiales)  are  grouped  around  the 
terminal  part  of  the  trachea  and  the  bronchi.  One  group  lies  on  the  dorsal  surface 
of  the  bifurcation  of  the  trachea,  and  is  continued  a  short  distance  backward  under 
the  oesophagus.  Others  lie  below  the  trachea  and  bronchi  and  also  occupy 
the  angle  between  the  aortic  arch  and  the  pulmonary  artery,  concealing  the 
left  recurrent  nerve  and  often  covering  the  vagus  in  this  part  of  its  course. 
Small  glands  occur  along  the  chief  bronchi  in  the  substance  of  the  lungs  (Lg.  pul- 
monales).  They  receive  the  deep  and  most  of  the  superficial  lymph  vessels  of  the 
lungs,  and  the  efferents  from  the  posterior  mediastinal  glands.  Their  efferent 
vessels  go  to  the  thoracic  duct  and  the  anterior  mediastinal  glands.  The  deep 
lymph  vessels  of  the  lung  arise  in  plexuses  which  surround  the  terminal  bronchi 
and  accompany  the  bronchi  to  the  root  of  the  lung.  The  superficial  vessels  form 
a  rich  network  under  the  pleura;  most  of  them  pass  to  the  bronchial  glands,  but 
some  go  to  the  posterior  mediastinal  glands. 

The  bronchial  glands  are  commonly  pigmented  (except  in  young  subjects)  and  are  often 
enlarged  and  indurated. 

4.  The  posterior  mediastinal  lymph  glands  (Lgg.  mediastinales  caudales)  are 
^  These  glands  appear  to  be  more  numerous  in  the  young  subject  than  they  are  later  in  life. 


THE    LYMPH    GLANDS    AND    VESSELS    OF   THE    ABDOMEN    AND    PELVIS  701 

usually  small  and  are  scattered  along  the  posterior  mediastinum  chiefly  above  the 
oesophagus.  They  receive  afferent  vessels  from  the  oesophagus,  mediastinum, 
diaphragm,  pleura,  and  liver.  The  efferents  go  to  the  bronchial  and  anterior  medi- 
astinal lymph  glands,  partly  to  the  thoracic  duct  directly. 

Sometimes  one  or  two  small  glands  are  situated  in  the  acute  angle  between  the 
posterior  vena  cava  and  the  diaphragm ;  and  the  occurrence  is  recorded  of  a  gland 
between  the  apex  of  the  pericardium  and  the  sternal  insertion  of  the  diaphragm. 

THE  LYMPH  GLANDS  AND  VESSELS  OF  THE  ABDOMEN  AND  PELVIS 
The  abdominal  and  pelvic  lymph  glands  (Lgg.  abdominales  et  pelvinse)  consist 
of  two  main  groups,  parietal  and  visceral.  The  parietal  glands  lie  in  the  subserous 
or  subcutaneous  tissue;  they  receive  the  lymph  vessels  from  the  abdominal  and 
pelvic  walls,  from  parts  of  the  viscera,  and  from  the  proximal  lymph  glands  of  the 
pelvic  limbs.  The  visceral  glands  lie  on  the  walls  of  the  viscera  or  in  the  peritoneal 
folds  which  connect  the  organs  with  the  wall  or  with  adjacent  viscera.  They  receive 
all  or  most  of  the  lymph  vessels  from  the  organs  with  which  they  are  connected. 
The  parietal  glands  comprise  the  following : 

1.  The  lumbar  lymph  glands  (Lgg.  lumbales)  lie  along  the  course  of  the  abdom- 
inal aorta  and  posterior  vena  cava  (Fig.  575).  Some  are  placed  along  the  ventral 
surface  and  sides  of  the  vessels,  others  above.  A  few  small  glands  may  be  found 
above  the  sublumbar  muscles.  The  small  nodes  which  are  situated  at  the  hilus 
of  the  kidneys  are  often  termed  the  renal  lymph  glands  (Lgg.  renales).  They  re- 
ceive afferent  vessels  from  the  lumbar  wall  of  the  abdomen  and  the  paired  viscera 
(kidneys,  adrenals,  genital  organs),  also  the  inguinal  vessels  and  the  efferents  of  the 
iliac  glands.  Their  efferents  go  to  the  thoracic  duct,  constituting  the  lumbar  trunks 
of  origin  of  that  vessel. 

2.  The  internal  iliac  lymph  glands  (Lgg.  iliacse  internee)  are  grouped  about  the 
terminal  part  of  the  aorta  and  the  origins  of  the  iliac  arteries  (Fig.  575).  Their 
afferent  vessels  come  chiefly  from  the  pelvis,  pelvic  viscera,  and  tail,  and  they  re- 
ceive efferent  vessels  of  the  external  iliac  and  deep  inguinal  glands. 

3.  The  external  iliac  lymph  glands  (Lgg.  iliacse  externae)  form  a  group  on  either 
side  on  the  iliac  fascia,  at  the  bifurcation  of  the  circumflex  iliac  artery  (Fig.  575). 
Their  afferent  vessels  come  from  the  flank  and  abdominal  floor,  the  lateral  surface 
of  the  thigh,  and  the  prefemoral  glands.  The  efferent  vessels  go  to  the  lumbar  and 
internal  iliac  glands. 

4.  The  sacral  lymph  glands  (Lgg.  sacrales)  are  small  nodes  situated  along  the 
borders  of  the  sacrum  and  on  its  pelvic  surface.  They  receive  afferents  from  the 
roof  of  the  pelvis  and  from  the  tail,  and  their  efferent  vessels  pass  to  the  internal 
ihac  glands. 

5.  The  superficial  inguinal  lymph  glands  (Lgg.  inguinales  superficiales)  lie  on 
the  abdominal  tunic  in  front  of  the  external  inguinal  ring  (Fig.  582).^  They  form 
an  elongated  group  along  the  course  of  the  subcutaneous  abdominal  artery,  on 
either  side  of  the  penis  in  the  male,  above  the  mammary  glands  in  the  female; 
in  the  latter  they  are  often  termed  mammary.  Their  afferents  come  from  the 
medial  surface  of  the  thigh,  the  abdominal  floor,  the  sheath,  penis,  and  scrotum  in 
the  male,  and  the  mammary  glands  in  the  female.  The  efferent  vessels  ascend 
through  the  inguinal  canal  and  go  to  the  deep  inguinal,  internal  iliac,  and  lumbar 
glands. 

6.  The  ischiatic  lymph  glands  (Lgg.  ischiadicae)  are  small  nodes  on  the  upper 
part  of  the  sacro-sciatic  ligament  along  the  course  of  the  posterior  gluteal  artery. 
They  receive  lymph  from  the  adjacent  parts  and  from  the  popliteal  glands,  and  send 
efferents  to  the  sacral  and  internal  iliac  glands. 

1  In  rare  cases  two  or  three  of  these  glands  are  found  behind  the  ring. 


702  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

The  visceral  glands  include  the  f oHowing : 

1.  The  gastric  lymph  glands  (Lgg.  gastricje)  are  situated  along  the  course  of 
the  gastric  arteries.  Several  occur  on  the  saccus  csecus  ventral  to  the  left  part  of 
the  pancreas,  and  along  the  attachment  of  the  gastro-phrenic  ligament.  A  group 
lies  at  the  lesser  curvature  a  short  distance  below  the  cardia.  There  is  another 
small  group  on  the  visceral  surface  where  the  posterior  gastric  artery  divides  into 
its  primary  branches.  There  are  usually  two  or  three  small  nodes  on  the  ventral 
aspect  of  the  pylorus.  Other  small  glands  are  scattered  along  the  course  of  the 
gastro-epiploic  and  short  gastric  arteries,  in  the  great  and  gastro-splenic  omenta. 
The  efferent  vessels  pass  largely  to  the  coeliac  radicle  of  the  cisterna  chyli,  but  along 
the  left  part  of  the  great  curvature  they  go  to  the  splenic  glands. 

2.  The  hepatic  lymph  glands  (Lgg.  hepaticae)  lie  along  the  portal  vein  and 
hepatic  artery  and  in  the  lesser  omentum.  Their  efferent  vessels  go  to  the 
coeliac  radicle  of  the  cisterna  chyli. 

Many  of  the  lymph  vessels  from  the  parietal  surface  of  the  liver  pass  in  the  falciform  and 
lateral  ligaments  to  the  diaphragm  and  join  the  lymphatics  of  the  latter.  Some  pass  through  the 
diaphi'agm  with  the  vena  cava  and  go  to  the  mediastmal  glands. 

The  pancreatic  lymph  vessels  follow  the  course  of  the  blood-vessels  which 
supply  the  gland;   most  of  them  go  to  the  splenic  and  hepatic  glands. 

3.  The  splenic  lymph  glands  (Lgg.  lienales)  lie  along  the  course  of  the  splenic 
blood-vessels  in  the  hilus  of  the  spleen  and  the  gastro-splenic  omentum.  Their 
afferent  vessels  come  from  the  subcapsular  network  of  the  spleen,  from  the  greater 
curvature  of  the  stomach,  and  from  the  left  part  of  the  pancreas.  The  efferents 
pass  to  the  glands  of  the  saccus  csecus  of  the  stomach  and  to  the  cceHac  radicle  of  the 
cisterna  chyli. 

4.  The  mesenteric  lymph  glands  (Lgg.  mesentericse)  are  situated  in  the  great 
mesentery  near  its  root.  They  are  numerous  and  hence  lie  close  together.  They 
receive  a  very  large  number  of  afferent  vessels  (400  to  500)  from  the  small  intestine. 
They  have  several  considerable  efferents,  which  concur  in  the  formation  of  the  in- 
testinal radicles  of  the  cisterna  chyli. 

The  lymph  vessels  of  the  intestine  form  three  sets  of  capillary  plexuses,  viz.,  in  the  subserosa, 
submucosa,  and  mucosa.  The  lymph  follicles,  solitary  and  aggregate,  lie  in  the  zone  of  the  plexus 
of  the  mucosa.     The  collecting  vessels  arise  from  the  subserous  plexus. 

5.  The  caecal  lymph  glands  (Lgg.  csecales)  are  numerous  and  are  distributed 
along  the  course  of  the  csecal  blood-vessels.  Their  efferents  enter  into  the  formation 
of  an  intestinal  radicle  of  the  cisterna  chyli. 

6.  The  colic  lymph  glands  (Lgg.  colicse)  comprise  those  of  the  great  colon  and 
those  of  the  small  colon.  The  glands  of  the  great  colon  are  extremely  numerous 
and  are  placed  close  together  along  the  colic  blood-vessels.  Their  efferent  vessels 
are  large  and  numerous.  They  converge  to  two  large  trunks  which  concur  with 
those  of  the  caecum  and  small  intestine  to  form  an  intestinal  radicle  of  the  cisterna 
chyli.  The  glands  of  the  small  colon  are  situated  in  part  on  the  wall  of  the  bowel 
along  the  attachment  of  the  mesentery,  in  part  between  the  layers  of  the  latter 
along  the  course  of  the  blood-vessels.  The  efferent  vessels  go  to  the  lumbar  glands 
and  to  the  posterior  intestinal  radicle  of  the  thoracic  duct. 

The  intestinal  radicles  of  the  cisterna  chyli  are  formed  by  the  confluence  of  efferents  from 
the  intestinal  lymph  glands.  The  anterior  trunk  lies  on  the  left  side  of  the  anterior  mesenteric 
artery,  passes  between  that  vessel  and  the  ca?liac  artery,  turns  sharply  backward  across  the  right 
renal  vessels,  and  opens  into  the  cisterna.  It  is  formed  by  the  miion  of  the  coeliac  trunk  with 
efferents  from  the  glands  of  the  small  intestine,  ciECum,  and  colon.  It  is  about  four  inches  (ca. 
10  cm.)  in  length  and  is  ampullate.  The  posterior  trunk  receives  vessels  from  the  small  intestine 
and  small  colon.  It  usually  opens  into  a  trunk  formed  by  the  union  of  the  right  and  left  lum]:)ar 
ducts.  It  is  usually  ampullate  at  its  termination  (Franck).  The  arrangement  of  these  collecting 
trunks  is,  however,  very  variable. 

The  rectal  lymph  glands  (Lgg.  rectales)  form  a  chain  along  the  dorsal  surface 


THE    LYMPH    GLANDS   AND    VESSELS    OF   THE    PELVIC    LIMB  703 

of  the  bowel.     They  receive  afferent  vessels  from  the  rectum  and  anus,  and  their 
efferent  vessels  pass  chiefly  to  the  internal  iliac  glands. 

7.  The  anal  lymph  glands  (Lg.  anales)  form  a  small  group  of  three  or  four  on 
either  side  of  the  sphincter  ani  externus  (Figs.  578) .  They  receive  afferents  from  the 
anus,  perineum,  and  tail.     Their  efferents  go  to  the  internal  iliac  glands. 


THE  LYMPH  GLANDS  AND  VESSELS  OF  THE  THORACIC  LIMB 

1.  The  axillary  lymph  glands  (Lgg.  axillares)  (Fig.  590),  some  ten  to  twelve  in 
number,  are  grouped  on  the  medial  face  of  the  distal  part  of  the  teres  major  and  the 
tendon  of  the  latissimus  dorsi  at  the  angle  of  junction  of  the  external  thoracic  and 
subscapular  veins  with  the  brachial  (Fig.  566) .  Their  afferents  include  most  of  the 
lymph  vessels  of  the  limb,  which  come  directly  or  as  efferents  from  the  cubital  glands. 
They  receive  also  lymph  vessels  from  the  thoracic  wall.  The  efferents  accompany 
the  brachial  blood-vessels  and  end  in  the  posterior  cervical  glands  and  the  thoracic 
and  right  h^mphatic  ducts. 

2.  The  cubital  lymph  glands  (Lg.  cubitales),  usually  eight  to  ten  in  number, 
form  a  discoid  oval  group  at  the  medial  side  of  the  distal  part  of  the  shaft  of  the 
humerus  (Figs.  566,  590).  They  lie  behind  the  biceps  muscle  on  the  brachial 
vessels  and  median  nerve,  and  are  covered  by  the  deep  fascia  and  the  posterior 
superficial  pectoral  muscle.  They  receive  as  afferents  most  of  the  vessels  from  the 
limb  below  this  point.  Their  efferents  pass  chiefly  to  the  axillary  glands,  but  in 
part  to  the  prescapular  glands  also. 

In  quite  exceptional  cases  a  lymph  gland  may  be  found  on  the  brachial  vessels  about  the  mid- 
dle of  the  arm. 

A  number  of  superficial  lymph  vessels  ascend  with  or  near  the  subcutaneous 
veins  (cephalic  and  accessory  cephalic),  and  join  the  prescapular  and  prepectoral 
glands.  Superficial  vessels  from  the  chest-wall  and  shoulder  run  across  the  latter 
to  the  prescapular  glands.  The  superficial  lymphatics  of  the  pectoral  region  form 
a  plexus  which  drains  into  the  posterior  cervical  and  prescapular  glands  by  a  number 
of  vessels  which  accompany  the  cephalic  vein.  The  deep  lymph  vessels  of  the  pec- 
toral region  run  with  the  external  thoracic  vein  to  the  axillary  glands. 

In  one  subject  the  author  observed  several  small  glands  along  the  posterior 
branch  of  the  dorsal  artery,  under  cover  of  the  rhomboideus. 


THE  LYMPH  GLANDS  AND  VESSELS  OF  THE  PELVIC  LIMB 

1.  The  prefemoral  or  subiliac  lymph  glands  (Lgg.  prefemorales  s.  subiliacse)  are 
situated  in  the  fold  of  the  groin  on  the  anterior  border  of  the  tensor  fasciae  latse, 
about  midway  between  the  point  of  the  hip  and  the  patella  (Figs.  575,  576,  582). 
They  lie  on  the  course  of  the  posterior  branch  of  the  circumflex  iliac  artery,  and 
number  usually  about  a  dozen.  They  receive  superficial  lymph  vessels  from  the 
hip,  thigh,  and  flank.  Their  efi'erent  vessels  ascend  with  the  posterior  circumflex 
iliac  vein,  enter  the  abdomen  near  the  tuber  coxse,  and  join  the  external  iliac  lymph 
glands. 

2.  The  deep  inguinal  lymph  glands  (Lg.  inguinales  profundse)  form  a  large 
group  situated  in  the  proximal  part  of  the  femoral  canal,  between  the  pectineus  and 
sartorius  muscles  (Figs.  576,  582).  The  group  is  elongated  and  is  commonly  four 
or  five  inches  (ca.  10-12  cm.)  in  length.  They  cover  the  femoral  vessels  and  are 
related  superficially  to  the  inguinal  ligament.  They  receive  nearly  all  of  the  lymph 
vessels  of  the  limb  below  them.  Their  efferent  vessels  ascend  to  the  internal  iliac 
glands. 

3.  The  popliteal  lymph  glands  (Lg.  popliteae),  usually  four  to  six  in  number, 


704  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

lie  behind  the  origin  of  the  gastrocnemius  and  between  the  biceps  femoris  and  semi- 
tendinosus  at  the  division  of  the  posterior  femoral  artery  into  its  primary  branches 
(Fig.  580).  They  receive  the  deep  lymph  vessels  of  the  distal  part  of  the  limb. 
Their  efferent  vessels  chiefly  follow  the  course  of  the  femoral  vessels  to  the  deep 
inguinal  glands,  but  one  or  two  ascend  in  company  with  a  vein  along  the  great 
sciatic  nerve  and  may  enter  an  ischiatic  gland  or  accompany  the  internal  pudic 
vein  and  join  the  internal  iliac  glands. 

Several  superficial  lymph  vessels  ascend  with  or  near  the  medial  metatarsal  and  saphenous 
veins,  enter  the  femoral  canal,  and  end  in  the  deep  inguinal  glands. 


The  Fcetal  Circulation 

The  blood  of  the  foetus  is  oxygenated,  receives  nutrient  matter,  and  gives  off 
waste  matter  by  close  contiguity  with  the  maternal  blood  in  the  placenta.  The 
chief  differences  in  the  blood-vascular  system  as  compared  with  that  which  obtains 
after  birth  are  correlated  with  this  interchange. 

The  umbilical  arteries,  right  and  left,  are  large  vessels  which  arise  from  the 
internal  iliac  arteries  and  pass  downward  and  forward  in  the  umbilical  folds  of  peri- 
toneum on  either  side  of  the  bladder  to  the  umbilicus.  Here  they  are  incorporated 
w^ith  the  umbilical  vein  and  the  urachus  in  the  umbilical  cord,  ramify  in  the  allan- 
tois,  and  end  as  the  capillaries  of  the  fa?tal  placenta.  They  conduct  the  impure 
blood  to  the  placenta.  After  birth  these  vessels  retract  with  the  bladder  to  the 
pelvic  cavity;  their  lumen  becomes  greatly  reduced  and  the  wall  thickened  so 
that  they  are  cord-like  and  are  usually  termed  the  round  ligaments  of  the  bladder. 

The  umbilical  vein  receives  the  oxygenated  blood  from  the  placenta.  Its 
radicles  converge  to  form  in  the  horse  a  single  large  trunk  which  separates  from  the 
other  constituents  of  the  umbilical  cord  on  entering  the  abdomen  and  passes  for- 
ward along  the  abdominal  floor  in  the  free  border  of  the  falciform  ligament  of  the 
liver.  It  enters  the  latter  at  the  umbilical  fissure  and  joins  the  portal  vein,  so 
that  the  blood  conveyed  by  it  passes  through  the  capillaries  of  the  liver  before 
entering  the  posterior  vena  cava.     The  vein  contains  no  valves. 

In  the  ox  and  dog  some  of  the  blood  in  the  umbilical  vein  is  conveyed  directly 
to  the  vena  cava  by  the  ductus  venosus.  This  vessel  is  given  off  within  the  liver 
from  a  venous  sinus  formed  by  the  confluence  of  the  portal  and  umbilical  veins 
and  passes  directly  to  the  posterior  vena  cava. 

The  foramen  ovale  is  an  opening  in  the  septum  between  the  atria  of  the  heart, 
by  which  the  latter  communicate  with  each  other.  It  is  guarded  by  a  valve  (Val- 
vula  foraminis  ovalis)  which  prevents  the  blood  from  passing  from  the  left  atrium 
to  the  right.  After  birth  the  foramen  soon  closes,  but  this  part  of  the  septum 
remains  membranous,  and  there  is  a  deep  fossa  ovalis  in  the  right  atrium  which 
indicates  the  position  of  the  former  opening.  In  some  cases  the  foramen  persists 
to  a  variable  extent  in  the  adult  without  apparent  disturbance  of  the  circulation. 

The  pulmonary  circulation  is  very  limited  in  the  foetus,  and  most  of  the  blood 
which  enters  the  pulmonary  artery  passes  through  the  ductus  arteriosus  to  the 
aorta.  This  vessel  is  larger  than  the  divisions  of  the  pulmonary  artery  which  go  to 
the  lungs,  and  joins  the  left  side  of  the  aortic  arch.  After  birth  the  pulmonary 
circulation  undergoes  promptly  an  enormous  increase  and  the  ductus  is  rapidly 
transformed  into  a  fibrous  cord — the  ligamentum  arteriosum. 

The  only  arterial  blood  in  the  foetus  is  that  carried  by  the  umbilical  vein. 
This  blood  is  mixed  in  the  liver  with  the  venous  blood  of  the  portal  vein,  and  after 
passing  through  the  capillaries  of  the  liver  is  carried  by  the  hepatic  veins  to  the 
posterior  vena  cava.  The  latter  receives  also  the  venous  blood  from  the  posterior 
part  of  the  trunk  and  the  pelvic  limbs.     It  is  generally  believed  that  the  blood  car- 


THE    BLOOD-VASCULAR   SYSTEM    OF   THE    OX  705 

ried  into  the  right  atrium  by  the  posterior  vena  cava  passes  largely,  if  not  entirely, 
through  the  foramen  ovale  into  the  left  atrium,  while  the  blood  flowing  into  it 
through  the  anterior  vena  cava  passes  into  the  right  ventricle.  On  this  basis  the 
blood  received  by  the  left  atrium  consists  chiefly  of  mixed  blood  from  the  posterior 
vena  cava,  since  the  small  amount  of  blood  conveyed  by  the  pulmonary  veins  is 
venous.  This  mixed  blood  passes  into  the  left  ventricle  and  is  forced  into  the 
systemic  arteries.  The  venous  blood  from  the  anterior  part  of  the  body  and  the 
thoracic  limbs  is  conveyed  by  the  anterior  vena  cava  to  the  right  atrium,  passes 
into  the  right  ventricle,  and  is  forced  into  the  pulmonary  artery,  A  small  amount 
is  carried  to  the  lungs,  but  the  bulk  of  it  passes  by  the  ductus  arteriosus  into  the 
aorta  behind  the  point  of  origin  of  the  brachiocephalic  trunk,  and  is  carried  to  the 
posterior  part  of  the  body,  a  large  part  passing  by  the  umbilical  arteries  to  the 
placenta. 


THE  BLOOD-VASCULAR  SYSTEM  OF  THE  OX 
The  Pericardium  and  Heart 

The  pericardium  is  attached  to  the  sternum  opposite  the  facets  for  the  sixth 
costal  cartilages  by  two  fibrous  bands,  the  sterno-pericardiac  ligaments  (Ligg. 
sternopericardiaca) ;  these  ligaments,  right  and  left,  are  embedded  in  the  mass  of  fat 
which  separates  the  apex  of  the  pericardium  from  the  floor  of  the  thorax.  On  the 
left  side  the  greater  part  of  the  pericardium  is  in  contact  with  the  chest  wall  as  far 
back  as  the  fourth  intercostal  space.  On  the  right  side  the  pericardium  is  com- 
monly covered  by  the  lung,  and  has  therefore  no  contact  with  the  lateral  chest  wall. 
But  in  some  cases  there  is  a  small  cardiac  notch  on  the  right  lung  opposite  to  the 
ventral  part  of  the  third  rib  and  intercostal  space. 

The  heart  of  the  adult  ox  has  an  average  weight  of  about  five  and  a  half  pounds 
(ca.  2.5  kg.),  or  about  0.4  to  0.5  per  cent,  of  the  body-weight.  Its  length  from  base 
to  apex  is  relatively  longer  than  that  of  the  horse,  and  the  base  is  smaller  in  both 
its  cliameters.  The  ventricular  part  is  more  regularly  conical  and  more  pointed. 
A  shallow  intermediate  groove  (Sulcus  intermedins)  extends  from  the  coronary 
groove  down  the  left  side  of  the  posterior  border,  but  does  not  reach  the  apex.  The 
amount  of  fat  in  and  near  the  grooves  is  much  greater  than  in  the  horse.  Even 
more  of  the  heart  is  situated  to  the  left  of  the  median  plane  than  in  the  horse.  The 
base  is  opposite  the  chest  wall  from  the  third  rib  to  the  fifth  intercostal  space,  both 
inclusive.  The  apex  is  opposite  to  the  fifth  interchondral  space;  it  is  just  to  the 
left  of  the  median  plane,  and  is  about  an  inch  (ca.  2.5  cm.)  from  the  diaphragm. 
The  long  axis  is  much  less  oblique  than  in  the  horse.  The  posterior  border  is 
opposite  to  the  fifth  intercostal  space;  it  is  practically  vertical  and  is  slightly  con- 
cave. 

The  pulmonary  orifice  is  opposite  to  the  third  rib  in  part  and  the  third  intercostal  space, 
about  a  handbreadth  (ca.  10-12  cm.)  above  the  sternal  ends  of  the  ribs.  The  aortic  orifice  is 
chiefly  opposite  to  the  fourth  rib.  The  right  atrio-ventricular  orifice  is  opposite  to  the  third  inter- 
costal space  and  fourth  rib  and  space.  The  left  atrio-ventricular  orifice  is  chiefly  opposite  to  the 
fourth  mtercostal  space  and  fifth  rib. 

The  left  longitudinal  groove  corresponds  to  the  fourth  rib.  The  right  groove  is  chiefly  pos- 
terior; it  begins  below  the  termination  of  the  posterior  vena  cava.  The  intermediate  groove 
begins  below  the  posterior  end  of  the  left  auricle,  and  in  its  descent  inclines  gradually  to  the  left 
side  of  the  apex. 

The  vena  hemiazygos  usually  unites  with  the  terminal  part  of  the  great  cardiac 
vein,  thus  forming  a  trunk  which  opens  into  the  right  atrium  below  the  posterior 
vena  cava. 

Two  bones,  the  ossa  cordis,  develop  in  the  aortic  fibrous  ring.  The  right  one 
45 


706 


THE    BLOOD-VASCULAR   SYSTEM    OF   THE    OX 


is  in  apposition  with  the  atrio-ventricular  rings,  and  is  irregularly  triangular  in 
form.  Its  left  face  is  concave  and  gives  attachment  to  the  right  posterior  cusp  of 
the  aortic  valve.  The  right  surface  is  convex  from  before  backward.  The  base 
is  dorsal.  The  posterior  border  bears  two  projections  separated  by  a  notch.  It 
is  usualh"  a  little  more  than  an  inch  (ca.  4  cm.)  in  length.  The  left  bone  is  smaller 
and  is  inconstant.  Its  concave  right  border  gives  attachment  to  the  left  posterior 
cusp  of  the  aortic  valve.     There  is  a  large  muscular  moderator  band  in  the  right 

Aurta 

L iga m e nt um  arteriosum 

Left  branch  of  -pulmonary  artery 
Pulmonary  veins 
I  \\  Posterior  vena  cava 


Anterior  vena 
cava 


Brachiocephalit 
trunk 


Right  auricle 
Pulmonary  artery 


Right  ventricle 
Left  coronary  artery 


Vena  hemiazygos 
I^ft  auricle 


Posterior  branch  of  left 
coronary  artery  in 
intermediate  groove 
Left  ventricle 


Fig.  592. — Heart  op  Ox;  Left  View. 
The  ventricles  are  contracted. 

ventricle,  which  extends  from  the  base  of  the  anterior  septal  papillary  muscle  to  the 
lateral  wall  at  the  base  of  the  papillary  muscle  there.  In  the  left  ventricle  there 
are  several  branched  moderator  bands. 


The  Arteries! 

The  great  arterial  trunks  in  the  thorax  resemble  those  of  the  horse  in  general 
disposition. 

1  Only  the  most  important  differential  features  of  the  arrangement  of  the  vessels  as  compared 
with  those  of  the  horse  will  be  considered. 


THE    COMMON    CAROTID   ARTERY  707 

The  left  coronary  artery  is  much  larger  than  the  right  one;  it  gives  off  a  branch 
which  descends  in  the  intermediate  groove,  and  terminates  by  running  downward 
in  the  right  longitudinal  groove.  The  right  coronary  artery,  after  emerging  from 
the  interval  between  the  right  auricle  and  the  pulmonary  artery,  divides  into 
branches  which  are  distributed  to  the  wall  of  the  right  ventricle. 

The  brachiocephalic  trunk  (anterior  aorta)  is  usually  four  or  five  inches  (ca. 
10-12  cm.)  in  length. 

The  brachial  arteries  give  off  in  the  thorax  the  following  branches : 

1.  A  common  trunk  for  the  dorsal,  deep  cervical,  and  vertebral  arteries. 

(1)  The  subcostal  artery  commonly  arises  separately  and  runs  forward  along 
the  sides  of  the  l^odies  of  the  vertebra.  It  supplies  the  second  to  the  fifth  inter- 
costal arteries. 

(2)  The  dorsal  artery  is  relatively  small.  It  usually  ascends  in  front  of  the 
first  costo-vertebral  joint,  and  is  distributed  as  in  the  horse.  It  gives  off  the  first 
intercostal  artery. 

(3)  The  deep  cervical  artery  may  arise  from  a  common  stem  (Truncus  vertebro- 
cervicalis)  with  the  vertebral,  or  may  constitute  a  branch  of  that  artery.  It  passes 
up  between  transverse  processes  of  the  first  thoracic  and  last  cervical  vertebra,  or  be- 
tween the  sixth  and  seventh  cervical,  and  is  distributed  as  in  the  horse. 

(4)  The  vertebral  artery  passes  along  the  neck  as  in  the  horse  to  the  inter- 
vertebral foramen  between  the  second  and  third  cervical  vertebrae,  gives  off  a 
muscular  branch,  and  enters  the  vertebral  canal  (Fig.  594).  It  runs  forward  on 
the  floor  of  the  canal — connected  with  its  fellow  by  two  or  three  transverse  anas- 
tomoses— and  divides  in  the  atlas  into  two  branches.  The  smaller  medial  division 
(cerebrospinal  artery)  passes  forward  to  the  floor  of  the  cranium  and  concurs  with 
the  condyloid  artery  and  branches  of  the  internal  maxillary  in  the  formation  of  a 
large  rete  mirabile.  The  large  lateral  branch  emerges  through  the  intervertebral 
foramen  of  the  atlas  and  ramifies  in  the  muscles  of  the  neck  in  that  region,  com- 
pensating for  the  smallness  of  the  branches  of  the  occipital  artery.  It  also  sends  a 
branch  to  the  rete  mirabile.  The  collateral  branches  detached  to  the  cervical  mus- 
cles are  large  and  compensate  for  the  small  size  of  the  deep  cervical  artery.  The 
spinal  branches  pass  through  the  intervertebral  foramina,  divide  into  anterior  and 
posterior  branches,  and  form  two  longitudinal  trunks  which  are  connected  by  cross- 
branches  so  as  to  form  irregular  polygonal  figures. 

2.  The  internal  thoracic  artery  presents  no  remarkable  features. 

3.  The  inferior  cervical  artery  corresponds  usually  to  the  ascending  branch  of 
that  vessel  in  the  horse. 

4.  The  external  thoracic  artery  is  large  and  usually  gives  off  a  branch  which  is 
•equivalent  to  the  descending  branch  of  the  inferior  cervical  artery  of  the  horse. 


THE  COMMON  CAROTID  ARTERY 

The  carotid  arteries  usually  arise  from  a  common  trunk  about  two  inches  (ca. 
5  cm.)  in  length,  but  in  exceptional  cases  are  given  off  separately  from  the  brachio- 
cephalic. Each  pursues  a  course  similar  to  that  of  the  horse,  and  is  accompanied 
by  the  small  internal  jugular  vein,  but  is  separated  from  the  external  jugular  vein 
by  the  omo-hyoid  and  sterno-mastoid  muscles.  It  divides  at  the  digastricus  into 
occipital,  external  maxillary,  and  external  carotid  arteries.  In  addition  to  tracheal, 
oesophageal,  and  muscular  branches,  it  gives  off  the  thyroid,  laryngeal  and  inferior 
parotid  arteries.  The  thyroid  artery  (A.  thyreoidea  cranialis)  bends  around  the 
anterior  end  of  the  thyroid  gland,  in  which  it  ramifies.  The  accessory  thyroid 
artery  is  usually  absent.     The  laryngeal  artery  may  arise  with  the  thyroid. 

1.  The  occipital  artery  is  relatively  small.     It  gives  off  the  following: 


708 


THE    BLOOD-VASCULAR   SYSTEM    OF   THE    OX 


(1)  The  pharyngeal  artery  (A.  palatina  ascendens)  goes  to  the  phars^nx  and 
soft  palate;  it  may  arise  from  the  external  carotid. 

(2)  Muscular  branches  go  chiefly  to  the  ventral  straight  muscles  of  the  head 
and  supply  twigs  to  the  atlanto-occipital  joint. 

(3)  The  condyloid  artery  passes  into  the  cranium  through  the  anterior  foramen 
in  the  condj^loid  fossa,  and  joins  the  vertebral  in  the  formation  of  the  rete  mirabile 
about  the  pituitary  gland.  Before  entering  the  cranium  it  gives  off  a  branch  to 
the  pharyngeal  lymph  glands  and  the  middle  meningeal  artery;   the  latter  passes 


Fig.  593. — Schema  of  Chief  Arteries  of  Head  of  Cow. 
7,  Common  carotid  artery;  ^,  thyro-laryngeal;  3,  thyroid;  4>  laryngeal;  5,  pharyngeal ;  6,  occipital;  7,  condyloid; 
8,  middle  meningeal;  9,  pharyngeal;  10,  external  maxillary;  11,  lingual;  12,  sublingual;  13,  superior  labial;  14,  in- 
ternal maxillary;  15,  masseteric;  16,  inferior  alveolar;  17,  buccinator;  IS,  great  palatine;  19,  sphenopalatine;  20, 
posterior  auricular;  21,  superficial  temporal;  22,  posterior  meningeal;  23,  anterior  auricular;  24,  artery  to  corium  of 
horn;  :35,  deep  temporal;  ^5,  arteries  to  rete  mirabile ;  ^7,  frontal;  ^<S,  malar;  .g<S',  dorsal  nasal  continuation  of  malar; 
29,  infraorbital;  29',  lateral  nasal  continuation  of  29. 


through  the  foramen  lacerum.  Another  branch  enters  the  temporal  canal  and  gives 
twigs  to  the  temporalis  muscle  and  the  mucous  membrane  of  the  frontal  sinus.  A 
muscular  branch  emerges  from  the  intervertebral  foramen  of  the  atlas.  A  diploic 
branch  goes  into  the  occipital  condyle  and  squama,  and  emits  twigs  to  the  occipital 
muscles. 

2.  The  external  maxillary  artery  is  smaller  than  that  of  the  horse,  but  pursues 
a  similar  course. ^  It  gives  off  several  branches  to  the  parotid  and  mandibular 
glands.     The  lingual  artery  is  large,  and  often  arises  separately  from  the  common 

^  In  the  sheep  the  artery  crosses  the  masseter  muscle  about  its  middle  and  is  continued  as 
the  superior  labial  artery. 


THE    COMMON    CAROTID    ARTERY 


709 


carotid;  it  gives  off  a  branch  to  the  mandibular  gland,  and  the  sublingual  artery. 
After  turning  around  the  j  aw  the  facial  gives  off  the  two  labial  arteries.  The  inferior 
labial  artery  is  small;  it  runs  forward  along  the  ventral  margin  of  the  depressor 
labii  inferioris.  The  superior  labial  is  large;  it  passes  forward  ventral  to  the 
depressor  labii  superioris,  and  usually  gives  off  a  muscular  branch  which  runs  for- 
ward almost  parallel  with  the  lateral  nasal.  The  angular  artery  is  very  small  or 
absent,  and  the  lateral  and  dorsal  nasal  arteries  spring  from  branches  of  the  in- 
ternal maxillary. 

3.  The  external  carotid  artery  passes  upward  between  the  stylo-hyoideus 
and  the  great  cornu  of  the  hyoid  bone,  turns  forward  across  the  lateral  face  of  the 
latter,  and  divides  into  superficial  temporal  and  internal  maxillary  arteries.  It 
gives  off  the  following  collateral  branches : 

(1)  The  pharyngeal  artery  may  be  a  branch  of  the  external  carotid,  but  often 
arises  from  the  occipital. 

(2)  The  posterior  auricular  artery,  which  resembles  that  of  the  horse,  sends  a 


Fig.  594. — ^Floor  of  Cranium  and  Anterior  Part  op  Vertebral  Canal  op  Ox. 
1,  Vertebral  artery;  2,  muscular  branches  of  /;  3,  branches  of  1  to  the  rete  mirabile;  4.  5,  branches  of  internal  max- 
illary artery  to  rete;  6,  branch  of  internal  maxillary  artery  entering  cranium  through  foramen  ovale;  7,  condyloid  ar- 
tery; 8,  emergent  artery  from  rete, distributed  like  internal  carotid  artery  of  horse;  9,  9',  longitudinal  vertebral  sinuses; 
a,  cribriform  plate;  6,  optic  formina;  c,  for.  orbito-rotundum;  d,  foramen  ovale;  e,  occipital  condyle;  /,  g,  h,  first, 
second,  and  third  cervical  vertebrse.     (After  Leisering's  Atlas.) 


stylo-mastoid  branch  into  the  tympanum.     It  may  arise  from  the  superficial 
temporal. 

(3)  The  superior  parotid  artery  arises  near  the  termination  of  the  external 
carotid  and  enters  the  upper  part  of  the  parotid  gland. 

(4)  The  masseteric  artery  resembles  that  of  the  horse,  but  is  smaller;  it  may 
arise  from  the  internal  maxillary  artery. 

The  superficial  temporal  artery  is  large  and  presents  the  following  special 
features:  (1)  The  transverse  facial  artery  passes  into  the  central  part  of  the  masse- 
ter.  (2)  It  gives  off  a  branch  which  corresponds  to  the  posterior  meningeal  artery 
of  the  horse,  enters  the  temporal  canal,  and  ramifies  in  the  dura  mater,  giving  off 
twigs  to  the  external  ear,  the  temporal  muscle,  and  the  frontal  sinus.  (3)  It 
usually  gives  off  the  anterior  auricular  artery.  (4)  A  large  branch  passes  around 
the  outer  side  of  the  base  of  the  horn-core,  supplies  the  corium  of  the  horn,  and 
anastomoses  across  the  back  of  the  frontal  eminence  with  the  artery  of  the  opposite 
side.  (5)  Other  branches  go  to  the  frontal  muscles  and  skin  and  to  the  orbital 
fat,  the  lacrimal  glands,  and  the  eyelids. 


710  THE    BLOOD-VASCULAR   SYSTEM    OF   THE    OX 

The  internal  maxillary  artery  is  entirely  extraosseous,  since  the  alar  canal  is 
absent.  It  passes  forward  along  the  side  of  the  pharynx  and  the  lateral  pterygoid 
muscle  and  forms  a  double  curve  at  the  infratemporal  fossa.  It  then  runs  forward 
to  the  pterygo-palatine  fossa  and  divides  into  two  terminal  trunks;  one  of  these 
divides  into  malar  and  infraorbital  arteries,  the  other  into  sphenopalatine  and 
greater  palatine.  It  gives  off  branches  to  the  pterygoid  muscles,  and  the  principal 
differential  features  in  its  branching  are  as  follows : 

(1)  The  buccinator  artery  arises  from  the  first  curve  of  the  internal  maxillary; 
it  is  relatively  large,  supplies  the  superior  buccal  glands,  and  divides  into  two 
branches.  One  of  these  enters  the  buccinator;  the  other,  which  is  much  larger, 
ramifies  in  the  deep  part  of  the  masseter. 

(2)  The  anterior  deep  temporal  artery  usually  arises  by  a  common  trunk  with 
the  middle  meningeal  artery.  The  latter  enters  the  cranial  cavity  through  the 
foramen  ovale  and  concurs  in  the  formation  of  the  rete  mirabile  cerebrale. 

(3)  The  ophthalmic  artery  forms  a  rete  mirabile  within  the  periorl)ita.^  Its 
frontal  branch  enters  the  supraorbital  canal  and  ramifies  chiefly  in  the  frontal  sinus. 

(4)  Several  branches  which  take  the  place  of  the  internal  carotid  artery  enter 
the  cranial  cavity  through  the  foramen  orbito-rotundum.  They  concur  with  the 
vertebral,  middle  meningeal,  and  condyloid  arteries  in  the  formation  of  an  ex- 
tensive rete  mirabile  cerebrale  on  the  cranial  floor  around  the  sella  turcica.  From 
each  side  of  the  rete  an  artery  arises  which  is  distributed  in  general  like  the  internal 
carotid  and  basilar  arteries  of  the  horse. ^ 

(5)  The  malar  artery  is  large;  it  arises  by  a  common  trunk  with  the  infra- 
orbital and  gives  off  the  dorsal  nasal  and  the  angular  artery  of  the  eye. 

(6)  The  infraorbital  artery  is  large  and  emerges  from  the  infraorbital  foramen 
to  form  the  lateral  nasal  artery. 

(7)  The  greater  palatine  artery  usually  arises  by  a  common  trunk  with  the 
sphenopalatine.  It  passes  through  the  palatine  canal  and  along  the  palatine  groove, 
enters  the  nasal  cavity  through  the  incisive  fissure,  and  does  not  go  to  the  upper  lip. 
It  forms  a  rete  mirabile  about  the  incisive  canal  and  terminates  in  the  mucous 
membrane  of  the  anterior  part  of  the  nasal  cavity. 


ARTERIES  OF  THE  THORACIC  LIMB 
The  brachial  artery  pursues  the  same  course  in  the  arm  as  that  of  the  horse. 
At  the  elbow  it  becomes  the  median.'^     The  chief  differential  features  in  its  branches 
are  as  follows: 

1.  The  subscapular  artery  is  almost  as  large  as  the  continuation  of  the  brachial. 
The  posterior  circumflex  artery  is  large ;  it  sends  branches  backward  and  downward 
into  the  triceps,  taking  the  place  in  part  of  the  deep  brachial  artery.  The  thoracico- 
dorsal  artery  supplies  branches  to  the  pectoral  muscles  and  the  triceps  as  well  as 
the  teres  major  and  latissimus  dorsi;   it  may  arise  directly  from  the  brachial. 

2.  The  smallness  of  the  deep  brachial  artery  is  compensated,  as  noted  al)ovc, 
by  the  large  size  of  the  posterior  circumflex. 

3.  The  proximal  collateral  ulnar  artery  is  often  double,  and  does  not  extend  to 
the  carpus.  Its  superficial  descending  branch  goes  to  the  superficial  pectoral 
muscle  and  the  skin,  and  its  ascending  branch  is  distributed  chiefly  to  the  medial 
head  of  the  triceps  and  the  anconeus. 

(4)  The  (distal)  collateral  radial  artery,  which  is  given  off  at  the  elbow  joint, 

1  This  may  be  distinguished  as  the  rete  mirabilf  orbitale. 

^  The  arteries  which  concur  in  the  formation  of  the  rete  may  be  termed  the  arteri»  retis 
mirabiUs  cerebrahs. 

^  The  homologies  of  the  vessels  of  the  lower  parts  of  the  limbs  are  still  uncertain.  The  ac- 
count given  here  is  mainly  based  on  the  views  of  Sussdorf  and  Baum. 


ARTERIES   OF   THE   THORACIC    LIMB 


711 


sends  branches  to  the  biceps,  brachiahs,  and  extensor  muscles;   it  also  supplies  the 
nutrient  artery  of  the  humerus.     It  does  not  descend  to  the  carpus. 

The  median  artery  descends  along  the  medial  part  of  the  posterior  surface  of 
the  radius  and  divides  near  the  middle  of  the  forearm  into  the  radial  and  ulnar 
arteries.  It  gives  off  at  the  proximal  third  of  the  forearm  the  common  interosseous 
artery,  a  large  vessel  which  anastomoses  with  the  deep  brachial,  passes  through  the 
proximal  interosseous  space,  and  descends  as  the  dorsal  interosseous  artery  in  the 
groove  between  the  radius  and  ulna,  and  concurs  in  the  formation  of  the  rete  carpi 


Fig.  595. — Arteries  of  Distal  P.^rt  of  Right  Fore 
Limb  of  Ox;  Dorsal  View. 
a.  Interosseous  artery;  b,  dorsal  branch  of  radial 
artery;  c,  rete  carpi  dorsale;  d,  dorsal  metacarpal  ar- 
tery; e,  dorsal  common  digital  artery;  /,  /,  dorsal  proper 
digital  arteries. 


Fig.  596. — Arteries  of  Distal  Part  of  Right  Poke 
Limb  of  Ox;  Volar  View. 
g.  Ulnar  artery;  h,  radial  artery;  i,  volar  branch 
of  common  interosseous  artery;  k,  I,  m,  deep  volar 
metacarpal  arteries;  A.v.,  volar  arches;  n,  volar  com- 
mon digital  artery;   o,  o',  p,  volar  proper  digital  arteries. 


dorsale.  At  the  distal  end  of  the  forearm  it  sends  a  branch  through  the  distal 
interosseous  space,  which  passes  downward,  assists  in  forming  the  rete  carpi  volare, 
and  is  continued  in  the  metacarpus  as  the  lateral  deep  volar  metacarpal  artery. 
This  is  a  small  vessel  which  passes  down  under  the  lateral  border  of  the  suspensory 
ligament  and  assists  in  forming  the  deep  volar  arch  near  the  fetlock.  The  recurrent 
interosseous  artery  arises  from  the  common  interosseous  and  ascends  to  the  lateral 
surface  of  the  elbow.  A  large  muscular  branch  arises  from  the  median  at  the 
proximal  end  of  the  forearm;  it  is  distributed  chiefly  to  the  flexor  muscles. 


712  THE    BLOOD-VASCULAR    SYSTEM    OF   THE    OX 

The  radial  artery  is  the  smaller  of  the  two  terminal  branches  of  the  median.  It 
descends  on  the  flexor  carpi  radialis,  passes  over  the  medio-volar  surface  of  the 
carpus,  and  is  continued  as  the  medial  deep  volar  metacarpal  artery.  At  the  distal 
end  of  the  forearm  and  at  the  carpus  it  furnishes  branches  to  the  retia  carpi.  An- 
other branch  (A.  met.  perforans  proximalis)  runs  outward  between  the  suspensory 
ligament  and  the  large  metacarpal  bone,  passes  through  the  proximal  foramen  of 
the  bone,  and  unites  with  the  dorsal  metacarpal  artery;  before  passing  through  the 
foramen  it  detaches  the  middle  deep  volar  metacarpal  artery  (A.  met.  volaris  prof. 
III.).  This  descends  on  the  volar  face  of  the  metacarpal  bone,  receives  an  anasto- 
motic branch  from  the  medial  deep  artery,  and  concurs  in  the  formation  of  the  deep 
volar  arch  above  the  fetlock.  The  medial  deep  volar  metacarpal  artery  (A.  met. 
volaris  prof.  II.)  descends  along  the  medial  part  of  the  volar  surface  of  the  large 
metacarpal  bone  and  is  continued  as  the  medial  volar  proper  digital  artery.  At  the 
distal  part  of  the  metacarpus  it  is  connected  by  a  transverse  branch  with  the  middle 
deep  volar  metacarpal  artery,  and  similarly  with  the  volar  common  digital,  forming 
with  the  latter  the  superficial  volar  arch. 

The  ulnar  artery,  the  larger  of  the  two  divisions  of  the  median,  descends  under 
cover  of  the  fiexor  carpi  radialis  without  giving  off  any  large  branches  in  the  fore- 
arm. It  passes  through  the  carpal  canal  and  continues  along  the  medial  side  of  the 
deep  flexor  tendon  as  the  volar  common  digital  artery  (A.  met.  volaris  superficialis 
III.).  At  the  distal  third  of  the  metacarpus  this  vessel  is  joined  by  a  branch  from 
the  medial  deep  volar  metacarpal  artery,  forming  the  superficial  volar  arch.  Near 
this  another  branch  of  the  common  digital  (or  of  the  medial  digital)  passes  around 
the  lateral  border  of  the  flexor  tendons  to  the  posterior  face  of  the  metacarpal  bone 
and  concurs  with  the  deep  volar  metacarpal  arteries  in  the  formation  of  the  deep 
volar  arch.  A  branch  from  the  arch  (A.  met.  perforans  distalis)  passes  forward 
through  the  distal  foramen  of  the  metacarpal  bone  and  joins  the  dorsal  metacarpal 
artery  which  descends  from  the  rete  carpi  dorsale  in  the  dorsal  metacarpal  groove. 

The  volar  common  digital  artery  (A.  metacarpea  volaris  superficialis  III.) 
passes  into  the  interdigital  space  and  divides  into  two  volar  proper  digital  arteries, 
which  descend  along  the  interdigital  surfaces  of  the  chief  digits  and  pass  through 
the  foramina  at  the  proximal  part  of  the  interdigital  surfaces  of  the  third  phalanges, 
enter  the  cavities  in  these  bones,  and  ramify  in  a  manner  similar  to  the  correspond- 
ing vessels  in  the  horse.  The  volar  common  digital  detaches  a  branch  (A.  inter- 
digitalis  perforans)  which  passes  forward  through  the  upper  part  of  the  interdigital 
space  and  anastomoses  with  the  dorsal  metacarpal  artery. 

The  volar  proper  digital  arteries  (or  the  common  digital)  give  off,  in  addition  to  other  col- 
laterals, branches  which  correspond  to  the  arteries  of  the  digital  cushion  of  the  horse.  These 
pass  to  the  bulbs  of  the  claws  and  anastomose  with  each  other  and  with  the  medial  and  lateral 
digital  arteries,  forming  an  arch  from  which  numerous  branches  are  distributed  to  the  corium 
of  the  hoofs. 

The  dorsal  metacarpal  artery  (A.  met.  dorsalis  III.)  is  a  small  vessel  which 
arises  from  the  rete  carpi  dorsale,  descends  in  the  groove  on  the  dorsal  face  of  the 
metacarpal  bone,  and  is  joined  by  the  distal  perforating  metacarpal  artery  from 
the  deep  volar  arch  to  constitute  the  dorsal  common  digital  artery.  This  vessel 
(A.  digitalis  communis  dorsalis  III.)  divides  into  two  dorsal  proper  digital  arteries. 

The  medial  volar  digital  artery  (A.  digiti  III.  medialis)  is  the  continuation  of  the 
medial  deep  volar  metacarpal  artery.  It  descends  on  the  medial  side  of  the  medial 
digit  and  terminates  at  the  bulb  of  the  claw  by  anastomosing  with  the  corresponding 
volar  proper  digital  artery.  It  gives  off  a  branch  to  the  rudimentary  digit  and 
forms  a  transverse  anastomosis  behind  the  first  phalanx  with  the  volar  common 
digital  or  its  medial  division. 

The  lateral  volar  digital  artery  (A.  digiti  IV.  lateralis)  arises  from  the  deep  volar 


BRANCHES  OF  THE  ABDOMINAL  AORTA  713 

arch,  passes  down  on  the  lateral  side  of  the  lateral  digit,  and  is  distributed  like  the 
medial  one. 

BRANCHES  OF  THE  THORACIC  AORTA 
The  bronchial  and  oesophageal  arteries  often  arise  separately. 
There  are  thirteen  pairs  of  intercostal  arteries.     The  first  comes  from  the 

dorsal,  the  next  four  from  the  subcostal,  and  the  remainder  from  the  aorta  directly. 
The  two  phrenic  arteries  are  very  variable  in  origin.     They  may  come  from 

the  aorta,  the  coeliac,  left  ruminal,  or  an  intercostal  or  lumbar  artery. 


BRANCHES  OF  THE  ABDOMINAL  AORTA 
The  coeliac  artery  is  about  four  to  five  inches  (ca.  10-12  cm.)  in  length.     It 
passes  ventrally  and  curves  forward  between  the  rumen  and  pancreas  on  the  left 
and  the  right  crus  of  the  diaphragm  and  the  posterior  vena  cava  on  the  right.     It 
gives  off  five  chief  branches. 

1.  The  hepatic  artery  arises  from  the  convex  side  of  the  curve  of  the  coeliac 
artery  as  it  crosses  the  posterior  vena  cava.  It  passes  downward,  forward,  and  to 
the  right  above  the  portal  vein  to  the  portal  fissure,  and  gives  off  the  following 
branches : 

(1)  Pancreatic  branches. 

(2)  Dorsal  and  ventral  branches  go  to  the  corresponding  lobes  of  the  liver. 
The  ventral  branch  is  the  larger;  it  gives  off  the  right  gastric  artery,  which  runs  in 
the  lesser  omentum  to  supply  the  origin  of  the  duodenum  and  the  pylorus,  anas- 
tomosing with  the  dorsal  branch  of  the  omaso-abomasal  artery. 

(3)  The  cystic  artery  supplies  the  gall-bladder. 

(4)  The  gastro-duodenal  artery  divides  into  right  gastro-epiploic  and  pan- 
creatico-duodenal  branches.  The  right  gastro-epiploic  artery  anastomoses  with 
the  left  gastro-epiploic.  The  pancreatico-duodenal  artery  anastomoses  with  the 
first  intestinal  branch  of  the  anterior  mesenteric  artery. 

2.  The  right  ruminal  artery  (A.  ruminalis  dextra)  is  the  largest  branch,  and 
usually  arises  by  a  short  common  trunk  with  the  splenic.  It  runs  downward  and 
backward  on  the  right  face  of  the  dorsal  sac  of  the  rumen  to  the  posterior  transverse 
fissure,  in  which  it  turns  around  to  the  left  and  anastomoses  with  branches  of  the 
left  ruminal  artery.  It  gives  off  a  pancreatic  branch,  dorsal  and  ventral  coronary 
arteries,  branches  to  the  great  omentum,  and  ramifies  on  both  surfaces  of  the  rumen. 

3.  The  left  ruminal  artery  (A.  ruminalis  sinistra)  descends  on  the  anterior  part 
of  the  right  face  of  the  rumen,  enters  the  anterior  furrow,  in  which  it  runs  from 
right  to  left,  and  continues  backward  in  the  left  longitudinal  groove,  anastomosing 
with  branches  of  the  right  artery.  It  supplies  chiefly  the  left  face  of  the  rumen, 
but  not  its  posterior  part.     It  usually  gives  off  near  its  origin  the  reticular  artery 

(A.  reticularis) ;  this  rather  small  vessel  passes  forward  on  the  dorsal  curvature  of 
the  rumen  and  turns  downward  in  the  rumino-reticular  groove,  in  the  bottom  of 
which  it  runs  around  ventrally  to  the  right  side.  It  gives  off  a  branch  which  passes 
to  the  left  of  the  cardia  and  along  the  lesser  curvature  of  the  reticulum  to  the  neck 
of  the  omasum.  The  reticular  branches  anastomose  with  the  omaso-abomasal  and 
left  ruminal  arteries. 

4.  The  omaso-abomasal  artery  (A.  gastrica  sinistra)  appears  as  the  continua- 
tion of  the  coeliac.  It  passes  forward  and  downward  to  the  greater  curvature  of 
the  omasum,  and  divides  after  a  course  of  four  or  five  inches  into  two  branches. 
The  dorsal  branch  curves  sharply  backward  on  the  dorsal  surface  of  the  omasum, 
continues  along  the  lesser  curvature  of  the  abomasum,  and  anastomoses  with  the 
hepatic  artery.     It  supplies  branches  to  the  omasum  and  to  the  lesser  curvature 


714 


THE    BLOOD-VASCULAR    SYSTEM    OF   THE    OX 


Fig.  597. — Gastric  Arteries  of  Ox;  Right  View  (Partly  Schematic). 
i,  Coeliac;   ^,  right  ruminal;   3,  splenic;   4 >  reticular;   5,  left  ruminal;   ff,  omaso-abomasal;    7,  dorsal  branch  of  6' 
S,  ventral  branch  oi  6  {=  left  gastro-epiploic) ;   A,  dorsal  sac  of  rumen;   B,  ventral  sac  of  rumen;   C,  C,  posterior  blind 
sacs;   D,  oesophagus;   i^,  reticulum;   F,  omasum;   G,  abomasum;   i/,  duodenum;  J,  right  longitudinal  furrow  of  rumen. 
By  an  oversight  the  reticular  artery  is  shown  as  arising  from  the  omaso-abomasal. 


Fig.  598. — Gastric  Arteries  of  Ox;  Left  View  (Partly  Schematic). 
1,  Left  ruminal  artery;  3,  continuation  of  right  ruminal  artery;   3,  reticular  artery,  which  disappears  into  i 
reticular  groove ;   A,  dorsal  sac  of  rumen;   B,  ventral  sac  of  rumen;   C,  C,  posterior  blind  sacs;  D,  cEsophagus;  £,  reticu- 
lum; F,  rumino-reticular  groove;   (1,  left  longitudinal  furrow  of  rumen. 


BRANCHES  OF  THE  ABDOMINAL  AORTA 


715 


and  pyloric  part  of  the  abomasum.  The  ventral  branch  (A.  gastro-epiploica 
sinistra)  runs  forward  and  downward  over  the  anterior  extremity  of  the  omasum, 
passes  backward  in  the  great  omentum  close  to  the  ventral  curvature  of  the  aboma- 
sum, and  anastomoses  with  the  right  gastro-epiploic.  A  considerable  branch  from  it 
curves  around  in  front  of  the  neck  of  the  omasum  to  communicate  with  the  reticular 
artery.  Another  branch  runs  back  across  the  left  side  of  the  omaso-abomasal 
junction,  and  a  third  goes  to  the  lesser  curvature  of  the  omasum. 

5.  The  splenic  artery  usually  arises  by  a  common  trunk  with  the  right  ruminal 


•Small 


Fig.  599. — Plan  of  Branches  of  Anterior  Mesenteric  Artery  op  Ox. 
/,  Anterior  mesenteric  artery;   2,  middle  colic  artery;   3,  ileo-cseco-colic  artery;   4,  ramus  collateralis;  6,  continua- 
tion of  anterior  mesenteric  artery,  giving  off  branches  to  small  intestine;   6,  caecal  artery;    7,  colic  branch  of  posterior 
mesenteric  artery;    A,  termination  of  duodenum. 


artery.  It  passes  forward  antl  to  the  left  across  the  dorsal  curvature  of  the  rumen 
and  enters  the  hilus  of  the  spleen. 

The  anterior  mesenteric  artery  arises  from  the  aorta  just  behind  the  cceliac, 
and  has  about  the  same  caliber  as  the  latter.  It  descends,  inclining  a  little  to 
the  right,  and  crosses  the  colon  as  the  latter  emerges  from  the  spiral  to  run  backward. 
After  detaching  twigs  to  the  pancreas  it  gives  off  in  succession  the  following  branches: 

1.  The  middle  colic  artery  (A.  colica  media)  passes  to  the  colon  as  it  emerges 
from  the  spiral  arrangement.  This  artery  is  comparable  to  the  middle  colic  or 
artery  of  the  small  colon  of  the  horse;  it  runs  backward  along  the  terminal  part  of 
the  colon,  which  it  supplies. 


716 


THE    BLOOD-VASCULAR   SYSTEM    OF   THE    OX 


2.  The  ileo-caeco-colic  artery  ramifies  on  the  right  face  of  the  spiral  part  of  the 
colon.     It  gives  off  the  ileo-caecal  artery,  which  divides  into  ileal  and  csecal  arteries. 

3.  The  ramus  collateralis  runs  in  the  mesentery  in  a  curve  along  the  ventral 
border  of  the  coils  of  the  colon.      (This  vessel  is  absent  in  the  sheep.) 

4.  The  continuing  trunk  (Truncus  intestinalis)  of  the  anterior  mesenteric 
pursues  a  course  in  the  mesentery  corresponding  to  the  series  of  mesenteric  lymph 
glands  and  is  connected  with  the  ramus  collateralis. 

The  two  preceding  vessels  are  essentially  the  arteries  of  the  small  intestine, 
which  they  supply  with  the  exception  of  its  initial  and  terminal  parts.  The  ramus 
collateralis  gives  off  no  considerable  branches  in  its  course  along  the  ventral  border 
of  the  coils  of  the  colon,  but  on  curving  upward  along  the  latter  it  anastomoses  with 


Fig.  600. — Pelvic  Arteries  op  Cow. 
Part  of  the  right  wall  of  the  uterus  and  vagina  is  removed  and  the  cervix  uteri  is  shown  in  sagittal  section,  o. 
Aorta;  6,  utero-ovarian  artery;  h',  ovarian,  and  6",  uterine  branch  of  h;  c,  external  iliac  artery;  d,  right  internal  iliac 
artery;  e,  common  trunk  of  umbilical  artery  (e')  and  middle  uterine  artery  (/) ;  g,  ilio-lumbar  artery;  h,  anterior  gluteal 
arteries;  i,  middle  hsemorrhoidal  artery;  k,  posterior  uterine  artery;  I,  perineal  artery;  m,  posterior  gluteal  artery;  n, 
obturator  arteries;  o,  artery  of  clitoris;  p,  posterior  mesenteric  artery;  r,  anterior  hsemorrhoidal  artery;  s,  middle 
sacral  artery;  /,  ovary;  ^,  apparent  body  of  uterus,  really  apposed  horns;  2',  horn  of  uterus;  3,  vagina;  4,  neck  of  uterus; 
4',  external  orifice  of  uterus  (os  uteri);  5,  5',  broad  ligaments,  large  part  of  right  one  removed;  6,  urinary  bladder;  7t 
rectum;   8,  sacrum;   9,  symphysis  pelvis.     (After  Zieger.) 


the  continuing  trunk  of  the  anterior  mesenteric  artery  and  detaches  numerous 
branches  to  the  small  intestine  which  form  series  of  superposed  anastomotic  arches. 
It  supplies,  roughly  speaking,  about  one-third  of  the  small  intestine  and  terminates 
by  joining  the  ileal  artery.  The  continuing  trunk  gives  off  numerous  branches 
which  also  form  arches  and  supply  about  the  first  two-thirds  of  the  small  intestine, 
exclusive  of  the  small  part  supplied  by  branches  of  the  cceliac  artery.  Both  arteries 
give  branches  to  the  lymph  glands.^ 

The  posterior  mesenteric  artery  arises  from  the  aorta  near  its  termination.  It 
is  small  and  supplies  branches  to  the  terminal  part  of  the  colon  and  to  the  rectum 
(A.  colica  sinistra;   A.  haemorrhoidalis  cranialis). 

^  It  is  difficult  to  make  the  arrangement  of  these  vessels  clear  in  a  brief  textual  description, 
hut  a  reference  to  the  schematic  figure  will  explain  the  main  facts. 


ARTERIES    OF   THE    PELVIC    LIMB  717 

The  renal  arteries  arise  from  the  aorta  close  together.  The  right  one  passes 
outward  and  forward  across  the  dorsal  face  of  the  posterior  vena  cava  to  the  hilus 
of  the  kidney.  The  left  one  runs  backward,  but  necessarily  varies  in  direction  in 
conformity  with  the  position  of  the  kidney  (g.  v.). 

The  spermatic  arteries  resemble  those  of  the  horse. 

The  utero-ovarian  arteries  are  small. 

The  five  pairs  of  lumbar  arteries  derived  from  the  aorta  are  distributed  much 
as  in  the  horse.     The  sixth  usually  comes  from  the  internal  iliac  artery. 

The  middle  sacral  artery  is  a  vessel  about  5  mm.  in  diameter  which  continues 
the  aorta.  It  arises  from  the  dorsal  face  of  the  aorta  at  the  angle  of  divergence  of 
the  internal  iliacs,  runs  backward  on  the  pelvic  surface  of  the  sacrum  a  little  to  the 
left  of  the  median  line,  and  is  continued  as  the  middle  coccygeal  artery.  It  gives 
off  small  collateral  branches  to  the  spinal  cord  and  the  muscles  of  the  tail  and  the 
lateral  coccygeal  arteries.  The  latter  may  have  a  common  trunk  of  origin,  and 
each  divides  into  dorsal  and  ventral  branches.  The  middle  coccygeal  artery  runs 
through  the  ventral  (haemal)  arches  of  the  coccygeal  vertebrae.  The  coccygeal 
arteries  are  connected  at  pretty  regular  intervals  by  segmental  anastomoses. 

The  internal  iliac  arteries  are  much  longer  than  in  the  horse.  Each  passes 
backward  on  the  sacro-sciatic  ligament  and  divides  about  the  middle  of  the  pelvic 
wall  into  posterior  gluteal  and  internal  pudic  branches.  The  chief  differences  in 
its  distribution  are:  (1)  A  large  trunk  gives  origin  to  the  umbilical  and  middle 
uterine  arteries.  The  umbilical  artery  is  usually  largely  obliterated,  and  its  terminal 
branches  receive  their  blood  through  anastomoses  with  the  internal  pudic.  It 
gives  off  near  its  origin  two  small  vessels,  the  ureteral  artery  (A.  ureterica)  and  the 
deferential  artery  (A.  deferentialis),  which  accompany  the  ureter  and  the  ductus 
deferens  respectively.  The  middle  uterine  artery  (A.  uterina  media)  is  very  large. 
It  is  distributed  chiefly  to  the  cornu  of  the  uterus,  and  compensates  for  the  small 
size  of  the  utero-ovarian  artery.  (2)  The  ilio-lumbar  artery  is  relatively  small 
and  is  distributed  chiefly  to  the  sublumbar  muscles.  It  is  sometimes  replaced  by 
branches  of  the  circumflex  iliac  and  gluteal  arteries.  (3)  The  anterior  gluteal 
artery  is  commonly  represented  by  several  vessels.  (4)  The  obturator  artery  is 
represented  by  several  small  branches  which  supply  the  obturator  and  adductor 
muscles.  (5)  The  iliaco-femoral  and  lateral  sacral  arteries  are  absent.  The 
absence  of  the  latter  is  compensated  by  the  middle  sacral  and  gluteal  arteries.  (6) 
The  posterior  gluteal  artery  is  large.  It  emerges  through  the  lesser  sciatic  notch 
and  ramifies  in  the  biceps  femoris  and  adjacent  muscles.  (7)  The  internal  pudic 
artery  (A.  urethro-genitalis)  is  the  direct  continuation  of  the  internal  iliac.  It 
gives  off  branches  to  the  rectum,  bladder,  urethra,  and  genital  organs.  In  the 
male  it  supplies  the  accessory  genital  glands  and  divides  into  dorsal  and  deep  arteries 
of  the  penis ;  the  a.  dorsalis  penis  runs  along  the  dorsum  penis  to  the  glans  and  gives 
twigs  to  the  prepuce;  the  a.  profunda  penis  gives  ofi  a  perineal  branch  and  enters 
the  corpus  cavernosum  penis.  In  the  female  it  gives  off  the  large  posterior  uterine 
artery,  which  supplies  the  posterior  part  of  the  uterus  and  gives  branches  to  the 
vagina  and  bladder.  It  ends  as  the  a.  clitoridis,  which  supplies  the  clitoris  and 
adjacent  parts. 

ARTERIES  OF  THE  PELVIC  LIMB 

The  external  iliac  artery  has  the  same  course  as  in  the  horse.  The  circumflex 
iliac  artery  is  large.  A  branch  from  it  emerges  between  the  abdominal  and  lumbar 
muscles  near  the  tuber  coxae  and  ramifies  like  the  terminals  of  the  ilio-lumbar 
artery  of  the  horse. 

The  femoral  and  popliteal  arteries  pursue  a  similar  course  to  those  of  the  horse. 
The  chief  differences  in  their  branches  are  as  follows: 

1.  The  external  pudic  artery  is  distributed  chiefly  to  the  scrotum  in  the  male. 


718 


THE    BLOOD-VASCULAR    SYSTEM    OF   THE    OX 


In  the  cow  it  is  usually  termed  the  mammary  and  is  very  large,  especially  during 
lactation.  Each  divides  at  the  base  of  the  mammary  gland  into  two  branches 
which  are  distributed  to  the  anterior  and  posterior  parts  ("quarters")  of  the  gland. 
A  small  branch  accompanies  the  subcutaneous  abdominal  vein  to  the  xiphoid  region. 
2.  The  deep  femoral  artery  gives  off  an  obturator  branch  which  passes  up 
through  the  obturator  foramen  to  supply  the  obturator  internus  and  compensates 
otherwise  for  the  absence  of  the  obturator  artery. 


9' 


Fig.  601. — Arteries  of  Distal  Part  of  Right  Hind 
Limb  of  Ox;  Dorsal  View. 
a,  Anterior  tibial  artery;  b,  proximal  perforating 
metatarsal  artery;  c,  dorsal  metatarsal  artery;  d,  dorsal 
common  digital  artery;  e,  e',  dorsal  proper  digital  ar- 
teries. 


Fig.  602. — Arteries  of  Distal  Part  of  Right  Hind 
Limb  of  Ox;  Plantar  View. 
c,  Saphenous  artery;  /,  /',  internal  and  external 
plantar  arteries;  g,  g' ,  medial  and  lateral  superficial 
plantar  metatarsal  arteries;  h,  deep  plantar  metatarsal 
artery;  i,  j,  medial  and  lateral  plantar  digital  arteries, 
k,  plantar  common  digital  artery;  I,  /',  medial  and  lat- 
eral plantar  digital  arteries. 


3.  The  anterior  femoral  artery  is  large.  It  often  gives  off  the  external  cir- 
cumflex artery  of  the  thigh,  which  perforates  the  proximal  end  of  the  quadriceps, 
gives  branches  to  that  muscle,  the  iliacus,  glutei,  anfl  tensor  fascise  lata?. 

4.  The  saphenous  artery  is  large.  It  descends  in  front  of  the  homonymous 
vein  over  the  medial  surface  of  the  leg,  and  divides  near  the  hock  into  lateral 
and  medial  tarsal  arteries.  The  lateral  tarsal  artery  is  small  and  is  distributed 
on  the  outer  part  of  the  hock.     The  medial  tarsal  artery  is  the  direct  continuation 


THE   VEINS  719 

of  the  saphenous.  It  descends  along  the  medial  border  of  the  superficial  flexor 
tendon  and  divides  into  medial  and  lateral  plantar  arteries.  The  medial  plantar 
artery  descends  along  the  medial  side  of  the  deep  flexor  tendon  with  the  medial 
plantar  nerve.  It  anastomoses  at  the  proximal  end  of  the  metatarsus  with  the 
perforating  tarsal  artery,  assisting  in  the  formation  of  the  proximal  plantar 
arch,  and  continues  distally  as  the  a.  met.  plant,  superfic.  med.  along  the  medial 
border  of  the  deep  flexor  tendon.  Near  the  fetlock  it  concurs  with  the  perforating 
branch  of  the  dorsal  metatarsal  artery  and  with  a  branch  of  the  corresponding 
lateral  artery  in  the  formation  of  the  distal  plantar  arch.  Below  this  it  is  continued 
as  the  medial  digital  artery.  The  lateral  plantar  artery  is  small. ^  It  descends 
along  the  lateral  border  of  the  deep  flexor  tendon  with  the  lateral  plantar  nerve, 
concurs  with  the  perforating  tarsal  and  medial  plantar  arteries  in  the  formation 
of  the  proximal  plantar  arch,  and  gives  branches  to  the  rete  tarsi  dorsale.  Continu- 
ing downward  along  the  deep  flexor  tendon  as  the  a.  met.  plant,  superfic.  lat.,  it 
assists  in  forming  the  distal  plantar  arch  and  becomes  the  lateral  digital  artery. 

The  posterior  tibial  artery  is  relatively  small  and  is  distributed  chiefly  to  the 
muscles  on  the  posterior  surface  of  the  tibia.  Lower  down  it  is  replaced  by  the 
saphenous  artery,  as  described  above. 

The  anterior  tibial  artery  has  the  same  course  as  in  the  horse.  It  is  continued 
down  the  groove  on  the  front  of  the  metatarsal  bone  as  the  dorsal  metatarsal  artery. 
At  the  tarsus  branches  are  given  off  which  concur  with  the  lateral  tarsal  artery  in 
the  formation  of  the  rete  tarsi  dorsale.  The  perforating  tarsal  artery  passes  back 
through  the  vascular  canal  and  anastomoses  with  the  plantar  arteries,  thus  forming 
the  proximal  plantar  arch.  From  this  the  small  deep  plantar  metatarsal  artery 
descends  in  the  plantar  groove  of  the  large  metatarsal  bone  to  the  distal  plantar 
arch.  The  dorsal  metatarsal  artery  (A.  met.  dorsalis)  is  the  chief  artery  of  the 
region  and  is  accompanied  by  two  veins.  Near  the  distal  end  of  the  metatarsal 
bone  it  gives  off  the  perforating  metatarsal  artery,  which  passes  back  through  the 
distal  metatarsal  foramen  and  assists  in  forming  the  distal  plantar  arch. 

The  dorsal  common  digital  artery  is  the  direct  continuation  of  the  dorsal 
metatarsal.  It  divides  into  two  branches  which  unite  in  the  interdigital  space  with 
the  corresponding  branches  of  the  plantar  common  digital  to  form  the  proper 
digital  arteries. 

The  plantar  common  digital  artery  descends  from  the  distal  plantar  arch, 
anastomoses  in  the  interdigital  space  with  the  medial  and  lateral  digitals,  and 
divides  into  two  branches  which  join  those  of  the  dorsal  common  digital  artery  as 
before  mentioned. 

The  foregoing  is  a  brief  statement  of  the  more  common  arrangement  of  the 
vessels  in  the  distal  part  of  the  limb,  but  minor  variations  are  very  common. 


The  Veins  2 

The  vena  hemiazygos  takes  the  place  of  the  vena  azygos.  It  lies  along  the 
left  side  of  the  aorta  and  the  bodies  of  the  thoracic  vertebrse,  turns  down  across 
the  left  face  of  the  aorta  and  left  pulmonary  artery,  runs  back  over  the  left  auricle, 
and  usually  joins  the  great  cardiac  vein,  but  may  open  into  the  right  atrium.  It 
receives  the  dorsal  intercostal  veins. 

Two  jugular  veins  occur  on  either  side.  The  internal  jugular  vein  (V.  jugu- 
laris  interna)  is  a  relatively  small  vessel  which  accompanies  the  carotid  artery.     It 

^  This  vessel  may  arise  instead  from  the  rete  tarsi  dorsale. 

2  Most  of  the  differences  in  the  veins  of  the  ox  are  correlated  with  those  of  the  arteries  of 
which  they  are  satellites,  and  will  not  be  described.  The  account  here  given  consists  chiefly  of 
those  differential  features  which  could  not  be  deduced  from  a  knowledge  of  the  arteries. 


720  THE   BLOOD-VASCULAR   SYSTEM    OF  THE   OX 

arises  by  occipital,  laryngeal,  and  thyroid  radicles,  receives  tracheal,  oesophageal, 
and  muscular  branches,  and  joins  the  external  jugular  near  its  termination.  It  is 
sometimes  absent,  but  in  some  cases  it  appears,  on  the  other  hand,  to  be  large 
enough  to  interfere  with  venesection  practised  on  the  external  jugular.  The 
external  jugular  vein  (V.  jugularis  externa)  is  very  large  and  corresponds  to  the 
jugular  of  the  horse.  It  is  separated  from  the  carotid  artery  in  the  greater  part 
of  its  course  by  the  sterno-cephalicus  and  omo-hyoideus  muscles. 

The  ventral  cerebral  vein  usually  does  not  unite  with  the  occipital ;  the  latter 
is  continued  by  the  internal  jugular  vein. 

The  ventral  longitudinal  sinus  is  represented  by  a  vein.  There  is  an  anterior  intercavernous 
sinus.  The  transverse  sinus  is  connected  with  the  basilar  plexus  by  a  vein  which  traverses  the 
condyloid  canal.     In  the  sheep  there  are  two  ventral  occipital  sinuses  in  place  of  the  basilar  plexus. 

The  orbital  veins  form  a  network  between  the  periorbita  and  the  muscles  of 
the  eyeball.  This  plexus  communicates  with  the  cavernous  sinus  and  with  the 
dorsal  cerebral  vein.  It  is  also  drained  by  the  frontal  vein,  which  runs  in  the 
supraorbital  canal  and  groove  and  joins  the  angular  vein  of  the  eye. 

The  dorsal  nasal  vein  is  usually  double. 

The  superior  labial  vein  usuall}^  joins  the  infraorbital. 

The  vena  reflexa  is  absent,  and  the  radicles  which  are  received  by  it  in  the  horse 
go  to  the  internal  maxillary  vein. 

The  sublingual  vein  is  very  large. 

The  veins  of  the  thoracic  limb  differ  chiefly  in  the  distal  part;  the  special 
features  are  as  follows : 

The  dorsal  digital  veins  ascend  on  the  front  of  the  digits  and  are  connected 
with  the  other  digital  veins  by  transverse  branches.  They  unite  near  the  fetlock 
to  form  the  dorsal  metacarpal  vein.  This  runs  upward  on  the  dorsal  face  of  the 
metacarpus  and  carpus,  inclines  to  the  medial  surface  of  the  radius,  and  joins  the 
cephalic  or  the  accessory  cephalic  vein. 

The  volar  digital  veins  are  larger  than  the  dorsal  veins.  They  lie  on  the  inter- 
digital  surfaces  of  the  digits  and  unite  in  the  interdigital  space  to  form  a  trunk  which 
is  a  satellite  of  the  volar  common  digital  artery.  This  trunk,  the  volar  common, 
digital  vein,  which  is  often  double,  is  connected  distally  by  transverse  branches 
with  the  lateral  and  medial  digital  veins  to  form  the  superficial  volar  arch;  it  is 
continued  upward  as  the  satellite  of  the  ulnar  artery. 

The  medial  and  lateral  digital  veins  lie  in  front  of  the  corresponding  arteries. 
They  are  connected  with  the  volar  digital  vein  by  a  large  branch  which  passes 
between  the  flexor  tendons  and  the  first  phalanx.  At  the  distal  end  of  the  meta- 
carpus each  inclines  forward  and  anastomoses  with  the  volar  common  digital  vein 
to  form  the  volar  venous  arch.  The  medial  vein  is  continued  as  the  medial  volar 
metacarpal  vein  along  the  medial  border  of  the  suspensory  ligament,  and  becomes  a 
satellite  of  the  radial  artery  in  the  forearm,  while  the  lateral  one  is  continued  on  the 
volar  face  of  the  metacarpal  bone  by  the  lateral  volar  metacarpal  vein.  The  latter 
unites  at  the  proximal  part  of  the  metacarpus  with  the  middle  volar  metacarpal 
vein,  and  the  trunk  thus  formed  joins  the  medial  vein  to  form  the  deep  plantar  arch. 
They  unite  below  the  carpus  or  join  the  volar  common  digital  vein. 

The  digital  veins  arise  from  the  venous  plexuses  of  the  corium  of  the  hoof.  They  form  by 
anastomotic  branches  a  venous  circle  at  the  coronary  border  of  the  hoof,  which  may  be  termed  the 
coronary  circle.  A  vein  which  emerges  from  the  foramen  on  the  proximal  part  of  the  interdigital 
surface  of  the  third  phalanx  is  the  principal  radicle  of  the  dorsal  digital  vein. 

The  accessory  cephalic  vein  is  the  upward  continuation  of  the  dorsal  meta- 
carpal vein  and  is  much  larger  than  in  the  horse. 

The  posterior  vena  cava  is  partially  embedded  in  the  medial  border  of  the 
liver.     Its  abdominal  part  has  a  thicker  wall  than  in  the  horse.     Its  affluents 


THE   VEINS  721 

correspond  to  the  arteries  of  which  they  are  satelhtes.  The  renal  veins  are  large 
and  thick-walled;  the}^  run  obliquely  forward  and  join  the  vena  cava  at  an  acute 
angle.     The  left  one  is  much  the  longer. 

Two  middle  sacral  veins  usually  accompany  the  artery. 

The  veins  of  the  mammary  glands  deserve  special  notice.     They  converge  to 
a  venous  circle  at  the  base  of  the  udder,  which  is  drained  chiefly  by  two  pairs  of 
veins.     The  subcutaneous  abdominal  vein  (anterior  mammary  or  "milk"  vein) 
is  very  large  in  animals  of  the  dairy  breeds,  and  its  course  along  the  ventral  wall  of 
the  abdomen  is  easily  followed.     It  is  usually  flexuous.     It  emerges  at  the  anterior 
border  of  the  udder  abou^^jtwo  or  three  inches  (ca.  5-8^cm.)  from  the  lineaalba^ 
rmisTorward"Xdeviating"a  little"  outward),  dips  under  tKe  cutaneus^  passes^rough_ 
a  foramen  in  the^abdommai  wail  about  a  handbrjadth  IromThe  median  plane7^nd~ 
"Joins  the  mternal  thoracic_jyein73T^he  two  veinsare  coflnected  by  a  transverse_ 
^anSstOTnosis  at  the  anterior  border  of  the  base  oftFe  udder,  aiKTeach  anastomoses 


behind  with  a  branchoTthFexterhglp!^^  The^externaTpudic  vein  (middle 

"mammary  veirl)~is^so  of  considerable  size.  It  ascends  in  the  inguinal  canal  as^a 
satellite  of  the  artery  and  joins  the  external  iliac  veinT  'Ihe  right  and  left  veins" 
are  connected  at  the  posterior  border  of  the  base  of  the  udder  by  a  large  transverse 
branch.  From  the  latter^ arises  the  perineal  vein  (posterior  mammary  vein), 
which  runs  mediallv  upward  and  backward  to  the  jperineum,  turns  around  the_ 
ischialarch,  aiid  joins"Hie  internal  pudicjvein.  Two  veins  may  present  In  the 
male^ese  veins  are  relatively  small. 

The  deep  veins  of  the  thigh  and  leg  resemble  those  of  the  horse,  but  there  is 
no  recurrent  til)ial  vein. 

The  saphenous  vein  is  much  smaller  than  in  the  horse.  It  may  be  regarded 
chiefly  as  the  upward  continuation  of  the  medial  tarsal  vein,  which  arises  from  the 
deep  plantar  arch. 

The  recurrent  tarsal  vein^  is  large.  It  is  the  upward  continuation  of  the  dorsal 
metatarsal  vein  and  anastomoses  with  the  anterior  tibial  and  saphenous  veins.  It 
arises  on  the  lateral  face  of  the  hock,  ascends  at  first  in  front  of  the  tendo  Achillis, 
then  crosses  the  latter  laterally,  passes  up  between  the  biceps  femoris  and  semi- 
tendinosus,  and  joins  the  posterior  femoral  vein. 

There  are  three  chief  metatarsal  veins.  The  large  dorsal  metatarsal  vein 
arises  at  the  distal  part  of  the  metatarsus  by  the  union  of  the  dorsal  digital  vein 
and  a  large  branch  from  the  venous  arch  above  the  sesamoids.  It  ascends  super- 
ficially between  the  long  and  lateral  extensor  tendons  and  may  be  regarded  as  being 
continued  in  the  leg  by  the  recurrent  tarsal  vein;  it  also  furnishes  a  large  chief 
radicle  of  the  anterior  tibial  vein.  The  medial  plantar  metatarsal  vein  arises  from 
the  venous  arch  above  the  fetlock,  ascends  between  the  medial  border  of  the  sus- 
pensory ligament  and  the  plantar  surface  of  the  metatarsal  bone;  it  is  connected 
with  the  corresponding  lateral  vein  at  the  proximal  end  of  the  metatarsus  by  a 
transverse  anastomosis,  thus  forming  the  deep  plantar  arch.  From  this  the  per- 
forating tarsal  vein  passes  through  the  vascular  canal  of  the  metatarsus  and  centro- 
tarsal  (as  the  perforating  tarsal)  and  joins  the  anterior  tibial  vein.  The  lateral 
plantar  metatarsal  vein  pursues  a  similar  course  laterally,  and  is  continued  by  the 
lateral  tarsal  vein,  which  joins  the  recurrent  tarsal  vein  above  the  hock.  It  passes 
superficially  over  the  lateral  face  of  the  hock  and  is  continued  by  the  recurrent  tarsal 
vein. 

The  digital  veins  differ  from  those  of  the  forelimb  chiefly  in  that  the  dorsal 
common  vein  is  large  and  the  plantar  absent  or  small. 

The  dorsal  common  digital  vein  arises  at  the  distal  part  of  the  interdigital  space  by  the  union 
of  branches  coming  from  the  venous  plexuses  of  each  digit.  It  deviates  outward  at  the  fetlock  and 
joins  the  lateral  digital  vein  to  form  the  dorsal  metatarsal  vem.     The  medial  digital  vem  ascends 

1  Also  termed  the  external  saphenous  vein. 
46 


722  LYMPHATIC    SYSTEM    OF   THE    OX    AND    SHEEP 

along  the  medial  surface  of  the  medial  chief  digit,  turns  laterally  above  the  fetlock  joint,  and  is  con- 
nected with  the  corresponding  lateral  vein  to  form  the  plantar  venous  arch.  From  this  the  three 
chief  metatarsal  veins  ascend  and  to  it  come  small  veins  from  the  rudimentary  digits. 

The  portal  vein  is  formed  usuall}^  by  the  confluence  of  two  radicles,  gastric 
and  mesenteric.  It  receives  the  gastro-duodenal  vein  and  veins  of  the  pancreas. 
The  gastric  vein  is  the  largest  affluent.  It  is  formed  by  the  junction  of  two  trunks. 
One  of  these,  the  right  ruminal  vein,  receives  the  splenic  vein.  The  other  is  a 
short  trunk  which  is  formed  by  the  confluence  of  the  left  rmninal  and  omaso- 
abomasal  veins;  it  receives  the  reticular  vein.  The  anterior  mesenteric  vein  is 
formed  by  the  confluence  of  three  chief  radicles  which  return  the  blood  from  the 
entire  intestine,  with  the  exception  of  part  of  the  duodenum  and  rectum;  from 
these  the  blood  is  conveyed  by  the  gastro-duodenal  and  internal  pudic  veins.  The 
portal  tributaries  are  in  general  satellites  of  the  corresponding  arteries. 


LYMPHATIC  SYSTEM  OF  THE  OX  AND  SHEEP 

The  lymph  glands  of  the  ox  are  in  general  less  numerous  but  larger  than  those 
of  the  horse;  in  some  situations  a  single  large  gland  occurs  instead  of  a  group  of 
small  ones,  as  found  in  the  latter  animal. 

The  thoracic  duct  arises  from  the  cisterna  chyli  at  the  hiatus  aorticus.  In 
some  cases  it  remains  single,  as  is  most  common  in  the  horse,  pursues  a  similar 
course  and  opens  into  the  origin  of  the  anterior  vena  cava,  or  into  the  left  common 
jugular  vein.  But  in  many  cases  the  duct  divides  into  two  branches  which  lie  on 
the  right  and  left  sides  of  the  dorsal  face  of  the  aorta.  The  two  ducts  are  united 
by  anastomotic  branches  and  are  embedded  in  fat.  They  usually  unite  about  the 
fifth  thoracic  vertebra.  The  terminal  part  is  often  ampullate,  but  the  lymphatico- 
venous  opening  is  small.  When  single,  the  duct  is  6-10  mm.  in  diameter.  The 
duct  may  receive  efferent  vessels  from  the  intercostal,  mediastinal,  and  bronchial 
lymph  glands. 

Many  other  variations  have  been  described.  In  the  anterior  mediastinum  there  may  be 
three  or  even  four  ducts  (with  connecting  branches),  which  usually  unite  just  before  the  lym- 
phatico-venous  opening,  but  may  open  separately. 

The  cisterna  chyU  lies  in  the  hiatus  aorticus,  dorsal  to  the  aorta  and  venti-al 
to  the  last  thoracic  and  first  lumbar  vertebrae.  It  receives  the  lumbar  and  intestinal 
lymph  trunks.  It  is  very  variable  in  form  and  is  commonly  about  three-fourths 
of  an  inch  (1.5-2  cm.)  wide. 

The  intestinal  trunk  (Truncus  intestinalis)  is  formed  at  the  ventral  face  of  the 
posterior  vena  cava,  just  behind  the  dorsal  border  of  the  liver.  It  results  from  the 
union  of  the  common  efferent  vessels  of  the  gastric  and  intestinal  lymph  glands. 

The  trunk  is  a  centimeter  or  less  in  diameter  in  the  adult.  It  runs  backward  a  short  distance, 
bends  sharply  dorsally  between  the  aorta  and  vena  cava,  and  unites  (usually)  with  the  lumbar 
trunk  to  form  the  cisterna  chyli. 

The  lumbar  tnmk  (Truncus  lumbalis)  is  formed  in  the  sublumbar  region  by 
the  confluence  of  efferent  vessels  from  the  iliac  lymph  glands.  It  concurs  with  the 
intestinal  trunk  in  the  formation  of  the  cisterna  chyli.  It  receives  efferent  vessels 
of  the  lumbar  and  renal  lymph  glands.  The  trunk  is  very  variable  in  regard  to 
its  mode  of  formation  and  two  may  be  present. 

The  mandibular  lymph  glands  are  usually  two  in  number,  one  on  each  side. 
The  gland  is  situated  between  the  sterno-cephalicus  muscle  and  the  ventral  part  of 
the  mandibular  salivary  gland,  and  is  usually  related  dorsally  to  the  external  maxil- 
lary vein.     The  gland  is  oval  and  is  commonly  about  an  inch  and  a  half  (ca.  3-4  cm.) 


LYMPHATIC    SYSTEM    OF    THE    OX    AND    SHEEP 


f23 


long  and  an  inch  (ca.  2-3  cm.)  wide.  In  some  cases  a  second,  smaller  gland  is 
present.  Its  position  is  variable;  it  may  be  behind  or  dorsal-medial  to  the  large 
gland,  or  may  be  on  the  deep  face  of  the  ventral  end  of  the  mandibular  salivary  gland. 
Haemolymph  glands  often  occur  in  this  vicinity.  The  efferent  vessels  come  from 
the  muzzle,  lips,  cheeks,  hard  palate,  the  anterior  part  of  the  turbinates  and  septum 
nasi,  the  gums  (in  part) ;  the  sublingual  and  parotid  glands;  the  tip  of  the  tongue, 
the  muscles  of  the  head,  except  those  of  the  eye,  ear,  tongue,  and  hyoid  bone;  the 
mandible,  premaxilla,  and  nasal  bone;  the  skin  of  the  face  in  part.  It  also  receives 
the  efferent  vessels  of  the  pterygoid  lymph  gland  when  present.  The  efferent 
vessels,  two  to  four  in  number,  go  to  the  atlantal  gland. 

The  parotid  lymph  gland  (Lg.  parotidea)  lies  on  the  posterior  part  of  the  mas- 
seter  muscle  and  is  partly  covered  by  the  dorsal  end  of  the  parotid  salivary  gland. 
It  is  related  deeply  to  the  internal  maxillary  and  superficial  temporal  vessels  and 
the  superficial  temporal  nerve.  It  is  about  three  inches  (ca.  6-8  cm.)  long  and  about 
an  inch  (ca.  2-3  cm.)  wide.     In  some  cases  there  are  instead  two  smaller  glands. 


Fig.  603. — Superfk 
1,  Mandibular;    2,  parotid;    3,  at  Ian 


LvMPH  Glands  of  Cow  Projected  on  Surface  of  Body. 

4.  parapharyngeal;    S,  anterior  cervical:    6,  middle  cervical;      7,  prescapular; 


S,  prefemoral.      (With  use  of  fig.  in  Ellenberger-Baum,  Anat.  f.  Kiinstler.) 


The  afferent  vessels  come  from  the  muzzle,  lips,  the  gums  (in  part),  the  anterior 
part  of  the  turbinates  and  septum  nasi;  the  parotid  salivary  gland;  most  of  the 
muscles  of  the  head,  including  those  of  the  eye  and  ear;  the  eyelids,  lacrimal  gland 
and  external  ear;  the  frontal,  malar,  nasal  and  premaxillary  bones  and  the  mandible; 
the  skin  of  the  head  in  great  part.  The  efferent  vessels,  eight  to  twelve  in  number, 
go  to  the  atlantal  gland. 

The  supraphar5aigeal  Ijrmph  glands  (Lgg.  suprapharyngese)^  are  usually  two 
in  number,  right  and  left.  They  are  situated  about  an  inch  apart,  medial  to  the 
great  cornu  of  the  hyoid  bone,  and  between  the  phar\^lx  and  the  ventral  straight 
muscles  of  the  head  (Fig.  386).  They  average  about  three  inches  (ca.  6-8  cm.) 
in  length.  In  some  cases  an  additional  gland  is  present.  The  afferent  vessels  come 
from  the  tongue,  the  floor  of  the  mouth,  the  hard  palate,  the  soft  palate,  the  gums 
(in  part),  the  pharynx,  the  sublingual  and  mandibular  salivary  glands;  the  posterior 
^  Also  commonly  termed  the  retropharyngeal  glands. 


724  LYMPHATIC    SYSTEM    OF   THE    OX   AND    SHEEP 

part  of  the  nasal  cavity,  the  maxillary  and  palatine  sinuses,  and  the  larynx;  and  the 
rectus  capitis  ventralis  major.  The  efferent  vessels,  four  to  eight  in  number,  con- 
cur in  forming  the  tracheal  h-mph  duct. 

A  small  parapharjoigeal  l5rmph  gland  is  usually  present  on  the  lateral  wall  of 
the  pharjTix,  under  cover  of  the  mandibular  salivary  gland  or  at  its  posterior  border. 
It  is  ventral  to  the  carotid  artery  and  the  atlantal  gland.  Its  afferent  and  efferent 
vessels  are  similar  to  those  of  the  atlantal  gland. 

The  atlantal  l)rmph  gland  is  situated  ventral  to  the  wing  of  the  atlas,  on  the 
cleido-mastoideus  tendon,  and  partly  under  cover  of  the  mandibular  salivary  gland. 
It  is  related  ventrally  to  the  carotid  artery.  It  is  usually  discoid  and  an  inch  and  a 
half  to  two  inches  (ca.  4-5  cm.)  in  length.  One  or  more  small  l>Tnph  nodes  may 
occur  near  the  large  constant  one,  and  small  hsemolymph  glands  are  commonly 
present  here.  The  afferent  vessels  come  from  the  tongue,  the  salivary  glands,  the 
gums  in  part;  the  cervical  part  of  the  thymus;  most  of  the  hyoid  and  cervical 
muscles.  It  also  receives  vessels  from  the  parotid,  mandibular,  and  suprapharjoi- 
geal  lymph  glands.  The  efferent  vessels,  three  to  six  in  number,  concur  in  forming 
the  tracheal  lymph  duct. 

The  pterygoid  lymph  gland  (Lg.  pterygoidea),  which  is  present  in  the  majority 
of  cases,  is  situated  on  the  dorsal  part  of  the  lateral  face  of  the  pterygoid  muscle, 
close  to  the  maxillary  tuberosity.  It  is  usually  about  half  an  inch  (ca.  1-1.5  cm.) 
in  length  and  width,  but  may  be  much  smaller  and  escape  observation.  Its  affer- 
ent vessels  come  from  the  hard  palate  and  adjacent  part  of  the  gums.  The  efferent 
vessels,  to  or  three  in  number,  go  to  the  mandibular  lymph  gland. 

The  hyoid  l5rmph  glands  (Lgg.  hyoidese)  occur  in  about  20  per  cent,  of  cases.  The  anterior 
hyoid  gland  (Lg.  hyoidea  oralis)  lies  on  the  thyroid  cornu  of  the  hyoid  bone,  at  the  insertion  of  the 
stylohyoideus  muscle.  It  is  about  half  an  inch  (ca.  1-1.5  cm.)  long.  It  receives  afferent  vessels 
from  the  tongue.  The  efferent  vessels,  two  or  three  in  number,  go  to  the  atlantal  gland,  and  may 
go  in  part  to  the  suprapharyngeal  gland.  The  posterior  hyoid  gland  (Lg.  hyoidea  aboralis)  lies 
on  the  dorsal  end  of  the  great  cornu  of  the  hyoid  bone  or  in  the  angle  between  the  bone  and  the 
occipito-hyoideus  muscle.  It  receives  lymph  vessels  from  the  mandible  which  issue  from  the 
mandibular  foramen.     The  efferent  vessels  go  to  the  atlantal  gland. 

The  anterior  cervical  l3rmph  glands  (Lgg.  cervicales  craniales)  are  situated  on 
the  anterior  part  of  the  trachea,  along  the  course  of  the  carotid  artery.  They  are 
variable  in  number  and  size.  Four  or  five  may  be  present.  They  vary  in  length 
from  about  half  an  inch  to  two  inches    (ca.  1-2.5  cm.). 

The-middle  cervical  Ijrmph  glands  (Lgg.  cervicales  media)  lie  on  each  side  of 
the  trachea,  in  the  middle  third  of  the  neck.  They  vary  in  position,  number,  and 
size.  The  series  may  extend  to  the  anterior  group,  or  may  reach  back  almost  to 
the  posterior  group.  The  number  appears  to  vary  from  one  to  seven  on  either  side. 
Their  length  ranges  from  about  one-fourth  inch  to  an  inch  or  more  (ca.  0.5-3  cm.). 
There  are  usually  hsemolymph  glands  near  them. 

The  posterior  cervical  lymph  glands  (Lgg.  cervicales  caudales)  are  situated 
near  the  thoracic  inlet.  One  of  them  lies  dorsal  to  the  manubrium  sterni  and  the 
cervical  muscles  attached  to  it.  It  is  usually  about  half  an  inch  (ca.  1-1.5  cm.) 
long.  Three  or  four  others  usually  occur  on  either  side.  Of  these,  one  is  ventral 
to  the  brachial  vein  at  the  first  rib,  one  or  two  lie  on  the  brachial  vessels  here,  and 
others  are  dorsal  and  ventral  to  the  jugular  vein.  Hsemolymph  glands  usually  are 
present  in  the  fat  about  this  group. 

The  cervical  lymph  glands  receive  afferent  vessels  from  the  ventral  muscles  of 
the  neck,  the  oesophagus,  the  larynx,  the  trachea,  the  thyroid  gland,  and  the  cervical 
part  of  the  thymus.  The  anterior  cervical  glands  receive  efferent  vessels  of  the 
atlantal  gland.  The  efferent  vessels  go  in  general  to  the  tracheal  lymph  ducts,  but 
efferents  from  some  of  the  posterior  group  may  go  to  the  terminal  part  of  the  thora- 
cic duct  or  to  the  common  jugular  vein. 


LYMPHATIC    SYSTEM    OF   THE    OX   AND    SHEEP  725 

The  costo-cervical  l5niiph  gland  (Lg.  costo-cervicalis)i  is  situated  lateral  to  the 
trachea  and  oesophagus  and  dorsal  to  the  carotid  artery  and  the  vago-sympathetic 
trunk.  It  lies  usually  just  in  front  of  the  first  rib,  under  cover  of  the  scalenus 
muscle,  but  it  may  be  partly  medial  to  the  first  rib.  Its  length  varies  from  about 
half  an  inch  to  an  inch  or  more  (1.5-3  cm.).  Its  afferent  vessels  come  from  the 
muscles  of  the  neck  and  shoulder,  the  costal  pleura,  the  trachea,  and  the  intercostal 
and  anterior  mediastinal  glands.  The  efferent  vessels  on  the  right  side  usually  go 
to  the  right  tracheal  duct  or  join  the  efferent  vessel  of  the  prescapular  gland;  on  the 
left  they  go  most  often  to  the  end  of  the  thoracic  duct,  but  are  very  variable. 

The  tracheal  lymph  ducts  (Ductus  tracheales),  right  and  left,  are  formed 
essentially  by  the  confluence  of  efferent  vessels  from  the  atlantal  gland.  They 
usually  receive  efferent  vessels  from  the  cervical,  costo-cervical,  and  prescapular 
glands.  The  ducts  pass  along  each  side  of  the  trachea  and  oesophagus;  the  right 
one  usually  opens  into  the  right  common  jugular  vein;  the  left  one  joins  the  terminal 
part  of  the  thoracic  duct  or  opens  into  the  left  common  jugular  vein. 

These  ducts  are  very  variable  in  regard  to  formation,  affluents,  and  termination.  There 
may  be  an  accessory  tracheal  duct,  which  receives  part  of  the  lymph  vessels  that  otherwise  go  to 
the  chief  duct;  this  accessory  duct  runs  a  variable  distance  along  the  neck  practically  parallel 
with  the  chief  duct,  and  unites  with  the  latter. 

A  short  right  lymphatic  duct  may  be  formed  by  the  junction  with  the  terminal 
part  of  the  right  tracheal  duct  of  efferent  vessels  from  the  right  cervical,  costo-cer- 
vical, and  prescapular  lymph  glands.  It  also  usually  receives  an  efferent  vessel 
from  the  anterior  sternal  lymph  gland. 

The  prescapular  or  posterior  superficial  cervical  Ijrmph  gland  (Lg.  cervicalis 
superficialis  caudalis)  is  situated  at  the  anterior  border  of  the  supraspinatus,  a  little 
above  the  level  of  the  shoulder  joint;  it  is  covered  by  the  omo-transversarius  and 
brachiocephalicus  muscle.  It  is  elongated  and  may  attain  a  length  of  four  or  five 
inches  (ca.  10-12  cm.)  and  a  width  of  an  inch  or  more  (ca.  3  cm.).  Its  deep  face 
has  a  long  and  distinct  hilus.  It  receives  afferents  from  the  skin  of  the  neck, 
shoulder,  part  of  the  ventral  and  lateral  surfaces  of  the  thorax,  and  the  thoracic 
limb;  from  the  muscles  of  the  shoulder-girdle,  and  from  the  external  scapular 
muscles;  from  the  tendons  of  the  muscles  of  the  forearm  and  digit  and  the  fascia 
of  the  forearm;  from  the  joints  of  the  carpus  and  digit.  The  efferent  vessel  de- 
scends over  the  scalenus  muscle  and  opens  on  the  right  side  into  the  end  of  the  right 
tracheal  duct,  on  the  left  into  the  terminal  part  of  the  thoracic  duct  or  the  left 
tracheal  duct. 

In  one  case  Baum  found  two  efferent  vessels  on  the  right  side:  one  opened  into  the  end  of 
the  tracheal  duct,  the  other  went  to  a  posterior  cervical  gland. 

A  chain  of  small  nodes,  five  to  ten  in  number,  extends  along  the  border  of  the  supraspinatus, 
dorsal  to  the  prescapular  gland,  and  covered  by  the  trapezius  and  omo-transversarius.  These 
nodes,  termed  by  Baum  lymphoglandulse  cervicales  nuchales,  are  in  most  cases  dark  red  in  color, 
and  most  of  them  are  hsemolymph  glands.  But  some  are  lymph  glands,  smce  they  receive  afferent 
vessels  from  adjacent  muscles  and  send  efferent  vessels  to  the  prescapular  lymph  gland  or  to 
another  gland  of  the  group. 

The  intercostal  lymph  glands  are  situated  in  the  dorsal  ends  of  the  intercostal 
spaces,  on  the  course  of  the  intercostal  vessels,  and  embedded  in  fat.  Most  of  them 
are  small,  but  some  may  be  nearly  an  inch  (ca.  2  cm.)  long.  Not  all  of  the  spaces 
contain  glands,  and  quite  exceptionally  two  may  occur  in  one  space.  Associated 
with  them  are  hsemolymph  glands.  The  afferent  vessels  come  chiefly  from  the 
intercostal  and  spinal  muscles,  the  serrati,  latissimus  dorsi,  trapezius,  subscapularis, 
longus  colli,  obliquus  abdominis  externus;  from  the  costal  pleura  and  the  peri- 
toneum; from  the  thoracic  vertebrae  and  the  ribs.  The  efferent  vessels  go  to  the 
mediastinal  lymph  glands. 

1  This  gland  has  been  included  in  the  posterior  cervical  group,  but  forms  a  connecting  link, 
as  it  were,  between  the  cervical  and  mediastinal  glands.  Baum  has  given  it  the  above  name  and 
has  shown  that  it  receives  lymph  vessels  from  the  pleura. 


726  LYMPHATIC    SYSTEM    OF   THE    OX   AND    SHEEP 

The  dorsal  mediastinal  lymph  glands  (Lgg.  mediastinales  dorsales)  are  situated 
on  each  side  of  the  thoracic  aorta,  in  the  fat  which  levels  up  the  space  between  that 
vessel  and  the  bodies  of  the  vertebrae.  On  the  right  side  they  lie  chiefly  dorsal  to 
the  thoracic  duct,  and  on  the  left  side  they  are  related  to  the  vena  hemiazygos. 
They  are  irregular  in  arrangement  and  their  length  varies  from  about  half  an  inch 
to  an  inch  and  a  half  (ca.  1-3.5  cm.).  They  are  in  series  with  the  anterior  medias- 
tinal glands. 

Their  afferent  vessels  come  from  the  same  parts  as  those  of  the  intercostal 
glands;  also  from  the  diaphragm,  the  mediastinum,  the  pericardium,  the  ribs,  and 
the  intercostal  lymph  glands.  The  efferent  vessels  go  chiefly  to  the  thoracic  duct 
or  join  the  common  efferent  duct  of  the  posterior  mediastinal  glands. 

The  ventral  mediastinal  Ijmiph  glands  (Lgg.  mediastinales  ventrales)  are 
situated  on  the  transversus  thoracis  muscle.  Several  (2-5)  occur  constantly  in 
the  fat  about  the  apex  of  the  pericardium;  they  vary  in  length  from  about  half  an 
inch  to  an  inch  or  more  (ca.  1-3  cm.).  In  some  cases  other  glands  are  present 
further  forward.  The  afferent  vessels  come  from  the  costal  and  mediastinal 
pleura,  the  diaphragm,  the  pericardium,  and  the  ribs.  The  efferent  vessels  usually 
unite  to  form  a  trunk  which  goes  to  the  anterior  sternal  lymph  gland.  Hsemolymph 
glands  may  be  present  in  this  region. 

The  anterior  mediastinal  lymph  glands  (Lgg.  mediastinales  craniales)  are 
situated  in  part-  at  the  thoracic  inlet,  in  part  along  the  oesophagus,  trachea,  anterior 
vena  cava,  and  brachiocephalic  trunk.  The  former  group  comprises  two  to  four 
glands  on  either  side,  ventral  to  the  trachea  and  oesophagus.  Usually  the  largest 
of  these,  which  may  be  an  inch  or  more  (ca.  2-3  cm.)  in  length,  lies  along  the  origin 
of  the  internal  thoracic  artery.  The  second  group  differs  somewhat  on  the  two  sides. 
On  the  right  side  there  is  usually  a  large  gland,  which  may  be  two  or  three  inches 
(ca.  5-7  cm.)  in  length;  it  lies  on  the  oesophagus  and  is  crossed  laterally  by  the 
dorsal  vein.  Behind  this  there  are  commonly  two  or  three  glands  on  the  oesophagus 
or  the  longus  colli,  and  in  front  two  or  three  are  placed  similarly  and  on  the  trachea. 
On  the  left  side  a  variable  number  (2-7)  are  situated  on  the  oesophagus,  trachea, 
brachiocephalic  trunk,  and  anterior  vena  cava;  glands  may  be  between  the  vessels, 
or  between  the  vessels  and  the  trachea,  and  escape  superficial  examination.  Hsemo- 
lymph glands  are  often  present  in  the  vicinity  of  these  glands.  The  afferent  vessels 
come  from  the  thoracic  part  of  the  oesophagus,  trachea,  and  thymus;  from  the  lungs, 
pericardium,  heart,  costal  and  mediastinal  pleura;  from  the  intercostal  glands  of 
the  first  four  spaces  and  from  the  gland  on  the  apical  bronchus.  In  some  cases  these 
glands  receive  also  efferent  vessels  from  the  anterior  sternal,  left  bronchial,  and 
other  mediastinal  glands.  The  efferent  vessels  for  the  most  part  go  to  the  thoracic 
duct,  the  right  tracheal  duct,  and  the  costo-cervical  glands. 

The  posterior  mediastinal  l3rmph  glands  (Lgg.  mediastinales  caudales)  are 
situated  along  the  oesophagus,  from  the  aortic  arch  backward.  The  largest  of  these 
may  be  eight  inches  (ca.  20  cm.)  or  more  in  length;  its  anterior  part  is  dorsal  to  the 
oesophagus,  while  posteriorly  it  lies  in  the  angle  between  the  aorta  and  the  diaphragm 
(P'ig.  389).  But  in  some  subjects  there  are  two  glands  in  place  of  this  large  one;  in 
these  cases  the  additional  posterior  one  is  usually  the  smaller.  Several  other  glands 
of  smaller  size  lie  in  front  of  the  large  one,  in  the  angle  between  the  aorta  and  the 
oesophagus.  In  front  of  these  there  are  usually  two  or  three  on  the  right  side  on  the 
aorta  and  the  oesophagus.^  The  afferent  vessels  come  from  the  oesophagus,  the 
lungs,  the  pericardium,  the  mediastinum,  the  diaphragm,  the  peritoneum,  the  liver, 
and  the  spleen.  The  efferent  vessels  unite  to  form  a  common  trunk  which  joins  the 
thoracic  duct. 

The  diaphragmatic  lymph  glands  (Lgg.  diaphragmaticae)  are  small  nodes  which 
may  be  present  at  the  foramen  venae  cavse  and  the  termination  of  the  phrenic 
^  These  are  termed  by  Baum  the  middle  mediastinal  lymph  glands. 


LYMPHATIC    SYSTEM    OF   THE    OX   AND    SHEEP  727 

nerves.  The  one  most  often  present  is  at  the  acute  angle  between  the  vena  cava 
and  the  chaphragm.  The  afferent  vessels  come  from  the  diaphragm  and  medias- 
tinum.    The  efferent  vessels  go  to  the  posterior  mediastinal  glands. 

The  bronchial  Ijnnph  glands  (Lgg.  bronchiales)  are  situated  on  the  termination 
of  the  trachea  and  on  the  bronchi.  Commonly  three  or  four  are  present.  One  (Lg. 
bifurcationis  sinistra)  constantly  occurs  on  the  left  side  in  the  angle  between  the  aortic 
arch  and  the  left  division  of  the  pulmonary  artery  (Fig.  389) ;  it  is  crossed  laterally 
by  the  vena  hemiazygos.  This  gland  is  about  an  inch  to  an  inch  and  a  half  (ca.  2.5- 
3.5  cm.)  in  length  and  an  inch  (ca.  2.5  cm.)  in  width;  it  is  often  very  irregular  in 
shape.  A  gland  (Lg.  bifurcationis  dextra)  is  similarly  situated  on  the  right  side  in 
the  majority  of  cases.  It  is  smaller  than  the  left  gland  and  appears  to  be  absent 
in  about  25  per  cent,  of  subjects;  in  some  cases,  on  the  other  hand,  two  glands  occur 
here.  In  about  half  of  the  cases  a  small  gland  (Lg.  bifurcationis  dorsalis)  is  situated 
above  the  bifurcation  of  the  trachea.  Another  gland  (Lg.  eparterialis)  occurs  at  the 
origin  of  the  bronchus  of  the  apical  lobe  of  the  lung.  Exceptionally  a  second  small 
gland  is  present  here.  The  afferent  vessels  of  these  glands  come  chiefly  from  the 
lungs  and  the  pulmonary  lymph  glands,  the  thoracic  part  of  the  oesophagus,  and  the 
heart. ^  The  efferent  vessels  of  the  left  gland  are  quite  variable.  They  may  join  the 
common  efferent  of  the  posterior  mediastinal  glands.  Those  of  the  right  gland  go 
to  a  middle  mediastinal  gland,  those  of  the  dorsal  gland  go  to  the  right  gland,  and 
those  of  the  apical  gland  go  to  anterior  mediastinal  glands. 

The  pulmonary  lymph  glands  (Lgg.  pulmonales)  are  inconstant  and  variable 
nodes  which  may  be  found  on  the  chief  bronchi  in  the  lungs.  They  appear  to  be 
absent  in  one-third  to  one-half  of  the  cases  on  one  side  or  both.  They  vary  in  size 
from  a  fifth  to  half  an  inch  or  more  (ca.  0.5-1.5  cm.)  in  length.  The  afferent  vessels 
come  from  the  lungs,  and  the  efferent  vessels  go  to  the  bronchial  and  posterior 
mediastinal  glands. 

It  is  worthy  of  note  that  in  some  cases  lymph  vessels  of  the  left  lung  go  to  glands  on  the  right 
(middle  mediastinal  glands),  and  lymph  vessels  of  the  right  Imig  go  to  the  left  bronchial  gland. 

The  pericardiac  l3miph  glands  (Lgg.  pericardiacse)  are  small  and  variable  nodes 
which  lie  on  the  pericardium.  The  left  gland  is  usually  present  and  is  situated  at 
the  space  between  the  aortic  arch  and  the  vena  hemiazygos.  In  some  cases  it  may 
be  unusually  large — nearly  three  inches  (ca.  7  cm.)  in  length — and  extend  back  to 
the  left  bronchial  gland.  Other  small  glands  may  be  found  in  this  vicinity  or  lower 
down.  The  right  gland  is  only  exceptionally  present.  It  is  situated  just  ventral 
to  the  termination  of  the  posterior  vena  cava.  The  afferent  vessels  come  from  the 
pericardium,  and  the  efferents  go  to  the  dorsal  mediastinal  glands  (or  their  efferents) 
or  to  the  left  bronchial  gland  on  the  left  side,  to  the  apical  bronchial  gland  or  an 
anterior  mediastinal  gland  on  the  right  side. 

The  sternal  lymph  glands  (Lgg.  sternales)  are  situated  along  the  course  of  the 
internal  thoracic  vessels.  The  largest,  distinguished  as  the  anterior  sternal  gland 
(Lg.  sternalis  cranialis),  is  embedded  in  the  fat  in  front  of  the  transversus  thoracis. 
It  is  about  half  an  inch  to  an  inch  (ca.  1.5-2.5  cm.)  in  length.  The  other  glands  are 
covered  by  the  transversus  thoracis,  and  vary  in  size,  number,  and  arrangement. 
There  is  not  one  at  every  interchondral  space,  and,  on  the  other  hand,  two  may  occur 
at  one  space.  The  last  of  the  series  is  often  situated  in  the  angle  between  the  eighth 
and  ninth  costal  cartilages  and  the  sterninn  and  may  escape  notice."  The  afferent 
vessels  come  from  the  diaphragm,  the  intercostal,  deep  pectoral,  serratus  ventralis, 
rectus  thoracis,  and  abdominal  nmscles;    the  costal  and  mediastinal  pleura,  the 

1  Baum  notes  the  curious  fact  that  in  many  cases  in  which  he  injected  the  lyrnph  vessels  of 
the  diaphragmatic  lobes  the  vessels  went  around  the  dorsal  gland  without  entering  it. 

-  Attention  was  recently  drawn  to  this  gland  by  Stroh,  who  designated  it  the  xiphoid  gland. 
It  is  not  always  present. 


728  LYMPHATIC    SYSTEM    OF   THE    OX   AND    SHEEP 

pericardium,  the  peritoneum;  the  hver;  the  ribs,  costal  cartilages,  and  sternum; 
the  ventral  mediastinal  glands.  The  efferent  vessels  usually  concur  in  forming 
one  or  two  trunks  which  run  forward  along  the  internal  thoracic  vessels  to  the 
anterior  gland.  From  the  latter  one  or  two  efferents  go  to  the  anterior  mediastinal 
glands  or  directly  to  the  end  of  the  right  tracheal  duct  or  the  thoracic  duct  (on  the 
left  side). 

The  axillary  l3niiph  gland  lies  on  the  medial  face  of  the  distal  part  of  the  teres 
major  on  the  course  of  the  vein  from  the  latissimus  dorsi.  It  is  oval  in  outline  and 
is  usually  a  little  more  than  an  inch  (ca.  3  cm.)  in  length.  Quite  exceptionally  two 
glands  may  be  present.  The  efferent  vessels  come  from  most  of  the  muscles  of  the 
shoulder  and  arm,  the  muscles  of  the  forearm,  the  trapezius,  latissimus  dorsi,  pec- 
toralis  profundus,  and  cutaneus;  the  fascia  of  the  forearm;  the  shoulder,  elbow,  and 
carpal  joints;  the  scapula,  humerus,  radius,  ulna,  and  carpus;  the  infraspinatus 
gland.     The  efferent  vessels  (one  to  three)  go  to  the  posterior  cervical  glands. 

The  infraspinatus  lymph  gland  (Lg.  infraspinata)  is  a  small  node  which  is  present  in 
somewhat  less  tliaii  ;i  fourth  of  tlic^  rases  (Baum).  It  is  situated  at  or  near  the  posterior  border  of 
the  infraspinatus,  about  on  a  level  with  the  proximal  end  of  the  caput  longum.  It  receives  lymph 
vessels  from  the  latissimus  dorsi  and  sends  an  efferent  vessel  to  the  axillary  gland. 

The  rhomboid  lymph  gland  (Lg.  rhomboidea)  is  small  and  only  present  in  about  15  per 
cent,  of  subjects  (Baumj.  It  is  situated  under  the  rhomboideus  cervicalis  near  its  ventral  border 
and  the  cervical  angle  of  the  scapula.  It  receives  afferents  from  the  rhomboideus,  supras- 
pinatus,  and  serratus  ventralis,  and  sends  efferents  to  the  costocervical  gland. 

The  lumbar  lymph  glands  (Lgg.  lumbales)  are  situated  along  the  abdominal 
aorta  and  the  posterior  vena  cava,  and  in  some  of  the  spaces  between  the  transverse 
processes.^  Some  of  the  glands  are  dorsal  to  the  vessels.  Haemolymph  glands  also 
occur  in  this  region.  The  afferent  vessels  come  from  the  spinal,  sublumbar,  ab- 
dominal, and  serratus  dorsalis  muscles;  the  lumbo-dorsal  fascia;  the  kidneys, 
adrenals,  and  the  peritoneum;  the  lumbar  vertebrse.  The  efferent  vessels  go  to 
the  lumbar  trunk  and  the  cisterna  chyli. 

The  renal  l3miph  glands  (Lgg.  renales)  belong  in  reality  to  the  preceding  group, 
from  which  they  are  only  conventionally  distinguished.  They  are  situated  on  the 
course  of  the  renal  vessels  and  vary  in  size  and  number.  Their  afferent  vessels  come 
from  the  kidneys  and  adrenals,  and  the  efferent  vessels  go  mainly  to  the  cisterna 
chyli. 

The  cceliac  lymph  glands  (Lgg.  coeliacse) ,  two  to  five  in  number,  are  situated  on 
and  near  the  cceliac  and  anterior  mesenteric  arteries,  and  in  relation  to  the  left 
extremity  of  the  pancreas,  the  dorsal  curvature  of  the  rumen,  and  the  posterior 
vena  cava.  One  is  a  large  discoid  gland  which  lies  on  the  cceliac  artery  and  the 
origin  of  the  chief  branches  of  that  vessel  (Fig.  389).  It  is  heart-shaped,  marked 
by  a  deep  notch,  and  is  about  two  inches  (ca.  5-6  cm.)  long  and  an  inch  and  a  half 
(ca.  3-4  cm.)  wide.  Their  afferent  vessels  come  from  the  spleen.  The  efferent 
vessels  go  to  the  common  efferent  vessel  of  the  gastric  lymph  glands,  or  to  the 
intestinal  trunk,  or  to  the  cisterna  chyh. 

The  internal  iliac  l5niiph  glands  are  situated  in  relation  to  the  terminal  branches 
of  the  aorta  and  the  radicles  of  the  posterior  vena  cava.  They  number  commonly 
six  to  eight  and  vary  in  length  from  half  an  inch  to  two  inches  (ca.  1-5  cm.).  Their 
afferent  vessels  come  chiefly  from  muscles  of  the  sublumbar  region,  pelvis,  tail,  and 
thigh;  from  the  genital  organs;  from  the  kidneys,  bladder,  and  urethra.  They  also 
receive  vessels  which  are  efferents  of  the  external  iliac,  sacral,  ischiatic,  deep  in- 
guinal, prefemoral,  and  coxal  glands.  Their  efferent  vessels  go  chiefly  to  the  lumbar 
trunk. 

'  Baum  distinguishes  those  about  the  vessels  as  lgg.  lumbales  aorticse,  and  terms  those  in 
the  intertransverse  spaces  lgg.  lumbales  propria;,  and  regards  them  as  corresponding  to  the  dorsal 
mediastinal  and  intercostal  glands  respectively. 


LYMPHATIC    SYSTEM    OF    THE    OX    AND    SHEEP  729 

The  deep  inguinal  lymph  gland^  is  situated  ventral  to  the  psoas  minor,  at  the 
angle  of  divergence  of  the  circumflex  iliac  from  the  external  iliac  artery.  It  is 
discoid  and  is  commonly  two  to  three  inches  (ca.  5-7.5  cm.)  in  length.  A  smaller 
gland  may  be  present  near  the  large  one  or  at  the  origin  of  the  prepubic  artery.  The 
afferent  vessels  come  chiefly  from  the  abdominal  muscles;  the  pelvic  limb;  the 
urinary  organs,  the  vesiculae  seminales,  tunica  vaginalis,  cremaster  muscle;  and 
the  superficial  inguinal,  external  iliac,  sacral,  prefemoral,  and  popliteal  glands. 
The  efferent  vessels  go  in  part  to  the  internal  iliac  glands,  in  part  directly  to  the 
lumbar  trunk. 

The  external  iliac  lymph  glands  (Lgg.  iliacae  laterales)  number  one  or  two  on 
each  side,  and  are  situated  at  the  bifurcation  of  the  circumflex  iliac  artery.  In  the 
majority  of  cases  a  single  gland  is  found  just  in  front  of  the  origin  of  the  anterior 
branch  of  the  artery,  but  another  may  lie  in  the  angle  between  the  two  branches. 
The  more  constant  one  is  half  an  inch  to  an  inch  (ca.  1.25-2.5  cm.)  in  diameter. 
They  may  be  absent  on  one  side  or  (quite  exceptionally)  on  both  sides.  The 
afferent  vessels  come  from  the  abdominal  muscles,  the  gluteus  profundus,  the  tensor 
fasciae  latae,  the  fascia  lata;  the  peritoneum  of  the  adjacent  region;  the  pelvic  bones. 
They  also  receive  vessels  from  the  prefemoral  and  coxal  glands.  The  efferent  ves- 
sels go  in  part  to  the  lumbar  trunk,  in  part  to  the  internal  iliac  or  deep  inguinal 
glands. 

The  epigastric  Ijrmph  gland  (Lg.  epigastrica)  is  small  and  inconstant.  It  is  situated 
on  the  course  of  the  posterior  aladommal  artery  near  the  pubis.  It  receives  afferent  vessels  from 
the  adjacent  part  of  the  peritoneum  and  abdominal  muscles,  and  sends  an  efferent  vessel  to  the 
deep  inguinal  gland. 

The  paralumbar  lymph  glands  (Lgg.  paralumbales)  are  small  and  inconstant 
nodes,  variable  in  number,  which  may  be  found  under  the  skin  of  the  upper  part 
of  the  flank.  Their  afferent  vessels  come  from  the  adjacent  skin,  and  the  efferents 
go  in  part  to  the  prefemoral  gland,  in  part  to  the  deep  inguinal  gland.  Hsemolymph 
glands  occur  in  this  region. 

The  superficial  inguinal  lymph  glands  (Lgg.  inguinales  superficiales)  differ  in 
the  two  sexes.  (1)  In  the  bull  they  are  situated  below  the  prepubic  tendon  and  in 
the  narrow  interfemoral  space.  They  lie  in  the  mass  of  fat  about  the  neck  of  the 
scrotum  and  behind  the  spermatic  cord,  and  are  covered  (in  part)  by  the  retractor 
of  the  prepuce.  It  is  usual  to  find  one  or  two  on  each  side  of  the  penis,  but  in  ex- 
ceptional cases  one  or  two  more  may  be  present.  A  central  one  above  the  penis 
has  been  observed,  and  there  may  be  one  further  back.  The  afferent  vessels  come 
from  the  external  genital  organs  (except  the  testicles);  also  from  the  skin  of  the 
adjacent  region,  the  medial  and  posterior  surface  of  the  thigh,  and  the  medial  sur- 
face of  the  leg.  The  efferent  vessels  ascend  through  the  inguinal  canal  to  the  deep 
inguinal  gland  at  the  side  of  the  pelvic  inlet.  (2)  In  the  cow  they  are  usually 
termed  the  supramammary  lymph  glands  (Lgg.  supramammaricse) ,  since  they  are 
situated  above  the  posterior  border  of  the  base  of  the  mammary  glands.^  Usually 
two  are  present  on  either  side.  The  larger  ones  are  in  apposition  medially  and  are 
sometimes  united.  The  smaller  glands  are  above  or  in  front  of  the  large  ones. 
Exceptionally  a  third  gland  may  be  present  or  there  may  be  only  one  on  one  side. 
The  large  glands  are  usually  two  or  four  inches  (ca.  6-10  cm.)  long,  the  smaller 
ones  a  fourth  to  one-half  as  large.  The  afferent  vessels  come  from  the  udder,  the 
external  genital  organs,  and  part  of  the  skin  of  the  thigh  and  leg.  The  efferent 
vessels  converge  to  two  or  three  large  trunks  which  go  to  the  deep  inguinal  glands 
at  the  side  of  the  pelvic  inlet. 

^  This  gland,  designated  by  Chauveau-Lesbre  as  external  iliac,  is  here  named  in  accorda,nce 
with  the  observations  of  Baum,  who  found  that  it,  together  with  the  deep  femoral  gland,  derives 
its  afferent  vessels  from  substantially  the  same  region  as  the  deep  inguinal  glands  of  the  horse. 

2  When  enlarged,  they  can  easily  be  felt,  and  when  much  enlarged,  may  produce  a  prominence. 


730  LYMPHATIC    SYSTEM    OF    THP]    OX   AND    SHEEP 

The  efferent  vessels  run  forward  on  the  base  of  the  udder,  then  incUne  outward  and  pass 
through  the  aponeuroses  of  the  obhque  abdominal  muscles  at  the  lateral  edge  of  the  rectus  ab- 
flominis,  a  handbreadth  or  more  in  front  of  the  pubis.  On  reaching  the  femoral  ring  they  follow 
the  course  of  the  external  iliac  vessels  to  the  deep  inguinal  gland.  When  the  deep  femoral  gland 
on  the  upper  part  of  the  quadriceps  femoris  is  present,  some  efferents  go  to  it.  Baum  states  that 
efferents  of  one  side  may  go  to  a  supramammary  or  deep  inguinal  gland  of  the  opposite  side. 

The  sacral  lymph  glands  (Lgg.  sacrales)  may  be  subdivided  into  two  groups.^ 

(1)  The  medial  sacral  lymph  glands  (Lgg.  sacrales  mediales)  are  quite  in- 
constant. When  present,  there  is  a  gland  on  either  side  on  the  deep  surface  of  the 
sacro-sciatic  ligament,  in  the  fat  between  the  ligament  and  the  rectum  or  the  re- 
tractor ani.  Its  afferent  vessels  come  from  the  pelvic  urethra  and  urethral  muscle, 
the  root  of  the  penis  and  its  muscles,  the  prostate,  the  vagina  and  urethra,  and  the 
coccygeal  muscles.     The  efferent  vessels  usually  go  to  the  internal  iliac  glands. 

(2)  The  lateral  sacral  lymph  glands  (Lgg.  sacrales  laterales)  comprise  one  or 
two  inconstant  nodes  on  the  upper  part  of  the  outer  surface  of  the  sacro-sciatic 
ligament.  One  occurs  in  the  majority  of  cases  at  the  greater  sciatic  foramen;  the 
other,  which  is  further  back,  under  the  origin  of  the  biceps  femoris,  is  absent  on  one 
side  or  both  in  more  than  half  the  cases.  Their  afferent  vessels  come  from  the 
gluteus  profundus,  the  lumbo-dorsal  fascia,  the  pelvic  bones,  and  the  hip  joint. 
The  efferent  vessels  go  to  the  internal  iliac  and  deep  inguinal  glands. 

The  ischiatic  lymph  glands  (Lgg.  ischiadicsB)  are  one  or  two  in  number.  The 
one  which  appears  to  be  constant  lies  on  the  sacro-sciatic  ligament,  about  an  inch 
(ca.  2-3  cm.)  above  the  lesser  sciatic  notch,  and  under  cover  of  the  biceps  femoris. 
It  is  discoid  and  is  an  inch  or  more  (ca.  2.5-3.5  cm.)  in  diameter.  A  second  gland 
occurs  in  the  majority  of  cases  at  the  medial  side  of  the  tuber  ischii  and  the  attach- 
ment of  the  sacro-sciatic  ligament,  covered  only  by  the  skin  and  subcutaneous  fat.^ 
The  afferent  vessels  come  from  the  rectum  and  anus;  the  vulva,  the  root  of  the 
penis,  the  prostate,  the  bulbo-urethral  glands,  the  urethra  and  urethral  muscle; 
the  glutei,  biceps  femoris,  semitendinosus,  obturator  internus,  and  gemellus,  and 
the  lumbodorsal  fascia;  the  skin  of  the  hip  and  tail;  the  hip  joint.  They  also 
receive  efferent  vessels  of  the  popliteal  gland.  The  efferent  vessels  go  to  the  internal 
iliac  glands.^ 

The  gastric  Ijonph  glands  (Lgg.  gastricse)  are  numerous,  as  might  be  expected, 
and  are  difficult  to  group  satisfactorily.     They  comprise  the  following: 

(1)  The  atrial  lymph  glands  (Lgg.  atriales)  lie  chiefly  on  the  visceral  surface 
of  the  atrium,  just  behind  the  eardia;  commonly  three  or  four  are  present.  Their 
afferent  vessels  come  from  the  atrium,  from  the  adjacent  part  of  the  nun  en  and 
reticulum,  and  from  the  spleen.  They  receive  efferent  vessels  of  the  right  and 
anterior  ruminal,  reticular,  omasal,  and  dorsal  abomasal,  glands.  Their  efferent 
vessels  commonly  converge  to  a  large  trunk,  the  common  efferent  vessel  (Vas 
efferens  commune)  of  the  gastric  lymph  glands.  This  runs  upward  and  backward 
in  relation  to  the  coeliac  artery  and  reaches  the  ventral  face  of  the  posterior  vena 
cava;  here  it  unites  with  the  common  efferent  vessels  of  the  mesenteric  glands  to 
form  the  intestinal  trunk. 

(2)  The  right  ruminal  Ijrmph  glands  (Lgg.  ruminales  dextrse)  lie  along  the 
course  of  the  right  ruminal  artery.  Commonly  four  or  five  are  present,  and  they 
are  half  an  inch  to  an  inch  and  a  half  (ca.  1-3.5  cm.)  long.  Their  afferent  vessels 
come  chiefly  from  the  rumen.  They  also  receive  efferent  vessels  of  the  other 
ruminal  glands.  The  efferent  vessels  go  from  the  anterior  part  of  the  series  to  the 
reticular  glands  and  the  common  gastric  efferent. 

^  Baum  distinguishes  three  groups  of  sacral  glands  and  terms  the  glands  about  the  termina- 
tion of  the  aorta  and  the  origin  of  the  vena  cava  as  the  lgg.  sacrales  hypogastricse.  These  have 
been  included  in  the  internal  iliac  group  of  this  description. 

2  This  gland  is  termed  by  Baum  the  Ig.  tuberosa. 

3  Many  variations  occur  in  the  arrangement  of  those  efferent  vessels.  An  efferent  may  go 
to  a  cceliac  or  mesenteric  gland  or  to  the  intestinal  trunk  or  cisterna  chyli  directly. 


LYMPHATIC    SYSTEM    OF    THE    OX   AND    SHEEP  731 

(3)  The  left  ruminal  lymph  glands  (Lgg.  ruminales  sinistrse)  are  inconstant. 
One  or  two  may  be  present  in  the  left  groove  of  the  rumen.  Their  afferent  vessels 
come  from  the  rumen,  and  the  efferent  vessels  go  to  the  anterior  or  the  right  ruminal 
glands. 

(4)  The  anterior  ruminal  glands  (Lgg.  ruminales  craniales)  are  deeply  situated 
in  the  anterior  groove  of  the  rumen.  They  average  four  or  five  in  number  and  about 
half  an  inch  (ca.  1.5  cm.)  in  length.  They  receive  lymph  vessels  from  the  rumen 
and  from  the  left  ruminal  glands,  and  their  efferent  vessels  go  to  the  right  ruminal 
and  atrial  glands. 

(5)  The  reticular  lymph  glands  (Lgg.  reticulares)  are  situated  on  the  reticulum 
above  and  below  its  junction  with  the  omasum.  They  receive  afferent  vessels 
chiefly  from  the  reticulum  and  the  adjacent  parts  of  the  omasum  and  abomasum. 
Their  efferent  vessels  go  chiefly  to  the  atrial  lymph  glands. 

(6)  The  omasal  l3nnph  glands  (Lgg.  omasicse)  lie  on  the  omasum  chiefly  along 
the  course  of  the  dorsal  omasal  vessels.  Their  afferent  vessels  come  from  the 
omasum,  and  the  efferent  vessels  go  chiefly  to  the  atrial  lymph  glands. 

(7)  The  dorsal  abomasal  lymph  glands  (Lgg.  abomasicse  dorsales)  form  a  series 
along  the  lesser  curvature  of  the  abomasum.  They  receive  afferent  vessels  from 
the  abomasum,  duodenum,  and  ventral  part  of  the  omasum.  The  efferent  vessels 
go  chiefly  in  the  lesser  omentum  to  the  hepatic  lymph  glands,  but  some  from  the 
anterior  part  of  the  series  go  to  the  omasal  and  reticular  glands. 

(8)  The  ventral  abomasal  l5miph  glands  (Lgg.  abomasicse  ventrales)  comprise 
a  few  nodes  in  the  fat  along  the  greater  curvature  of  the  pyloric  part  of  the  abo- 
masum or  in  the  omentum  an  inch  or  two  distant  from  the  abomasum.^  They 
receive  afferent  vessels  from  the  abomasum  and  the  duodenum  and  their  efferent 
vessels  go  to  the  hepatic  lymph  glands. 

The  mesenteric  lymph  glands  (Lgg.  mesentericae)  comprise  a  large  number  of 
nodes  which  receive  lymph  from  the  intestine.  The  following  groups  may  be 
recognized,  although  the  distinction  is  in  part  conventional. 

(1)  The  duodenal  Ijmiph  glands  (Lgg.  duodenales)  are  small  nodes  in  the 
anterior  part  of  the  mesoduodenum.  They  receive  afferent  vessels  from  the  duo- 
denum and  their  efferent  vessels  go  to  the  hepatic  lymph  glands. 

(2)  The  jejuno-ileal  lymph  gland  (Lgg.  jejuno-ileales)  lie  in  the  part  of  the 
mesentery  to  which  the  coils  of  the  jejuno-ileum  are  attached.  They  vary  in 
number  from  ten  to  fifty,  and  in  length  from  about  a  quarter  of  an  inch  to  four  feet 
(ca.  0.5-120  cm.).  As  a  rule,  the  long  narrow  glands  are  in  the  peripheral  part  of  the 
mesentery,  while  numerous  small  nodes  are  scattered  throughout  the  mesentery 
and  extend  centrally  to  the  coils  of  the  colon.  Their  afferent  vessels  come  from  the 
mesenteric  part  of  the  small  intestine.  The  efferent  vessels  converge  to  form  a 
large  common  efferent  vessel.  This  receives  efferent  vessels  of  the  csecal  and  colic 
lymph  glands,  runs  upward  and  forward  on  the  right  side  of  the  spiral  mass  of  the 
colon,  and  reaches  the  ventral  face  of  the  posterior  vena  cava  just  behind  the  an- 
terior mesenteric  artery;  here  it  unites  with  the  common  efferent  vessel  of  the 
gastric  lymph  glands  to  form  the  intestinal  trunk. 

(3)  The  caecal  l5anph  glands  (Lgg.  csecales) ,  usually  not  more  than  two  or  three 
in  number,  are  situated  along  the  attached  surface  of  the  caecum.  Their  efferent 
vessels  come  from  the  caecum  and  ileum.  The  efferent  vessels  go  to  colic  or  ileal 
glands  or  to  the  common  efferent  ves.sel. 

(4)  The  colic  l3rmph  glands  (Lgg.  colicae)  are  situated  in  part  superficially  on 
the  right  side  of  the  spiral  mass  of  the  colon,  in  part  deeply  between  the  coils.  One 
or  two  are  constantly  present  on  the  initial  part  of  the  colon,  near  the  termination 
of  the  ileum.     The  afferent  vessels  come  from  the  colon  chiefly,  but  some  of  the 

1  These  glands  are  often  difficult  to  find  in  the  large  mass  of  fat  in  which  they  are  usually 
embedded;  they  are  not  always  present. 


732  LYMPHATIC    SYSTEM    OF   THE    OX   AND    SHEEP 

glands  receive  vessels  from  the  ileum  and  csecum  and  their  lymph  glands.     The 
efferent  vessels  go  to  the  common  intestinal  efferent  or  to  other  colic  glands. 

(5)  The  rectal  l5rmph  glands  (Lgg.  rectales)  are  situated  along  the  dorsal  and 
lateral  surfaces  of  the  rectum.  They  receive  afferent  vessels  from  the  rectum, 
anus,  and  terminal  part  of  the  colon.  Most  of  the  efferent  vessels  go  to  other 
glands  of  the  group,  but  some  unite  to  form  one  or  two  large  trunks  which  end  in  the 
internal  iliac  lymph  glands.  There  are  many  small  hsemolymph  glands  in  relation 
to  the  rectal  lymph  glands. 

(6)  The  pancreatico-intestinal  lymph  glands  (Lgg.  pancreatico-intestinales) 
lie  on  the  ventral  surface  of  the  pancreas  and  along  the  right  part  of  the  latter  in 
relation  to  the  duodenum.  Some  are  at  the  pancreatic  notch  about  the  portal  vein 
and  its  affluents,  and  others  are  covered  by  the  adhesion  of  the  colon  to  the  gland. 
Their  afferent  vessels  come  from  the  pancreas,  the  duodenum,  and  the  adjacent 
part  of  the  colon.     The  efferent  vessels  go  to  the  common  intestinal  efferent. 


Fig.  604. — Ixtestine  of  Ox,  Spread  Odt. 
Ca,  Caecum;    C,  colon;    D,  duodenum;     II,  ileum;     J,  jejunum;     R,  rectum;     m,  mesenteric  lymph  glands.      (After 

Edelmann.) 

(7)  The  hepatic  Ijrmph  glands  (Lgg.  hepaticse)  are  situated  in  and  ventral  to 
the  portal  fissure.  Most  of  them  are  grouped  about  the  portal  vein,  the  hepatic 
artery,  and  the  bile  duct,  and  are  covered  by  the  pancreas;  but  some  are  ventral 
to  the  pancreas.  Their  average  number  is  ten  to  fifteen,  but  twenty  or  more  have 
been  counted.  Their  length  varies  from  less  than  half  an  inch  to  three  inches  (ca. 
1-7  cm.).  They  receive  vessels  from  the  liver,  pancreas,  and  duodenum,  and  from 
the  abomasal  lymph  glands.  Their  efferent  vessels  converge  to  a  large  trunk 
which  passes  along  the  portal  vein  and  joins  the  common  efferent  vessel  of  the 
intestinal  glands  or  that  of  the  gastric  glands. 

The  prefemoral  or  subiliac  lymph  gland ^  is  situated  on  the  aponeurosis  of  the 

obliquus  abdominis  externus,  at  the  anterior  border  of  the  tensor  fasciae  latse  and 

about  a  handbreadth  above  the   patella.     It  has  an  elongated   elliptical  outline 

and  is  flattened.     Its  average  length  is  three  or  four  inches  (ca.  8-10  cm.),  and  its 

^  This  is  also  termed  the  precrural  or  suprapatellar  gland. 


LYMPHATIC    SYSTEM    OF   THE    OX   AND    SHEEP  733 

width  about  an  inch  (ca.  2.5  cm.)  in  the  adult,  but  it  may  be  considerably  larger. 
In  some  cases  a  second  small  gland  is  present  above  or  below  the  large  one.  It 
receives  afferent  vessels  from  the  skin  of  the  posterior  part  of  the  thorax,  the  ab- 
domen, pelvis,  thigh,  and  leg;  also  from  the  tensor  fasciae  latae  and  the  prepuce. 
The  efferent  vessels  ascend  on  the  deep  face  of  the  tensor  fasciae  latae  and  end 
chiefly  in  the  deep  inguinal  gland,  but  in  some  cases  some  go  to  the  iliac  glands. 

The  popliteal  lymph  gland  (I.g.  poplitea)  is  situated  in  a  mass  of  fat  on  the 
gastrocnemius  muscle,  behind  the  tibial  and  peroneal  nerves  and  between  the  biceps 
femoris  and  semitendinosus.  Its  average  length  is  about  an  inch  and  a  half  (ca. 
3-4  cm.)  and  its  width  about  an  inch  (ca.  2-3  cm.).  The  gland  receives  afferent 
vessels  from  the  lateral  and  posterior  part  of  the  leg  and  from  the  distal  part  of  the 
limb;  vessels  from  the  biceps  femoris  and  semitendinosus  also  go  to  it.  The 
efferent  vessels  go  chiefly  to  the  deep  inguinal  gland,  but  some  end  in  the  ischiatic 
or  internal  iliac  glands. 

The  coxal  lymph  gland  (Lg.  coxalis)  is  situated  in  front  of  the  proximal  part  of 
the  quadriceps  femoris,  under  cover  of  the  tensor  fasciae  latae.  It  is  present  in  the 
majority  of  subjects  on  one  side  or  both  and  may  be  an  inch  or  more  (ca.  2.5-3  cm.) 
in  length.  It  receives  vessels  from  the  quadriceps  femoris,  tensor  fasciae  latae, 
fascia  lata,  and  the  prefemoral  gland.  The  efferent  vessels  go  to  the  iliac  or  the 
deep  inguinal  glands. 

One  or  two  lymph  glands  are  commonly  present  on  the  superficial  face  of  the 
tensor  fasciae  latae,  an  inch  or  two  from  the  anterior  border  of  the  muscle  and  five 
or  six  inches  from  the  tuber  coxae.  They  are  often  partially  embedded  in  the  muscle, 
and  are  usually  small,  but  may  be  almost  an  inch  (ca.  2  cm.)  long.  Haemolymph 
glands  may  be  found  here  and  in  some  cases  appear  to  take  the  place  of  the  l^rniph 
gland.  The  afferent  vessels  come  from  the  skin  of  the  hip  and  the  efferent  vessels 
go  to  the  prefemoral  or  deep  inguinal  gland. 

The  Ijrmph  glands  of  the  sheep  resemble  in  general  those  of  the  ox,  but  a  few 
special  features  may  be  noted.  Homolymph  glands  are  numerous,  especially  along 
the  course  of  the  aorta;  they  are  dark  red  or  black  and  hence  are  easily  seen,  in 
spite  of  their  small  size,  in  the  fat  in  which  they  are  chiefly  embedded. 

The  mandibular  lymph  glands  are  usually  two  in  number  on  each  side,  and  are 
situated  behind  the  angle  of  the  jaw  on  the  course  of  the  external  maxillary  vein. 
The  larger  one  is  flattened  and  kidney  shaped  and  may  be  nearly  an  inch  (ca.  2  cm.) 
long. 

The  parotid  l3rmph  gland  lies  on  the  posterior  border  of  the  masseter  muscle, 
about  midway  between  the  mandibular  joint  and  the  angle  of  the  jaw.  It  is 
related  to  and  commonly  partly  covered  by  the  anterior  border  of  the  parotid 
salivary  gland.  It  is  flattened  and  has  a  deep  notch  posteriorly.  It  is  usually  a 
little  less  than  an  inch  (ca.  2  cm.)  long. 

The  suprapharyngeal  lymph  glands,  two  in  number,  have  an  elongated  oval 
outline.  They  are  situated  on  the  dorsal  wall  of  the  pharynx,  a  quarter  of  an  inch 
or  less  (ca.  0.5  cm.)  apart.  They  are  related  laterally  to  the  dorsal  end  of  the  great 
cornu  of  the  hyoid  bone,  and  dorsally  to  the  ventral  straight  muscles  of  the  head. 
They  are  about  an  inch  (ca.  2-3  cm.)  long,  and  half  as  wide. 

The  atlantal  l3rmph  gland  is  related  to  the  ventral  part  of  the  paramastoid 
process  and  is  dorsal  to  the  carotid  artery.  It  is  discoid,  oval  in  outhne,  and  about 
half  an  inch  (ca.  1.5  cm.)  long.  Commonly  there  is  a  small  node  behind  the  at- 
lantal gland  and  one  or  more  haemoljnnph  glands  occur  here. 

The  sternal  l3miph  gland,  which  overlies  the  first  segment  of  the  sternum,  is 
about  the  size  of  a  hazel  nut. 

The  mesenteric  lymph  glands  consist  chiefly  of  long  narrow  elongated  masses 
instead  of  isolated  small  nodes. 

The  prefemoral  Ijntnph  gland  is  in  front  of  the  anterior  border  of  the  tensor 


734 


CIRCULATORY    SYSTEM    OF   THE    PIG 


fasciae  latae,  about  midAvay  between  the  tuber  coxae  and  the  patella.  It  is  kidney- 
shaped  and  is  a  little  more  than  an  inch  (ca.  3  cm.)  long  and  nearly  an  inch  (ca. 
2  cm.)  wide. 

The  superficial  inguinal  or  mammary  lymph  glands  are  usually  two  in  numl^er 
on  each  side.  The  larger  one  is  kidney-shaped;  it  may  be  an  inch  and  a  half  (ca. 
3.5  cm.)  long  and  about  half  as  wide.  The  smaller  gland  is  oval  and  usually  about 
half  an  inch  (ca.  1  cm.)  in  length. 


CIRCULATORY  SYSTEM  OF  THE  PIG 
THE  HEART 

The  pericardium  is  attached  to  the  sternum  from  a  point  opposite  to  the  third 
rib  as  far  as  the  xiphoid  cartilage,  and  also  to  the  sternal  part  of  the  diaphragm. 


Vena  hemiazygos 


Aorta 


Left  brachial  artery 

Pulmonary  artery 
Brachinci  pJidlic 
rtn-ij 


:=■  Pulmonary  veins 


Posterior  vena 
cava, 


Anterior  vena 
cava 
Right  auricle 


Right  ventricle 


Fig.  605.— Heart  of  Pig;  Left  View. 
1,  Conus  arteriosu.s;  2,  great  cardiac  vein  in  left  longitudinal  groove;   3,  cardiac  vein  in  intermediate  groove;   4,  apex. 


It  has  extensive  contact  with  the  chest  wall  from  the  second  intercostal  space  to  the 
fifth  rib. 


THE   HEART 


735 


The  heart  is  small  in  proportion  to  the  body-weight,  especially  in  fat  animals. 
Its  weight  in  a  large  adult  is  usually  less  than  a  pound.  It  is  broad,  short,  and  blunt. 
When  hardened  in  situ  it  is  compressed  dorso-ventrally.  The  ventral  or  sterno- 
costal surface  (Facies  sternocostalis)  is  only  moderately  convex;  it  overlies  the 
sternum  from  the  second  sternebra  to  the  anterior  part  of  the  last  one.  The  left 
longitudinal  groove  is  on  its  left  part,  and  is  almost  parallel  with  the  left  border. 
The  dorsal  or  diaphragmatic  surface  is  more  convex.  The  right  longitudinal  groove 
runs  obliquely  across  this  surface;  it  begins  below  the  end  of  the  posterior  vena 
cava  and  extends  to  the  left  border.  There  is  often  an  intermediate  groove  on  the 
left  border;   it  may  extend  to  the  apex,  but  it  is  frequently  small  and  is  sometimes 


Vena  hemiazygos 
Pulmonary  artery 
Left  auricle 


Right  atrium 


I'i'AMiy    I 


Left  veiitricle 


^^Ml  Right  ventricle 


Fig.  606. — ^Heart  of  Pig,  Diaphragmatic  Surface. 

1-5,  Pulmonary  veins;    6,  left  pulmonary  artery;    7,  8,   branches  of  right  pulmonary  artery;   9,  vena  azygos;   10, 

fat  in  coronary  groove;  11,  vessels  and  fat  in  right  longitudinal  groove;   12,  apex. 

absent.  The  apex  is  blunt  and  is  almost  median;  it  overlies  the  anterior  part  of 
the  last  sternebra,  and  is  about  a  quarter  of  an  inch  (ca.  5-6  mm.)  from  the  sternal 
part  of  the  diaphragm.  When  the  ventricles  are  dilated,  there  is  a  notch  at  the  apex 
(Incisura  apicis  cordis) .  The  lower  border  of  the  left  auricle  is  marked  by  several 
notches  and  is  situated  at  a  lower  level  than  the  right  one. 


In  the  right  atrium  the  large  orifice  of  the  vena  hemiazygos  is  seen  below  that  of  the  posterior 
vena  cava;  the  two  are  separated  by  a  valvular  fold  with  a  concave  free  edge.  The  intervenous 
crest  is  broad  and  rounded,  not  prominent,  as  in  the  horse.  The  musculi  pectinati  radiate  from 
a  distinct  crista  terminalis  and  form  a  highly  developed  network  in  the  auricle.  The  fossa 
ovalis  is  extensive.     There  is  a  large  moderator  band  in  the  right  ventricle. 


736  CIRCULATORY   SYSTEM    OF   THE    PIG 


The  Arteries 


The  pulmonary  vessels  present  no  remarkable  features. 

The  aorta  resembles  that  of  the  horse  and  ox  in  its  course  and  relations,  but  the 
arch  is  much  more  strongly  curved.     There  is  no  common  brachiocephalic  trunk. 

The  brachiocephalic  artery  arises  first  from  the  aortic  arch  and  passes  forward 
below  the  trachea  to  the  first  rib.  Here  it  gives  off  the  common  carotid  arteries, 
separately  or  by  a  very  short  bicarotid  trunk,  and  is  continued  around  the  first  rib 
as  the  right  brachial  artery. 

The  left  brachial  artery  arises  from  the  aortic  arch  just  above  the  brachio- 
cephalic. It  curves  forward  and  downward  and  turns  around  the  anterior  border 
of  the  first  rib. 

The  branches  given  off  by  the  brachial  arteries  are  as  follows : 

There  is  usually  a  common  trunk  for  the  dorsal,  deep  cervical,  and  vertebral 
arteries.  This  trunk  or  the  dorsal  artery  gives  off  the  subcostal  artery,  which  sup- 
plies usually  the  third,  fourth,  and  fifth  intercostal  arteries.  The  second  inter- 
costal artery  arises  separately.  The  dorsal  artery  emerges  through  the  dorsal  end 
of  the  second  intercostal  space  and  divides  into  dorsal  and  cervical  branches ;  the 
dorsal  branch  passes  upward  and  backward  and  ramifies  in  the  deep  muscles  of  the 
anterior  part  of  the  back ;  the  cervical  branch  passes  deeply  to  the  atlantal  region, 
where  it  anastomoses  with  the  occipital  artery.  The  deep  cervical  artery  is  a 
much  smaller  vessel,  which  emerges  through  the  first  intercostal  space;  it  gives  off 
the  first  intercostal  artery,  passes  upward  and  forward  deeply,  and  ramifies  chiefly 
in  the  complexus  and  muhifidus.     The  vertebral  artery  resembles  that  of  the  horse. 

The  inferior  cervical  artery  is  large ;  its  ascending  branch  gives  off  the  posterior 
thyroid  artery  and  parotid  branches. 

The  internal  and  external  thoracic  arteries  give  branches  to  the  pectoral 
mammary  glands;   the  external  artery  may  be  absent. 

The  common  carotid  arteries  arise  from  the  brachiocephalic  close  together  or 
by  a  very  short  common  trunk;  they  are  accompanied  by  an  internal  jugular  vein 
of  considerable  size,  and  their  collaterals  are  similar  to  those  of  the  horse.  They 
terminate  in  occipital  and  internal  and  external  carotid  divisions. 

The  occipital  artery  resembles  that  of  the  horse. 

The  internal  carotid  artery  usually  arises  by  a  common  trunk  with  the  occipital. 
After  giving  off  a  large  meningeal  branch  which  enters  the  cranium  through  the 
mastoid  foramen,  it  passes  through  the  foramen  lacerum  and  forms  with  the  oppo- 
site artery  a  rete  mirabile  which  resembles  that  of  the  ox,  but  is  smaller;  it  is  not 
connected  with  the  vertebral  and  condyloid  arteries,  but  the  meningeal  branch  just 
mentioned  and  the  middle  meningeal  artery  concur  in  its  formation. 

The  external  carotid  artery  has  the  same  course  and  termination  as  in  the  horse. 
Its  collateral  branches  present  the  following  special  features:  (1)  The  lingual 
artery  is  relatively  large  and  supplies  the  pharyngeal  artery,  the  sublingual  artery, 
muscular  branches,  and  branches  to  the  soft  palate,  mandibular  gland,  and  larynx. 
(2)  The  external  maxillary  artery  is  represented  by  a  small  vessel  which  ends  in  the 
masseter  muscle;  it  gives  branches  to  the  pterygoideus  medialis,  the  parotid  and 
mandibular  glands,  and  the  mandibular  lymph  glands,  the  masseter  and  the  cuta- 
neus.  It  does  not  extend  upon  the  lateral  surface  of  the  face.  (3)  The  posterior 
auricular  artery  is  long  and  relatively  large ;  it  ascends  along  the  anterior  border  of 
the  paramastoid  process  and  ramifies  on  the  convex  surface  of  the  external  ear.  It 
gives  off  the  posterior  meningeal  artery,  which  enters  the  cranial  cavity  through  the 
mastoid  foramen. 

The  internal  maxillary  artery  pursues  a  flexuous  course  between  the  ramus  of 
the  mandible  and  the  pterygoid  muscles  to  the  maxillary  recess  and  divides  into 
infraorbital  and  palatine  branches.    Its  branches  offer  the  following  special  features: 


THE    ARTERIES  737 

(1)  The  inferior  alveolar  artery  is  large;  branches  from  it  emerge  through  four  or 
five  mental  foramina  and  take  the  place  of  the  inferior  labial.  (2)  The  middle 
meningeal  artery  enters  the  cranial  cavity  through  the  foramen  ovale  and  concurs 
in  the  formation  of  the  rete  mirabile.  (3)  The  buccinator  artery  is  large  and  partly 
compensates  for  the  lack  of  a  facial  artery.  It  ramifies  in  the  cheek  and  its  fine 
terminal  branches  extend  to  the  lips.  (4)  The  large  infraorbital  artery  extends  to 
the  snout  and  replaces  the  superior  labial  largely  and  the  lateral  nasal  in  part.  The 
malar  branch  compensates  largely  for  the  absence  of  the  lateral  and  dorsal  nasal 
arteries.     (5)  The  palatine  artery  is  small. 

The  superficial  temporal  artery  ascends  behind  the  temporo-mandibular 
articulation  and  ramifies  in  the  temporalis  muscle;  it  is  small  and  may  be  absent. 
In  the  latter  case  the  anterior  auricular  and  transverse  facial  arteries  arise  separately 
from  the  external  carotid  artery,  which  is  directly  continued  by  the  internal  maxil- 
lary artery. 

The  intercostal  arteries  number  usually  fourteen  or  fifteen  on  either  side;  of 
these  ten  to  twelve  arise  from  the  aorta,  usually  by  short  common  trunks.  Fre- 
quently an  intercostal  artery  is  given  off  from  that  of  an  adjacent  space. 

The  bronchial  and  oesophageal  arteries  usually  arise  separately. 

The  ccehac  artery  is  half  an  inch  to  an  inch  long.  It  supplies  a  branch  to  the 
left  crus  of  the  diaphragm,  and  divides  into  two  primary  branches,  gastro-hepatic 
and  splenic.  The  gastro-hepatic  artery  is  the  larger.  It  gives  off  pancreatic 
branches,  the  anterior  gastric  artery,  branches  to  the  lesser  curvature  of  the  stomach, 
pyloric,  and  gastro-duodenal  arteries.  The  latter  divides  into  pancreatico-duo- 
denal  and  right  gastro-epiploic.  The  anterior  gastric  usually  supplies  the  oesopha- 
geal artery.  The  continuing  trunk  (A.  hepatica  propria)  gives  off  a  cystic  branch 
and  divides  in  the  portal  fissure  into  three  or  four  branches  which  ramify  in  the 
liver.  The  splenic  artery  gives  off  the  posterior  gastric  (usually),  a  branch  to  the 
stomach  above  the  cardia  (A.  diverticuli),  twigs  to  the  pancreas,  short  gastric 
arteries  to  the  left  part  of  the  great  curvature,  and  splenic  branches,  and  is  con- 
tinued as  the  left  gastro-epiploic  artery. 

The  posterior  gastric  may  arise  from  the  gastro-hepatic  or  in  the  angle  of  divergence  of  the 
two  primary  divisions  of  the  coeliac.  The  oesophageal  branch  may  come  from  the  posterior  gas- 
tric or  the  splenic.     Other  variations  occur. 

The  anterior  mesenteric  artery  arises  an  inch  or  more  behind  the  coeliac  and 
is  long,  like  that  of  the  ox.  It  gives  twigs  to  the  pancreas  and  is  continued  in  the 
mesentery  as  the  artery  of  the  small  intestine  or  tnincus  intestinalis.  This  gives  off 
about  a  dozen  branches  which  form  a  series  of  arches  along  the  mesenteric  lymph 
glands.  From  these  is  formed  a  rich  network  which  gives  off  innumerable  fine 
branches  placed  close  together.  The  ileo-caeco-colic  artery  gives  off  ileal  and  caecal 
arteries,  and  enters  the  axis  of  the  spiral  coil  of  the  colon.  Here  it  pursues  a  spiral 
course  and  gives  off  branches  which  form  remarkable  plexuses;  from  the  latter 
numerous  fine  branches  go  to  the  centripetal  coils.  A  short  trunk  gives  origin  to 
right  and  middle  colic  branches.  The  right  colic  artery  is  arranged  hke  the  colic 
branch  of  the  ileo-cseco-colic  artery,  with  which  it  anastomoses  at  the  apex  of  the 
coil;  it  supplies  the  centrifugal  parts  of  the  coil.  The  middle  colic  artery  goes  to 
the  colon  as  it  emerges  from  the  coil  and  anastomoses  with  the  posterior  mesenteric 
artery. 

A  phrenico-abdominal  artery  arises  on  either  side  a  little  in  front  of  the  renal 
arteries.  It  divides  into  branches  which  go  to  the  costal  part  of  the  diaphragm 
and  the  abdominal  muscles. 

The  renal  and  spermatic  arteries  present  no  special  characters. 

The  posterior  mesenteric  artery  arises  near  the  termination  of  the  aorta.     It 
is  small  and  is  distributed  like  that  of  the  ox. 
47 


738 


CIRCULATORY    SYSTEM    OF    THE    PIG 


Six  pairs  of  lumbar  arteries  arise  from  the  aorta.  The  seventh  comes  from 
the  middle  sacral. 

The  terminal  branches  of  the  aorta  resemble  those  of  the  ox. 

The  arteries  of  the  shoulder,  arm,  and  forearm  resemble  in  general  those  of 
the  ox. 

The  brachial  artery  is  continued  over  the  medial  surface  of  the  elbow  by  the 
median  artery.  The  latter  divides  near  the  middle  of  the  forearm  into  radial  and 
ulnar  arteries. 

The  radial  artery  is  the  smaller  of  the  two  terminal  branches  of  the  median. 
It  descends  along  the  medial  border  of  the  radius  and  divides  at  the  proximal  end 


Fig.  607. — Arteries  of  Dir»TAL  Part  of  Right  Fore 
Limb  of  Pig;  Dorsal  View. 
a.  Terminal  part  of  volar  interosseous  artery;  6, 
dorsal  interosseous  artery;  c,  rete  carpi  dorsale;  d,  dorsal 
metacarpal  arteries;  e,  dorsal  common  digital  arteries; 
/,  dorsal  proper  digital  arteries. 


Fig.  608. — Arteries  of  Distal  Part  of  Right  Fore 
Limb  of  Pig;  Volar  View. 
g.  Ulnar  artery;  h,  superficial  branch  of  radial 
artery;  ;,  collateral  ulnar  artery/ j,  volar  interosseous  ar- 
tery; h,  deep  branch  of  radial  artery;  k,  deep  volar  meta- 
carpal arteries;  /,  superficial  volar  metacarpal  arteries; 
m,  volar  common  digital  artery;  n,  volar  proper  digital 
arteries. 


of  the  metacarpus  into  two  branches.  The  superficial  branch  descends  in  the  space 
between  the  second  and  third  metacarpal  bones  and  unites  with  the  ulnar  artery 
or  with  the  lateral  superficial  volar  metacarpal  artery  to  form  the  superficial  volar 
arch.  The  deep  branch  joins  the  volar  interosseous  artery  at  the  proximal  end  of 
the  metacarpus  to  form  the  deep  volar  arch.  There  is  also  a  communicating  branch 
between  the  radial  and  ulnar  arteries  at  the  carpus. 

The  ulnar  artery  descends  along  the  medial  side  of  the  deep  digital  flexor  and 
connects  with  the  superficial  branch  of  the  radial  artery  to  form  the  superficial 
volar  arch. 


THE    ARTERIES 


739 


The  main  facts  as  to  the  metacarpal  and  digital  arteries  are  as  follows:  The 
rete  carpi  dorsale  is  formed  essentially  by  the  terminals  of  the  interosseous  artery 
of  the  forearm.  It  gives  rise  to  three  dorsal  metacarpal  arteries,  which  descend  in 
the  corresponding  interosseous  spaces  and  unite  with  branches  of  the  volar  meta- 
carpals to  form  three  common  digital  arteries.  Each  of  these  divides  into  two 
proper  digital  arteries,  which  descend  along  the  interdigital  surfaces  of  the  digits. 
From  the  superficial  and  deep  volar  arches  described  above  there  arise  three  super- 
ficial and  three  deep  volar  metacarpal  arteries.  The  deep  arteries  unite  near  the 
distal  end  of  the  space  between  the  principal  metacarpal  bones  to  form  a  stem 
which  unites  with  the  middle  (third)  superficial  artery.     The  superficial  arteries 


Fig.  609. — Arteries  of  Distal  Part  of  Right  Hind 
Limb  of  Pig;  Dorsal  View. 
a.  Anterior  tibial  artery,  continued  on  tarsus  as  the 
dorsalis  pedis;  6,  perforating  tarsal  artery;  c,  dorsal 
metatarsal  arteries;  d,  common  digital  arteries;  e, 
proper  digital  arteries. 


Fig.  610. — Arteries  of  Distal  Part  of  Right  Hixd 
Limb  of  Pig;  Plantar  View. 
/,  Saphenous  artery,  continued  as  medial  tarsal 
artery;  g,  lateral  tarsal  artery;  h,  medial  plantar  artery, 
h',  lateral  plantar  artery;  i,  perforating  tarsal  artery; 
J,  deep  plantar  metatarsal  arteries;  k,  common  digital 
artery;    /,  proper  digital  arteries. 


unite  to  form  an  arch  from  which  proper  digital  arteries  are  given  off  to  the  axial 
aspect  of  the  small  digits,  and  a  common  digital  which  supplies  two  volar  proper 
digital  arteries  to  each  of  the  chief  digits. 

The  arteries  of  the  hip,  thigh,  and  leg  are  arranged  much  as  in  the  ox.  A  few 
special  features  may  be  noted. 

The  ilio-ltmibar  artery  gives  off  a  branch  to  the  quadriceps  femoris  and  lateral 
muscles  of  the  thigh,  and  ramifies  in  the  abdominal  muscles.  It  may  also  supply 
the  posterior  abdominal  artery,  which  otherwise  arises  from  the  deep  femoral. 

The  deep  femoral  artery  is  given  off  above  the  level  of  the  pubis.  It  is  large 
and  compensates  for  the  absence  of  the  obturator  artery.     The  posterior  abdominal 


740  CIRCULATORY    SYSTEM    OF   THE    PIG 

and  external  pudic  arteries  may  arise  from  it  by  a  short  common  trunk  or  separately. 
The  external  pudic  gives  branches  to  the  prepuce  and  preputial  bursa  but  not  to 
the  penis.  In  the  female  it  supplies  the  inguinal  and  abdominal  mammary  glands 
and  anastomoses  with  the  external  thoracic  artery.  The  popliteal  artery  gives  off 
the  peroneal. 

The  femoral  artery  gives  off  a  short  trunk  which  divides  into  anterior  femoral 
and  lateral  circumflex  arteries,  the  latter  being  much  the  larger. 

The  saphenous  artery  is  large.  It  descends  as  in  the  ox  on  the  medial  surface 
of  the  leg  and  divides  near  the  hock  into  lateral  and  medial  tarsal  arteries.  The 
latter  is  the  real  continuation  of  the  saphenous;  it  divides  into  medial  and  lateral 
plantar  arteries,  which  concur  with  the  perforating  tarsal  artery  in  forming  the 
proximal  plantar  arch. 

The  posterior  tibial  artery  is  small,  being  replaced  distally  by  the  saphenous. 
It  gives  branches  to  the  muscles  on  the  posterior  face  of  the  tibia  and  supplies  the 
nutrient  artery  of  that  bone. 

The  anterior  tibial  artery  is  continued  as  the  dorsalis  pedis  on  the  dorsal  sur- 
face of  the  tarsus.  This  gives  off  the  perforating  tarsal  artery,  which  passes  back 
through  the  vascular  canal  of  the  tarsus  and  unites  with  the  plantar  arteries  to 
form  the  proximal  plantar  arch. 

The  metatarsal  and  digital  arteries  resemble  in  arrangement  the  corresponding 
vessels  of  the  limb. 

The  Veins 

The  veins  resemble  in  general  those  of  the  ox.  Thus  there  is  a  hemiazygos 
vein  and  two  jugular  veins,  the  internal  one  being  relatively  larger  than  in  the  ox. 
A  few  differential  features  may  be  noted. 

The  buccinator  vein  resembles  that  of  the  horse,  and  unites  with  the  vena 
refiexa  to  form  a  short  common  trunk  which  joins  the  external  maxillary  vein. 

The  external  maxillary  vein  resembles  in  general  that  of  the  horse.  The  dorsal 
nasal  vein  is  large,  receives  the  veins  from  the  snout,  runs  backward  in  the  groove 
of  the  nasal  bone,  and  joins  the  frontal  vein;  it  is  connected  with  its  fellow  by  a 
transverse  branch,  and  anastomoses  freely  with  the  malar  and  facial  veins. 

The  veins  of  the  distal  parts  of  the  limbs  naturally  present  differences  which 
are  correlated  with  those  of  the  arteries. 


The  Lymphatic  System 

The  thoracic  duct  often  divides  near  its  termination  into  two  branches  which 
unite  to  form  an  ampulla.  The  latter  suddenly  contracts  and  opens  into  the  termi- 
nal part  of  the  left  jugular  vein.  The  lymph  glands  of  animals  in  good  condition 
are  almost  all  embedded  in  fat. 

The  mandibular  lymph  glands  are  situated  in  the  space  between  the  omo- 
hyoid and  medial  pterygoid  muscles,  in  relation  to  the  lower  part  of  the  anterior 
border  of  the  mandibular  salivary  gland.  There  are  commonly  two  on  each  side, 
one  large,  the  other  small. 

The  parotid  lymph  glands  (Fig.  415)  are  reddish-brown  in  color.  There  are 
usually  four  of  considerable  size  and  several  smaller  ones  on  either  side.  One  is 
situated  at  the  upper  part  of  the  posterior  border  of  the  masseter,  partly  covered 
by  the  parotid  salivary  gland.  A  large  subparotid  gland  lies  below  the  base  of  the 
ear  on  the  terminal  part  of  the  brachiocephalicus  muscle.  Ventral  to  this  are  two 
smaller  glands,  one  above  and  one  below  the  external  maxillary  vein. 

The  supraphar3mgeal  lymph  glands  (Fig.  416)  are  situated  on  the  dorsal  wall 
of  the  pharynx,  dorsal  to  the  external  carotid  artery  and  below  and  behind  the 
paramastoid  process.     There  are  usually  two  of  considerable  size  on  either  side. 


THE   LYMPHATIC   SYSTEM 


741 


They  are  related  deeply  to  the  rectus  capitis  ventralis  major  and  are  covered  by  the 
cleido-mastoideus. 

The  middle  cervical  lymph  glands  form  a  group  on  the  brachiocephalicus 
on  the  course  of  the  external  jugular  vein.  Other  small  nodes  are  present  in  the 
fat  around  the  trachea. 

The  prescapular  lymph  glands  are  situated  at  the  anterior  border  of  the  an- 
terior deep  pectoral  muscle,  under  cover  of  the  trapezius  and  omo-transversarius. 

The  posterior  cervical  or  prepectoral  lymph  glands  are  reddish  in  color  and 
usually  three  in  number.  The  largest  is  placed  centrally  under  the  trachea;  the 
others  are  situated  on  the  brachial  vessels  as  thev  turn  around  the  first  rib. 


Jig.  611. — Stomach  and  Part  of  Intestine  of  Pig,  Spread  Odt. 

o,  Pyloric  part  of  stomach-    6,   duodenum;    c,   jejunum;   d,  cacum;   e,   /,   colon;   g,  pancreas;   h,  epiploic  foramen; 

I,  portal  vein;  A:,  hepatic  lymph  glands;  i,  gastric  lymph  glands;   m,  oesophagus.     (After  Edelmann.j 


The  axillary  lymph  glands  are  usually  absent,  but  very  small  nodes  may  be 
found  near  the  insertion  of  the  latissimus  dorsi.     Cubital  glands  are  not  present. 

The  thoracic  lymph  glands  comprise  the  following: 

(1)  A  sternal  lymph  gland  of  relatively  large  size  lies  on  the  first  segment  cf  the 
sternum.  (2)  The  mediastinal  l5miph  glands  include:  a  number  of  small  reddish 
nodes  in  the  fat  along  the  dorsal  surface  of  the  aorta;  a  gland  on  the  left  side  of  the 
trachea  in  front  of  the  aortic  arch ;  a  gland  on  the  aorta  where  it  is  crossed  by  the 
vena  hemiazygos;  two  or  three  glands  in  the  posterior  mediastinum  along  ohe 
ventral  surface  of  the  aorta;  several  glands  along  the  ventral  surface  of  the  trachea. 
(3)  The  bronchial  lymph  glands  include  one  on  the  bifurcation  of  the  trachea  and 
another  at  the  apical  bronchus  of  the  right  lung. 


742  CIRCULATORY  SYSTEM  OF  THE  DOG 

The  lumbar  lymph  glands  are  scattered  along  the  abdominal  aorta  and  the  vena 
cava.     Those  placed  near  the  hilus  of  the  kidney  are  often  designated  renal. 

The  internal  iliac  lymph  glands  are  rounded  and  relatively  large.  They 
comprise:  (1)  Three  or  four  glands  situated  on  and  between  the  origin  of  the  cir- 
cumflex iliac  and  the  external  and  internal  iliac  arteries;  (2)  a  gland  in  the  angle 
of  divergence  of  the  internal  iliac  arteries;  (3)  several  glands  along  the  course  of 
the  external  iliac  artery,  the  most  ventral  of  which  is  usually  the  largest,  and  might 
be  regarded  as  a  deep  inguinal  gland. 

The  external  iliac  lymph  glands  are  small,  three  or  four  in  number,  and  lie  in 
front  of  the  circumflex  iliac  vessels. 

The  visceral  lymph  glands  of  the  abdomen  comprise  the  following: 

1.  The  gastric  lymph  glands  are  situated  on  the  lesser  curvature  of  the  stomach, 
covered  by  the  pancreas  in  situ.  They  are  commonly  five  or  six  in  number  and  are 
in  series  with  the  hepatic  glands. 

2.  Several  hepatic  lymph  glands  (Fig.  429)  are  present  about  the  portal  vein 
at  the  portal  fissure.     The  largest  ones  are  about  an  inch  (ca.  2-3  cm.)  long. 

3.  A  long  splenic  lymph  gland  lies  on  the  splenic  vessels  near  the  dorsal  end 
of  the  spleen. 

4.  The  mesenteric  lymph  glands  are  situated  along  the  anastomotic  arches 
formed  by  the  vessels  of  the  small  intestine. 

5.  Several  caecal  lymph  glands  are  situated  along  the  first  part  of  the  csecal 
vessels. 

6.  Two  series  of  colic  lymph  glands  accompany  the  arteries  of  the  spiral  part  of 
the  colon,  and  are  exposed  by  separating  the  coils  of  the  bowel.  Small  glands  are 
placed  in  the  colic  mesentery  and  above  the  rectum. 

7.  The  anal  lymph  glands  are  situated  on  either  side  on  the  retractor  ani. 

A  small  ischiatic  lymph  gland  is  found  on  the  sacro-sciatic  ligament  near  the 
lesser  sciatic  notch. 

The  prefemoral  lymph  gland  is  situated  on  the  aponeurosis  of  the  external 
oblique  muscle  at  the  anterior  border  of  the  tensor  fasciae  latae,  and  a  little  above  the 
middle  of  the  thigh.  It  has  an  elongated  oval  outline,  and  in  the  adult  may  be 
about  two  inches  (ca.  5  cm.)  long,  and  nearly  an  inch  (ca.  2  cm.)  wide.  It  is  em- 
bedded in  fat. 

The  superficial  inguinal  lymph  glands  form  an  extensive  group,  which  may  be 
five  inches  or  more  (ca.  10-12  cm.)  in  length.  The  middle  part  of  the  group  is  at 
the  external  inguinal  ring,  and  the  series  extends  back  on  the  upper  part  of  the 
gracilis  and  forward  and  outward  on  the  aponeurosis  of  the  obliquus  abdominis 
externus.  They  number  about  a  dozen;  the  largest  are  about  an  inch  (ca.  2-3  cm.) 
long,  and  the  others  about  the  size  of  a  pea. 

The  popliteal  lymph  glands  are  small  normally  and  may  escape  notice.  They 
are  more  superficially  placed  than  in  the  other  animals,  and  are  in  part  in  contact 
with  the  skin. 

A  few  small  tarsal  glands  occur  in  front  of  the  distal  part  of  the  tendo  Achillis. 
The  occurrence  of  a  gland  in  the  subcutaneous  fat  about  a  handbreadth  above  the 
tuber  calcis  has  been  noted  by  Hartenstein;  it  varies  from  the  size  of  a  pea  to  that 
of  a  hazel  nut. 


CIRCULATORY  SYSTEM  OF  THE  DOG 
Tpie  Pericardium  and  Heart 

The  pericardium  is  attached  to  the  sternal  part  of  the  diaphragm  by  a  fibrous 
band,  the  pericardiaco-phrenic  ligament  (Lig.  pericardiaco-phrenicum).  and  is  con- 
nected with  the  sternum  only  by  the  mediastinal  pleura. 


THE    PERICARDIUM   AND    HEART  743 

The  area  of  contact  of  the  pericardium  with  the  chest  wall  is  chiefly  ventral,  and  is  best  seen 
with  the  subject  on  its  back.  In  this  position  (after  removal  of  the  intercostal  and  rectus  thoracis 
muscles),  the  area  is  seen  to  be  almost  triangular.  The  anterior  border  of  the  triangle  (formed  by 
the  apical  lobe  of  the  right  lung)  is  at  the  right  fourth  costal  cartilage  and  extends  across  the  median 
plane,  ending  at  the  third  interchondral  space  near  the  costo-chondral  junction.  The  right  border 
extends  from  the  sternal  end  of  the  fourth  rib  to  the  eighth  chondro- sternal  joint.  The  left  border 
begins  at  the  left  end  of  the  anterior  border,  crosses  the  fourth  cartilage  nearly  an  inch  from  its 
jimction  with  the  rib  and  the  fifth  and  sixth  chondro-costal  junctions. 

The  heart  differs  greatly  in  form  and  position  from  that  of  the  larger  animals. 
In  diastole  it  is  ovoid  and  the  apex  is  blunt  and  rounded.  Its  long  axis  is  very- 
oblique.  Thus  the  base  faces  chiefly  toward  the  thoracic  inlet  and  is  opposite  to 
the  ventral  part  of  the  third  rib.  The  apex  is  on  the  left  side  at  the  sixth  inter- 
chondral space  or  seventh  costal  cartilage,  and  in  close  relation  to  the  sternal  part 
of  the  diaphragm.  The  sterno-costal  surface  corresponds  largely  to  the  floor  of 
the  thorax  from  the  fifth  chondro-sternal  joint  backward.     It  is  crossed  obliquely 

Aorta 

^^      Lieji  piu- 

Pulmonary  veins 


Left  brachial      ■^//fn^mmt^^  m^^B^^^-^^S  T^BH^^^^  Posterior  vena  cava 

artery 

Brachiocephalic  " 
artery 
Anterior  vena  - 
cava 

Right  auricle 

Pulmonary  artery  ""^^UF  ■^^  7^^^!*^^"**^     '^ ^ \'^^^l^^^,^  Left  ventricle 

Conns  arteriosus 


Right  ventricle  . 

Apex 

Fig.  612. — Heart  of  Dog;  Left  View. 
1,  Pulmonary  veins;    3,  left  auricle;   3,  vessels  and   fat  in  coronary  groove;  4,  vessels  and  fat  in  left  or  ventral  longitu- 
dinal groove;   5,  vessels  and  fat  in  intermediate  groove. 

by  the  left  (or  ventral)  longitudinal  groove,  which  begins  behind  the  origin  of  the 
pulmonary  artery,  and  joins  the  right  (or  dorsal)  groove  at  the  right  border,  thus 
forming  a  notch  not  far  from  the  apex.  The  diaphragmatic  surface  is  less  ex- 
tensive and  less  convex.  On  it  is  the  right  (or  dorsal)  longitudinal  groove,  which 
begins  at  the  coronary  groove  just  behind  the  termination  of  the  posterior  vena 
cava  and  joins  the  left  (or  ventral)  groove  to  the  right  of  the  apex.  There  is  fre- 
quently an  intermediate  groove  between  these  on  the  left  ventricle,  which  extends 
a  variable  distance  toward  the  apex.  The  weight  of  the  heart  of  a  dog  of  medium 
size  is  five  to  six  ounces,  and  is  about  1  per  cent,  of  the  body  weight. 

The  relative  weight  is  subject  to  wide  variation.  It  is  large  in  hunting  dogs  and  such  as  are 
trained  for  speed  or  worked.     In  fat  dogs  of  sedentary  habit  it  may  be  only  about  0.5  per  cent. 

The  fossa  ovalis  is  very  shallow  and  is  bounded  in  front  by  the  intervenous  crest.  The  musculi 
pectinati  form  a  rich  network  in  the  right  auricle.  The  tricuspid  valve  has  two  chief  cusps  and 
three  or  four  small  ones.  There  are  four  musculi  papillares  in  the  right  ventricle,  all  of  which 
spring  from  the  septal  wall.  They  diminish  in  size  from  before  backward,  the  anterior  ones  being 
long  and  cylindrical.     Their  bases  are  connected  with  the  lateral  wall  by  trabecular  camese.     Usu- 


744 


CIRCULATORY  SYSTEM  OF  THE  DOG 


alh'  sLx  pulmonary  veins  open  into  the  left  atrium.  The  bicuspid  valve  consists  of  two  large  cusps 
and  four  or  five  small  ones.  There  are  two  musculi  papillares  in  the  left  ventricle,  both  of  which 
arise  from  the  lateral  wall;   they  are  much  larger  than  those  of  the  right  ventricle. 

The  Arteries 

The  two  coronary  arteries  usually  spring  separately  from  the  origin  of  the  aorta, 
but  may  arise  by  a  common  trunk.  Each  divides  into  circumflex  and  descending 
branches.  The  left  artery  is  twice  as  large  as  the  right  one;  it  commonly  gives  off 
a  branch  of  considerable  size  which  runs  in  the  intermediate  groove. 


Fig.  61.3. — Vessels,  Nerves,  Etc.,  op  Thorax  of  Dog;  Right  View. 
i,  First  rib  (stump) ;  ^,  sceruum;  ^^  mauuDnum  sterni;  .2",  xipnoid  cartilage;  3,  trachea;  .^.oesophagus;  6-8, 
ventral  branches  of  tilth  to  eigntn  cervical  nerves;  9,  ventral  branch  ot  hrst  thoracic  nerve;  10,  Iff ,  muscular  and  ten- 
dinous parts  of  diaphragm;  11,  11',  left  ventricle  and  atrium  of  heart;  12,  12' ,  right  ventricle  and  auricle  of  heart;  IS, 
coronary  groove;  H,  right  coronary  artery;  15,  middle  cardiac  vein;  16,  pulmonary  veins;  17,  aorta;  18,  thoracic 
duct;  i5,  anterior  vena  cava;  ;20,  posterior  vena  cava;  ;2i,  dorsal  intercostal  vessels;  ;2^,  intercostal  nerve;  i^3,  inferior 
cervical  (or  omo-cervical)  artery;  ^4.  external  thoracic  artery;  25,  brachial  vessels;  26,  common  jugular  vein;  27,  in- 
ternal thoracic  vessels;  28,  sternal  branches  of  internal  thoracic  vessels;  29,  mediastinal  arteries;  30,  musculo-phrenic 
artery;  SI,  anterior  abdominal  artery;  S2,  m.  iongus  colU;  3S,  anterior  mediastinal  lymph  glands;  3^,  sternal  lymph 
glands;  a,  a',  right  brachial  artery  and  vein;  b,  common  carotid  artery;  c,  deep  cervical  vessels;  d,  vertebral  vessels; 
e,  dorsal  vessels;  /,  subcostal  vessels;  ff,  A,  dorso-cervical  trunks;  i,  vena  azygos;  ^,  recurrent  nerve;  i,  vago-sympathetic 
nerve;  I',  I",  dorsal  and  ventral  branches  of  vagus;  rn,  phrenic  nerve;  n,  roots  of  phrenic  nerve;  o,  thoracic  trunk  of 
sympathetic;  o',  nerve  loop  formed  around  brachial  artery  by  branches  which  connect  posterior  cervical  and  first  tho- 
racic ganglia  of  sympathetic  (Ansa  subclavia) ;  p,  thoracic  ganglia  of  sympathetic;  q,  rami  communicantes;  r,  posterior 
cervical  ganglion;  s,  first  thoracic  ganglion;  t,  u,  v,  rami  communicantes  between  s  and  seventh  cervical,  first  thoracic, 
and  eighth  cervical  nerves;  w,  cardiac  branch  of  first  thoracic  ganglion;  J-,  cardiac  branches  of  posterior  cervical  gan- 
glion:  y,  bronchial  branches  of  vagus;  z,  depressor  nerve.     (After  Bucher.) 


The  aorta  runs  at  first  almost  straight  forward  and  then  turns  backward, 
forming  a  very  sharply  curved  arch.  It  gives  off  at  its  origin  the  two  coronary 
arteries.  From  the  convexity  of  the  arch  two  large  vessels  arise.  The  first  and 
larger  of  these  is  the  brachiocephalic  artery;  this  runs  forward  at  first  on  the 
ventral  surface  of  the  oesophagus,  then  under  the  trachea.  It  gives  off  in  succession 
the  left  and  right  common  carotid  arteries,  and  turns  around  the  first  rib  as  the 
right  brachial  artery.  The  left  brachial  artery  passes  forward  on  the  left  face  of 
the  oesophagus,  forming  a  slight  arch  (concave  ventrally),  and  turns  around  the  first 
rib.     The  intrathoracic  branches  of  the  brachial  arteries  are  as  follows: 


THE   ARTERIES 


745 


(1)  The  vertebral  artery  arises  opposite  the  first  intercostal  space  from  the 
dorsal  face  of  the  parent  trunk.  It  runs  forward  on  the  longus  colli  (crossing  the 
trachea  on  the  right  side),  and  passes  along  the  neck  in  typical  fashion  to  the  third 
cervical  vertebra,  where  it  divides  into  three  branches.  The  largest  of  these  supplies 
the  muscles  in  this  region,  compensating  for  the  absence  of  branches  of  the  deep 
cervical  artery.  The  second  passes  between  the  second  and  third  cervical  vertebrae 
into  the  vertebral  canal  and  unites  with  the  opposite  artery  and  a  branch  of  the 
occipital  artery  to  form  the  basilar  artery.     The  third  branch  is  the  small  continua- 


FiG.  614. — Vessels,  Nerves,  Etc.,  op  Thorax  or  Dog;  Left  View. 
1,  First  rib  (stump) :  2,  sternum;  2',  manubrium  sterni;  2'',  xiphoid  cartilage;  3,  trachea;  3',  bifurcation  of  trachea; 
4,  oesophagus;  6-8,  ventral  branches  of  fifth  to  eighth  cervical  nerves;  5,  ventral  branch  of  first  thoracic  nerve;  10,  Iff, 
muscular  and  tendinous  parts  of  diaphragm;  11,  11',  left  ventricle  and  auricle  of  heart;  12,  12',  right  ventricle  and  auricle 
of  heart;  13,  13' ,  left  coronary  artery  (descending  branch)  and  great  cardiac  vein;  H,  branch  of  left  coronary  artery  in 
intermediate  groove;  ^5,  pulmonary  artery;  / 6,  pulmonary  veins;  17,  18,  auorta.;  / 5,  anterior  vena  cava;  20,  20',  20", 
intercostal  nerve,  artery,  and  vein;  21,  thoracic  duct;  22,  22',  internal  thoracic  vessels;  23,  sternal  branches  of  22;  24, 
mediastinal  arteries;  25,  musculo-phrenic  artery;  26,  anterior  abdominal  artery;  27,  inferior  cervical  (or  omo-cervical) 
artery;  28,  brachial  vessels;  29,  external  thoracic  artery;  30,  left  common  jugular  vein;  31,  m.  longus  colli;  32,  an- 
terior mediastinal  lymph  glands;  S3,  sternal  lymph  glands;  a,  brachiocephalic  artery;  h,  b',  common  carotid  arteries; 
c,  c',  brachial  arteries;  d,  left  brachial  vein;  e,  e',  dorso-cervical  vessels;  /,  /',  vertebral  vessels;  g,  dorsal  vessels;  h, 
subcostal  vessels;  i,  deep  cervical  vessels;  k,  recurrent  nerve;  I,  vago-sympathetic  trunk;  /',  I",  dorsal  and  ventral 
branches  of  vagus;  m,  phrenic  nerve;  n,  roots  of  phrenic  nerve  from  fifth  to  seventh  cervical  nerves;  o,  thoracic  trunk 
of  sympathetic;  o',  ansa  subclavia  formed  by  branches  connecting  posterior  cervical  and  first  thoracic  ganglia;  o", 
great  splanchnic  nerve;  p,  thoracic  ganglia  of  sympathetic;  g,  rami  communicantes;  r,  posterior  cervical  ganglion;  s, 
first  thoracic  ganglion  of  sympathetic;  t,  v,v,  rami  communicantes  connecting  s  with  seventh  and  eighth  cervical  and 
first  thoracic  nerves;  w,  cardiac  branch  of  first  thoracic  nerve;  x,  cardiac  nerves  from  posterior  cervical  ganglion ;  y, 
bronchial  branches  of  vagus ;  2,  depressor  nerve,     (.\fter  Bucher.) 


tion  of  the  parent  trunk;    it  passes  to  the  wing  of  the  atlas  and  anastomoses  with 
the  occipital  artery. 

(2),  (3)  The  dorsal  and  deep  cervical  arteries  arise  by  a  common  trunk  close 
to  the  vertebral.  The  trunk  crosses  the  lateral  face  of  the  latter,  ascends  on  the 
longus  colli,  and  divides  into  two  branches.  The  anterior  branch,  the  deep  cervical 
artery,  emerges  medial  to  the  upper  end  of  the  first  rib  and  ramifies  in  the  deep 
muscles  of  the  neck.  The  dorsal  artery  gives  off  the  subcostal  artery  (which 
supplies  two  or  three  intercostal  arteries)  and  emerges  through  the  dorsal  end  of 
the  first  intercostal  space  and  ramifies  in  the  spinal  muscles. 


746 


CIRCULATORY  SYSTEM  OF  THE  DOG 


(4)  The  inferior  cervical  artery  arises  at  the  first  rib,  and  gives  off  the  ascending 
cervical  and  transverse  scapular  arteries.  The  former  runs  on  the  deep  face  of  the 
brachiocephahcus,  in  which  it  ramifies.  Tlie  latter  goes  to  the  anterior  border  of 
the  subscapularis,  and  its  largest  branch  (equivalent  to  the  prescapular  of  the  horse) 
accompanies  the  suprascapular  nerve. 

(5)  The  internal  thoracic  artery  is  large  and  sends  perforating  branches  to  the 
pectoral  mammary  glands. 

The  axillary  part  of  the  brachial  artery  gives  off  the  thoraco-acromial  and  ex- 
ternal thoracic  arteries. 

The  thoraco-acromial  artery  supplies  branches  to  the  deltoid  and  pectoral 
muscles. 

The  external  thoracic  artery  passes  backward  under  cover  of  the  deep  pectoral 


Fig.  615. — Superficial  Vessels  of  Head  of  Dog. 
1,  Facial  artery;  3,  inferior  labial  artery;  3,  artery  of  angle  of  mouth;  4t  superior  labial  artery;  6,  lateral  nasal 
artery;  6,  dorsal  nasal  artery;  7,  superficial  temporal  artery;  S,  transverse  facial  artery;  9,  anterior  auricular  artery; 
iO,  zygomatico-orbital  artery;  7/,  satellite  vein  of  iO;  /^,  ant.  auricular  vein;  i 5,  superficial  temporal  vein;  74.  internal 
maxillary  vein;  lo,  post,  auricular  vein;  IG,  17,  external  jugular  vein;  IS,  external  maxillary  vein;  19,  23,  facial  vein; 
;?0,  inf.  labial  vein;  ^7,  buccinator  vein;  ;92,  vena  reflexa ;  ;?4,  superior  labial  vem;  £5,  vena  angularis  oculi;  26,AoTsa.\ 
nasal  vein;  a,  concha;  b,  parotid  gland;  c,  mandibular  gland;  d,  mandibular  lymph  glands;  e,  mylo-hyoideus;  /, 
digastricus;  g,  masseter;  h,  zygomaticus;  i,  scutularis;  k,  temporalis;  I,  orbicularis  oculi;  m,  zygomatic  arch;  n,  re- 
tractor anguli  oris;   o,  buccinator.      (EUenberger-Baum,  Anat.  d.  Hundes.) 


muscle  and  ends  in  the  abdominal  cutaneous  muscle.  It  sends  branches  to  the 
mammary  glands. 

The  common  carotid  arteries,  left  and  right,  arise  in  that  order  from  the 
brachiocephalic.  In  the  neck  the  right  one  lies  on  the  trachea,  the  left  on  the 
oesophagus.  Collateral  branches  are  the  posterior  th3n:oid  (which  may,  however, 
arise  from  the  right  or  left  ])rachial  or  the  inferior  cervical),  pharyngeal,  anterior 
thjrroid,  larjmgeal,  muscular,  tracheal,  and  glandular  (to  the  mandibular  gland). 
Each  carotid  divides  under  the  wing  of  the  atlas  into  occipital  and  internal  and  ex- 
ternal carotid  branches. 

The  occipital  artery  is  small;  it  ascends  behind  the  hypoglossal  nerve  to  the 
paramastoid  process,  crossing  laterally  the  internal  carotid  artery  and  vagus  and 
sympathetic  nerves.    It  curves  over  the  paramastoid  process  and  pursues  a  flexuous 


THE    ARTERIES  747 

course  on  the  nuchal  surface  of  the  occipital  bone  parallel  with  the  nuchal  crest, 
anastomoses  with  the  opposite  artery,  and  ramifies  in  the  nuchal  muscles.  It 
gives  collateral  branches  to  the  ventral  straight  muscles  and  to  the  pharynx.  It 
also  gives  off  the  condyloid  and  posterior  meningeal  arteries.  The  latter  passes 
through  the  mastoid  foramen  and  ramifies  in  the  dura  mater.  The  cerebrospinal 
artery  passes  through  the  intervertebral  foramen,  and  unites  in  the  vertebral  canal 
with  its  fellow  and  a  branch  from  the  vertebral  artery  to  form  the  basilar  artery. 
The  recurrent  branch  anastomoses  with  the  vertebral  as  in  the  horse. 

The  internal  carotid  artery,  also  small,  arises  just  behind  the  occipito-mandib- 
ularis  muscle;  it  passes  to  the  foramen  lacerum  posterius,  enters  the  carotid  canal, 
and  forms  a  bend  before  entering  the  cranial  cavity  through  the  carotid  foramen. 
It  forms  a  plexus  which  is  connected  by  branches  with  the  middle  meningeal  and 
external  ophthalmic  arteries.  It  then  perforates  the  dura  mater  and  enters  into 
the  formation  of  the  circulus  arteriosus,  which  is  formed  in  a  manner  similar  to  that 
of  the  horse.  The  anterior  cerebral  artery  gives  off  the  internal  ophthalmic  artery 
which  accompanies  the  optic  nerve  to  the  eyeball.  The  middle  cerebral  artery  is 
large,  and  gives  off  the  choroid  artery. 

The  external  carotid  artery  is  the  direct  continuation  of  the  common  carotid. 
It  passes  along  the  lateral  wall  of  the  pharynx,  emerges  from  beneath  the  occipito- 
mandibularis,  and  divides  behind  the  postglenoid  process  into  superficial  temporal 
and  internal  maxillary  arteries.  It  gives  off  the  following  collateral  branches: 
The  large  flexuous  lingual  artery  passes  to  the  side  of  the  root  of  the  tongue,  runs 
forward  under  cover  of  the  hyo-glossus,  and  continues  to  the  tip  of  the  tongue  in 
company  with  a  satellite  vein  and  the  hypoglossal  nerve.  It  ramifies  in  the 
tongue  and  gives  collateral  branches  to  the  pharynx  and  soft  palate.  The  external 
maxillary  artery,  smaller  than  the  lingual,  passes  along  the  upper  border  of  the  occipi- 
to-mandiljularis,  gives  off  the  sublingual,  gains  the  anterior  border  of  the  masseter, 
and  divides  into  superior  and  inferior  labial  and  the  angularis  oris.  The  last-named 
vessel  passes  forward  on  the  cheek  between  the  labials  to  the  angle  of  the  mouth. 
The  sublingual  artery  passes  along  the  upper  border  of  the  occipito-mandibularis, 
then  between  the  mylo-hyoideus  and  the  ramus  of  the  mandible.  The  great  auric- 
ular artery  arises  at  the  anterior  border  of  the  occipito-mandibularis,  gives  branches 
to  the  parotid  and  mandibular  salivary  glands  and  the  adjacent  muscles,  and  ter- 
minates in  three  auricular  branches  which  ramifj^  on  the  convex  face  of  the  concha. 
These  branches  anastomose  with  each  other  and  the  anterior  auricular  artery. 

The  superficial  temporal  artery,  after  giving  off  the  anterior  auricular  artery 
and  a  small  transverse  facial  artery,  turns  forward  under  the  temporal  fascia  toward 
the  eye,  and  divides  into  upper  and  lower  branches  which  supply  the  frontal  region 
and  the  eyelids.  It  also  supplies  branches  to  the  parotid  gland  and  the  masseter 
and  temporalis  muscles. 

The  internal  maxillary  artery  pursues  a  course  similar  to  that  of  the  horse, 
and  ends  in  the  pterygo-palatine  fossa  by  dividing  into  the  infraorbital  artery  and  a 
common  trunk  for  the  greater  jjalatine  and  sphenopalatine  arteries.  The  mental 
branches  of  the  inferior  alveolar  artery  are  of  considerable  size  and  are  distributed 
in  the  lower  lip  and  gums.  Two  or  three  deep  temporal  arteries  are  present;  the 
anterior  one  may  arise  from  the  buccinator  artery.  The  middle  meningeal  artery 
enters  the  cranium  through  the  foramen  ovale,  ramifies  in  the  dura  mater,  and  sends 
a  branch  to  the  carotid  plexus.  The  external  ophthalmic  artery  is  comiected  with 
the  internal  carotid  by  a  large  ramus  anastomoticus  which  passes  through  the 
orbital  foramen.  The  superficial  branches  of  the  infraorbital  artery  replace  the 
dorsal  and  lateral  nasal  arteries,  and  compensate  for  the  small  size  of  the  superior 
labial. 

The  brachial  artery  in  its  course  in  the  arm  presents  no  special  features.  At 
the  elbow  it  passes  l^etween  the  biceps  and  the  pronator  teres,  descends  as  the 


748 


CIRCULATORY  SYSTEM  OF  THE  DOG 


median  artery  under  the  flexor  carpi  radialis  about  a  third  of  the  way  down  the 
forearm,  and  divides  into  radial  and  ulnar  arteries.  Among  its  collateral  branches 
axe  the  following:    (1)  The  large  subscapular  artery  passes  up  between  the  sub- 


FiG.  616. — Vessels  and  Nerves  op  Medial  Surface 
OF  Shoulder  and  Arm  of  Dog. 
a,  b,  Brachial  artery;  c,  subscapular  vessels;  d, 
thoraco-dorsal  vessels;  c,  deep  brachial  vessels;  /,  prox- 
iDial  collateral  ulnar  vessels;  g,  brachial  vein;  h,  h", 
cephalic  vein;  h',  mediano-radial  vein;  i,  anterior  tho- 
racic nerves;  k,  musculo-cutaneoua  nerve;  I,  median 
nerve;  m,  ulnar  nerve;  n,  radial  nerve;  o,  thoraco- 
dorsal nerve;  1,  aubscapularis  muscle;  2,  supraspinatus 
muscle;  3,  teres  major;  4,  latissimus  dorsi;  5,  deep 
pectoral  muscle;  6,  biceps  brachii;  7,  long  head  of  tri- 
ceps; 8,  tensor  fasciae  antibrachii;  9,  medial  head  of 
triceps;  10,  pronator  teres.  (EUenberger-Baum,  Anat. 
d.  Hundes.^ 


Fig.  617. — Arteries  op  Forearm  op  Dog;  Medial 
View. 
Arteries:  a.  Brachial;  a',  median;  f,  common  interos- 
seous; d,  volar  antibrachial;  e,  radial;  e',  e",  dorsal 
and  volar  branches  of  e;  f,  /',  cutaneous  branches  of  e; 
g,  ulnar.  Muscles:  1,  Biceps  brachii;  2,  extensor  carpi 
radialis;  3,  pronator  teres;  4.  deep  digital  flexor;  5, 
radius;  6,  superficial  digital  flexor;  7,  flexor  carpi  radi- 
aUs;  S,  ulnaris  lateralis;  9,  humerus.  ( Ellenberger- 
Baum,  Anat.  d.  Hundes.) 


scapularis  and  teres  major,  turns  around  the  posterior  angle  of  the  scapula,  and 
terminates  in  the  supraspinatus,  deltoid,  trapezius,  and  brachiocephalicus.  In 
about  half  the  cases  it  gives  off  the  anterior  circumflex,  which  often  arises  with  the 


THE    ARTERIES  749 

posterior  circumflex.  Its  other  branches  resemble  those  of  the  horse.  (2)  The 
anterior  circumflex  artery  in  about  half  the  cases  arises  from  the  brachial.  (3) 
The  deep  brachial  artery  arises  about  a  third  of  the  way  down  the  arm.  (4)  The 
bicipital  artery  (for  the  biceps)  is  given  off  at  the  distal  third  of  the  arm.  (5)  The 
proximal  collateral  ulnar  artery  arises  almost  opposite  to  the  preceding  vessel.  It 
ramifies  chiefly  in  the  distal  part  of  the  triceps,  and  sends  a  superficial  branch  to  the 
medial  and  posterior  surfaces  of  the  proximal  part  of  the  forearm.  (6)  The  proxi- 
mal collateral  radial  artery  (not  present  in  the  horse)  arises  at  the  distal  fourth  of 
the  arm,  crosses  over  the  terminal  part  of  the  biceps,  descends  on  the  extensor 
carpi  radialis,  and  concurs  with  a  branch  of  the  volar  interosseous  artery  in  forming 
the  rete  carpi  dorsale.  It  often  supplies  the  bicipital  artery.  (7)  The  distal  col- 
lateral radial  artery  is  very  small;  it  accompanies  the  deep  branch  of  the  radial 
nerve  on  the  dorsal  surface  of  the  forearm  and  supplies  branches  to  the  elbow  joint 
and  the  brachialis,  supinator,  and  extensor  muscles.  (8)  The  common  interosseous 
artery  is  given  off  from  the  median  a  little  below  the  elbow.  It  supplies 
branches  to  the  flexor  muscles  and  gives  off  the  dorsal  interosseous  artery, 
which  passes  through  the  interosseous  space,  gives  branches  to  the  extensor  muscles, 
and  by  its  terminal  twigs  concurs  in  the  formation  of  the  rete  carpi  dorsale.  The 
direct  continuation  of  tne  trunk  is  the  volar  interosseous  artery,  which  descends 
along  the  interosseous  space  undei  cover  of  the  pronator  quadratus,  gives  off  a 
branch  to  the  rete  carpi  dorsale  and  the  fifth  volar  metacarpal  artery,  and  termin- 
ates by  joining  the  volar  branch  of  the  radial  artery  to  form  the  deep  volar  arch. 
(9)  The  volar  antibrachial  artery  (Ramus  volaris  antibrachii)  arises  below  the 
interosseous  and  descends  at  first  under  the  flexor  carpi  radialis,  then  between  the 
heads  of  the  deep  flexor,  and  divides  into  ascending  and  descending  branches  which 
ramify  in  the  muscles  mentioned. 

The  radial  artery,  the  smaller  terminal  of  the  mechan,  descends  along  the 
medial  border  of  the  radius,  and  divides  near  the  carpus  into  dorsal  and  volar 
branches.  The  dorsal  branch  assists  in  forming  the  rete  carpi  dorsale.  The  larger 
volar  branch  descends  behind  the  medial  border  of  the  carpus  and  joins  the  end  of 
the  volar  interosseous  in  forming  the  deep  volar  arch.  The  arch  extends  across 
the  interossei  at  the  proximal  part  of  the  metacarpus.  From  this  arch  three  deep 
volar  metacarpal  arteries  descend  in  the  second,  third,  and  fourth  intermetacarpal 
spaces  and  concur  with  the  corresponding  superficial  volar  and  the  dorsal  meta- 
carpal arteries  to  form  the  common  digital  arteries. 

The  ulnar  artery  is  much  the  larger  of  the  two  terminal  branches  of  the  median. 
It  descends  with  the  median  nerve  along  the  medial  border  of  the  deep  flexor  of  the 
digit,  and  sends  a  connecting  branch  to  the  radial  above  the  carpus.  It  then  in- 
clines somewhat  laterally  and  passes  between  the  superficial  and  deep  flexor  tendons. 
Near  the  middle  of  the  metacarpus  it  gives  off  the  first  volar  metacarpal  artery  and 
divides  into  the  second,  third,  and  fourth  superficial  volar  metacarpal  arteries. 
The  first  volar  artery  unites  with  the  corresponding  dorsal  artery  to  form  the  first 
common  digital  artery,  which  supplies  proper  digital  arteries  for  the  opposed  sur- 
faces of  the  first  and  second  digits.  The  superficial  volar  arteries  descend  in  the 
spaces  between  the  other  metacarpal  bones,  and  unite  near  the  metacarpo-phalangeal 
joints  with  the  corresponding  deep  volar  and  dorsal  metacarpal  arteries  to  form 
three  common  digital  arteries.  Each  of  the  latter  divides  after  a  short  course  into 
two  proper  digital  arteries,  which  run  along  the  opposed  surfaces  of  the  second  to 
the  fifth  digits.  The  lateral  digital  artery  of  the  fifth  digit  comes  from  the  super- 
ficial volar  arch  formed  by  the  union  of  a  branch  of  the  volar  interosseous  with  the 
fourth  superficial  volar  metacarpal  artery. 

The  rete  carpi  dorsale  gives  off  four  dorsal  metacarpal  arteries  which  descend 
in  the  intermetacarpal  spaces  and  unite  near  the  metacarpo-phalangeal  joints  with 
the  volar  arteries  to  form  the  common  digitals. 


750 


CIRCULATORY   SYSTEM    OF   THE    DOG 


The  thoracic  aorta  supplies  the  last  nine  or  ten  pairs  of  intercostal  arteries, 
but  no  anterior  phrenic  arteries.  It  gives  off  two  or  more  oesophageal  branches,  in 
addition  to  the  broncho-cesophageal,  which  arises  close  to  or  with  the  sixth  inter- 
costal and  ramifies  in  the  usual  manner. 

The  abdominal  aorta,  after  giving  off  the  external  iliac  arteries,  continues 
about  half  an  inch  to  an  inch  (ca.  1-3  cm.)  under  the  last  lumbar  vertebra,  gives 
off  the  internal  iliac  arteries,  and  is  continued  by  the  middle  sacral  artery  (Fig. 
624),  This  small  vessel  runs  backward  under  the  sacrum  and  coccygeal  vertebrae 
and  gives  off  branches  in  segmental  fashion.  Six  pairs  of  lumbar  arteries  are  given 
off  from  the  aorta,  the  seventh  coming  from  the  internal  iliac  artery. 


Fig.  618. — -Arteries  of  Distal  Part  of  Right  Fore 
Limb  of  Dog,  Dorsal  View. 
a,  Branch  of  volar  interosseous  artery;  6,  proximal 
collateral  radial  artery  (lateral  branch) ;  c,  radial  artery 
(dorsal  branch);  d,  rete  carpi  dorsale;  e,  deep  dorsal 
metacarpal  arteries;  /,  superficial  dorsal  metacarpal 
arteries;  g,  common  digital  arteries;  h,  proper  digital 
arteries. 


Fig.  (519. — Arteries  of  Distal  Part  of  Right  Fore 
Limb  of  Dog;  Volar  View. 
i',  Radial  artery;  j,  ulnar  artery;  k,  volar  inter- 
osseous artery;  I,  deep  volar  arch;  m,  fifth  volar  meta- 
carpal artery;  n,  deep  volar  metacarpal  arteries;  p,  super- 
ficial volar  metacarpal  arteries;  o,  q,  common  digital 
arteries;  r,  proper  digital  arteries. 


The  coeliac  artery  gives  off  the  hepatic  artery  and  forms  a  short  trunk  from 
which  the  gastric  and  splenic  arteries  arise.  The  hepatic  artery,  after  giving  off 
several  proper  hepatic  arteries,  and  the  right  gastric  artery,  which  passes  along  the 
lesser  curvature  of  the  stomach  and  anastomoses  with  the  left  gastric  artery,  is  con- 
tinued by  the  gastro-duodenal  artery.  This  divides  near  the  pylorus  into  right 
gastro-epiploic  and  pancreatico-duodenal  arteries;  the  former  supplies  branches 
to  the  pyloric  part  of  the  stomach  and  passes  along  the  greater  curvature  of  that 
viscus  in  the  omentum  and  anastomoses  with  the  left  gastro-epiploic.  The  left 
gastric  artery  passes  to  the  lesser  curvature  of  the  stomach  and  ramifies  chiefly  on 


THE    ARTERIES 


751 


the  left  part  of  the  stomach,  giving  off  a  branch  which  anastomoses  with  the  right 
gastric  artery.  The  splenic  artery  gives  off  pancreatic  branches,  and  reaches  the 
ventral  part  of  the  spleen.  It  gives  off  the  left  gastro-epiploic  and  a  gastro- 
splenic  branch  which  passes  to  the  dorsal  end  of  the  spleen,  which  it  supplies, 
besides  giving  off  twigs  to  the  left  extremity  of  the  stomach. 

The  anterior  mesenteric  artery  arises  close  behind  the  coeliac.  It  gives  off  a 
common  trunk  for  two  colic  arteries  and  the  ileo-caeco-colic.  The  right  colic 
artery  is  a  small  vessel  which  goes  to  the  right  part  of  the  colon.  The  middle 
colic  artery,  much  the  largest  of  the  colic  vessels,  supplies  the  transverse  colon 
and  part  of  the  left  colon.  The  ileo-caeco-colic  gives  off  ileal,  caecal,  and  colic 
branches.  Anastomoses  are  established  between  the  colic  arteries,  and  the  ileal 
branch  anastomoses  with  the  last  jejunal  artery.     The  trunk  is  continued  as  the 


Fig.  620. — End  Branches  of  Aorta  and  Radicles  of  Posterior  Vena  Cava  of  Dog. 
a,  Abdominal  aorta;  6,  posterior  mesenteric  artery;  c,  lumbar  arteries;  <-',  circumflex  iliac  artery;  e,  external  iliac 
artery ;/,  deep  femoral  artery ;  s,  posterior  abdominal  artery ;  /i,  external  pudic  artery;  o,  femoral  artery;  i,  i,  internal 
iliac  arteries;  k,  visceral  branch  of  i;  I,  parietal  branch  of  i;  m,  ilio-lumbar  artery;  n,  anterior  gluteal  artery;  o,  lateral 
coccygeal  artery ;  p,  posterior  gluteal  artery;  g,  umbilical  artery;  r,  middle  haemorrhoidal  artery;  /3,  posterior  haemor- 
rhoidal  artery;  s,  perineal  artery;  t,  art.  profunda  penis;  n,  art.  bulbi  urethra;  v,  art.  dorsalis  penis;  w,  middle  sacral 
artery;  o',  posterior  vena  cava;  other  veins  are  satellites  of  arteries  and  correspondingly  named;  1,  iho-psoas  muscle; 
;2,  tendon  of  psoas  minor;  3,  abdominal  muscles;  4.  sartorius;  5,  rectus  femoris;  5',  vastus  medialis;  ^;,  pectineus;  6", 
adductor;  7,  gracilis;  8,  symphysis  pelvis;  9,  ilium;  10,  piriformis;  11,  gluteus  superficialis ;  12,  obturator  internus; 
13,  penis;   14,  lumbar  vertebree.      (After  Ellenberger,  in  Leisering's  Atlas.) 


artery  of  the  small  intestine,  giving  off  fourteen  to  sixteen  branches  (Aa.  jejunales), 
which  form  a  series  of  anastomotic  arches  in  the  mesentery  near  the  bowel. 

Two  phrenico-abdominal  arteries  (Aa.  phrenicae  caudales)  come  off  from  the 
aorta  behind  the  anterior  mesenteric,  and  divide  into  phrenic  and  abdominal 
branches.  Each  phrenic  artery  diverges  from  its  fellow  in  descending  on  the  ab- 
dominal surface  of  the  corresponding  crus  of  the  diaphragm  to  the  sternal  part. 
The  medial  branches  anastomose  with  those  of  the  opposite  artery,  the  lateral 
branches  with  intercostal  arteries  chiefly.  The  abdominal  arteries  pass  outward 
across  the  psoas  muscles,  give  branches  to  the  lumbar  muscles,  the  renal  fat  and 
adrenals,  and  ramify  in  the  oblique  abdominal  muscles. 

The  renal  and  spermatic  arteries  offer  no  special  features. 

The  utero-ovarian  artery  divides  near  the  ovary  into  three  or  four  branches 


752 


CIRCULATORY  SYSTEM  OF  THE  DOG 


Pig.  621. — Arteries  of  Pelvic 
Limb  of  Dog;  Medial  Vie^v 
o,  Abdominal  aorta;  b,  fem- 
oral; c,  c',  deep  femoral;  d,  pos- 
terior abdominal;  e,  external  pudic;  /,  medial  cir- 
cumflex; g,  anterior  femoral  (accompanied  by  an- 
terior branch  of,  femoral  nerve) ;  h,  lateral  circum- 
flex; 1,  k,  muscular  branches;  I,  articular  branch;  m, 
saphenous;  n,  o,  plantar  and  dorsal  branches  of  saphen- 
ous; g,  saphenous  nerve;  r,  obturator  nerve;  1,  ilio- 
psoas; 2,  ilium;  3,  gracilis;  4,  semitendinosus;  5, 
adductor  magnus;  6,  adductor  longus;  7,  quadri- 
ceps femoris;  8,  sartorius;  9,  semimembranosus;  10, 
gastrocnemius;  i/.  tibialis  anterior;  7^,  tibia.  (Ellen- 
berger-Baum,  Anat.  d.  Hundes.) 


which  supply  the  ovary  and  uterine  tube 
and  anterior  part  of  the  cornu  of  the 
uterus,  anastomosing  with  the  uterine 
artery. 

The  posterior  mesenteric  artery  is 
small.  It  divides  into  two  branches  which 
supply  the  terminal  part  of  the  colon  and 
the  anterior  part  of  the  rectum;  the 
former  (A.  colica  sinistra)  passes  forward 
along  the  left  part  of  the  colon  and  anas- 
tomoses with  the  middle  colic  branch  of 
the  anterior  mesenteric  artery;  the  latter 
(A.  hsemorrhoidalis  cranialis)  anastomoses 
with  the  middle  hsemorrhoidal  branch  of 
the  internal  pudic  artery. 

The  circumflex  iliac  artery  usually 
arises  from  the  terminal  part  of  the 
aorta. 

The  external  iliac  artery  usually  gives 
off  no  collateral  branches. 

The  femoral  artery  has  the  usual 
course  in  the  femoral  triangle  and  canal. 
The  deep  femoral  artery  gives  off  the 
posterior  abdominal  and  external  pudic 
arteries  by  a  very  short  common  trunk 
or  separately.  In  the  female  the  external 
pudic  divides  into  anterior  and  posterior 
branches;  the  former  runs  forward,  sup- 
plies branches  to  the  superficial  inguinal 
lymph  glands,  the  mammary  glands  and 
skin,  and  anastomoses  with  the  mammary 
branch  of  the  internal  thoracic  artery ;  the 
posterior  branch  pursues  a  flexuous  course 
between  the  thighs  to  the  vulva,  where  its 
terminal  branches  anastomose  with  the 
internal  pudic  artery.  In  the  male  the 
artery  crosses  the  medial  side  of  the  sper- 
matic cord  and  runs  forward  to  the 
umbilical  region;  it  supplies  the  inguinal 
lymph  glands,  prepuce,  and  skin.  The 
anterior  femoral  artery  may  arise  by  a 
short  common  trunk  with  the  lateral  cir- 
cumflex. The  former,  accompanied  by 
the  anterior  branch  of  the  femoral  nerve, 
dips  in  between  the  rectus  femoris  and 
vastus  medialis.  The  lateral  circumflex 
artery  passes  forward  between  the  sar- 
torius medially  and  the  rectus  femoris 
and  tensor  fasciae  latse  laterally  and  sup- 
plies branches  to  these  muscles  and  the 
glutei.  In  addition  to  muscular  branches 
of  considerable  size,  an  articular  branch 
(A.  genu  suprema)  arises  a  little  below 
the  middle  of  the  thigh  and  runs  down- 


THE    ARTERIES 


753 


ward  and  forward  to  the  medial  face  of  the  stifle  joint.  The  saphenous  artery  is 
large.  It  arises  from  the  medial  surface  of  the  femoral  a  little  below  the  middle  of  the 
thigh,  descends  superficially  to  the  proximal  part  of  the  leg,  and  divides  into  two 
branches.  The  smaller  dorsal  branch  (Ramus  dorsalis)  passes  obliquely  downward 
and  forward  across  the  medial  surface  of  the  tibia  to  the  flexion  surface  of  the  hock  and 
gives  off  the  second,  third,  and  fourth  superficial  dorsal  metatarsal  arteries.  These 
descend  along  the  grooves  between  the  metatarsal  bones  and  each  divides  into  two 
proper  digital  arteries.     The  plantar  branch  (Ramus  plantaris),  which  is  much  the 


Fig.  622. — Arteries  of  Distal  Part  of  Right  Hind 
Limb  of  Dog;  Dorsal  View. 
a.  Lateral  branch  of  anterior  tibial  artery;  b,  an- 
terior tibial  artery;  c,  saphenous  artery  (dorsal  branch); 
d,  perforating  metatarsal  artery;  e,  dorsal  metatarsal 
arteries;  /,  deep  dorsal  metatarsal  arteries;  g,  super- 
ficial dorsa!  metatarsal  arteries;  h,  anastomoses  between 
dorsal  and  plantar  arteries;  i,  common  digital  arteries; 
i,  proper  digital  arteries. 


Fig.  623. — Arteries  of  Distal  Part  of  Right  Hind 
Limb  of  Dog;  Plantar  View. 
k,  Saphenous  arterj'  (plantar  branch);  I,  I',  medial 
and  lateral  plantar  arteries;  m,  perforating  metatarsal 
artery;  7i,  deep  plantar  metatarsal  arteries;  o,  super- 
ficial plantar  metatarsal  arteries;  p,  common  digital 
artery;  q,  proper  digital  arteries. 


larger,  descends  on  the  medial  face  of  the  gastrocnemius  and  the  long  digital  flexor. 
It  gives  off  the  lateral  tarsal  artery  to  the  lateral  surface  of  the  tarsus,  and  at  the 
plantar  face  of  the  tarsus  detaches  the  medial  and  lateral  plantar  arteries ;  these 
descend  on  either  side  of  the  deep  flexor  tendon  and  unite  with  the  perforating 
metatarsal  artery  to  form  the  proximal  plantar  arch.  The  artery  continues 
down  the  middle  of  the  plantar  surface  of  the  metatarsus  and  divides  near  the 
metacarpo-phalangeal  joints  into  three  superficial  plantar  metatarsal  arteries 
(II,  III,  IV).  These  vessels  unite  with  three  deep  plantar  metatarsal  arteries,  which 
descend  from  the  proximal  plantar  arch  and  with  branches  from  ctie  dorsal  meia- 
48 


754  CIRCULATORY   SYSTEM    OF   THE   DOG 

tarsal  arteries.  From  these  anastomoses  four  plantar  digital  arteries  result;  of 
these,  the  central  two  have  a  common  digital  trunk. 

The  popliteal  and  posterior  femoral  arteries  present  nothing  of  special  interest. 

The  posterior  tibial  artery  is  very  small,  being  replaced  largely  by  the  saph- 
enous.    It  supplies  twigs  to  the  flexor  muscles  at  the  proximal  part  of  the  leg. 

The  anterior  tibial  artery  descends  on  the  anterior  face  of  the  tibia  and  tarsus 
and  is  continued  as  the  perforating  metatarsal  artery,  which  passes  through  the 
upper  part  of  the  space  between  the  second  and  third  metatarsal  bones  and  concurs 
with  the  plantar  arteries  in  the  formation  of  the  proximal  plantar  arch.  Besides 
muscular  and  articular  branches,  the  anterior  tibial  supplies  the  fifth  dorsal  meta- 
tarsal artery  for  the  lateral  side  of  the  fifth  digit.  At  the  proximal  part  of  the  meta- 
tarsus it  gives  off  three  deep  dorsal  metatarsal  arteries  which  descend  in  the  in- 
tervals between  the  metatarsal  bones  and  concur  with  the  superficial  dorsal  meta- 
tarsal and  the  plantar  arteries  in  the  formation  of  the  digital  arteries.  The  latter 
resemble  in  general  arrangement  the  corresponding  arteries  of  the  thoracic  limb. 

The  internal  iliac  artery  (Fig.  620)  runs  backward  and  a  little  outward  across 
the  ilio-psoas,  and  on  reaching  the  ilium  divides  into  parietal  and  visceral  branches; 
it  gives  off  the  seventh  lumbar  artery.  The  parietal  branch  is  the  larger.  It  runs 
backward  on  the  lateral  wall  of  the  pelvis,  passes  out  through  the  lesser  sciatic 
notch,  and  breaks  up  into  branches  which  supply  the  muscles  of  this  region;  this 
terminal  part  may  be  regarded  as  the  posterior  gluteal  artery.  It  gives  off  the 
following  branches:  (1)  The  ilio-lumbar  artery  passes  outward  between  the  ilio- 
psoas and  the  shaft  of  the  ilium  and  ramifies  in  the  gluteus  medius,  giving  branches 
to  the  ilio-psoas  and  tensor  fasciae  latse;  it  may  arise  from  the  internal  iliac.  (2) 
The  anterior  gluteal  artery  passes  out  through  the  greater  sciatic  foramen  and  sup- 
plies branches  to  the  glutei.  (3)  Muscular  branches  go  to  the  obturator  internus, 
coccygeus,  and  retractor  ani.  (4)  The  superficial  lateral  coccygeal  artery  (A.  cau- 
dalis  lateralis  superficialis)  passes  back  at  first  on  the  lateral  face  of  the  coccygeus  and 
continues  beneath  the  skin  along  the  side  of  the  tail.  The  visceral  branch  is  equiva- 
lent to  the  internal  pudic  artery ;  it  passes  back  below  the  parietal  branch  on  the 
lateral  face  of  the  rectum,  retractor  ani,  and  coccygeus.  Its  chief  collateral  branches 
are:  (1)  The  umbilical  artery,  which  pursues  a  flexuous  course  and  supplies  twigs  to 
the  bladder,  ureter,  and  ductus  deferens.  In  the  bitch  it  gives  off  a  large  uterine 
artery  which  ramifies  chiefly  in  the  body  and  neck  of  the  uterus  and  the  vagina 
and  anastomoses  with  the  utero-ovarian.  (2)  The  middle  haemorrhoidal  artery 
arises  near  the  ischial  arch,  passes  upward  and  forward  on  the  lateral  surface  of  the 
rectum,  gains  its  dorsal  surface,  and  anastomoses  with  the  posterior  mesenteric ;  it 
supplies  the  rectum  and  the  anus,  together  with  its  muscles  and  glands.  (3)  A 
small  perineal  artery  is  detached  to  the  perineum.  In  the  male  the  trunk  turns 
around  the  ischial  arch  as  the  artery  of  the  penis  (A.  penis).  This  vessel,  after 
giving  off  the  deep  artery  of  the  penis  (A.  profunda  penis),  which  supplies  the 
artery  of  the  bulb  (A.  bulbi  urethrie)  and  enters  the  corpus  cavernosum,  is  con- 
tinued as  the  dorsal  artery  of  the  penis  (A.  dorsalis  penis)  along  the  dorsum  penis. 
In  the  female  the  terminal  branches  of  the  trunk  go  to  the  vulva,  vestibular  bulb, 
and  clitoris. 


The  Veins  1 

The  arrangement  of  the  veins  is,  of  course,  correlated  in  general  with  the 
arterial  system,  but  a  few  special  features  are  worthy  of  mention. 

The  coronary  sinus  is  a  large  but  short  trunk  formed  by  the  confluence  of  the 
cardiac  veins;   it  opens  into  the  right  atrium  below  the  posterior  vena  cava.     The 

1  Many  of  the  veins  are  shown  in  the  illustrations  of  the  arteries. 


THE    VEINS  755 

great  cardiac  vein  ascends  in  the  left  longitudinal  groove  of  the  heart  to  the  coronary 
groove,  in  which  it  courses  to  the  diaphragmatic  surface.  Here  it  is  joined  bj^  one 
or  two  lesser  cardiac  veins,  which  are  satellites  of  the  right  coronary  artery,  thus 
forming  the  coronary  sinus.  There  is  commonly  a  vein  in  the  intermediate  groove 
which  joins  the  great  cardiac  vein. 

The  anterior  vena  cava  (Figs.  613,  614)  is  formed  by  the  junction  of  short  right 
and  left  brachiocephalic  veins,  and  each  of  the  latter  results  from  the  confluence 
of  jugular  and  brachial  veins. 

The  vena  azygos  (Fig.  613)  is  continuous  behind  with  the  first  lumbar  vein;  it 
resembles  that  of  the  horse,  and  receives  at  the  ninth  or  tenth  thoracic  vertebra  a 
vena  hemiazygos. 

Two  jugular  veins  are  present  on  each  side.  The  external  jugular  vein  is  the 
chief  vein  of  the  neck;  it  is  formed  by  the  union  of  external  and  internal  maxillary 
veins  at  the  posterior  border  of  the  mandiliular  gland.  The  two  external  jugulars 
are  commonly  united  by  a  transverse  branch  below  the  cricoid  cartilage.  Each 
passes  along  the  neck  on  the  sterno-cephalicus,  covered  only  by  the  skin  and  cu- 
taneous muscle,  dips  under  the  cleido-cervicalis,  and  joins  the  internal  jugular. 
The  internal  jugular  vein  is  the  satellite  of  the  connnon  carotid  artery.  It  results 
usually  from  the  junction  of  laryngeal  and  thyroid  veins,  but  in  some  cases  it  is 
formed  by  the  confluence  of  the  ventral  cerebral  and  occipital  veins. 

The  external  maxillary  vein  arises  on  the  lateral  nasal  region  by  the  junction 
of  the  dorsal  nasal  vein  with  the  angularis  oculi.  Near  the  infraorbital  foramen  it 
receives  the  lateral  nasal  vein,  and  a  little  lower  the  superior  labial.  In  its  course 
along  the  anterior  border  of  the  masseter  it  receives  the  vena  reflexa,  which  arises 
in  the  pterygo-palatine  fossa  by  the  junction  of  infraorbital,  sphenopalatine,  and 
palatine  radicles,  together  with  a  branch  from  the  cavernous  sinus.  At  the  ventral 
border  of  the  mandible  it  is  joined  by  the  inferior  labial  vein,  which  receives  the 
buccinator  vein.  The  lingual  vein  is  connected  with  its  fellow  by  a  superficial 
transverse  branch  at  the  insertion  of  the  sterno-hyoidei.  The  sublingual  and 
submental  veins  terminate  in  a  variable  manner,  but  often  form  a  common  trunk 
which  joins  the  lingual. 

The  internal  maxillary  vein  arises  from  the  pterygoid  plexus,  formed  chiefly 
by  dorsal  lingual,  inferior  alveolar,  deep  temporal,  pterygoid,  and  meningeal  tribu- 
taries. It  receives  the  dorsal  cerebral,  auricular,  superficial  temporal,  transverse 
facial,  and  masseteric  veins,  and  often  a  trunk  formed  by  the  union  of  the  ventral 
cerebral  and  occipital  veins. 

The  brachial  and  radial  veins  are  satellites  of  the  arteries. 

The  ulnar  vein  is  usually  double.  It  unites  below  the  carpus  with  a  branch  of 
the  interosseous  vein  to  form  the  superficial  venous  arch. 

The  cephalic  vein  accompanies  the  ulnar  artery  in  the  forearm  and  joins  the 
superficial  venous  arch  below. 

The  accessory  cephalic  vein  arises  from  the  union  of  three  dorsal  metacarpal 
veins.     It  joins  the  cephalic  vein  about  the  middle  of  the  forearm. 

There  are  three  short  volar  metacarpal  veins  which  open  into  the  superficial 
venous  arch.  They  are  formed  above  the  metacarpo-phalangeal  joints  by  the 
junction  of  the  volar  digital  veins,  of  which  there  are  two  for  each  of  the  chief 
digits.     The  volar  vein  of  the  first  digit  joins  the  superficial  venous  arch. 

Each  of  the  chief  digits  has  two  dorsal  digital  veins,  while  the  first  digit  has  one. 

The  portal  vein  (Fig.  625)  is  formed  by  the  union  of  a  common  intestinal  or 
mesenteric  vein  with  the  gastro-splenic  vein.  It  receives  the  gastro-duodenal  vein. 
The  intestinal  trunk  is  formed  in  the  mesentery  by  the  confluence  of  veins  from 
the  jejunum;   it  receives  an  ileo-caeco-colic  vein. 

The  posterior  vena  cava,  its  collateral  affluents,  and  common  iliac  radicles 
present  no  special  features  of  importance. 


756  CIRCULATORY    SYSTEM    OF   THE    DOG 

The  internal  iliac  vein  corresponds  in  regard  to  its  tributaries  with  the  branches 
of  the  artery,  except  that  it  is  not  divided  into  parietal  and  visceral  branches. 

The  external  iliac,  femoral,  and  popliteal  veins  with  their  collateral  tributaries 
are  satellites  of  the  arteries. 

The  anterior  tibial  vein  is  usually  double,  and  the  posterior  tibial  vein  is  very 
small. 

The  saphenous  vein  is  the  upward  continuation  of  the  medial  plantar  meta- 
tarsal vein.  It  communicates  by  a  large  branch  with  the  dorsal  metatarsal  vein, 
and  ascends  the  leg  as  a  satellite  of  the  saphenous  artery  and  its  plantar  branch. 
The  recurrent  tarsal  vein  is  larger.  It  is  formed  at  the  lower  part  of  the  leg  by  the 
union  of  dorsal  metatarsal  and  lateral  plantar  metatarsal  veins,  crosses  the  lateral 
surface  of  the  leg  obliquely  upward  and  backward,  ascends  behind  the  gastrocnemius, 
and  joins  the  femoral  vein. 

The  metatarsal  and  digital  veins  resemble  in  general  the  corresponding  vessels 
of  the  forelimb. 


The  Lymphatic  System 

The  cisterna  chyli  is  relatively  large  and  is  fusiform;  it  is  ventral  to  the  last 
thoracic  and  first  lumbar  vertebrae  and  is  related  ventro-medially  to  the  aorta, 
dorsally  and  laterally  to  the  right  crus  of  the  diaphragm  and  the  psoas  minor.  The 
thoracic  duct  passes  forward  to  the  right  of  the  aorta  and  ventral  to  the  vena  azygos 
as  far  as  the  sixth  thoracic  vertebra;  here  it  crosses  to  the  left  face  of  the  oesophagus 
and  runs  forward,  turns  ventrally  at  the  thoracic  inlet,  and  opens  into  the  left 
brachiocephalic  or  the  common  jugular  vein.  The  duct  may  be  single  throughout, 
but  often  divides  anteriorly  into  two  branches,  which  may  then  unite  and  form  a 
dilatation  which  receives  the  left  tracheal  duct  and  the  vessels  from  the  forelimb. 
Other  variations  occur  and  the  primitive  plexiform  arrangement  persists  in  varying 
degree.  The  tracheal  lymph  ducts  accompany  the  internal  jugular  veins.  The 
right  duct  opens  into  the  right  brachiocephalic  vein. 

The  mandibular  lymph  glands  (Fig.  615)  are  commonly  two  or  three  in  number 
on  each  side,  but  as  many  as  five  have  been  observed.  They  are  situated  in  the 
angle  between  the  masseter  and  the  mandibular  salivary  gland,  above  and  below 
the  external  maxillary  vein,  and  covered  only  by  the  skin  and  cutaneus  muscle. 

A  small  round  parotid  lymph  gland  is  situated  superficially  between  the  upper 
part  of  the  posterior  border  of  the  masseter  and  the  parotid  salivary  gland  or  partly 
or  completely  under  cover  of  the  latter.     Exceptionally  two  or  three  may  be  present. 

The  suprapharyngeal  lymph  glands,  usually  one  on  each  side,  lie  dorsal  to  the 
pharynx,  under  cover  of  the  sterno-mastoideus  and  the  mandibular  salivary  gland. 
They  are  related  deeply  to  the  rectus  capitis  ventralis  and  the  carotid  artery,  and 
the  anterior  end  is  just  behind  the  occipito-mandibularis  (Fig.  433).  Each  is  about 
two  inches  (ca.  5  cm.)  long  in  a  good-sized  dog.  In  a  good  many  cases  a  second 
gland  is  present. 

Anterior  cervical  lymph  glands  appear  to  be  absent  in  the  majority  of  subjects, 
but  in  other  cases  small  nodes  may  be  present  in  relation  to  the  anterior  end  of  the 
thyroid  gland.  It  should  be  noted,  however,  that  parathyroids  may  l^e  mistaken 
for  lymph  nodes  unless  a  microscopic  examination  is  made.  Middle  cervical 
Ijnnph  glands  are  apparently  not  present,  and  the  same  is  usually  the  case  in  regard 
to  the  posterior  cervical  lymph  glands ;  but  in  some  cases  one  or  more  of  the  latter 
occur  on  the  ventral  face  of  the  trachea  near  the  thoracic  inlet. 

The  prescapular  or  superficial  cervical  lymph  glands  lie  on  the  serratus  ven- 
tralis, at  the  anterior  border  of  the  supraspinatus,  embedded  in  a  mass  of  fat.  Usu- 
ally two  are  present  on  each  side,  but  there  may  be  three  or  only  one.  They  are 
oval  and  are  about  an  inch  long  in  a  dog  of  medium  size  when  two  are  present. 


TIIIO    LYMPHATIC    SYSTEM 


757 


The  axillary  lymph  gland  li(>s  in  a  mass  of  fat  on  the  mc(Hal  face  of  the  cHstal 
part  of  the  teres  major.     It  is  (Hseoid  and  is  about  an  ineli  (ca.  5  cm.)  wide  in  a 
lar^e  dog.    Exceptionally  a  se(;ond  smaller 
gland  is  present. 

The  cubital  lymph  gland  is  usually 
absent.  When  ])resent,  it  is  situated  on 
the  medial  face  of  tlu;  long  head  of  the 
triceps  or  on  the  latissimus  dorsi. 

Intercostal  lymph  glands  do  not  ap- 
pear to  b(>  present. 

Two  sternal  lymph  glands  (Fig.  ()18) 
are  usually  i)reseiit,  one  on  each  side. 
They  are  situated  on  the  course  of  tlu; 
internal  thoracic  vessels,  usually  at  tho, 
second  sternebra.  A  third  node  may  bo 
present  in  front  of  the  more  constant  one, 
and  in  some  cases,  on  the  other  hand,  the 
gland  is  absent  on  one  side.  In  large;  dogs 
the  gland  may  be  nearly  an  inch  long. 

The  mediastinal  lymph  glands  arc 
variable  in  number  and  arrangement. 
None  have  been  found  in  the  posterior 
mediastinum,  and  the  following  statement 
is  to  be  underst(^od  merely  as  an  ac(H)vmt 
of  what  is  most  often  found.  Two  or  three 
glands  usually  o(;cur  on  the  ventral  face  of 
the  trachea,  oesophagus,  and  brachioceph- 
alic artery  to  the  left  of  i\w  anterior  vena 
cava;  thc^y  are  related  v(>ntrally  to  the;  thy- 
mus, wh(m  the  latter  is  not  too  mu(!h  re- 
duced. Others  may  be  found  on  the  lat(u-al 
face  of  the  brachiocephalic  artery.  One 
or  two  glands  are  usually  present  between 
the  tra(;hea  and  the  anterior  vena  near 
the  thoracic  inlet,  and  one  or  two  are  on 
the  right  side  of  the;  trachea,  dorso-lateral 
to  the  right  l:)rachial  artery.  Another  lies 
on  the  trachea  at  the  crossing  of  the  vena 
azygos  over  that  tube. 

The  bronchial  lymph  glands  are  usu- 
ally four  in  number.  The  largest  one  (Lg. 
bifurcationis)  is  situated  in  the  angh;  of 
divergence  of  the  chief  bronchi,  to  whic^h 
it  is  adapted,  so  that  it  is  som(!what  V- 
shay)ed.  Another  lies  on  the  left  })ron(;hus 
at  its  bifurcation  and  in  the  angle  betw(!(!n 
the  aortic  arch  and  the;  left  pulmonary 
artery.  A  third  smaller  one  lies  on  the 
right  bronchus,  lateral  to  the  oesophagus; 

it  is  not  always  present,  A  fourth  is  anterior  to  the  root  of  the  apical  bronchus,  in 
relation  in  front  to  the  vena  azygos.  These  glands  are  {H)nunonly  black,  and  tho 
same  is  true  of  the  gland  on  the  right  side  of  tlu;  trachea  in  relation  to  the  vena 
azygos,  indicating  that  all  of  these  glands  re(;eiv(!  lymph  from  th(!  lungs. 

Minute  pulmonary  lymph  glands  occur  in  the  lungs  along  the  bronchial  branches. 


Fio.  024. — SnHLUMBAR  AND  Pblvic  Lymph  Glands 
OF  DoQ. 
L  1',  Ileiial  lymph  ulands;  2,  lumbar  lymph  KlandH; 
.3,  '.i',  l,  4',  internal  iliac  lymph  Kl^nds;  5,  .5',  mcrdial 
sacral  lymph  glands;  G,  (>',  lateral  sacral  lymph  Klands; 
7,  7',  external  iliac  lymph  glands;  a,  a',  kidneys;  b,  b', 
crura  of  diaphragm;  c,  c',  psoas  minor;  d,  d',  ilio- 
psoas; e,  e',  sacro-coccj^ous  ventralis;  /,  /',  coccy- 
geus;  I,  posterior  vena  cava;  //,  abdominal  aorta; 
///,  III',  renal  arteries;  77,  IV',  renal  veins;  V,  V, 
17,  VI',  circumflex  iliac  vessels;  VII,  VII',  external 
iliac  arteries;  VIII,  VIII',  internal  iliac  arteries;  IX, 
middle  sacral  artery;  -Y,  X' ,  parietal  branches  of  in- 
ternal iliac  arteries;  XI,  XI',  visceral  branches  of  in- 
ternal iliac  arteries;  XII,  XII',  common  iliac  veins; 
XIII,  Xlir,  external  iliac  veins;  XIV,  XIV',  in- 
ternal iliac  veins.     (After  Merzdorf). 


758  CIRCULATORY   SYSTEM    OF   THE   DOG 

The  lumbar  l3rmph  glands  are  situated  in  the  sublumbar  region  around  and 
l)etween  the  aorta  and  posterior  vena  cava.  Most  of  them  are  very  small  and  are 
difficult  to  find  in  the  fat  in  which  they  are  usually  embedded.  Their  nmnber  is 
verj'  variable;    as  many  as  fifteen  have  been  counted. 

Usually  two  large  internal  iliac  lymph  glands  are  present.  The  right  one  lies 
along  the  posterior  part  of  the  posterior  vena  cava  and  the  common  iliac  vein;  the 
left  one  is  similarly  placed  in  relation  to  the  aorta  and  left  common  iliac  vein.  Thej' 
may  be  two  inches  or  more  (ca.  5-6  cm.)  in  length  and  nearly  an  inch  (ca.  2  cm.) 
wide  in  large  dogs.  In  some  cases  there  is  a  third  small  gland  anterior  to  the  large 
one  in  relation  to  the  origin  of  the  circumflex  iliac  vessels.  In  most  cases  there  is  a 
gland  on  each  side  of  the  middle  sacral  artery,  between  that  vessel  and  the  internal 
iliac  artery  and  its  visceral  branch.  The  gland  may  be  absent  on  one  side  or  there 
maj'  be  instead  two  or  three  glands. 


Fig.  625. — Lymph  Gl.\nds  of  Abdominal  Visceha  of  Dog. 
l-d.  Portal  lymph  glands;  7,  8,  mesenteric  lymph  glands;  9-11,  cseco-colic  lymph  glands;  a,  liver;  6,  stomach; 
c,  spleen;  d,  duodenum  (cut  off  and  indicated  by  dotted  line) ;  c,  jejunum;  /.ileum;  g,  ca-cum;  /i,  i,  i-,  right,  transverse, 
and  left  parts  of  colon;  /,  portal  vein;  /J,  gastro-duodenal  vein ;  ///,  gastro-splenic  vein;  /!',  splenic  vein;  T,  common 
gastric  vein;  VI,  radicles  of  splenic  vein;  VII,  ileo-cseco-colic  vein;  VIII,  left  colic  vein;  IX,  middle  colic  vein;  A', 
right  colic  vein;  XJ,  caecal  vein;  A'/7,  ileal  vein;  A'///,  jejunal  venous  trunk.     (After  Alerzdorf.) 

The  external  iliac  lymph  glands  are  situated  on  the  ventral  surface  of  the  psoas 
minor,  between  the  diverging  external  and  internal  iliac  veins. ^  They  are  inconstant 
and  variable.     One  may  occur  on  each  side  or  two  on  one  side  and  none  on  the  other. 

The  sacral  lymph  glands  are  situated  along  the  roof  of  the  pelvic  cavity  and 
may  easily  escape  notice  on  account  of  the  fat  in  which  they  are  embedded.  Their 
size,  number,  and  arrangement  are  very  variable.  In  the  majority  of  subjects 
there  are  two  or  three  glands  on  the  anterior  part  of  the  sacro-coccygeus  ventralis 
in  relation  to  the  middle  coccygeal  artery.  In  some  cases  one  or  two  glands  occur 
at  the  interspace  Ijetween  the  sacro-coccygeus  ventralis  and  the  coccygeus.  In 
other  cases  glands  are  present  centrally  or  on  one  side  only  or  appear  to  be  absent. 

The  term  portal  lymph  glands  may  be  applied  to  those  which  occur  along  the 
course  of  the  portal  vein  and  some  of  its  affluents.  The  larger  and  more  constant 
of  these  are  as  follows:    One  lies  to  the  left  of  the  portal  vein,  on  the  origin  of  the 

1  It  seems  not  unlikely  that  these  glands  correspond  regionally  to  the  deep  inguinal  glands 
of  the  horse. 


THE    LYMPHATIC    SYSTEM  759 

duodenum  and  the  duodenal  angle  (or  head)  of  the  pancreas.  In  most  cases  two 
glands  occur  on  the  right  of  the  portal  vein  and  further  back  along  the  mesenteric 
vein.  Glands  of  variable  size  and  number  occur  in  the  gastro-splenic  part  of  the 
omentum  along  the  splenic  vein  and  its  radicles. 

The  mesenteric  lymph  glands  consist  chiefly  of  two  elongated  nodes  which 
extend  from  the  root  of  the  mesentery  of  the  jejuno-ileum  along  the  course  of  the 
artery  of  the  small  intestine  and  the  corresponding  vein. 

The  colic  lymph  glands  comprise  a  variable  number  of  nodes  (5-8)  in  the  meso- 
colon. One  is  at  the  origin  of  the  ileo-cseco-colic  vein;  a  second  one  may  be  found 
here.  One  or  two  may  be  found  in  the  transverse  mesocolon  and  others  (2-5) 
occur  at  the  terminal  part  of  the  colon. 

The  renal  lymph  glands,  one  on  each  side  of  the  aorta,  are  in  relation  to  the 
origin  of  the  renal  arteries;   the  right  one  is  concealed  by  the  vena  cava. 

The  superficial  inguinal  l3miph  glands  are  embedded  in  the  fat  about  the  ex- 
ternal inguinal  ring  in  relation  to  the  external  pudic  vessels.  In  the  male  they  are 
related  medially  to  the  penis;  in  the  female  they  are  commonly  termed  supra- 
mammary  on  account  of  their  relation  to  the  base  of  the  inguinal  mammary  glands. 
In  the  majority  of  cases  two  are  present  on  each  side,  but  there  is  often  only  one, 
and  sometimes  three  occur  on  one  side. 

The  popliteal  lymph  gland  is  situated  in  a  mass  of  fat  on  the  gastrocnemius 
at  the  level  of  the  stifle  joint.  It  is  between  the  biceps  femoris  and  semitendinosus, 
but  is  more  superficial  than  in  the  other  animals,  and  hence  is  commonly  palpable. 
It  is  oval  and  in  large  dogs  may  be  nearly  two  inches  (ca.  4.5  cm.)  long  and  more 
than  an  inch  (ca.  3  cm.)  wide. 


NEUROLOGY 

THE  NERVOUS  SYSTEM 

The  nervous  system  (Systema  nervorum)  is  a  complex  mechanism  by  which  the 
organism  is  brought  into  functional  relation  with  its  environment,  and  its  various 
parts  are  coordinated.  For  purposes  of  gross  description  it  is  divided  primarily 
into  two  parts,  central  and  peripheral.  The  central  nervous  system  (Systema  ner- 
vorum centrale)  comprises — (a)  the  spinal  cord  (Medulla  spinalis),  and  (b)  the  brain 
(Encephalon).  The  peripheral  nervous  system  (Systema  nervorum  periphericum) 
includes — (a)  the  cranial  and  spinal  nerves  with  their  ganglia,  and  (6)  the  sympa- 
thetic nervous  system. 

The  division  into  central  and  peripheral  parts  is  quite  arbitrary,  and  is  employed  purely 
as  a  matter  of  convenience  of  description.  The  fibers  of  which  the  nerves  are  composed  either 
arise  or  end  within  the  central  system,  and  therefore  constitute  an  integral  part  of  the  latter. 
The  structural  and  functional  unit  of  the  nervous  system  is  the  neurone,  which  consists  of  the 
cell-body,  usually  termed  the  nerve-cell,  and  all  its  processes.  The  processes  arise  as  out- 
growths from  the  cell-body  and  conduct  impulses  to  or  from  the  cell;  they  vary  greatly  in  length, 
some  being  less  than  a  millimeter  long,  while  others  extend  from  a  cell  in  the  spinal  cord  to  the 
distal  end  of  a  limb.  A  nerve  is  composed  of  such  processes,  usually  enclosed  in  a  protecting 
and  insulating  sheath,  and  united  into  bundles  by  areolar  tissue.  The  neurones  are  embedded 
in  a  peculiar  supporting  tissue  termed  neuroglia.  This  consists  of  a  very  intricate  feltwork 
of  glia-fibers,  many  of  which  are  connected  with  the  small  glia-cells  or  astrocytes.  In  addition 
the  nervous  tissue  is  invested  closely  by  a  vascular  layer  of  connective  tissue,  the  pia  mater,  from 
which  ingrowths  extend  into  the  nervous  substance  proper.^ 

To  the  naked  eye  the  central  nervous  system  appears  to  be  composed  chiefly 
of  two  kinds  of  substance,  white  and  gray.  The  white  matter  (Substantia  alba)  is 
dead  white  in  color  and  is  soft  in  the  natural  state.  It  consists  largely  of  meduUated 
nerve-fibers,  packed  closely  together  and  arranged  more  or  less  clearly  in  large  or 
small  bundles  or  tracts  (funiculi,  fasciculi).  The  gray  matter  (Substantia  grisea) 
is  usually  brownish-gray  in  color,  often  with  a  tinge  of  pink.  It  is  softer  than  the 
white  substance  and  much  more  vascular.  It  is  composed  chiefly  of  cell-bodies 
and  non-medullated  processes.  In  some  situations  it  is  modified  to  form  the 
gelatinous  substance  (Substantia  gelatinosa),  which  is  pale  yellowish-gray  and 
jelly-like. 

Ganglia  are  gray  masses  found  on  the  dorsal  roots  of  the  spinal  nerves  and 
on  the  course  of  many  nerves.  They  are  commonly  ovoid  in  form,  but  some 
are  irregular  in  shape  and  branched.  They  vary  greatly  in  size;  some  are  micro- 
scopic, while  others  are  several  inches  long.  They  are  enclosed  in  a  fibrous  capsule. 
They  are  composed  largely  of  the  cell-bodies  of  neurones,  but  have  connected  with 
and  passing  through  them  nerve-fibers  (processes)  which  extend  peripherally  and 
centrally.  In  origin  and  function  the  spinal  ganglia  belong  properly  to  the  central 
system,  but  it  is  customary  to  include  them  with  the  peripheral  part  in  gross  ana- 
tomical descriptions. 

Nerves  (Nervi)  are  conducting  trunks  composed  of  bundles  of  parallel  nerve- 
fibers.  They  are  enveloped  in  a  fibro-elastic  sheath,  the  epineurium,  which  contains 
the  blood  and  lymph  vessels.  They  are  classified  according  to  their  central  connec- 
tions as  cranial  or  cerebral,  spinal,  and  sympathetic.  The  groups  of  cells  of  which 
the  nerve-fibers  are  processes  are  termed  the  nuclei  of  origin  (Nuclei  originis)  or 
terminal  nuclei  (Nuclei  terminales)  of  the  nerves,  according  as  the  latter  conduct 

1  Limitations  of  space  and  the  purpose  of  this  work  preclude  consideration  of  the  finer 
structure  of  the  nervous  system,  for  which  ample  literature  is  available. 

760 


THE    MENINGES  761 

impulses  in  a  peripheral  or  central  direction.  ^  On  the  same  basis  the  nerve-fibers 
are  designated  efferent  and  afferent  respectively.  A  bundle  of  fibers  which  passes 
from  one  nerve-trunk  to  another  is  called  an  anastomotic  branch  (Ramus  anasto- 
moticus).  In  some  situations  the  exchange  of  branches  between  adjacent  nerves 
is  so  free  as  to  constitute  a  nerve-plexus  (Plexus  nervorum).  The  term  ramus 
commimicans  is  properly  restricted  to  branches  which  connect  the  ventral  divisions 
of  the  spinal  nerves  with  adjacent  ganglia  or  nerves  of  the  sympathetic  system. 
The  terminal  twigs  of  the  nerves  are  designated,  according  to  their  distribution,  as 
muscular  branches  (Rami  musculares),  cutaneous  nerves  (Nervi  cutanei),  and 
articular  nerves  (Nervi  articulares) .  The  muscular  branches  are  motor  in  function, 
the  cutaneous  and  articular  sensory,  but  all  contain  vasomotor  fibers  which  control 
the  caliber  of  the  blood-vessels. 


THE  MENINGES 
The  central  organs  of  the  nervous  system  are  enclosed  in  three  meninges  or 
membranes.     From  without  inward  these  are:    (1)  the  dura  mater,  (2)  the  arach- 
noidea,  and  (3)  the  pia  mater. 

The  Dura  Mater 

The  dura  mater  is  a  dense,  resistant  membrane  of  white  fibrous  tissue ;  in  the 
fresh  state  it  is  bluish-white  in  color.  On  account  of  the  difference  in  its  arrange- 
ment within  the  cranium  from  that  in  the  spinal  canal  it  is  customary  to  describe 
it  as  consisting  of  two  parts,  cerebral  and  spinal;  these  portions  are  continuous  with 
each  other  at  the  foramen  magnum. 

The  cerebral  dura  mater  (Dura  mater  encephali)  is  adherent  to  the  interior 
of  the  cranium,  and  may  be  regarded  as  forming  an  internal  periosteum  for  the 
bones  here  as  well  as  being  an  envelope  of  the  brain.  Its  outer  surface  is  connected 
with  the  bony  wall  of  the  cranial  cavity  by  numerous  fine  fibrous  strands  and  by 
blood-vessels;  hence  it  appears  rough  in  many  places  when  separated  from  the  wall. 
The  degree  of  adhesion  varies  greatly  at  different  points.  It  is  most  firmly  attached 
at  the  various  projections,  e.  g.,  the  internal  parietal  crest,  the  tentorium  osseum, 
the  petrosal  crest;  also  at  the  base  and  the  foramen  magnum.  Before  the  sutures 
are  closed  the  dura  is  connected  with  the  sutural  ligaments  and  through  them  is 
continuous  with  the  external  periosteum.  The  cranial  nerves  receive  sheaths  from 
the  dura,  which  is  thus  continuous  without  the  cranium  with  the  epineurium  and 
periosteum.  Along  the  roof  and  sides  (except  as  noted  above)  the  adhesion  is 
relatively  slight,  and  lymph  spaces  are  said  to  exist  between  the  dura  and  the  bone. 
The  internal  surface  of  the  dura  is  smooth  and  glistening,  since  it  is  lined  by  endo- 
thelium and  is  moistened  by  a  fluid  resembling  lymph;  it  forms  the  outer  boundary 
of  the  subdural  space.  In  accordance  with  its  double  function  the  dura  is  composed 
of  two  layers,  which  are,  however,  intimately  adherent  to  each  other  in  most  places 
in  the  adult.  The  venous  sinuses  are  channels  between  the  two  layers  and  are  lined 
by  endothelium.  They  have  been  described  with  the  other  vessels.  Two  folds  or 
septa  given  off  from  the  irmer  surface  of  the  dura  project  into  the  cranial  cavity 
between  the  gross  subdivisions  of  the  brain.  These  are:  (1)  the  falx  cerebri;  (2) 
the  tentorium  cerebelli. 

The  falx  cerebri  is  a  sickle-shaped  median  partition  which  is  situated  in  the 
longitudinal  fissure  between  the  cerebral  hemispheres.  It  is  attached  dorsally 
to  the  internal  parietal  crest,  in  front  to  the  crista  galli,  and  behind  to  the 
tentorium  osseum.     Its  dorsal  border  is  convex  and  separates  into  two  layers 

^ These  cell-groups  are  the  real  origin  or  termination  of  a  nerve.  The  term  "apparent 
origin"  is  a  convenient  designation  for  the  point  at  which  a  nerve  is  connected  with  the  surface 
of  the  brain. 


762  THE   NERVOUS    SYSTEM 

which  enclose  the  dorsal  longitudinal  sinus.  Its  ventral  border  is  concave  and 
lies  over  the  corpus  callosum.  The  falx  is  thick  above,  but  much  thinner  below, 
and  is  in  some  places  cribriform. '^ 

The  tentorium  cerebelli  is  a  crescentic  transverse  fold  which  occupies  the 
transverse  fissure  between  the  cerebellum  and  the  cerebral  hemispheres.  It  is 
attached  dorsally  to  the  tentorium  osseum  and  laterally  to  the  petrosal  crest.  Its 
ventral  border  is  thin,  concave,  and  free ;  it  forms  the  dorsal  and  lateral  boundaries 
of  an  opening  (Incisura  tentorii)  in  which  the  mid-brain  is  situated. 

The  diaphragm  sellae  is  a  thickening  of  the  dura  which  roofs  over  the  pitui- 
tary fossa;  it  covers  the  pituitary  body  and  the  cavernous  and  intercavernous 
sinuses.  It  is  perforated  centrally  by  an  opening  (Foramen  diaphragmatis)  for 
the  infundibulum. 

The  falx  cerebelli,  a  sickle-shaped  fold  which  projects  into  the  median  notch  between  the 
cerebellar  hemispheres  in  man,  is  not  present  in  the  domesticated  animals.  There  is  instead 
merely  a  slight  thickening  of  the  dura. 

The  spinal  dura  mater  (Dura  mater  spinalis)  forms  a  tube  around  the  spinal 
cord  from  the  foramen  magnum  to  the  second  or  third  segment  of  the  sacrum.  It 
is  separated  from  the  periosteum  of  the  spinal  canal  by  a  considerable  epidural 
space  (Cavum  epidurale),  which  is  occupied  by  fatty  connective  tissue  and  veins. 
It  is  held  in  position  chiefly  by  the  sheaths  which  it  furnishes  to  the  roots  of  the 
spinal  nerves,  and  in  its  anterior  part  by  two  ligaments;  the  latter  connect  it  with 
the  ventral  atlanto-occipital  membrane  and  with  the  dens  of  the  axis.  It  is  large 
in  proportion  to  its  contents,  but  its  diameter  is  not  uniform.  It  is  largest  in  the 
atlas,  small  in  the  thoracic  region,  and  becomes  very  small  in  its  terminal  part, 
where  it  encloses  the  delicate  filum  terminale  of  the  spinal  cord. 

The  subdural  space  (Cavum  subdurale)  is  the  cavity  between  the  inner  surface 
of  the  dura  mater  and  the  arachnoidea.  It  is  a  mere  capillary  space  which  contains 
just  sufficient  fluid  to  moisten  its  surfaces;  this  fluid  is  usually  regarded  as  lymph, 
which  is  replenished  by  filtration  through  the  walls  of  the  blood-vessels.  The 
space  is  in  communication  with  the  lymph  paths  of  the  nerve  sheaths. 

The  Arachnoidea 

The  arachnoidea  is  a  very  delicate  and  transparent  membrane  which  is  situated 
between  the  dura  and  pia  mater.  Its  outer  surface  forms  the  inner  wall  of  the  sub- 
dural space  and  is  covered  by  a  layer  of  endothelium  continuous  with  that  of  the 
opposed  surface  of  the  dura  mater.  Between  it  and  the  pia  mater  is  the  subarach- 
noid space  (Cavum  subarachnoideale) ,  which  contains  the  cerebrospinal  fluid.  An 
inner  surface  can  scarcely  be  said  to  exist,  since  deeply  the  membrane  becomes  a 
reticidum  of  fine  fibers  which  traverse  the  subarachnoid  space  and  are  attached 
to  the  pia  mater.  The  arachnoidea  furnishes  sheaths  to  the  cerebral  nerves  from 
their  superficial  origins  to  a  variable  but  usually  short  distance  beyond  the  emer- 
gence from  the  sac.     In  the  case  of  the  optic  nerve  this  sheath  extends  to  the  eyeball. 

The  cerebral  arachnoidea  (Arachnoidea  encephali),  except  in  the  case  of  the 
great  longitudinal  and  transverse  fissures,  does  not  dip  into  the  sulci  on  the  surface 
of  the  brain.  On  the  summits  of  the  gyri  it  is  so  closely  attached  to  the  pia  mater 
that  the  two  form  practically  a  single  membrane.  Its  outer  part  bridges  over  the 
sulci,  and  here  the  subarachnoid  space  is  partially  divided  up  by  the  loose  arach- 
noid tissue  into  intercommunicating  cavities.  In  certain  situations  the  arach- 
noidea is  separated  from  the  pia  by  spaces  of  consideral^le  depth  and  extent.  These 
enlargements  of  the  subarachnoid  space  are  termed  subarachnoid  cisterns  (Cisternse 
subarachnoidales) .     In  them  the  subarachnoid  tissue  does  not  form  a  close  network, 

1  In  the  horse  the  posterior  part  of  the  falx  cerebri  does  not  extend  to  the  corpus  callosum,  and 
the  cerebral  hemispheres  are  here  in  contact  and  adherent  to  each  other  over  a  small  area.  In  the 
other  animals  the  falx  does  not  descend  so  far  as  in  the  horse. 


PIA    MATER  763 

but  consists  of  a  relatively  small  number  of  long,  thread-like  strands  which  traverse 
the  cavity. 

The  chief  cistemse  are:  (1)  the  cistema  magna,  which  is  at  the  angle  formed  between  the 
posterior  face  of  the  cerebellum  and  the  dorsal  surface  of  the  medulla  oblongata.  It  communi- 
cates with  the  fourth  ventricle  through  lateral  openings  in  the  latter,  and  behind  with  the  wide 
subarachnoid  space  of  the  spinal  cord;  (2)  the  cisterna  pontis,  on  the  ventral  surface  of  the  pons; 
(3)  the  cisterna  basolis,  which  lies  at  the  base  of  the  cerebrum  and  is  divided  by  the  optic  chiasma 
into  two  parts  (cisterna  chiasmatis,  cisterna  interpeduncularis) ;  (4)  the  cisterna  fossae  lateralis, 
situated  at  the  lower  part  of  the  lateral  fissure  and  continuous  with  the  cisterna  basalis. 

Along  the  dorsal  border  of  the  falx  cerebri  the  arachnoidea  bears  bulbous 
excrescences,  the  arachnoid  granulations.^  These  are  enclosed  in  thin  evaginations 
of  the  dura  mater  and  project  into  the  dorsal  longitudinal  sinus  or  the  parasinoidal 
sinuses  along  either  side  of  it.  In  some  cases  they  are  sufficienth^  large  to  exert 
pressure  on  the  bone  and  produce  in  it  depressions  of  variable  depth. 

The  spinal  arachnoidea  (Arachnoidea  spinalis)  is  continuous  with  that  of  the 
brain  at  the  foramen  magnum.  It  forms  a  relatively  wide  tube  around  the  spinal 
cord,  so  that  the  latter  (enclosed  in  the  pia)  is  surrounded  by  a  very  considerable 
quantity  of  cerebrospinal  fluid.  The  spinal  subarachnoid  space  is  traversed  by 
fewer  trabeculse  than  is  the  case  in  the  cranium.  It  is  partially  subdivided  by  three 
imperfect  septa.  One  of  these,  the  septum  dorsale,  is  median  and  dorsal.  The 
other  two,  the  ligamenta  denticulata,  are  lateral  and  will  be  described  with  the  pia 
mater. 

Pia  Mater 

The  pia  mater  is  a  delicate  and  very  vascular  membrane,  which  invests  closely 
the  surface  of  the  brain  and  spinal  cord  and  sends  processes  into  their  substance. 
It  also  furnishes  sheaths  to  the  nerves,  which  blend  outside  of  the  dural  sac  with  the 
epineurium. 

The  cerebral  pia  mater  (Pia  mater  encephali)  follows  accurately  all  the  in- 
equalities of  the  surface,  dipping  into  all  the  fissures  and  sulci  of  the  cerebrum,  and 
into  the  larger  fissures  of  the  cerebellum.  Its  external  surface,  which  forms  the 
inner  boundary  of  the  subarachnoid  space,  is  covered  by  a  layer  of  endothelium. 
From  its  deep  face  numerous  trabeculse  are  given  off  which  penetrate  into  the  sub- 
stance of  the  brain,  forming  a  path  for  the  blood-vessels,  and  concurring  with  the 
neuroglia  in  forming  the  supporting  tissue  of  the  nervous  substance  proper.  The 
larger  blood-vessels  of  the  brain  lie  wdthin  the  subarachnoid  space,  but  the  smaller 
vessels  ramify  in  the  pia,  forming  rich  plexuses.  The  twigs  which  penetrate  into 
the  gray  matter  are  enclosed  in  pial  sheaths.  They  are  end-arteries,  i.e.,  constitute 
the  entire  supply  of  the  district  which  they  enter  and  do  not  anastomose  with 
adjacent  vessels. 

Important  folds  of  the  pia  extend  into  two  of  the  great  fissures  of  the  brain. 
One  of  these  passes  in  at  the  transverse  fissure  between  the  cerebellum  and 
the  cerebral  hemispheres,  and  is  continued  so  as  to  overlie  the  third  ventricle;  it 
forms  the  tela  chorioidea  of  that  cavity.  Another  fold  passes  in  at  the  fissure 
between  the  cerebellum  and  the  medulla  oblongata  and  forms  the  tela  chorioidea 
of  the  fourth  ventricle.  They  constitute  paths  for  the  deeper  vessels  and  their 
edges  contain  vascular  convolutions  which  are  known  as  chorioid  plexuses.  They 
will  receive  further  consideration  more  appropriately  later. 

The  spinal  pia  mater  (Pia  mater  spinalis)  is  thicker  and  denser  than  that  of 
the  brain.  It  has  a  strong  outer  layer  of  fibrous  tissue,  most  of  the  fibers  of  which 
are  longitudinal.  The  inner  layer  is  vascular  and  adheres  closely  to  the  surface 
of  the  spinal  cord,  because  numerous  processes  extend  into  the  latter  from  it.  It 
sends  a  fold  into  the  median  ventral  fissure  and  also  helps  to  form  the  median 
dorsal  septum  of  the  cord.  Along  the  median  ventral  line  it  forms  a  band-like 
1  They  are  also  known  as  Pacchionian  bodies. 


764  NERVOUS   SYSTEM    OF   THE   HORSE 

thickening,  the  linea  splendens,  along  which  the  ventral  spinal  artery  runs.  On 
each  side  the  pia  mater  gives  off  a  strong  longitudinal  band,  the  ligamentum  den- 
ticulatum,  which  is  connected  externally  with  the  dura  mater.  The  inner  or  pial 
border  extends  in  a  line  between  the  dorsal  and  ventral  roots  of  the  nerves.  The 
outer  or  dural  border  is  denticulated  and  to  a  large  extent  free.  The  denticulations 
are  attached  to  the  dura  between  the  nerve-roots. 


NERVOUS  SYSTEM  OF  THE  HORSE 
The  Spinal  Cord 

The  spinal  cord  (Medulla  spinalis)  is  the  part  of  the  central  nervous  system 
which  is  situated  in  the  vertebral  canal.  It  extends  from  the  foramen  magnum  to 
about  the  middle  of  the  sacrum.  Its  average  length  is  about  76  to  78  inches  (ca. 
190-195  cm.),  and  its  weight  about  83^2  to  9  ounces  (ca.  240-255  grams). 

It  is  approximately  cylindrical,  but  more  or  less  flattened  dorso-ventrally. 
There  is  no  natural  line  of  demarcation  between  it  and  the  medulla  oblongata,  but 
for  descriptive  purposes  the  division  is  usually  assumed  to  be  at  the  plane  of  the 
foramen  magnum.  Its  posterior  part  tapers  rapidly  to  a  point,  forming  the  conus 
medullaris.     This  is  prolonged  for  a  short  distance  by  the  slender  filum  terminale. 

Forty-two  pairs  of  spinal  nerves  are  connected  with  the  sides  of  the  spinal  cord. 
They  are  classified  as  eight  cervical,  eighteen  thoracic,  six  lumbar,  five  sacral,  and 
five  coccygeal.  According  to  the  attachments  of  these  series  of  nerves  the  spinal 
cord  is  divided  into  cervical,  thoracic,  lumbgir,  and  sacral  parts.^ 

In  the  embryo  these  divisions  correspond  primitively  to  the  regions  of  the 
vertebral  column,  but  later,  through  unequal  growth  of  the  cord  and  spine,  the 
correspondence  between  the  two  is  not  at  all  exact  in  the  anterior  regions  and  is 
lost  in  the  last  two.  The  lumbar  part  of  the  cord  in  the  horse  ends  at  the  junction 
of  the  fifth  and  sixth  lumbar  vertebrae,  so  that  the  roots  of  the  last  lumbar  nerve 
must  run  backward  the  length  of  the  last  lumbar  vertebra  to  reach  the  interverte- 
bral foramen  through  which  it  emerges.  The  conus  medullaris  reaches  only  to  the 
anterior  part  of  the  sacral  canal,  so  that  the  roots  of  the  sacral  and  coccygeal  nerves 
extend  backward  in  the  spinal  canal  for  a  considerable  distance,  forming  a  leash 
of  bundles,  in  the  center  of  which  lie  the  conus  medullaris  and  the  filum  terminale. 
This  arrangement  is  expressively  designated  the  cauda  equina. 

Each  pair  of  spinal  nerves  is  attached  by  its  root-fibers  to  a  certain  length  of 
the  cord,  and  the  latter  is,  therefore,  regarded  as  consisting  of  as  many  segments 
as  there  are  pairs  of  nerves.  It  is  to  be  noted,  however,  that  there  is  no  line  of 
demarcation  between  the  segments  other  than  the  intervals  between  the  root-fibers 
of  adjacent  nerves. 

The  segments  are  of  different  lengths;  the  longest  are  the  third  to  the  sixth  cervical,  which 
measure  11,  10,  10,  and  8.5  cm.  fespectively.  The  spinal  nerves  are  in  general  designated  accord- 
ing to  the  vertebrae  behind  which  they  emerge  from  the  vertebral  canal.  In  the  neck,  however, 
there  are  eight  pairs  of  nerves  and  only  seven  vertebrae;  here  the  first  nerve  emerges  through  the 
intervertebral  foramen  of  the  atlas  and  the  eighth  between  the  last  cervical  and  the  first  thoracic 
vertebra?. 

In  the  greater  part  of  the  thoracic  region  the  spinal  cord  is  fairly  uniform  in 
size,  but  there  are  two  conspicuous  enlargements  which  involve  the  segments  with 
which  the  nerves  of  the  limbs  are  connected.  The  cervical  enlargement  (Intumes- 
centia  cervicalis)  begins  gradually  in  the  fifth  cervical  vertebra  and  subsides  in 

1  In  a  horse  about  16J4  hands  high  these  parts  measured  65  cm.  (ca.  26  in.),  86  cm.  (ca.  34.4 
in.),  27  cm.  (ca.  10.8  in.),  and  15  cm.  (ca.  6  in.)  respectively  (Dexler). 


THE    SPINAL    CORD 


765 


the  second  thoracic.  Its  maximum  transverse  diameter  is  about  an  inch  (ca.  25 
mm.)  and  its  dorso-ventral  nearly  half  an  inch  (ca.  12  mm.).  The  lumbar  enlarge- 
ment (Intumescentia  lumbalis)  is  situated  in  the  fourth  and  fifth  lumbar  vertebrae. 

It  is  a  little  narrower  than  the  cervi- 
cal enlargement,  and  its  dorso-ventral 
diameter  is  also  slightly  smaller.  Be- 
hind this  the  cord  tapers  rapidly  to 
form  the  conus  medullaris.  The  tip 
of  the  latter  is  continued  by  a  delicate 
glistening  strand,  the  filimi  terminale, 
which  is  composed  largely  of  fibrous 
tissue  continued  from  the  pia  mater, 
covered  by  arachnoid. 


Fig.  626. — Ventral  View  of  Medulla  Oblongata 
AND  First  and  Second  Segments  of  Spinal 
Cord  of  Horse;  the  Membranes  are  Cut  and 
Reflected. 

1,  Lig.  suspensorium  arachnoideale ;  2,  right  cere- 
brospinal artery;  3,  5,  digitations  of  lig.  denticulatum; 
4,  free  border  of  lig.  denticulatum;  6,  middle  spinal 
artery;  7,  basilar  artery;  S,  pons;  9,  arachnoidea; 
10,  dura  mater;  11,  12,  ventral  root-bundles  of  first 
and  second  segments  of  spinal  cord;  VI,  N.  abducens; 
IX,  X,  glosso-pharyngeus  and  vagus;  AT,  accessory, 
medullary  part;  XI',  accessory,  spinal  part;  a,  line 
between  medulla  oblongata  and  spinal  cord.  (Dexler, 
in  Ellenberger-Baum,  Anat.  d.  Haustiere.) 


Fig.  627. — Cauda  Equina. 
1,  Dura  and  arachnoidea  divided  and  reflected;  S, 
spinal  cord;  3,  nerve-roots.     (From  Leisering's  Atlas,  re- 
duced.) 


The  surface  of  the   spinal  cord  is 
divided   into  two   similar  halves  by  a 
dorsal   median    groove   and   a   ventral 
median  fissure.     On  either  side  of  the 
former  is  the  dorso-lateral  groove  (Sul- 
cus dorsalis  lateralis) ,  at  which  the  fibers 
of  the  dorsal  nerve-roots  enter  the  cord; 
it  is  faint  except  at  the  enlargements,  and  is  represented  by  two  grooves  in  the  first 
cervical  segment.     The  ventral  root-fibers  as  they  emerge  from  the  cord  do  not 
form  a  continuous  series,  but  arise  from  a  zone  (Area  radicularis  ventralis)  3  to  5 


766 


NERVOUS   SYSTEM    OF   THE   HORSE 


mm.  in  A\adth,  a  little  lateral  to  the  ventral  median  fissure,  and  no  groove  is  found 
here.  In  the  greater  part  of  the  cervical  region  and  the  anterior  part  of  the  thoracic 
region  there  is  a  shallow  dorsal  intermediate  groove  (Sulcus  intermedius  dorsalis)  a 
short  distance  lateral  to  the  median  groove.  These  grooves  indicate  the  division 
of  the  white  matter  of  the  cord  into  columns  to  be  described  later. 

Examination  of  cross-sections  of  the  spinal  cord  shows  that  it  is  a  bilaterally 
symmetrical  structure,  incompletely  divided  into  right  and  left  halves  by  a  ventral 
fissure  and  a  dorsal  septum.  The  ventral  median  fissure  (Fissura  mediana  ven- 
tralis)  is  narrow  and  penetrates  nearly  to  the  middle  of  the  dorso-ventral  diameter 
of  the  cord.  It  is  occupied  by  a  fold  of  pia  mater.  The  dorsal  median  septvmi 
(Septum  medianum  dorsale)  is  a  partition  which  descends  from  the  dorsal  median 
groove  to  about  the  middle  of  the  cord.  It  apparently  consists  of  condensed  neu- 
roglia with  an  admixture  of  pial  tissue.     The  two  halves  of  the  cord  are  connected 


Fig.  62S.— 
1,  Dorsal  column;   3, 


^ROSS-SECTION  OF  SPINAL  CoRD   ill  situ,  ENLARGED  AND  IN  PaRT  SCHEMATIC. 

iteral  column;   3,  ventral  column;   4i  dorsal  horn;   5,  ventral  horn;   6,  gray  commissure;   7, 


white  commissure;  <S,  central  canal;  5,  dorsal  septum;  /O,  ventral  fissure;  i/,  dorsal  nerve-root ;  /^,  ventral  nerve-root. 
13,  spinal  ganglion;  14,  spinal  nerve;  13,  intervertebral  foramen;  16,  arch  of  vertebra;  17,  epidural  space;  IS,  dura 
mater  (represented  a  little  too  thick);  10,  ligamentum  denticulatum;  20,  30,  longitudinal  venous  sinuses;  31,  middle 
spina!  artery;  32,  body  of  vertebra.  The  subdural  and  subarachnoid  spaces  (black)  are  traversed  by  delicate  trabec- 
ulae.     The  outer  part  of  the  arachnoid  and  the  pia  mater  are  not  shown. 


by  commissures  of  gray  and  white  matter.  The  gray  commissure  (Commissura 
grisea)  is  a  transverse  band  of  gray  matter  at  the  ventral  end  of  the  dorsal  septum. 
It  is  divided  into  dorsal  and  ventral  parts  by  the  central  canal  of  the  cord.  The 
white  commissure  (Commissura  alba)  is  a  bridge  of  white  matter  which  connects 
the  ventral  columns  of  the  cord  over  the  dorsal  end  of  the  ventral  median  fissure, 
and  constitutes  a  conducting  path  from  one  side  to  the  other. 

The  central  canal  of  the  spinal  cord  (Canalis  centralis),  the  spinal  vestige  of  the 
lumen  of  the  embryonal  neural  tube,  is  a  minute  passage  which  tunnels  the  gray 
commissure.  It  opens  at  its  anterior  end  into  the  posterior  part  of  the  fourth 
ventricle  of  the  brain,  and  its  terminal  part  in  the  conus  medullaris  forms  a  slight 
dilatation,  the  ventriculus  terminalis.  It  is  lined  by  epithelium  and  is  surrounded 
by  a  layer  of  modified  neuroglia  (Substantia  grisea  centralis). 

The  gray  matter  of  the  spinal  cord  as  seen  in  cross-sections  resembles  roughly 


THE    SPINAL    CORD  767 

a  capital  H,  the  cross-bar  of  the  letter  being  formed  by  the  gray  commissure. 
Each  lateral  part  is  considered  as  consisting  of  dorsal  and  ventral  gray  columns 
(Columna  grisea  dorsalis,  ventralis),  which  appear  in  cross-section  as  the  so-called 
horns  (Cornu  dorsale,  ventrale) .  In  the  greater  part  of  the  cord  the  dorsal  column 
or  horn  is  elongated  and  narrow  and  tapers  to  a  point  which  extends  almost  to  tho 
surface  of  the  cord  at  the  attachment  of  the  dorsal  root-fibers  of  the  spinal  nerves. 
Its  apex  or  tip  consists  of  gray  matter  which  is  lighter  in  color  and  less  opaque 
than  that  of  the  rest  of  the  horn,  and  is  termed  the  substantia  gelatinosa.  The 
ventral  column  or  horn  is  short,  thick,  and  rounded,  and  is  separated  from  the  surface 
of  the  cord  by  a  thick  layer  of  white  matter,  through  which  the  fibers  of  the  ventral 
roots  of  the  spinal  nerves  pass.  From  the  middle  of  the  cervical  region  to  the 
lumbar  region  there  is  a  medial  projection  of  gray  matter  on  the  ventral  part  of  the 
dorsal  column;  this  is  the  nucleus  dorsalis. ^  In  the  anterior  part  of  the  cord  there 
is  an  outward  projection  of  the  gray  matter  at  the  base  of  the  ventral  horn;  this 
is  termed  the  lateral  column  or  horn.  The  demarcation  between  the  gray  and 
white  matter  is  in  many  places  indistinct;  this  is  especially  the  case  laterally, 
where  processes  of  gray  matter  extend  into  the  white  substance,  producing  what 
is  known  as  the  formatio  reticularis. 

Cross-sections  of  the  spinal  cord  present  the  following  gross  regional  characters:  (1)  The 
cervical  cord  near  the  medulla  is  compressed  dorso-ventrally.  Its  width  is  about  18  mm.  and 
its  greatest  thickness  about  8  mm.  It  has  dorsally  a  deep  median  sulcus  and  a  distinct  dorso- 
lateral sulcus.  Lateral  grooves  are  also  present.  The  dorsal  cornua  are  strongly  everted.  Each 
has  an  expanded  head,  which  comes  very  close  to  the  surface  of  the  cord,  and  has  an  extensive 
cap  of  substantia  gelatinosa.  The  neck  is  distinct.  The  ventral  cornua  are  short  and  blunt  and 
diverge  very  little.  The  gray  commissure  is  about  in  the  middle  of  the  section,  and  2.5  mm. 
in  length.  According  to  Dexler,  the  column  between  the  median  and  lateral  grooves  dorsally 
is  the  funiculus  cuneatus,  the  funiculus  gracilis  being  very  small  and  not  showing  on  the  surface 
in  this  region.  In  the  middle  of  the  cervical  region  the  diameters  are  about  16  mm.  and  10  mm. 
respectively.  The  ventral  surface  is  somewhat  flattened.  The  dorsal  cornua  have  pointed  ends 
and  turn  decidedly  outward.  The  ventral  cornua  are  short  and  thick  and  are  directed  very  slightly 
outward;  their  ends  are  about  4  mm.  from  the  ventral  surface.  The  gray  commissure  is  just 
above  the  middle  of  the  section  and  is  about  2  mm.  long.  The  cervical  enlargement  measures 
about  25  mm.  transversely  and  12  mm.  vertically.  The  dorsal  cornua  are  smaller  than  the  ventral 
and  have  a  large  cap  of  substantia  gelatinosa.  The  ventral  cornua  are  short  and  thick,  curve 
strongly  outward,  and  are  about  4  mm.  from  the  ventral  surface.  Each  bears  a  prominence  on  its 
medial  side  near  the  base.  The  gray  commissure  is  considerably  above  the  middle  of  the  section 
and  is  about  4  mm.  long.  (2)  In  the  middle  of  the  thoracic  region  the  cross-section  is  biconvex, 
the  ventral  surface  being  the  more  strongly  curved.  The  transverse  diameter  is  about  15  mm. 
and  the  dorso-ventral  about  10  nmi.  The  gray  columns  are  close  together,  the  gray  commissure 
being  only  about  1  mm.  in  length,  and  lying  considerably  above  the  middle  of  the  section.  The 
dorsal  cornua  are  short  and  have  slightly  enlarged  ends.  The  ventral  comua  have  a  uniform  diame- 
ter, turn  very  little  outward,  and  end  about  3  mm.  from  the  ventral  surface.  (3)  The  lumbar  enlarge- 
ment is  much  flattened,  especially  dorsally.  The  transverse  diameter  is  about  22  mm.  and  the 
dorso-ventral  9  to  10  mm.  The  cornua  are  very  large.  The  ventral  cornua  are  thick  and  rounded 
and  turn  sharply  outward;  they  end  about  2  mm.  from  the  ventral  surface.  The  dorsal  cornua 
are  smaller  and  shorter  and  do  not  diverge  so  strongly.  The  gray  commissure  is  about  in  the 
middle  of  the  section  and  is  about  3  nmi.  long.  In  the  third  lumbar  vertebra  the  cord  is  about 
3  mm.  narrower  and  thicker,  and  both  surfaces  are  about  equally  convex.  The  dorsal  cornua  are 
smaller,  considerably  everted,  and  constricted  in  the  middle.  The  ventral  cornua  are  very  short 
and  do  not  turn  outward.  (4)  In  the  first  sacral  vertebra  the  cord  is  almost  round  and  is  5  to  6  mm. 
in  diameter;  the  cornua  are  relatively  very  large  and  the  commissure  has  the  form  of  a  high  inter- 
mediate mass. 

The  ventral  horn  contains  large  cells,  the  axones  of  which  emerge  as  the  fibers  of  the  ventral 
nerv^e-roots  (Fila  radicularia).  The  axones  of  many  cells  cross  to  the  opposite  side  in  the  white 
commissure  and  pass  out  in  a  ventral  root  of  that  side,  or  enter  the  white  matter  and  pass  forward 
and  backward,  associating  various  segments  of  the  cord.  Some  pass  to  the  ventral  horn  of  the 
opposite  side  at  the  same  or  at  different  levels.  Others  pass  to  the  periphery  of  the  cord,  join 
the  cerebellospinal  fasciculus,  and  extend  to  the  cerebellum.  Scattered  through  the  gray  matter 
are  many  smaller  cells  with  axones  which  pursue  a  short  course  and  serve  to  connect  different 
parts  of  the  gray  matter. 

The  white  matter  of  the  spinal  cord  is  divided  into  three  pairs  of  columns. 
The  dorsal  columns  (Funiculi  dorsales)  lie  on  either  side  of  the  dorsal  median  septum 
and  extend  outward  to  the  dorso-lateral  groove  and  the  dorsal  gray  column.     The 
1  Also  known  as  Clarke's  column. 


768  NERVOUS    SYSTEM   OF   THE   HORSE 

ventral  columns  (Funiculi  ventrales)  are  situated  on  either  side  between  the  median 
fissure  and  the  ventral  gray  columns.  They  are  connected  above  the  fissure  by 
the  white  commissure.  The  lateral  coliinins  (Funiculi  laterales)  are  lateral  to  the 
gray  columns  on  either  side;  their  limits  are  indicated  superficially  by  the  dorso- 
lateral groove  and  the  emergence  of  the  ventral  root-fibers.  The  intermediate 
groove  (where  present)  indicates  a  subdivision  of  the  dorsal  column  into  two  fasci- 
culi or  tracts;  the  medial  of  these  is  the  fasciculus  gracilis;  the  lateral  one  is  the 
fasciculus  cuneatus.^ 

The  amounts  of  gray  and  white  matter  vary  greatly  in  different  parts  of  the 
cord  both  absolutely  and  relatively.  In  cross-section  the  absolute  areas  of  both  are 
greatest  in  the  enlargements.  The  relative  area  of  gray  matter  is  smallest  in  the 
thoracic  region  (except  at  its  anterior  end),  and  increases  from  the  lumbar  enlarge- 
ment backward. 

Investigations  have  shown  that  in  man  the  columns  of  white  matter  are  subdivided  into 
fasciculi  or  tracts,  which  constitute  definite  conducting  paths  of  greater  or  less  length.  Our 
knowledge  of  the  tracts  in  the  domesticated  animals  is  very  limited,  and  it  is  quite  unsafe  to  make 
inferences  from  the  arrangement  in  man.  As  evidence  of  this  it  may  be  noted  that  the  ventral 
cerebrospinal  or  direct  pyramidal  tract  of  man  cannot  be  recognized  as  such. 

The  dorsal  white  columns  consist  essentially  of  two  sets  of  axones.  The  afferent  or  sensory 
axones  which  come  from  the  cells  of  the  spinal  ganglia  enter  as  the  dorsal  roots  of  the  spinal  nerves 
and  divide  into  two  branches  in  the  vicinity  of  the  dorsal  gray  column.  The  anterior  branches 
form  the  direct  sensory  path  to  the  brain  and  extend  m  the  fasciculus  cuneatus  and  fasciculus 
gracilis  or  corresponding  tracts  to  nuclei  in  the  medulla  oblongata.  The  posterior  branches 
extend  backward  for  varying  distances  and  give  off  numerous  collaterals  to  cells  of  the  gray  column, 
thus  forming  part  of  the  mechanism  for  the  mediation  of  reflex  action.  Some  collaterals  cross 
in  the  white  commissure  to  the  opposite  side.  Many  of  these  fibers  are  collected  in  the  comma- 
shaped  tract  between  the  fasciculus  gracilis  and  cuneatus.  The  second  set  of  axones  arises  from 
the  smaller  cells  of  the  gray  column.  They  enter  the  white  matter,  divide  into  anterior  and 
posterior  branches,  forming  the  fasciculi  proprii  or  ground  bundles  of  the  cord.  Some  branches 
cross  to  the  opposite  side.  The  f miction  of  this  set  of  axones  is  chiefly  to  associate  various  levels 
of  the  cord. 

The  lateral  columns  contain  some  axones  of  the  dorsal  nerve-roots,  which  (in  man)  are 
grouped  in  the  marginal  tract  of  Lissauer,  situated  just  dorsal  to  the  apex  of  the  dorsal  hom. 
The  cerebellospinal  fasciculus  (direct  cerebellar  tract  of  Flechsig)  extends  along  the  periphery 
of  the  lateral  column.  It  contains  the  axones  of  the  cells  of  the  nucleus  dorsalis  (Clarke's  column), 
which  proceed  to  the  medulla  oblongata  and  enter  the  cerebellum  by  the  restiform  body.  The 
rubrospinal  tract  (of  Monakow)  appears  to  take  the  place  of  the  lateral  cerebrospinal  fasciculus  or 
crossed  pyramidal  tract  of  m.an.  It  lies  at  the  medial  side  of  the  cerebellospinal  fasciculus.  Its 
fibers  arise  in  the  nucleus  ruber  of  the  mid-brain,  cross  the  median  plane  (decussation  of  Forel), 
and  pass  backward  in  the  tegmentum  and  medulla  oblongata  to  the  lateral  column  of  the  cord. 
It  is  a  path  for  motor  impulses  coming  from  the  cerebral  cortex  and  the  cerebellum .  The  lateral 
fasciculus  proprius  or  ground-bundle  is  deeply  situated  at  the  side  of  the  gray  columns.  The 
bulk  of  its  fibers  are  axones  of  cells  of  the  dorsal  column  which  divide  into  anterior  and  posterior 
branches.  They  are  intersegmental  paths  which  associate  different  levels  of  the  gray  matter  of 
the  cord.     The  significance  of  the  remaming  fibers  is  not  yet  knowni. 

The  ventral  white  columns  do  not  contain  a  ventral  cerebrospinal  or  direct  pyramidal  tract, 
as  in  man.  There  is  a  small  tract  (Fasciculus  intracommissuralis  ventralis)  dorsal  to  the  white 
commissure,  which  separates  it  from  the  rest  of  the  ventral  column.  It  extends  to  the  middle  of 
the  thoracic  region.  It  consists  of  intersegmental  fibers,  and  contains  in  the  anterior  part  of 
the  cervical  cord  in  the  sheep  and  goat  both  crossed  and  direct  pyramidal  fibers.  The  descending 
cerebellospinal  fasciculus  extends  from  the  cerebellum  to  the  lumbar  region.  In  the  cervical 
region  it  occupies  a  semilunai  area  which  reaches  almost  to  the  surface  ventro-laterally.  Scattered 
fibers  belonging  to  it  lie  also  in  the  medial  part  of  the  ventral  column.  Posteriorly  it  diminishes 
in  size  and  comes  to  occupy  a  position  next  to  the  ventral  median  fissure,  corresponding  to  the 
sulco-marginal  fasciculus  of  man  (Dexler). 


The  Brain 

The  brain  or  encephalon  is  the  part  of  the  central  nervous  system  that  is 

situated  in  the  cranial  cavity.     It  is  the  enlarged  and  highly  modified  cephalic 

part  of  the  primitive  neural  tube.     It  conforms  in  great  part  in  size  and  shape  to 

the  cavity  in  which  it  lies.     Its  average  weight  without  the  dura  mater  is  about 

^  These  are  also  known  as  the  columns  of  Goll  and  of  Burdach  respectively. 


THE    BRAIN  769 

23  ounces  (ca.  650  gm.),  and  forms  about  y  of  1  per  cent,  of  the  body-weight  in  a 
subject  of  medium  size. 

It  is  desirable  to  examine  the  general  external  configuration  of  the  brain  before 
studying  its  various  parts  in  detail.^ 

When  divested  of  its  membranes  and  vessels  (Fig.  629),  its  ventral  surface  or 
base  presents  the  median  brain  stem  (Caudex  encephali),  which  is  continuous  with 
the  spinal  cord  without  any  natural  line  of  demarcation;  it  divides  in  front  into 
two  branches,  the  cerebral  peduncles,  each  of  which  disappears  into  the  mass  of 
the  corresponding  cerebral  hemisphere.  The  brain  stem  consists  of  three  parts. 
The  medulla  oblongata  is  the  posterior  part  which  extends  forward  as  the  direct 
continuation  of  the  spinal  cord.  The  pons  is  a  transversely  elongated  mass  which 
appears  to  turn  up  on  either  side  into  the  cerebellum.  The  cerebral  peduncles 
(Pedunculi  cerebri)  extend  forward  from  the  pons  and  diverge  to  plunge  into  the 
ventral  part  of  the  cerebral  hemispheres.  The  area  between  them  is  the  inter- 
peduncular fossa.  It  is  largely  covered  by  the  hjrpophysis  cerebri  or  pituitary 
body,  a  yellowish-brown,  discoid  structure,  which  is  connected  with  the  base  of 
the  cerebrum  by  a  delicate  tube  called  the  infundibulum.''  On  drawing  the  pitu- 
itary body  gently  aside,  the  infundibulum  is  seen  to  be  attached  to  a  slight  gray 
eminence,  the  tuber  cinereum.  Behind  this  is  the  mammillary  body  (Corpus 
mamillare),  a  well-marked  round  prominence.  The  posterior  part  of  the  space 
is  perforated  by  numerous  openings  for  the  passage  of  small  arteries,  and  hence 
is  termed  the  substantia  perforata  posterior.  A  large  band  of  white  matter,  the 
optic  tract  (Tractus  opticus),  crosses  the  anterior  end  of  the  cerebral  peduncle  ob- 
liquely, and  unites  with  the  opposite  tract  to  constitute  the  optic  chiasm  or  commis- 
sure (Chiasma  opticum),  and  form  the  anterior  boundary  of  the  interpeduncular 
fossa.  Above  and  in  front  of  the  chiasm  the  hemispheres  are  separated  by  the 
median  longitudinal  fissure.  In  contact  with  the  anterior  extremity  of  each 
hemisphere  is  the  olfactory  bulb  (Bulbus  olfactorius),  an  oval  enlargement  which 
occupies  the  ethmoidal  fossa  of  the  cranium.  This  appears  as  a  gray  swelling 
on  a  wide  flat  band,  the  olfactory  tract  or  peduncle  (Tractus  olfactorius),  which 
is  continued  behind  by  two  divergent  bands,  the  olfactory  striae.  The  medial 
stria  (Stria  medialis)  disappears  after  a  very  short  course  on  to  the  medial  surface 
of  the  hemisphere.  The  lateral  stria  (Stria  lateralis)  is  larger  and  longer;  it  runs 
backward,  inclines  at  first  outward  and  then  curves  medially  and  disappears  on 
the  concealed  or  tentorial  surface  of  the  hemispheres.  It  is  separated  from  the 
lateral  cerebral  gyri  by  a  distinct  groove  (Sulcus  rhinalis).  Along  the  medial  side 
of  the  stria  are  two  eminences.  The  anterior  of  these  is  the  trigonum  oLfactoriimi, 
a  gray  elevation  situated  in  the  angle  of  divergence  of  the  medial  and  lateral  strise. 
Behind  this  is  a  depression,  the  fossa  lateralis,  which  is  continued  across  the  lateral 
stria  and  sharply  limits  the  second  and  much  larger  eminence,  the  piriform  lobe. 

The  superficial  origins  of  most  of  the  cranial  nerves  are  visible  on  the  base  of 
the  brain. 

The  olfactory  nerve-fibers  join  the  convex  surface  of  the  olfactory  bulb  and  give 
it  a  shaggy  appearance  in  specimens  which  have  been  removed  intact — a  difficult 
proceeding. 

The  second  or  optic  nerves  converge  to  the  optic  chiasm. 

The  third  or  oculomotor  nerve  arises  from  the  mechal  part  of  the  cerebral 
peduncle. 

1  The  description  given  here  is  intended  to  present  the  chief  facts  in  regard  to  the  brain  as 
they  may  be  studied  in  the  dissecting-room.  The  vessels  and  membranes,  which  must  be  exam- 
ined first,  have  been  described. 

2  Unless  care  is  used  in  removing  the  brain,  the  infimdibulum  is  hkely  to  be  torn  and  the 
hypophysis  left  in  the  cranium.  In  this  case  there  is  a  small  opening  which  communicates  with 
the  third  ^'entricle. 

49 


770 


NERVOUS    SYSTEM    OF   THE    HORSE 


The  fourth  or  trochlear  nerve  may  be  seen  emerging  between  the  pons  and  the 
cerebral  hemisphere,  but  its  connection  ^ith  the  brain  is  not  visible. 

The  fifth  or  trigeminal  nerve  is  connected  with  the  lateral  part  of  the  pons. 


Fig.  629.— Base  of  Bkai.n  of  House    About  Natural  Size. 
Hardened  in  situ 

The  sixth  or  abducent  nerve  arises  just  behind  the  pons  and  lateral  to  the 
pyramid  of  the  medulla. 

•     +  I^^-  ^^^^"*^  0^  ^^^^^^  and  the  eighth  or  acoustic  nerves  arise  close  together 
just  behmd  the  pons  on  the  extremity  of  the  corpus  trapezoideum. 


THE    BRAIN 


71 


The  ninth  or  glosso-pharyngeal,  the  tenth  or  vagus,  and  the  eleventh  or  spinal 
accessory  nerves  are  connected  by  a  Hnear  series  of  roots  with  the  lateral  aspect  of 
the  ventral  surface  of  the  medulla.  The  spinal  part  of  the  accessory  nerve  comes 
forward  along  the  edge  of  the  medulla  to  join  its  medullary  root. 

The  twelfth  or  hypoglossal  nerve  arises  from  the  posterior  part  of  the  medulla 
along  the  lateral  edge  of  the  pyramid. 

The  parts  that  are  visible  when  the  brain  is  viewed  from  above  are  the  cerebral 
hemispheres,  the  cerebellum,  and  part  of  the  medulla  oblongata.  The  cerebral 
hemispheres  (Hemisphseria  cerebri)  form  an  ovoid  mass,  and  are  separated  from 
each  other  by  the  median  longitudinal  fissure   (Fissura  longitudinalis  cerebri), 

Lonrjil  udinal  fiss  ure 


Sulcus  rhinalis  v^ 
Oplic  nerve  ^ 
Optic  chiasma-^^^ 
Tuber  cinereum 
Piriform  lobe 
Pituitary  body  -' 
Oculomotor  nerve 

sensory  root  ^^ 

motor  root  — 

Cerebellum-^ 

Tuberculum  faciale  — 

Glosso-pharyngeal  nerve 

Vagus  nerve 

Accessory  nerve  {medullary  root) 

Accessory  nerve  {spinal  root) 

Hypoglossal  nerve  - 


Fig.  630. — Line  Drawing  of 
VI,  Abducent  nerve; 


Trigeminal 
nerve 


—  Olfactory  bulb 
^^^  Olfactory  tract 

__^--  Medial  stria 

—  Lateral  stria 
—  Trigonum  olfactorium, 

~  Fossa  lateralis 
-Cerebral  peduncle 
-  Tractus  ped.  transversus 
'—.  Intel-peduncular  fossa 

—  Pons 
Co7-pus  trapezoideum 

Pyramid 
Medulla  oblongata 

^-—  Chorioid  plexus  of  fourth 
ventricle 
-Median  fissure  and   de- 
cussation of  pyramids 
'  Spinal  cord 


!ase  of  Brain  of  Horse.     (Key  to  Fig.  629.) 
'II,  facial  nerve;    VIII,  acoustic  nerve. 


in  which  the  falx  cerebri  is  situated.  Their  surfaces  are  marked  by  thick  ridges, 
the  gyri  cerebri,  separated  by  sulci.  The  upturned  ends  of  the  olfactory  bulbs 
are  seen  in  front  of  the  frontal  poles  of  the  hemispheres.  The  occipital  poles  of 
the  hemispheres  overlie  the  anterior  part  of  the  cerebellum,  from  which  they  are 
separated  by  the  transverse  fissure  (Fissura  transversa  cerebri)  and  the  tentorium 
cerebelli  contained  in  it.  The  cerebellum  is  a  much  smaller  rounded  mass  which  con- 
ceals the  greater  part  of  the  medulla  oblongata.  Its  surface  is  divided  into  a  middle 
lobe,  the  vermis  cerebelli,  and  two  lateral  hemispheres  (Hemisphseria  cerebelli).  It 
is  marked  by  numerous  gyvi  and  narrow  sulci  which  have  in  general  a  transverse  direc- 
tion.    The  posterior  third  of  the  medulla  oblongata  is  not  covered  by  the  cerebellum. 

The  brain  is  developed  from  the  expanded  cephalic  part  of  the  neural  tube  of  the  enibryo. 
The  process  comprises  a  series  of  thickenings,  flexures,  and  unequal  growth  and  expansion  of 


772 


NERVOUS   SYSTEM   OF   THE   HORSE 


various  parts  of  the  tube.  In  the  higher  animals  the  resuh-  is  that  the  tubular  character  of  the 
brain  is  not  very  evident,  since  the  lumen  comes  to  consist  of  four  irregular  cavities,  the  cerebral 
ventricles,  which  are  connected  by  narrow  passages.  The  tube  is  first  subdivided  by  two  con- 
strictions into  three  brain  vesicles,  termed  respectively  the  hind-brain  or  rhombencephalon,  the 
mid-brain  or  mesencephalon,  and  the  fore-brain  or  prosencephalon.  The  hind-brain  gives  rise  to 
three  secondarj^  segments  and  the  fore-brain  to  two.  The  annexed  table  indicates  the  origin  of  the 
principal  structures  of  the  fully  developed  brain  from  the  primitive  vesicles.  It  has  become 
customary  to  describe  the  brain  with  reference  to  its  embryological  relations. 


Longitvdinal 
fissure 


Transverse 


Olfactory  bulb 

Frontal  ■pole  of  hemisphere 


Cerebrum 


Occipital  pole  of 
hemisphere 


Cerebellum 


Medulla  oblongata 


Fig.  631. — Brain  of  Horse;  Dorsal  View,  About  f  Natural  Size.     Hardened  in  situ. 
1,  Entomarginal  fissure;  2,  marginal  fissure;  3,  ectomarginal  fissure;  4t  suprasylvian  fissure. 


TABLE  INDICATING  THE  DERIVATION  OF  THE  PRINCIPAL  PARTS  OF  THE 


Primary  Segments. 


Rhombencephalon     (pos- 
terior vesicle) 


Mesencephalon      (middle 
vesicle) 


Prosencephalon        (ante- 
rior vesicle) 


BRAIN 

Secondary  Segments.  Derivatives. 

Myelencephalon Medulla  oblongata.  .  . 

Pons 


Anterior  cerebellar  peduncles. 
Anterior  medullary  velum  .  .  . 


Cavities. 
Fourth  ventricle 


Metencephalon |  Cerebellum 

Isthmus  rhombencephali 

Mesencephalon {  g°X^^,  ^^^f^S'!^.^.  :::::::}  Cerebral  aqueduct 

Diencephalon 


Optic  thalami 

Hypothalamic  tegmenta. 


Telencephalon. 


Pineal  body . 

Pituitary  body 

Optic  nerves  and  retinae.  . 
Cerebral  hemispheres  .  .  .  . 
Olfactory  tracts  and  bulb. 


Posterior  part  of  third 
ventricle 

Anterior  part   of   third 
ventricle.  Lateral 

ventricles   and  olfac- 
tory continuations. 


THE    RHOMBENCEPHALON  773 


THE  RHOMBENCEPHALON 
The  Medulla  Oblongata 

The  meduUa  oblongata  (Figs.  629,  632,  635)  lies  on  the  basilar  part  of  the 
occipital  bone.  It  is  quadrilateral  in  outline,  but  much  wider  in  front  than  behind, 
and  compressed  dorso-ventrally.  Its  length,  measured  from  the  root  of  the  first 
cervical  nerve  to  the  pons,  is  about  two  inches  (ca.  5  cm.). 

Its  ventral  surface  is  convex  in  the  transverse  direction,  and  presents  a  ventral 
median  fissure  (Fissura  mediana  ventralis),  which  is  continuous  behind  with  the 
similar  fissure  of  the  spinal  cord.  The  posterior  part  of  the  fissure  is  faintly  marked, 
but  in  front  it  becomes  deeper  and  ends  in  a  small  depression  (Foramen  caecum) 
behind  the  central  part  of  a  transverse  band,  the  corpus  trapezoideum.  On  either 
side  of  the  fissure  is  a  rounded  tract,  the  p3rrainid  (Pyramis),  which  is  bounded 
laterally  by  a  faint  groove  (Sulcus  intermedins  ventralis).  The  pyramids  join 
the  pons  in  front ;  behind  they  become  narrower  and  disappear  into  the  substance 
of  the  medulla,  in  which  their  fibers  intercross,  forming  the  decussation  of  the 
pyramids  (Decussatio  pyramidum).^  The  superficial  origin  of  the  oculomotor 
nerve  (N.  oculomotorius)  is  just  lateral  to  the  anterior  end  of  the  pyramid.  The 
corpus  trapezoideimi  is  a  transverse  band  which  extends  across  the  surface  imme- 
diately behind  the  pons.  It  is  crossed  by  the  pyramids,  which  cut  off  a  small 
central  part.  The  lateral  part  extends  out  to  the  roots  of  the  seventh  and  eighth 
nerves  on  either  side.  Behind  the  lateral  part  of  the  corpus  trapezoideum  there 
is  a  variably  developed  rounded  eminence,  the  tuberculum  faciale.  The  root- 
fibers  of  the  hypoglossal  nerve  form  an  oblique  linear  series  lateral  to  the  posterior 
part  of  the  pyramid. 

The  dorsal  surface  is  largely  concealed  by  the  cerebellum  and  forms  the  greater 
part  of  the  floor  of  the  fourth  ventricle.  The  dorsal  median  fissure  (Fissura 
mediana  dorsalis) ,  the  direct  continuation  of  the  corresponding  groove  of  the  spinal 
cord,  extends  forward  to  about  the  middle  of  the  surface.  Here  the  restiform 
bodies,  which  constitute  the  lips  of  the  fissure,  diverge  to  form  the  lateral  boun- 
daries of  a  triangular  depression;  this  is  the  posterior  part  of  the  rhomboid  fossa  or 
floor  of  the  fourth  ventricle  of  the  brain.  The  dorso-lateral  groove  winds  outward 
and  forward  to  the  lateral  aspect  of  the  medulla,  where  it  presents  the  roots  of  the 
glosso-pharyngeal,  vagus,  and  accessory  nerves.  Lateral  to  it  is  a  distinct  oval 
eminence  on  the  anterior  part  of  the  lateral  column,  termed  the  tuberculum  cin- 
ereum.  The  central  canal  of  the  cord  is  continued  in  the  posterior  part  of  the 
medulla,  inclines  dorsally,  and  opens  in  the  posterior  angle  of  the  fourth  ventricle. 
Hence  it  is  customary  to  distinguish  a  closed  and  an  open  part  of  the  medulla. 
The  dorsal  aspect  of  the  latter,  which  is  concealed  at  present,  will  be  considered 
later  in  the  description  of  the  fourth  ventricle. 

The  lateral  surface  is  narrow  behind,  wider  and  rounded  in  front.  From  it 
the  root-fibers  of  the  ninth,  tenth,  "and  eleventh  cranial  nerves  arise  in  a  linear 
series,  and  alongside  of  it  the  spinal  part  of  the  eleventh  nerve  passes  forward  to 
join  the  medullary  root.  Close  inspection  reveals  the  presence  of  strige  which 
curve  ventrally  and  backward  from  the  surface  of  the  restiform  body  toward  the 
hypoglossal  root-fibers;  these  are  the  external  arcuate  fibers  (Fibrse  arcuatae 
externse) .  The  recess  between  the  lateral  aspect  of  the  medulla  and  the  cerebellum 
is  occupied  by  an  irregular  mass  of  villous  projections  of  the  pia  mater,  containing 
tufts  of  vessels;  this  is  the  chorioid  plexus  of  the  fourth  ventricle,  and  is  the  lateral 
edge  of  the  tela  chorioidea  of  the  ventricle.  On  raising  the  chorioid  plexus,  it  is 
seen  that  the  tela  chorioidea  is  attached  to  the  dorsal  aspect  of  the  medulla,  and 
reinforces  here  the  wall  of  the  fourth  ventricle;    also  that  the  restiform  body  ter- 

1  The  decussation  varies  superficially  in  different  specimens.  In  some  there  is  a  distinct 
superficial  crossing  of  fibers  so  that  the  median  fissure  is  practically  effaced  at  this  point. 


774  NERVOUS   SYSTEM    OF   THE   HORSE 

minates  in  front  bj^  entering  the  base  of  tlie  cerebellum,  forming  its  posterior 
peduncle. 

In  the  medulla  the  fiber  tracts  of  the  spinal  cord  either  terminate  in  the  nuclei  of  the  gray 
matter  or  undergo  changes  in  their  relative  position,  and  new  tracts  appear.  The  gray  matter 
is  highly  modified  and  forms  masses  which  have  no  homologues  in  the  cord.  The  central  canal 
of  the  closed  part  of  the  medulla  is  surrounded  by  a  thicker  layer  of  gray  matter  than  is  the  case 
in  the  spinal  cord.  As  the  medulla  opens  out  this  gray  matter  is  naturally  spread  in  the  floor  of 
the  fourth  ventricle.  The  dorsal  horns  of  gray  matter  become  wide,  siM-ca/l  apart,  and  are  broken 
up  to  a  great  extent  in  the  formatio  reticularis.  Two  elongated  masses  of  cells  appear  above  the 
centr.al  gray  matter;  these  are  the  nucleus  gracilis  anfl  nucleus  cuneatus,  and  in  them  the 
fasciculi  of  like  name  gradually  end.  In  front  of  these  are  the  terminal  nuclei  of  the  afferent  or 
sensory  cranial  nerves  and  of  the  sensory  portions  of  the  mixed  ner\-es.  The  ventral  horns  are 
succeeded  by  the  nuclei  of  origin  ot  the  efferent  or  motor  cranial  ner\'es  and  the  motor  root-fibers 
of  the  mixed  nerves.  Of  the  twelve  pairs  of  cranial  nerves,  the  last  eight  are  cormected  with 
nuclei  in  the  medulla  and  pons.  The  posterior  olivary  nucleus  (Nucleus  olivaris  caudalis)  is  a 
conspicuous  gray  mass  which  lies  dorsal  to  the  pyramid  on  each  side.     On  cross-sections  it  appears 


Transverse  fissure 

Cerebellum 


Medulla 
oblongata 


Olfactory 
tract 

Cerebral 
peduncle 

Fig.  632. — Brain  of  Horse;  Left  View. 
1,  Lateral  fissure;   2,  suprasylvian  fissure;   3,  presylvian  fissure;   4.  ectomarginal  fissure;   5,  5',  sulcus  rhinalis  an- 
terior et  posterior;   L.  p.,  piriform  lobe;   B.  p.,  middle  peduncle  of  cerebellum  (brachium  pontis) ;  P.  c,  choroid  plexus 
of  fourth  ventricle.     Roman  numerals  indicate  roots  of  cranial  nerves. 


as  a  wavy  layer  ot  gray  matter  which  is  folded  on  itself  so  as  to  enclose  a  mass  of  white  matter. 
It  is  about  2  cm.  long  in  the  horse,  but  is  smaller  in  circumference  than  in  man  and  hence  does 
not  cause  any  very  distinct  external  enlargement  (olivary  eminence),  as  in  the  latter.  It  is  con- 
nected with  the  opposite  side  of  the  cerebellum  by  the  cerebello-olivary  fibers.  At  its  medial  side 
are  two  small  accessory  olivary  nuclei.  The  pyramidal  tracts,  which  are  small  in  ungulates,  send 
most  of  their  fibers  across  to  the  opposite  side  in  the  posterior  part  of  the  medulla,  forming  the 
pyramidal  decussation.  Some  fibers,  however,  continue  in  the  ventral  column  of  the  same  side 
of  the  cord,  and  others  are  eonnect(>d  with  the  nuclei  of  the  motor  nerve-roots.  From  the  nu- 
cleus gracilis  and  nucleus  cuneatus  iiln-rs  arise  which  are  traceable  fonvard  to  the  thalamus. 
These  are  the  internal  arcuate  fibers  (Fibra?  arcuatte  internae),  which  curve  across  the  median 
plane  ventral  to  the  central  gray  matter  and  form  with  those  of  the  opposite  side  the  decussation 
of  the  fillet  (Decussatio  lemniscorum).  Beyond  the  decussation  the  fibers  form  an  important 
longitudmal  tract  which  extends  forward  in  the  mid-brain.  This  is  the  fillet  or  lemniscus,  the 
chief  continuation  of  the  sensory  conducting  path  from  the  dorsal  roots  of  the  spinal  nerves. 
The  external  arcuate  fibers  (Fibrse  arcuatse  extemse),  some  of  which  were  seen  on  the  lateral 
aspect  of  the  medulla,  have  a  similar  origin.  Part  of  them  (Fibra;  dorsales)  pass  directly  to  the 
dorsal  aspect  of  the  restiform  body  of  the  same  side;  others  (Fibrse  ventrales)  cross  to  the  opposite 
side,  descend  close  to  the  ventral  fissure,  and  then  curve  upward  and  forward  to  the  restiform  l:)ody. 
The  decussation  of  the  arcuate  fibers  forms  the  distinct  median  raphe  seen  on  cross-sections  of  the 
medulla  anterior  to  the  pyramidal  decussation.  The  restiform  body,  situated  dorso-laterally, 
contains,  in  addition  to  the  arcuate  fibers,  the  cerebello-olivary  fasciculus  before  mentioned, 


THE    PONS 


775 


and  the  cerebellospinal  fasciculus  or  direct  cerebellar  tract.  The  dorsal  longitudinal  fascic- 
ulus corresponds  to  the  ventral  grountl-bundle  of  the  spinal  cord,  displaced  dorsally  by  the  decus- 
sation of  the  pyramids  and  fillet.  In  the  posterior  part  of  the  medulla  it  is  not  marked  off  from 
the  fillet,  along  the  dorsal  edge  of  which  it  lies.  From  the  level  of  the  hypoglossal  nucleus  forward 
it  is  distinct  and  can  be  traced  as  a  conspicuous  tract  in  the  ventral  margin  of  the  gray  matter  of  the 
floor  of  the  fourth  ventricle  and  of  the  central  gray  matter  of  the  mid-brain.  Ventral  to  the  resti- 
form  body  and  related  laterally  to  the  external  arcuate  fibers  there  is  a  considerable  bundle  of 
longitudinal  fibers,  the  spinal  root  (Tractus  spinalis)  of  the  fifth  nerve;  medial  to  it  is  the 
terminal  nucleus  of  the  sensory  root  of  the  nerve. 


^"^m^ 


Fig.  63.3. — Cross-section  of  Medulla  Oblongata  of  Horse,  Passing  through  Facial  Nucleus. 
Cr,  Corpus  restiforme ;   Z),  dorsal  longitudinal  fasciculus;   Fa,  ascending  part  of  facial  nerve;    L,  fillet;   A''?',  nucleus 
of  facial  nerve;  N8,  triangular  nucleus  of  of  vestibular  root  of  eighth  nerve;   NS',  spinal  root  of  eighth  nerve;  Py,  pyra- 
mid; /?a,  raphe;   ff7,  radicular  part  of  facial  nerve;   flS,  vestibular  root  of  eighth  nerve;  S;/,  substantia  gelatinosa;   Ta, 
posterior  end  of  tuberculum  acusticum;   V,  spinal  root  of  trigeminus.     (EUenberger-Baum,  Anat.  d.  Haustiere.) 


C 


K 


\ 


f,    K 


Fig.   6.34. — Cross-section  of  Medulla  Oblongata  of  Horse;  Section  Passes  through    Middle   of  Corpus 

Tr.^pezoideum. 
Cr,  Corpus  restiforme;  D,  dorsal  longitudinal  bundle;  Fa,  ascending  part  of  facial  nerve;  Fa',  emergent  or  de- 
scending part  of  facial  nerve;  L,  fillet;  M,  central  white  matter  of  cerebellum;  N6,  abducens  nucleus;  A',?,  triangular 
nucleus;  N8',  nucleus  of  Deiters;  N8",  tuberculum  acusticum;  Oo,  anterior  olive;  Pi/,  pyramid;  R6,  root  of  abducens 
nerve;  R7,  root  of  facial  nerve;  Re,  cochlear  nerve;  Rv,  vestibular  nerve;  Sg,  substantia  gelatinosa;  T,  corpus 
trapezoideum;    V,  spinal  root  of  trigeminus.     (Ellenberger-Baum,  Anat.  d.  Haustiere.) 


The  Pons 
The  pons  is  that  part  of  the  brain  stem  which  Hes  between  the  medulla  and 
the  cerel^ral  peduncles;    it  is  marked  off  from  these  ventrally  by  anterior  and 


776  NERVOUS    SYSTEM    OF   THE   HORSE 

posterior  grooves.  Viewed  ventrally,  it  is  elongated  transversely,  convex  in 
both  directions,  and  presents  a  -wide  shallow  median  groove  (Sulcus  basilaris), 
which  lodges  the  basilar  artery.  Laterally  a  large  part  of  its  mass  curves  dorsally 
and  backward  into  the  base  of  the  cerebellum,  forming  the  middle  cerebellar 
peduncle  (Brachium  pontis).  The  superficial  origin  of  the  trigeminal  (fifth)  nerve 
is  at  the  lateral  limit  of  the  ventral  surface.  Transverse  striations  indicate  the 
course  of  superficial  (ventral)  fibers  which  connect  the  two  sides  of  the  cerebellum. 
The  dorsal  surface  is  blended  on  either  side  with  the  overlying  anterior  peduncles 
of  the  cerebellum;  the  central  free  portion  forms  the  anterior  part  of  the  floor  of 
the  fourth  ventricle,  and  will  be  considered  in  the  account  of  that  cavity. 

On  cross-section  the  pons  is  seen  to  be  composed  of  dorsal  and  ventral  parts.  The  dorsal 
part  (Pars  dorsaUs  pontis)  consists  superficially  of  a  layer  of  gray  matter  covered  by  the  epen- 
dyma  of  the  fourth  ventricle.  Beneath  this  the  median  raphe  of  the  medulla  is  continued  into 
the  pons,  di\dding  it  into  similar  halves.  In  the  anterior  part  of  the  pons  the  fillet  div-ides  into 
a  medial  and  a  lateral  part,  the  medial  and  lateral  fillets  (Lemniscus  mediahs,  lateralis) ;  the  latter 
arches  outward  to  reach  the  outer  side  of  the  anterior  cerebellar  peduncle.  The  dorsal  longitudinal 
fasciculus  becomes  sharply  defined  into  a  round  bundle  which  hes  close  to  the  raphe  under  the 
gray  matter  of  the  floor  of  the  fourth  ventricle.  In  cross-section  the  formatio  reticularis  forms 
a  large  area  below  the  superficial  gray  matter  and  the  longitudinal  bundles.  Dorso-lateraUy  is 
the  large  rounded  section  of  the  anterior  cerebellar  peduncle.  Lower  down  is  a  large  bundle,  the 
sensory  root  of  the  fifth  nerve.  In  front  of  this  is  the  motor  nucleus  of  the  same  nerve,  lateral 
to  which  is  its  motor  root.  The  basilar  or  ventral  part  of  the  pons  (Pars  basilaris  pontis)  is  com- 
posed of  transverse  and  longitudinal  fibers,  and  a  large  amount  of  gray  matter  which  is  broken  up 
into  small  masses  (Nuclei  pontis)  by  the  intersection  of  the  fibers.  The  transverse  fibers  are  gath- 
ered laterally  into  a  compact  mass  which  turns  dorsally  and  backward  and  enters  the  central  white 
matter  of  the  cerebellum,  forming  the  middle  cerebellar  peduncle.  Centrally  the  fibers  are  ar- 
ranged in  bundles  which  intercross.  The  transverse  fibers  are  chiefly  of  two  kinds.  Some  arise 
from  the  Purkinje  cells  of  the  cerebellar  cortex  and  pass  either  to  the  opposite  side  of  the  cere- 
bellum or  turn  at  the  raphe  and  run  forward  and  backward  in  the  brain  stem.  Others  are  axones 
of  cells  of  the  nuclei  pontis,  and  pass  to  the  hemispheres  of  the  cerebellum.  The  corpus  trape- 
zoideum  is  mainly  the  central  continuation  of  the  cochlear  division  of  the  acoustic  nerve.  Above 
it  is  the  smaU  anterior  olivary  nucleus  (Nucleus  ohvaris  nasaUs).  The  longitudinal  fibers  of  the 
ventral  part  of  the  pons  consist  chiefly  of  the  cerebrospinal  or  pyramidal  fasciculi.  These  come 
from  the  ventral  part  (basis)  of  the  cerebral  peduncles  and  are  situated  laterally,  interspersed 
among  the  deep  transverse  fibers  in  the  anterior  part  of  the  pons.  Toward  the  posterior  part  the 
bundles  inchne  toward  the  median  plane  and  become  collected  into  a  compact  mass  which  appears 
superficially  at  the  posterior  border.  Many  fibers  come  from  the  cerebral  cortex  and  terminate 
in  the  nuclei  of  the  gray  matter  of  the  pons;  they  may  be  designated  corticopontile  fibers. 


The  Cerebelujm 

The  cerebellum  is  situated  in  the  posterior  fossa  of  the  cranium,  and  is  sep- 
arated from  the  cerebral  hemispheres  by  the  transverse  fissure  and  the  tentorium 
cerebelli  which  occupies  it.  It  overlies  the  pons  and  the  greater  part  of  the  medulla, 
from  which  it  is  separated  by  the  fourth  ventricle.  Its  average  weight  is  about  two 
ounces  (ca.  60  gm.),  or  about  9  per  cent,  of  the  weight  of  the  entire  brain.  Its 
shape  is  approximately  globular  but  very  irregular.  It  is  somewhat  compressed 
dorso-ventrally  and  its  transverse  diameter  is  the  greatest. 

The  anterior  surface  faces  dorsally  and  forward  and  is  covered  partially  by 
the  tentorium  cerebelli.  The  posterior  surface  is  almost  vertical.  The  ventral 
siuiace  or  base  lies  over  the  fourth  ventricle,  and  is  connected  by  three  pairs  of 
peduncles  \vith  the  medulla,  pons,  and  mid-brain. 

It  is  customary  to  recognize  three  gross  divisions  of  the  cerebellum,  viz.,  the 
median  vermis  and  two  lateral  hemispheres.  The  vermis  cerebelli  is  curved  in  a 
circular  manner  so  that  its  two  extremities  are  close  together,  or  even  in  contact 
on  the  ventral  surface.  The  anterior  extremity  is  termed  the  lingula;  it  lies 
between  the  cerebellar  peduncles  and  gives  attachment  to  the  anterior  medullary 
velum  (Velum  medullare  orale),  a  thin  lamina  which  forms  the  anterior  part  of  the 
roof  of  the  fourth  ventricle.  The  posterior  extremity,  the  nodulus,  gives  attach- 
ment to  the  posterior  medullary  velum  (Velum  medullare  aborale),  which  covers  the 
posterior  recess  of  the  fourth  ventricle.     The  hemispheres  (Hemisphseria  cerebelli) 


THE    CEREBELLUM  777 

are  separated  from  the  vermis  by  two  deep  paramedian  fissures.     They  lie  in  the 
lateral  depressions  of  the  cerebellar  compartment  of  the  cranium. 

In  tracing  the  fissures  from  behind  forward  it  will  be  noticed  that  they  are  nearly  sagittal 
as  far  as  the  anterior  surface,  where  they  diverge  widely,  so  that  the  vermis  forms  all  of  the  fore 
part  of  the  cerebellum. 

The  surface  of  the  cerebellum  is  further  cut  up  into  numerous  g3Ti  (cerebelli) 
by  narrow  and  relatively  deep  sulci  (cerebelli),  many  of  which  approach  a  trans- 
verse direction.  Certain  of  the  sulci  are  more  pronounced  than  the  others,  and  by 
means  of  them  it  is  possible  to  define  groups  of  gyri.  Such  groups  are  termed 
lobes,  and  have  received  specific  names,  derived  chiefly  from  the  systematic  de- 
scriptions of  the  human  cerebellum. 

The  lobes  of  the  vermis  are  readily  distinguished  on  median  section.  Enumerated  from 
the  anterior  to  the  posterior  extremity  they  are:  (1)  lingula,  (2)  lob  us  centralis,  (3)  lob  us  ascendens, 
(4)  lobus  culminis,  (5)  lobus  chvi,  (6)  tuber  vermis,  (7)  pyramis,  (8)  uvula,  (9)  nodulus.  Each 
hemisphere  is  cut  into  laterally  by  two  sulci  which  mark  off  two  sagittal  discoid  masses,  termed  by 
Ziehen  tabulations.  The  lateral  tabulation  consists  of  four  or  five  lobules,  the  lowest  of  which 
is  regarded  as  the  flocculus.  The  medial  part  of  the  hemisphere  is  divided  into  three  or  four  lobes. 
Martin  proposes  the  term  tractus  for  the  sagittal  masses;  on  tliis  basis  the  vermis  would  become 
the  tractus  medianus,  and  the  others  tractus  laterales  (primus,  secundus,  etc.).  In  the  absence 
of  a  satisfactory  morphological  basis  it  seems  undesirable  to  deal  with  the  lobation  of  the  cere- 
bellum in  further  detail. 

The  cerebellar  peduncles  (Pedunculi  cerebelli),  three  on  each  side,  join  the 
central  white  matter  of  the  cerebellum  at  the  base.  The  posterior  peduncle  is  the 
restiform  body  of  the  medulla,  a  large  rounded  tract  derived  from  the  lateral  and 
ventral  columns  of  the  cord.  Near  the  middle  of  the  medulla  it  inclines  outward, 
forms  the  lateral  wall  of  the  fourth  ventricle,  and  ends  by  entering  the  central  white 
matter  of  the  cerebellum.  The  middle  peduncle  is  formed,  as  previously  seen,  by 
the  brachium  pontis.  The  anterior  peduncles  (Brachia  conjunctiva)  pass  forward 
on  either  side  on  the  dorsal  surface  of  the  pons,  forming  the  lateral  boundary  of  the 
fore  part  of  the  fourth  ventricle.  They  disappear  under  the  corpora  quadrigemina 
into  the  substance  of  the  mid-brain.  At  the  point  of  disappearance  the  trochlear 
(fourth)  nerve  emerges  from  the  mid-brain.  In  some  cases  two  or  three  bundles  of 
fibers  (Fila  lateralia  pontis)  arise  in  the  angle  between  the  middle  and  anterior 
peduncle,  curve  obliquely  forward  and  downward  over  the  outer  aspect  of  the 
latter,  and  spread  out  on  the  ventral  face  of  the  cerebral  peduncle  just  in  front  of 
the  pons. 

On  sagittal  section  the  cerebellum  is  seen  to  consist  of  a  layer  of  gray  cortical 
substance  (Substantia  corticalis)  and  the  white  meduUary  substance.  The  white 
matter  consists  of  a  large  basal  mass  (Corpus  meduUare),  which  is  joined  by  the 
peduncles  and  gives  off  primary  laminae  (Laminae  medullares)  to  the  lobules; 
from  these  secondary  and  tertiary  laminae  arise,  the  latter  entering  the  gyri.  The 
arrangement  on  sagittal  section  is  tree-like,  hence  the  term  "arbor  meduUaris," 
which  is  applied  to  it.^  The  central  gray  matter  consists  of  groups  of  cells  which 
form  small  nuclei  embedded  in  the  central  white  substance. 

The  principal  connections  estabUshed  by  the  peduncular  fibers  of  the  cerebellum  are  as 
follows:  The  posterior  peduncle  (Corpus  restiforme)  is  composed  of  afferent  and  efferent  fibers 
which  connect  the  cerebellum  with  the  medulla  and  spinal  cord.  The  cerebello-spinal  fascicu- 
lus or  direct  cerebellar  tract,  which  arises  from  the  cells  of  the  nucleus  dorsahs  (Clarke's  column) 
of  the  cord,  ends  in  the  cortex  of  the  vermis;  many  of  its  fibers  cross  to  the  opposite  side.  Nu- 
merous arcuate  fibers  from  the  nucleus  gracilis  and  nucleus  cuneatus  of  the  same  and  opposite 
sides  estabhsh  connections  with  cells  of  the  cerebellar  cortex.  Olivo-cerebellar  fibers  (chiefly 
afferent)  connect  with  the  ohvary  nucleus  of  the  same  and  of  the  opposite  side  of  the  medulla 
oblongata.  The  nucleo-cerebellar  fasciculus  comprises  fibers  derived  from  the  nuclei  of  the 
fifth,  eighth,  and  tenth  cranial  nerves  (Edinger).  The  descending  cerebello-spinal  fasciculus 
consists  of  fibers  wliich  terminate  in  relation  with  cells  of  the  ventral  horns  of  the  spinal  cord. 
The  chief  facts  concerning  the  middle  peduncle  have  been  mentioned  in  the  description  of  the 
pons.     The  anterior  peduncle  is  essentially  an  efferent  tract,  the  fibers  of  which  pass  forward 

^  Also  known  as  the  "arbor  vitae." 


778 


NERVOUS    SYSTEM    OF   THE    HORSE 


to  the  tegmentum  of  the  cerebral  peduncle,  the  hypothalamic  region,  and  the  thalamus.  After 
the  peduncles  disappear  under  the  corpora  quadrigemina,  they  converge  and  many  of  their  fibers 
intercross,  forming  the  decussation  of  the  anterior  peduncles.  A  considerable  number  of  fibers 
end  in  tlic  nucleus  ruber.  Thence  impulses  are  transmitted  in  two  directions:  first,  by  thalamo- 
cortical fibers  to  the  cerebral  cortex;  second,  by  the  rubro-spinal  tract  through  the  brain  stem 
and  lateral  columns  of  the  cord  to  the  ventral  horn  cells.  The  ventro-lateral  cerebellospinal 
fasciculus  (Gowers'  tract)  is  an  ill-defined  tract  which  connects  the  spinal  cord  with  the  cere- 
bellum. Its  fibers  appear  to  be  axones  of  cells  of  the  dorsal  columns  of  the  cord;  they  pass 
in  the  lateral  column  of  the  cord,  become  scattered  in  passing  through  the  reticular  formation 
of  the  medulla  and  pons,  and  enter  the  cerebellum  by  way  of  the  anterior  medullary  velum. 

The  Fourth  Ventricle 
The  fourth  ventricle  (Ventriculus  quartus)  is  the  cavity  of  the  rhombencepha- 
lon;  it  communicates  with  the  central  canal  of  the  spinal  cord  behind  and  through 


Corpus  callosum  {section)         Lateral  vtnlrich 


Plrxiis  chorioideus 

Cor/)us  quddrigt'tninum 

(in(('i-ius 

Corpus  qudflrigt-mirium 

posterius 


Septum  pellucidum 

Nucleus  caudatus 

I'halantus  {anterior 
tubercle) 

Stria  terminalis 


Corpus  geniculatum 
Idterale 

Corpus  geniculatum  mediate 

Peduiiculus  cerebri 

Velum  medullare  anterius 


Brachium  conjunctivum 
Brachium  pontis 


Corpus  restiforme 

Ca  la  m  us  scri  plori  us 
Tuberculum  cinereum 

Fissura  mediana 


Fig.  635. — Dissection  of  Brain  Stem  and  Basal  Ganglia  of  Horse;  Dorsal  View. 
/,  Columns  of  fornix  (section) ;  2,  remnant  of  hippocampus;  3,  taenia  thalami;  4,  pineal  body;  S,  eminentia  medialia; 
e,  sulcus  inedianus;  7,  sulcus  limitans;   V.IIL,  third  ventricle;  V.IV.,  fourth  ventricle.     Stump.s  of  cranial  nerves  are 
indicated  by  Roman  numerals. 


Tuberculu m  acusticum 
Tcenia  ventriculi  quarti 


the  cerebral  aqueduct  with  the  third  ventricle  in  front.     It  is  somewhat  rhomboid 
in  outline,  elongatetl  from  before  backward,  and  narrowest  behind.     It  is  lined 
completely  by  an  epithelium  (Ependyma)  and  contains  a  small  amount  of  fluid. 
Its  floor,  the  fossa  rhomboidea,  is  formed  by  the  medulla  oblongata  and  pons 


THE    FOURTH    VENTRICLE  779 

and  is  marked  by  three  longitudinal  furrows  which  converge  behind.  It  is  widest 
and  deepest  a  little  in  front  of  its  middle.  The  posterior  part  narrows  to  a  point  at 
the  opening  of  the  central  canal  of  the  spinal  cord,  and  on  account  of  its  appearance 
in  man  it  has  been  termed  the  calamus  scriptorius.  The  median  sulcus  (Sulcus 
medianus)  extends  the  entire  length  of  the  floor  and  is  deepest  toward  the  ends. 
The  limiting  sulci  (Sulci  limitantes)  begin  on  either  side  of  the  opening  of  the  central 
canal  and  extend  forward  as  the  lateral  limits  of  the  rhomboid  fossa.  Just  beyond 
the  middle  of  the  fossa  they  expand  into  a  shallow  depression,  the  anterior  fovea 
(Fovea  oralis).  On  either  side  of  the  median  sulcus  and  margined  laterally  by  the 
limiting  sulcus  is  a  slightly  rounded  column,  the  eminentia  medialis.  Opposite  the 
fovea  this  presents  an  elongated  prominence,  the  coUiculus  facialis,  so  named  be- 
cause it  overlies  the  bend  formed  by  the  fibers  of  origin  of  the  facial  nerve.  Lateral 
to  the  limiting  sulcus  is  a  long  fusiform  elevation,  the  area  acustica,  from  which  a 
band  of  fibers  (Striae  acusticae)  winds  over  the  anterior  end  of  the  restiform  body  to 
the  superficial  origin  of  the  cochlear  nerve. 

The  lateral  wall  is  formed  by  the  restiform  body  and  the  anterior  peduncle 
of  the  cerebellum. 

The  roof  (Tegmen  ventriculi  quarti)  is  formed  in  its  middle  part  by  the  vermis 


S         T  t 
Fig.  636. — Brain  Stem  and  Basal  Ganglia  or  Horse;  Right  View. 
F.a.,  External  arcuate  fibers;    C.r.,  corpus  restiforme;   P,  pyramid;    T,  corpus  trapezoideum;   B.  p.,  middle  pe- 
duncle of  cerebellum;  P.  f.,  cerebral  peduncle;   S,  sulcus  lateralis;   TJ.,  tractus  transversus;  L,  trigonum  lemnisci;   C.a., 
corpus  quad,  ant.;    C.p.,  corpus  quad,  post.;    B,  commissure  of  C.p.;   G,  corpus  geniculatum  mediale;    T.o.,  olfactory 
peduncle;   B.o.,  olfactory  bulb. 

of  the  cerebellum,  covered  by  the  epithelium  before  mentioned.  There  is  com- 
monly a  dorsal  recess  (Fastigium)  between  the  extremities  of  the  vermis.  The 
anterior  part  of  the  roof  is  formed  by  a  thin  lamina  of  white  substance,  the  anterior 
medullary  velum  (Velum  medullare  anterius),^  which  extends  backward  from  the 
corpora  quadrigemina,  and  is  attached  on  either  side  to  the  anterior  peduncles  of 
the  cerebellum.  Its  anterior  part  is  relatively  thick  and  contains  the  decussation 
of  the  fibers  of  the  trochlear  nerves.  Posteriorly  it  blends  with  the  white  matter 
of  the  cerebellum.  A  thin  lamina  of  white  matter,  the  posterior  medullary  velum 
(Velum  medullare  posterius),  backed  by  pia  mater,  completes  the  roof  posteriorly 
After  removal  of  the  cerebellum  the  line  of  attachment  (Taenia  ventriculi  quarti)  to 
the  medulla  is  seen;  it  begins  centrally  over  the  opening  of  the  central  canal,  runs 
forward  on  the  inner  face  of  the  restiform  body,  and  turns  outward  behind  the 
brachium  pontis.  The  thick  part  which  stretches  over  the  posterior  angle  of  the 
ventricle  is  termed  the  obex.  The  posterior  part  of  the  ventricle  forms  three 
recesses,  of  which  two  are  lateral  and  the  third  median  and  posterior.  The  lateral 
recesses  (Recessus  lateralis)  communicate  with  the  subarachnoid  space  by  lateral 
apertures  (Aperturse  laterales).  The  layer  of  pia  mater  which  actually  forms  the 
roof  here  is  named  the  tela  chorioidea  of  the  fourth  ventricle.  It  is  triangular  in 
outline  and  closely  adherent  to  the  velum.  It  forms  three  fringed  masses  which 
1  Formerly  termed  the  valve  of  Vieussens. 


780  NERVOUS    SYSTEM    OF    THE    HORSE 

contain  vascular  convolutions  and  are  designated  the  median  and  lateral  chorioid 
plexuses  of  the  fourth  ventricle  (Plexus  chorioides  ventriculi  quarti).  They  appear 
to  lie  ^\^thin  the  ventricle,  but  are  really  excluded  from  the  cavity  by  the  epithelial 
lining,  which  they  invaginate. 

THE  MESENCEPHALON 

The  mesencephalon  or  mid-brain  connects  the  rhombencephalon  with  the 
fore-brain.  In  the  undissected  brain  it  is  covered  dorsally  by  the  cerebral  hemi- 
spheres. It  consists  of  a  dorsal  part,  the  corpora  quadrigemina,  and  a  larger 
ventral  part,  the  cerebral  peduncles,  which  are  visible  on  the  base  of  the  brain. 
It  is  traversed  longitudinally  by  a  narrow  canal,  the  cerebral  aqueduct,  which  con- 
nects the  fourth  ventricle  with  the  third  (Fig.  639). 

The  corpora  quadrigemina^  are  four  rounded  eminences  which  lie  under  the 
posterior  part  of  the  cerebral  hemispheres.  They  consist  of  two  pairs,  separated 
bj^  a  transverse  groove.  The  anterior  pair  (Colliculi  nasales)  are  larger  and  much 
higher  than  the  posterior  pair.  They  are  gray  in  color,  almost  hemispherical,  and 
are  separated  by  a  narrow  furrow  which  leads  forward  to  the  subpineal  fovea. 
A  wide  groove  intervenes  between  them  and  the  optic  thalami.  The  posterior  pair 
(Colliculi  caudales)  are  relatively  small  and  are  paler  than  the  anterior  pair.  They 
are  marked  by  a  wide  median  depression,  and  are  limited  behind  bj'  a  transverse 
furrow  (Sulcus  postquadrigeminus),  at  either  side  of  which  the  trochlear  (fourth) 
nerve  emerges.  Laterally  each  is  prolonged  to  the  medial  geniculate  body  by  a 
band  of  white  matter  termed  the  posterior  peduncle  (Brachium  aborale).^ 

The  cerebral  pedimcles  (Pedunculi  cerebri)^  appear  on  the  base  of  the  brain 
as  two  large,  rope-like  stalks  which  emerge  from  the  pons  close  together  and  diverge 
as  they  extend  forward  to  enter  the  cerebrum.  At  the  point  of  disappearance  the 
optic  tract  winds  obliquely  across  the  peduncle.  About  half  an  inch  further  back 
a  small  tract  (Tractus  peduncularis  transversus)  curves  across  the  peduncles,  and 
behind  this,  near  the  median  line,  is  the  superficial  origin  of  the  oculomotor  nerve. 
The  triangular  depression  between  the  diverging  peduncles  is  the  interpedimcular 
fossa  (Fossa  interpeduncularis) .  It  is  covered  to  a  large  extent  by  the  hypophysis 
cerebri  or  pituitary  body,  a  discoid  brown  mass  which  is  connected  with  the  base  of 
the  brain  by  a  hollow  stalk,  the  infimdibulum.  The  posterior  part  of  the  fossa  is 
pierced  by  numerous  minute  openings  which  transmit  blood-vessels,  and  is  therefore 
termed  the  substantia  perforata  posterior.  The  objects  here  belong  to  the  dien- 
cephalon,  and  wiW  be  described  later.  The  lateral  aspect  of  the  peduncle  is  marked 
by  a  groove  (Sulcus  lateralis  mesencephali)  which  indicates  the  division  into  a 
dorsal  part,  the  tegmentimi,  and  a  ventral  part,  the  basis  pedimculi;  these  are 
separated  by  a  layer  of  dark  gray  matter,  the  substantia  nigra.  The  triangular 
area  (Trigonum  lemnisci)  above  the  lateral  groove  is  faintly  marked  by  fibers 
passing  dorsally  and  backward  to  the  anterior  cerebellar  peduncle;  these  belong 
to  the  fillet  or  lemniscus,  an  important  tract  that  connects  the  thalamus  and  corpora 
quadrigemina  with,  the  sensory  reception  nuclei  of  the  opposite  side  of  the  medulla. 

The  aqueduct  of  the  cerebrtmi  (Aquseductus  cerebri)^  is  the  canal  which  extends- 
through  the  mid-])rain  from  the  third  to  the  fourth  ventricle.  It  is  largest  beneath 
the  posterior  pair  of  corpora  quadrigemina.  It  is  surrounded  by  a  layer  of  gray  mat- 
ter (Stratiun  griseum  centrale),  in  the  ventral  part  of  which  are  the  nuclei  of  origin 

1  In  the  new  nomenclature  the  term  lamina  quadrigemina  is  applied  to  the  dorsal  mass  of 
the  mid-brain,  and  the  four  eminences  which  it  bears  are  the  corpora  quadrigemina. 

2  In  man  a  distinct  superior  brachium  connects  the  superior  pair  with  the  lateral  geniculate 
body,  but  in  the  domesticated  animals  the  imion  with  the  optic  thalamus  is  too  direct  to  allow  of 
any  definite  arm  being  recognized. 

'  Also  termed  the  crura  cerebri. 

*  Also  termed  the  aqueduct  of  Sylvius. 


THE    DIENCEPHALON  781 

of  the  oculomotor  and  trochlear  nerves,  and  laterally  nuclei  of  the  mesencephalic 
roots  of  the  trigeminal  nerves. 


THE  DIENCEPHALON 

The  diencephalon  or  inter-brain  comprises  the  thalamus  and  a  number  of 
other  structures  grouped  about  the  third  ventricle,  the  cavity  of  this  division  of  the 
brain.^  To  expose  its  dorsal  aspect,  the  greater  part  of  the  cerebral  hemispheres, 
the  corpus  callosum,  the  fornix,  the  hippocampus,  and  the  tela  chorioidea  of  the 
third  ventricle  must  be  removed  (Fig.  635). 

The  thalamus  is  the  principal  body  in  this  part  of  the  brain.  It  is  a  large 
ovoid  mass  placed  obliquely  across  the  dorsal  face  of  each  cerebral  peduncle,  so 
that  the  long  axes  of  the  two  thalami  would  meet  in  front  about  at  a  right  angle. 
Medially  they  are  fused  to  a  large  extent,  and  around  the  area  of  adhesion  they 
are  separated  by  a  sagittal  circular  space,  the  third  ventricle.  The  dorsal  surface 
is  convex,  and  is  separated  from  the  overlying  hippocampus  by  the  tela  chorioidea. 
Laterally  it  is  separated  from  the  nucleus  caudatus  by  an  oblique  groove  in  which 
there  is  a  band  of  white  matter  termed  the  stria  terminalis.  When  the  tela  chori- 
oidea of  the  lateral  ventricle  has  been  detached  from  this  band  it  leaves  a  torn  edge, 
the  taenia  chorioidea.  Medially  it  is  bounded  by  a  narrow  white  band,  the  stria 
medullaris ;  to  this  the  tela  chorioidea  of  the  third  ventricle  is  attached,  and  when 
the  latter  is  removed  in  dissection,  there  remains  a  thin  irregular  edge  termed  the 
taenia  thalami.  The  striae  unite  posteriorly  and  blend  with  the  stalk  of  the  pineal 
body.  Near  this  point  they  present  a  small  enlargement  caused  by  the  nucleus 
habenulae.  Anteriorly  there  is  a  small  eminence,  the  anterior  tubercle  of  the 
thalamus  (Tuberculum  orale  thalami) .  The  posterior  part  of  the  thalamus  has  the 
form  of  a  rounded  ridge  which  is  continuous  laterally  with  the  optic  tract.^  Behind 
the  point  of  origin  of  the  tract,  in  the  angle  between  the  thalamus  and  the  cerebral 
peduncle,  is  the  medial  geniculate  body  (Corpus  geniculatum  mediale),  a  well- 
defined  oval  prominence. 

The  lateral  surface  is  separated  from  the  lenticular  nucleus  by  the  internal  capsule,  an 
important  mass  of  white  matter  composed  of  fibers  passing  to  and  from  the  cerebral  cortex. 
These  fibers  go  to  form  a  large  part  of  the  ventral  portion  (basis)  of  the  cerebral  peduncle.  From 
the  entire  lateral  surface  of  the  thalamus  fibers  pass  into  the  internal  capsule  and  radiate  to  reach 
the  cerebral  cortex;  similarly  fibers  coming  from  the  cortex  converge  in  the  internal  capsule 
to  enter  the  thalamus.  This  arrangement  is  termed  the  thalamic  radiation.  Ventral  to  the 
thalamus  proper  is  the  hypothalamic  tegmental  region.  This  is  the  continuation  of  the  tegmental 
part  of  the  cerebral  peduncle  into  the  diencephalon.  It  contains  the  red  nucleus  (Nucleus  ruber), 
an  important  ganglion  on  the  course  of  the  motor  tracts.  It  receives  numerous  fibers  from  the 
cerebral  cortex  and  the  corpus  striatum.  From  it  fibers  proceed  to  the  thalamus  and  to  the 
spinal  cord;  the  fibers  to  the  cord,  which  constitute  the  rubro-spinal  tract  (Tractus  rubro-spinalis), 
cross  to  the  opposite  side  and  extend  back  in  the  tegmentum  to  the  lateral  columns  of  the  cord. 
Lateral  to  the  red  nucleus  a  conspicuous  lenticular  area  of  dark  gi-ay  matter  is  visible  on  cross- 
sections  of  the  hypothalamic  region;  this  is  the  hypothalamic  nucleus  (Nucleus  hypothalamicus 
Luysi),  which  consists  of  pigmented  nerve-cells  scattered  through  a  dense  network  of  fine  medul- 
lated  fibers,  and  is  richly  supplied  with  capillary  blood-vessels.  The  two  nuclei  are  connected 
by  a  transverse  commissure  (Commissura  hypothalamica) ,  which  crosses  the  floor  of  the  third 
ventricle  above  the  mammiUary  body. 

The  pineal  body  or  epiphysis  cerebri  (Corpus  pineale)  is  a  small  ovoid  or  fusi- 
form red-browm  mass  situated  in  a  deep  central  depression  between  the  thalami  and 
corpora  quadrigemina.  It  is  variable  in  size,  but  is  commonly  about  10  to  12 
mm.  long  and  6  mm.  wide.  It  is  attached  at  the  poster o-superior  quadrant  of 
the  third  ventricle  by  a  short  stalk,  in  which  is  a  small  recess  of  that  cavity.     Its 

1  On  a  strictly  embryological  basis  the  optic  part  of  the  hjrpothalamus,  comprising  the 
anterior  part  of  the  third  ventricle  and  the  structures  associated  with  it,  belongs  to  the  telen- 
cephalon, but  wiU  be  considered  here  as  a  matter  of  convenience. 

2  This  backward  projection  of  the  thalamus  is  equivalent  to  the  pulvinar  and  lateral  genicu- 
late body  of  man,  which  are  not  superficially  divided  in  the  horse. 


782 


NERVOUS   SYSTEM    OF   THE   HORSE 


base  blends  in  front  with  the  junction  of  the  striae  medullares  of  the  thalamus. 
Immediately  under  the  posterior  part  of  the  stalk  is  a  short  transverse  band  of  white 
matter,  the  posterior  commissure  of  the  cerebrum  (Commissura  aboralis  cerebri). 

The  pineal  body  is  enclosed  in  a  fibrous  capsule  from  which  numerous  trabeculae  pass  inward, 
dividing  the  organ  into  spaces  occupied  by  round  epithelial  cells  of  the  same  origin  as  the  epen- 
dyma  of  the  ventricle. 

The  mammillary  body  (Corpus  mammillare)  is  a  white,  round  elevation  a  little 
larger  than  a  pea  which  projects  ventrally  at  the  anterior  end  of  the  median  furrow 
of  the  interpeduncular  fossa.     While  it  is  a  single  body  in  external  form  in  the  horse. 


Sulcus  rhinali 
Ventral  horn  of 
lateral  ventricle 


<  )])tic  tract 


thalami 


Fig.  637. — Cross-section  of  Brain  of  Horse,  Natural  Size. 
Section  passes  through  posterior  part  of  third  ventricle  and  is  viewed  from  behind.  1,  Longitudinal  fissure;  2, 
hippocampus;  2',  fimbria;  S,  septum  pellucidum;  4,  lateral  ventricle;  5,  thalamus;  6,  habenula;  7,  third  ventricle; 
8,  cerebral  peduncle;  8',  hypothalmus;  ,9,  mammillary  body;  10,  hypophysis  or  pituitary  body;  11,  piriform  lobe; 
12,  ventral  end  of  hippocampus;  13,  amygdaloid  nucleus.  Between  the  upper  parts  of  the  taenise  thalami  is  the  chorioid 
plexus  of  the  third  ventricle,  and  above  this  are  the  internal  cerebral  veins. 


sections  show  that  it  is  double  in  structure  and  contains  a  nucleus  of  gray  matter 
on  either  side  (Fig.  637). 

Three  sets  of  fibers  are  connected  with  the  mammillary  body.  The  column  of  the 
fornix  curves  down  in  the  lateral  wall  of  the  third  ventricle  to  the  body  and  many  of  the  fornix 
fibers  end  in  it.  A  bundle  (Fasciculus  thalamo-mammillaris)  passes  dorsally  and  backward 
from  it  into  the  anterior  part  of  the  thalamus,  and  a  tract  (Fasciculus  pedunculo-mammillaris) 
extends  back  in  the  floor  of  the  third  ventricle  to  the  tegmentum  of  the  mid-brain. 

The  h5rpophysis  cerebri  or  pituitary  body  was  mentioned  as  covering  part  of  the 
interpeduncular  fossa.  It  is  oval  in  outline,  flattened  dorso-ventrally,  and  nearly  an 
inch  (ca.  2  cm.)  in  width.  It  is  attached  by  a  delicate  tubular  stalk,  the  infundibu- 
lum,  to  the  tuber  cinereum,  a  small  gray  prominence  situated  between  the  optic 
chiasm  in  front  and  the  mammillary  body  behind.  A  fibrous  capsule,  derived  from 
the  dura  mater,  encloses  and  is  intimately  adherent  to  it. 

The  body  consists  of  two  parts  which  can  be  distinguished  on  sections  by  their  color  (Fig.  639). 
The  glandular  lobe  is  brown  in  color  and  forms  the  external  and  greater  part  of  the  body.     It  is 


THE   TELENCEPHALON  783 

glandulax  in  character  a,nd  there  is  good  ground  for  the  view  that  it  is  an  organ  of  internal  se- 
cretion. Besides  the  cliief  cells,  which  stain  lightly,  it  contains  large,  deeply  staining  chromophile 
cells.  It  arises  as  an  outgrowth  from  the  dorsal  wall  of  the  primitive  mouth  cavity.  The  cerebral 
lobe  is  pale  and  is  connected  with  the  infundibulum  so  as  to  form  a  rather  flask-shaped  arrange- 
ment. It  is  almost  entirely  enclosed  by  the  glandular  part.  It  arises  as  an  outgrowth  from  the 
primitive  diencephalon,  but  loses  most  of  its  earher  nervous  character. 

The  optic  chiasm  and  tracts  form  the  anterior  boundary  of  the  interpeduncular 
fossa  (Figs.  629,  636).  The  optic  chiasm  (Chiasma  opticum)  is  formed  by  the 
convergence  of  the  optic  nerves  and  the  crossing  of  the  major  part  of  the  fibers  of 
the  nerve  of  one  side  to  the  tract  of  the  opposite  side.  From  the  chiasm  each  optic 
tract  (Tractus  opticus)  curves  obhquely  around  the  cerebral  peduncle  to  the  pos- 
terior part  of  the  thalamus  and  the  medial  geniculate  body;  some  fibers  reach  the 
anterior  quadrigeminal  body. 

AH  the  fibers  in  the  chiasm  are  not  derived  from  the  optic  nerves.  The  posterior  part 
contains  fibers  which  pass  from  one  tract  to  the  other  and  are  connected  with  the  medial  genicu- 
late bodies;  this  bundb  is  called  the  ventral  commissure  (Commissura  ventralis).  Above  it  is 
the  dorsal  commissure  (Commissura  dorsahs),  the  fibers  of  which  enter  the  hypothalamic  body.^ 

The  third  ventricle  (Ventriculus  tertius)  is  the  narrow  annular  space  between 
the  thalami.  It  communicates  by  means  of  the  cerebral  aqueduct  with  the  fourth 
ventricle  behind,  and  in  front  it  is  continuous  with  the  lateral  ventricle  on  each  side 
through  the  interventricular  foramen.  Its  floor  is  formed  by  the  structures  of  the 
interpeduncular  fossa,  and  to  a  small  extent  by  the  tegmentum  of  the  cerebral 
peduncles.  The  roof  is  formed  in  the  strict  sense  only  by  the  ependyma,  above 
which  is  a  fold  of  pia  mater,  termed  the  tela  chorioidea  of  the  third  ventricle.-  The 
roof  is  invaginated  by  the  two  delicate  chorioid  plexuses  (Plexus  chorioidei  ventriculi 
tertii)  which  appear  to  lie  within  the  ventricle,  although  they  are  excluded  from  the 
cavity  by  the  epithelium.  When  the  tela  is  removed,  the  delicate  ependyma  of  the 
roof  is  torn  away  with  it,  leaving  the  line  of  attachment  to  the  stria  medullaris  to 
constitute  the  taenia  thalami.  The  anterior  wall  is  formed  by  the  lamina  terminalis, 
a  thin  layer  of  gray  matter  which  extends  from  the  optic  chiasm  dorsally  to  the 
corpus  callosum.  A  distinct  rounded  band  of  white  matter  extends  across  its 
posterior  face,  bulging  into  the  ventricle.  This  is  the  anterior  commissure  (Com- 
missura oralis)  of  the  cerebrum;  its  fibers  extend  to  the  olfactory  bulb  and  to  the 
piriform  lobe.  A  similar  but  more  slender  posterior  commissure  (Commissura 
aboralis)  crosses  the  posterior  wall  above  the  entrance  to  the  cerebral  aqueduct; 
the  connections  of  its  fibers  are  not  yet  clearly  known.  The  interventricular 
foramen^  is  situated  on  either  side  of  the  anterior  part  of  the  ventricle,  and  leads 
outward  and  slightly  dorsally  between  the  column  of  the  fornix  and  the  anterior 
tubercle  of  the  thalamus  (Fig.  639).  The  cavity  presents  three  recesses  or  diver- 
ticula, of  which  two  are  ventral  and  the  third  is  posterior.  The  optic  recess  (Re- 
cessus  opticus)  lies  above  the  optic  chiasm.  Just  behind  it  is  the  infundibular 
recess  (Recessus  infundibuli),  which  extends  through  the  infundibulum  to  the 
pituitary  body.  The  pineal  recess  (Recessus  pinealis)  is  in  the  stalk  of  the  pineal 
body. 

THE  TELENCEPHALON 
The  telencephalon  or  end-brain  comprises  two  principal  parts,  the  cerebral 
hemispheres  and  the  optic  part  of  the  hypothalamus.     The  latter  has  been  con- 
sidered as  a  matter  of  convenience  in  the  description  of  the  diencephalon. 

The  Cerebral  Hemispheres 
The  cerebral  hemispheres  (Hemisphseria)  form  the  greater  part  of  the  fully 
developed  brain.     Viewed  from  above   (Fig.   631)  they  form  an  ovoid  mass,  of 
1  These  are  commonly  termed  Gudden's  and  Meynert's  commissures  respectively. 
^  Also  commonly  termed  the  velum  interpositum.         ^  Also  termed  the  foramen  of  Monro. 


784  NERVOUS    SYSTEM    OF   THE    HORSE 

which  the  broader  end  is  posterior,  and  the  greatest  transverse  diameter  is  a  Httle 
behind  the  middle.  The  two  hemispheres  are  separated  by  a  deep  median  cleft, 
the  longitudinal  fissure  of  the  cerebrmn  (Fissura  longitudinalis  cerebri),  which  is 
occupied  by  a  sickle-shaped  fold  of  dura  mater,  the  falx  cerebri.  In  front  the 
separation  is  complete,  and  it  appears  to  be  behind  also,  but  here  the  two  hemi- 
spheres are  attached  to  each  other  over  a  small  area  by  the  pia  mater.  When  the 
hemispheres  are  gently  drawn  apart,  it  is  seen  that  the  fissure  is  interrupted  in  its 
middle  part  at  a  depth  of  a  little  more  than  an  inch  (ca.  3  cm.)  by  a  white  commis- 
sural mass,  the  corpus  callosum ;  this  connects  the  hemispheres  for  about  half  of 
their  length.  The  transverse  fissure  (Fissura  transversa  cerebri)  separates  the 
hemispheres  from  the  cerebellum,  and  contains  the  tentorium  cerebelli. 

The  convex  or  dorso-lateral  surface  (Facies  convexa  cerebri)  conforms  closely 
to  the  cranial  wall.  The  medial  surface  (Facies  medialis  cerebri)  (Fig.  639)  is  flat 
and  sagittal  and  bounds  the  longitudinal  fissure ;  to  a  large  extent  it  is  in  contact  with 
the  falx  cerebri,  but  behind  the  great  cerebral  vein  the  two  hemispheres  are  in 
contact  and  are  attached  to  each  other  over  a  small  area  as  noted  above.     In  well- 


FiG.  638. — Left  Cerebral  Hemisphere  of  Horse;  Lateral  View.     The  Olfactort  Bulb  is  Cut  Off. 

1,  Lateral  fissure  (of  Sylvius) ;  ;2,  5,  4.  rniddle,  posterior,  and  anterior  branches  of /,•   .5,  presylvian  fissure;   6,  6',  sulcus 

rhinalis,  anterior  et  posterior;   7,  suprasylvian  fissure;  8,  ectomarginal  fissure;  9,  9',  ectosylvian  fissure. 

hardened  specimens  there  is  usually  an  impression  for  the  vein  in  front  of  the  area 
of  adhesion.  The  base  or  ventral  surface  (Basis  cerebri)  (Fig.  629)  is  irregular. 
Its  anterior  two-thirds  is  adapted  to  the  cerebral  fossa  of  the  cranial  floor.  Cross- 
ing this  area  in  front  of  the  optic  tract  is  a  depression,  the  lateral  fossa  (Fossa 
lateralis),  which  leads  outward  to  the  lateral  fissure  (Fissura  lateralis),^  and  lodges 
the  middle  cerebral  artery.  In  front  of  the  fossa  there  is  a  considerable  rounded 
elevation  knowai  as  the  trigonum  olfactorium.  The  trigonum  and  the  medial  part 
of  the  fossa  are  pierced  by  numerous  openings  for  the  passage  of  small  blood-vessels 
and  are  equivalent  to  the  suljstantia  perforata  anterior  of  man.  Behind  the  lateral 
part  of  the  fossa  is  the  rounded  anterior  end  of  the  piriform  lobe  (Lobus  piriformis) . 
Traced  backward,  the  lobe  curves  dorso-medially  over  the  optic  tract  and  the 
thalamus  to  the  tentorial  aspect  of  the  hemisphere;  its  continuation,  the  hippo- 
campus, forms  part  of  the  floor  of  the  lateral  ventricle,  and  will  be  examined  later. 
The  tentorial  surface  (Fig.  640)  is  flattened,  faces  medially  and  backward  as  well 
as  ventrally,  and  rests  largely  on  the  tentorium  cerebelli;  on  its  anterior  part  there 
is  a  shallow  depression  adapted  to  the  corpora  quadrigemina  and  the  pineal  body. 
^  Also  commonly  known  as  the  fissm-e  of  Sylvius. 


THE    CEREBRAL   HEMISPHERES  785 

The  frontal  pole  or  anterior  extremity  (exclusive  of  the  olfactory  bulb)  is 
compressed  laterally,  and  the  occipital  pole  or  posterior  extremity  forms  a  blunt 
point. 

The  hemisphere  comprises:  (1)  The  pallium,  which  consists  of  an  outer  layer 
of  gray  matter,  the  cortex  (Substantia  corticalis),  covering  a  large  mass  of  white 
matter  (Centrum  semiovale) ;  (2)  the  rhinencephalon  or  olfactory  portion  of  the 
brain;  (3)  the  corpus  callosum  and  fornix,  the  great  commissural  white  masses; 
(4)  the  lateral  ventricle  and  certain  important  structures  associated  therewith. 

The  pallium  is  throwai  into  numerous  folds,  the  gyri  cerebri,  which  are  sep- 
arated by  sulci  or  fissures  of  varying  depth.  The  general  pattern  of  the  gyri  and 
sulci  is  similar  in  normal  brains  of  the  same  species,  but  the  details  are  very  variable 
and  are  never  alike  on  the  two  hemispheres  of  the  same  brain.  In  the  horse  the 
arrangement  is  complicated  by  the  existence  of  numerous  short  accessory  fissures 
which  cut  into  the  gyri  at  right  angles  and  tend  to  confuse  the  observer.  The 
principal  fissures  and  sulci  of  the  convex  surface  (Figs.  631,  632,  638)  are  as  follows:^ 

1.  The  lateral  fissure  (Fissura  lateralis  Sylvii)  ascends  on  the  lateral  surface 
of  the  hemisphere  as  the  continuation  of  the  fossa  lateralis  in  front  of  the  piriform 
lobe.  After  crossing  the  lateral  olfactory  stria  it  divides  into  three  branches; 
of  these  one  passes  dorsally,  one  runs  obliquely  forward  and  dorsally,  and  the  third 
is  directed  dorsally  and  backward.     It  contains  the  middle  cerebral  artery. 

2.  The  suprasylvian  fissure  (F.  suprasylvia)-  is  long  and  divides  a  large  part 
of  the  convex  surface  of  the  hemisphere  into  dorsal  and  lateral  portions.  It  begins 
on  the  dorso-medial  border  near  its  anterior  end,  and,  inclining  gradually  do^vnward, 
passes  back  to  end  on  reaching  the  tentorial  surface.  It  is  usually  continuous 
medially  with  the  transverse  fissure  and  in  front  with  the  presylvian  fissure. 

3.  The  presylvian  fissure  (F.  prsesylvia)  is  on  the  anterior  part  of  the  hemi- 
sphere, passes  forward  and  ventro-laterally  almost  to  the  frontal  pole,  and  then 
inclines  backward  to  end  at  the  groove  which  marks  the  dorsal  limit  of  the  rhinen- 
cephalon (Sulcus  rhinalis). 

4.  The  marginal  fissure  (F.  marginalis)  extends  along  the  dorso-medial  border. 
It  begins  a  little  in  front  of  the  middle  of  the  border  and  turns  around  the  occipital 
pole  to  end  on  its  tentorial  aspect. 

5.  The  entomarginal  fissure  (F.  entomarginalis)  lies  medial  to  the  dorso- 
medial  border.  It  does  not  extend  quite  as  far  forward  as  the  marginal  fissure, 
from  which  it  is  separated  by  a  narrow  gyrus. 

6.  The  ectomarginal  fissure  (F.  ectomarginalis)  lies  about  midway  between  the 
marginal  fissure  and  the  posterior  part  of  the  suprasylvian  fissure. 

7.  The  sulcus  rhinalis  is  a  very  distinct  furrow  on  the  ventral  part  of  the 
lateral  surface  which  marks  off  the  olfactory  part  of  the  brain  (rhinencephalon)  from 
the  rest  of  the  hemisphere.  It  is  undulating  and  is  highest  where  it  is  crossed  by 
the  lateral  fissure. 

Just  above  this  point  is  a  lobe  which  is  homologous  with  the  insula  of  man.  When  the 
overhanging  gyri  which  partly  conceal  it — forming  the  operculum — ^are  removed,  there  are  dis- 
closed several  short,  deeply  placed  gjTi  (Gyi'i  breves). 

1 
On  the  medial  surface  (Fig.  639)  the  main  fissures  and  sulci  are  as  follows: 
1.  The  calloso-marginal  fissure  (F.  callosomarginalis)  is  extensive  and  well 
defined.  It  is  approximately  parallel  to  the  dorso-medial  border  of  the  hemisphere, 
from  which  it  is  about  half  an  inch  distant.  It  begins  in  front  a  short  distance 
below  and  in  front  of  the  genu  of  the  corpus  callosum,  and  forms  a  C-shaped  curve, 
its  posterior  part  extending  on  the  tentorial  surface  to  a  point  behind  the  depression 

1  The  homologies  and  terminology  of  many  fissures  of  the  brain  in  the  domesticated  animals 
are  still  in  a  chaotic  state.     Only  a  few  of  the  most  important  and  constant  ones  are  given  here. 

2  Termed  by  Lesbre  the  parietal  fissure  and  by  M'Fadyean  the  great  oblique  fissure. 

50 


786 


NERVOUS    SYSTEM    OF    THE    HORSE 


for  the  corpora  quadrigemina.     It  separates  the  marginal  gyri  above  from  the  gyrus 
fornicatus,  which  extends  down  to  the  corpus  callosum. 

2.  The  transverse  fissure  (F.  transversa)  begins  a  Httle  behind  the  middle  of 
the  calloso-marginal  fissure,  passes  obliquely  dorsally  and  forward  to  the  dorso- 
medial  border — into  which  it  cuts  deeply — and  usually  joins  the  suprasylvian 
fissure.^ 

3.  The  subfimbic  fissure  (F.  sublimbica)  curves  over  the  gyrus  fornicatus  a 
short  distance  above  the  corpus  callosum.  Its  middle  part  is  commonly  indistinct, 
and  it  is  often  divided  into  anterior  and  posterior  parts. 


Trnnnverse     Calloso-mar- 
Gynin  furiiiculus  fissure        ginal  fissure 

1 


Marginal  fissure 


-  Entomarginal  fissure 


A  nterior  com- 
missure   Lamina     Chiasm  a 
terminalis  opiicum 


Posterior      I 
commissure   ■ 


Anterior     Fourth 
Hypophysis    Cerebral    medul-     ventricle 
'cerebri         aqueduct      lary 


velum. 

Fig.  639. — Median  Section  of  Brain  of  Horse. 
The  membranes  and  vessels  are  removed.  C,  Central  white  matter  (corpus  meduUare)  of  cerebellum;  P.c,  cere-- 
bral  peduncle;  C.q.,  corpora  quadrigemina;  P,  pineal  body;  Th.,  thalamus;  V.III.,  third  ventricle;  r,  optic  recess; 
r',  infundibular  recess;  Cm.,  mammillary  body;  s,  subcallosal  gyrus;  A.p.,  area  parolfactoria;  G,  genu  of  corpus 
callosum;  .S,  splenium  of  same;  F.i.,  interventricular  foramen;  B.o.,  olfactorj'  bulb;  C.p..  choroid  plexus  of  lateral 
ventricle.     The  cerebral  lobe  of  the  hypophysis  cerebri  or  pituitary  body  is  distinguished  by  its  lighter  color. 


4.  The  callosal  sulcus  (Sulcus  corporis  callosi)  separates  the  corpus  callosum 
from  the  gyrus  fornicatus. 

The  hippocampus'-  is  a  gyrus  which  curves  from  the  deep  face  of  the  piriform 
lobe  around  the  thalamus  and  forms  the  posterior  part  of  the  floor  of  the  lateral 
ventricle.  It  can  be  displayed  by  cutting  away  the  brain  stem  up  to  the  optic 
tract  and  the  interventricular  foramen.  Viewed  from  below,  the  hippocampal 
gyrus  is  seen  to  form  a  semicircular  curve  from  the  apex  of  the  piriform  lobe  to 
the  angle  of  divergence  of  the  crura  of  the  fornix,  i.  e.,  to  a  point  under  the  central 
part  of  the  corpus  callosum.  It  is  separated  deeply  by  the  hippocampal  fissure 
from  the  gyrus  dentatus  (Fig.  640).     Along  the  concave  margin  of  the  latter  is  a 

^  By  some  authors  this  is  regarded  as  the  homologue  of  the  cruciate  fissure  of  the  dog,  but  it 
seems  likely  tliat  the  latter  is  represented  by  a  short  and  inconstant  sulcus  situated  further  forward. 
^  Also  termed  the  cornu  Ammonis. 


THE    CEREBRAL   HEMISPHERES 


787 


band  of  white  matter,  termed  the  fimbria,  which  is  the  prolongation  of  the  greater 
part  of  the  crus  of  the  fornix  into  this  region.  The  ventricular  surface  of  the 
hippocampus  (Fig.  642)  is  covered  with  a  thin  layer  of  white  matter,  the  alveus, 
which  is  also  derived  from  the  crus  of  the  fornix,  and  is  therefore  continuous  with 
the  fimbria.  The  two  hippocampi  are  connected  at  their  highest  parts  by  trans- 
verse fibers  which  constitute  the  hippocampal  commissure. 

The  interval  between  the  hippocampus  and  fimbria  on  the  one  hand,  and  the 
brain  stem  on  the  other,  is  a  lateral  continuation  of  the  transverse  fissure  of  the 
brain,  and  is  occupied  by  a  fold  of  pia  mater,  the  tela  chorioidea  of  the  third  ven- 
tricle. This  fold  is  triangular  in  outline  and  its  apex  reaches  to  the  interventricular 
foramen.  Its  base  is  continuous  at  the  transverse  fissure  with  the  pia  which  covers 
the  surface  of  the  brain.  Its  middle  part  lies  over  the  epithelial  roof  of  the  third 
ventricle,  as  has  been  seen  (Fig.  637).     The  lateral  borders  will  be  seen  on  the  floor 


Subliinbic  fissure   [ant.  part) 


Inter  ventricular  foramen  rr                   r 

r,           r       ■     t  Irons  verse   fissure 

iTi/rus  jormcatus  ^,   ,,       •          ■     , 

t        •  ,^  I       Caltoso-marqinol 


arginol  fissure 

Sublimhic  fissure  (post,  port") 


Entomarqinal  fissure 

Marginal  fissure 


Sulcus  rhinab's  anterior 


Ectomarginal  fissure 


Hippocampal  fissure 


Sulcus  rhinalis  posterior 


Fig.  040. — Medio-ventral  Aspect  of  Right  Cerebral  Hemisphere  op  Horse. 
The  olfactory  bulb  is  cut  off.     T.oL,  Olfactory  tract;    A. p.,  area  parolfactoria;    Tr.o.,    trigonum  olfactorium; 
Tr.op.,  optic  tract;  Co.,  chiasma  opticum;  G.s.,  subcallosal  gyrus;  C.c,  corpus  callosum;  S.p.,  septum  pellucidum;  F, 
fornix;   F',  fimbria;   G.c,    callosal   gyrus;    T,   cut   surface   of   thalamus;    G.d.,  gyrus   dentatus;  L.p.,   piriform  lobe; 
G.h.,  hippocampal  gyrus. 


of  the  lateral  ventricles,  where  they  form  thick,  rounded  bands  containing  convolu- 
tions of  blood-vessels,  known  as  the  chorioid  plexuses  of  the  lateral  ventricles  (Fig. 
642). 

When  the  tela  is  pulled  out,  one  may  easily  get  the  impression  that  the  lateral  ventricle 
communicates  with  the  exterior  by  means  of  the  chorioid  fissure.  Such  is  not  the  case,  since  the 
chorioid  plexus  is  covered  by  the  epithelial  lining  of  the  ventricle,  which  has  been  torn  away. 

The  rhinencephalon  or  olfactory  part  of  the  brain  comprises  the  olfactory 
bulb,  tract,  and  striae,  the  trigonum  olfactorium,  the  area  parolfactoria,  and  the 
piriform  lobe.^ 

The  olfactory  bulb  (Bulbus  olfactorius)  is  an  oval  enlargement  which  curves 
upward  in  front  of  the  frontal  pole  of  the  hemisphere.  Its  convex  superficial  face 
fits  into  the  ethmoidal  fossa  and  receives  numerous  olfactory  nerve-fibers  through 
the  cribriform  plate;  hence  it  is  very  difficult  to  remove  the  bulb  intact.  It  con- 
tains a  considerable  cavity,  the  ventricle  of  the  olfactory  bulb  (Ventriculus  bulbi 

1  From  the  morphological  point  of  view  other  structures  should  be  included,  but  in  descriptive 
anatomy  it  is  usual  to  limit  the  application  of  the  term  to  the  parts  enumerated  above. 


788  NERVOUS    SYSTEM    OF   THE   HORSE 

olfactorii)  which  is  connected  with  the  lateral  ventricle  by  a  small  canal  in  the 
olfactory  tract.  The  deep  face  is  largely  in  contact  with  the  frontal  pole  of  the 
hemisphere  and  is  connected  with  the  olfactory  tract. 

The  gray  matter  of  the  bulb  is  external  and  is  thickest  on  the  convex  anterior  surface.  The 
posterior  part  consists  to  a  large  extent  of  fibers  which  are  the  axones  of  the  mitral  cells  of  the 
deep  layer  of  the  gray  substance  and  go  to  form  the  tract  and  stria. 

The  olfactory  tract  (Tractus  olfactorius)i  jg  g^  ygj.y  short  but  wide  band  of 
white  substance  which  arises  in  the  olfactory  bulb  and  extends  back  to  be  continued 
by  the  olfactory  striae.  It  contains  a  canal  which  connects  the  ventricle  of  the 
bulb  with  the  lateral  ventricle. 

The  olfactory  striae  (Striae  olfactorii)^  are  two  in  number.  The  lateral  stria 
(Stria  lateralis)  is  much  the  largest  and  most  distinct.  It  passes  backward,  upward, 
and  outward,  widens  out  and  joins  the  piriform  lobe.  It  is  clearly  defined  dorsally 
by  the  sulcus  rhinalis  and  is  marked  off  from  the  trigonum  olfactorium  by  the 
sulcus  arcuatus.     The  medial  stria  (Stria  medialis)  is  smaller,  short,  and  not  so 


Fig.  641. — Lateral  View  op  Cast  of  Cavities  of  Brain  of  Horse. 
Bo,  Cavity  of  olfactory  bulb,  which  communicates  through  the  canal  /  with  a  lateral  ventricle;  Ca,  anterior  horn, 
Cm,  body,  Ci,  ventral  horn  of  lateral  ventricle;  M,  interventricular  foramen  which  connects  lateral  and  third  ventricles; 
Ep,  suprapineal  recess,  below  which  is  the  small  infrapineal  recess  (not  visible) ;  Ro,  optic  recess;  Rh,  infundibular 
and  pituitary  recess;  S,  aqueduct;  Fl,  ridge  corresponding  to  sulcus  hmitans;  Rl,  lateral  recess,  Rm,  posterior 
recess  of  fourth  ventricle;   Cc,  beginning  of  central  canal  of  spinal  cord.     (Dexler.) 

well  defined;  it  bends  over  to  the  parolfactory  area  on  the  medial  face  of  the  hemi- 
sphere below  the  genu  of  the  corpus  callosum.^ 

The  trigonum  olfactorium  is  the  prominent  gray  area  situated  in  the  angle  of 
divergence  of  the  medial  and  lateral  olfactory  striae.  It  is  bounded  laterally  by  the 
lateral  olfactory  stria,  from  which  it  is  defined  by  the  sulcus  arcuatus.  It  is  con- 
tinuous with  the  area  parolfactoria  on  the  medial  surface;  behind  the  latter  a  band 
descends  from  the  rostrum  of  the  corpus  callosum  and  is  continuous  below  Avith  the 
anterior  perforated  substance;  it  is  termed  the  subcallosal  gyrus  (Gyrus  sub- 
callosus). 

The  piriform  lobe  (Lobus  piriformis)  is  the  well-marked  prominence  on  the 
base  lateral  to  the  optic  tract  and  cerebral  peduncle,  from  which  it  is  separated  by  a 
deep  fissure.  Its  nipple-like  apex  lies  behind  the  fossa  lateralis  and  covers  the 
optic  tract.  The  external  surface  is  marked  by  one  or  two  sulci  (lobi  piriformis). 
The  lobe  contains  a  cavity,  the  ventral  horn  of  the  lateral  ventricle. 

1  Commonly  termed  the  peduncle.  2  Commonly  termed  the  tracts. 

^  An  intermediate  or  middle  stria  has  been  described;  its  presence  cannot  be  demonstrated 
m  the  horse. 


THE   CEREBRAL  HEMISPHERES 


789 


The  fibers  of  the  olfactory  striae  go  to  the  piriform  lobe  and  hippocampus,  the  trigonum 
olfactormm,  the  area  parolfactoria,  the  subcallosal  gyrus,  and  part  of  the  gyrus  fornicatus.  The 
central  connections  of  the  olfactory  apparatus  are  complex  and  are  not  yet  fully  understood.  The 
anterior  cerebral  commissui-e  contains  fibers  which  pass  from  the  oKactory  bulb  of  one  side  by 
way  of  the  medial  striae  to  the  bulb  of  the  opposite  side;  also  fibers  which  cross  in  it  from  the 
naedial  striae  of  one  side  to  the  piriform  lobe  of  the  opposite  side.  Many  fibers  pass  to  the 
hippocampus  by  way  of  the  septum  pellucidum,  fornix,  and  fimbria.  Other  fibers  pass  in  the 
column  of  the  fornix  to  the  mammillary  body  and  thence  to  the  thalamus  by  the  thalamo-mam- 
millary  bundle. 

The  corpus  callosum  is  the  great  transverse  commissure  which  connects  the 
two  cerebral  hemispheres  through  about  half  of  their  length.     On  median  section 


Olfactory  bulb 


^  -  '  "  Cortex  cerebri 

-i  Corpus  medullar e 

Caudate  nucleus 

Chorioid  plexus 
Fornix 
'~i  -  -Hippocampus 


-Brain  of  Horse,  with  Lateral  Ventricles  Opened  by  Removal  of  Upper  Part  of  Cerebral 
Hemispheres  and  Most  of  the  Corpus  Callosum. 


(Fig.  639)  it  is  seen  to  be  arched  from  before  backward,  white  in  color,  and  com- 
posed substantially  of  transverse  fibers.  The  middle  part  or  truncus  (Truncus 
corporis  callosi)  slopes  downward  and  forward  and  is  thinner  than  the  ends.  The 
anterior  thickened  end,  the  genu,  bends  ventrally  and  backward  and  thins  out  to 
form  the  rostrum ;  the  latter  is  continuous  with  the  lamina  terminalis.  The  pos- 
terior end,  the  splenium,  also  thick,  lies  at  a  considerably  higher  level  than  the 
genu.  The  dorsal  surface  is  convex  in  its  length,  concave  transversely;  it  forms 
the  floor  of  the  longitudinal  fissure.  It  is  covered  by  a  thin  layer  of  gray  matter 
(Induseum  griseum),  in  which  are  strands  of  longitudinal  fibers  (Striae  longitudi- 
nales) ;  the  latter  are  arranged  in  medial  and  lateral  bundles  (Stria  medialis,  striae 


790 


NERVOUS    SYSTEM    OF   THE   HORSE 


laterales).^  The  ventral  surface  has  the  reverse  configuration,  and  presents  trans- 
verse ridges  and  grooves.  It  forms  the  roof  of  the  lateral  ventricles,  and  the 
septum  pellucidum  is  attached  to  it  medially.  The  fibers  of  the  corpus  cailosum 
(with  the  exception  of  the  longitudinal  striae)  run  transversely  and  spread  out 
laterally  in  all  directions  in  the  central  white  matter  of  the  hemispheres  to  the  cor- 
tex, forming  the  radiation  of  the  corpus  cailosum  (Radiatio  corporis  callosi). 

The  fornix  is  a  bilateral  structure  composed  of  white  fibers  which  arch  chiefly 
over  the  thalamus  and  the  third  ventricle.  It  is  described  as  consisting  of  a  body, 
two  columns,  and  two  crura.  The  body  (Corpus  fornicis)  is  formed  by  the  fusion  of 
the  two  arches  of  which  the  fornix  is  composed.  It  is  triangular  and  overlies  the  an- 
terior parts  of  the  thalami  and  the  third  ventricle.     The  dorsal  surface  gives 


Opttc 
chiasm 


^ 


hdcrrcnlricidar  Jorainen 
\nU rior  cu iii in lss u rt 


Optic  trad 


Fio.  643. — Cross-section  of  Brain  of  Horse,  About  Natural  Size. 
Section  passes  through   optic  chiasm,  and  is  viewed   from   in  front.     1,  Longitudinal  fissure;    2,  septum  pellu- 
cidum;   3,  columns  of  fornix;    4,  lateral  ventricle;    5,  chorioid  plexus;    6,  corpus  moduUare  (central  white  matter)  of 
hemisphere;   7,  caudate  nucleus;  5,  lenticular  nucleus;  9,  internal  capsule;   iO,  external  capsule;   n,  insula. 


attachment  medially  to  the  septum  pellucidum,  and  on  either  side  forms  part  of  the 
floor  of  the  lateral  ventricle.  The  lateral  border  is  related  to  the  chorioid  plexus  of 
the  lateral  ventricle  and  forms  the  inner  boundary  of  the  interventricular  foramen. 
The  columns  (Columnae  fornicis)  (Fig.  643)2  are  two  slender  round  bundles  which 
emerge  from  the  body  in  front  of  the  interventricular  foramen  and  diverge 
slightly  as  they  curve  ventrally  and  backward  to  the  mammillary  body. 

From  the  mammillary  body  the  greater  part  of  these  fornix  fibers  are  continued  to  the 
thalamus  by  the  thalamo-mammillary  fasciculus  (or  bundle  of  Vicq  d'Azyr).  Others  pass  to 
the  cerebral  peduncle.  A  portion  of  the  fibers  cross  to  the  opposite  thalamus  and  cerebral 
peduncle. 

The  crura  (Crura  fornicis)^  are  much  larger  bands  which  diverge  widely  from 

^  It  is  generally  believed  that  these  constitute  an  olfactory  path. 

*  Also  known  as  the  anterior  pillars.  ^  ^igQ  termed  the  posterior  pillars. 


THE    CEREBRAL    HEMISPHERES  791 

the  posterior  angles  of  the  body.  Each  curves  outward  and  backward  over  the 
thalamus  (from  which  it  is  separated  by  the  tela  chorioidea),  and  is  chiefly  continued 
as  the  fimbria  along  the  concave  border  of  the  hippocampus.  The  crura  give  off 
fibers  to  form  the  alveus,  a  layer  of  white  matter  which  covers  the  ventricular  face 
of  the  hippocampi,  and  between  them  are  transverse  fibers  which  constitute  the 
hippocampal  commissure  (Commissura  hippocampi). 

The  septum  pellucidum  is  the  median  partition  between  the  two  lateral  ven- 
tricles. Its  convex  dorsal  border  blends  with  the  corpus  callosum  and  its  concave 
ventral  border  joins  the  fornix.  Its  anterior  part  is  received  into  the  genu  of  the 
corpus  callosum.  Traced  backward,  it  diminishes  in  height  and  the  two  edges  meet 
at  an  acute  angle  at  the  splenium. 

The  septum  consists  of  two  layers  (Laminae  septi  pellucidi)  which  are  in  contact  with  each 
other.  They  consist  of  medullated  nerve-fibers  and  2;ray  matter.  The  latter  exists  in  considerable 
amount  m  the  thicker  part  of  the  septum  adjacent  to  the  columns  of  the  fornix.  Many  of  the 
fibers  of  the  septum  pass  up  through  the  corpus  callosum  to  the  gyrus  fornicatus.  Others  are 
connected  with  the  subcallosal  gyrus  and  the  paroKactory  area. 


Fig.  644. — Sagittal  Section  of  Brain  of  Horse. 
Section  is  cut  about  1.5  cm.  to  the  right  of  the  median  plane.     M,  Medulla  oblongata;   P,  pons;  P.c.  (above  M), 
chorioid  plexus  of  fourth  ventricle;    Cm.,  central  white  matter  (corpus  medullare)  of  cerebellum  and  of  cerebrum; 
P.c.  (in  front  of  P),  cerebral  peduncle;    //,  hippocampus;    V,  lateral  ventricle;    T,  thalamus;    N.c,  caudate  nucleus; 
C.i.,  internal  capsule;  N.I.,  lenticular  nucleus;  B.o.,  olfactory  bulb. 

The  lateral  ventricle  (Ventriculus  lateralis  cerebri)  is  the  irregular  cavity  in  the 
interior  of  each  cerebral  hemisphere.^  Each  communicates  with  the  third  ventricle 
through  the  interventricular  foramen  (Foramen  interventriculare),-  and  by  a  small 
canal  with  the  cavity  of  the  olfactory  bulb.  It  is  usual  to  describe  the  ventricle 
as  consisting  of  three  parts,  viz.,  the  central  part  or  body,  and  anterior  and  ventral 
horns.  The  central  part  (Pars  centralis)  extends  back  to  the  splenium  of  the  corpus 
callosum.  It  opens  into  the  third  ventricle  through  the  interventricular  foramen, 
which  is  situated  between  the  fornix  and  the  anterior  part  of  the  thalamus.  The 
anterior  horn  (Cornu  orale)  is  the  part  in  front  of  the  interventricular  foramen; 
it  communicates  ventrally  with  the  olfactory  cavity.  The  ventral  horn  (Cornu 
ventrale)  curves  downward  and  forward  into  the  piriform  lobe.  The  roof  of  the 
ventricle  is  formed  by  the  corpus  callosum,  and  the  medial  wall  is  the  septum  pellu- 
cidum.    After  removal  of  the  roof  the  floor  is  seen  to  be  formed  chiefly  by  two  bodies. 

1  It  is  hardly  possible  to  get  an  accurate  idea  of  the  shape  of  the  ventricle  except  by  studying 
a  cast  of  it  (Fig.  641).  The  size  of  the  ventricles  varies  in  different  subjects,  and  it  is  conunon  to 
find  more  or  less  disparity  between  the  two  ventricles  of  the  same  brain. 

-  Formerly  termed  the  foramen  of  Monro. 


792  NERVOUS    SYSTEM    OF   THE    HORSE 

The  anterior  one  is  the  caudate  nucleus  (Nucleus  caudatus),  a  somewhat  pear- 
shaped  gray  eminence,  the  long  axis  of  which  is  directed  obliquely  upward,  back- 
ward, and  outward.  Its  anterior  large  end  is  termed  the  head  (Caput  nuclei 
caudati),  and  the  posterior  long  tapering  end  the  tail  (Cauda  nuclei  caudati).  The 
posterior  body,  the  hippocampus,  is  white  on  its  ventricular  surface,  which  is 
strongly  convex.  It  curves  outward  and  backward  and  then  turns  ventrally  and 
forward  to  join  the  piriform  lobe.  The  two  bodies  are  separated  by  an  oblique 
groove  which  is  occupied  by  the  chorioid  plexus  of  the  lateral  ventricle  (Plexus 
chorioideus  ventriculi  lateralis) .  This  is  the  thickened  edge  of  a  fold  of  pia  mater, 
the  tela  chorioidea  of  the  third  ventricle,  which  lies  between  the  hippocampus  and 
the  thalamus.  It  contains  convolutions  of  small  blood-vessels,  and  in  old  subjects 
there  are  often  calcareous  concretions  in  it.  The  plexuses  of  the  two  sides  are 
continuous  through  the  interventricular  foramen.  On  drawing  the  chorioid  plexus 
backward,  a  narrow  white  band,  the  stria  terminaUs,^  is  seen  along  the  margin  of  the 
caudate  nucleus,  where  it  bounds  the  intermediate  groove.  The  plexus  partially 
covers  a  mder  white  band  which  is  blended  with  the  white  substance  of  the  hippo- 
campus; this  is  the  cms  of  the  fornix  and  its  continuation,  the  fimbria. 

The  corpus  striatimi-  is  the  great  basal  ganglion  of  the  hemisphere.  It  is  sit- 
uated in  front  of  the  thalamus  and  the  cerebral  peduncle,  and  its  anterior  rounded 
end  appears  on  the  base  of  the  hemisphere  at  the  trigonum  olfactorium.  It  is 
composed  of  two  masses  of  gray  matter,  the  caudate  and  lenticular  nuclei,  separated 
incompletely  bj^  tracts  of  white  matter  which  are  known  collectively  as  the  internal 
capsule.  The  caudate  nucleus  (Nucleus  caudatus)  is  the  dorso-medial  and  larger 
of  the  two  gray  masses;  it  was  seen  in  the  examination  of  the  lateral  ventricle. 
The  lenticular  nucleus  (Nucleus  lentif ormis)  lies  ventro-laterally,  over  the  trigonum 
olfactorium  and  the  fossa  lateralis.  It  is  related  externally  to  a  layer  of  white 
matter  termed  the  external  capsule  (Capsula  externa),  which  separates  it  from  a 
stratum  of  gray  substance  kno^vn  as  the  claustrum.  The  two  nuclei  are  fused  in 
front,  and  further  back  they  are  connected  by  strands  of  gray  matter  which  inter- 
sect the  internal  capsule. 

The  amygdaloid  nucleus  (Nucleus  amygdalse)  (Fig.  637)  is  an  ovoid  mass  of 
gray  matter  lateral  to  the  ventral  horn  of  the  lateral  ventricle  and  ventral  to  the 
posterior  part  of  the  lenticular  nucleus.  Some  fibers  of  the  stria  terminalis  are 
connected  with  it. 

The  internal  capsule  (Capsula  interna)  is  a  broad  band  of  white  matter  situated 
between  the  thalamus  and  caudate  nucleus  medially  and  the  lenticular  nucleus 
laterally.  A  sagittal  section  through  the  brain  (Fig.  644)  shows  that  it  is  in  great 
part  directly  continuous  with  the  basis  or  ventral  part  of  the  cerebral  peduncle. 
It  contains  most  of  the  so-called  projection  fibers  of  the  hemisphere,  which  con- 
nect the  cerebral  cortex  with  nuclei  of  other  and  more  posterior  parts  of  the  brain. 
When  the  fibers  of  the  internal  capsule  are  traced  forward  it  is  evident  that  they 
spread  out  in  all  directions  to  reach  the  cerebral  cortex.  This  arrangement,  in 
which  the  fibers  of  the  corpus  callosum  participate,  is  termed  the  corona  radiata. 

The  internal  capsule  also  contains  fibers  which  connect  the  corpus  striatum  with  the  thala- 
mus. These  are  termed  the  thalamo-striate  and  strio-thalamic  fibers  respectively,  according  to 
the  direction  in  which  they  conduct  impulses. 

The  fibers  of  the  stria  terminaUs  connect  the  amygdaloid  nucleus  with  the  septum  pelluci- 
dum  and  trigonum  oKactorium.  It  is  therefore  probably  part  of  the  complex  connections  be- 
tween the  primary  and  secondary  olfactory  centers. 

Blood-vessels  of  the  Brain.— The  arteries  which  supply  the  brain  are  derived 
chiefly  from  the  internal  carotid  and  occipital  arteries.  The  basilar  artery,  formed 
by  the  union  of  the  right  and  left  cerebral  branches  of  the  occipital  artery,  enters 

^  Formerly  termed  the  tgenia  semicircular  is. 

-  The  term  arose  from  the  striated  appearance  of  the  mass  in  sections  cut  in  certain  planes, 
the  gray  matter  being  cut  up  into  strands  by  tracts  of  white  fibers. 


THE    CRANIAL   NERVES THE    OPTIC    NERVE  793 

the  cranial  cavity  through  the  foramen  magnum,  and  divides  at  the  interpeduncular 
fossa  into  the  two  posterior  cerebral  arteries.  These  concur  with  branches  of  the 
internal  carotid  arteries  in  forming  the  remarkable  arterial  circle  on  the  base  of  the 
cerebrum.  From  these  emanate  basal  arteries  which  supply  in  general  the  brain 
stem  and  basal  ganglia,  and  cortical  arteries  which  in  general  run  superficially 
and  supply  the  cortical  substance  and  medullary  white  substance. 

The  veins  enter  the  sinuses  of  the  dura  mater,  and  in  the  main  are  not  satel- 
lites of  the  arteries.  The  sinuses  communicate  with  the  ophthalmic,  dorsal  and 
ventral  cerebral,  and  spinal  veins. 


The  Cranial  Nerves 

The  cranial  or  cerebral  nerves  (Nn.  cerebrales)  comprise  twelve  pairs  which 
are  designated  from  before  backward  numerically  and  by  name.  Their  number, 
names,  and  functional  characters  are  given  in  the  subjoined  table: 

I.  Olfactory Sensory  (Smell) 

II.  Optic Sensory  (Sight) 

III.  Oculomotor Motor 

IV.  Trochlear Motor 

V.  Trigeminal Mixed 

VI.  Abducent Motor 

VII.  Facial Mixed 

VIII.  Acoustic Sensory  (Hearing  and  Equihbration) 

IX.  Glosso-pharyngeal Mixed 

X.  Vagus Mixed 

XI.  Spinal  accessory Motor 

XII.  Hypoglossal Motor 


THE  OLFACTORY  NERVE 
The  olfactory  nerve  (N.  olfactorius)  is  peculiar  in  that  its  fibers  are  not  aggre- 
gated to  form  a  trunk,  but  are  connected  in  small  bundles  with  the  olfactory  Ijulb. 
They  are  non-medullated,  and  are  the  central  processes  of  the  olfactory  cells  which 
are  situated  in  the  olfactory  region  of  the  mucous  membrane  of  the  nasal  cavity. 
This  region  is  distinguished  by  its  brown  color  and  comprises  the  posterior  part  of 
the  lateral  mass  of  the  ethmoid,  a  small  adjacent  area  of  the  dorsal  turbinate,  and 
the  corresponding  surface  of  the  septum  nasi.  The  nerve-bundles  are  enclosed  in 
sheaths  derived  from  the  membranes  of  the  brain  and  pass  through  the  foramina  of 
the  cribriform  plate  to  join  the  convex  surface  of  the  olfactory  bulb.  Some 
fibers  come  from  the  vomero-nasal  organ. 


THE  OPTIC  NERVE 

The  optic  nerve  (N.  opticus)  is  composed  of  fibers  which  are  the  central  proc- 
esses of  the  ganglion  cells  of  the  retina.  The  fibers  converge  within  the  eyeball  to 
the  optic  papilla,  where  they  are  collected  into  a  round  trunk,  the  optic  nerve.  The 
nerve  thus  formed  pierces  the  chorioid  and  sclera,  emerges  from  the  posterior  part 
of  the  eyeball,  and  passes  backward  and  medially  to  the  optic  foramen.  After 
traversing  the  latter  it  decussates  vnih  its  fellow  of  the  opposite  side  to  form  the 
optic  chiasma.  In  the  orbit  the  nerve  is  slightly  flexuous  and  is  embedded  in  the 
fat  behind  the  eyeball  and  surrounded  by  the  retractor  oculi  muscle.  Its  intraos- 
seous part  is  an  inch  or  more  (ca.  3  cm.)  long.  The  sheath  of  the  nerve  is  formed  by 
prolongations  of  the  membranes  of  the  brain,  and  includes  continuations  of  the 
subdural  and  subarachnoid  spaces. 

The  greater  part  of  the  fibers  of  the  optic  nerve  cross  in  the  chiasma  to  the  tract  of  the  oppo- 
site side.     In  the  tract  the  fibers  proceed  to  (1)  the  medial  geniculate  body,  (2)  the  posterior 


794 


NERVOUS    SYSTEM    OF    THE    HORSE 


part  of  the  thalamus,  and  (3)  the  anterior  quadrigeminal  body  (indirectly).  The  fibers  which 
go  to  the  medial  geniculate  body  appear  to  belong  to  Gudden's  commissure  and  to  be  non-visual 
in  function.  The  visual  fibers,  which  come  from  the  lateral  part  of  the  retina  of  the  same  side 
and  the  medial  part  of  tlie  retina  of  the  opposite  side,  terminate  about  cells  in  the  anterior  quad- 
rigeminal body  and  the  part  of  the  thalamus  which  corresponds  to  the  pulvinar  and  lateral  genicu- 
late body  of  man.  From  the  cells  of  the  former  fibers  pass  to  the  nuclei  of  the  motor  nerves  of 
the  eyeball,  and  complete  the  reflex  arc.  Fibers  proceed  from  the  cells  of  the  thalamus  to  the 
visual  area  of  the  cortex  in  the  occipital  part  of  the  hemisphere. 


THE  OCULOMOTOR  NERVE 

The  oculomotor  nerve  (N.  oculomotorius)  arises  by  several  radicles  from  the 
basal  surface  of  the  cerebral  peduncle,  a  little  lateral  to  the  interpeduncular  furrow. 

It  turns  sharply  outward  and  for- 
ward, crosses  over  the  cavernous 
sinus,  and  continues  above  the 
maxillary  nerve  and  in  company 
with  the  ophthalmic  nerve  to  the 
foramen  orbitale.  It  emerges 
through  the  foramen  with  the  lat- 
ter nerve  and  the  abducens  and 
divides  into  two  branches.  The 
dorsal  branch  is  short  and  divides 
into  two  twigs  which  supply  the 
rectus  dorsalis  and  levator  pal- 
pebrae  superioris.  The  ventral 
branch  (Figs.  563,  564)  is  larger 
and  much  longer.  It  supplies  the 
motor  fibers  to  the  ciliary  gan- 
glion (which  lies  directly  on  this 
branch  in  the  horse)  and  short 
branches  to  the  rectus  medialis 
and  rectus  ventralis,  and  con- 
tinues forward  on  the  latter  to 
end  in  the  ventral  oblique  mus- 
cle. 

The  deep  origin  of  the  fibers  of 
the  oculomotor  nerve  is  in  the  oculo- 
motor nucleus,  situated  in  the  gray  mat- 
ter of  the  floor  of  the  cerebral  aque- 
duct in  the  region  of  the  anterior  cor- 
pora quadrigemina. 


Fig.  645. — Floor  of  Cr.\nial  Cavity  of  Horse. 
The  roots  of  the  cranial  nerves  are  shown  on  the  left  side 
and  are  designated  by  number:  /,  Anterior  cranial  fossa;  //, 
middle  cranial  fossa;  III,  posterior  cranial  fossa;  a,  ethmoidal 
fossa;  6,  ethmoidal  foramen;  c,  foramen  for  nasal  branch  of 
ophthalmic  arterj';  d,  orbital  wing  of  sphenoid  bone;  e,  optic 
groove;  /,  hypophyseal  fossa;  g,  spheno-occipital  crest;  h,  h',  con- 
tour of  hypophysis  or  pituitary  body;  h",  slight  elevation  repre- 
senting dorsum  sellse;  i,  k,  grooves  for  nerves  and  cavernous  sinus; 
I,  depression  for  piriform  lobe  of  cerebrum;  m,  groove  for  middle 
meningeal  artery;  n,  depression  for  pons;  o,  foramen  lacerum  an- 
terius;  p,  foramen  lacerum  posterius;  q,  incisura  carotica;  q',  inci- 
sura  ovalis;  q",  incisura  spinosa;  r,  depression  for  medulla  oblongata; 
s,  hypoglossal  foramen;  t,  internal  acoustic  meatus;  u,  foramen 
magnum;  v,  frontal  sinus;  u\  zygomatic  process  of  temporal  bone; 
X,  section  of  petrous  temporal;  y,  section  of  occipital  bone;  z,  crista 
galli;  1,  1',  1",  dotted  lines  indicating  position  of  olfactorj'  strise 
and  tract.     (After  Ellenberger-Baum,  Top.  Anat.  d.  Pferdes.) 


THE  TROCHLEAR  NERVE 

The  trochlear  nerve  (N.  tro- 
chlearis)^  is  the  smallest  of  the 
cranial  nerves.  It  arises  from 
the  anterior  cerebellar  peduncle 
just  behind  the  corpora  quadri- 
gemina, curves  outward  and  for- 
ward, pierces  the  tentorium  cere- 
belli,  and  passes  forward  along 
the  lateral  border  of  the  maxillary 
nerve  (Figs.  635,  636).  It  emerges  from  the  cranium  through  a  small  foramen 
1  Formerly  termed  the  nervus  patheticus. 


THE    TRIGEMINAL    NERVE  795 

immediately  above  the  foramen  orbitale  or  through  the  latter  and  passes  forward 
along  the  medial  wall  of  the  orbit  to  end  in  the  posterior  part  of  the  dorsal  oblique 
muscle  of  the  eyeball  (Fig.  564). 

The  fibers  of  the  fourth  nerve  spring  from  a  nucleus  in  the  gray  matter  of  the  floor  of  the 
cerebral  aqueduct  behind  the  oculomotor  nucleus.  The  fibers  run  backward  in  the  tegmentum, 
then  turn  dorso-medially,  and  undergo  total  decussation  with  those  of  the  opposite  nerve  in  the 
anterior  part  of  the  anterior  medullary  velum.  In  addition  to  this  peculiarity  it  is  the  only  nerve 
which  is  connected  with  the  dorsal  aspect  of  the  brain. 


THE  TRIGEMINAL  NERVE 

The  trigeminal  nerve  (N.  trigeminus) ^  is  the  largest  of  the  cranial  series.  It 
is  connected  with  the  lateral  part  of  the  pons  by  a  large  sensory  root  and  a  smaller 
motor  root  (Fig.  629). 

The  sensory  root  (Portio  major)  extends  forward  through  a  notch  on  the  lower 
part  of  the  petrosal  crest  and  widens  out  to  join  the  semilunar  ganglion. 

The  semilunar  ganglion  (Ganglion  semilunare)-  is  a  crescent-shaped  mass  of 
nerve-fibers  and  cells  which  overlies  the  antero-lateral  part  of  the  foramen  lacerum 
basis  cranii,  and  is  partly  embedded  in  the  dense  fibrous  tissue  which  occupies  the 
foramen  except  where  vessels  and  nerves  pass  through.  Its  long  axis,  which  is 
about  an  inch  (2.5  cm.)  in  length,  is  directed  forward  and  medially  and  its  convex 
anterior  face  gives  rise  to  the  ophthalmic,  the  maxillary,  and  the  sensory  part  of 
the  mandibular  division  of  the  nerve.  The  surface  of  the  ganglion  is  irregularly 
striated.  It  is  connected  by  filam«ents  with  the  adjacent  carotid  plexus  of  the  sym- 
pathetic, and  sends  delicate  twigs  to  the  dura  mater. 

The  fibers  of  the  sensory  root  arise  from  the  ganglion  as  axones  of  the  gangUon  cells,  and  the 
fibers  of  the  nerves  which  extend  peripherally  from  the  ganglion  are  dendrites  of  the  cells.  The 
sensory  root-fibers  enter  the  tegmentum  of  the  pons  and  divide  into  anterior  and  posterior  branches, 
which  terminate  about  the  cells  of  the  sensory  nucleus  of  termination  of  the  trigeminus.  This 
nucleus  extends  from  the  pons  to  the  sixth  cervical  segment  of  the  spinal  cord  (Dcxler).  The 
posterior  branches  of  the  fibers  are  collected  into  a  compact  bundle,  the  spinal  tract  or  root  of  the 
trigeminus,  which  lies  lateral  to  the  substantia  gelatinosa  in  the  medulla.  The  central  connections 
of  the  sensory  part  of  the  trigeminus  are  very  extensive.  The  most  important  paths  are:  (1) 
Axones  of  cells  of  the  sensory  nucleus  and  the  substantia  gelatinosa  pass  chiefly  as  arcuate  fibers 
across  the  raphe  to  the  thalamus,  whence  impulses  are  transmitted  by  thalamo-cortical  fibers 
to  the  cerebral  cortex.  In  ungulates  a  distinct  tract  extends  from  the  anterior  part  of  the  sensory 
nucleus  to  the  thalamus  of  the  same  side  (Wallenberg).  It  is  probable  that  collaterals  of  the 
arcuate  fibers  go  to  the  motor  nuclei  of  the  fifth,  seventh,  ninth,  and  tenth  cranial  nerves.  (2) 
Axones  of  cells  of  the  sensory  nucleus  enter  the  posterior  cerebellar  peduncle  of  the  same  side 
and  reach  the  cerebellar  cortex.  (3)  Collaterals  are  distributed  to  the  nuclei  of  origin  of  the 
hypoglossal  and  of  the  motor  part  of  the  trigeminal  and  facial  nerves. 

The  motor  root  (Portio  minor)  extends  forward  beneath  the  sensory  root  and 
the  semilunar  ganglion  and  is  incorporated  with  the  mandibular  division  of  the 
nerve.  Its  fibers  arise  chiefly  from  the  so-called  masticatory  nucleus,  which  is 
situated  in  the  pons  near  the  inner  face  of  the  sensory  nucleus;  a  few  of  these  fillers 
come  from  the  nucleus  of  the  opposite  side  and  cross  in  the  raphe.  Other  fibers, 
which  constitute  the  mesencephalic  root,  arise  from  cells  in  the  outer  part  of  the 
central  gray  matter  of  the  mid-brain. 

It  is  evident  from  the  foregoing  statements  that  the  trigeminus  has  essentially 
the  same  arrangement  as  a  typical  spinal  nerve.     It  divides  into  three  branches. 

I.  The  ophthalmic  nerve  (N.  ophthalmicus)  (Figs.  563,  564,  565)  is  purely 
sensory  and  is  the  smallest  of  the  three  branches  of  the  trigeminus.  It  arises  from 
the  medial  part  of  the  front  of  the  semilunar  ganglion,  passes  forward  along  the  outer 
side  of  the  cavernous  sinus,  and  is  blended  with  the  maxillary  nerve  for  some  dis- 
tance. It  enters  the  foramen  orbitale  with  the  third  and  sixth  nerves  and  divides 
into  three  branches. 

1.  The  lacrimal  nerve  (N.  lacrimalis)  runs  forward  on  the  rectus  dorsalis  and 

1  Also  known  as  the  trifacial  nerve.  -  Formerly  termed  the  Gasserian  ganglion. 


796  NERVOUS    SYSTEM    OF   THE    HORSE 

the  levator  palpebrse  superioris  and  ramifies  chiefly  in  the  lacrimal  gland  and  the 
upper  eyelid.  A  branch  (Ramus  zygomatico-temporalis)  exchanges  twigs  with  the 
z3^gomatic  branch  of  the  maxillary  nerve,  perforates  the  periorbita,  and  emerges 
from  the  orbital  fossa  behind  the  supraorbital  process;  it  forms  a  plexus  with 
branches  of  the  auriculo-palpebral  and  frontal  nerves,  and  ramifies  in  the  skin  of 
the  temporal  region. 

2.  The  frontal  nerve  (N.  frontalis),  also  termed  the  supraorbital,  runs  forward 
almost  parallel  with  the  dorsal  oblique  muscle,  at  first  within,  then  outside  of,  the 
periorbita.  It  passes  through  the  supraorbital  foramen  with  the  artery  of  like 
name  and  ramifies  in  the  skin  of  the  forehead  and  upper  eyelid,  forming  a  plexus 
with  the  lacrimal  and  auriculo-palpebral  nerves.     It  divides  into  three  branches. 

3.  The  naso-ciliary  nerve  (N.  nasociliaris),  also  termed  the  palpebro-nasal, 
runs  forward  along  the  medial  side  of  the  optic  nerve  between  parts  of  the  retractor 
muscle  and  divides  into  two  branches.  Of  these,  the  ethmoidal  nerve  (N.  ethmoid- 
alis)  is  the  continuation  of  the  parent  trunk.  It  accompanies  the  ethmoidal 
artery  through  the  foramen  of  like  name  into  the  cranial  cavity  and  crosses  the 
lower  part  of  the  ethmoidal  fossa.  Leaving  the  cranium  through  an  opening  in  the 
cribi'iform  plate  close  to  the  crista  galli,  it  enters  the  nasal  cavity  and  ramifies  in 
the  nmcous  membrane  of  the  septum  nasi  and  the  dorsal  turbinate.  The  infra- 
trochlear  nerve  (N.  infratrochlearis)  runs  forward  to  the  medial  canthus  and  rami- 
fies in  the  skin  in  this  region;  it  detaches  twigs  to  the  conjunctiva  and  caruncula 
lacrimalis,  and  a  long  branch  which  supplies  the  third  eyelid  and  the  lacrimal  ducts 
and  sac.  The  naso-ciliary  nerve  furnishes  the  sensory  or  long  root  (Radix  longa) 
of  the  ciliary  ganglion. 

The  ciliary  ganglion  is  placed  on  the  ventral  branch  of  the  oculomotor  nerve, 
close  to  its  origin  from  the  latter.  It  is  usually  not  larger  than  a  millet-seed,  and 
is  best  found  by  following  the  nerve  to  the  ventral  oblique  muscle  back  to  its  origin. 
The  ganglion  receives — (a)  sensory  fibers  from  the  naso-ciliary  nerve;  (6)  motor 
fibers  from  the  oculomotor  nerve;  and  (c)  sympathetic  fibers  from  the  spheno- 
palatine plexus.  It  detaches  filaments  which  unite  with  twigs  from  the  ophthalmic 
and  maxillary  nerves  and  from  the  sphenopalatine  ganglion  to  form  the  ciliary 
plexus.  From  the  latter  emanate  five  to  eight  delicate  short  ciliary  nerves  (Nn. 
ciliares  breves),  which  pursue  a  somewhat  flexuous  course  along  the  optic  nerve, 
pierce  the  sclera  near  the  entrance  of  that  nerve,  and  run  forward  between  the 
sclera  and  chorioidea  to  the  circumference  of  the  iris.  Here  the  branches  of  ad- 
jacent nerves  anastomose  to  form  a  circular  plexus  (Plexus  gangliosus  ciliaris), 
from  which  filaments  go  to  the  ciliary  body,  iris,  and  cornea. 

The  circular  fibers  of  the  iris  and  the  ciliary  muscle  are  innervated  by  fibers  derived  from  the 
oculomotor  nerve,  the  radial  fibers  of  the  iris  by  the  sympathetic. 

II.  The  maxillary  nerve  (N.  maxillaris)^  is  purely  sensory  and  is  much  larger 
than  the  ophthalmic.  It  extends  forward  from  the  semilunar  ganglion  in  the  middle 
cranial  fossa  in  the  large  groove  on  the  root  of  the  temporal  wing  of  the  sphenoid. 
It  is  related  medially  to  the  cavernous  sinus  and  dorsaliy  to  the  ophthalmic  nerve, 
with  which  it  is  blended  for  some  distance.  It  emerges  through  the  foramen 
rotundum,  passes  forward  in  the  ptery go-palatine  fossa  above  the  internal  maxillary 
artery  and  embedded  in  fat,  and  is  continued  in  the  infraorbital  canal  as  the  in- 
fraorbital nerve  (Fig.  564) .     Its  branches  are  as  follows : 

1.  The  zygomatic  nerve  (N.  zygomaticus  s.  subcutaneus  malse),  also  termed 
the  orbital  branch,  arises  before  the  maxillary  nerve  reaches  the  pterygo-palatine 
fossa  (Figs.  563,  564,  646).  It  pierces  the  periorbita  and  divides  into  two  or  three 
delicate  branches  which  pass  along  the  surface  of  the  lateral  straight  muscle  to 

^  This  is  also  termed  the  superior  maxillary  brancli. 


THE   TRIGEMINAL   NERVE 


797 


the  lateral  canthus  and  ramify  chiefly  in  the  lower  lid  and  the  adjacent  skin.     Anas- 
tomoses are  formed  with  branches  of  the  lacrimal  nerve. 

2.  The  sphenopalatine  nerve  (N.  sphenopalatinus)  is  given  off  in  the  pterygo- 
palatine fossa  from  the  ventral  border  of  the  maxillary  nerve  (Fig.  564).  It  is 
broad  and  flat  and  forms  a  plexus  in  which  several  small  sphenopalatine  ganglia 


Fig.  646. — Dissection  of  Head  op  Horse. 
The  masseter  and  superficial  muscles  and  the  parotid  gland  are  in  great  part  removed,  a,  a.  Levator  labii  superi- 
oris  proprius;  6,  6,  levator  nasolabialis;  c,  dilatator  naris  inferior;  d,  buccinator;  e,  common  mass  of  buccinator  and 
depressor  labii  inferioris;  /,  depressor  labii  inferioris;  g,  masseter;  h,  orbicularis  oculi;  i,  temporalis;  k,  occipito- 
hyoideus;  k',  occipito-mandibularis;  I,  sterno-cephalicus;  I',  tendon  of  same;  m,  omo-hyoideus;  n,  crico-pharyngeus; 
o,  mastoid  tendon  of  brachiocephahcus;  p,  splenius;  q,  inferior  buccal  and  labial  glands;  r,  superior  buccal  glands; 
s,  remnant  of  parotid  gland;  t,  mandibular  gland;  u,  anterior  cervical  lymph  glands;  v,  probe  passed  into  diverticulum 
nasi;  w,  cornu  of  alar  cartilage;  x,  medial  palpebral  hgament;  y,  wing  of  atlas;  z,  scutiform  cartilage  of  ear;  1,  lateral 
nasal  nerve;  2,  anterior  nasal  nerve;  3,  superior  labial  nerve;  4-,  anterior  part  of  superior  buccal  nerve;  5,  buccinator 
nerve;  6,  6',  inferior  alveolar  nerve;  6",  mental  nerve — continuation  of  6;  7,  masseteric  nerve;  8,  facial  nerve  (cut) ; 
fl,  superficial  temporal  nerve;  ^0,  anastomosis  between  9a.nd8;  11,  internal  auricular  nerve;  7;?,  posterior  auricular 
nerve;  i 3,  digastric  nerve;  i^i  cervical  branch  of  facial  nerve  (cut);  75,  auriculo-palpebral  nerve;  iff,  lacrimal  nerve; 
77,  frontal  nerve;  i<S,  infratrochlear  nerve;  iS,  zygomatic  nerve;  ^0,  spinal  accessory  nerve;  £1,  ventral  branch  of 
spinal  accessory  nerve  (to  sterno-cephalicus);  ££,  ventral  end  branch  of  first  cervical  nerve;  33,  thyro-laryngeal 
artery;  24,  internal  maxillary  artery;  23,  masseteric  artery;  26,  great  (posterior)  auricular  artery;  27,  external  branch 
of  ^6;  ^S,  deep  auricular  artery;  ^5,  anterior  auricular  artery;  50,  transverse  facial  artery;  5/,  facial  artery;  ^3,  inferior 
labial  artery;  33,  superior  labial  artery;  34,  lateral  nasal  artery;  3o,  dorsal  nasal  artery;  36,  angular  artery  of  eye;  37, 
terminal  branches  of  superior  labial  nerve ;  S5,  branch  of  buccinator  artery;  3S,  buccinator  vein;  40,  vena  reflexa;  4^, 
jugular  vein;  4^,  external  maxillary  vein;  44i  ventral  cerebral  vein;  4-5.  stump  of  great  auricular  vein;  4^,  ramus  of 
mandible;  47,  facial  crest;  43,  zygomatic  arch;  4S,  parotid  duct.     (After  Ellenberger-Baum,  Top.  Anat.  d.  Pferdes.) 


are  interposed.  It  divides  into  posterior  nasal,  and  greater  and  lesser  palatine 
nerves.  (1)  The  posterior  nasal  nerve  (N.  nasalis  aboralis)  passes  through  the 
sphenopalatine  foramen,  in  which  it  bears  one  or  more  minute  ganglia,  enters  the 
nasal  cavity,  and  divides  into  medial  and  lateral  branches  (Figs.  565,  588).  The 
medial  branch  (N.  septi  narium)  runs  forward  in  the  submucous  tissue  of  the  lower 
part  of  the  septum  nasi,  gives  twigs  to  the  mucous  membrane  here  and  to  the 
vomero-nasal  organ,  passes  through  the  palatine  fissure,  and  ramifies  in  the  anterior 


798  NERVOUS    SYSTEM    OF    THE    HORSE 

part  of  the  hard  palate.  The  lateral  branch  (Ramus  lateralis)  ramifies  in  the 
mucous  membrane  of  the  ventral  turbinate  and  the  middle  and  ventral  meatus  nasi. 
(2)  The  greater  or  anterior  palatine  nerve  (N.  palatinus  major  s.  oralis)  (Figs. 
563,  564)  is  the  largest  of  the  three  branches.  It  runs  forward  in  the  palatine  canal 
and  groove  and  ramifies  in  the  hard  palate  and  gums.  It  also  supplies  twigs  to  the 
soft  palate,  and  gives  off  branches  which  pass  through  the  accessory  palatine  for- 
amina to  supply  the  mucous  membrane  of  the  ventral  meatus. 

The  branches  of  the  two  nerves  anastomose  in  the  hard  palate  and  form  a  plexus  about  the 
branches  of  the  palatine  arteries. 

(3)  The  lesser  or  posterior  palatine  nerve  (N.  palatinus  minor  s.  aboralis), 
also  termed  the  staphyline,  is  much  the  smallest  of  the  three  branches  (Figs.  563, 
564) .  It  passes  downward  and  forward  with  the  palatine  vein  in  the  groove  at  the 
medial  side  of  the  tuber  maxillare  and  ramifies  in  the  soft  palate. 

The  sphenopalatine  gangUa  and  plexus  (Fig.  647)  lie  on  the  perpendicular  part  of  the  palatine 
bone  and  the  pterygoid  process,  under  cover  of  the  maxillary  nerve.  The  afferent  fibers  of  the 
plexus  and  ganglia  come  chiefly  from  the  branches  of  the  sphenopalatine  nerve  and  the  nerve  of 
the  pterygoid  canal.  Interspersed  in  these  are  several  minute  gangUa  and  one  or  more  larger 
ones.  The  nerve  of  the  pterygoid  canal  (N.  canaUs  pterygoidei)i  is  formed  by  the  union  of  sym- 
pathetic fibers  with  the  superficial  petrosal  branch  of  the  facial  nerve.  It  passes  forward  at  first 
between  the  Eustachian  tube  and  the  sphenoid  bone,  enters  the  canal  between  the  pterygoid  bone 
and  process,  and  joins  the  posterior  part  of  the  plexus.  It  is  probable  that  it  furnishes  the  motor 
fibers  to  the  levator  palati  and  palatinus  muscles.  Efferent  filaments  go  to  the  periorbita  and  the 
ophthalmic  vessels,  and  others  accompany  the  branches  of  the  maxillary  nerve,  around  which  they 
have  a  plexiform  arrangement. 

3.  The  infraorbital  nerve  (N.  infraorbitalis)-  is  the  continuation  of  the  maxillary 
trunk.  It  traverses  the  infraorbital  canal,  emerges  through  the  infraorbital  fora- 
men, and  divides  into  nasal  and  superior  labial  branches.  Along  its  course  it  gives 
off  maxillary  alveolar  or  dental  branches  (Rami  alveolares  maxillae),  which  supply 
the  teeth,  alveolar  periosteum,  and  gums. 

Small  posterior  alveolar  branches  (Rami  alveolares  maxilte  aborales)  are  given  off  in  the 
pterygo-palatine  fossa,  pass  through  small  foramina  in  the  tuber  maxillare,  and  supply  the  posterior 
molar  teeth  and  the  maxillary  sinus.  The  middle  alveolar  branches  (Rami  alveolares  maxillae 
medii)  are  given  off  in  the  infraorbital  canal,  and  constitute  the  chief  nerve-supply  to  the  cheek 
teeth  and  the  maxillary  sinus.  The  maxillary  incisor  branch  (Ramus  alveolaris  maxillae  incisivus) 
runs  forward  in  the  incisor  canal  and  supplies  branches  to  the  canine  and  incisor  teeth.  The  fore- 
going unite  with  each  other  to  form  the  maxillary  dental  plexus  (Plexus  dentalis  maxilla^)  from 
which  the  dental  and  gingival  branches  are  given  off. 

The  external  nasal  branches  (Rami  nasales  externi),  two  or  three  in  number, 
accompany  the  levator  labii  superioris  proprius  and  ramifj'  in  the  dorsum  nasi  and 
the  nasal  diverticulum. 

The  large  anterior  nasal  branch  (Ramus  nasalis  oralis)  gives  branches  to  the 
upper  lip  and  nostril,  passes  over  the  nasal  process  of  the  premaxilla  under  cover 
of  the  lateralis  nasi,  and  ramifies  in  the  mucous  membrane  of  the  nasal  vestibule. 

The  superior  labial  branch  (Ramus  labialis  dorsalis)  is  the  largest  of  the  termi- 
nals of  the  infraorbital  nerve.  It  passes  downward  and  forward  under  cover  of  the 
levator  nasolabialis  and,  after  supplying  the  skin  of  the  anterior  part  of  the  cheek, 
forms  a  rich  terminal  ramification  in  the  skin  and  mucous  membrane  of  the  upper 
ip.     It  anastomoses  with  the  superior  buccal  branch  of  the  facial  nerve. 

III.  The  mandibular  nerve  (N.  mandibularis)^  is  formed  by  the  union  of  two 
roots;  of  these,  the  large  sensory  root  comes  from  the  semilunar  ganglion,  and  the 
small  motor  root  is  the  pars  minor  of  the  trigeminus.  It  emerges  from  the  cranium 
through  the  oval  notch  of  the  foramen  lacerum,  and  passes  between  the  temporal 
wing  of  the  sphenoid  bone  and  the  muscular  process  of  the  petrous  temporal.  It 
then  runs  forward,  downward,  and  a  little  outward,  between  the  ventral  surface  of 

^  Also  known  as  the  Vidian  nerve.  2  ^his  is  also  called  the  superior  dental  nerve. 

'  This  is  also  termed  the  inferior  maxillary  branch. 


THE   TRIGEMINAL   NERVE 


799 


the  pterygoideus  medialis  and  the  guttural  pouch,  and  on  reaching  the  lateral 
surface  of  the  pterygoideus  lateralis,  it  divides  into  two  terminal  branches— the 
inferior  alveolar  and  lingual  nerves.     It  gives  off  the  following  branches: 

1.  The  masseteric  nerve  (N.  massetericus)  (Figs.  562,  646)  passes  outward 
through  the  sigmoid  notch  of  the  mandible  across  the  anterior  surface  of  the  tem- 
poro-mandibular  articulation  and  enters  the  deep  face  of  the  masseter  muscle,  in 
which  it  ramifies. 

2.  The  deep  temporal  nerves  (Nn.  temporales  profundi)  (Fig.  562),  two  or 
three  in  number,  arise  from,  or  by  a  common  trunk  with,  the  masseteric.  They 
supply  the  temporalis  muscle. 

3.  The  buccinator  nerve  (N.  buccinatorius)  passes  downward  and  forward 
at  first  across  the  medial  surface  of  the  temporo-mandibular  articulation,  then 
through  the  anterior  part  of  the  lateral  pterygoid  muscle,  then  between  the  bucci- 


FiG.  647. — Deep  Dissection  op  Base  of  Cranium,  Viewed  from  the  Right  and  Below. 
The  tympanic  cavity  is  opened  and  the  paramastoid  process  is  sawn  off.  a,  Occipital  condyle;  h,  body  of  sphenoid; 
c,  external  acoustic  meatus  (part  removed) ;  (i,  malleus;  e,  incus;  ;,  stump  of  ophthalmic  nerve;  ^,  stump  of  maxillary 
nerve;  5,  sphenopalatine  plexus;  4,  nerve  of  pterygoid  canal;  4',  deep  petrosal  nerve;  4",  branch  to  tympanic  plexus; 
4'",  superficial  petrosal  nerve;  .5,  superficial  temporal  nerve  (cut  off);  6,  masseteric  nerve  (cut  off);  7,  mandibular 
nerve  (raised);  S,  lingual  nerve  (cut  off);  9,  pterygoid  nerve  (cut);  10,  nerve  to  tensor  tympani;  11,  otic  ganglion; 
12,  facial  nerve;  13,  stapedial  nerve;  14,  chorda  tympani;  15,  glosso-pharyngeal  nerve  (cut);  16,  tympanic  nerve;  17, 
vagus  (cut  off);  18,  auricular  branch  of  vagus;  19,  spinal  accessory  nerve  (cut  off);  SO,  hypoglossal  nerve  (cut  off; 
iil,  sympathetic  nerve  (cut  off) ;  S3,  internal  carotid  artery.     (After  EUenberger,  in  Leisering's  Atlas.) 


nator  vein  and  the  tuber  maxillare  (Fig.  646).  It  continues  forward  in  the  sub- 
mucous tissue  of  the  cheek  along  the  ventral  border  of  the  depressor  labii  inferioris 
and  divides  into  branches  which  ramify  in  the  mucous  membrane  and  glands  of  the 
lips  in  the  vicinity  of  the  commissure.  It  supplies  small  branches  to  the  lateral 
pterygoid  and  temporal  muscles  and  detaches  numerous  collateral  twigs  to  the 
mucous  membrane  of  the  cheek  and  to  the  buccal  glands.  It  also  communicates 
with  the  inferior  buccal  branch  of  the  facial  nerve. 

4.  The  pterygoid  nerve  (N.  pterygoideus)  arises  in  common  with  the  preceding, 
passes  downward  and  forward  under  cover  of  the  parent  trunk,  and  divides  into 
branches  which  enter  the  posterior  part  of  the  pterygoideus  medialis  at  the  division 
between  the  two  layers  of  the  muscle  (Fig.  647) . 

The  otic  ganglion  (G.  oticum)  is  situated  on  the  mandibular  near  the  origin  of 
the  buccinator  nerve,  and  is  related  medially  to  the  tensor  palati  and  the  Eustachian 
tube.     It  receives  motor  fibers  from  the  pterygoid  nerve  and  sensory  fibers  by  the 


800  NERVOUS    SYSTEM   OF  THE   HORSE 

small  superficial  petrosal  nerve  from  the  tympanic  plexus,  through  which  communi- 
cations are  made  with  the  facial  and  glosso-pharyngeal  nerves.  Sympathetic 
fibers  are  derived  from  the  plexus  on  the  internal  maxillary  artery.  Efferent  fila- 
ments go  to  the  tensor  palati,  tensor  tympani,  and  pterygoid  muscles  and  to  the 
Eustachian  tube. 

The  ganglion  is  small  and  somewhat  difficult  to  find,  and  in  many  cases  it  is  replaced  by 
a  number  of  minute  ganglia  interspersed  in  a  fine  plexus. 

5.  The  superficial  temporal  nerve  (N.  temporalis  superficialis)  (Figs.  562, 
646,  647)  runs  outward  across  the  pterygoideus  lateralis,  passes  between  the  parotid 
gland  and  the  neck  of  the  ramus  of  the  mandible,  turns  around  the  latter,  and  di- 
vides into  two  branches.  The  transverse  facial  branch  (Ramus  transversus  faciei) 
accompanies  the  transverse  facial  vessels  and  ramifies  in  the  skin  of  the  cheek. 
The  larger  ventral  branch  unites  with  the  ventral  buccal  division  of  the  facial  nerve. 
Before  its  division  the  nerve  gives  off  twigs  to  the  guttural  pouch,  the  parotid 
gland,  the  external  ear,  and  the  skin  of  the  external  acoustic  meatus  and  the  mem- 


FiG.  648. — Part  of  Branch  of  Lower  Jaw  of  Horse;  Medial  View. 
The  bone  has  been  removed  to  show  the  vessels  and  nerves.     1,  1',  Mandibular  alveolar  nerve;   3,  2,  branches  to 
cheek  teeth  and  gums;   2',  branch  to  canine  and  incisor  teeth;   3,  S',  alveolar  artery;   4<  satellite  vein.     (After  Leiser- 
ing'a  Atlas.) 

brana  tympani.     Branches  from  it  concur  with  filaments  from  the  cervical  branch 
of  the  facial  nerve  in  the  formation  of  the  auricular  plexus. 

6.  The  mandibular  alveolar  nerve  (N.  alveolaris  mandibulae)  (Figs.  561,  562, 
646)^  arises  with  the  lingual  by  a  common  trunk  which  passes  forward  at  first  on 
the  lateral  pterygoid  muscle,  then  inclines  ventrally  between  the  medial  pterygoid 
and  the  ramus  of  the  mandible.  The  lingual  and  alveolar  separate  at  an  acute 
angle,  and  the  latter  enters  the  mandibular  foramen  and  courses  in  the  canal 
within  the  ramus  (Fig.  648).  Emerging  at  the  mental  foramen,  it  terminates  by 
dividing  into  six  to  eight  inferior  labial  and  mental  branches,  which  ramify  in  the 
lower  lip  and  chin.  Before  entering  the  bone,  the  nerve  detaches  the  mylo-hyoid 
nerve  (N.  mylohyoideus) ,  which  runs  downward  and  forward  between  the  ramus 
and  the  mylo-hyoid  muscle;  it  supplies  that  muscle,  the  anterior  belly  of  the 
digastricus,  and  the  skin  of  the  anterior  part  of  the  mandibular  space.  The  dental 
and  gingival  branches  detached  from  the  nerve  within  the  mandible  are  arranged 
like  the  corresponding  nerves  of  the  upper  jaw. 

7.  The  lingual  nerve  (N.  lingualis)  arises  by  a  common  trunk  with  the  mandib- 
ular alveolar  nerve   (Figs.  561,  562).     After  separating  from  the  latter  it  runs 

^  Also  termed  the  inferior  dental  nerve. 


THE   ABDUCENT   NERVE — THE    FACIAL   NERVE  801 

downward  and  forward,  lying  at  first  between  the  ramus  of  the  mandible  and  the 
medial  pterygoid  muscle,  then  on  the  medial  face  of  the  mylo-hyoid.  On  reaching 
the  root  of  the  tongue  it  divides  into  superficial  and  deep  branches.  The  super- 
ficial branch  (Ramus  superficialis)  runs  forward  on  the  stylo-glossus  and  accom- 
panies the  mandibular  duct  on  the  deep  face  of  the  sublingual  gland.  It  supplies 
the  mucous  membrane  of  the  tongue  and  the  floor  of  the  mouth.  At  the  root  of  the 
tongue  it  gives  off  a  recurrent  branch  to  the  isthmus  faucium,  which  communicates 
with  the  lingual  branch  of  the  glosso-pharyngeal  nerve.  The  larger  deep  branch 
(Ramus  profundus)  turns  around  the  lower  edge  of  the  stylo-glossus  and  hyo- 
glossus,  passes  upward  and  forward  between  the  latter  muscle  and  the  genio- 
glossus,  and  continues  forward  on  the  latter  to  the  tip  of  the  tongue.  At  the  turn 
it  gives  off  one  or  more  ascending  branches  which  ramify  on  the  deep  face  of  the 
hyo-glossus.  It  gives  branches  to  the  mucous  membrane  and  the  fungiform  papillsB 
of  the  tongue,  and  anastomoses  with  branches  of  the  hypoglossal  nerve  and  with 
the  superficial  branch.  Minute  ganglia  occur  on  the  finer  branches  of  the  lingual 
nerve.  The  chorda  tympani  branch  of  the  facial  joins  the  lingual  nerve  at  the  origin 
of  the  latter  and  is  incorporated  with  it  in  its  distribution  to  the  tongue. 


THE  ABDUCENT  NERVE 
The  abducent  nerve  (N.  abducens)  emerges  from  the  brain  behind  the  pons 
and  just  lateral  to  the  pyramid  (Fig.  629).  It  passes  forward  across  the  pons, 
pierces  the  dura  mater,  and  accompanies  the  third  and  ophthalmic  nerves,  below 
which  it  emerges  through  the  foramen  orbitale.  In  the  orbit  it  divides  into  two 
branches  which  innervate  the  rectus  lateralis  and  the  retractor  muscle  of  the  eye- 
ball. Within  the  cranium  it  receives  filaments  from  the  carotid  plexus  of  the  sym- 
pathetic. 

The  fibers  of  the  abducent  nei-ve  are  axones  of  the  large  multipolar  cells  of  the  abducent 
nucleus  which  is  situated  beneath  the  eminentia  teres  of  the  floor  of  the  fourth  ventricle.  The 
nucleus  Ues  within  the  loop  formed  by  the  fibers  of  origin  of  the  facial  nerve.  It  is  connected 
with  (a)  the  anterior  olive;  (6)  the  oculomotor  nucleus  of  the  opposite  side;  (c)  the  motor  area  of 
the  cerebral  cortex  by  means  of  the  pyramidal  tract  of  the  opposite  side. 


THE  FACIAL  NERVE 

The  facial  nerve  (N.  facialis)  has  its  superficial  origin  at  the  lateral  part  of  the 
corpus  trapezoideum,  immediately  behind  the  pons  (Fig.  629).  It  passes  outward 
in  front  of  the  eighth  nerve  and  enters  the  internal  acoustic  meatus.  At  the  bottom 
of  the  meatus  the  two  nerves  part  company,  the  facial  coursing  in  the  facial  canal 
of  the  petrous  temporal  bone.  The  canal  and  nerve  are  at  first  directed  outward 
between  the  vestibule  and  the  cochlea,  then  curve  backward  and  ventrally  in  the 
posterior  wall  of  the  tympanum  to  end  at  the  stylo-mastoid  foramen.  The  bend 
formed  by  the  nerve  is  called  the  knee  (Geniculum  n.  faciahs),  and  bears  at  its 
highest  point  the  round  geniculate  ganglion  (G.  geniculi). 

The  nerve  consists  of  two  parts,  motor  and  sensory.  The  motor  part  constitutes  the  bulk 
of  the  nerve.  Its  deep  origin  is  from  the  cells  of  the  facial  nucleus,  which  is  situated  in  the  meduUa 
above  the  facial  tubercle.  On  lea\'ing  the  nucleus  the  root-fibers  pass  dorso-medially,  incHne  for- 
ward close  to  the  median  plane,  and  then  bend  sharply  downward  to  the  point  of  emergence.  The 
highest  point  of  the  bend  is  subjacent  to  the  gray  matter  of  the  eminentia  teres  in  the  floor  of  the 
fourth  ventricle,  and  the  abducent  nucleus  lies  in  the  concavity  of  the  cm-ve.  The  small  sensory 
part  (N.  intermedins)  consists  of  axones  of  cells  of  the  geniculate  ganghon,  which  is  interposed  on 
the  facial  nerve  as  it  bends  downward  in  the  facial  canal.  The  fibers  of  this  part,  after  entering 
the  medulla,  pass  to  the  nucleus  of  termination  which  it  shares  with  the  ninth  and  tenth  nerves. 
The  peripheral  fibers  from  the  geniculate  ganglion  constitute  the  chorda  tympani. 

After  its  emergence  through  the  stylo-mastoid  foramen  (Fig.  646)  the  nerve 
passes  ventrally,  forward,  and  outward  on  the  guttural  pouch  under  cover  of  the 
51 


802  NERVOUS   SYSTEM   OF  THE   HORSE 

parotid  gland,  and  passes  between  the  origin  of  the  superficial  temporal  and 
internal  maxillary  arteries  medially  and  the  superficial  temporal  vein  laterally.  It 
then  crosses  the  posterior  border  of  the  ramus  of  the  mandi]3le  ventral  to  the  trans- 
verse facial  artery  and  about  an  inch  and  a  half  (ca.  3.5-4  cm.)  below  the  articu- 
lation of  the  jaw.  Emerging  from  beneath  the  parotid  gland  upon  the  masseter 
muscle,  it  receives  the  ventral  branch  of  the  superficial  temporal  nerve,  and  divides 
into  dorsal  and  ventral  buccal  branches.  The  follo^ving  collateral  branches  are 
given  off,  the  first  five  being  detached  \vdthin  the  facial  canal,  and  the  others 
between  the  stylo-mast  old  foramen  and  the  border  of  the  jaw. 

1.  The  great  superficial  petrosal  nerve  (N.  petrosus  superficialis  major)  arises 
from  the  gcmculate  ganglion.^  It  passes  through  the  petrosal  canal,  contributing 
a  filament  to  the  tympanic  plexus,  receives  the  deep  petrosal  nerve  from  the  carotid 
plexus  of  the  sjTiipathetic,  emerges  through  the  foramen  lacerum,  and  is  continued 
as  the  nerve  of  the  pterygoid  canal  to  the  sphenopalatine  plexus  and  ganglia  (Fig. 
647). 

2.  A  delicate  branch  (R.  anastomoticus  cum  plexu  tympanico)  emerges  from 
the  geniculate  ganglion  and  unites  with  a  filament  issuing  from  the  t\anpanic  plexus 
to  fonn  the  small  superficial  petrosal  nerve  (N.  petrosus  superficialis  minor) ;  this 
ends  in  the  otic  ganglion. 

3.  The  stapedial  nerve  (N.  stapedius)  (Fig.  647)  is  a  short  filament  detached 
from  the  facial  nerve  as  it  turns  down  in  the  facial  canal.  It  innervates  the  stape- 
dius muscle. 

4.  The  chorda  tympani  (Fig.  647)  is  a  small  nerve  which  arises  a  little  below  the 
preceding  and  pursues  a  recurrent  course  in  a  small  canal  in  the  mastoid  part  of 
the  temporal  bone  (Canaliculus  chordae  tjanpani),  to  reach  the  tympanic  cavity. 
It  traverses  the  latter,  passing  between  the  handle  of  the  malleus  and  the  long  branch 
of  the  incus.  Emerging  through  the  petrotympamc  fissure,  the  nerve  passes  down- 
ward and  forward  on  the  guttural  pouch,  crosses  beneath  the  internal  maxillary 
artery,  and  joins  the  lingual  nerve.  It  sends  twigs  to  the  mandibular  and  sublingual 
glands,  and  through  its  incorporation  with  the  lingual  nerve  furnishes  fibers  to  the 
mucous  membrane  of  the  anterior  two-thirds  of  the  tongue  which  are  believed  to 
mediate  the  sense  of  taste. 

5.  Anastomotic  filaments  unite  with  the  auricular  branch  of  the  vagus  near 
the  stylomastoid  foramen. 

6.  The  posterior  auricular  nerve  (N.  auricularis  aboralis)  arises  from  the 
facial  at  its  emergence  from  the  facial  canal  (Fig.  646).  It  runs  upward  and  back- 
ward with  the  posterior  auricular  artery  under  cover  of  the  parotid  gland,  and  sup- 
plies the  posterior  and  dorsal  auricular  muscles  and  the  skin  of  the  convex  surface 
of  the  external  ear.  It  anastomoses  with  branches  of  the  first  and  second  cervical 
nerves. 

7.  The  internal  auricular  nerve  (N.  auricularis  internus)  springs  from  the 
facial  close  to  or  in  common  with  the  preceding  (Fig.  646).  It  ascends  in  the 
parotid  gland  just  behind  the  styloid  process  of  the  conchal  cartilage,  passes 
through  an  opening  in  the  cartilage,  and  ramifies  in  the  skin  of  the  concave  surface 
of  the  ear. 

8.  The  digastric  branch  (R.  digastricus)  (Fig.  646)  arises  from  the  facial  below 
the  auricular  nerves  and  descends  under  cover  of  the  parotid  gland.  Its  branches 
innervate  the  posterior  belly  of  the  digastricus,  the  stylo-hyoideus,  and  the  occipito- 
hyoideus.  At  its  origin  it  gives  off  a  small  branch  which  forms  a  loop  around  the 
great  auricular  artery  or  its  posterior  branch  and  rejoins  the  trunk. 

9.  The  auriculo-palpebral  nerve  (N.  auriculopalpebralis)  (Fig.  646)  arises 
from  the  upper  edge  of  the  facial  near  the  posterior  border  of  the  ramus.     It  ascends 

1  Although  this  nerve  springs  directly  from  the  ganglion,  it  contains  motor  as  weU  as  sensory 
fibers. 


THE   ACOUSTIC    NERVE  803 

in  the  parotid  gland  behind  the  superficial  temporal  artery,  and  terminates  in 
anterior  auricular  and  temporal  branches.  The  small  anterior  auricular  branches 
form  with  the  frontal  and  lacrimal  branches  of  the  trigeminus  the  anterior  auricular 
plexus.  They  innervate  the  anterior  auricular  and  parotido-auricularis  muscles. 
The  temporal  branch  runs  forward  and  inward  over  the  temporal  muscle  to  the 
medial  canthus  of  the  eye,  forms  a  plexus  with  the  terminal  branches  of  the  ophthal- 
mic nerve,  and  is  distributed  to  the  orbicularis  oculi,  corrugator  supercilii,  and 
levator  nasolabialis. 

10.  The  cervical  branch  (R.  colli)  (Fig.  560)  is  small;  it  arises  from  the  ventral 
border  of  the  facial  opposite  to  the  preceding  nerve.  It  passes  obliquely  through  the 
parotid  gland,  emerging  under  cover  of  the  parotido-auricularis,  passes  downward 
and  backward  on  or  near  the  jugular  vein,  and  anastomoses  with  the  cutaneous 
branches  of  the  cervical  nerves.  It  gives  branches  to  the  parotido-auricularis  and 
the  cervical  cutaneous  muscle.  In  its  course  along  the  neck  the  nerve  is  reinforced 
by  twigs  from  the  cutaneous  branches  of  the  second  to  the  sixth  cervical  nerves. 

11.  Small  branches  are  detached  to  the  guttural  pouch  and  the  parotid  gland. 
The  latter  (Rami  parotide!)  concur  with  branches  of  the  superficial  temporal  nerve 
in  forming  the  parotid  plexus. 

The  facial  nerve  usually  terminates  after  a  short  course  on  the  surface  of  the 
masseter  by  dividing  into  two  buccal  branches  (Fig.  560). 

1.  The  dorsal  buccal  nerve  (N.  buccalis  dorsalis)  passes  forward  on  the  upper 
part  of  the  masseter,  dips  under  the  zygomaticus,  and  reaches  the  ventral  border  of 
the  dilatator  naris  lateralis.  It  continues  under  cover  of  the  last-named  muscle 
and  the  levator  nasolabialis  in  company  with  the  superior  labial  artery  and  ramifies 
in  the  muscles  of  the  upper  lip  and  nostril.  It  gives  collateral  branches  to  the 
buccinator  and  anastomoses  with  the  infraorbital  and  ventral  buccal  nerve. 

2.  The  ventral  buccal  nerve  (N.  buccalis  ventralis)  crosses  the  masseter 
obliquely  and  continues  forward  along  the  depressor  labii  inferioris.  It  is  connected 
by  variable  anastomotic  branches  with  the  dorsal  nerve.  It  gives  collateral 
branches  to  the  cutaneus,  buccinator,  and  depressor  labii  inferioris,  and  ramifies 
in  the  muscles  of  the  lower  lip. 

The  buccal  nerves  are  subject  to  much  variation  in  regard  to  their  course,  anastomoses, 
and  relations  to  the  sensory  components  derived  from  the  superficial  temporal  nerve.  Their 
distribution  is  constant.  The  point  at  which  the  branch  of  the  superficial  temporal  nerve  joins 
the  facial  is  variable. 


THE  ACOUSTIC  NERVE 
The  acoustic  nerve  (N.  acusticus)  is  connected  with  the  lateral  aspect  of  the 
medulla  just  behind  and  lateral  to  the  facial  (Fig.  629).     It  has  two  roots,  vestib- 
ular and  cochlear  (Radix  vestibularis,  cochlearis). 

The  acoustic  nerve  consists  of  two  distinct  parts  which  might  well  be  regarded  as  separate 
nerves.  The  cochlear  part  mediates  the  sense  of  hearing,  while  1  he  vestibular  part  is  not  auditory 
in  function,  but  is  concerned  in  the  sense  of  the  position  of  the  body  and  the  mechanism  of 
equiUbration. 

The  nerve  passes  outward  to  the  internal  acoustic  meatus,  which  it  enters 
behind  the  facial  nerve.  In  the  meatus  it  divides  into  two  nerves,  of  which  the 
upper  is  the  vestibular  and  the  lower  is  the  cochlear  nerve. 

1.  The  vestibular  nerve  (N.  vestibuli)  is  distributed  to  the  utriculus,  the  saccu- 
lus,  and  to  the  ampullae  of  the  semicircular  ducts  of  the  internal  ear.  In  the 
internal  acoustic  meatus  the  nerve  is  connected  by  filaments  with  the  geniculate 
ganglion  of  the  facial  nerve.  At  the  bottom  of  the  meatus  it  bears  the  vestibular 
ganglion  (G.  vestibulare),  from  the  cells  of  which  the  fibers  of  the  nerve  arise. 

2.  The  cochlear  nerve  (N.  cochleae)  detaches  a  filament  to  the  sacculus,  passes 


804  NERVOUS    SYSTEM    OF   THE    HORSE 

through  the  lamina  cribrosa  to  the  labyrinth,  and  is  distributed  to  the  organ  of 
Corti  in  the  cochlea. 

The  fibers  of  the  vestibular  nerve  arise  from  the  vestibular  ganglion  as  central  processes 
(axones)  of  the  bipolar  cells  of  the  ganglion.  The  peripheral  processes  (dendrites)  of  the  cells 
form  arborizations  about  the  deep  ends  of  the  hair-cells  of  the  macula)  and  cristse  acusticse  of  the 
utriculus,  sacculus,  and  semicircular  ducts.  The  fibers  enter  the  medulla,  pass  between  the 
restiform  body  and  the  spinal  tract  of  the  trigeminus,  and  spread  out  to  end  in  the  vestibular 
nucleus  in  the  floor  of  the  fourth  ventricle.  Among  the  central  connections  of  the  vestibular 
nerve  are:  (1)  fibers  which  connect  its  nucleus  with  centers  in  the  cerebellum  (chiefly  of  the  oppo- 
site side);  (2)  the  vestibulo-spinal  tract,  which  conveys  impulses  to  the  motor  cells  of  the  ventral 
colmnns  of  the  spinal  cord;  (3)  fibers  which  connect  the  nucleus  with  those  of  the  abducent  nerve 
of  the  same  side,  the  tliu'd  and  fom'th  nerves,  and  the  motor  part  of  the  trigeminus  of  both  sides. 

The  fibers  of  the  cochlear  nerve  are  the  central  processes  of  the  bipolar  cells  of  the  spiral 
ganghon  of  the  cochlea.  The  peripheral  processes  of  these  cells  end  in  relation  to  the  hair-cells 
of  the  organ  of  Corti.  Some  of  the  nerve-fibers  enter  the  ventral  cochlear  nucleus  in  the  medulla 
close  to  the  superficial  origin  of  the  nerve;  others  end  in  the  dorsal  nucleus  of  the  tuberculum 
acusticum  at  the  lateral  angle  of  the  floor  of  the  fourth  ventricle.  From  the  ventral  nucleus 
fibers  pass  in  the  corpus  trapezoideum  to  the  anterior  olivary  nucleus  of  the  same  and  of  the 
opposite  side.  Thence  tracts  pass  to  the  nuclei  of  the  motor  nerves  of  the  eye,  and  through  the 
lateral  fillet  to  the  posterior  quadrigeminal  body  and  the  medial  geniculate  body.  The  axones 
of  the  cells  of  the  dorsal  nucleus  pass  largely  (as  the  strise  acusticee)  over  the  restiform  body  and 
across  the  floor  of  the  fourth  ventricle  toward  the  median  plane.  They  then  turn  ventrally, 
cross  to  the  opposite  side,  and  are  continued  by  the  lateral  fillet.  From  the  mid-brain  a  tract 
proceeds  to  the  cortex  of  the  temporal  part  of  the  cerebral  hemisphere. 


THE  GLOSSO-PHARYNGEAL  NERVE 

The  glosso-phar5mgeal  nerve  (N.  glossopharyngeus)  is  attached  to  the  anterior 
part  of  the  lateral  aspect  of  the  medulla  by  several  filaments  (Fig.  629) .  The  root- 
bundles  enter  the  furrow  ventral  to  the  restiform  body;  they  are  separated  by  a 
short  interval  from  the  origin  of  the  facial  nerve,  but  are  not  marked  off  behind  from 
the  roots  of  the  vagus.  The  bundles  converge  laterally  to  form  a  nerve  which  per- 
forates the  dura  mater  and  emerges  through  the  foramen  lacerum  posterius  just 
in  front  of  the  tenth  nerve  (Fig.  647).  As  it  issues  from  the  cranium  the  nerve 
bears  a  considerable  ovoid  gray  enlargement,  the  petrous  ganglion  (G.  petrosum).^ 
It  then  curves  downward  and  forward  over  the  guttural  pouch  and  behind  the  great 
comu  of  the  hyoid  bone,  crosses  the  deep  face  of  the  external  carotid  artery,  and 
divides  into  pharyngeal  and  lingual  branches  (Fig.  562).  The  collateral  branches 
are  as  follows: 

1.  The  tympanic  nerve  (N.  tympanicus)  (Fig.  647)  arises  from  the  petrous 
ganglion  and  passes  upward  between  the  petrous  and  tympanic  parts  of  the  temporal 
bone  to  reach  the  cavity  of  the  tympanum.  Here  it  breaks  up  into  branches  to 
form,  along  with  branches  from  the  carotid  plexus  of  the  sympathetic,  the  t3rmpanic 
plexus.  From  the  plexus  branches  pass  to  the  mucous  membrane  of  the  tympanum 
and  the  Eustachian  tube.  The  continuation  of  the  nerve  issues  from  the  plexus 
and  unites  with  a  filament  from  the  geniculate  ganglion  of  the  facial  to  form  the 
small  superficial  petrosal  nerve;   this  runs  forward  and  ends  in  the  otic  ganglion. 

Filaments  also  connect  the  petrous  ganglion  with  the  jugular  ganglion  of  the  vagus  nerve 
and  with  the  anterior  cervical  ganglion  of  the  sympathetic. 

2.  A  considerable  branch  runs  backward  on  the  guttural  pouch,  contributes 
filaments  to  the  pharyngeal  plexus,  and  concurs  with  twigs  from  the  vagus  and  the 
sympathetic  in  forming  the  carotid  plexus  on  the  terminal  part  of  the  carotid 
artery  and  on  its  chief  branches.     In  this  plexus  is  the  small  ganglion  intercaroticum. 

3.  The  very  small  nerve  to  the  stylo-pharyngeus  muscle  (N.  stylopharyngeus) 
arises  from  the  dorsal  border  of  the  nerve. 

The  pharyngeal  branch  (R.  pharyngeus)  (Fig.  562)  is  the  smaller  of  the  two 
terminal  branches.     It  runs  forward  across  the  deep  face  of  the  great  cornu  of  the 

1  This  ganglion  appears  to  be  equivalent  to  the  jugular  or  superior  and  petrous  ganglia  of  man. 


THE    VAGUS    NERVE  805 

hyoid  bone  and  concurs  with  the  pharyngeal  branches  of  the  vagus  and  with  sym- 
pathetic filaments  in  forming  the  pharyngeal  plexus;  from  this  branches  pass  to 
the  muscles  and  mucous  membrane  of  the  pharynx. 

The  lingual  branch  (R.  lingualis)  is  the  continuation  of  the  trunk  (Fig.  562). 
It  runs  along  the  posterior  border  of  the  great  cornu  of  the  hyoid  bone  in  front  of 
the  external  maxillary  artery,  and  dips  under  the  hyo-glossus  muscle.  It  gives 
collateral  branches  to  the  soft  palate,  isthmus  faucium,  and  tonsil,  and  ends  in 
the  mucous  membrane  of  the  posterior  part  of  the  tongue,  where  it  supplies  gusta- 
tory fibers  to  the  vallate  papillae.  A  considerable  branch  unites  with  a  twig  from 
the  lingual  nerve. 

The  glosso-pharyngeal  is  a  mixed  nerve,  containing  both  motor  and  sensory  fibers.  The 
latter  constitute  the  bulk  of  the  nerve  and  include  those  which  mediate  tlie  special  sense  of  taste. 
They  are  processes  of  the  cells  of  the  petrous  ganglion.  The  central  processes  of  the  gangUon 
cells  enter  the  medulla,  pass  dorso-medially  through  the  formatio  reticularis,  and  end  in  the 
nucleus  of  termination  in  the  floor  of  the  fourth  ventricle.  The  motor  fibers  arise  from  dorsal  and 
ventral  efferent  nuclei  in  the  medulla.  The  glosso-pharyngeal  shares  these  nuclei  with  the  vagus 
and  has  practically  the  same  central  connections  as  that  nerve  {q.  v.). 


THE  VAGUS  NERVE 
The  vagus  (N.  vagus)  ^  is  the  longest  and  most  widely  distributed  of  the 
cranial  nerves;  it  is  also  remarkable  for  the  comiections  which  it  forms  with 
adjacent  nerves  and  with  the  sympathetic.  It  is  attached  to  the  lateral  aspect  of  the 
medulla  by  several  filaments  which  are  in  series  with  those  of  the  ninth  nerve  in 
front  and  the  eleventh  nerve  behind  (Fig.  629).  The  bundles  converge  to  form  a 
trunk  which  passes  outward,  pierces  the  dura  mater,  and  emerges  from  the  cranium 
through  the  foramen  lacerum  posterius  (Fig.  647) .  In  the  foramen  the  nerve  bears 
on  its  lateral  aspect  the  elongated  flattened  jugular  ganglion  (G.  jugulare). 

The  ganglion  communicates  with — (a)  the  tympanic  nerve,  (b)  The  petrous  ganglion  of  the 
glosso-pharyngeal  nerve,  (c)  the  spinal  accessory,  and  {d)  the  hj'iDoglossal.  It  also  gives  off  the 
auricular  branch  (R.  auricularis),  wliich  runs  forward  below  the  petrous  ganglion  and  passes  tlii'ough 
a  small  canal  in  the  petrous  temporal  bone  to  gain  the  facial  canal.  Here  it  gives  filaments  to  the 
facial  and  emerges  with  that  nerve  through  the  stylo-mastoid  foramen.  It  ascends  beliind  the 
external  acoustic  meatus,  dips  under  the  deep  auricular  muscles,  and  passes  through  a  foramen 
in  the  conchal  cartilage  to  ramify  in  the  integument  which  lines  the  meatus  and  the  adjacent 
part  of  the  ear.  It  may  be  noted  that  many  fibers  of  the  vagus  pass  over  the  medial  face  of  the 
gangUon  without  entering  it. 

A  ganglion  nodosum  in  the  form  of  a  compact  mass  is  not  present  in  the  horse.  It  appears 
to  be  represented  by  masses  of  ganglion  cells  in  the  nerve  trunk  which  begin  in  front  of  the  origin 
of  the  pharyngeal  branch  and  continue  a  considerable  distance  behind  the  origin  of  the  anterior 
laryngeal  nerve. 

Beyond  the  ganglion  the  vagus  runs  backward  and  downward  with  the  spinal 
accessory  in  a  fold  of  the  guttural  pouch  (Fig.  562).  Then  the  two  nerves  separate, 
allowing  the  hjqooglossal  to  pass  between  them,  and  the  vagus  descends  with  the 
internal  carotid  artery  and  crosses  the  medial  face  of  the  origin  of  the  occipital 
artery.  Here  it  is  joined  by  the  cervical  trunk  of  the  sympathetic,  and  the  two 
nerves  continue  along  the  dorsal  aspect  of  the  common  carotid  artery  in  a  common 
sheath  (Fig.  558).-  At  the  root  of  the  neck  the  vagus  separates  from  the  sym- 
pathetic, and  from  this  point  backward  the  relations  of  the  right  and  left  vagi  differ 
somewhat  and  must  be  described  separately. 

The  right  vagus  nerve  (Fig.  554)  enters  the  thorax  in  the  angle  of  divergence  of 
the  right  brachial  artery  and  the  truncus  bicaroticus.  It  then  passes  backward  and 
slightly  upward,  crossing  obliquely  the  lateral  surface  of  the  brachiocephalic  artery 
and  the  right  face  of  the  trachea.  Reaching  the  dorsal  surface  of  the  latter  near 
the  bifurcation,  it  divides  into  dorsal  and  ventral  branches. 

1  Also  commonly  termed  the  pneumogastric  nerve. 

2  There  is  formed  thus  a  vago-sympathetic  trunk. 


806 


NERVOUS    SYSTEM    OF   THE   HORSE 


The  left  vagus  nerve  (Fig.  553)  enters  the  thorax  on  the  lateral  or  the  ventral 
face  of  the  oesophagus,  crosses  obliquely  under  the  left  brachial  artery,  and  passes 
back  on  the  lateral  surface  of  that  vessel  in  company  with  a  large  cardiac  nerve.^ 
Separating  from  the  latter,  the  vagus  continues  backward  on  the  left  face  of  the 


Lig.  nuchce 
Splenius          n^    y 

Nuchal  fat 

Complexus  tendon 

Branch  oj  occipital  artery  ^>^^S*^ 
Complexus  "v^^^l^^l^ 

^m^ 

/Rectus  capitis 
.      y  dorsalis  minor 
J^V      Rectus  capitis 
^l^(;^ dorsalis  major 

Spinal 

accessory 

nerve 

{dorsal 

branch) 

Brack 
cephahcus 
Vagus 

Sympathetic 
Carotid  artery 


Spinal  accessory 
nerve  (dorsal 
branch) 
Rectus  capitis 
ventralis  major 

lar  vein 

TJiyro-laryngcal 
artery 

Anterior  cervical 
lymph  glands 


Sterno-cephalicus 
Omo-hyoideus  and  slerno-hyoideus 


Tliyroid  gland 


Sterno-ihyroideus 


Fig.  649. — Cross-section  of  Neck  of  Horse,  Passing  through  Posterior  Part  of  Atlas. 

The  head  and  neck  were  extended.     1,  Dorsal  arch  of  atlas;   2,  dens  of  axis;   S,   ligament  of  dens;   4.  vertebral 

sinuses;   5,  dura   mater;   6,  spinal  cord;    7,  vertebral   artery;    8,   wing  of  atlas;    '9,  atlanto-axial   joint   cavity;    10, 

oesophagus;  11,  II,  recurrent  nerves;   12,  12,  ventral  branches  of  spinal  accessory  nerves.     By  an  oversight  the  obliquua 

cap.  post,  (above  wing  of  atlas)  is  unmarked;   also  the  parotid  gland  between  the  jugular  and  external  maxillary  vein- 


aorta,  inclines  to  the  upper  surface  of  the  left  bronchus,  and  divides  into  dorsal  and 
ventral  branches. 

The  dorsal  and  ventral  ])ranches  unite  with  the  corresponding  branches  of  the 
opposite  nerve,  thus  forming  dorsal  and  ventral  oesophageal  trunks   (Truncus 

'  In  some  cases  the  left  vagus  pa.sses  back  below  the  junction  of  the  jugular  veins  and  the 
termination  of  the  left  bracliial  vein.  It  then  runs  backward  and  somewhat  dorsally  across  the 
left  face  of  the  anterior  vena  cava  to  reach  its  usual  position. 


THE   VAGUS   NERVE  807 

oesophageus  dorsalis,  ventralis).  These  run  backward  in  the  posterior  mediastinum, 
dorsal  and  ventral  to  the  oesophagus  respectively,  and  enter  the  abdominal  cavity- 
through  the  hiatus  oesophageus;  they  supply  branches  to  the  oesophagus  and 
anastomose  with  each  other.  The  dorsal  trunk  receives  the  major  part  of  its  fibers 
from  the  right  vagus.  After  entering  the  abdomen  it  passes  to  the  left  of  the 
cardia,  and  divides  into  gastric  and  cceliac  branches;  the  former  gives  branches  to 
the  visceral  surface  of  the  stomach,  forming  the  posterior  gastric  plexus;  the  latter 
ends  in  the  right  coeliaco-mesenteric  ganglion  and  the  anterior  interganglionic  cord. 
The  smaller  ventral  trunk  passes  to  the  lesser  curvature  of  the  stomach  and  ramifies 
on  the  parietal  surface  of  the  stomach;  it  forms  here  the  anterior  gastric  plexus 
from  which  branches  are  supplied  also  to  the  first  part  of  the  duodenum  and  to  the 
liver  and  pancreas.^ 

The  collateral  branches  of  the  vagus  are  as  follows: 

1.  The  pharyngeal  branch  (R.  pharjaigeus)  is  given  off  in  relation  to  the 
anterior  cervical  ganglion,  turns  around  the  internal  carotid  artery,  and  runs 
ventrally  and  forward  on  the  guttural  pouch  to  the  dorsal  wall  of  the  pharynx 
(Fig.  562).  Here  its  branches  concur  with  the  pharyngeal  branch  of  the  glosso- 
pharyngeal nerve  and  with  filaments  from  the  spinal  accessory  and  the  sympathetic 
in  forming  the  pharyngeal  plexus.  This  supplies  the  muscles  of  the  pharynx  and 
of  the  soft  palate  (except  the  tensor  palati),  delicate  filaments  to  the  anterior 
cervical  ganglion  of  the  sympathetic,  and  a  larger  branch  which  passes  along  the 
side  of  the  oesophagus  and  ramifies  in  its  cervical  part. 

According  to  Ellenberger  and  Baum,  the  pharyngeal  plexus  receives  filaments  also  from  the 
digastric,  anterior  laryngeal,  hypoglossal,  and  first  cervical  nerves.  The  branches  of  the  plexus 
form  secondary  intermuscular  and  submucous  plexuses,  in  which  there  are  numerous  minute 
ganglia. 

2.  The  anterior  (or  superior)  laryngeal  nerve  (N.  laryngeus  cranialis)  is  larger 
than  the  preceding  and  arises  a  little  behind  it  (Fig.  562).  It  crosses  the  deep  face 
of  the  origin  of  the  external  carotid  artery,  runs  downward  and  forward  over  the 
lateral  wall  of  the  pharynx  behind  the  hypoglossal  nerve,  and  passes  through  the 
foramen  below  the  anterior  cornu  of  the  thyroid  cartilage.  Its  terminal  branches 
ramify  in  the  mucous  membrane  of  the  larynx,  the  floor  of  the  pharynx,  and  the 
entrance  to  the  oesophagus;  they  anastomose  with  those  of  the  recurrent.  At 
its  origin  the  nerve  gives  off  its  small  external  branch  (R.  externus) ;  this  descends 
to  the  crico-thyroid  muscle,  which  it  supplies,  and  sends  filaments  to  the  crico- 
pharyngeus  also.  It  often  arises  from  the  vagus  just  below  the  anterior  laryngeal 
and  may  come  from  the  pharyngeal  branch. 

At  the  point  of  origin  of  the  anterior  laryngeal  nerve  there  is  a  plexiform  widening  which  is 
regarded  by  some  authors  as  the  homologue  of  the  ganglion  nodosum  of  man;  it  often  contains 
minute  ganglia.  From  it  a  filament  arises  wliich,  after  a  short  course,  rejoins  the  vagus  or  enters 
the  sympathetic  trunk.  Stimulation  of  its  central  end  causes  a  reduction  of  the  blood-pressure, 
and  it  is  therefore  termed  the  depressor  nerve  (N.  depressor).  On  reaching  the  heart  it  passes 
between  the  aorta  and  the  pulmonary  artery  and  is  distributed  to  the  myocardium. 

3.  The  recurrent  nerve  (N.  recurrens),  also  termed  the  inferior  or  posterior 
laryngeal  nerve,  differs  on  the  two  sides  in  its  point  of  origin  and  in  the  first  part  of 
its  course.  The  right  nerve  (Fig.  554)  is  given  off  opposite  the  second  ril),  turns 
around  the  dorso-cervical  artery  from  without  inward,  runs  forward  on  the  ventral 
part  of  the  lateral  surface  of  the  trachea,  and  ascends  in  the  neck  on  the  ventral 
face  of  the  common  carotid  artery.  The  left  nerve  (Fig.  553)  arises  from  the  vagus 
where  the  latter  begins  to  cross  the  aortic  arch.  It  passes  back  over  the  ligamentum 
arteriosum,  winds  around  the  concavity  of  the  aortic  arch  from  without  inward, 

1  It  will  be  noted  that  the  formation  of  the  ventral  oesophageal  trunk  usually  occurs  at  the 
root  of  the  lungs,  while  the  union  of  the  dorsal  branches  of  the  two  vagi  generally  occurs  nearer  the 
hiatus  oesophageus. 


808  NERVOUS    SYSTEM   OF   THE   HORSE 

runs  forward  on  the  ventral  part  of  the  left  face  of  the  trachea,  and  continues  in  the 
neck  in  a  position  similar  to  the  right  nerve. 

It  is  worthy  of  note  that  the  left  nerve  passes  beneath  the  bronchial  lymph  glands  as  it 
winds  around  the  aorta;  also  that  in  the  next  part  of  its  course  it  hes  between  the  left  surface  of 
the  trachea  and  the  deep  face  of  the  aorta,  and  is  then  related  to  lymph  glands  which  Ue  along 
the  ventral  tuspect  of  the  trachea.  The  left  reciu-rent  is  often  incorporated  in  part  of  its  coiu-se 
in  the  anterior  mediastinum  with  a  deep  cardiac  nerve.  Further,  the  left  nerve  hes  at  first  ven- 
tral to,  and  then  upon,  the  oesophagus  in  the  neck.  The  right  reciu-rent  is  given  off  from,  or  in 
common  with,  a  considerable  trunk  which  connects  the  vagus  with  the  first  thoracic  ganghon 
of  the  sjTnpathetic.  The  arrangement  here  is  commonly  more  or  less  plexiform,  and  from  it 
one  or  two  cardiac  nerves  arise. 

The  terminal  part  of  each  nerve  (Fig.  649)  lies  on  the  dorsal  surface  of  the 
trachea,  in  relation  to  the  oesophagus  medially  and  the  carotid  artery  dorsally.^  It 
passes  between  the  crico-arytenoideus  dorsalis  and  the  crico-pharjoigeus,  and 
enters  the  lar>Tix  at  the  medial  side  of  the  lamina  of  the  thyroid  cartilage.  Before 
entering  it  gives  branches  to  the  crico-arytenoideus  dorsalis  and  arytenoideus 
transversus,  and  aftenvard  supplies  the  internal  muscles  of  the  larynx.  It  also 
communicates  by  delicate  filaments  with  branches  of  the  anterior  laryngeal  nerve.^ 
Collateral  branches  are  given  off  to  the  cardiac  plexus  (Rami  cardiaci),  to  the 
trachea  (Rr.  tracheales),  to  the  oesophagus  (Rr.  cesophagei),  and  to  the  posterior 
cervical  ganglion  of  the  sjanpathetic. 

4.  Cardiac  branches  (Rr.  cardiaci),  usually  two  or  three  in  number,  are  given 
off  from  each  vagus  within  the  thorax  (Figs.  553,  554).  These  concur  with  the 
cardiac  branches  of  the  sympathetic  and  recurrent  nerves  to  form  the  'cardiac 
plexus,  which  innervates  the  heart  and  great  vessels. 

5.  Small  tracheal  and  oesophageal  branches  (Rr.  tracheales  et  cesophagei) 
are  given  off  from  both  vagi  in  the  thorax.  These  concur  with  branches  from  the 
recurrent  nerves  and  the  posterior  cervical  and  anterior  thoracic  ganglia  of  the 
sympathetic  in  forming  the  posterior  tracheal  and  oesophageal  plexuses,  from 
which  Uvigs  go  to  the  trachea,  oesophagus,  heart,  and  large  vessels. 

6.  Bronchial  branches  (Rr.  bronchiales)  are  detached  at  the  roots  of  the  lungs 
and  unite  ^vith  sympathetic  filaments  in  forming  the  pulmonary  plexuses.  From 
the  latter  numerous  branches  proceed  in  a  plexiform  manner  along  the  bronchi 
and  vessels  into  the  substance  of  the  lungs. 

The  vagus  and  glosso-pharyngeal  nerves  are  so  closely  associated  in  origin  and  central 
connections  that  they  may  be  described  together  in  this  respect. 

The  sensory  fibers  arise  from  the  petrous  and  jugular  ganglia,  and  their  central  parts  enter 
the  lateral  aspect  of  the  medulla  and  divide  into  anterior  and  posterior  branches  hke  the  fibers  of 
the  dorsal  roots  of  the  spinal  nerves.  Most  of  the  fibers  end  in  arborizations  about  the  cells  of  the 
vago-glosso-pharyngeal  nucleus  of  termination,  which  consists  of  two  parts.  Of  these,  the  dorsal 
sensory  nucleus  (Nucleus  alse  cinerese)  is  situated  in  the  posterior  part  of  the  floor  of  the  fourth 
ventricle  and  in  the  adjacent  part  of  the  closed  portion  of  the  medulla  near  the  median  plane. 
The  other  part  is  termed  the  nucleus  of  the  solitary  tract,  and  is  so  named  because  its  cells  are 
grouped  about  the  bundle  (Tractus  solitarius)  formed  by  the  posterior  di\'isions  of  the  afferent 
nerve-fibers.  It  ends  about  the  level  of  tlie  pyramidal  decussation.  The  secondary  central  con- 
nections are  similar  to  those  of  the  .sensory  part  of  the  trigeminus. 

The  motor  fibers  (and  those  of  the  medullary  part  of  the  accessory)  arise  from  the  dorsal 
motor  nucleus  and  the  ventral  motor  nucleus.  The  cells  of  the  former  lie  in  gi-oups  along  the 
ventro-medial  side  of  the  dorsal  sensory  nucleus.  The  latter,  also  termed  the  nucleus  ambiguus, 
is  situated  more  deeply  in  the  lateral  part  of  the  formatio  reticulai'is. 


THE  SPINAL  ACCESSORY  NERVE 

The  spinal  accessory  nerve  (N.  accessorius)  is  purely  motor.  It  consists  of 
two  parts  which  differ  in  origin  and  function. 

^The  nerve  lies  here  about  a  finger's  breadth  above  the  thyroid  gland.  If,  however,  the 
gland  is  enlarged  it  may  come  in  contact  with  the  nerve.  The  same  is  true  in  regard  to  the  rela- 
tion to  the  anterior  cervical  lymph  glands. 

■  The  recurrent  nerves  innervate  all  the  intrinsic  muscles  of  the  larynx  except  the  crico- 
thyroid. 


THE   SPINAL  ACCESSORY   NERVE 


809 


The  meduUary  part  arises  from  the  lateral  aspect  of  the  medulla  by  several 
rootlets  which  are  behind  and  in  series  with  those  of  the  vagus  (Fig.  629).  The 
spinal  part  arises  from  the  cervical  part  of  the  spinal  cord  by  a  series  of  fasciculi 
which  emerge  between  the  dorsal  and  ventral  roots.  The  bundles  unite  to  form 
a  trunk  which  is  very  small  at  its  origin  at  the  fifth  segment  of  the  cord,  but 
mcreases  in  size  when  traced  toward  the  brain,  since  it  continually  receives  accessions 
of  fibers.     It  passes  through  the  foramen  magnum  and  joins  the  medullary  part. 


Fig.  650. — Neck  of  Horse,  After  Removal  of  Part  of  Cutaneus  and  Trapezius. 
a,  a',  Brachiocephalicus;  b,  anterior  superficial  pectoral  muscle;  c,  cervical  cutaneus;  d,  sterno-cephalicus;  e, 
omo-hyoideus ;  /,  sterno-thyro-hyoideus;  g,  trachea;  h,  h',  h",  tendons  of  splenius,  brachiocephalicus,  and  longissimus 
atlantis;  i,  trapezius  cervicalis;  k,  supraspinatus;  I,  anterior  deep  pectoral  muscle;  m,  rhomboideus  cervicalis 
n,  serratus  cer\'icis;  o,  splenius,  upper  and  lower  borders  of  which  are  indicated  by  dotted  lines;  p,  parotid  gland 
q,  parotido-auricularis  muscle;  r,  wing  of  atlas;  s,  spine  of  scapula;  /,  external  maxillarj'  vein;  2,  S,  jugular  vein 
4,  carotid  artery ;  5,  descending  branch  of  inferior  cervical  artery ;  6,  cephalic  vein ;  7-1 1 ,  ventral  branches  of  second  to 
seventh  cervical  nerves;  13,  cutaneous  branch  of  second  cervical  nerve;  13,  cervical  branch  of  facial  nerve;  14,  terminal 
branches  of  dorsal  divisions  of  cervical  nerves;  15,  dorsal  branch  of  spinal  accessory  nerve.  (After  Ellenberger-Baum, 
Top.  Anat.  d.  Pferdes.) 


The  trunk  thus  formed  sends  its  medullary  fibers  to  the  vagus  and  glosso-pharyngeal 
nerves  and  emerges  through  the  foramen  lacerum  posterius.  It  then  runs  backward 
and  downward  ^vith  the  vagus  in  a  fold  of  the  guttural  pouch,  separates  from  that 
nerve,  crosses  the  deep  face  of  the  mandibular  gland  and  the  occipital  artery,  and 
divides  in  the  recessus  atlantis  into  dorsal  and  ventral  branches. 

It  is  connected  by  anastomotic  branches  with  the  vagus  and  hypoglossal  nerves  and  the 
anterior  cervical  gangUon  of  the  sympathetic,  and  contributes  a  branch  to  the  pharyngeal  plexus. 


glO  NERVOUS   SYSTEM    OF   THE   HORSE 

The  dorsal  branch  (R.  dorsalis)  (Figs.  558,  649,  650)  receives  a  twig  from  the 
second  and  third  cervical  nerves  and  turns  around  the  atlantal  tendon  of  the  splenius 
under  cover  of  the  brachiocephahcus.  It  then  passes  obhquely  through  the  latter 
muscle  and  continues  backward  on  the  cervical  part  of  the  serratus,  inclines  upward 
across  the  anterior  deep  pectoral  and  the  supraspinatus,  and  enters  the  deep  face 
of  the  trapezius,  in  which  it  ramifies. 

The  ventral  branch  (R.  ventralis)  (Fig.  561)  is  smaller  and  much  shorter.  It 
passes  do"s\Tiward  and  backward  under  cover  of  the  cervical  angle  of  the  parotid 
gland  and  enters  the  deep  face  of  the  sterno-cephalicus  muscle  at  the  junction  of  the 
muscular  substance  -v^dth  the  tendon  of  insertion.  It  usually  crosses  over  the 
carotid  artery  just  behind  the  lateral  lobe  of  the  thyroid  gland. 

The  fibers  of  the  spinal  part  of  the  accessory  arise  from  the  ventro-lateral  cells  of  the  ventral 
gray  column  of  the  cord  as  far  back  as  the  fifth  cervical  segment.  The  fibers  of  the  medullary 
part  come  chiefly  from  the  nucleus  ambiguus  in  common  with  the  motor  fibers  of  the  vagus. 

THE  HYPOGLOSSAL  NERVE 

The  h5rpoglossal  nerve  (N.  hypoglossus)  is  purely  motor;  it  innervates  the 
muscles  of  the  tongue  and  the  genio-hyoideus  (Fig.  562) .  Its  root-fibers  arise  from 
the  ventral  face  of  the  medulla  in  linear  series  about  3  to  4  mm.  lateral  to  the  poste- 
rior half  of  the  pyramid  (Fig.  629) .  The  filaments  converge  to  three  or  four  bundles 
which  perforate  the  dura  mater  and  unite  to  form  the  trunk.  The  latter  emerges 
through  the  hypoglossal  foramen  (Fig.  647)  and  runs  downward  and  backward 
between  the  guttural  pouch  and  the  capsule  of  the  atlanto-occipital  articulation 
for  a  distance  of  a  little  less  than  an  inch  (ca.  2  cm.).  It  then  passes  between  the 
vagus  and  accessory  nerves,  turns  downward  and  forward,  crosses  the  lateral  face 
of  the  external  carotid  artery,  and  continues  over  the  pharynx  parallel  with  the 
great  cornu  of  the  hyoid  bone  and  behind  the  external  maxillary  artery.  It  then 
crosses  beneath  the  artery,  runs  forward  on  the  lateral  face  of  the  hyo-glossus  muscle, 
and  divides  into  its  terminal  branches  (Rami  linguales).  The  smaller  branch 
supplies  the  stylo-glossus,  hyo-glossus,  and  lingualis.  The  larger  branch  passes 
upward  and  forward  between  the  hyo-glossus  and  genio-glossus,  ramifies  on  the  latter, 
and  supplies  the  remaining  muscles  and  the  genio-hyoideus.  Anastomoses  occur 
with  branches  of  the  lingual  nerve. 

In  the  first  part  of  its  course  the  nerve  communicates  with  the  anterior  cervical 
ganglion  and  ^\^th  the  ventral  branch  of  the  first  cervical  nerve,  and  gives  filaments 
to  the  pharjaigeal  branch  of  the  vagus  and  the  pharyngeal  plexus. 

The  fibers  of  the  nerve  arise  from  the  hypoglossal  nucleus,  an  elongated  gi'oup  of  large  multi- 
polar cells  situated  chiefly  under  the  posterior  part  of  the  floor  of  the  fourth  ventricle,  close  to  the 
median  plane.  The  two  nuclei  are  connected  by  commissural  fibers.  The  other  central  connec- 
tions include:  (a)  communications  by  the  medial  longitudinal  fasciculus  with  the  nuclei  of  ter- 
mination of  other  cranial  nerves;  (p)  cortico-nuclear  fibers  which  come  from  the  cortex  by  way  of 
the  internal  capsule  and  the  pyramids  and  go  largely  to  the  nucleus  of  the  opposite  side;  (c)  fibers 
which  join  the  dorsal  longitudinal  bundle  of  Schiitz,  a  tract  which  underlies  the  floor  of  the  fourth 
ventricle  and  is  traceable  forward  below  the  cerebral  aqueduct. 


THE  SPINAL  NERVES 

The  spinal  nerves  (Nervi  spinales)  are  arranged  in  pairs,  of  which  there  are 
usually  forty-two  in  the  horse.  They  are  designated  according  to  their  relations  to 
the  vertebral  column  as  cervical  (8),  thoracic  (18),  lumbar  (6),  sacral  (5),  and 
coccygeal  (5).  Each  nerve  is  connected  with  the  spinal  cord  by  two  roots,  dorsal 
and  ventral  (Fig.  628). 

The  dorsal  root  (Radix  dorsalis)  is  the  larger  of  the  two.  Its  fibers  (Fila 
radicularia)  spread  out  in  fan  shape  and  join  the  cord  in  a  linear  series  along  the 
dorso-lateral  groove.     The  fibers  converge  laterally  to  form  a  compact  bundle,  on 


THE    SPINAL   NERVES 


811 


which  there  is  a  gray  nodular  enlargement,  the  spinal  ganglion  (Ganglion  spinale). 
Beyond  the  ganglion  the  dorsal  root  joins  the  ventral  root  to  constitute  the  nerve. 
The  ganglia  are  external  to  the  dura  mater,  and  are  situated  in  the  interverteljral 
foramina,  except  in  the  case  of  the  sacral  and  coccygeal  nerves,  the  ganglia  of  which 
lie  within  the  vertebral  canal.     Those  of  the  coccygeal  nerves  are  intradural. 

The  ganglia  vary  greatly  in  size;  that  of  the  first  cervical  nerve  is  scarcely  as  large  as  a  hemp- 
seed,  while  that  of  the  eighth  cervical  is  about  2  cm.  long  and  1  cm.  wide.  On  the  large  roots 
connected  with  the  cervical  and  lumbar  enlargement  of  the  cord  there  are  multiple  ganglia  of 
varying  sizes  mterposed  in  the  com-se  of  the  root-bundles.  The  fibers  of  the  dorsal  roots  arise 
from  the  cells  of  the  spinal  gangUa;  connected  with  each  ganglion  cell  there  is  a  process  which 
bifurcates,  giving  rise  to  a  fiber  wlaich  enters  the  spinal  cord  and  another  which  passes  into  the  nerve. 


The  ventral  root  (Radix  ventralis)  contains  fewer  fibers  than  the  dorsal  root, 
except  in  the  case  of  the  first  cervical  nerve.  It  arises  from  the  ventral  surface  of 
the  spinal  cord  (Fig.  626)  by  means  of  numerous  small  bundles  of  fibers  which  do 
not  form  a  linear  series,  but  emerge  from  the  cord  over  an  area  three  to  five 
millimeters  in  width  (ventral  root  zone).  The  fibers  are  processes  of  the 
large  cells  of  the  ventral  gray 

columns    of     the     spinal    cord.  Spinal  branch  of  intercostal  artery 

There    is   no  ganglion   on   the 
ventral  root. 


Spinal  ganglion 
Dura  mater 
Lig.  denticnlatum 


Dorsal  root  bundles 


Dorsal  longitudinal  ligament 


Conjugal  ligament 


Fig.  651. 


-Vertebral  Canal  Opened  by  Sawing  off  the  Arches. 

(After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


In  the  cervical,  thoracic,  and 
anterior  lumbar  regions  the  bundle^ 
of  both  roots  pass  through  separite 
openings  in  hnear  series  in  the  dura 
mater  before  uniting  into  a  root 
proper.  Further  back  the  bundkb 
of  each  root  unite  within  the  dui  i 
In  the  anterior  part  of  the  cervi(  d 
region  and  in  the  thoracic  part  of  t  he 
cord  there  are  intervals  of  varying 
length  between  adjacent  roots,  but  in 
some  places  the  fibers  of  adjac(Mit 
roots  overlap  and  an  exchange  ot 
fibers  may  be  observed.  Many  of  t  h( 
roots  are  directed  almost  straight  out- 
ward or  incUne  slightly  backward,  but 
the  posterior  lumbar,  sacral,  and  coc- 
cygeal roots  and  nerves  run  backward 
to  reach  the  foramina,  tlirough  which 
they  emerge.  The  distance  thus  to 
be  traversed  increases  from  before 
backward,  so  that  these  nerves  form 
a   tapering   sheaf   around   the   conus 

meduUaris  and  filum  terminale  in  the  last  lumbar  vertebra  and  the  sacrum,  wliich  is  known  as  the 
Cauda  equina. 

The  size  of  the  spinal  nerves  varies  greatly.  The  largest  are  connected  with 
the  cervical  and  lumbar  enlargements. 

In,  or  immediately  after  its  emergence  from,  the  intervertebral  foramen  each 
spinal  nerve  gives  off  a  small  meningeal  branch  (Ramus  meningeus).  This  is 
joined  by  a  bundle  of  fibers  from  the  ramus  communicans  and  enters  the  vertebral 
canal,  in  which  it  is  distributed.  Each  nerve  then  divides  into  two  primary- 
branches,  dorsal  and  ventral  (Ramus  dorsalis,  ventralis).  The  dorsal  branches 
are  smaller  than  the  ventral,  except  in  the  cervical  region.  They  are  distributed 
chiefly  to  the  muscles  and  skin  of  the  dorsal  part  of  the  body.  The  ventral  branches 
supply  in  general  the  muscles  and  skin  of  the  ventral  parts  of  the  body,  including 
the  limbs.  Each  nerve  or  its  ventral  branch  is  connected  ^vith  an  adjacent  ganglion 
of  the  sympathetic  system  by  at  least  one  small  short  branch  known  as  a  ramus 
communicans.  Many  nerves  have  two  and  some  have  three  such  rami.  A  nerve 
may  be  connected  with  two  ganglia,  and  a  ganglion  may  be  connected  with  two 


812  NERVOUS   SYSTEM   OF   THE   HORSE 

The  dorsal  root  is  sensory  or  afferent,  i.  e.,  it  conveys  impulses  to  the  central  system.  Its 
fibers  are  axones  of  the  cells  of  the  spinal  gangUon.  The  ventral  root  is  motor  or  efferent,  and 
conveys  impulses  toward  the  periphery.  Its  fibers  are  axones  of  the  large  cells  in  the  ventral 
gray  columns  of  the  spinal  cord.  The  common  trunk  or  nerve  formed  by  the  union  of  the  two 
roots  contains  both  kinds  of  fibers,  as  do  also  their  primary  divisions.  In  addition  to  these  fibers, 
which  are  distributed  to  the  skeletal  muscles  and  the  skin,  the  spinal  nerves  contain  fibers  derived 
from  the  sjTnpathetic  system  through  the  rami  communicantes;  these  go  to  the  glands  and 
imstriped  muscle  and  are  designated  secretory  and  vasomotor  fibers. 


THE  CERVICAL  NERVES 

The  cervical  nerves  (Nervi  cervicales)  (Figs.  556,  558,  650,  655)  number  eight 
pairs.  The  first  of  these  emerges  through  the  intervertebral  foramen  of  the  atlas, 
the  second  through  that  of  the  axis,  and  the  eighth  between  the  last  cervical  and 
the  first  thoracic  vertebrae. 

The  dorsal  branches  are  distributed  to  the  dorso-lateral  muscles  and  skin  of 
the  neck.  They  divide  usually  into  lateral  and  medial  branches.  The  medial 
branches  (Rami  mediales)  run  in  general  across  the  multifidus  and  the  lamellar  part 
of  the  ligamentum  nuchas  to  the  skin  of  the  dorsal  border  of  the  neck;  they  supply 
the  deep  lateral  muscles  and  the  skin.  The  lateral  branches  (Rami  laterales)  are 
chiefly  muscular  in  their  distribution.  The  dorsal  branches  of  the  third  to  the 
sixth  nerves  are  connected  by  anastomotic  branches  to  form  the  dorsal  cervical 
plexus. 

The  ventral  branches  are  smaller  than  the  dorsal  ones — an  exception  to  the 
general  rule.  They  increase  in  size  from  first  to  last.  They  supply  in  general  the 
muscles  and  skin  over  the  lateral  and  ventral  aspect  of  the  vertebrae,  but  the  last 
three  enter  into  the  formation  of  the  brachial  plexus,  and  the  two  or  three  preceding 
the  last  give  ofT  the  roots  of  the  phrenic  nerve.  An  irregular  ventral  cervical  plexus 
is  formed  by  anastomoses  established  between  the  ventral  branches.  The  follo\\dng 
special  features  may  be  noted: 

The  first  cervical  nerve  emerges  through  the  intervertebral  foramen  of  the 
atlas.  Its  dorsal  branch  (N.  occipitalis)  passes  dorso-laterally  between  the  obliqui 
capitis  and  the  recti  capitis  dorsales  and  supplies  branches  to  these  muscles,  the 
scutularis  and  posterior  auricular  muscles,  and  the  skin  of  the  poll.  The  ventral 
branch  descends  through  the  alar  foramen  of  the  atlas,  crosses  over  the  ventral 
straight  muscles  and  the  carotid  artery  under  cover  of  the  parotid  gland,  and  divides 
into  two  branches.  The  anterior  branch  enters  the  omo-hyoideus  muscle.  The 
posterior  branch  passes  downward  and  backward  under  cover  of  that  muscle,  unites 
with  a  branch  of  the  ventral  division  of  the  second  cervical  nerve,  and  continues  its 
course  on  the  ventro-lateral  surface  of  the  trachea  to  enter  the  sterno-thyro-hyoideus 
behind  the  intermediate  tendon.  In  the  recessus  atlantis  the  ventral  branch  is 
connected  by  one  or  more  twigs  with  the  anterior  cervical  ganglion  of  the  sjtti- 
pathetic,  and  a  little  lower  with  the  hypoglossal  nerve.  It  also  sends  branches  to 
the  ventral  straight  muscles  of  the  head  and  the  thyro-hyoideus.  Below  the  atlas 
the  ventral  branch  is  crossed  superficially  by  the  spinal  accessory  nerve,  the  occi- 
pital artery,  and  the  ventral  cerebral  vein. 

The  second  cervical  nerve  is  larger  than  the  first.  It  emerges  from  the  verte- 
bral canal  through  the  intervertebral  foramen  of  the  anterior  part  of  the  arch  of  the 
axis.  Its  dorsal  branch  ascends  between  the  complexus  and  the  ligamentum 
nuchae  and  ramifies  in  the  skin  of  the  poll.  The  ventral  branch  gives  off  muscular 
branches  to  the  rectus  capitis  ventralis  major,  and  anastomotic  branches  to  the 
spinal  accessory  and  the  ventral  divisions  of  the  first  and  third  cervical  nerves; 
one  of  these  crosses  over  the  carotid  artery  and  concurs  in  the  formation  of  the  nerve 
to  the  sterno-thyro-hyoideus  mentioned  above.  The  ventral  branch  then  becomes 
superficial  by  passing  between  the  two  parts  of  the  brachiocephalicus,  and  divides 
into  posterior  auricular  and  cutaneous  branches.     The  posterior  auricular  nerve 


PHRENIC    NERVE  813 

passes  upward  and  forward  on  the  parotid  gland  parallel  with  the  posterior  border 
of  the  parotido-auricularis  to  ramify  on  the  convex  face  of  the  external  ear.  The 
cutaneous  nerve  of  the  neck  (N.  cutaneus  colli)  crosses  the  brachiocephalicus  muscle 
and  turns  backward  along  the  course  of  the  jugular  vein.  On  the  lower  part  of 
the  parotid  gland  it  is  connected  by  a  twig  with  the  cervical  cutaneous  branch  of 
the  facial  nerve.  It  gives  off  twigs  to  the  subcutaneous  muscles  and  the  skin  of 
the  parotid  and  laryngeal  regions,  and  a  long  branch  which  passes  forward  in  the 
mandibular  space. 

The  third  cervical  nerve  leaves  the  vertebral  canal  through  the  foramen  be- 
tween the  second  and  third  cervical  vertebrae.  Its  dorsal  branch  emerges  between 
two  bundles  of  the  intertransversalis  muscle,  accompanied  by  a  branch  of  the  verte- 
bral artery,  turns  dorsally  on  the  multifidus,  and  divides  into  several  branches  which 
radiate  on  the  deep  face  of  the  complexus.  It  gives  branches  to  these  muscles  and 
to  the  skin,  and  a  twig  which  joins  the  corresponding  branch  of  the  fourth  nerve. 
The  ventral  branch  emerges  through  the  intertransversalis  below  the  bundle  above 
which  the  dorsal  branch  appears.  It  gives  branches  to  the  longissimus  capitis  et 
atlantis,  rectus  capitis  ventralis  major,  longus  colli,  splenius,  and  brachiocephalicus. 
It  also  gives  off  a  large  cutaneous  nerve  which  passes  out  between  the  two  parts  of 
the  brachiocephalicus  and  divides  into  several  divergent  branches. 

The  fourth  and  fifth  cervical  nerves  are  distributed  in  general  like  the  third. 
Their  dorsal  branches  are  united  by  anastomotic  twigs  with  each  other  and  with 
those  of  the  third  and  sixth  nerves  to  form  the  dorsal  cervical  plexus.  The  ventral 
branch  of  the  fifth  nerve  often  contributes  a  small  twig  to  the  phrenic  nerve. 

The  sixth  cervical  nerve  has  a  smaller  dorsal  branch  than  the  fifth.  Its 
ventral  branch  is  larger  and  goes  in  part  to  the  brachial  plexus;  it  supplies  twigs 
to  the  intertransversales,  the  longus  colli,  the  brachiocephalicus,  and  the  cervical 
parts  of  the  serratus  and  rhomboideus,  furnishes  a  root  of  the  phrenic  nerve,  and 
gives  off  several  considerable  subcutaneous  branches.  One  of  the  latter  ramifies 
on  the  thick  part  of  the  cervical  cutaneus,  to  which  it  gives  branches;  another  and 
larger  branch  (N.  supraclavicularis)  sends  twigs  to  the  skin  over  the  shoulder  joint, 
and  descends  to  the  skin  over  the  superficial  pectoral  muscles  (Fig.  590). 

The  seventh  and  eighth  cervical  nerves  have  small  dorsal  branches,  which 
ascend  between  the  longissimus  and  multifidus,  giving  twigs  to  these  muscles,  the 
spinalis  and  semispinalis,  the  rhomboideus,  and  the  skin.  Their  ventral  branches 
are  very  large  and  go  almost  entirely  to  the  brachial  plexus;  that  of  the  seventh 
nerve  contributes  the  posterior  root  of  the  phrenic  nerve. 

Phrenic  Nerve 
The  phrenic  nerve  (N.  phrenicus)  (Figs.  553,  554,  558),  the  motor  nerve  to  the 
diaphragm,  is  formed  by  the  union  of  two  or  three  roots  which  run  obliquely  down- 
ward and  backward  over  the  superficial  face  of  the  scalenus  muscle.  The  chief 
roots  come  from  the  ventral  branches  of  the  sixth  and  seventh  cervical  nerves.  The 
root  derived  from  the  fifth  nerve  is  small  and  inconstant.  The  root  from  the 
seventh  cervical  comes  by  way  of  the  brachial  plexus.  The  nerve  crosses  the  ventral 
border  of  the  scalenus  a  fingerbreadth  in  front  of  the  first  rib,  passes  through  the 
angle  of  divergence  of  the  inferior  cervical  and  brachial  arteries,  and  enters  the 
thorax  by  passing  between  the  latter  vessel  and  the  anterior  vena  cava.  Beyond 
this  the  course  of  the  nerve  is  not  the  same  on  both  sides.  The  right  nerve  courses 
backward  and  somewhat  downward  over  the  right  face  of  the  anterior  vena  cava, 
crosses  the  pericardium,  and  continues  along  the  posterior  vena  cava  to  the  dia- 
phragm. In  the  latter  part  of  its  course  it  is  enclosed  in  a  special  fold  of  the  right 
pleura  and  inclines  gradually  to  the  ventral  face  of  the  vein.  The  left  nerve,  in 
part  with  the  vagus,  runs  its  entire  course  in  the  mediastinum.  In  the  anterior 
mediastinum  it  lies  along  the  lateral  face  of  the  brachiocephalic  artery  ventral  to 


324  NERVOUS   SYSTEM    OF   THE    HORSE 

the  left  vagus  and  a  cardiac  nCrve,  and  crosses  over  the  dorso-cervical  vein.  It 
then  parts  company  with  the  vagus,  passes  over  the  upper  part  of  the  pericardium, 
and  runs  backward  in  the  posterior  mediastinum  to  reach  the  tendinous  center  of 
the  diaphragm  considerably  to  the  left  of  the  median  plane.  Each  nerve  is  usually 
connected  near  its  origin  with  the  first  thoracic  ganglion  of  the  sympathetic  by  a 
ramus  communicans,  and  each  terminates  by  dividing  into  several  branches  which 
are  distributed  to  the  corresponding  part  of  the  diaphragm. 

The  Brachial  Plexus 
The  brachial  plexus  (Plexus  brachialis)  (Fig.  558)  results  from  anastomoses 
established  between  the  ventral  branches  of  the  last  three  cervical  and  first  two 
thoracic  nerves.  It  appears  as  a  thick,  wide  band  between  the  two  parts  of  the 
scalenus  muscle,  and  is  covered  by  the  anterior  deep  pectoral  and  subscapularis 
muscles.  Each  of  the  three  chief  roots,  i.  e.,  those  from  the  last  two  cervical  and  the 
first  thoracic  nerve,  is  connected  with  the  sympathetic  by  a  ramus  communicans. 

The  root  derived  from  the  sixth  cervical  nerve  is  very  small,  while  the  ventral  branches  of 
the  seventh  and  eighth  cervical  nerves  go  almost  entirely  to  the  plexus.  The  first  thoracic  nerve 
furnishes  the  largest  root;  its  whole  ventral  branch  goes  to  the  plexus  with  the  exception  of  its 
small  first  intercostal  branch.  The  root  from  the  second  thoracic  nerve  is  small,  since  most  of  its 
ventral  branch  goes  to  form  the  second  intercostal  nerve. 

The  branches  emanating  from  the  plexus  go  for  the  most  part  to  the  thoracic 
limb,  but  some  are  distributed  on  the  chest- wall.  The  names  of  the  branches,  and 
their  arrangement  so  far  as  they  can  be  conveniently  examined  before  removal  of 
the  forelimb,  are  as  follows  ■} 

1.  The  large  suprascapular  nerve  (N.  suprascapularis)  arises  from  the  anterior 
part  of  the  plexus,  passes  ventro-laterally,  and  disappears  between  the  supraspinatus 
and  subscapularis  muscles. 

2.  The  much  smaller  subscapular  nerves  (Nn.  subscapulares),  usually  two 
primary  trunks,  arise  close  behind  the  suprascapular,  run  backward  a  short  dis- 
tance, and  divide  into  several  branches  which  enter  the  distal  third  of  the  subscap- 
ularis muscle. 

3.  The  anterior  thoracic  or  pectoral  nerves  (Nn.  pectorales  craniales),  three  or 
four  in  number,  arise  from  the  anterior  part  of  the  plexus  and  from  the  loop  formed 
by  the  musculo-cutaneous  and  median  nerves.  One  enters  the  anterior  deep 
pectoral  muscle.  Another  passes  between  the  divisions  of  the  deep  pectoral  to 
supply  the  superficial  pectoral  and  brachiocephalicus,  giving  a  twig  usually  to  the 
posterior  deep  muscle.     The  latter  receives  one  or  two  other  nerves. 

4.  The  musculo-cutaneous  nerve  (N.  musculocutaneus)  arises  from  the  ante- 
rior part  of  the  plexus  and  descends  over  the  lateral  face  of  the  brachial  artery, 
below  which  it  is  connected  by  a  large  but  short  branch  with  the  median  nerve, 
thus  forming  a  loop  in  which  the  artery  lies.^  One  or  two  branches  to  the  pectoral 
muscles  are  given  off  from  the  nerve  or  the  loop. 

5.  The  median  nerve  (N.  medianus)  is  usually  the  largest  branch  of  the  bra- 
chial plexus.  It  descends  over  the  insertion  of  the  scalenus,  crosses  the  medial 
face  of  the  brachial  artery,  and  reaches  the  anterior  border  of  that  vessel.  It  is 
easily  recognized  by  its  large  size  and  the  loop  which  it  forms  with  the  musculo- 
cutaneous nerve. 

6.  The  ulnar  nerve  (N.  ulnaris)  arises  with  the  median  by  a  short  common 

1  In  order  to  examine  the  plexus  and  the  origins  of  its  chief  branches  conveniently  and  with 
as  little  disturbance  of  relation  as  possible,  the  subject  should  be  suspended  in  imitation  of  the 
natural  position  and  the  foreUmb  abducted  as  much  as  is  necessary.  In  doing  this  some  distm'b- 
ance  of  the  position  and  relations  of  the  nerves  and  vessels  takes  place.  The  braclnal  vessels  are 
drawn  away  from  the  chest-wall  so  that  their  lateral  surface  now  faces  forward,  and  the  nerves 
are  similarly  affected. 

^  The  loop  may  be  absent  or  double. 


SUPRASCAPULAR   NERVE — MUSCULO-CUTANEOUS   NERVE  815 

trunk.     It  descends  behind  the  brachial  artery  and  is  accompanied  a  short  distance 
by  the  radial  nerve,  from  which  it  can  be  distinguished  by  its  smaller  size. 

7.  The  radial  nerve  (N.  radialis)  arises  from  the  posterior  part  of  the  plexus 
and  is  sometimes  the  largest  branch.  It  descends  with  the  ulnar  nerve  over  the 
medial  face  of  the  origin  of  the  subscapular  artery  and  the  lower  part  of  the  teres 
major  and  dips  into  the  interstice  between  that  muscle  and  the  long  and 
medial  heads  of  the  triceps. 

8.  The  axillary  nerve  (N.  axillaris)  arises  behind  the  musculo-cutaneous.  It 
passes  downward  and  backward  on  the  medial  face  of  the  subscapularis  and  dis- 
appears between  that  muscle  and  the  subscapular  artery. 

9.  The  long  thoracic  nerve  (N.  thoracalis  longus)  is  wide  and  thin.  It  arises 
from  the  anterior  end  of  the  plexus,  gives  off  (usually)  three  branches  to  the  ser- 
ratus  ventralis  at  the  junction  of  its  cervical  and  thoracic  parts,  and  passes  back- 
ward across  the  surface  of  the  serratus  thoracis,  to  which  it  is  distributed.  The 
branches  which  enter  the  muscle  are  given  off  both  upward  and  downward  in  fairly 
regular  fashion. 

10.  The  thoraco-dorsal  nerve  (N.  thoracodorsalis)  passes  upward  and  back- 
ward across  the  subscapularis  muscle  to  ramify  in  the  latissimus  dorsi. 

11.  The  external  thoracic  nerve  (N.  thoracalis  lateralis)  arises  by  a  common 
trunk  with  the  ulnar.  It  passes  backward  and  ventrally  across  the  medial  surface  of 
the  humeral  tendon  of  the  cutaneus  muscle,  and  continues  backward  in  company  with 
the  external  thoracic  vein.  Its  terminal  branches  ramify  in  the  cutaneus  and  the 
skin  of  the  abdominal  wall  as  far  back  as  the  flank.  It  gives  collateral  branches 
to  the  deep  pectoral  muscle  and  others  which  anastomose  with  perforating  branches 
of  intercostal  nerves.  A  branch  from  it,  accompanied  by  a  large  perforating  inter- 
costal branch,  winds  around  the  ventral  border  of  the  latissimus  dorsi  and  ramifies 
in  the  cutaneus  on  the  lateral  surface  of  the  arm. 

The  term  posterior  thoracic  or  pectoral  nerves  (Nn.  pectorales  caudales)  may  be  used  to 
include  9,  10,  and  11. 

Suprascapular  Nerve 
The  suprascapular  nerve  (Fig.  566),  short  but  large,  is  usually  derived  chiefly, 
if  not  exclusively,  from  the  sixth  and  seventh  cervical  components  of  the  brachial 
plexus.  It  passes  between  the  supraspinatus  and  subscapularis  muscles  and  turns 
around  the  distal  fourth  of  the  anterior  border  of  the  scapula  to  reach  the  supra- 
spinous fossa.  It  gives  branches  to  the  supraspinatus  and  continues  backward 
and  upward  into  the  infraspinous  fossa,  and  terminates  in  several  branches  which 
innervate  the  infraspinatus. 

The  direct  relation  of  this  nerve  to  the  scapula  renders  it  Uable  to  injury,  the  result  'of  which 
may  be  paralysis  and  atrophy  of  the  muscles  supplied  by  it.  There  is,  however,  a  small  tendinous 
band  which  extends  over  the  nerve  as  it  turns  around  the  edge  of  the  scapula. 

Musculo-cutaneous  Nerve 
The  musculo-cutaneous  nerve  (Fig.  566)  arises  close  behind  the  suprascapular, 
and  is  derived  chiefly  from  the  part  of  the  brachial  plexus  which  is  supplied  by  the 
seventh  and  eighth  cervical  nerves.  It  descends  across  the  lateral  surface  of  the 
brachial  artery,  below  which  a  great  part  of  the  nerve  unites  with  the  median  to 
form  the  loop  previously  mentioned.  It  gives  off  a  branch  which  enters  the  proxi- 
mal part  of  the  belly  of  the  coraco-brachialis,  passes  downward  and  forward  in 
company  with  the  anterior  circumflex  vessels  between  the  two  parts  of  that  muscle 
or  between  the  muscle  and  the  bone,  and  divides  into  branches  which  enter  the  biceps 
brachii.  It  contributes  one  of  the  nerves  to  the  pectoral  muscles.  In  some  cases 
this  nerve  sends  a  branch  to  join  the  cutaneous  branch  of  the  median. 


816 


NERVOUS    SYSTEM    OF   THE    HORSE 


Axillary  Nerve 
The  axillary  nerve  (Figs.  566,  652)  ^  derives  its  fibers  chiefly  from  the  eighth 
cervical  root  of  the  brachial  plexus.  It  runs  downward  and  backward  across 
the  distal  part  of  the  subscapularis,  and,  in  company 
with  the  posterior  circumflex  artery,  dips  in  between  that 
muscle  and  the  subscapular  artery  at  the  level  of  the 
shoulder  joint.  Continuing  outward  in  the  interval  between 
the  teres  minor  and  the  long  and  lateral  heads  of  the  triceps, 
it  reaches  the  deep  face  of  the  deltoid  and  divides  into  several 
divergent  branches.  The  muscular  branches  supply  the  teres 
major,  capsularis,  teres  minor,  deltoid,  and  brachiocephali- 
cus.  The  cutaneous  branch  (N.  cutaneus  brachii  lateralis) 
runs  downward  and  a  little  forward  across  the  lateral  head 
of  the  triceps  and  ramifies  on  the  fascia  on  the  front  of  the 
forearm  and  on  the  superficial  pectoral  muscle. 

Radial  Nerve 
The  radial  nerve^  (Figs.  566,  568,  652)  is  sometimes  the 
largest  branch  of  the  brachial  plexus.  Its  fibers  are  derived 
chiefly  from  the  first  thoracic  root  of  the  plexus.  It  passes 
downward  and  backward  over  the  medial  surface  of  the  origin 
of  the  subscapular  artery  and  the  distal  part  of  the  teres 
major.  In  this  part  of  its  course  it  is  related  in  front  to  the 
ulnar  nerve,  which  separates  it  from  the  brachial  vein.^  It 
detaches  a  branch  to  the  tensor  fasciae  antibrachii,  passes  out- 
ward in  the  interval  between  the  teres  major  and  the  long 
and  medial  heads  of  the  triceps,  and  gains  the  musculo-spiral 
groove  of  the  humerus.  Accompanied  by  a  branch  of  the 
deep  brachial  arterj^,  it  runs  obliquely  downward  and  outward 
in  the  groove,  covered  laterally  by  the  lateral  head  of  the  tri- 
ceps and  the  extensor  carpi  radialis,  and  reaches  the  flexion 
surface  of  the  elbow  joint.  In  this  part  of  its  course  it  gives 
off  muscular  branches  to  the  three  heads  of  the  triceps  and 
to  the  anconeus,  and  a  cutaneous  nerve  (N.  cutaneus  anti- 
brachii dorsalis);  branches  of  the  latter  emerge  below  or 
through  the  lateral  head  of  the  triceps  and  ramify  on  the 
dorso-lateral  surface  of  the  forearm.  At  the  elbow  the  nerve 
descends  with  the  anterior  radial  vessels  on  the  joint  capsule, 
between  the  brachialis  and  extensor  carpi  radialis,  and  sup- 
plies branches  to  the  extensor  carpi  and  the  common  extensor 
of  the  digit  and  (inconstantly)  to  the  brachialis.  Below  the 
elbow  joint  the  nerve  detaches  a  large  branch  which  passes 
back  between  the  lateral  extensor  and  the  radius  to  the  ulnaris 
lateralis,  and  terminates  by  small  branches  which  descend  on 
the  radius  to  enter  the  radial  and  ulnar  heads  of  the  common 
and  lateral  extensors  of  the  digit,  and  the  oblique  extensor  of 
the  carpus.  Thus  the  radial  nerve  innervates  the  extensors 
of  the  elbow,  carpal,  and  digital  joints,  and  supplies  also 
the  lateral  flexor  of  the  carpus.^ 

'  Also  termed  the  circumflex  nerve. 

^  This  is  also  known  as  the  musculo-spiral  nerve. 

^  The  relative  positions  of  the  vessels  and  nerves  here  are  variable;  not  rarely  the  ulnar  nerve 
between  the  subscapular  artery  and  vein. 

■*  Morphologically  the  last-named  muscle  belongs  to  the  extensor  group.     In  man  and  in 
many  ammals  it  is  an  extensor  in  function. 


Fig.     652. — Cutaneous 
Nerves   op   Right 

FORELIMB     OF     HoRSE; 

Lateral  Face. 

a,  Cutaneous  branch 
of  axillary  nerve;  b,  cu- 
taneous branches  of  radial 
nerve;  c,  posterior  cutane- 
ous branch  of  ulnar  nerve; 
d,  cutaneous  branch  of  me- 
dian nerve;  e,  superficial 
branch  of  ulnar  nerve;  /, 
lateral  volar  nerve;  g,  anas- 
tomotic branch  connecting 
medial  and  lateral  volar 
nerves;  1,  lateral  head  of 
triceps:  3,  extensor  carpi 
radiaUs;  3,  common  ex- 
tensor; 4t  ulnaris  lateralis. 
(After  Ellenberger,  in  Leis- 
ering's  Atlas.) 


ULNAR   NERVE 


817 


Ulnar  Nerve 
The  ulnar  nerve  (Figs.  566,  567,  568,  652)  arises  with  the  median  from  the 
thoracic  components  of  the  brachial  plexus.  It  descends  between  the  brachial 
artery  and  vein,  accompanied  for  a  short  distance  by  the  radial  nerve.  It  then 
crosses  the  vein  and  continues  behind  the  latter  along  the  anterior  border  of  the 
tensor  fascia  antibrachii  and  dips  under  that  muscle  near  the  elbow.  Here  it  is 
joined  by  the  ulnar  vessels  and  passes  downward  and  backward  over  the  medial 
epicondyle  of  the  humerus.  In  the  forearm  it  crosses  obliquely  the  deep  face  of  the 
ulnar  head  of  the  flexor  carpi  ulnaris  and  descends  under  the  deep  fascia  with  the 


Extensor  cu7  pi  rudialis 


Intermuscular  septum 


Conininn  extetisor  of  digit 


Intermuscular  septum 

Lateral  extensor  of  digit 
Intermuscular  septum 

Ulnaris  lateralis  "^'- 
Deep  digital  flexor 
{humeral  head) 


Superficial  digital  flexor 
Deep  digital  flexor  (ulnar  head) 


Ulnar  vein  Ulnar  7ierve 

Uhuir  artery 

Fig.  653. — Cross-section  of  Forearm  of  Horse  about  Three  Inches  (ca.  S  cm.)  below  the  Elbow  Joint. 
The  deep  fascia  is  designated  by  red  line.     A',  A ,  V,  Dorsal  interosseous  vessels  and  nerve. 


Accessory  cephalic  vein 

Vein 

Cephalic  vein 
Medial  ligament  of  elbow 

-  Median  nerve 
Median  veins 
Median  artery 

Flexor  carpi  radialis 


Flexor  carpi  uhuiris 


vessels,  at  first  on  the  ulnar  head  of  the  deep  flexor,  and  then  l)etween  the  middle 
and  lateral  flexors  of  the  carpus.  Near  the  level  of  the  accessory  carpal  bone  it 
divides  into  two  terminal  branches,  superficial  and  deep.  It  gives  off  two  principal 
collateral  branches.  The  cutaneous  branch  (Ramus  cutaneus  volaris)  is  detached 
just  before  the  nerve  passes  under  the  tensor  fasciae  antibrachii;  it  runs  downward 
and  backward  on  that  muscle  under  cover  of  the  posterior  superficial  pectoral, 
becomes  superficial  below  the  elbow,  and  ramifies  on  the  posterior  surface  and  both 
sides  of  the  forearm.  The  muscular  branches,  which  are  given  off  at  the  elbow, 
supply  the  superficial  digital  flexor,  the  ulnar  head  of  the  deep  flexor,  and  the  flexor 
carpi  ulnaris.  Of  the  two  terminals,  the  superficial  branch  (Ramus  superficialis) 
emerges  between  the  tendons  of  insertion  of  the  lateral  and  middle  flexors  of  the 
carpus  and  ramifies  on  the  dorso-lateral  aspect  of  the  carpus  and  metacarpus.  The 
deep  branch  (Ramus  profundus),  after  a  very  short  course,  unites  under  cover  of 
52 


818 


NERVOUS    SYSTEM    OF    THE    HORSE 


the  tendon  of  the  ulnaris  lateralis  with  the  lateral  branch  of  the  median  nerve  to 
form  the  lateral  volar  nerve. 

Median  Nerve 
The  median  nerve  (Figs.  566,  567,  572,  652,  653)  derives  its  fibers  chiefly  from 
the  eighth  cervical  and  first  thoracic  roots  of  the  brachial  plexus.  It  is  usually  the 
largest  branch,  and  it  accompanies  the  chief  arterial  trunks  to  the  distal  part  of  the 
limb.  It  descends  over  the  medial  face  of  the  brachial  artery,  which  it  crosses 
obliquely,  and  continues  down  the  arm  in  front  of  the  artery.     Near  its  origin  it  is 


Medial  metacarpal  vtin 

Volar  nerve 

Digital  arte  i  y 


Dorsal  digital  branch 
Volar  digital  branch 


Coronary  plexm 


Distal  end  of  lateral  small  meta- 
carpal bone 

Large  metacarpal  bone 
Suspensory  ligament 


Superficial  flexor  tendon 

Posterior  annular  ligament  of 
fetlock 


Extensor  branch  of  suspensory 

ligament 

Oblique  or  middle  distal 

sesamoidean  ligament 

Volar  ligament  of  pastern  joint 

Proximal  annular  ligament  of  digit 

Deep  flexor  tendon 

Distal  annular  ligament  of  digit 


Fig.  654. — Dissection  of  Distal  Part  of  Right  Fore  Limb  of  Horse;  Volar  Surface. 

1,  Cartilage  of  third  phalanx;  S,  3,  4,  ligaments  from  first  phalanx  to  distal  sesamoid,  bulb  of  heel  and  cartilage  of  third 

phalanx.      (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


joined  by  a  large  branch  with  the  musculo-cutaneous  nerve,  thus  forming  a  loop  in 
which  the  artery  appears  to  be  suspended.  Near  the  elbow  it  usually  crosses 
obliquely  over  the  median  artery  and  lies  behind  it  on  the  medial  ligament. 
Below  the  joint  it  again  crosses  the  artery  and  lies  behind  the  radius  and  the 
lower  part  of  the  long  medial  ligament. 

At  the  elbow  the  nerve  is  covered  by  the  posterior  superficial  pectoral  muscle  and  is  crossed 
by  the  large  obUque  connection  between  the  cephalic  and  brachial  veins.  The  variable  and  often 
plexiform  venous  arrangement  renders  approach  to  the  nerve  here  undesirable.  It  can  be  reached 
best  by  an  incision  just  behind  the  lower  part  of  the  long  medial  ligament;  here  the  nerve 
lies  under  the  deep  fascia  in  the  furrow  between  the  radius  and  the  anterior  border  of  the  flexor 
carpi  radiahs,  overlapped  by  the  latter.  Not  uncommonly  the  nerve  retains  its  position  in  front 
of  the  artery  at  the  elbow;  in  other  cases  it  lies  upon  the  artery,  and  rarely  it  crosses  the  deep  face 
of  the  artery. 


MEDIAN   NERVE  819 

Passing  beneath  the  medial  flexor  of  the  carpus,  the  nerve  continues  down- 
ward in  the  forearm  with  the  median  vessels,  and  divides  at  a  variable  distance 
above  the  carpus  into  two  branches;  these  are  the  medial  volar  nerve,  and  the 
lateral  branch,  which  unites  with  the  ulnar  to  form  the  corresponding  lateral  volar 
nerve. 

At  the  proximal  part  of  the  forearm  the  nerve  runs  almost  straight  downward  along  the 
posterior  border  of  the  long  medial  ligament,  while  the  artery  here  inclines  somewhat  backward. 
Thus  the  nerve  is  superficial  to  the  artery  for  a  short  distance,  then  lies  in  front  of  the  latter  to 
about  the  middle  of  the  region,  where  it  incUnes  a  little  backward  and  arrives  at  the  interval 
between  the  radial  and  ulnar  flexors  of  the  carpus.  The  division  may  occur  about  the  middle  of 
the  region  or  even  higher,  but  commonly  takes  place  in  the  distal  third  or  fourth. 

The  collateral  branches  are  as  follows: 

1.  The  musculo-cutaneous  branch  is  in  reality  the  continuation  of  the  nerve  of 
that  name.  It  is  given  off  about  the  middle  of  the  arm,  passes  beneath  the  lower 
part  of  the  biceps,  and  divides  into  muscular  and  cutaneous  branches.  The  mus- 
cular branch  enters  the  brachialis.  The  cutaneous  branch  emerges  between  the 
brachiocephalicus  and  the  biceps  and  divides  into  two  branches;  these  descend 
on  the  fascia  of  the  forearm  with  the  cephalic  vein  and  its  accessory,  and  ramify 
on  the  front  and  medial  face  of  the  forearm,  carpus,  and  metacarpus. 

2.  Muscular  branches  to  the  radial  flexor  of  the  carpus  and  the  humeral  head 
of  the  deep  flexor  of  the  digit  are  given  off  just  as  the  nerve  passes  under  the  first 
named  muscle. 

3.  The  small  interosseous  nerve  passes  through  the  interosseous  space  and 
is  distributed  chiefly  to  the  periosteum,  but  in  some  cases  twigs  may  go  to  the 
extensor  muscles. 

The  volar  or  metacarpal  nerves/  medial  and  lateral,  are  the  continuations 
of  the  median  and  ulnar  nerves  in  the  distal  part  of  the  limb. 

The  medial  volar  nerve  (N.  volaris  medialis)  arises  as  the  medial  terminal 
branch  of  the  median  nerve  at  a  variable  distance  above  the  carpus  (Fig.  567). 
It  descends  through  the  carpal  canal  along  the  medial  border  of  the  superficial 
flexor  tendon,  and  lies  at  first  in  front  of  the  common  digital  artery.  It  then  passes 
behind  the  artery  to  the  distal  third  of  the  metacarpus,  where  it  lies  behind  the  vein, 
the  artery  here  becoming  deeper  in  position.  In  addition  to  cutaneous  twigs,  the 
nerve  gives  off  near  the  middle  of  the  metacarpus  a  considerable  anastomotic 
branch  which  winds  obliquely  over  the  flexor  tendons  and  joins  the  lateral  nerve 
below  the  middle  of  the  metacarpus  (Fig.  572).  ^Near  the  fetlock  the  nerve  divides 
into  two  digital  branches. 

1.  The  dorsal  (or  anterior)  digital  branch  (Ramus  dorsalis)  descends  at  first 
between  the  digital  artery  and  vein,  then  crosses  over  the  vein  and  ramifies  in  the 
skin  and  the  corium  of  the  hoof  on  the  dorsal  face  of  the  digit. 

2.  The  volar  (or  posterior)  digital  branch  (Ramus  volaris)  is  the  direct  con- 
tinuation of  the  trunk.  It  descends  behind  the  digital  artery,  which  it  accompanies 
in  its  ramification.  A  middle  digital  branch  is  sometimes  described  as  descending 
behind  the  vein.  In  some  cases  this  branch  is  distinct,  but  usually  there  are  instead 
several  small  twigs  derived  from  the  volar  branch,  which  cross  very  obliquely 
over  the  artery  and  anastomose  in  a  variable  manner  with  each  other  and  with  the 
dorsal  branch. 

The  lateral  volar  nerve  (N.  volaris  lateralis)  is  formed  by  the  union  of  the 
lateral  terminal  branch  of  the  median  with  the  deep  branch  of  the  ulnar  nerve 
(Fig.  567).  It  descends  with  the  lateral  volar  metacarpal  artery  in  the  texture  of 
the  posterior  annular  ligament  of  the  carpus.  In  the  metacarpus  it  descends  along 
the  lateral  border  of  the  deep  flexor  tendon  behind  the  lateral  metacarpal  vein,  and 
is  accompanied  by  a  small  artery  from  the  volar  subcarpal  arch.     Toward  the 

1  In  veterinary  works  these  are  frequently  termed  plantar  nerves,  which  is  an  unfortunate 
misnomer. 


820  NERVOUS    SYSTEM    OF   THE    HORSE 

distal  end  of  the  metacarpus  it  is  joined  by  the  obhque  branch  from  the  medial 
nerve,  and  beyond  this  is  arranged  Hke  the  latter.  Below  the  carpus  it  detaches  a 
deep  branch  to  the  suspensory  ligament  and  the  interossei,  and  also  supplies  twigs 
to  the  skin.^ 

THE  THORACIC  NERVES 

The  thoracic  nerves  (Nn.  thoracales)  number  eighteen  on  either  side  in  the 
horse.  Thej^^  are  designated  numericall}^  according  to  the  vertebrae  behind  which 
they  emerge.  Most  of  them  are  arranged  in  a  very  similar  manner  and  therefore 
do  not  require  separate  description.  Each  divides  into  a  dorsal  and  a  ventral 
branch,  the  latter  being  the  larger. 

The  dorsal  branches  (Rami  dorsales)  emerge  behind  the  levatores  costarum 
and  divide  into  medial  and  lateral  branches.  The  medial  branches  ascend  on  the 
multifidus  and  supply  the  dorsal  spinal  muscles.  The  lateral  branches  run  outward 
under  the  longissimus  dorsi  and  emerge  between  that  muscle  and  the  longissimus 
costarum;  after  giving  twigs  to  these  muscles  they  pass  through  the  latissimus 
dorsi  and  the  lumbo-dorsal  fascia  and  ramify  as  dorsal  cutaneous  nerves  under  the 
skin  of  the  back  (Fig.  655) .  In  the  region  of  the  Avithers  they  give  branches  to  the 
serratus  dorsalis  and  rhomboideus,  and  their  cutaneous  terminals  pass  through 
these  muscles  and  the  dorso-scapular  ligament  to  supply  the  skin  over  the  liga- 
mentum  nuchse  and  the  scapular  cartilage. 

The  ventral  branches  or  intercostal  nerves  (Nn .  intercostales)  are  much  larger 
than  the  preceding,  and  are  connected  with  the  sympathetic  by  rami  communi- 
cantes.  The  first  goes  almost  entirely  to  the  brachial  plexus,  but  sends  a  small 
branch  do\vnward  in  the  first  intercostal  space,  which  is  expended  in  the  muscle 
there  without  reaching  the  lower  end  of  the  space.  The  second  ventral  branch 
furnishes  a  considerable  root  to  the  brachial  plexus,  but  its  intercostal  continuation 
is  typical.  The  intercostal  nerves  (Fig.  273)  descend  in  the  intercostal  spaces 
wdth  the  vessels  of  like  name,  at  first  between  the  intercostal  muscles,  and  lower  down 
chiefly  between  the  pleura  and  the  internal  intercostal  muscle.  In  the  anterior 
spaces  the  artery  lies  along  the  posterior  border  of  the  rib,  with  the  nerve  in  front 
of  it;  further  back  the  nerve  lies  behind  the  border  of  the  rib,  with  the  arterj'  in 
front  of  it.  They  supply  the  intercostal  muscles,  give  off  lateral  perforating  branches, 
and  terminate  in  the  following  manner:  The  second  to  the  sixth  inclusive  emerge 
through  the  spaces  between  the  costal  cartilages  and  concur  in  supplying  the  pectoral 
muscles.  The  second  to  the  eighth  give  branches  to  the  transversus  thoracis. 
The  succeeding  ones  give  branches  to  the  diaphragm,  pass  between  the  transverse 
and  internal  oblique  abdominal  muscles,  give  twigs  to  these,  and  end  in  the  rectus 
abdominis.  There  are  three  series  of  cutaneous  nerves  given  off  by  the  intercostal 
nerves.  The  dorsal  nerves  emerge  through  the  serratus  ventralis  and  the  external 
intercostals  about  parallel  with  the  digitations  of  the  external  oblique.  The  middle 
ones  perforate  the  origin  of  the  latter  muscle.  The  ventral  ones  appear  through 
the  abdominal  tunic.  They  supply  branches  to  the  abdominal  muscles,  the  cu- 
taneus,  and  the  skin.  Some  of  the  anterior  ones  anastomose  with  the  posterior 
thoracic  branches  of  the  brachial  plexus.  The  posterior  three  supply  in  part  the 
skin  of  the  flank.  The  ventral  branch  of  the  last  thoracic  nerve  runs  outward 
l)ehind  the  last  rib  across  the  dorsal  surface  of  the  psoas  major  and  divides  into 
superficial  and  deep  branches.  The  superficial  branch  passes  over  the  superficial 
face  of  the  transversus  abdominis,  perforates  the  obliquus  externus,  and  ramifies 
under  the  skin  of  the  flank  (Fig.  657).  The  deep  branch  descends  on  the  deep  face 
of  the  internal  o])lique  to  the  rectus  abdominis,  in  which  it  ends. 

^  Anastomoses  are  established  between  the  digital  branches,  and  the  areas  innervated  by 
them  are  not  well  defined,  but  really  overlap  each  other.  In  certain  diseased  conditions,  however, 
in  which  the  lesions  are  confined  to  the  volar  structures,  reli<if  from  pain  may  be  afforded  by  sec- 
tion of  tlie  volar  branches  only. 


822 


NERVOUS   SYSTEM   OF  THE   HORSE 


THE  LUMBAR  NERVES 

There  are  six  pairs  of  lumbar  nerves  (Nn.  lumbales)  in  the  horse,  the  last  of 
which  emerge  between  the  last  lumbar  vertebra  and  the  sacrum.  The  anterior  two 
or  three  are  about  the  same  size  as  the  thoracic  nerves,  but  the  others  are  much 
larger. 

Their  dorsal  branches  are  small  in  comparison  with  the  ventral  ones.  They 
are  distributed  to  the  muscles  and  skin  of  the  loins  and  croup  in  a  fashion  similar 
to  those  of  the  thoracic  nerves. 

The  ventral  branches  are  connected  with  the  sympathetic  by  small  rami 
communicantes,  and  give  branches  to  the  sublumbar  muscles.  Those  of  the  first 
two  nerves  are  arranged  in  a  manner  analogous  to  the  corresponding  branch  of  the 
last  thoracic  nerve. 

The  ventral  branch  of  the  first  lumbar  nerve  is  termed  the  ilio-hypogastric 
nerve   (N.  iliohypogastricus) .     It  passes  outward  between  the  quadratus  lum- 


Crura  of  diapludgm^^ 


Dia-phragm. 

Last  thoracic 
nerve 

Ilio-hypogastric 
nerve 
Ilio-inguinal  nerve - 
External  spermatic 
nerve 
External  cutaneous 
nerve 


Splanchnic  nerve 
L,~  Last  inti  rcostal  arteries 
First  lumbar  arteries 


Attachments  of  psoas  major 
^  Body  of  vertebra 

Eztcrrial  spermatic  nerve 
'     ■  Trunk  of  lumbar  arteries 


Sixth  lumbar  artery 


Sympathetic 
trunks 

Insertion  of  quad- 
ratus lumhorum 

Anterior  part  of  /, 
lumbosacral  plexus  \: 

Obturator  nervi 
Femoral  nerve 

Fig.  656. — Lumbar  Nerves  of  Horse;  Ventral  View.     (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


Ventral  sacro-iliac 
ligament 


borum  and  the  psoas  major,  and  divides  at  the  lateral  border  of  the  latter  into  a 
superficial  and  deep  branch.  The  superficial  or  cutaneous  branch  passes  over  the 
dorsal  edge  of  the  internal  oblique,  descends  between  that  muscle  and  the  external 
oblique,  perforates  the  latter,  and  runs  downward  and  backward  and  ramifies 
under  the  skin  of  the  posterior  part  of  the  flank  and  the  lateral  surface  of  the  thigh. 
It  gives  branches  to  the  transversus  and  obliquus  externus  abdominis.  The  deep 
(or  muscular)  branch  is  smaller;  it  runs  downward  and  backward  beneath  the 
peritoneum  to  the  lateral  border  of  the  rectus  abdominis,  gives  branches  to  the 
internal  oblique,  and  terminates  in  the  rectus  abdominis. 

The  ventral  branch  of  the  second  limibar  nerve  is  usually  connected  by  an 
anastomotic  branch  with  that  of  the  third  nerve.  It  gives  off  a  large  branch  to  the 
psoas  major  and  is  continued  as  the  ilio-inguinal  nerve  (N.  ilioinguinalis).  This 
divides  like  the  ilio-hypogastric  into  superficial  and  deep  branches.  Its  superfi- 
cial branch  perforates  the  external  oblique  muscle  a  little  in  front  of  the  point  of 
the  hip,  runs  downward  on  the  front  of  the  thigh  and  the  lateral  surface  of  the 
stifle,  and  gives  off  cutaneous  branches.  The  deep  branch  runs  behind  and  parallel 
with  that  of  the  ilio-hypogastricus  and  detaches  branches  to  the  abdominal  muscles. 


THE    LUMBAR   NERVES 


823 


It  joins  a  branch  of  the  external  spermatic  nerve,  and  the  trunk  so  formed  de- 
scends the  inguinal  canal,  to  be  distributed  to  the  external  genital  organs  and  the 
surrounding  skin  in  the  inguinal  region. 

The  ventral  branch  of  the  third  lumbar  nerve  is  connected  by  a  small  anasto- 
motic branch  with  the  second  nerve  and  furnishes  a  root  of  the  lumbo-sacral  plexus. 
It  gives  off  a  branch  to  the  psoas  muscles,  the  external  spermatic  nerve,  and 
is    continued    as    the    lateral 

cutaneous    nerve.       The    ex-  j^,_  j 

temal  spermatic  nerve  (N. 
spermaticus  externus)  passes 
backward  in  the  substance  of 
the  psoas  minor  and  divides 
into  two  branches.  One  of 
these,  the  muscular  branch, 
emerges  in  front  of  the  circum- 
flex iliac  vessels  and  goes  to  the 
cremaster  and  internal  oblique 
muscles.  The  other,  the  in- 
guinal branch,  emerges  behind 
the  vessels  just  mentioned.  It 
then  runs  lateral  to  and  parallel 
with  the  external  iliac  artery 
and  descends  in  the  medial 
part  of  the  inguinal  canal.  It 
emerges  at  the  external  ring 
with  the  external  pudic  artery 
and  ramifies  in  the  external 
genital  organs  and  the  skin  of 
the  inguinal  region.  The  lat- 
eral cutaneous  nerve  of  the 
thigh  (N.  cutaneus  femoris 
lateralis)  runs  backward  in 
the  substance  of  the  psoas 
muscles  and  emerges  at  the 
lateral  border  of  the  psoas 
minor.  It  then  passes  outward 
and  backward  on  the  iliac  fas- 
cia and  accompanies  the  pos- 
terior branch  of  the  circumflex 
iliac  artery.  With  this  vessel 
it  perforates  the  abdominal 
wall  by  passing  between  the 
external  oblique  and  the  iliacus 
a  short  distance  below  the 
point  of  the  hip,  descends  on 

the  medial  face  of  the  tensor  fasciae  latse  (near  its  anterior  border),  and  ramifies 
subcutaneously  in  the  region  of  the  stifle. 

The  origin  and  disposition  of  some  of  the  foregoing  nerves  are  variable.  In  some  cases  the 
ilio-inguinal  nerve  ends  in  the  psoas  major,  and  appears  then  to  be  absent.  The  mode  of  formation 
of  the  inguinal  nerves  is  inconstant. 

The  ventral  branches  of  the  fourth,  fifth,  and  sixth  lumbar  nerves  concur  in 
the  formation  of  the  lumbo-sacral  plexus. 


Fig.  6.57. — Superficial  Nerves  of  Pki/- 
VIC  Limb  and  Posterior  Part  of 
Trunk  of  Horse. 

a.  Cutaneous  branches  of  sixteenth 
and  seventeenth  thoracic  nerves;  b,  cuta- 
neous branches  of  lumbar  nerves;  c,  cu- 
taneous branches  of  sacral  nerves;  d, 
cutaneous  branches  of  coccygeal  nerves; 
e,  f,  9,  cutaneous  branches  of  last  thoracic 
and  first  and  second  lumbar  nerves;  g", 
end  of  lateral  cutaneous  nerve  of  thigh; 
h,  posterior  cutaneous  nerve  of  thigh;  i,  i, 
cutaneous  branches  of  great  sciatic  nerve-, 
k,  posterior  cutaneous  nerve  of  the  leg; 
I,  superficial  peroneal  nerve;  m,  terminal 
part  of  deep  peroneal  nerve;  n,  lateral  plantar  nerve;  1,  obUquus  ab- 
dominis externus;  3,  tensor  fascise  latse;  3,  gluteus  superficialis;  4. 
biceps  femoris;  S,  semitendinosus;  G,  common  extensor;  7,  lateral  ex- 
tensor; 8,  flexor  tendons;  9,  great  metatarsal  artery.  (After  Ellen- 
berger,  in  Leisering's  Atlas.) 


g24  NERVOUS   SYSTEM   OF   THE    HORSE 

LUMBO-SACRAL  PLEXUS 

This  plexus  (Fig.  576)  results  substantially  from  the  union  of  the  ventral 
branches  of  the  last  three  lumbar  and  the  first  two  sacral  nerves,  but  it  derives  a 
small  root  from  the  third  lumbar  nerve  also.  The  anterior  part  of  the  plexus  lies 
in  front  of  the  internal  iliac  artery,  between  the  lumbar  transverse  processes  and  the 
psoas  minor.  It  supplies  branches  to  the  ilio-psoas  (designated  by  Girard  the 
iliaco-muscular  nerves).  The  posterior  part  lies  partly  upon  and  partly  in  the 
texture  of  the  sacro-sciatic  ligament.  From  the  plexus  are  derived  the  nerves  of  the 
pelvic  limb,  which  are  now  to  be  described. 

Femobial  Nerve 

The  femoral  nerve  (N.  femoralis)^  is  derived  chiefly  from  the  fourth  and  fifth 
lumbar  nerves,  but  commonly,  if  not  always,  receives  a  fasciculus  from  the  third 
nerve  also  (Fig.  656).  It  is  the  larger  of  the  two  nerves  which  are  given  off  from 
the  anterior  part  of  the  lumbo-sacral  plexus.  It  runs  ventrally  and  backward,  at 
first  between  the  psoas  major  and  minor,  then  crosses  the  deep  face  of  the  tendon 
of  insertion  of  the  latter,  and  descends  under  cover  of  the  sartorius  over  the  termi- 
nal part  of  the  ilio-psoas.  It  gives  off  the  saphenous  nerve,  and  divides  into  several 
terminal  branches  which  dip  into  the  interstice  between  the  rectus  femoris  and  the 
vastus  medialis  (Fig.  575),  These  branches  are  accompanied  by  the  anterior 
femoral  vessels  and  innervate  the  quadriceps  femoris.  A  collateral  branch  is  given 
off  to  the  ilio-psoas. 

The  saphenous  nerve  (N.  saphenus)  (Figs.  575,  576,  582)  is  given  off  as  the 
femoral  crosses  the  terminal  part  of  the  ilio-psoas.  It  gives  off  a  branch  which 
enters  the  deep  face  of  the  sartorius,  and  descends  with  the  femoral  vessels  in  the 
femoral  canal.  About  the  middle  of  the  thigh  it  divides  into  several  branches 
which  emerge  from  between  the  sartorius  and  gracilis,  perforate  the  deep  fascia,  and 
ramify  on  the  medial  surface  and  the  front  of  the  limb  as  far  downward  as  the  hock. 
The  longer  posterior  branches  accompany  the  saphenous  vessels,  while  the  anterior 
branches  deviate  forward  toward  the  stifle  and  the  anterior  surface  of  the  leg. 

Obturator  Nerve 

The  obturator  nerve  (N.  obturatorius)  is  derived  chiefly  from  the  ventral 
branches  of  the  fourth  and  fifth  lumbar  nerves,  but  may  receive  fibers  from  the 
third  or  the  sixth  (Fig.  656).  It  runs  downward  and  backward,  at  first  above 
and  then  upon  the  external  iliac  vein,  inclines  inward  across  the  obturator  vein,  and 
passes  through  the  anterior  part  of  the  obturator  foramen  (Fig.  576).  It  continues 
downward  through  the  obturator  externus,  and  divides  into  several  branches  which 
innervate  the  obturator  externus,  pectineus,  adductor,  and  gracilis  muscles  (Fig. 
581). 

Anterior  Gluteal  Nerve 

The  anterior  gluteal  nerve  (N.  gluta?us  cranialis)  is  derived  chiefly  from  the 
last  lumbar  and  first  sacral  nerves,  but  commonly  has  a  fifth  lumbar  root.  It 
divides  into  four  or  five  branches  which  emerge  through  the  greater  sciatic 
foramen  Avith  the  divisions  of  the  anterior  gluteal  artery  and  supply  the  glutei, 
tensor  fasciae  lata^,  and  capsularis  (Fig.  658).  The  nerve  to  the  tensor  fasciae  latae 
and  the  anterior  part  of  the  superficial  gluteus  passes  between  the  deep  part  of  the 
gluteus  medius  and  the  gluteus  profundus,  and  is  accompanied  on  the  iliacus  by 
branches  of  the  lateral  circumflex  vessels. 

Posterior  Gluteal  Nerve 
The  posterior  gluteal  nerve  (N.  glutaeus  caudalis)  is  derived  mainly  from  the 
sacral  roots  of  the  lumbo-sacral  plexus  (Figs.  576,  658).     It  divides  into  two  trunks 
*  Also  termed  the  anterior  crural  nerve. 


GREAT   SCIATIC   NERVE 


825 


which  emerge  above  the  great  sciatic  nerve.  The  dorsal  nerve  passes  backward 
on  the  upper  part  of  the  sacro-sciatic  hgament  and  divides  into  branches  which 
enter  the  biceps  femoris;  it  suppUes  a  branch  to  the  posterior  part  of  the  middle 
gluteus,  and  a  nerve  which  turns  around  the  posterior  border  of  the  latter  and  enters 
the  posterior  head  of  the  superficial  gluteus.  The  ventral  nerve  runs  downward 
and  backward  on  the  sacro-sciatic  ligament  and  divides  into  the  posterior  cutaneous 
nerve  of  the  thigh  (N.  cutaneus  femoris  caudalis)  and  muscular  branches  which 
supply  the  semitendinosus.  The  former  passes  through  the  biceps  femoris,  emerges 
between  that  muscle  and  the  semitendinosus  at  or  a  little  below  the  level  of  the  tuber 
ischii,  and  ramifies  subcutaneously  on  the  lateral  and  posterior  surfaces  of  the  hip 
and  thigh  (Fig.  657).  The  deep  part  of  the  nerve  is  connected  by  filaments  with 
the  pudic  nerve. 

Great  Sciatic  Nerve 
The  great  sciatic  nerve  (N.  ischiadicus)  (Figs.  574,  580,  658),  the  largest  in 
the  body,  is  derived  chiefly  from  the  sixth  lumbar  and  first  sacral  roots  of  the  lumbo- 


Lateral  'ia(  n>-  f       '^_"  4^  ^r' 
iliac  ligamt  id  \      ^^Jifif0^%^ 


Sacral  spines 


Sacro-scialic 
ligament 


Iliaco-fhmund  or  lateral  circumflex  vessels 


Piiliic  tuhercle 


Lesser  Gemel-  Anastomosis 
sciatic  his  between  ob- 
foramen  turator  and 

internal  pudic 
veins 


'^Obturator  artery 
^Obturator  internus 
^Obturator  vein 


()t 


Fig.  658. — Vessels  and  Nerves  on  Pelvic  Wall  of  Horse. 

Nervus  ischiadicus  =  great  sciatic  nerve;    n.  glut.  inf.  =  posterior  gluteal  nerve;    n.  pudendus  =  pudic  nerve.     (After 

Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


sacral  plexus,  but  usually  has  a  fifth  lumbar  root  and  may  receive  a  fasciculus  from 
the  second  sacral  nerve.  It  emerges  through  the  greater  sciatic  foramen  as  a 
broad  flat  band  which  is  blended  at  first  with  the  posterior  gluteal  nerve  and 
passes  downward  and  backward  on  the  lower  part  of  the  sacro-sciatic  ligament  and 
on  the  origin  of  the  deep  gluteus  muscle.     It  turns  downward  in  the  hollow  between 


826  NERVOUS    SYSTEM   OF  THE   HORSE 

the  trochanter  major  and  the  tuber  ischii  over  the  gemellus,  the  tendon  of  the 
obturator  internus,  and  the  quadratus  femoris.  In  its  descent  in  the  thigh  it  lies 
between  the  biceps  femoris  laterally  and  the  adductor,  semimembranosus,  and 
semitendinosus  medially,  and  is  continued  between  the  two  heads  of  the  gastroc- 
nemius as  the  tibial  nerve.     Its  chief  branches  are  as  follows: 

1.  In  the  pelvic  part  of  its  course  the  sciatic  nerve  supplies  small  muscular 
branches  to  the  obturator  internus,  gemellus,  and  quadratus  femoris;  the  branch 
to  the  obturator  internus  reaches  the  muscle  by  passing  through  the  anterior  end 
of  the  lesser  sciatic  foramen. 

These  very  small  nerves  arise  from  the  upper  border  or  deep  face  of  the  great  sciatic,  about 
haK  way  between  the  two  sciatic  foramina.  The  nerve  to  the  obturator  internus  lies  along  the 
dorsal  margin  of  the  sciatic  and  divides  into  branches  for  both  heads  of  the  muscle.  The  nerves 
to  the  gemellus  and  quadratus  femoris  commonly  arise  from  the  deep  face  of  the  sciatic  by  a  com- 
mon trunk  which  passes  back  between  the  latter  and  the  sacro-sciatic  ligament  to  the  posterior 
border  of  the  gluteus  profundus,  where  it  divides. 

2.  As  the  sciatic  nerve  turns  down  behind  the  hip  joint  it  gives  off  a  large 
muscular  branch  (Ramus  muscularis  proximalis),  which  divides  to  supply  the 
semimembranosus  and  the  short  heads  of  the  biceps  femoris  and  semitendinosus. 

3.  The  posterior  cutaneous  nerve  of  the  leg  or  external  saphenous  nerve  (N. 
cutaneus  sura?  caudalis)  is  detached  from  the  sciatic  about  the  middle  of  the  thigh. 
It  receives  a  fasciculus  from  the  peroneal  nerve  and  descends  with  the  recurrent 
tarsal  vein  on  the  lateral  face  of  the  gastrocnemius  to  the  distal  third  of  the  leg. 
Here  it  perforates  the  deep  fascia  and  ramifies  under  the  skin  on  the  lateral  surface 
of  the  tarsus  and  metatarsus  (Fig.  657). 

4.  The  peroneal  nerve  (N.  peronaius)  (Figs.  580,  585,  659)^  is  a  large  trunk 
which  arises  from  the  great  sciatic  nerve  very  shortly  after  the  latter  emerges  from 
the  pelvic  cavity.  It  descends  with  the  parent  trunk  to  the  origin  of  the  gastroc- 
nemius; here  the  peroneal  nerve  deviates  outward  and  forward  across  the  lateral 
face  of  the  gastrocnemius  under  cover  of  the  biceps  femoris,  and  divides  at  the 
origin  of  the  lateral  extensor  muscle  into  superficial  and  deep  branches.  The 
collateral  branches  include  one  to  the  biceps  femoris,  the  reinforcing  fasciculus 
detached  about  the  middle  of  the  thigh  to  the  posterior  cutaneous  nerve,  and, 
lower  down,  the  lateral  cutaneous  nerve  of  the  leg  (Ramus  cutaneus  surae  later- 
alis).^  The  latter  emerges  between  the  middle  and  posterior  divisions  of  the 
biceps  femoris  at  the  level  of  the  stifle  joint  and  ramifies  under  the  skin.  The 
superficial  peroneal  nerve  (N.  peronseus  superficialis)^  furnishes  branches  to  the 
lateral  extensor,  and  descends  in  the  furrow  between  that  muscle  and  the  long 
extensor,  perforates  the  deep  fascia  of  the  leg,  and  ramifies  under  the  skin  on  the 
front  and  the  lateral  face  of  the  tarsus  and  metatarsus.  The  deep  peroneal  nerve 
(N.  peronseus  profundus)^  is  the  direct  continuation  in  point  of  size  of  the  peroneal 
trunk.  It  dips  in  between  the  lateral  and  long  extensors  of  the  digit,  gives  branches 
to  these  muscles  and  the  tibialis  anterior,  and  descends  in  front  of  the  intermuscular 
septum  which  separates  the  two  muscles  first  named.  It  continues  do"v\Tiward 
behind  the  tendon  of  the  long  extensor  and  divides  on  the  front  of  the  hock  into 
medial  and  lateral  branches.  The  medial  branch  (Ramus  medialis)  passes  down 
under  the  skin  on  the  anterior  face  of  the  metatarsus  and  supplies  the  cutaneous 
fibers  of  this  region.  The  lateral  branch  (Ramus  lateralis)  furnishes  a  twig  to  the 
extensor  brevis  muscle  and  descends  with  the  great  metatarsal  artery.  It  supplies 
the  skin  on  the  lateral  face  of  the  metatarsus  and  the  fetlock. 

In  the  greater  part  of  its  course  in  the  leg  the  deep  peroneal  nerve  is  separated  from  the 
anterior  tibial  vessels  by  the  tibialis  anterior.     It  should  be  noted  that  the  lateral  one  of  the  two 

^  Also  known  as  the  external  popliteal  ner\'e. 
^  Also  termed  the  peroneal  cutaneous  nerve. 
'  Also  termed  the  musculo-cutaneous  nerve. 
*  Also  termed  the  anterior  tibial  nerve. 


TIBIAL   NERVE 


827 


veins  which  ahnost  always  accompany  the  artery  here  is  usually  very  large,  and  the  layer  of  muscle 
which  intervenes  between  it  and  the  nerve  is  often  exceedingly  thin.  In  the  distal  part  of  the  leg 
the  nerve  is  in  direct  contact  with  the  vein,  and  on  the  front  of  the  hock  it  Ues  behind  the  vessels. 
In  very  exceptional  cases  the  nerve  lies  for  a  variable  distance  in  the  middle  of  the  leg  in  the  lateral 
part  of  the  tibiahs  anterior. 

Tibial  Nerve 

The  tibial  nerve  (N.  tibialis)  ^  is  the  direct  continuation  of  the  great  sciatic 

nerve  (Figs.  576,  580,  583,  584,  659).     It  passes  down  between  the  two  heads  of  the 

gastrocnemius,  and  accompanies  the  recurrent  tibial  vessels  to  the  distal  third  of 

the  leg,  where  it  divides  into  the  two  plantar  nerves.     In  the  proximal  third  of  the 


Long  digital  extensor 

Anterior  tibial  vessels 

Deep  peroneal  nerve 
Superficial  peroneal 
nerve 
Intermuscular  septum 
Fibrous  band 

Lateral  extensor 
Intermuscular  septum 


Deep  head  of  deep 

flexor  (flex,  hall, 

longus) 


Peroneus  tertius 


Tibialis  posterior 
N.  cutaneus  surce 
Recurrent  tarsal  vein 
and  artery 

Soleus 


Tibialis  anterior 


Saphenous  vein' 
Saphenous  artery 


Posterior  tibial  vessels 

Tendon  of  long  digital 

flexor 


Recurrent  tibial  vein 
Recurrent  tibial  artery 
Tibial  nerve 

Tarsal  tendon  of  biceps  femoris 

and  semitendinosus 


Superficial  flexor  tendon 


Gastrocnemius  tendon 

Fig.  659. — Cross-section  of  Dist.*.l  Third  of  Left  Leg  of  Horse. 

The  deep  fascia  is  shown  by  red  line. 


leg  it  lies  along  the  medial  side  of  the  superficial  flexor  under  cover  of  the  medial 
head  of  the  gastrocnemius;  lower  down  it  is  covered  by  the  common  deep  fascia 
and  is  situated  in  the  space  between  the  deep  flexor  and  the  medial  border  of  the 
tendo  calcaneus  (Achillis). 

At  the  usual  point  of  election  for  tibial  neurectomy,  i.  e.,  about  a  handbreadth  above  the 
level  of  the  tuber  calcis,  the  nerve  hes  in  areolar  tissue  and  fat  in  a  fascial  compartment  formed  by 
the  special  fascia  of  the  deep  flexor  in  front  and  by  the  common  fascia  and  the  tarsal  tendon  of  the 
semitendinosus  and  biceps  femoris  behind  and  medially. 

At  its  origin  the  tibial  nerve  gives  off  a  muscular  branch  (Ramus  muscularis 
distalis),  the  divisions  of  which  pass  between  the  two  heads  of  the  gastrocnemius 
1  Also  termed  the  posterior  tibial  nerve. 


828  NERVOUS    SYSTEM    OF   THE    HORSE 

and  radiate  to  supply  that  muscle,  the  popliteus,  the  soleus,  and  the  flexors  of  the 
digit.     Small  cutaneous  twigs  are  also  detached  along  the  course  of  the  nerve. 

Plantar  Nerves 
The  plantar  nerves,  medial  and  lateral  (N.  plantaris  medialis,  lateralis), 
result  from  the  bifurcation  of  the  tibial  nerve  in  the  distal  part  of  the  leg  (Figs. 
583,  584).  They  continue  at  first  in  the  same  direction  and  relations  as  the  parent 
trunk,  in  direct  apposition  and  enclosed  in  a  common  sheath.  At  the  hock  they 
diverge  at  a  very  acute  angle  and  descend  in  the  tarsal  canal  behind  the  deep  flexor 
tendon  in  company  with  the  plantar  arteries.  The  medial  plantar  nerve  supplies 
cutaneous  nerves  to  the  medial  aspect  of  the  tarsus  and  metatarsus,  descends  along 
the  medial  border  of  the  flexor  tendons  behind  the  superficial  plantar  metatarsal 
vessels,  and  is  otherwise  arranged  like  the  corresponding  volar  nerve  of  the  fore- 
limb.  The  lateral  plantar  nerve  deviates  outward  between  the  two  flexor  tendons 
to  reach  their  lateral  border.  It  supplies  a  branch  to  the  suspensory  ligament,  and 
in  its  further  course  resembles  the  corresponding  nerve  of  the  fore  limb. 

In  so-called  "tibial"  neurectomy  the  operator  really  cuts  the  two  plantar  nerves  which  have 
not  yet  separated.  The  anastomotic  branch  between  the  two  plantar  nerves  is  smaller  and  more 
distal  than  that  which  connects  the  corresponding  nerves  of  the  fore  limb,  and  is  absent  in  30  per 
cent,  of  the  cases  according  to  Rudert. 

Sacral  Nerves 

Five  pairs  of  sacral  nerves  (Nn.  sacrales)  are  present  in  the  horse. 

The  small  dorsal  branches  emerge  through  the  dorsal  sacral  foramina  and  the 
space  between  the  sacrum  and  the  first  coccygeal  vertebra,  and  ramify  in  the 
muscles  and  skin  of  the  sacral  region  and  the  adjacent  part  of  the  tail  (Fig.  657). 
The  fifth  anastomoses  with  the  dorsal  branch  of  the  first  coccygeal  nerve. 

The  ventral  branches  leave  the  vertebral  canal  through  the  ventral  sacral 
foramina  and  the  interval  between  the  sacrum  and  first  coccygeal  vertebra.  They 
are  connected  with  the  sympathetic  by  rami  communicantes,  and  contribute 
branches  to  the  pelvic  plexus.  The  first  and  second  are  the  largest,  and  unite  with 
each  other  and  with  those  of  the  last  three  lumbar  nerves  to  form  the  lumbo-sacral 
plexus.  The  third  and  fourth  are  connected  with  each  other,  and  the  majority  of 
their  fibers  go  to  form  the  pudic  and  posterior  hsemorrhoidal  nerves. 

The  pudic  nerve  (N.  pudendus)  (Figs.  576,  580,  658)  passes  downward  and 
backward  partly  embedded  in  the  sacro-sciatic  ligament,  then  accompanies  the 
internal  pudic  artery  to  the  ischial  arch,  turns  around  the  latter,  parting  company 
with  the  artery,  and  pursues  a  flexuous  course  along  the  dorsum  penis  as  the  nervus 
dorsalis  penis  and  ramifies  in  the  glans  penis  and  the  penile  layer  of  the  prepuce. 
Within  the  pelvis  it  anastomoses  with  the  posterior  hsemorrhoidal  nerve,  and  gives 
branches  to  the  bladder  and  urethra,  the  terminal  part  of  the  rectum,  and  the  skin 
and  muscles  of  the  anus  (Fig.  577) .  It  also  supplies  the  nerve  to  the  ischio-caverno- 
sus  muscle  and  numerous  branches  to  the  corpus  cavernosum  of  the  penis  and 
urethra.     In  the  female  it  terminates  in  the  clitoris  and  vulva  (Fig.  578). 

The  posterior  haemorrhoidal  nerve  (N.  hsemorrhoidalis  caudalis)  passes  do^\^l- 
ward  and  backward  above  the  pudic  nerve,  with  which  it  anastomoses.  It  gives 
twigs  to  the  terminal  part  of  the  rectum,  the  sphincter  ani  externus,  and  the  sur- 
rounding skin  (Fig.  577).  In  the  female  it  supplies  twigs  to  the  vulva  also  (Fig. 
578). 

The  ventral  branch  of  the  fifth  nerve  is  small.  It  gives  twigs  to  the  sacro- 
coccygeus  ventralis  lateralis  and  the  skin  of  the  root  of  the  tail  and  joins  the  first 
coccygeal  nerve. 


THE    SYMPATHETIC   NERVOUS    SYSTEM  829 


Coccygeal  Nerves 
The  coccygeal  nerves  (Nn.  coccygei)  commonly  number  five  pairs.  Their 
dorsal  and  ventral  branches  anastomose  to  form  respectively  two  trunks  on  either 
side,  which  extend  to  the  tip  of  the  tail  and  supply  its  muscular  and  cutaneous 
nerves.  The  dorsal  trunk  runs  with  the  dorso-lateral  artery  between  the  sacro- 
coccygeus  dorsalis  and  intertransversales  muscles  (Fig.  579).  The  ventral  trunk 
accompanies  the  ventro-lateral  artery  below  the  intertransversales. 


The  Sympathetic  Nervous  System  ^ 

The  sympathetic  nervous  system  (Systema  nervorum  sympathicum)  is  that 
part  of  the  nervous  system  which  serves  (1)  to  transmit  stimuli  to  the  heart  muscle, 
unstriped  muscle,  and  glands;  (2)  to  conduct  impulses  from  the  viscera  to  the  cere- 
brospinal system. 

Many  of  the  fibers  are  derived  from  the  cerebrospinal  system  and  are  rearranged  and  dis- 
tributed in  the  sympathetic  system.  Numerous  sympathetic  fibers  are  contributed  to  the  cerebro- 
spinal nerves,  tlirough  which  they  are  distributed  to  the  unstriped  muscular  tissue  and  glands, 
as  vasomotor,  pilomotor,  and  secretory  nerves.  The  sympathetic,  like  the  cerebrospinal  system, 
consists  of  neurones,  each  of  which  comprises  the  cell-body,  an  axone,  and  numerous  branched 
dendrites.  The  cell-bodies  are  aggregated  into  ganglia,  some  of  which  are  large  and  more  or  less 
constant  in  position  and  form,  while  others  are  microscopic  and  are  scattered  in  an  irregular  man- 
ner through  the  peripheral  part  of  the  system.  Simple  visceral  reflexes  may  be  mediated  by  sym- 
pathetic neurones  alone. 

In  descriptive  anatomy  the  sympathetic  system  is  regarded  as  consisting  of 
(1)  a  chain  of  ganglia  extending  along  each  side  of  the  vertebral  column  and  con- 
nected by  association  fibers  to  form  the  sympathetic  trunk ;  (2)  central  branches 
to  and  from  the  cerebrospinal  nerves;  (3)  peripheral  branches,  which  form  plexuses 
(Plexus  sympathici)  with  each  other  and  the  cerebrospinal  nerves;  (4)  the  peripheral 
gangUa  which  are  interposed  in  the  plexuses  (Ganglia  plexuum  sympathicorum). 

The  S3nnpathetic  triink  (Truncus  sympathicus)  extends  on  either  side  from 
the  base  of  the  cranium  to  the  tail.  In  it  are  interposed,  at  intervals  of  varying 
regularity,  the  gangha  of  the  sympathetic  trunk  (Ganglia  trunci  sympathici). 
These  are  comiected  Avith  the  cerebrospinal  nerves  by  central  branches,  the  rami 
communicantes. 

Two  kinds  of  rami  communicantes  occm-.  Of  these,  one  type  consists  largely  of  medullated 
fibers  derived  from  the  spinal  nerves  and  ganglia;  they  have  therefore  a  wliite  appearance,  and 
are  termed  white  rami.  They  contain  both  efferent  and  afferent  fibers.  The  efferent  splanch- 
nic fibers  are  derived  from  the  ventral  roots  of  the  spinal  nerves  and  terminate  in  great  part 
about  the  cells  of  the  nearest  sympathetic  ganglion;  others  end  in  more  distant  or  in  peripheral 
gangUa.  The  afferent  splanchnic  fibers  are  chiefly  peripheral  processes  of  the  cells  of  the  spinal 
gangUa,  but  some  are  sympathetic  fibers  which  enter  the  spinal  nerve-trunk  and  terminate  about 
ceUs  of  the  spinal  ganglion.  The  gray  rami  consist  mainly  of  non-medullated  fibers  derived  from 
the  sympathetic  gangha  directly  or  through  the  trunk,  which  proceed  centrally  to  the  spinal 
nerves  and  are  distributed  along  the  somatic  divisions  of  the  latter  to  unstriped  muscle  and  glands 
as  vasomotor,  pilomotor,  and  secretory  fibers.  Some  go  to  the  membranes  of  the  spinal  cord, 
and  a  few  terminate  about  cells  of  the  spinal  gangha  as  sensory  sympathetic  fibers. 

Similar  but  more  complex  and  irregular  communications  which  exist  between 
the  sympathetic  system  and  the  cranial  nerves — with  the  exception  of  the  first 
and  second — have  been  referred  to  in  the  accounts  of  the  nerves. 

It  is  convenient  for  descriptive  purposes  to  divide  the  sympathetic  system  into 
cephalic,  cervical,  thoracic,  abdominal,  and  pelvic  parts. 

1.  The  cephaUc  part  (Pars  cephalica  systematis  sympathici)  comprises  the 
otic,  sphenopalatine,  and  cihary  ganglia,  which  may  be  regarded  as  homologues  of 
the  ganglia  of  the  trunk  of  other  regions.     It  also  includes  three  plexuses  formed  by 

1  The  special  statements  of  this  description  refer  to  the  system  of  the  horse.  A  few  important 
differential  features  will  be  mentioned  in  the  account  of  the  nervous  system  of  the  other  animals. 


830 


NERVOUS   SYSTEM   OF  THE   HORSE 


branches  derived  from  the  anterior  cervical  ganglion.  The  ganglion  gives  off  two 
or  three  filaments  which  subdivide  to  form  the  internal  carotid  plexus  (Plexus 
caroticus  internus)  around  the  artery  of  like  name.  The  cavernous  plexus  (Plexus 
cavernosus)  surrounds  the  artery  within  the  cavernous  sinus  and  communicates 
with  that  of  the  opposite  side.  The  external  carotid  plexus  (Plexus  caroticus 
externus)  is  formed  around  the  homonymous  artery,  and  filaments  from  it  go  to  the 
vessel  and  its  branches  and  to  the  salivary  glands. 

2.  The  cervical  part  (Pars  cervicalis  s.  sympathici)  includes  two  ganglia  and 
the  trunk  which  connects  them. 

The  anterior  or  superior  cervical  ganglion  (G.  cervicale  craniale)  lies  on  the 
guttural  pouch  below  the  occipito-atlantal  articulation  (Fig.  562).  It  is  reddish- 
gray  in  color,  fusiform,  and  about  an  inch  (ca.  2-3  cm.)  in  length.  It  is  connected 
by  rami  communicantes  with  the  last  four  cranial  and  first  cervical  nerves,  sends 
branches  to  form  the  plexuses  mentioned  above,  and  contributes  to  the  pharyngeal 
plexus. 

The  cervical  trunk  of  the  sympathetic  connects  the  anterior  and  posterior 


Fig.  660. — Right  Cervico-thoracic  Ganglion  and 
Rel.^.ted  Structures  of  Horse. 
G,  G',  Ganglia;  S,  sympathetic  trunk;  V,  vagus; 
R,  recurrent  nerve;  V.c,  cardiac  nerves,  CA'III,  T.I., 
rami  communicantes  from  eighth  cervical  and  first  thor- 
acic nerves;  -V./r.,  nervus  transversarius;  r.b.,  brachio- 
cephalic trunk;  A.d.c,  dorso-cervical  artery;  A.b.d., 
right  brachial  artery;  A.c.c,  common  carotid  artery. 


N-C. 


Fig.  661. — Left  Cervico-thoracic  G.u^glion  and 
Related  Structures  of  Hokse. 
G,  6",  Ganglia;  S,  sympathetic  trunk;  V,  vagus; 
R,  recurrent  nerve;  C.VII,  C.VIII,  T.I,  rami  com- 
municantes from  last  two  cervical  and  first  thoracic 
nerves;  N.tr.,  nervus  transversarius;  N.c,  cardiac 
nerves. 


cervical  ganglia.  On  leaving  the  former  it  is  associated  in  a  common  sheath  with 
the  vagus  along  the  dorsal  face  of  the  common  carotid  artery.  At  the  root  of  the 
neck  it  separates  from  the  vagus  and  joins  the  posterior  cervical  ganglion. 

The  posterior  or  inferior  cervical  ganglion  (G.  cervicale  caudale)  is  situated 
imder  cover  of  the  first  rib  and  the  insertion  of  the  scalenus  (Figs.  660,  661).  On 
the  right  side  it  lies  upon  the  longus  colli  and  the  trachea,  on  the  left  side  upon  the 
same  muscle  and  the  oesophagus.  It  is  flattened,  very  irregular  and  variable  in 
outline,  and  is  blended  more  or  less  with  the  first  thoracic  ganglion,^  so  that  the  two 
may  be  considered  together  as  the  ganglion  stellatum.  This  receives  at  its  antero- 
dorsal  angle  the  nervus  transversarius,  which  accompanies  the  vertebral  artery 
in  the  canalis  transversarius;  it  is  a  trunk  formed  by  the  rami  communicantes  of 
the  cervical  nerves  except  the  first  and  last.  Large  rami  connect  with  the  last 
cervical  and  first  and  second  thoracic  nerves.  Filaments  also  connect  with  the 
vagus.  From  the  ventral  part  of  the  ganglion  proceed  the  carchac  nerves  now  to 
be  described. 

1  In  some  cases  there  exists  a  more  or  less  distinct  middle  cer\acal  ganglion  which  receives 
the  filaments  from  the  vagus  and  is  connected  with  the  posterior  cervical  ganghon  by  a  trunk.  It 
occurs  oftenest  on  the  right  side  and  gives  off  one  or  two  cardiac  nerves. 


THE    SYMPATHETIC    NERVOUS    SYSTEM  831 

The  cardiac  nerves  (Nn.  cardiaci)  are  formed  by  branches  from  the  posterior 
cervical  and  first  thoracic  gangha,  together  with  twigs  from  the  sympathetic  trunks 
and  the  vagi.  They  form  the  cardiac  plexus  (P.  cardiacus)  on  the  ventral  face  of  the 
trachea  with  each  other  and  with  branches  of  the  vagus  and  recurrent  nerves. 
They  are  subject  to  considerable  variation,  but  their  general  arrangement  may  be 
stated  as  follows: 

(a)  On  the  right  side  there  are  usually  two  cardiac  nerves.  Of  these  one 
passes  back  with  the  vagus  in  the  angle  between  the  right  brachial  artery  and  the 
bicarotid  trunk,  pierces  the  pericardium,  crosses  the  aortic  arch,  and  divides  into 
branches  which  are  mingled  with  those  of  the  left  nerves.  The  second  crosses 
obliquely  over  the  right  face  of  the  trachea  and  joins  the  vagus,  where  the  latter 
gives  off  the  right  recurrent  nerve;  a  small  plexus  is  formed  here,  from  which  two 
or  three  cardiac  branches  are  detached.  These  pass  back  beneath  the  trachea  and 
ramify  on  the  atria  and  ventricles. 

(6)  On  the  left  side  there  are  commonly  three  cardiac  nerves.  One  of  these  is 
distributed  to  the  great  vessels  in  the  anterior  mediastinum.  The  largest  passes 
back  at  first  with  the  vagus  beneath  the  arch  of  the  left  brachial  artery,  inclines 
downward,  perforates  the  pericardium,  and  divides  into  two  branches.  One 
branch  passes  beneath  the  bifurcation  of  the  pulmonary  artery  and  is  distributed 
to  the  left  atrium.  The  larger  branch  dips  in  between  the  aorta  and  the  pulmonary 
artery,  gives  tAvigs  to  these  vessels,  and  ramifies  on  the  ventricles,  especially  along 
the  course  of  the  right  coronary  artery.  The  third  nerve  crosses  the  deep  face  of 
the  left  brachial  artery,  passes  back  below  the  trachea,  and  unites  with  filaments 
of  a  right  cardiac  nerve.  It  passes  around  the  aorta  and  ramifies  chiefly  along  the 
course  of  the  left  coronary  artery  on  the  left  face  of  the  ventricles. 

3.  The  thoracic  part  (Pars  thoracalis  systematis  sympathici)  extends  back- 
ward ventral  to  the  costo-vertebral  joints  from  the  posterior  cervical  ganglion  to  the 
crura  of  the  diaphragm,  and  passes  between  the  latter  and  the  psoas  minor  to  be  con- 
tinued by  the  abdominal  part. 

The  trunk  is  concealed  in  the  first  part  of  its  course  by  the  subcostal  vessels 
and  the  lateral  border  of  the  longus  colli,  but  further  back  it  is  visible  under  the 
pleura. 

The  ganglia  are  arranged  segmentally  at  each  intercostal  space  and  partly  on 
the  heads  of  the  ribs.  They  are  flattened  and  are  small  and  fusiform,  with  the 
exception  of  the  first.  This  (G.  thoracale  primum)  is  extensive,  irregularly  quadri- 
lateral in  outline,  and  is  united  with  the  posterior  cervical  ganglion,  as  previously 
mentioned.  The  ganglia  are  connected  with  the  thoracic  nerves  by  white  and  gray 
rami  communicantes.  Distinct  ganglia  may  be  absent  at  two  or  three  spaces 
succeeding  the  first,  and  here  the  trunk  is  thickened  and  contains  ganglion  cells. 

The  visceral  branches  comprise  aortic,  cardiac,  pulmonary,  and  oesophageal 
branches,  and  the  splanchnic  nerves.  The  aortic  branches  ramify  on  the  thoracic 
aorta,  forming  around  that  vessel  the  thoracic  aortic  plexus  (P.  aorticus  thoracalis). 
The  cardiac  branches  concur  with  those  of  the  vagus  in  forming  the  cardiac  plexus 
(P.  cardiacus).  From  this  branches  go  to  form  the  coronary  plexuses  (P.  coronarii) 
along  the  course  of  the  vessels  of  like  name.  The  pubnonary  branches  join  with 
corresponding  branches  of  the  vagus  and  filaments  from  the  cardiac  plexus  in 
forming  the  pulmonary  plexus  (P.  pulmonalis)  at  the  root  of  the  lung.  Branches 
of  the  plexus,  on  which  are  minute  ganglia,  ramify  with  the  bronchi  in  the  substance 
of  the  lung.^  The  oesophageal  branches  join  with  those  of  the  vagus  in  the  forma- 
tion of  the  oesophageal  plexus  (P.  oesophageus). 

The  great  splanchnic  nerve  (N.  splanchnicus  major)  arises  by  a  series  of  roots 
derived  from  the  sixth  or  seventh  to  the  fourteenth  or  fifteenth  thoracic  ganglia 

1  The  right  and  left  plexuses  communicate  with  each  other,  so  that  both  lungs  receive  fibers 
from  both  vagi. 


832  NERVOUS    SYSTEM   OF   THE   HORSE 

inclusive.  It  extends  along  the  bodies  of  the  vertebrae  medio-ventral  to  the  thoracic 
trunk,  then  crosses  the  latter  ventrally,  passes  back  between  the  crus  of  the  dia- 
phragm and  the  lateral  border  of  the  psoas  minor,  and  joins  the  coeliaco-mesenteric 
ganglion.  It  is  small  at  its  origin,  but  becomes  considerably  larger  than  the  sym- 
pathetic trunk.  Near  its  termination  it  may  present  a  small  splanchnic  ganglion, 
from  which  and  from  the  nerve  filaments  go  to  the  aorta,  the  oesophagus,  and  the 
vertebrae.  The  fibers  of  the  nerve  are  derived  chiefly  from  the  spinal  cord;  hence 
its  white  appearance  as  compared  with  the  sympathetic  trunk. 

The  small  splanchnic  nerve  (N.  splanchnicus  minor)  is  formed  by  roots  derived 
from  the  last  two  or  three  thoracic  ganglia.  It  runs  back  with  the  great  splanchnic 
nerve,  but  ends  in  the  coeliac  or  in  the  renal  and  adrenal  plexuses. 

The  splanchnic  nerves  are  quite  variable.  The  greater  splanchnic  is  often  blended  more  or 
less  with  the  sympathetic  trunk  and  may  be  separate  only  in  the  posterior  part  of  the  thorax. 
The  lesser  splanchnic  may  be  included  in  the  greater,  and  thus  appear  to  be  absent.  Its  roots 
communicate  by  filaments  with  the  great  splanchnic. 

4.  The  abdominal  part  of  the  sympathetic  trunk  (Pars  abdominalis  systematis 
sympathici)  lies  along  the  medial  border  of  the  psoas  minor,  above  the  aorta  on  the 
left  side  and  the  posterior  vena  cava  on  the  right  (Fig.  656) .  The  trunk  is  smaller 
than  the  thoracic  part,  and  presents  usually  six  small  fusiform  lumbar  ganglia  (G. 
lumbalia),  which  are  connected  by  rami  communicantes  with  the  ventral  divisions 
of  the  lumbar  nerves.  Visceral  branches  go  to  the  aortic  and  pelvic  plexuses 
and  to  the  coeliaco-mesenteric  ganglion. 

5.  The  pelvic  and  caudal  part  of  the  sympathetic  trunk  (Pars  pelvina  et  cau- 
dalis  systematis  sympathici)  begins  at  the  last  lumbar  ganglion  and  extends  along 
the  pelvic  surface  of  the  sacrum  medial  to  the  emergence  of  the  veni^ral  branches 
of  the  sacral  nerves  (Fig.  576).  At  the  third  or  fourth  segment  of  the  sacrum  the 
trunk  divides  into  medial  and  lateral  branches.  The  medial  branch  inclines  to  the 
median  plane  and  unites  with  the  opposite  branch.  At  the  junction  there  is  often 
found  the  small  coccygeal  ganglion  (G.  impar),  which  lies  on  the  coccygeal  artery 
at  the  joint  between  the  first  and  second  coccygeal  vertebrae.  A  filament  from  the 
ganglion  accompanies  the  artery.  The  lateral  branch  communicates  with  the  last 
two  sacral  nerves  and  joins  the  ventral  coccygeal  nerves.  Sacral  ganglia  (G. 
sacralia)  occur  near  each  of  the  first  three  sacral  foramina,  and  are  connected  by 
gray  rami  communicantes  with  the  ventral  branches  of  the  sacral  nerves.  The 
visceral  branches  are  distributed  through  the  pelvic  plexus.  They  supply  motor 
fibers  to  the  longitudinal,  and  inhibitory  fibers  to  the  circular,  muscular  coat  of  the 
rectum;  motor  fibers  to  the  bladder  and  uterus;  and  the  vaso-dilator  fibers  (Nn. 
erigentes)  to  the  penis. 

According  to  von  Schumacher,  minute  segmental  coccygeal  ganglia  occur  along  the  caudal 
branches  of  the  sympathetic  trunk.  The  lateral  branch  is  regarded  by  van  der  Broek  as  an 
aggregate  of  rami  communicantes. 


THE  ABDOMINAL  AND  PELVIC  PLEXUSES 
The  chief  plexuses  which  distribute  nerves  to  the  viscera  and  vessels  of  the 
abdominal  and  pelvic  cavities  are  two  in  number,  the  coeliac  and  the  pelvic.     From 
them  fibers  proceed  to  form  numerous  subsidiary  plexuses  which  are  named  accord- 
ing to  the  organs  which  they  supply  or  the  vessels  which  they  enlace. 

The  coeliac  plexus  (Fig.  575)^  is  situated  on  the  dorsal  wall  of  the  abdominal 
cavity,  in  relation  to  the  aorta  and  the  origin  of  its  chief  visceral  branches.  It  is 
formed  by  the  splanchnic  nerves,  branches  of  the  vagi,  and  filaments  from  the 
anterior  lumbar  ganglia  of  the  sympathetic.  It  contains  the  coeliaco-mesenteric 
ganglia.  From  the  coeliac  plexus  and  its  ganglia  subsidiary  plexuses  are  continued 
upon  the  branches  of  the  aorta. 

^  Also  known  as  the  solai*  plexxis. 


THE   ABDOMINAL   AND    PELVIC    PLEXUSES  833 

The  ccBliaco-mesenteric  ganglia  (G.  coeliaco-mesenterica)i  are  two  in  number, 
right  and  left.  They  are  situated  on  each  side  of  the  aorta,  in  relation  to  the  origin 
of  the  coeliac  and  anterior  mesenteric  arteries.  The  right  ganglion  is  concealed  by 
the  posterior  vena  cava;  it  is  irregularly  quadrilateral  and  is  about  two  inches  (4- 
6  cm.)  in  length.  The  left  ganglion  is  largely  covered  by  the  left  adrenal;  it  is 
narrower  than  the  right  one  and  is  three  or  four  inches  (ca.  8-10  cm.)  long.  The 
two  ganglia  are  united  by  irregular  connecting  branches  in  front  of  and  behind  the 
anterior  mesenteric  artery.^  Each  receives  the  great  splanchnic  nerve  of  its  own 
side  and  branches  from  the  dorsal  oesophageal  continuation  of  the  vagus  nerves. 
Branches  from  the  ganglia  and  the  cords  which  connect  them  pass  back  to  the 
posterior  mesenteric  ganglion  which  is  situated  at  the  origin  of  the  posterior  mesen- 
teric artery. 

The  following  unpaired  plexuses  proceed  from  the  coeliac  plexus  and  coeliaco- 
mesenteric  ganglia : 

1.  The  abdominal  aortic  plexus  (P.  aorticus  abdominalis)  occurs  along  the 
abdominal  aorta.  It  is  connected  with  the  renal  plexuses  and  behind  with  the 
pelvic  plexus.     It  receives  filaments  from  some  of  the  sympathetic  lumbar  ganglia. 

2.  The  gastric  plexus  (P.  gastricus)  enlaces  the  gastric  artery  and  divides  like 
the  artery  into  two  parts,  forming  the  anterior  and  posterior  gastric  plexuses. 
These  receive  branches  of  the  vagus  nerves. 

3.  The  hepatic  plexus  (P.  hepaticus)  is  formed  by  several  nerves  of  consider- 
able size  which  accompany  the  hepatic  artery  and  the  portal  vein.  It  receives 
fibers  from  the  left  vagus,  ramifies  in  the  liver,  and  gives  off  branches  which 
accompany  the  collateral  branches  of  the  hepatic  artery  and  supply  the  areas  in 
which  these  vessels  are  distributed. 

4.  The  splenic  plexus  (P.  lienalis)  resembles  the  preceding  in  its  arrangement. 
In  addition  to  its  terminal  branches  to  the  spleen  it  gives  collateral  twigs  to  the 
pancreas  and  the  left  part  of  the  greater  curvature  of  the  stomach. 

5.  The  anterior  mesenteric  plexus  (P.  mesentericus  cranialis)  is  formed 
mainly  by  branches  from  the  posterior  part  of  the  cceliaco-mesenteric  ganglia;  it 
is  continuous  with  the  coeliac  plexus  in  front  and  the  posterior  mesenteric  behind. 
It  surrounds  the  anterior  mesenteric  trunk  and  its  branches,  and  supplies  the  viscera 
to  which  these  vessels  are  distributed. 

The  posterior  mesenteric  ganglion  (G.  mesentericum  caudale)  is  unpaired;  it 
is  irregularly  stellate,  and  is  situated  on  the  origin  of  the  posterior  mesenteric 
artery.  It  is  connected  with  the  cceliaco-mesenteric  ganglia  by  anastomosing 
branches  which  concur  in  the  formation  of  the  aortic  plexus.  Two  or  more  pairs 
of  nerves  proceed  from  it  posteriorly.  One  of  these,  the  internal  spermatic  nerve 
(N.  spermaticus  internus),  accompanies  the  spermatic  artery  to  the  spermatic  cord 
and  testicle  in  the  male;  in  the  female  it  goes  to  the  ovary,  uterine  tubes,  and 
adjacent  part  of  the  uterine  horn.  These  concur  in  the  formation  of  the  spermatic 
and  utero-ovarian  plexuses.  The  other  branches  from  the  ganglion  pass  back  to 
the  pelvis  ventral  to  the  great  vessels  and  concur  in  the  formation  of  the  pelvic 
plexuses. 

The  posterior  mesenteric  plexus  (P.  mesentericus  caudalis)  accompanies  the 
artery  of  like  name  in  its  distribution. 

The  secondary  plexuses  which  accompany  the  branches  of  the  mesenteric  arteries  give  off 
branches  which  form  two  fine  peripheral  plexuses  in  the  wall  of  the  intestine.  One  of  these,  the 
myenteric  plexus  (P.  myentericus) ,  or  plexTis  of  Auerbach,  hes  between  the  layers  of  the  mus- 
ciUar  coat,  and  is  provided  wdth  microscopic  gangha.  The  other  is  in  the  submucous  tissue,  and 
is  therefore  termed  the  submucous  plexus  (P.  submucosus)  or  plexus  of  Meissner. 

1  It  has  been  customary  to  designate  these  in  veterinary  works  as  the  semilunar  or  coeliac 
ganglia,  but  in  the  horse  they  evidently  include  the  anterior  mesenteric  gangUa  as  well. 

2  A  good  preparation  of  the  ganglia  in  the  horse  is  often  difficult  to  obtain  on  account  of 
aneurysm  of  the  artery  and  the  formation  of  a  quantity  of  connective  tissue  about  it. 

53 


834  THE   NEKVOUS    SYSTEM    OF  THE   OX 

The  following  paired  plexuses  are  derived  mainly  from  branches  of  the  coeliac 
and  aortic  plexuses: 

1.  The  renal  plexuses  (P.  renales)  proceed  largely  from  the  coeliaco-mesenteric 
ganglia,  but  receive  fibers  also  from  the  small  splanchnic  nerves.  They  enlace  the 
renal  arteries  and  supply  the  kidneys.  Minute  renal  ganglia  occur  on  the  course 
of  the  nerves  along  the  renal  vessels. 

2.  The  adrenal  plexuses  (P.  suprarenales)  are  formed  by  a  relatively  very 
large  number  of  fine  fibers  derived  in  great  part  directly  from  the  coeliaco-mesen- 
teric ganglia.     Numerous  minute  ganglia  occur  in  their  meshes. 

3a.  The  spermatic  plexuses  (P.  spermatid)  proceed  from  the  aortic  plexus 
and  branches  from  the  posterior  mesenteric  ganglion.  Each  accompanies  the 
corresponding  (internal)  spermatic  artery  to  the  testicle. 

36.  The  utero-ovarian  plexuses  (P.  ovarici)  are  the  homologues  in  the  female 
of  the  preceding.  They  accompany  the  utero-ovarian  arteries  to  the  ovary  and  the 
cornua  of  the  uterus. 

The  pelvic  plexuses  (P.  hypogastrici)  are  the  pelvic  continuations  of  the  aortic 
and  posterior  mesenteric  plexuses.  Two  or  more  nerves  proceed  from  the  posterior 
mesenteric  ganglion  and  enter  the  pelvic  cavity  ventral  to  the  large  vessels,  anasto- 
mose with,  each  other  and  ^yith.  branches  from  the  sacral  nerves — especially  the 
third  and  fourth — and  ramify  on  the  pelvic  viscera.  The  peripheral  plexuses 
derived  therefrom  are  named  according  to  the  organs  which  they  supply;  the  chief 
of  these  are  the  haemorrhoidal,  vesical,  utero- vaginal,  prostatic,  cavernous  (of  the 
penis  or  clitoris)  (P.  hsemorrhoidalis,  vesicalis,  uterovaginalis,  cavernosus  penis  s. 
clitoridis,  etc.).    Others  enlace  the  arteries  (P.  iliacus,  femoralis,  etc.). 


THE  NERVOUS  SYSTEM  OF  THE  OX^ 

The  spinal  cord  resembles  that  of  the  horse  in  conformation  and  structure. 
In  cattle  of  medium  size  its  length  is  about  165  to  170  cm.  (ca.  65-67  inches),  and 
its  weight  about  240  to  250  grams  (ca.  8  ounces). 

In  a  cow  140  cm.  in  height  Dexler  found  the  weight  of  the  cord  (including  the  intradural 
nerve-roots)  to  be  260  gm.  and  the  length  162  cm.  The  lengths  of  the  regions  were:  cervical  41 
cm.,  thoracic  72  cm.,  lumbar  32  cm.,  sacral  7  cm. 

The  brain  has  an  average  weight  of  about  500  grams  (ca.  16-17  ounces). 
Its  differences  in  general  form  are  correlated  with  those  noted  in  the  consideration 
of  the  cranial  cavity. 

The  medulla  oblongata  is  short,  wide,  and  thick.  Its  ventral  face  is  strongly 
convex.  The  pyramids  are  narrow,  short,  and  close  together  in  front.  Near  the 
decussation  there  is  a  well-defined  oval  prominence  on  either  side  which  indicates 
the  position  of  the  posterior  olive.  The  corpus  trapezoideum  is  large;  it  has  no 
cer-tral  part  between  the  pyramids.  The  external  arcuate  fibers  are  distinct.  The 
restiform  bodies  are  short  and  thick  and  diverge  more  strongly  than  in  the  horse. 
The  floor  of  the  fourth  ventricle  is  only  about  two-thirds  as  long  as  in  the  horse. 
The  area  acustica  is  a  well-marked  oval  prominence  lateral  to  the  middle  part  of 
the  limiting  sulcus.  The  tuberculum  acusticum  at  the  origin  of  the  acoustic  nerve 
is  very  large.  The  anterior  fovea  is  distinct.  The  posterior  recess  of  the  fourth 
ventricle  communicates  through  a  median  aperture  (Apertura  mediana)-  with  the 
subarachnoid  space. 

^Only  the  most  salient  differences  as  compared  with  the  horse  will  be  mentioned. 
2  Also  known  as  the  foramen  of  Magendie. 


THE    NERVOUS    SYSTEM    OF   THE   OX 


835 


The  pons  is  smaller,  both  transversely  and  longitudinally,  than  that  of  the 
horse.     It  is  strongly  convex  and  has  a  distinct  central  depression. 

The  cerebellum  is  smaller  and  more  angular  in  form  than  in  the  horse.  The 
vermis  is  large  and  has  a  distinct  depression  on  its  anterior  face  for  the  posterior 
corpora  quadrigemina.  The  hemispheres  are  relatively  small  and  are  not  clearly 
divided  into  tabulations.     The  anterior  peduncles  are  very  short,. 

The  cerebral  peduncles  are  short.     A  small  eminence  in  the  interpeduncular 

Longitudinal       Olfactory 

fissure  bulb  Frontal  pole 


Transverse  fissure 


Occipital  pole 
'^rjhcllum 


Medulla  oblongata 


Fig.  662. — Brain  of  Ox;  Dorsal  View. 
1,  Lateral;    2,  suprasylvian ;   3,  coronal;   4,  transverse;   o,  marginal; 
Marginal  or  sagittal  pole. 


itomarginal ;  7,  ectomarginal.     8, 


is  caused  by  the  presence  of  the  interpeduncular  ganglion.  The  medial  gen- 
iculate body  is  prominent.  The  pineal  body  is  long  and  fusiform,  and  is  often 
pigmented  in  spots.  The  third  ventricle  forms  two  considerable  recesses  in  rela- 
tion to  the  pineal  body:  one  (R.  pinealis)  extends  up  into  the  body;  the  other 
(R.  suprapinealis)  is  a  long  tubular  prolongation  in  front  of  it. 

The  optic  tracts  cross  the  cerebral  peduncles  almost  at  a  right  angle. 

The  hypophysis  or  pituitary  body  is  situated  in  a  deep  fossa  and  is  surrounded 


836 


THE    NERVOUS    SYSTEM    OF   THE    OX 


l)y  a  plexus  of  vessels.     It  is  much  narrower  and  thicker  than  that  of  the  horse. 
The  infiindibulum  is  relatively  long  and  slopes  do\^^lward  and  backward. 

The  cerebral  hemispheres  are  shorter,  higher,  and  relatively  wider  than  in  the 
horse.  The  frontal  poles  are  small,  the  occipital,  large.  The  length  from  pole  to 
pole  is  about  the  same  as  the  greatest  transverse  diameter  of  the  two  hemispheres. 

Longitudinal  fissure 


Fig.  663. — Base  of  Brain  of  Ox. 
1,  Olfactory  bulb;  2,  2',  olfactory  strise;  3,  trigonum  olfactorium;  4,  fossa  lateralis;  5,  piriform  lobe;  6,  optic 
chiasma;  7,  optic  tract;  8,  tuber  cinereum;  9,  cerebral  peduncle;  10,  pons;  11,  corpus  trapezoideum;  12,  pyramid; 
IS,  cerebellum;  14,  chorioid  plexus  of  fourth  ventricle;  C.I.,  first  cervical  nerve  roots.  The  stumps  of  the  cranial  nerves 
are  designated  by  Roman  numerals.  The  hypophysis  has  been  removed  and  its  contour  is  indicated  by  dotted  line. 
The  central  black  area  is  the  infundibular  recess  of  the  third  ventricle  opened  up  when  the  infundibulum  is  torn  off. 


Viewed  from  the  side,  the  dorsal  surface  is  strongly  convex.  The  highest  point  of 
the  dorso-medial  border  is  a  little  in  front  of  its  middle  and  forms  a  marked  promi- 
nence termed  the  sagittal  or  marginal  pole  (Polus  sagittalis  s.  prominentia  mar- 
ginalis  dorsalis).  Anterior  to  this  the  border  drops  abruptly,  being  cut  into  by  the 
deep  transverse  fissure.  The  arachnoid  on  the  basal  and  anterior  parts  of  the 
hemispheres  is  usually  pigmented.     The  corpus  callosum  extends  through  a  little 


THE   NERVOUS   SYSTEM    OF   THE    OX 


837 


more  than  a  third  of  the  length  of  the  hemisphere.     The  pattern  of  the  fissures 
and  gyri  of  the  palHum  is  somewhat  simpler  than  in  the  horse. 

.•  n  ^"  ^^^  lateral  fissure  (of  Sylvius)  is  very  deep.  Its  middle  branch  extends  almost  ver- 
ticaUy  upward  on  the  middle  of  the  lateral  surface  of  the  hemisphere,  and  is  separated  by  a  gyrus 
■  X^^^}^'^^^  width  trom  the  suprasylvian  fissure.  The  anterior  branch  runs  forward  about  parallel 
with  the  sulcus  rhinahs  anterior,  from  which  it  is  separated  by  the  short  gyri  of  the  insula  The 
ktter  are  covered  to  a  small  extent  only  by  the  overhanging  gyri  (operculum).  The  posterior 
branch  may  run  back  a  distance  of  only  about  1.5  cm.  and  end  in  T-shaped  manner,  or  it  mav 
join  the  sulcus  rhinahs  posterior. 

2    The  suprasylvian  fissure  is  deep  and  very  distinct.     It  extends  in  an  undulating  manner 
trom  the  lateral  surface  of  the  occipital  pole  to  the  lateral  side  of  the  sagittal  pole.     Here  it  may 


Marginal  pole 


hell  II 


Olfactory     Olfactory 
I  nfundibulum        tract  bulb 

Hypophysis  or  pituitary  body 


Corpus 
Medulla  trape- 
oblongata     zoideum 

Fig.  664 
Fissures:  i,  Lateral;  iJ,  ;2,  suprasylvian;  3, 


Pons 


V  OF  Ox;  Right  View. 
4,  transverse;  J,  ectomarginal; 


diagonal;   7,  posterior  ecto- 

sylvian;  8,  presylvian;   9,  9',  rhinal  (anterior  and  posterior);    P.ch.,  chorioid  plexus  of  fourth  ventricle;  P.c,  cerebral 
peduncle;  L.p.,  piriform  lobe;   7,  insula.     Stumps  of  cranial  nerves  are  designated  by  Roman  numerals. 


be  interrupted  or  may  be  continued  by  the  coronal  fissure,  which  descends  to  the  frontal  pole 
and  divides  into  two  short  branches. 

3.  The  diagonal  fissure  (S.  diagonahs)  begins  in  front  of  the  stem  of  the  lateral  fissure  and 
runs  upward  and  forward.     Its  form  is  very  variable. 

4.  The  transverse  fissure  cuts  obUquely  into  the  dorsal  border  in  front  of  the  sagittal  pole. 
It  is  short  and  deep  and  commonly  communicates  with  the  suprasylvian  and  coronal  fissures,  but 
may  be  separated  from  the  former. 

5.  The  marginal  fissure  is  distinct.  It  extends  from  the  sagittal  pole  to  the  occipital  pole. 
It  is  flexuous  and  deviates  outward  somewhat  in  its  posterior  two-thirds. 

6.  The  entomarginal  fissure  hes  medial  and  parallel  to  the  posterior  part  of  the  preceding. 

7.  The  ectomarginal  fissure  is  lateral  and  parallel  to  the  marginal  fissure.  It  does  not  ex- 
tend so  far  in  either  direction  as  the  latter,  and  is  often  more  or  less  broken  up  by  annectant  gyri. 

8.  The  sulcus  rhinalis  is  more  open  than  in  the  horse,  since  it  is  not  overlapped  by  the  gyri 
above  it. 

9.  The  calloso-marginal  fissure  is  flexuous  and  not  so  regular  as  in  the  horse.  It  is  often 
interrupted  at  or  near  the  level  of  the  genu  of  the  corpus  callosum,  in  which  case  the  genual  fissure 
continues  it  downward. 

10.  The  cruciate  fissure  is  faint  and  is  confined  to  the  medial  surface.  It  lies  about  one  centi- 
meter in  front  of  the  transverse  fissure,  and  commonly  joins  the  caUoso-marginal  fissure  below. 


838 


THE    NERVOUS    SYSTEM    OF   THE    OX 


11.  Short  and  variable  fissures  occur  in  front  of  and  behind  the  middle  branch  of  the  lateral 
fissure  (F.  ectosyhna  anterior,  posterior). 

The  olfactory  bulb  is  much  smaller  than  m  the  horse.  The  lateral  olfactory 
stria  is  large,  the  medial  one  small  and  not  distinct. 

The  cranial  nerves  have  in  general  the  same  superficial  origin  as  in  the  horse. 
The  more  important  differences  in  other  respects  are  as  follows: 

The  oculomotor  nerve  is  larger  than  in  the  horse.  It  emerges  with  the  fourth, 
sixth,  ophthalmic  and  maxillary  nerves  through  the  foramen  orbito-rotundum. 

The  trigeminal  nerve  presents  the  following  differences  in  its  distribution: 


Cerebellum 


Olfactory 
bulb 


I  nfundibulum 
Hypophysis 


Pons     Cerebral 
peduncle 

Fig.  665. — Sagittal  Section  op  Brain  of  Ox. 
P.c,  choroid  plexuses;   V.m.,  anterior  medullary  velum;    A.c,  cerebral  aqueduct;  C.q., 


V.IV.  Fourth  ventricle 

corpora  quadrigemina;  C.p.,  posterior  commissure;  C.pin.,  pineal  body;  V.c.i.,  great  cerebral  vein;  T,  thalamus; 
y./7/.,  third  ventricle  (arrow  points  to  interventricular  foramen);  C.^v.  anterior  commissure;  L./.,  lamina  terminalis; 
Co.,  chiasma  opticum.     Fissures:   7,  callosal;  ^,  calloso-marginal;  S,  splenial;   4.  transverse;  5,  entomarginal. 


The  internal  branch  of  the  lacrimal  nerve  supplies  twigs  to  the  mucous  mem- 
brane of  the  frontal  sinus;  the  large  outer  branch  runs  backward  and  supplies  the 
corium  of  the  horn.  The  frontal  nerve  emerges  from  the  orbit  below  the  supraor- 
bital process.  The  naso-ciliary  nerve  is  large  and  sends  filaments  to  the  ocular 
muscles.  The  ciliary  ganglion  is  somewhat  larger  than  in  the  horse,  and  is  con- 
nected with  the  lower  division  of  the  oculomotor  nerve  by  several  short  filaments. 
In  consequence  of  the  absence  of  the  canine  and  upper  incisor  teeth  the  correspond- 
ing branch  of  the  infraorl^ital  nerve  is  naturally  wanting.  The  mandibular  nerve 
emerges  through  the  foramen  ovale.  The  superficial  temporal  nerve  gives  off  a 
large  branch  which  joins  the  superior  buccal  division  of  the  facial  on  the  masseter, 
about  half-way  between  the  zygomatic  arch  and  the  angle  of  the  jaw.  The  otic 
ganglion  is  larger  than  in  the  horse.  According  to  Moussu  the  buccinator  nerve 
furnishes  exeito-secretory  twigs  to  the  parotid  and  inferior  buccal  glands. 


THE    NERVOUS    SYSTEM    OF   THE    OX  839 

The  facial  nerve  divides  into  its  two  terminal  branches  before  reaching  the 
border  of  the  jaw.  The  superior  buccal  nerve  is  the  larger  of  the  two;  it  crosses 
the  masseter  much  lower  than  in  the  horse.  The  relatively  small  inferior  buccal 
nerve  runs  beneath  the  parotid  or  in  the  gland  substance  parallel  with  the  l^order 
of  the  lower  jaw,  crosses  under  the  insertion  of  the  sterno-cephalicus,  and  runs  for- 
ward along  the  depressor  labii  inferioris.     At  the  point  where  it  crosses  the  facial 


Fig.  666. — Superficial  Nerves  op  Head  of  Ox. 
Nerves:  a,  Facial;  a',  a",  a'",  superior  buccal  and  primary  branches;  6,  deep  auricular;  c,  posterior  auricular; 
rf,  d',  d",  auriculo-palpebral  and  primary  branches;  c,  parotid  plexus;  /,  digastric;  3,  ff',  inferior  buccal;  s",  anasto- 
mosis between  g  and  a';  h,  superficial  temporal;  i,  k,  I,  branches  of  infraorbital;  m,  buccinator;  m',  branch  of  m  to 
zygomaticus  and  malaris  muscles;  m",  branch  of  m  to  parotid  gland;  n,  branches  of  infra  trochlear;  o,  frontal;  p,  p', 
p",  lacrimal;  g,  dorsal  branch  of  accessory;  r,  auricular  branch  of  second  cervical;  r',  r",  branches  of  r;  s,  cutaneous 
branch  of  second  cervical;  s',  anastomotic  branch  connecting  s  and  t;  t,  t' ,  t",  third  cervical  and  branches;  u,  zygo- 
matic. Muscles:  1,  Frontalis  (part  removed) ;  2,  levator  nasolabialis  (part  removed);  3,  origin  of  levator  labii 
superioris  proprius;  4,  malaris;  5,  5',  stumps  of  zygomaticus;  6,  buccinator;  7,  masseter;  8,  sterno-cephaUcus;  10, 
cleido-mastoideus;  11,  11',  cleido-occipitalis;  12,  zygomatico-auricularis;  13,  fronto-scutularis;  14,  scuto-auricularia 
superficialis  superior;  13,  scuto-auricularis  superficialis  accessorius;  IS,  cervico-scutularis;  17,  17',  stumps  of  parot- 
ido-auricularis.  18,  18',  Remnants  of  parotid  gland;  19,  19',  mandibular  gland;  9,  jugular  vein;  30,  facial  vein. 
(.\fter  Schaehtschabel.) 

vein  and  parotid  duct  it  gives  off  an  anastomotic  branch  to  the  superior  nerve. 
The  auriculo-palpebral  nerve  is  large. 

The  vagus  bears — in  addition  to  the  relatively  large  jugular  ganglion — a 
ganglion  nodosum  at  the  point  of  origin  of  the  anterior  laryngeal  nerve.  The 
trunk  is  large.  The  phar)mgeal  branch  is  large  and  anastomoses  -with  the  anterior 
and  external  laryngeal  nerves.  The  latter  commonly  arises  directly  from  the  trunk. 
The  dorsal  oesophageal  trunk  communicates  with  the  splanchnic  nerve,  contri- 
butes twigs  to  the  hepatic  plexus,  and  ramifies  chiefly  on  the  right  surface  of  the 


840 


THE   NERVOUS    SYSTEM    OF   THE   OX 


rumen  and  the  adjacent  surface  of  the  abomasum.  The  ventral  oesophageal  trunk 
goes  to  the  left  surface  of  the  rumen;  it  supplies  branches  to  the  hepatic  plexus 
and  to  all  the  divisions  of  the  stomach. 

The  spinal  accessory  nerve  presents  two  special  features.  The  part  which 
joins  the  jugular  ganglion  bears  a  small  ganglion.  The  ventral  branch  supplies 
both  parts  of  the  sterno-cephalicus. 

The  hjrpoglossal  nerve  is  large.  It  is  connected  with  the  ventral  division  of 
the  first  cervical  nerve  by  a  branch  of  considerable  size,  and  detaches  a  long  branch 
which  runs  backward  along  the  carotid  artery. 


Median  nerve - 


nar  nerve 


Fig.  667. — Nerves  of  Distal  Part  of  Right  Fore- 
limb  OF  Ox;  Dorsal  View  (Schematic). 
p,  Dorsal  digital  nerves. 


Fig.  668. — Nerves  of  Distal  Part  of  Right  Fore- 
limb  OF  Ox;  Volar  View  (Schematic). 
;),  Volar  digital  nerves. 


The  spinal  nerves  resemble  those  of  the  horse  in  origin  and  general  arrange- 
ment. The  thoracic  nerves  number  thirteen  pairs.  The  more  important  differ- 
ences in  the  limb-plexuses  and  their  branches  are  as  follows : 

The  brachial  plexus  is  formed  by  the  ventral  branches  of  the  last  three  cervical 
and  first  thoracic  nerves;  the  second  thoracic  nerve  usually  furnishes  no  root,  but 
the  ventral  branch  of  the  sixth  cervical  goes  almost  entirely  to  the  plexus  after 
giving  off  the  nerve  to  the  rhomboideus  and  the  serratus  cervicis. 

The  differences  in  the  nerves  above  the  elbow  are  not  of  sufficient  moment 
to  receive  notice  in  this  brief  account,  but  below  this  point  there  are  naturally 


THE    NERVOUS    SYSTEM    OP   THE    OX  841 

important  special  features  correlated  chiefly  with  the  arrangement  of  the 
digits. 

The  radial  nerve  is  continued  below  the  elbow  by  a  large  cutaneous  branch. 
(N.  cutaneus  antibrachii  dorsalis)  which  emerges  at  the  lower  border  of  the  lateral 
head  of  the  triceps  and  descends  on  the  dorsal  aspect  of  the  limb.  It  commu- 
nicates above  the  carpus  with  the  lateral  cutaneous  branch  of  the  median  nerve  and 
terminates  in  three  dorsal  digital  nerves;  two  of  these  descend  along  the  axial 
or  interdigital  side  of  the  dorsal  surface  of  the  chief  digits,  and  the  third  along  the 
medial  (abaxial)  side  of  the  medial  chief  digit. 

The  ulnar  nerve  divides  at  a  variable  distance  down  the  forearm  into  two 
branches.  The  dorsal  (or  superficial)  branch  emerges  between  the  tendons  of  the 
ulnaris  lateralis  and  flexor  carpi  ulnaris,  and  is  continued  as  the  lateral  dorsal 
digital  nerve  on  the  lateral  chief  digit.  The  volar  (or  deep)  branch  descends  along 
the  superficial  digital  flexor,  gives  a  branch  to  the  suspensory  ligament  below  the 
carpus,  and  unites  with  the  lateral  branch  of  the  median  nerve  to  form  the  lateral 
volar  digital  nerve  (N.  digitalis  lateralis  digiti  IV). 

The  median  nerve  is  much  larger  than  the  ulnar.  It  passes  beneath  the  prona- 
tor teres,  descends  the  forearm  as  in  the  horse,  and  divides  in  the  distal  part  of  the 
metacarpus  into  two  branches.  The  medial  branch  gives  twigs  to  the  medial  small 
digit  and  is  continued  on  the  medial  side  of  the  volar  surface  of  the  medial  chief  digit 
as  the  medial  volar  digital  nerve  (N.  digitalis  medialis  digiti  III) ;  it  also  concurs 
with  the  lateral  branch  in  forming  the  two  digital  nerves  which  descend  along  the 
interdigital  aspect  of  the  chief  digits.  The  lateral  branch  is  larger.  It  bifurcates, 
and  one  division  unites  with  the  twig  from  the  medial  branch  to  form  a  common 
digital  trunk.  From  the  latter  two  digital  nerves  proceed  as  mentioned  above; 
these  are  the  lateral  and  medial  volar  digital  nerves  of  the  medial  and  lateral 
chief  digits  respectively  (N.  digitalis  volaris  lateralis  digiti  III,  medialis  digiti  IV). 
The  other  division  unites  with  the  volar  branch  of  the  ulnar  nerve  to  form  the 
lateral  volar  digital  nerve  of  the  lateral  chief  digit  (N.  digitalis  lateralis  digiti  IV). 

The  lumbo-sacral  plexus  and  its  branches  to  the  pelvis  and  thigh  present  no 
very  striking  special  features. 

The  superficial  peroneal  nerve  is  much  larger  than  in  the  horse.  After  crossing 
beneath  the  peroneus  longus  it  passes  down  on  the  front  of  the  tarsus  and  meta- 
tarsus and  divides  into  three  branches.  The  medial  and  lateral  branches  descend 
as  the  medial  and  lateral  dorsal  digital  nerves  on  the  chief  digits.  The  larger 
middle  branch  joins  a  branch  of  the  deep  peroneal  nerve  in  the  interdigital  space, 
and  from  this  union  proceed  the  dorsal  digital  nerves  which  descend  on  the  opposed 
surfaces  of  the  chief  digits. 

The  deep  peroneal  nerve  descends  in  the  leg  as  in  the  horse,  and  continues 
down  the  dorsal  groove  of  the  metatarsus  with  the  dorsal  metatarsal  artery.  It 
gives  collateral  branches  to  the  anterior  muscles  of  the  leg  and  to  the  extensor 
digitalis  brevis.  Its  terminal  branches  concur  with  branches  from  the  superficial 
peroneal  nerve  in  the  formation  of  the  two  axial  dorsal  digital  nerves  (N.  dig.  dors, 
lat.  dig.  Ill  et  dig.  dors.  med.  dig.  IV  pedis),  and  with  a  branch  of  the  medial 
plantar  nerve  in  the  formation  of  corresponding  plantar  digital  nerves. 

The  tibial  nerve  divides  at  the  back  of  the  hock  into  medial  and  lateral  plantar 
nerves.  The  medial  plantar  nerve  descends  between  the  superficial  flexor  tendon 
and  the  suspensory  ligament  and  divides  into  two  branches;  the  medial  branch 
descends  as  the  medial  plantar  digital  nerve  (N.  dig.  plant,  med.  dig.  Ill)  along  the 
medial  side  of  the  flexor  tendons  of  the  medial  chief  digit;  the  lateral  branch  turns 
around  the  flexor  tendons  to  reach  the  interdigital  space,  where  it  concurs  ^vith  a 
branch  of  the  deep  peroneal  nerve  in  the  formation  of  two  axial  plantar  digital 
nerves  (N.  dig.  plant,  lat.  dig.  Ill  et  dig.  plant,  med.  dig.  IV),  which  descend  on 
the  opposed  surfaces  of  the  chief  digits.     The  lateral  plantar  nerve  descends  along 


842 


THE   NERVOUS    SYSTEM    OF   THE    OX 


the  lateral  border  of  the  flexor  tendons,  gives  a  branch  to  the  suspensory  ligament 
and  to  the  lateral  small  digit,  and  continues  along  the  lateral  face  of  the  lateral 
digit  as  the  lateral  plantar  digital  nerve  (N.  dig.  plant,  lat.  dig.  IV). 

The  S5rmpathetic  system  closely  resembles  that  of  the  horse  in  its  general 
arrangement,  and  only  a  few  differential  features  will  receive  attention.  The 
anterior  cervical  ganglion  is  closer  to  the  cranial  base  and  is  thicker  than  in  the 
horse;  its  ])ranehes  to  the  carotid  and  cavernous  plexuses  are  large,  and  no  con- 
nection is  formed  with  the  spinal  accessory  nerve.     The  cerv'cal  trunk  is  smaller 


Superficial 

nerve . 
Deep  peroneal  nerve . 
Saphenous  nerve 


Tibial  nerve 


Branch  of  com- 
mon peroneal 
nerve 


Lateral  plantar 
nerve 


'~Deep  branch 


Fia.  669. — Nerves  op  Distal  Part  of  Right  Hind 

Limb  or  Ox;  Dorsal  View  (Schematic). 

p,  Dorsal  digital  nerves. 


Fig.  670. — Nerves  op  Distal  Part  of  Right  Hind 

Limb  of  Ox;  Plantar  View  (Schematic). 

p,  Plantar  digital  nerves. 


than  in  the  horse,  and  arises  by  two  or  three  bundles  from  the  anterior  cervical 
ganglion  behind  its  middle.  The  posterior  cervical  ganglion  is  distinctly  separable 
from  the  first  thoracic;  the  latter  is  large.  There  are  thirteen  pairs  of  thoracic 
ganglia.  The  great  splanchnic  nerve  begins  at  the  fifth  or  sixth  thoracic  ganglion 
and  receives  branches  from  the  succeeding  ones;  it  is  commonly  difficult  to  dis- 
tinguish clearly  from  the  thoracic  trunk.  The  small  splanchnic  nerve  is  repre- 
sented apparently  by  filaments  which  go  from  the  first  lumbar  ganglion  to  the 
adrenal  plexus  and  the  coeliac  ganglion.  The  coeliac  gangUon  is  rounded  and  lies 
on  the  coeliac  artery.     The  anterior  mesenteric  gangUon  is  longer  and  is  closely 


THE    NERVOUS    SYSTEM    OF   THE    PIG 


843 


related  to  the  anterior  mesenteric  artery.  The  two  are  connected  by  gangliated 
cords,  and  are  similarly  connected  with  the  ganglia  of  the  opposite  side,  so  that  the 
arrangement  is  plexiform.  The  coeliac  plexus  is  more  complex  than  that  of  the 
horse  in  correlation  with  the  compound  character  of  the  stomach.  The  posterior 
mesenteric  ganglion  is  small  and  is  situated  behind  the  artery  of  like  name.  It 
receives  fibers  from  the  last  three  or  four  lumbar  ganglia  and  two  fasciculi  from  the 
anterior  mesenteric  ganglia.  The  pelvic  viscera  receive  branches  from  the  posterior 
mesenteric  ganglion  and  from  the 


sacral  ganglia;  the  latter  number 
five  pairs,  and  the  right  and  left 
trunks  are  connected  here  by  trans- 
verse anastomoses.  The  coccygeal 
trunks  unite  at  a  single  fourth  coc- 
cygeal ganglion,  then  separate,  and 
reunite  at  the  sixth  coccygeal  gan- 
glion. 


Longitudinal  fissure      Frontal  pole 


THE    NERVOUS    SYSTEM    OF 
THE  PIG 

The  spinal  cord  weighs  about 
one  and  a  half  ounces  (ca.  42  gm.). 
It  is  almost  circular  in  cross-section, 
except  at  the  enlargements,  where 
it  is  somewhat  flattened  dorso-ven- 
trally.  The  conus  medullaris  ex- 
tends to  the  anterior  part  of  the 
third  sacral  segment.  The  epidural 
space  is  occupied  by  a  large  quan- 
tity of  fat. 

The  brain  in  adults  of  medium 
size  weighs  about  four  to  four  and 
a  half  ounces  (ca.  125  gm.).  When 
viewed  from  above,  the  cerebrum 
has  an  elongated  oval  form.  The 
hemispheres  are  widest  at  the  pos- 
terior third.  The  occipital  pole  is 
larger  than  the  frontal  pole.  The 
medulla  oblongata  is  relatively 
broad.  The  cuneate  tubercle  is  very 
large  and  is  limited  laterally  by  a 

groove.  The  corpus  trapezoideum  is  very  wide  laterally.  The  pons  is  less  promi- 
nent than  in  the  ox.  The  cerebellum  is  very  wide  and  short.  Its  anterior  face  is 
flattened  and  presents  a  depression  for  the  corpora  quadrigemina.  The  vermis  is 
large.  The  hemispheres  consist  of  a  large  medial  part  and  a  small  lateral  part. 
The  cerebral  peduncles  are  very  short.  The  posterior  corpora  quadrigemina  are 
wide  apart,  rounded,  and  relatively  large.  The  medial  geniculate  body  is  promi- 
nent. The  cerebral  hemispheres  are  somewhat  bean-shaped  in  lateral  profile,  the 
convex  border  being  dorsal.  The  arrangement  of  the  gyri  and  sulci  is  simpler  than 
in  the  horse  or  ox. 

The  principal  fissures  are  as  follows: 

1.  The  lateral   fissure  (of   Sylvius)  begins   at   the  sulcus  rhinalis  and  runs  upward  and 
somewhat  backward  on  the  depressed  part  of  the  lateral  surface  of  the  hemisphere;   it  appears 


Cerebellum 


Medulla  oblongata 


Fig.  C71. — Brain  of  Pig;  Dorsal  View. 
Fissures:  /,  Lateral,  S,  suprasylvian,  with  anterior  (2') 
and  dorsal  {2")  branches;  3,  diagonal;  4,  coronal;  5,  presyl- 
vian;  6,  marginal;  7,  ectomarginal;  8,  entomarginal ;  9,  cruciate. 
Two  different  arrangements  of  the  coronal  and  cruciate  fissures 
are  seen  on  the  two  sides. 


844 


THE   NERVOUS    SYSTEM    OF   THE    PIG 


unbranched  on  superficial  examination,  but  when  the  gyrus  which  almost  completely  conceals  the 
insula  is  raised,  an  anterior  branch  is  exposed  which  forms  the  dorsal  boimdary  of  the  msula. 

2.  The  suprasylvian  fissure  pursues  a  curved  course  approximately  parallel  with  the 
dorso-medial  border  of  the  hemisphere.  Its  posterior  end  is  separated  by  a  short  interval  from 
the  sulcus  rhinalis  posterior.  From  its  highest  point  a  branch  proceeds  obUquely  upward  and 
forward,  crosses  the  dorso-medial  border,  and  joins  the  cruciate  fissure. 

3.  The  diagonal  fisstire  crosses  the  anterior  part  of  the  lateral  surface.  It  is  directed 
obliquely  downward  and  backward. 

4.  The  coronal  fissure  is  constant  and  deep.  It  is  directed  upward  and  medially  over 
the  frontal  pole,  continues  backward  near  the  dorso-medial  border,  and  often  ends  by  passing 
obliquely  over  the  border  to  the  medial  surface  of  the  hemisphere.  It  is  usually  continuous  in 
front  with  the  presylvian  fissure. 

5.  The  presylvian  fissure  begins — apparently  as  a  branch  of  the  sulcus  rhinalis  anterior — 
about  2  cm.  in  front  of  the  lateral  fissure,  and  curves  over  the  lateral  aspect  of  the  frontal  pole. 

6.  The  marginal  fissure  begins  behind  the  cruciate  fissure  close  to  the  dorso-medial 
border  and  extends  in  a  gentle  curve  backward  to  the  occipital  pole. 


Transverse  fissure 


Cerebellum 


Olfactory  hulh 


Hrjpophysis     Pons 


Spinal  cord 


Medulla  oblongata 
Fig.  672. — Br.\in  of  Pig;  Left  View. 
Fissures:  7, /',  sulcus  rhinalis  (anterior  et  posterior) ;  ;2,  lateral;  S,  suprasylvian;  ^,  ectomarginal;   5,  coronal, 
of  cranial  nerves  indicated  by  Roman  numerals. 


Stumps 


7.  The  ectomarginal  fissure  lies  above  and  nearly  parallel  to  the  posterior  part  of  the 
suprasylvian  fissure. 

8.  The  entomarginal  fissure  lies  along  the  posterior  part  of  the  dorso-medial  border. 

9.  The  calloso-marginal  fissure  consists  of  two  separate  parts.  The  more  extensive  pos- 
terior part  is  termed  the  splenial  fissure.  It  extends  from  the  tentorial  aspect  of  the  hemi- 
sphere in  a  direction  parallel  with  the  corpus  callosum  nearly  to  the  middle  of  the  medial 
surface;  it  is  continued  by  the  cruciate  fissure  and  may  be  also  connected  with  the  coronal  fissure 
by  a  branch  which  passes  obliquely  upward  and  forward.  The  anterior  part,  the  genual  fissure, 
lies  about  midway  between  the  anterior  part  of  the  corpus  callosum  and  the  dorso-medial  border. 

10.  The  cruciate  fissure  runs  obliquely  upward  and  forward  from  the  anterior  end  of  the 
splenial  fissure  on  the  inner  surface  of  the  hemisphere,  cuts  obliquely  into  the  dorso-medial  margin 
about  its  middle,  and  usually  joins  the  dorsal  branch  of  the  suprasylvian  fissure. 

11.  The  sulcus  rhinalis  extends  in  an  undulating  manner  along  the  entire  lower  part 
of  the  lateral  surface  of  the  hemisphere  and  forms  the  upper  limit  of  the  rhinencephalon. 

The  olfactory  bulbs  are  \evy  large  and  the  tracts  extremely  broad  and  short. 

The  trigonum  olfactorium  is  so  prominent  as  to  suggest  the  designation  tuberculum 

olfactorium. 

The  cranial  nerves  present  the  following  special  features : 

The  third,  fourth,  sixth,  and  the  ophthalmic    and  maxillary  divisions  of  the 

fifth  nerve  emerge  together  as  in  the  ox. 


THE    NERVOUS   SYSTEM   OF   THE   PIG 


845 


The  lacrimal  nerve  resembles  that  of  the  horse,  the  frontal  that  of  the  ox. 
The  naso-ciliary  nerve  is  relatively  large  and  sends  numerous  filaments  to  the  ocular 
muscles.  The  maxillary  nerve  has  a  very  short  course  in  the  pterygo-palatine 
fossa.  The  infraorbital  nerve  is  large  in  correlation  with  the  development  of  the 
snout,  which  receives  numerous  branches.  The  mandibular  nerve  emerges  through 
the  foramen  lacerum  anterius.  The  superficial  temporal  nerve  is  small;  according 
to  Moussu  it  furnishes  the  excito-secretory  fibers  to  the  upper  part  of  the  parotid 
gland,  while  those  going  to  the  lower  part  are  derived  from  the  mylo-hyoid  nerve. 

The  inferior  buccal  nerve  passes  downward  and  forward  under  cover  of  the 
parotid  gland  and  accompanies  the  parotid  duct,  with  which  it  turns  around  the 
lower  border  of  the  jaw  in  front  of  the  masseter. 

The  vagus  bears  a  jugular  ganglion  and  a  ganglion  nodosum ;  the  latter  occurs 


Ulnar 
{dorsal  branch)  — ' 


Anastomotic   _ 
branch 


"f    '  Ulnar  nerve 
'"      Dorsal  branch 


^^Deep  branch 


Fig.  673. — Nerves  op  Distal  Part  of  Right  Fore- 
limb  OP  Pig;  Dorsal  View  (Schematic). 
•c,    Dorsal   common   digital   nerves;     p,   dorsal   proper 
digital  nerves. 


Fig.  674. — Nerves  op  Distal  Part  op  Right  Fore- 
limb  OF  Pig;  Volar  View  (Schematic). 
p.  Volar  proper  digital  nerves. 


at  the  point  of  origin  of  the  anterior  laryngeal  nerve,  and  may  be  as  large  as  a  small 
pea.  Proximal  to  this  the  vagus  is  easily  divided  into  two  strands,  one  of  which  is 
the  accessory  component.  The  oesophageal  trunks  form  a  posterior  oesophageal 
plexus,  as  in  man,  from  which  two  nerves  issue.  The  ventral  nerve  is  small  and 
ramifies  on  the  parietal  surface  of  the  stomach.  The  dorsal  nerve  is  much  larger; 
it  gives  branches  to  the  stomach,  crosses  the  lesser  curvature  of  that  organ,  and 
joins  the  coeliac  plexus. 

The  hypoglossal  nerve  may  present  a  small  dorsal  root,  on  which  there  is  a 
minute  hypoglossal  ganglion. 

The  spinal  nerves  number  on  each  side  eight  in  the  cervical  region,  fourteen 
(commonly)  in  the  thoracic,  seven  in  the  lumbar,  and  four  in  the  sacral.  Some 
of  the  special  features  of  the  nerves  of  the  limbs  are  as  follows: 


846 


THE   NERVOUS   SYSTEM    OF  THE    PIG 


The  brachial  plexus  is  derived  from  the  same  nerves  as  in  the  ox,  but  the  root 
furnished  by  the  sixth  cervical  is  relatively  smaller.  The  plexus  consists  of  two 
parts,  the  upper  of  which  emerges  above  the  scalenus,  the  lower  between  the  two 
parts  of  that  muscle.  The  more  important  differences  in  the  nerves  emanating 
from  the  plexus  from  the  arrangement  in  the  ox  occur  in  the  distal  part  of  the  limb. 
The  cutaneous  branch  of  the  radial  nerve  divides  at  the  carpus  into  branches  which 
concur  with  the  dorsal  branch  of  the  ulnar  nerve  in  supplying  the  dorsal  digital 
nerves,  two  for  each  digit.  The  volar  digital  nerves,  also  two  for  each  digit,  are 
formed  by  the  terminal  branches  of  the  median  nerve  and  the  volar  or  deep  branch 
of  the  ulnar  nerve.  The  formation  and  arrangement  of  the  digital  nerves  are 
indicated  in  the  annexed  schematic  figures. 

The  lumbo-sacral  plexus  is  derived  from  the  ventral  branches  of  the  last  three 


Deep  'peroneal 
nerve 


Superficial 
peroneal  nerve 


Tibial  nerve 


Medial  plantar  __ 
nerve 


Fig.  675. — Nerves  of  Distal  Part  op  Right  Hind 

Li.MB  OF  Pig;  Dorsal  View  (.Schematic). 

p,  Dorsal  proper  digital  nerves. 


Fig.  676. — Nerves  of  Distal  Part  of  Right  Hind 

Limb  of  Pig;  Pl.vntar  View  (Schematic). 

p,  Plantar  proper  digital  nerves. 


lumbar  and  first  sacral  nerves.  The  distribution  of  the  branches  of  the  plexus 
differs  chiefly  in  the  distal  part  of  the  limb.  The  superficial  peroneal  nerve  is 
large  and  terminates  by  forming  the  greater  part  of  the  dorsal  digital  nerves. 
The  latter,  two  for  each  digit,  are  also  in  part  formed  by  the  terminal  branches  of 
the  deep  peroneal  nerve. 

The  tibial  nerve  divides  at  the  tarsus  into  medial  and  lateral  plantar  nerves. 
The  latter  divide  to  form  the  plantar  digital  nerves,  two  for  each  digit.  In  addi- 
tion, the  lateral  plantar  nerve  supplies  a  branch  to  the  dorsal  aspect  of  the  lateral 
(fifth)  digit.  The  arrangement  of  the  digital  nerves  is  indicated  by  the  annexed 
schematic  figures. 

The  sympathetic  system  of  the  pig  has  received  very  little  attention  from 
anatomists.     The  anterior  cervical  ganglion  is  long  and  fusiform.     It  gives  off 


THE    NERVOUS   SYSTEM    OF   THE   DOG  847 

filaments  which  join  the  vagus  near  the  ganglion  nodosum.  The  cervical  trunk  is 
short  and  relatively  larger  than  in  the  ox;  it  is  enclosed  in  a  common  sheath  with 
the  vagus  in  the  neck  and  separates  from  that  nerve  to  join  the  middle  cervical 
ganglion  at  the  thoracic  inlet. 


THE  NERVOUS  SYSTEM  OF  THE  DOG 

The  spinal  cord  is  almost  circular  in  cross-section  except  at  the  well-marked 
cervical  and  lumbar  enlargements,  where  it  is  compressed  dorso-ventrally.  The 
conus  medullaris  lies  over  the  junction  of  the  sixth  and  seventh  lumbar  vertebrae. 
The  length  of  the  cord  of  a  rather  large  dog  was  found  to  be  about  fifteen  inches 
(ca.  38  cm.) ;  of  this,  the  cervical  part  was  about  four  and  a  half  inches  (ca.  11  cm.), 
the  thoracic  a  little  less  than  seven  inches  (17.4  cm.),  the  lumbar  a  little  less  than 
three  inches  (ca.  7  cm.),  and  the  sacro-coccygeal  about  an  inch  (ca.  2.6  cm.) 
(Flatau-Jacobson) . 

The  brain  weighs  about  two  to  two  and  a  half  ounces  (ca.  60-70  gm.)  in  dogs 
of  medium  size,  but  there  is,  of  course,  a  wide  range  of  weight  in  the  different  breeds. 
Thus  in  small  terriers  the  weight  is  about  an  ounce  (ca.  30  gm.)  or  even  less,  while 
in  very  large  dogs  it  may  exceed  five  ounces  (ca.  150  gm.).  It  corresponds  much 
more  closely  with  the  external  form  of  the  cranium  in  size  and  general  form  than  in 
the  animals  previously  described ;  this  is  specially  true  of  the  small  breeds,  in  which 
the  bony  crests  and  frontal  sinuses  are  little  developed. 

The  medulla  oblongata  is  broad  and  thick.  Its  ventral  surface  is  strongly 
convex  from  side  to  side.  The  pyramids  are  large  and  prominent  and  are  limited 
by  a  distinct  median  fissure  and  lateral  grooves.  The  median  fissure  ends  at  a 
small  depression,  the  foramen  caecimi,  just  behind  the  pons.  The  olivary  eminence 
is  a  well-defined  oval  elevation  situated  between  the  pyramid  and  the  superficial 
origin  of  the  hypoglossal  nerve.  The  external  arcuate  fibers  form  a  wide  band 
which  crosses  the  lateral  surface  obliquely  upward  and  forward,  and  obscures 
the  facial  tubercle  and  the  groove  which  limits  the  restiform  body  laterally.  The 
cuneate  tubercle  is  distinct.  The  rhomboid  fossa  is  deep  and  narrow.  The 
fourth  ventricle  communicates  with  the  subarachnoid  space  on  each  side  through 
a  lateral  aperture. 

The  pons  is  relatively  small,  and  in  correlation  with  this  fact  the  corpus  trape- 
zoideum  is  very  wide;  it  is  divided  by  the  pyramids  into  two  lateral  parts.  The 
cerebellum  is  very  broad,  but  is  low  and  also  compressed  from  before  backward. 
Rather  more  than  half  of  it  is  overlapped  by  the  cerebral  hemispheres.  The  an- 
terior surface  is  accurately  adapted  to  the  concave  tentorial  surfaces  of  the  hemi- 
spheres and  to  the  posterior  corpora  quadrigemina  and  their  commissure.  The 
posterior  surface  is  almost  vertical  and  is  convex  centrally  and  flattened  laterally. 
The  vermis  is  prominent  and  in  general  well  defined,  although  it  is  connected  in  its 
middle  part  with  the  hemispheres.  The  latter  are  three-sided  and  consist  of  four 
lobules.  The  small  lobule  lateral  to  the  origins  of  the  facial  and  acoustic  nerves 
is  the  flocculus.  Lateral  to  this,  and  separated  from  it  by  a  deep  fissure,  is  the 
paraflocculus;  this  is  divided  into  dorsal  and  ventral  parts  by  a  sagittal  fissure. 
The  anterior  peduncles  are  very  short. 

The  posterior  corpora  quadrigemina  are  large,  very  wide  apart,  and  prominent, 
and  are  connected  by  a  curved  commissure.  The  medial  geniculate  body  is  large 
and  distinct.  In  the  deep  interpeduncular  fossa  are  two  small  bands  which  indi- 
cate the  course  of  the  fasciculi  retroflexi,  tracts  which  connect  the  habenular  and 
interpeduncular  ganglia.  The  mammillary  body  is  double.  The  tuber  cinereum 
is  relatively  large.     The  hypophysis  or  pituitary  body  is  circular  and  rather  small. 


S48 


THE  NERVOUS  SYSTEM  OF  THE  DOQ 


Fig.  677. — Base  of  Brain  op  Dog. 

Longitudinal  fissure 


Optic  nerve 

Optic  chiasm 

Optic  tract 

Hypophysis 


Cerebral  peduncU 

Pom 


Chorioid  plexus  of  fourth 
ventricle 


Olfactory  bulb 


Olfactory  tract 
Sulcus  rhinalis 


Fossa  lateralis 
Piriform  lobe 
Oculo77iotor  nerve 

Trochlear  nerve 

Trigeminal  nerve 
Abducent  nerve 
Corpus  trapezoideum 
Glosso-pharyngeal  nerve 
Vagus  nerve 

Accessory  nerve 


Spinal  cord  Median  fissure        Pyramid 

FiQ.  678.— Key  to  Fig.  677. 


THE  NERVOUS  SYSTEM  OF  THE  DOG 


849 


The  cerebral  hemispheres  are  very  broad  behind  and  diminish  in  width  an- 
teriorly; there  is  a  sudden  narrowing  at  the  frontal  poles,  which  are  flattened 
laterally.  The  tentorial  surfaces  are  concave  and  form  a  deep  cavity  which  re- 
ceives the  anterior  part  of  the  cerebellum.  The  arrangement  of  the  fissures  and 
gyri  is  simpler  than  in  the  animals  previously  examined. 

The  chief  fissures  are  as  follows: 

1.  The  lateral  fissure  extends  upward  and  backward  from  the  sulcus  rhinalis  a  little  behind 
the  middle  of  the  lateral  sm-face  of  the  hemisphere. 

2.  The  ectosylvian  fissure  has  approximately  the  shape  of  an  inverted  U,  and  curves  over 
the  lateral  fissure.     It  is  regarded  as  consisting 

of  three  parts — anterior,    middle,  and  posterior 
(F.  ectosylvia  anterior,  media,  posterior). 

3.  The  suprasylvian  fissure  hes  above  and 
approximately  concentric  with  the  preceding.  It 
also  consists  of  three  parts — anterior,  middle, 
and  posterior. 

4.  The  ectomarginal  or  collateral  fissure 
runs  forward  on  the  dorsal  aspect  of  the  hemi- 
sphere ahTiost  parallel  with  the  dorso-medial  bor- 
der. A  Uttle  in  front  of  the  middle  of  the  surface 
it  gives  off  a  short  ansate  fissure  (F.  ansata) 
which  runs  obliquely  medially  and  forward.  It 
is  usually  continued  anteriorly  by  the  coronal 
fissure,  and  may  be  in  continuity  posteriorly 
with  the  medilateral  (or  post-lateral)  fissure. 


Longitudinal  fissure 


Olfdclory  bulb 
Fruulal  pole 


Fig.  679. — Brain  Stem  of  Dog;  Dorsal  View. 

a,  Spinal  cord;  6,  dorsal  median  groove;  c,  c',  funicu- 
lus gracilis;  c",  clava;  d,  d',  funiculus  cuneatus;  d",  tuber- 
culum  cuneatum;  f,  funiculus  lateralis:  e',  tuberculum  cin- 
ereum;  /,  medulla  oblongata;  7,  II,  III,  fovese  of  floor  of 
fourth  ventricle  (fossa  rhomboidea) ;  g,  limiting  groove;  h, 
median  fissure;  i,  eminentia  inedialis;  k,  ala  cinera;  1,  I', 
pons;  m,  posterior  peduncle,  and  n,  middle  peduncle,  of  cere- 
bellum (cut);  o,  anterior  peduncle  of  cerebellum;  p,  p',  cor- 
pora quadrigemina,  anterior  and  posterior;  q,  q',  peduncles 
(brachia)  of  corpora  quadrigemina;  r,  thalamus;  s,  massa 
intermedia;  t,  stria  meduUaris;  u,  anterior  tubercle  of 
thalamus;  v,  pulvinar;  w,  corpus  geniculatum  laterale;  x, 
corpus  geniculatum  mediale.  (After  Ellenberger,  in  Leiser- 
ing's  Atlas.) 


Cerebellum 

Medulla 
oblongata 

Fig.  680. — Brain  of  Dog;  Dorsal  View. 
Fissures:  1,  Lateral;  2,  ectosylvian;  5,  suprasyl- 
vian; 4t  ectomarginal  (or  collateral);  4'>  ansate;  S, 
coronal;  6,  ectolateral;  7,  entomarginal;  8,  presylvian 
(or  orbital);  9,  cruciate;  10,  medilateral  (separated 
from  entomarginal  on  right  side,  but  connected  with  it 
on  left  hemisphere) ;  11,  i.  proreae. 


5.  The  coronal  fissure  is  usually  the 
continuation  of  the  ectomarginal.  It  runs 
forward  and  downward,  curving  around  the 
cruciate  fissure,  and  ends  behind  the  middle 
of  the  presylvian  fi.ssure. 

6.  The  ectolateral  fissure  lies  between 
the  posterior  part  of  the  ectomarginal  fissure 
and  the  suprasylvian  fissure. 

7.  The  entomarginal  fissure  lies  between  the  anterior  part  of  the  ectomarginal  fissure  and 
the  dorso-medial  border.     It  is  often  indistinct  and  not  rarely  absent. 

8.  The  presylvian  fissure — sometimes  termed  the  orbital — begins  at  the  sulcus  rhinalis, 
a  little  in  front  of  its  middle,  and  curves  over  the  anterior  third  of  the  lateral  surface  of  the  hemi- 
sphere in  front  of  the  coronal  fissure. 

54 


350  THE   NERVOUS    SYSTEM   OF  THE   DOG 

9.  The  cruciate  fissure  is  the  deepest  and  most  characteristic.  It  cuts  deeply  into  the  an- 
terior third  of  the  dorso-medial  border  and  runs  ahnost  straight  outward.  It  is  continuous  on  the 
medial  surface  of  the  hemisphere  with  the  calloso-marginal  or  splenial  fissure. 

10.  The  sulcus  rhinalis  is  continued  on  the  tentorial 
surface  of  the  hemisphere  by  the  occipito-temporal  fissure. 

7i.___:^        -.^,^^  Anteriorly  it  is  prolonged  as  the  olfactory  fissure,  which 

^.-'•''''"^         (.  — '"**v!^/^       is  concealed  by  the  oKactory  bulb  and  tract.  . 

^jf^^^ii^n    *«ni  iiii    *\,Jl^k'  11.  The  calloso-marginal  fissure  usually  consists  of 

fy^^_.       f„— -— ^    T'^-'-f         t'^o  parts,  splenial  and  genual.     The    splenial   fissure   is 

/(  ^1^    /^  'i'^^-^?^  f  Ji    ^         parallel  with  the  splenium  and  middle  part  of  the  corpus 

V*-  ^*~        '  \     /      )/  callosum  on  the  medial  surface  of  the  hemisphere.     It  is 

^'^^^^Tainmiiiii'i    iilfi^^mr     ir""*^'*^"  continuous  in  front  with  the  cruciate  fissure  and  runs  for- 

^^^^^^NIH^^^^^^  ward  and  outward  across  the  tentorial  surface  to  join  the 

^^^^^"""^  occipito-temporal  or  calcarine  fissure.      It  gives  off  from 

„      ^_,      _         „  M„.„=»=..o^       its  highest  part  the  short  accessory  cruciate  fissure.     The 

Fig.  681. — Right  Cerebral  Hemisphere  t    ^  ■  •        i    i  n   i       -xi    xi.  e 

DM       L  View  genual  fissure  is  approximately  parallel  wath  the  genu  of 

OG, .  edia  .  ^^^  corpus  callosum. 

i,Corpu.s  callosum;  i ,  genu;  /  ,  splen-  ^2.  The   suprasplenial   fissure  runs  almost  parallel 

ium  of  corpus  callosum;  a,  genual  fissure;  ^^^i  the  posterior  part  of  the  calloso-marginal  fissure  on 

6,  splenial  fissure;  c,  suprasplemal  fissure;  ^^^  -^^^^^  ^^^  tentorial  surfaces  of  the  hemisphere. 
d,  hippocampal  fissure;  e,  sulcus  corporis  ^3    rpj^^  occipito-temporal  or  calcarine  fissure  is  the 

callosi;    /,  postsplemal  fissure;    g,  lesser  continuation  on  the  tentorial  surface  of  the  hemisphere  of 

cruciate  fissure;   h,  cruciate  fissure.     (After  ^-^e  splenial  fissure. 

Ellenberger,  in  Leisering's  Atlas.)  j4    ^j^p    hippocampal    fissure    forms    the    medial 

boundary  of  the  piriform  lobe. 

The  olfactory  bulb  is  large  and  is  compressed  laterally;  its  anterior  end  pro- 
jects beyond  the  frontal  pole  of  the  hemisphere.  The  tract  is  short  and  is  also 
flattened  laterally.  Both  contain  a  narrow  cavity  which  communicates  with  the 
lateral  ventricle.     The  piriform  lobe  is  large  and  rounded. 

The  cranial  nerves  present  the  follo^\^ng  special  features  which  are  worthy  of 
notice : 

The  ophthalmic  nerve  gives  off  frontal,  long  ciliary,  ethmoidal,  and  infratro- 
chlear  branches.  The  lacrimal  nerve  arises  from  the  ophthalmic  at  its  origin;^  its 
recurrent  branch  emerges  at  the  orbital  ligament  and  concurs  with  the  zygomatic 
and  frontal  nerves  in  the  formation  of  the  anterior  auricular  plexus.  The  frontal 
nerve  emerges  from  the  orbit  in  front  of  the  upper  end  of  the  orbital  ligament, 
ramifies  in  the  upper  lid  and  the  adjacent  skin  of  the  forehead,  and  sends  branches 
backward  to  the  anterior  auricular  plexus.  The  long  ciUary  nerve  accompanies 
the  optic  nerve  and  divides  into  several  branches  which  pierce  the  posterior  part  of 
the  sclera.  The  ethmoidal  nerve  gives  off  internal  nasal  branches  and  ends  in  the 
muzzle.  The  infratrochlear  nerve  runs  forward  between  the  medial  straight  and 
the  superior  oblique  muscles  of  the  eye  and  ramifies  on  the  face  in  the  vicinity  of 
the  medial  canthus. 

The  maxillary  nerve  emerges  through  the  foramen  rotundum  and  gives  off 
five  branches.  The  lacrimal  nerve  emerges  from  the  orbit  lateral  to  the  frontal; 
its  branches  concur  with  the  frontal  and  auriculo-palpebral  nerves  in  the  formation 
of  the  anterior  auricular  plexus.  The  zygomatic  nerve  emerges  through  an  opening 
in  the  upper  part  of  the  orbital  ligament  and  ramifies  in  the  lower  lid  and  on  the 
adjacent  surface  of  the  face.  The  infraorbital  nerves,  two  in  number,  divide  within 
the  infraorbital  canal  and  after  their  emergence  upon  the  face,  thus  forming  seven 
or  eight  external  nasal  and  superior  labial  branches.  The  sphenopalatine  nerve 
gives  off  lesser  and  greater  palatine  and  posterior  nasal  nerves. 

The  mandibular  nerve  passes  out  through  the  foramen  ovale.  The  superficial 
temporal  nerve  divides  into  auricular,  temporal,  and  malar  branches;  the  last- 
named  crosses  the  masseter  and  ramifies  with  the  buccal  nerves.  The  mylo-hyoid 
nerve  is  given  off  from  the  mandibular  nerve  almost  immediately  after  the  latter 
emerges  from  the  cranium;  it  innervates  the  mylo-hyoideus  and  occipito-mandib- 
ularis  and  gives  off  a  l^ranch  which  turns  around  the  lower  jaw,  joins  the  inferior 

1  The  origin  of  the  lacrimal  nerve  is  such  that  Ellenberger-Baum  and  Martin  describe  it 
as  a  branch  o(  the  maxillary  nerve. 


THE  NERVOUS  SYSTEM  OF  THE  DOG 


851 


buccal  nerve,  and  ramifies  on  the  lateral  surface  of  the  face.  The  inferior  alveolar 
nerve  arises  by  a  common  trunk  with  the  mylo-hyoid;  it  gives  off  dental  branches 
and  terminates  in  mental  and  inferior  labial  branches.  The  lingual  nerve  supplies 
vaso-dilator  and  excito-secretory  filaments  to  the  mandibular  and  sublingual 
salivary  glands;  these  fibers  are  derived  from  the  chorda  tympani. 

The  facial  nerve  divides  near  the  posterior  border  of  the  jaw  into  four  branches. 
The  upper  branch  is  the  auriculo-palpebral  nerve,  which  divides  after  a  very  short 
course  into  anterior  auricular  and  zygomatic  branches.  The  latter  curves  upward 
and  forward  across  the  zygomatic  arch  toward  the  eye,  and  divides  into  branches 
which  supply  the  eyelids  and  nasal  region  and  concur  with  the  frontal  and  lacrimal 
nerves  in  forming  the  anterior  auricular  plexus.  The  superior  buccal  nerve  ac- 
companies the  parotid  duct  across  the  masseter.  The  inferior  buccal  nerve  runs 
forward  along  the  lower  border  of  the  masseter  and  the  mandible.     The  two  nerves 


Fig.  682. — Deep  Dissection  of  Head  of  Dog,  Showing  Especially  Trigeminal  and  Hypoglossal  Nerves. 
a,  Hypoglossal  nerve;  6,  cervical  branch  of  a;  c,  mandibular  division  of  trigeminus;  d,  lingual  nerve;  e,  nerve  to 
mandibular  gland;  /,  deep  temporal  nerve;  g,  pterygoid  nerve;  h,  buccinator  nerve  (cut);  i,  inferior  alveolar  nerve; 
k,  staphyline  branch  of  lingual  nerve;  I,  chorda  tympani;  m,  mylo-hyoid  nerve;  n,  sphenopalatine  nerve;  o,  lesser 
palatine  nerve;  p,  great  palatine  nerve;  g,  infraorbital  nerves;  r,  n.  subcutaneus  mate;  s,  branch  of  oculomotor  nerve 
to  inferior  oblique  muscle;  <,  lacrimal  nerve;  m,  frontal  nerve;  i;,  trochlear  nerve ;  li),  abducens  nerve;  i,  carotid  artery; 
^.lingual  artery;  5,  internal  maxillary  artery;  4,  m.  thyro-pharyngeus;  5,  m.  hyo-pharyngeus;  S,  m.  thyro-hyoideus; 
7,  m  sterno-hyoideus;  5,  m.  hyo-glossus;  5,  m.  genio-hyoideus;  ^0,  m.  genio-glossus;  i^,  m.  stylo-glossus;  12,  m. 
pterygoideusmedialis;  i 3,  outline  of  mandibular  gland  (dotted) ;  i4>  atlas;  ;.5,  bulla  ossea;  iff,  zygomatic  arch  (dotted;; 
17,  m.  rectus  ocuU  inferior;   18,  m.  obhquus  oculi  inferior.     (EUenberger-Baum,  Anat.  d.  Hundes.) 


ramify  on  the  cheek  and  anastomose  with  each  other  and  the  infraorbital  nerves 
to  form  a  plexus  from  which  branches  go  to  the  muscles  of  the  lips  and  nostrils. 
The  cervical  branch  runs  downward  and  backward  over  the  mandibular  gland 
and  ramifies  in  the  cervical  cutaneus  muscle;  it  communicates  with  the  inferior 
buccal  nerve  and  sends  twigs  to  the  parotido-auricularis  muscle  and  the  mandibular 
space. 

The  vagus  bears  a  jugular  ganglion  and  a  ganglion  nodosum.  The  former  is 
situated  on  the  nerve  just  before  the  emergence  of  the  latter  from  the  cranium.  The 
latter  is  situated  near  the  anterior  cervical  ganglion  on  the  rectus  capitis  ventralis 
major  and  dorsal  to  the  internal  carotid  artery;  it  is  fusiform  and  may  be  about  half 
an  inch  (ca.  1-1.5  cm.)  long  in  a  large  dog.  In  its  course  in  the  neck  the  nerve  is 
inclosed  with  the  sympathetic  trunk  in  a  common  sheath  and  is  related  ventrally 


852 


THE  NERVOUS  SYSTEM  OF  THE  DOG 


to  the  common  carotid  artery.  The  two  nerves  separate  after  entering  the  thorax 
(Figs.  613,  614).  The  right  vagus  crosses  obliquely  over  the  right  face  of  the 
trachea  and  divides  a  short  distance  behind  the  bifurcation  of  the  latter  into  dorsal 
and  ventral  branches.  The  left  vagus  crosses  the  lateral  surface  of  the  aortic  arch 
and  divides  similarly.  By  the  union  of  the  dorsal  and  ventral  divisions  of  the  two 
nerves  there  are  formed  dorsal  and  ventral  oesophageal  trunks.  The  dorsal  trunk 
concurs  with  branches  of  the  coeliac  plexus  in  forming  the  posterior  gastric  plexus 
on  the  visceral  surface  of  the  stomach.  The  ventral  trunk  ramifies  on  the  parietal 
surface  of  the  stomach,  forming  the  anterior  gastric  plexus,  from  which  a  consider- 
able branch  passes  along  the  lesser  curvature  to  the  pylorus.  Some  special  features 
of  the  collateral  branches  are :  Two  pharyngeal  branches  are  present.  The  anterior 
pharyngeal  branch  arises  from  the  vagus  above  the  ganglion  nodosum.  It  passes 
under  the  deep  face  of  the  carotid  artery  and  descends  on  the  lateral  surface  of  the 
pharynx  to  end  in  the  crico-thyroid  muscle.  It  furnishes  a  root  of  the  inferior  pharyn- 
geal branch,  and  communicates  with  the  pharyngeal  branch  of  the  ninth  and  with  the 


Fig.  683. — Nerves  of  Face  of  Dog.  Parotid  Gland  is  Removed. 
Nerves:  a,  Facial;  b,  posterior  auricular;  c,  internal  auricular;  d,  digastric;  e,  inferior  buccal;  /,  cervical  branch 
of  facial;  3,  auriculo-palpebral;  A,  superior  buccal;  i,  temporal  branch;  A;,  i',  A",  zygomatic  branch;  Z,  auriculo-tem- 
poral;  m,  malar  branch  of  I;  n,  buccinator;  o,  mylo-hyoid  branch;  p,  subcutaneus  malse;  q,  lacrimal;  r,  frontal;  s, 
infratrochlear;  t,  infraorbital.  1,  Paramastoid  process;  2,  occipito-mandibularis;  3,  base  of  concha;  4.  masseter; 
5,  zygomaticus;  6,  scutularis;   7,  zygomatic  arch;   S,  maxilla.      (EUenberger-Baum,  Anat.  d.  Hundes.) 


anterior  laryngeal  and  hypoglossal  nerves.  The  posterior  pharjmgeal  branch  is 
formed  by  the  union  of  roots  derived  from  the  anterior  pharyngeal  nerve  and  the 
ganglion  nodosum,  together  with  filaments  from  the  anterior  cervical  ganglion. 
It  crosses  the  side  of  the  pharynx  behind  the  anterior  pharyngeal  and  ramifies  on 
the  posterior  constrictor  of  the  pharynx  and  the  origin  of  the  oesophagus.  It 
contributes  filaments  to  the  pharyngeal  plexus,  communicates  with  the  recurrent 
nerve,  and  supplies  twigs  to  the  thyroid  gland.  The  pharyngeal  plexus  is  formed 
on  the  lateral  surface  of  the  pharynx  by  branches  of  the  pharyngeal  nerves  and  the 
communications  above  described;  branches  from  it  iimervate  the  muscles  and 
mucous  membrane  of  the  pharynx.  The  anterior  lar3mgeal  nerve  arises  from  the 
ganglion  nodosum  and  descends  over  the  side  of  the  pharynx,  crossing  beneath  the 
carotid  artery  and  the  anterior  laryngeal  nerve.  It  passes  through  the  thyroid 
notch  and  ramifies  in  the  mucous  membrane  of  the  larynx.  It  communicates  with 
the  anterior  cervical  ganglion  and  the  anterior  pharyngeal  branch  of  the  vagus,  and 
gives  twigs  to  the  hyo-pharyngeus  muscle.  Immediately  after  its  entrance  into  the 
larynx  it  gives  off  a  large  branch  which,  instead  of  uniting  with  the  recurrent  as  in  the 


THE    NERVOUS   SYSTEM    OF   THE   DOG  853 

other  animals,  has  a  pecuHar  arrangement.  It  runs  back  near  the  dorsal  border  of  the 
thyroid  cartilage,  gives  a  branch  to  the  crico-arytenoideus  dorsalis  as  it  passes  over 
that  muscle,  and  continues  along  the  trachea  medial  to  the  recurrent  nerve.  At  the 
thoracic  inlet  it  communicates  with  the  posterior  cervical  ganglion  and  continues 
backward  to  unite  with  the  vagus  at  or  near  the  point  of  origin  of  the  recurrent 
nerve.  Its  collateral  filaments  supply  the  trachea  and  concur  with  the  posterior 
pharyngeal  branch  in  forming  a  plexus  on  the  cervical  part  of  the  oesophagus  which 
innervates  that  tube.^  The  recurrent  nerves  present  no  remarkable  special  features. 
The  depressor  nerve  is  a  very  delicate  filament  which  arises  usually  from  the  an- 
terior laryngeal  nerve  and  is  incorporated  in  the  vago-sympathetic  trunk  to  the 
thorax.  Here  the  nerve  separates  from  the  ventral  border  of  the  vago-sympathetic 
trunk.  The  right  nerve  passes  backward  between  the  anterior  vena  cava  and  the 
trachea,  inclines  to  the  left,  and  reaches  the  medial  surface  of  the  aortic  arch.  The 
left  nerve  passes  backward  ventral  to  the  vagus  and  across  the  lateral  (left)  face 
of  the  aortic  arch.  Both  nerves  give  filaments  to  the  cardiac  nerves  and  to  the 
aorta  and  pulmonary  artery.  Their  terminal  branches  pass  between  these  vessels 
and  enter  the  wall  of  the  heart.  The  pulmonary  and  posterior  oesophageal  plexuses 
are  highly  developed. 

The  hypoglossal  nerve  gives  off  a  long  branch  (R.  descendens)  which  runs 
downward  and  backward  across  the  pharynx  and  larynx,  communicates  with  the 
ventral  branch  of  the  first  cervical  nerve,  and  supplies  the  thyro-hyoid,  sterno- 
hyoid, and  sterno-thyroid  muscles. 

The  spinal  nerves  numl^er  thirty-six  or  thirty-seven  on  either  side,  and  com- 
prise eight  cervical,  thirteen  thoracic,  seven  lumbar,  and  five  or  six  coccygeal. 

The  brachial  plexus  (Fig.  616)  is  derived  from  the  ventral  branches  of  the  last 
four  cervical  and  first  thoracic  nerves;  the  root  supplied  by  the  fifth  cervical  nerve 
is  ver}^  small.  The  roots  unite  at  the  ventral  border  of  the  scalenus.  The  more 
important  special  features  in  the  arrangement  of  the  nerves  which  emanate  from 
the  plexus  are  as  follows: 

The  musculo-cutaneous  nerve  passes  between  the  coraco-brachialis  and  the 
brachial  artery  and  descends  in  the  arm  in  front  of  the  artery.  At  the  shoulder 
joint  it  gives  off  branches  to  the  biceps  and  coraco-brachialis,  and  in  the  distal  third 
of  the  arm  is  coiuiected  with  the  median  nerve  by  an  oblique  branch.  It  terminates 
near  the  elbow  by  dividing  into  a  branch  for  the  brachialis  and  a  small  cutaneous 
nerve  which  passes  down  over  the  medial  face  of  the  elbow  and,  inclining  a  little 
forward,  descends  over  the  deep  fascia  of  the  forearm  to  the  carpus. 

The  radial  nerve  descends  behind  the  ulnar  nerve,  gives  branches  to  the 
extensors  of  the  elbow,  dips  in  between  the  medial  head  of  the  triceps  and  the 
accessory  head  of  the  anconeus,  winds  around  the  arm,  and  divides  between  the 
brachialis  and  the  lateral  head  of  the  triceps  into  two  branches.  The  deep  branch 
(R.  profundus)  supplies  the  extensor  and  supinator  muscles  on  the  forearm.  The 
superficial  branch  (R.  superficialis)  emerges  upon  the  flexor  surface  of  the  elbow 
and  divides  into  two  branches  which  terminate  by  supplying  two  dorsal  digital 
nerves  to  each  digit,  except  the  fifth,  which  receives  its  lateral  dorsal  nerve  from  the 
ulnar.  The  medial  branch  descends  along  the  medial  side  of  the  cephalic  vein  to  the 
carpus,  where  it  divides  into  dorsal  nerves  for  the  first  digit  and  the  medial  side  of 
the  second.  The  lateral  branch  is  much  larger.  It  descends  on  the  middle  of  the 
front  of  the  forearm  and  supplies  the  remaining  dorsal  digital  nerves  except  that  to 
the  lateral  side  of  the  fifth  digit. 

The  ulnar  nerve  is  as  large  as  or  larger  than  the  median,  with  which  it  is  united 
for  some  distance.  At  the  distal  third  of  the  arm  it  separates  from  the  median 
and  passes  over  the  medial  epicondyle  of  the  humerus.     At  the  proximal  part  of 

1  Lesbre  terms  this  the  tracheo-oesophageal  branch,  and  considers  that  it  must  be  regarded 
as  an  accessory  or  internal  recurrent  nerve. 


854 


THE  NERVOUS  SYSTEM  OF  THE  DOG 


the  forearm  it  gives  off  the  dorsal  branch  (R.  dorsalis),  which  supplies  cutaneous 
twdgs  to  the  dorso-lateral  surface  of  the  distal  part  of  the  forearm  and  carpus  and 
terminates  as  the  lateral  dorsal  digital  nerve  of  the  fifth  digit.  Descending  under 
cover  of  the  flexor  carpi  ulnaris,  the  ulnar  inclines  medially  under  'he  tendon  of 
insertion  of  that  muscle  and  divides  into  superficial  and  deep  branches.  The 
superficial  branch  (R.  superficialis)  descends  along  the  lateral  border  of  the  flexor 
tendons,  gives  off  the  lateral  volar  digital  nerve  of  the  fifth  digit  (N.  dig.  vol.  lat.  dig. 
V),  and  a  branch  (N.  met.  vol.  IV)  which  descends  in  the  space  between  the  fourth 
and  fifth  metacarpal  bones  and  unites  with  the  deep  branch.  The  deep  branch 
(R.  profundus)  descends  in  the  carpal  canal  and  divides  under  the  deep  flexor 


Branches  o^ 
radial  nerve 


Median  nerve  -— 


Fig.  684. — Nerves  of  Distal  Part  of  Right  Fore- 
limb  OF  Dog;  Dorsal  View  (Schematic). 
p,  Dorsal  proper  digital  nerves. 


Fig.  685. — Nerves  of  Distal  Part  of  Right  Fore- 
limb  OF  Dog;  Vol.\r  View  (Schematic). 
p,  Volar  proper  digital  nerves. 


tendon  into  its  terminal  branches.  The  smaller  of  these  supply  the  volar  meta- 
carpal muscles.  The  larger  terminals  are  the  three  volar  common  digital  nerves 
(Nn.  dig.  col.  comm.  II,  III,  IV),  which  descend  along  the  second,  third,  and  fourth 
intermetacarpal  spaces,  subdivide,  and  concur  with  the  volar  metacarpal  branches 
of  the  median  nerve  in  forming  the  volar  proper  digital  nerves  (Nn.  dig.  vol.  proprii). 
The  median  nerve  descends  behind  the  brachial  artery,  passes  over  the  medial 
epicondjde  of  the  humerus,  then  under  the  pronator  teres,  and  continues  in  the 
forearm  under  cover  of  the  flexor  carpi  radialis.  It  gives  branches  below  the  elbow 
to  the  flexor  and  pronator  muscles,  and  lower  down  a  volar  branch  to  the  skin  on 
the  medial  and  volar  aspect  of  the  carpus,  and  terminates  between  the  superficial 
and  deep  flexor  tendons  by  dividing  into  three  volar  metacarpal  nerves  (N.  met.  vol. 


THE  NERVOUS  SYSTEM  OF  THE  DOG 


855 


I,  II,  III).  These  descend  in  the  first,  second,  and  third  intermetacarpal  spaces 
and  unite  with  the  volar  common  digital  nerves  in  forming  volar  proper  digital 
nerves.  The  arrangement  of  the  digital  nerves  is  indicated  in  the  annexed  sche- 
matic figures. 

The  lumbo-sacral  plexus  is  formed  from  the  ventral  branches  of  the  last  five 
lumbar  and  first  sacral  nerves.  The  more  important  special  facts  in  regard  to  the 
nerves  of  the  pelvic  limb  are  as  follows : 

The  saphenous  nerve  (Fig.  621)  is  relatively  large,  and,  in  fact,  might  be 
considered  as  the  continuation  of  the  femoral  nerve.  It  descends  at  first  in  front 
of  the  femoral  artery,  then  passes  over  the  lower  part  of  the  medial  surface  of  the 
thigh  with  the  saphenous  artery,  continues  down  the  leg  with  the  dorsal  branch  of 


Superficial  - 
peroneal  nerve 


Dorsal  common 
digital  nerves 


Medial  plantar 
nerve 


Plantar 
common 
digital 
nerves 


Fig.  686. — Nekves  op  Distal  Part  op  Right  Hind 

Limb  op  Dog,  Dorsal  View  (Schematic). 

p,  Dorsal  proper  digital  nerves. 


Fig.  687. — Nerves  op  Distal  Part  op  Right  Hind 

Limb  of  Dog,  Plaj^tar  View  (Schematic). 

p,  Plantar  proper  digital  nerves. 


that  vessel,  and  anastomoses  with  branches  of  the  superficial  peroneal  nerve.     It 
supplies  cutaneous  twigs  from  the  stifle  to  the  metatarsus. 

The  common  peroneal  nerve  separates  from  the  tibial  above  the  origin  of  the 
gastrocnemius,  runs  downward  and  forward  across  the  lateral  head  of  that  muscle, 
passes  between  the  deep  flexor  of  the  digit  and  the  peroneus  longus,  and  divides  into 
superficial  and  deep  branches.  The  superficial  peroneal  nerve  descends  the  leg 
along  the  peroneus  tertius  and  longus,  gives  off  a  dorsal  branch  to  the  first  digit  (N. 
cutaneus  dorsalis  medialis),  and  divides  at  the  proximal  part  of  the  metatarsus  into 
three  dorsal  common  digital  nerves  (Nn.  dig.  pedis  dors.  comm.  II,  III,  IV).  These 
descend  with  the  superficial  dorsal  metatarsal  arteries  and  concur  with  branches 
of  the  deep  peroneal  nerve  in  forming  dorsal  proper  digital  nerves  (Nn.  dig.  ped. 
prop,  dorsales).     The  deep  peroneal  nerve  passes  down  the  leg  with  the  anterior 


856  THE    NERVOUS    SYSTEM    OF   THE    DOG 

tibial  vessels.  It  gives  t^^'igs  to  the  hock  joint  and  the  extensor  brevis  muscle,  and 
divides  into  three  dorsal  metatarsal  nerves  (Nn.  met.  dors.  II,  III,  IV);  these 
descend  ^\ath  the  corresponding  arteries  along  the  intermetatarsal  spaces  and  unite 
with  the  dorsal  common  digital  nerves  in  supplying  the  dorsal  proper  digital  nerves. 

The  tibial  nerve  divides  at  the  tarsus  into  two  plantar  branches.  The  medial 
plantar  nerve  descends  along  the  medial  border  of  the  superficial  flexor  tendon  and 
divides  near  the  middle  of  the  metatarsus  into  two  branches.  Of  these,  the  medial 
branch  constitutes  the  first  plantar  common  digital  nerve  (N.  dig.  comm.  plant.  I). 
The  lateral  branch  descends  on  the  superficial  flexor  tendon  and  divides  into  three 
plantar  metatarsal  nerves  (Nn.  met.  plant.  II,  III,  IV),  which  unite  with  the 
plantar  common  digital  nerves.  The  lateral  plantar  nerve  passes  down  between 
the  flexor  tendons,  sends  twigs  to  the  muscles  on  the  plantar  surface  of  the  metatar- 
sus, and  divides  into  three  plantar  common  digital  nerves  (Nn.  dig.  comm.  plant.  II, 
III,  IV).  These  descend  mth  the  deep  plantar  metatarsal  arteries  in  the  second, 
third,  and  fourth  intermetatarsal  spaces,  receive  the  plantar  metatarsal  nerves, 
and  divide  into  plantar  proper  digital  nerves,  which  pass  down  the  opposed  surfaces 
of  the  second  to  the  fifth  digits. 

The  S3mipathetic  system  presents  few  special  features  worthy  of  mention. 
The  anterior  cervical  ganglion  is  situated  behind  the  bulla  ossea  in  close  relation 
to  the  internal  carotid  artery  and  the  ganglion  nodosum  of  the  vagus.  It  is  fusi- 
form and  is  a  little  less  than  half  an  inch  (ca.  1  cm.)  long  in  a  dog  of  medium  size. 
It  forms  connections  directly  or  through  the  carotid  plexus  with  the  last  seven 
cranial  and  first  cervical  nerves.  The  cervical  trtmk  unites  with  the  vagus  so  in- 
timately as  to  form  a  vago-sympathetic  trunk.  The  posterior  cervical  ganglion 
is  situated  at  the  point  where  the  sympathetic  trunk  separates  from  the  vagus 
(Figs.  613,  614).  It  is  usually  distinct  from  the  first  thoracic  ganglion,  which  is 
stellate  and  lies  on  the  longus  colli  opposite  the  first  space.  The  two  are  connected 
by  filaments  which  cross  each  side  of  the  brachial  artery,  forming  the  ansa  sub- 
clavia.  Two  or  three  cardiac  nerves  proceed  from  these  ganglia  on  the  left  side; 
they  pass  to  the  lateral  surface  of  the  aortic  arch,  where  they  ramify  and  concur 
with  the  nerves  of  the  right  side  in  the  formation  of  the  cardiac  plexus.  On  the 
right  side  one  or  two  cardiac  nerves  appear  to  come  from  the  vagus  and  one  from 
the  first  thoracic  ganglion.  They  ramify  on  the  right  side  of  the  trachea  and  with 
those  of  the  right  side  form  the  cardiac  plexus  at  the  base  of  the  heart.  From  the 
plexus  branches  go  to  the  heart,  pericardium,  and  pulmonary  artery.  The  greater 
splanchnic  nerve  separates  from  the  posterior  part  of  the  thoracic  trunk,  most  often 
from  the  twelfth  ganglion.  It  passes  into  the  abdomen  between  the  diaphragm 
and  the  psoas  minor  and  joins  a  small  adrenal  ganglion  close  to  the  coeliac  ganglion. 
The  lesser  splanchnic  nerve  arises  from  the  last  thoracic  and  first  lumbar  ganglia. 
It  may  be  divided  into  two  or  three  strands  which  go  to  the  adrenal  plexus. 

The  cceliac  and  anterior  mesenteric  ganglia  are  separate.  The  former  is 
elongated  and  lies  along  the  posterior  face  of  the  origin  of  the  coeliac  artery.  The 
latter  is  smaller  and  rounded  and  is  in  contact  with  the  origin  of  the  anterior  mesen- 
teric artery.  On  the  left  side  the  two  ganglia  are  connected  by  a  trunk  which  is 
ganglionic  in  character.  The  coeUac,  anterior  mesenteric,  and  subsidiary  plexuses 
enlace  the  corresponding  arteries.  There  is  a  small  elongated  posterior  mesenteric 
ganglion  in  relation  to  the  origin  of  the  posterior  mesenteric  artery.  The  posterior 
mesenteric  plexus  includes  left  colic,  anterior  hsemorrhoidal,  and  spermatic  plexuses. 
The  lumbar  trunk  is  deeply  placed  at  the  medial  side  of  the  psoas  minor.  It  has 
seven  ganglia,  which  are  very  small,  with  the  exception  of  the  last.  There  is  a  well- 
developed  aortic  plexus.  The  sacral  trimks  are  close  to  the  middle  sacral  artery 
and  have  each  three  ganglia  when  this  part  is  fully  developed.  The  caudal  trunks 
lie  on  each  side  of  the  coccygeal  artery;  the  number  and  arrangement  of  the  visible 
ganglia  are  variable.  The  pelvic  plexus  is  well  developed  and  contains  minute 
ganglia. 


>ESTHESIOLOGY 
THE  SENSE  ORGANS  AND  COMMON  INTEGUMENT 

The  organs  of  the  senses  (Organa  sensiium)  receive  external  stimuli  and  con- 
duct impulses  to  the  brain  which  result  in  sensations  of  sight,  hearing,  taste,  smell, 
and  touch.  They  consist  essentially  of  specially  differentiated  cells  (neuro-epithe- 
lium)  and  a  conduction  path  which  is  simple  in  the  more  generalized  sense  organs, 
elaborate  in  those  which  are  highly  specialized — the  eye  and  the  ear. 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 
The  Eye 

The  eye  or  organ  of  vision  (Organon  visus)  in  the  broader  sense  of  the  term 
comprises  the  eyeball  or  globe  of  the  eye,  the  optic  nerve,  and  certain  accessory 
organs  associated  therewith.  The  accessory  organs  (Organa  oculi  accessoria)  are  the 
orbital  fascise  and  muscles,  the 

eyelids  and  conjunctiva,   and  Upper  eyelid 

the  lacrimal  apparatus.    These  Third  eyelid  \ 

structures  will  be  considered  in  Caruncula.  ■  ■ 

the  order  in  which  they  may  be  lacrinmlis  -^^         ^     _  ^5, 

most   conveniently  examined,         SLv  ^^  '3^ 

taking  the  horse  as  a  type.  The  ^v.         \    -^ 

bony  walls  of  the  orbit  have 
been  described  in  connection 
with  the  skull;  the  periorbita, 
a  fibrous  membrane  which  en- 
closes the  eyeball  together  with 
its  muscles,  vessels,  and  nerves, 
may  be  appropriately  included 
in  the  account  of  the  fasciae. 


THE  EYELIDS  AND  CONJUNC- 
TIVA 


Lower  eyelid 
Fig.  688. — Left  Eye  of  Horse. 
9,  Zygomatic  arch;  10,  supraorbital  depression;  12,  supraorbital  proc- 
ess;   37,  facial  crest.    (After  Ellenberger-Baum,  Anat.  fiir  Kiinstlcr.) 


The  eyelids,  upper  and 
lower  (Palpebra  superior  et  in- 
ferior), are  movable  folds  of 
integument  situated  in  front 
of  the  eyeball.  When  closed 
anterior  surface  of  the  eyeball.  The  upper  lid 
more  movable  than  the  lower  one,  and  its  free 
interval  between  the  lids  is  termed  the  palpebral  fissure  (Rima  palpebrarum). 
When  the  eye  is  closed,  it  is  an  oblique  slit  about  two  inches  (ca.  5  cm.) 
in  length;  when  open,  it  is  biconvex  in  outline.  The  ends  of  the  fissure  are 
the  angles  or  canthi,  and  are  distinguished  as  medial  or  nasal,  and  lateral  or 

857 


they  cover  the  entrance  to  the  orbit  and  the 
is  much  more  extensive  and 
edge  is   more  concave.     The 


858 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 


temporal  (Angiilus  oculi  medialis,  lateralis).  The  lateral  angle  is  rounded  when  the 
eye  is  open,  but  the  medial  angle  is  narrowed  and  produced  to  form  a  3-shaped 
ba}^  or  recess,  termed  the  lacrimal  lake  (Lacus  lacrimalis) .  In  this  there  is  a  rounded 
pigmented  prominence  kno\\Ti  as  the  lacrimal  carimcle  (Caruncula  lacrimalis) ;  it 
is  about  the  size  of  a  small  pea,  and  is  covered  A\dth  modified  skin,  connected  with 
that  of  the  medial  commissure,  from  which  project  a  number  of  hairs  provided  with 
sebaceous  glands.     The  lids  unite  on  either  side  and  form  the  commissures,  medial 

and  lateral  (Commissura  palpebrarum 
medialis,  lateralis).  The  anterior  sur- 
face of  the  lids  (Facies  anterior  palpe- 
brarum) is  convex  and  is  covered  with 
very  short  hair.  A  considerable  num- 
ber of  tactile  hairs  are  scattered  over 
the  lower  part  of  the  lower  lid,  but  on 
the  upper  lid  they  are  very  scanty. 
The  infrapalpebral  depression  (Sulcus 
infrapalpebralis)  indicates  somewhat 
indistinctly  the  limit  of  the  lower  lid. 
The  upper  lid  is  marked  by  two  fur- 
rows when  raised.  The  posterior  sur- 
face (Facies  posterior  palpebrarum)  is 
adapted  to  the  free  surface  of  the  eye- 
ball and  is  covered  by  the  palpebral 
conjunctiva.  The  free  border  of  the 
lid  is  smooth  and  usually  black.  It 
has  a  well-defined  posterior  margin 
(Limbus  palpebralis  posterior),  along 
which  the  ducts  of  the  tarsal  glands 
open.  The  anterior  margin  (Limbus 
palpebralis  anterior)  bears  stiff  hairs 
termed  the  cilia  (eyelashes).  On  the 
upper  lid  the  cilia  are  long  and  num- 
erous except  at  its  medial  third,  where 
they  are  very  small  or  absent.  On 
the  lower  lid  the  cilia  are  often  scarcely 
distinguishable  from  the  ordinary  hairs; 
in  other  cases  they  may  be  clearly  seen 
except  near  the  lateral  canthus,  and 
are  much  finer  and  shorter  than  those 
of  the  upper  lid.  The  edge  of  each  lid 
is  pierced  near  the  medial  angle  by  a 
minute,  slit-like  opening,  the  pimctum 
lacrimale,  which  is  the  entrance  to 
the  lacrimal  duct. 
The  skin  of  the  eyelids  is  thin  and  freely  movable,  except  near  the  free  edge, 
where  it  is  more  firmly  attached.  The  underlying  subcutaneous  tissue  is  destitute 
of  fat.  The  muscular  layer  consists  chiefly  of  the  elliptical  bundles  of  the  orbicu- 
laris oculi,  with  which  are  associated  fibers  of  the  corrugator  supercilii  in  the  upper 
lid  and  the  malaris  in  the  lower  lid.  At  the  medial  side  there  is  a  fibrous  band,  the 
palpebral  ligament,  which  is  attached  to  the  lacrimal  tubercle  and  furnishes  origin 
to  some  fibers  of  the  orbicularis.  At  the  medial  commissure  a  bundle  detached 
from  the  orbicularis  passes  inward  behind  the  lacrimal  sac,  and  is  known  as  the  pars 
lacrimalis  (or  Horner's  muscle).  At  the  lateral  side  an  indistinct  palpebral  raphe 
occurs  where  fibers  of  the  orbicularis  decussate.     The  fibrous  layer  is  thicker  and 


'7  3 

Fig.  689. — Vertical  Section  of  Anterior  Part  of  Eye 
OF  Horse,  with  Lids  Half  Closed. 
1,  Tarsal  gland  of  upper  lid;  2,  palpebral  conjunctiva; 
3,  fornix  conjunctivEe;  4,  levator  palpebrse  superioris;  S, 
orbicularis  oculi;  6,  cornea;  7,  anterior  chamber;  S,  iris; 
9,  0',  granula  iridis;  10,  posterior  chamber;  11,  ciliary  proc- 
ess; 12,  ciliary  muscle;  13,  ciliary  zone  or  suspensory 
Ug.  of  lens;  H,  chorioid;  15,  sclera;  16,  lens;  17,  root  of 
tactile  hair.     (After  Bayer,  Augenheilkunde.) 


THE    CONJUNCTIVA  859 

denser  along  the  free  edge  of  the  Hd,  forming  here  the  tarsus.  The  tarsus  furnishes 
insertion  to  a  layer  of  unstriped  muscle  known  as  the  tarsal  muscle.  The  tarsal 
glands  (Glandulse  tarsales)i  are  partly  embedded  in  the  deep  face  of  the  tarsus,  and 
are  visible  when  the  lid  is  everted  if  the  conjunctiva  is  not  too  strongly  pigmented. 
They  are  arranged  in  a  linear  series,  close  together,  and  with  their  long  axes  per- 
pendicular to  the  free  edge  of  each  lid.  In  the  upper  lid  they  number  forty-five  to 
fifty;  in  the  lower,  thirty  to  thirty-five.  Each  consists  of  a  tubular  duct  beset 
with  numerous  alveoli,  in  which  a  fatty  substance,  the  palpebral  sebum,  is  secreted. 
The  palpebral  conjunctiva  lines  the  internal  surface  of  the  eyelids. 

The  conjunctiva  is  the  mucous  membrane  which  lines  the  lids  as  palpebral 
conjunctiva  (C.  palpebrarum),  and  is  reflected  upon  the  anterior  part  of  the  eyeball 
as  bulbar  conjunctiva  (C.  bulbi);  the  line  of  reflection  is  termed  the  fornix  con- 
junctivaB.  The  palpebral  part  is  closely  adherent  to  the  tarsus,  but  is  loosely  at- 
tached further  back.  It  is  papillated  and  is  covered  with  stratified  cylindrical 
epithelium  in  which  many  goblet-cells  are  present.  In  the  fornix  and  its  vicinity 
there  are  tubular  glands.  Near  the  medial  angle  there  are  numerous  lymph  nodules. 
The  conjunctiva  of  the  lateral  part  of  the  upper  lid  is  pierced  near  the  fornix  by  the 
orifices  of  the  excretory  ducts  of  the  lacrimal  gland — twelve  to  sixteen  in  number. 


m^ 


/. 

Fig.  690. — Piece  op  Upper  Eyelid;  Inner  Surface.  Fig.  691. — Cartilage  of  Third  Eyelid  of  Horse; 

1,  Cilia;    S,  limbus  palp,  posterior;    3,  tarsal  glands.  Convex  Surface. 

(After  EUenberger,  in  Leisering's  Atlas.)  /,  Gland;    2,  fat  surrounding  deep  part  of  cartilage. 

(After  EUenberger,  in  Leisering's  Atlas.) 

The  bulbar  conjunctiva  is  loosely  attached  to  the  anterior  part  of  the  sclera  and  is 
pigmented  in  the  vicinity  of  the  corneo-scleral  junction.  On  the  cornea  it  is  repre- 
sented by  a  stratified  epithelium. 

When  the  lids  are  in  apposition,  the  conjunctiva  (including  the  epithelium  of  the  cornea) 
encloses  a  capillary  space  between  the  lids  and  the  eyeball,  and  constitutes  what  is  known  as  the 
conjunctival  sac. 

The  third  eyelid  (Palpebra  tertia)  is  situated  at  the  medial  angle  of  the  eye. 
It  consists  of  a  semilunar  fold  of  the  conjunctiva,  known  as  the  membrana  nictitans, 
which  covers  and  partly  encloses  a  curved  plate  of  hyaline  cartilage.  Its  marginal 
part  is  thin  and  usually  more  or  less  pigmented.  The  cartilage  has  an  elongated 
quadrilateral  outline.  The  part  of  it  which  lies  in  the  membrana  is  wide  and  thin. 
The  deep  part  is  narrower  and  thicker  and  is  embedded  in  fat  at  the  inner  side  of  the 
eyeball.  Numerous  minute  lymph  nodules  occur  in  the  membrana  nictitans,  and 
the  deep  part  of  the  cartilage  is  surrounded  by  a  gland  which  resembles  the  lacrimal 
gland  in  structure  (Glandula  superficialis  palpebrse  tertise). 

Ordinarily  the  third  eyelid  extends  very  little  over  the  medial  end  of  the 
cornea,  but  when  the  eyeball  is  strongly  retracted,  the  membrana  is  protruded  over 
it  so  as  to  measure  about  an  inch  (ca.  2-3  cm.)  in  its  middle.  This  effect  results 
from  the  pressure  of  the  eyeball  and  its  muscles  on  the  fat  which  surrounds  the  deep 
part  of  the  cartilage. 

Vessels  and  Nerves. — The  arteries  which  chiefly  supply  the  eyelids  and  con- 
1  Also  known  as  the  Meibomian  glands. 


860  THE    SENSE    ORGANS   AND    SKIN    OF   THE    HORSE 

junctiva  are  branches  of  the  ophthalmic  and  facial  arteries,  and  the  blood  is  drained 
away  by  corresponding  veins.  The  sensory  nerves  are  branches  of  the  ophthalmic 
and  maxillary  divisions  of  the  trigeminus.  The  motor  nerves  to  the  orbicularis 
oculi,  corrugator  supercilii,  and  malaris  come  from  the  facial  nerve;  the  levator 
palpebrse  superioris  is  innervated  by  the  oculomotor  nerve  and  the  unstriped 
muscle  of  the  lids  by  the  sympathetic. 


THE  LACRIMAL  APPARATUS 

The  lacrimal  apparatus  (Apparatus  lacrimalis)  comprises:  (1)  the  lacrimal 
gland,  which  secretes  the  clear  lacrimal  fluid;  (2)  the  excretory  ducts  of  the  gland; 
(3)  the  two  lacrimal  ducts  or  canaliculi,  lacrimal  sac,  and  naso-lacrimal  duct,  which 
receive  the  fluid  and  convey  it  to  the  nostril. 

The  lacrimal  gland  (Glandula  lacrimalis)  is  situated  between  the  supraorbital 
process  and  the  dorso-lateral  surface  of  the  eyeball  (Fig.  563).  It  is  flattened,  oval 
in  outline,  and  measures  about  two  inches  (ca.  5  cm.)  transversely  and  an  inch  or 
more  (2.5-3  cm.)  in  the  sagittal  direction.  Its  superficial  face  is  convex  and  is 
related  to  the  concave  lower  surface  of  the  supraorbital  process.  The  deep  face  is 
concave  in  adaptation  to  the  eyeball,  from  which  it  is  separated  by  the  periorbita. 
The  excretory  ducts  (Ductuli  excretorii)  are  very  small  and  are  twelve  to  sixteen 
in  number;  they  open  into  the  lateral  part  of  the  conjunctival  sac  along  a  line  a 
little  in  front  of  the  fornix  conjunctivse  superior.  In  appearance  and  structure  the 
gland  resembles  the  parotid.  It  receives  its  blood-supply  chiefly  from  the  lacrimal 
artery.  The  sensory  nerve  is  the  lacrimal,  and  the  secretory  fibers  are  derived 
from  the  s>anpathetic. 

The  pimcta  lacrimalia  are  the  entrances  to  the  two  lacrimal  ducts.  Each  is  a 
fine,  slit-like  opening  (about  2  mm.  long),  situated  close  behind  the  free  edge  of  the 
lid  and  about  a  third  of  an  inch  (ca.  8  mm.)  from  the  medial  canthus.  The  lacri- 
mal ducts  (Ductus  lacrimales),  upper  and  lower,  begin  at  the  puncta  and  converge 
at  the  medial  commissure  to  open  into  the  lacrimal  sac.  The  latter  (Saccus  lacri- 
malis) may  be  regarded  as  the  dilated  origin  of  the  naso-lacrimal  duct.  It  occupies 
the  funnel-like  origin  of  the  bony  lacrimal  canal,  which  is  termed  the  fossa  of  the 
lacrimal  sac,  and  leads  to  the  naso-lacrimal  duct  (Ductus  nasolacrimalis),  which 
passes  forward  and  a  little  downward  along  the  outer  wall  of  the  frontal  sinus  and 
the  nasal  cavity  and  opens  near  the  lower  commissure  of  the  nostril.  Its  length 
is  about  ten  to  twelve  inches  (ca.  25-30  cm.).  In  the  first  part  of  its  course  it  is 
enclosed  in  the  osseous  lacrimal  canal ;  further  forward  it  lies  in  the  lacrimal  groove 
of  the  maxilla,  covered  at  first  by  a  plate  of  cartilage  and  then  by  the  mucous  mem- 
brane of  the  middle  meatus  (Fig.  59).  The  terminal  part  (Fig.  452)  lies  in  the 
ventral  turbinate  fold  and  opens  on  the  skin  of  the  floor  of  the  nostril  near  the  tran- 
sition to  mucous  membrane.     Accessory  openings  may  occur  a  little  further  back. 

The  first  part  of  the  duct,  about  6  to  7  mm.  in  diameter,  extends  in  a  gentle  curve,  convex 
dorsally,  from  the  medial  commissure  toward  a  point  just  above  the  level  of  the  infraorbital  fora- 
men. The  second  part  (isthmus)  is  narrower  (ca.  3-4  mm.);  it  extends  forward  and  a  httle 
ventrally  about  to  a  transverse  plane  through  the  first  cheek  tooth  and  lies  in  the  groove  above 
the  ventral  turbinate  crest.  Beyond  this  the  duct  incUnes  upward  and  widens  very  consider- 
ably, crosses  the  nasal  process  of  the  premaxilla  obUquely,  and  contracts  at  its  termination.  The 
mucous  membrane  may  present  valvular  folds,  the  most  distinct  of  which  is  situated  at  the 
origin. 

THE  PERIORBITA 

The  periorbita^  is  a  conical  fibrous  membrane  which  encloses  the  eyeball  with 

its  muscles,  vessels,  nerves,  etc.     Its  apex  is  attached  around  the  optic  and  orbital 

foramina,  and  its  base  is  in  part  attached  to  the  bony  rim  of  the  orbit,  in  part  con- 

1  Also  known  as  the  ocular  sheath. 


THE    ORBITAL   FASCIA    AND    OCULAR   MUSCLES  861 

tinuous  with  the  fibrous  laj^er  of  the  Uds.  Its  medial  part,  which  is  in  contact  with 
the  orbital  wall,  is  thin;  incorporated  with  it  beneath  the  root  of  the  supraorbital 
process  is  the  bar  of  cartilage  around  which  the  superior  oblique  muscle  is  reflected. 
The  lateral  part  is  thicker,  and  is  strengthened  by  an  elastic  band  which  is  attached 
to  the  pterygoid  crest  and  furnishes  origin  to  the  thin,  unstriped  orbital  muscle.  A 
quantity  of  fat  (Corpus  adiposum  extraorbitale)  lies  about  the  periorbita,  and  within 
it  is  the  intraorbital  adipose  tissue  (Corpus  adiposum  intraorbitale)  which  fills  the 
interstices  between  the  eyeball,  muscles,  etc. 


THE  ORBITAL  FASCLE  AND  OCULAR  MUSCLES  (Figs.  563,  564,  692) 
The  straight  muscles  of  the  ej^eball  and  the  oblique  muscles  in  part  are  enclosed 
in  fibrous  sheaths  (Fasciae  musculares),  formed  by  superficial  and  deep  layers  of 
fascia,  which  are  united  by  intermuscular  septa  in  the  interstices  between  the 
muscles.  The  superficial  fascia  is  thin;  it  blends  in  front  with  the  fibrous  layer  of 
the  eyelids  saul  is  attached  l^ehind  around  the  optic  foramen.  The  deep  fascia 
consists  anteriorly  of  two  layers,  one  of  which  is  continuous  with  the  fibrous  tissue 
of  the  lids,  while  the  other  is  attached  at  the  corneo-scleral  junction. 

The  posterior  part  of  the  eyeball  is  covered  by  the  fascia  bulbi,  so  that  between 
them  a  lymph  space  (Spatium  interfasciale)  is  enclosed  which  communicates  with 
the  subdural  space  along  the  course  of  the  optic  nerve. 

The  levator  palpebrae  superioris  muscle^  is  a  thin  band  about  half  an  inch  in 
width  which  lies  above  the  rectus  dorsaUs.  It  is  narrow  at  its  origin  above  and 
behind  the  ethmoidal  foramen  and  ends  by  an  expanded  tendon  in  the  upper  lid. 
Its  action  is  to  raise  the  upper  lid. 

The  muscles  of  the  eyeball  (Mm.  oculi)  are  seven  in  numl^er — four  straight, 
two  oblique,  and  a  retractor. 

The  straight  muscles  (Mm.  recti)  are  designated  according  to  their  positions  as 
j-ectus  dorsalis  s.  superior,  rectus  ventralis  s.  inferior,  rectus  medialis,  and  rectus 
lateralis.  They  are  all  band-like,  arise  close  together  around  the  optic  foramen, 
and  diverge  as  they  pass  forward  to  the  eyeball.  On  reaching  the  latter  they  end 
in  thin  tendons  which  are  inserted  into  the  sclera  in  front  of  the  equator  of  the  eye- 
ball. 

The  retractor  oculi  surrounds  the  optic  nerve,  and  is  incompletely  divided  into 
four  parts  which  alternate  with  the  recti.  They  arise  around  the  optic  nerve  and 
are  inserted  into  the  sclera  behind  the  recti. 

The  obliquus  dorsalis  s.  superior  is  the  longest  and  narrowest  of  the  ocular  mus- 
cles. It  arises  near  the  ethmoidal  foramen  and  passes  forward  medial  to  the  rectus 
medialis.  Under  the  root  of  the  supraorbital  process  it  is  reflected  almost  at  a 
right  angle  around  a  cartilaginous  pulley  (trochlea),  which  is  attached  to  the 
anterior  part  of  the  inner  wall  of  the  orbit,  a  bursa  being  interposed  here.  The 
muscle  is  then  directed  outward  and  somewhat  forward,  and  ends  in  a  thin  tendon 
which  passes  between  the  rectus  dorsalis  and  the  eyeball,  and  is  inserted  into  the 
sclera  between  the  dorsal  and  lateral  recti,  about  half  an  inch  behind  the  margin 
of  the  cornea. 

The  obliquus  ventralis  s.  inferior  is  wide  and  much  shorter  than  the  rectL 
It  arises  from  the  medial  wall  of  the  orbit  in  the  small  depression  (Fossa  muscularis) 
behind  the  lacrimal  fossa.  It  curves  around  the  rectus  ventralis  and  is  inserted 
into  the  sclera  near  and  partly  beneath  the  rectus  lateralis. 

Actions.— The  dorsal  and  ventral  recti  rotate  the  eyeball  about  a  transverse 
axis,  moving  the  vertex  of  the  cornea  upward  and  downward  respectively.^     Snni- 

1  This  belongs  to  the  upper  eyelid,  but  is  mentioned  here  on  account  of  its  position  and  the 
fact  that  in  dissection  it  must  be  dealt  with  before  the  muscles  of  the  eyeball. 

2  These  terms  are  used  vnth  reference  to  the  axis  of  the  eyebaU,  not  that  of  the  head. 


862 


THE   SENSE   ORGANS   AND    SKIN    OF   THE    HORSE 


larly  the  medial  and  lateral  recti  rotate  the  eyeball  about  a  vertical  axis,  turning 
the  vertex  of  the  cornea  inward  and  outward  respectively.  The  oblique  muscles 
rotate  the  eyeball  about  a  longitudinal  axis;  the  dorsal  oblique  raises  the  lateral 
end  of  the  pupil,  while  the  ventral  oblique  lowers  it.  The  retractor  as  a  whole 
draws  the  eyeball  backward,  and  its  parts  may  separately  reinforce  the  correspond- 
ing recti.     Also  the  four  recti  acting  together  will  retract  the  eyeball. 

The  actual  movements  of  the  eyeball  are  by  no  means  so  simple  as  might  be  inferred  from 
the  foregoing  general  statements.  Practically  all  movements  are  produced  by  the  coordinated 
actions  of  several  muscles,  involving  combinations  which  are  quite  complex  and  difficult  to  analyze 
accurately.     Further  complication  is  caused  by  the  fact  that  the  recti  are  not  inserted  at  equal 


Fig.  692. — Vertical  Axial  Section  of  Orbit  of  Horse. 
a,  Eyelids;  b,  fascia  bulbi;  c,  c',  retractor  oculi;  d,  rectus  ventralis;  e,  obliquus  ventralis  (in  cross-section);  /, 
rectus  donsalis;  g,  levator  palpebrse  superioris;  h,  obliquus  dorsalis  (in  cross-section);  i,  lacrimal  gland;  k,  k',  peri- 
orbita; /,  superficial  fascia;  m,  deep  fascia;  n,  skin;  o,  retrobulbar  fat;  p,  extraorbital  fat;  q,  temporalis  muscle;  r, 
supraorbital  process;  s,  cranial  wall;  1,  cornea;  2,  sclera;  3,  chorioidea;  4,  ciliary  muscle;  5,  iris;  6,  granula  iridis; 
7,  retina;  7',  optic  papilla;  5,  optic  nerve;  S,  crystalline  lens;  JO,  capsule  of  lens;  ii,  ciliary  zone;  i^,  posterior  cham- 
ber;  /3,  anterior  chamber;   74,  conjunctiva  bulbi;   7.5,  vitreous  body.     (After  EUenberger,  in  Leisering's  Atlas.) 

distances  from  the  equator  and  the  axes  of  rotation  of  the  oblique  muscles  do  not  correspond  to 
the  longitudinal  axis  of  the  eyeball. 

Nerve-supply. — The  oculomotor  nerve  supplies  the  foregoing  muscles,  with 
the  exception  of  the  rectus  lateralis  and  obliquus  dorsalis,  which  are  innervated  by 
the  abducens  and  trochlearis  respectively. 


THE  EYEBALL 

The  eyeball  (Bulbus  oculi)  is  situated  in  the  anterior  part  of  the  orbital  cavity. 
It  is  protected  in  front  by  the  eyelids  and  conjunctiva,  and  in  its  middle  by  the 
complete  orbital  ring,  and  is  related  behind  to  the  fascia  bulbi,  fat,  and  ocular 
muscles. 

It  has  the  form  approximately  of  an  oblate  spheroid,  but  is  composed  of  the 
segments  of  two  spheres  of  different  sizes.  The  anterior  transparent  segment, 
which  is  formed  by  the  cornea,  has  a  radius  of  curvature  of  about  17  mm.,  and  the 


THE    FIBROUS   TUNIC 


863 


posterior  opaque,  scleral  segment  one  of  about  25  mm.  The  anterior  segment 
therefore  projects  more  strongly,  and  the  junction  of  the  two  segments  is  marked 
externally  by  a  broad,  shallow  groove,  the  sulcus  sclerae.  The  central  points  of 
the  anterior  and  posterior  curvatures  of  the  eyeball  are  termed  respectively  the 
anterior  and  posterior  poles  (Polus  anterior,  posterior),  and  the  line  connecting  the 
poles  is  the  external  optic  axis  (Axis  oculi  externa).^  The  angle  of  divergence  of  the 
optic  axes  is  about  137  degrees.  The  equator  (^Equator)  is  an  imaginary  line  drawn 
around  the  eyeball  midway  between  its  poles,  and  meridians  (Meridiani)  are  lines 
drawn  around  it  through  the  poles. 

The  average  transverse  diameter  of  the  eyeball  is  about  5  cm.,  the  vertical  about  4.5  cm., 
and  the  axial  about  4.25  cm.  The  distance  from  the  anterior  pole  to  the  point  of  entrance  of  the 
optic  nerve  is  about  3  cm. 

The  eyeball  consists  of  three  concentric  tunics  or  coats,  within  which  three 
refractive  media  are  enclosed. 

The  Fibrous  Tunic 
The  fibrous  timic  (Tunica  fibrosa  oculi)  is  the  external  coat  and  is  composed 
of  a  posterior  opaque  part,  the  sclera,  and  a  transparent  anterior  part,  the  cornea. 
1 .  The  sclera-  is  a  dense  fibrous 

Lens  seen  through  cornea 

Corneoscleral      \ 
junction        \ 


Third 
eyelid 


Sclera 


~  -  Cornea 


Pupil 


membrane  which  forms  about  four- 
fifths  of  the  fibrous  tunic.  Thickest 
in  the  vicinity  of  the  posterior  pole 
(ca.  2  mm.),  it  thins  at  the  equator 
(ca.  0.4  mm.),  and  increases  in  thick- 
ness toward  the  junction  with  the 
cornea  (ca.  1.3  mm.).  It  is  in  gen- 
eral white,  ])ut  may  have  a  bluish 
tinge  in  its  thinnest  parts.  Its  ex- 
ternal surface  furnishes  insertion  to 
the  ocular  muscles  and  is  covered  by 
the  conjunctiva  sclerse  in  its  anterior 
part.  The  episcleral  tissue,  which  is 
richly  supplied  with  vessels  and 
nerves,  attaches  the  conjunctiva 
to  the  sclera;  it  is  abundant  and 
loosely  meshed  except  at  the  junc- 
tion with  the  cornea.  The  inner 
surface  is  attached  to  the  chorioid 
coat  by  a  layer  of  delicate,  pig- 
mented connective  tissue,  the 
lamina  fusca.  The  anterior  bor- 
der,  which   is   oval,  the  long  axis 

being  transverse,  is  continuous  with  the  cornea.  The  transition  from  the  opaque 
scleral  tissue  to  the  transparent  corneal  substance  occurs  in  such  manner  that  the 
sclera  appears  to  form  a  groove  (Rima  cornealis),  into  which  the  cornea  fits  some- 
what as  a  watch-glass  in  the  case.  Near  the  corneo-scleral  junction  there  is  a 
circular  venous  plexus,  the  plexus  s.  sinus  venosus  scleras.^  The  optic  nerve 
passes  through  the  posterior  part  of  the  sclera  a  little  below  and  lateral  to  the 
posterior  pole.  The  opening  for  the  nerve  is  crossed  by  interlacing  fibrous  strands, 
forming  the  lamina  cribrosa  sclerae.  The  sclera  consists  of  interlacing  bundles  of 
white  fibrous  tissue,  associated  with  which  there  are  a  few  elastic  fibers.     The 

1  The  term  internal  optic  axis  (Axis  ocuU  externa)  is  applied  to  a  coincident  line  from  the 
posterior  surface  of  the  cornea  to  the  anterior  surface  of  the  retina. 

2  Also  termed  the  sclerotic  coat,  and  popularly  known  as  the  "white  of  the  eye." 

3  Formerly  term.^-^  the  canal  of  Schlemm. 


Fig.  693. — Left  Eyeball  of  Horse,  in  situ.  After  Removal. 
OF  Upper  and  Lower  Lids. 
9,  Zygomatic  arch;    IS,  supraorbital   process;    19,  orbital 
fat;    27,    facial    crest.      (After    EUenberger-Baum,    Anat.    fur 
Kiinstler.) 


864 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 


bundles  are  arranged  chiefly  in  meridional  and  equatorial  layers.  The  very  limited 
blood-supph^  is  derived  from  the  ciliary  arteries,  and  the  veins  open  into  the  vense 
vorticosa?  and  ciliary  veins.  The  lymphatics  are  represented  by  intercommunicat- 
ing cell  spaces.     The  nerves  are  derived  from  the  ciliary  nerves. 

2.  The  cornea  forms  the  anterior  fifth  of  the  fibrous  tunic.  It  is  transparent, 
colorless,  and  non-vascular.  Viewed  from  in  front  it  is  oval  in  outline,  the  long 
axis  being  transverse  and  the  broad  end  medial;  it  appears  more  nearly  circular 
when  viewed  from  behind.  Its  anterior  surface  (Facies  anterior)  is  convex  and  is 
more  strongly  curved  than  the  sclera;  its  central  part  is  termed  the  vertex  comeae. 
The  posterior  surface  (Facies  posterior)  is  concave;  it  forms  the  anterior  lioundary 
of  the  anterior  chamber,  and  is  in  contact  with  the  aqueous  humor.  The  margin 
(Limbus  corneae)  joins  the  sclera;  the  latter  overlaps  the  cornea  more  in  front  than 
behind,  and  more  above  and  below  than  at  the  sides,  thus  explaining  the  apparent 


Sclera 


Optic  nerve  ■ 

Optic  papilla 
Retrobulbar  fat 


Rectus  oculi  inferior 


Reflection  of  conjunctiva 


Granula  iridis 


Cornea 


Lens 
Anterior  chamber 


Ciliary  processes 


Chorioid 


Fig.  694. — Vertical  Section  of  Etebaix  of  Horse,  abottt  S. 
The  contour  of  the  crystalline  lens  is  dotted. 


difference  in  outline  of  the  two  surfaces.  The  cornea  is  thinnest  at  the  vertex. 
The  cornea  consists,  from  before  backward,  of  the  following  layers  fl)  The  epi- 
thelium corneae  is  continuous  with  that  of  the  conjunctiva  sclera?,  and  is  of  the 
stratified  squamous  type.  (2)  The  lamina  limitans  anterior  is  merely  a  condensa- 
tion of  the  next  layer.  (3)  The  substantia  propria  forms  the  bulk  of  the  cornea 
and  is  composed  of  interlacing  bundles  of  connective  tissue,  arranged  in  part  in 
lamellae  disposed  parallel  with  the  surface.  In  the  amorphous  cement  substance 
between  the  lamellse  are  flattened  connective-tissue  cells,  the  corneal  corpuscles. 
These  have  branching  processes  which  unite  with  those  of  other  cells,  thus  form- 
ing a  protoplasmic  network.^     (4)  The  lamina  elastica  posterior-  is  a  thin  and 

1  According  to  Piersol,  the  system  of  spaces  and  canaliculi  in  the  substantia  propria  is  com- 
pletely filled  by  the  cells  and  their  processes,  upon  which  the  nutrition  of  the  cornea  largely  de- 
pends. Tlie  lamina  elastica  anterior  (Bowman's  membrane),  formerly  described  as  a  distinct 
layer  between  the  corneal  epithelium  and  the  substantia  propria,  does  not  exist  as  such,  but  there 
Is  a  condensation  of  the  superficial  part  of  the  latter,  which  Rollett  termed  the  anterior  limiting 
layer;  it  is  not  elastic. 

2  Also  known  as  the  membrane  of  Descemet  or  Demours 


THE   VASCULAR   TUNIC  865 

practically  homogeneous  membrane  which  is  less  intimately  attached  to  the  sub- 
stantia propria  than  the  anterior  lamina.  It  is  clear,  glistening,  and  elastic.  At 
the  periphery  the  lamina  divides  into  three  sets  of  fibers.  The  anterior  fibers  join 
the  sclera,  the  middle  give  attachment  to  the  ciliary  muscle,  while  the  posterior 
pass  into  the  iris  and  form  the  ligamentum  pectinatum  iridis.  (5)  The  endothelium 
of  the  anterior  chamber  (Endothelium  camerae  anterioris)  consists  of  a  layer  of 
flattened  polygonal  cells,  and  is  reflected  on  to  the  anterior  surface  of  the  iris.  The 
cornea  is  non-vascular  except  at  its  periphery,  where  the  terminal  twigs  of  the  vessels 
of  the  sclera  and  conjunctiva  form  loops.  The  nerves  are  derived  from  the  ciliary 
nerves.  They  form  a  plexus  around  the  periphery  (Plexus  annularis),  from  which 
fibers  pass  into  the  substantia  propria,  become  non-medullated,  and  form  the  funda- 
mental or  stroma  plexus.  From  this  perforating  branches  go  through  the  anterior 
limiting  layer  and  form  a  subepithelial  plexus,  from  which  filaments  pass  between 
the  epithelial  cells.  Other  branches  from  the  plexuses  in  the  substantia  propria 
end  as  fibrils  which  are  in  close  relation  with  the  corneal  corpuscles. 

The  Vascular  Tunic 
The  vascular  tunic  (Tunica  vasculosa  oculi)  lies  internal  to  the  fibrous  coat; 
it  comprises  three  parts — the  chorioid,  the  ciliary  body,  and  the  iris. 

1.  The  chorioid  (Chorioidea)  is  a  thin  membrane  which  lies  between  the  sclera 
and  retina.     It  is  in  general  rather  loosely  attached  to 

the  sclera  by  the  lamina  fusca,  but  is  intimately  adherent 
at  the  point  of  entrance  of  the  optic  nerve  and  less  closely 
in  places  where  the  ciliary  vessels  and  nerves  pass  through. 
The  inner  surface  is  in  contact  with  the  layer  of  pigmented 
cells  of  the  retina,  which  adhere  so  closely  to  the  chorioid 
that  they  were  formerly  regarded  as  a  part  of  the  latter. 
The  general  color  of  the  chorioid  is  dark  brown,  but  an 
extensive  semilunar  area  a  little  above  the  level  of  the 
optic  papilla  has  a  remarkable  metallic  luster,  and  is 
termed  the  tapetum  of  the  chorioid  (Tapetum  chorioidese). 
The  appearance  here  varies  in  different  individuals,  but  pj,,  695.— Tapetttm  of  Horse. 
the  prevailing  colors  in  most  cases  are  iridescent  blue  a,  Optic  papilla;  &,  lower  bor- 

and  green  in  various  nuances  shading  into  yellow.     Pos-     ^er  of  tapetum.    (After  EUen- 
teriorly  the  chorioid  is  perforated  by  the  optic  nerve,       ^^^^^'  *°   ^'^^"°e  ^ 
and  anteriorly  it  is  continuous  with  the  ciliary  body. 

The  chorioid  consists  of  four  layers,  which  from  without  inward  are  as  follows: 
(1)  The  lamina  suprachorioidea  consists  of  interlacing  fine  lamellae  of  fibrous  tissue, 
each  containing  a  network  of  elastic  tissue.  Among  these  are  large,  branched,  pig- 
mented, connective-tissue  cells.  The  spaces  between  the  lamellae  are  lined  with 
endothelium,  and  form  a  system  of  lymph-clefts  which  together  form  the  pericho- 
rioid  space  (Spatium  perichorioideale).  (2)  The  lamina  vasculosa  is  the  outer  part 
of  th«  proper  tissue  of  the  chorioid.  It  contains  the  larger  blood-vessels,  which 
are  supported  by  areolar  tissue.  (3)  The  lamina  choriocapillaris  consists  of  an 
extremely  rich  network  of  capillaries  embedded  in  an  almost  homogeneous  matrix. 
Between  it  and  the  lamina  vasculosa  is  a  layer  of  fibro-elastic  tissue,  the  tapetum 
fibrosum,  which  causes  the  metallic  luster  mentioned  above.  (4)  The  lamina 
basaUs  is  very  thin  and  transparent.  It  is  composed  of  an  inner  homogeneous  part 
and  an  outer  elastic  part. 

2.  The  ciliary  body  (Corpus  ciliare),  the  middle  part  of  the  vascular  coat,  con- 
nects the  chorioid  with  the  periphery  of  the  iris.  In  meridional  section  it  has  the 
form  of  a  narrow  triangle,  the  base  of  Avhich  is  next  to  the  iris.  On  its  inner  side 
are  the  ciliary  processes  and  on  its  outer  side  is  the  ciliary  muscle.  It  consists  of 
three  parts— the  ciliary  ring,  ciliary  processes,  and  ciliary  muscle.     The  ciUary 

55 


866 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 


ring  (Orbiculus  ciliaris)  is  the  posterior  zone,  which  is  distinguished  from  the  cho- 
rioid  mainly  by  its  greater  thickness  and  the  absence  of  the  chorio-capillaris.  Its 
inner  face  presents  numerous  fine  meridional  ridges,  by  the  union  of  which  the 
ciliary  processes  are  formed.  The  ciliary  processes  (Processus  ciliares),  more  than 
a  hundred  in  number,  form  a  circle  of  radial  folds  which  surround  the  lens  and  fur- 
nish attachment  to  the  zonula  ciliaris  (or  suspensory  ligament  of  the  lens).  They 
are  small  at  their  origin  on  the  ciliary  ring  and  become  much  thicker  and  higher 
toward  their  central  ends.  The  width  of  the  circle  formed  by  them  is  narrower 
at  the  medial  side  than  elsewhere.  Their  bases  extend  forward  to  the  peri- 
phery of  the  iris,  and  their  central 
ends  are  close  to  the  margin  of 
the  lens.  They  bear  numerous 
secondary  folds  (Plicae  ciliares). 
Their  inner  surface  is  covered  by  a 
continuation  of  the  lamina  basalis 
of  the  chorioid,  on  which  there  are 
two  layers  of  epithelial  cells  which 
constitute  the  pars  ciliaris  retinae. 
They  consist  of  a  rich  network  of 
tortuous  vessels  supported  in  pig- 
mented connective  tissue.  The  cil- 
iary muscle  (M.  ciliaris)  (Figs.  689, 
692,  696)  constitutes  the  outer  part 
of  the  ciliary  body,  and  lies  between 
the  sclera  and  the  ciliary  processes. 
It  forms  a  circular  band  of  unstriped 
muscle,  the  fibers  of  which  are  for 
the  most  part  directed  meridionally. 
They  arise  from  the  inner  surface  of 
the  sclera  and  from  the  ligamen- 
tum  pectinatum  iridis  close  to  the 
corneo-scleral  junction,  and  run 
l^ackward  along  the  sclera  to  be 
inserted  into  the  ciliary  processes 
and  ring.  When  the  muscle  con- 
tracts, it  pulls  the  processes  and 
ring  forward,  thus  slackening  the 
ciliary  zone  of  the  lens,  and  allowing  the  latter  to  become  more  convex.  This  is 
the  mechanism  of  accommodation  for  near  objects. 

In  man  the  muscle  has  the  form  of  a  prismatic  ring  which  is  triangular  in  meridional  section, 
the  base  being  directed  toward  the  periphery  of  the  iris.  It  consists  chiefly  of  meridional  fibers, 
but  a  ring  of  circular  fibers  forms  the  inner  angle  of  its  base.  In  the  h()rs(>  the  muscle  is  much 
less  developed,  and  has  the  form  of  a  flat  band;  it  does  not  contain  distinctly  circular  fibers,  l)ut 
the  arrangement  is  rendered  more  or  less  plexiform  by  the  existence  of  obhcjue  and  ecjuatorial  fibers. 

3.  The  iris  (Figs.  689,  694,  696)  is  a  muscular  diaphragm  placed  in  front  of  the 
lens,  and  is  visible  through  the  cornea.  It  is  pierced  centrally  by  an  elliptical 
opening,  the  pupil  (Pupilla),  which  varies  in  size  during  life  and  determines  the 
amount  of  light  admitted  to  act  on  the  retina.  In  strong  light  the  vertical  diameter 
of  the  pupil  is  very  short,  but  the  opening  is  almost  circular  when  the  pupil  is  fully 
dilated.  The  ciliary  border  (Margo  ciliaris)  is  continuous  with  the  ciliary  body 
and  is  connected  with  the  corneo-scleral  junction  by  strands  of  connective  tissue 
which  constitute  the  ligamentum  pectinatum  iridis.  The  bundles  of  the  ligament 
interlace  and  enclose  spaces  (Spatia  anguli  iridis)  which  are  lined  with  endothelium 
and   communicate   with   the   anterior   chamber.     The   pupillary  border    (INIargo 


Horse;   Front 


Fig.  696. — Vascular  Tunic  of  Kyeb. 
View. 
The  cornea  is  removed  and  the  sclera  is  reflected  in  flaps. 
/,  Sclera;  1',  lamina  fusca;  2,  chorioidea;  2',  ciliary  veins;  3, 
ciliary  muscle;  4.  iris;  5,  5',  granula  iridis;  6,  pupil,  through 
which  the  lens  is  visible.  (After  Ellenberger,  in  Leisering's 
Atlas.) 


THE    VASCULAR   TUNIC  867 

pupillaris)  surrounds  the  pupil.  Its  upper  part  bears  in  its  middle  several  black 
masses  of  variable  size,  termed  the  granula  iridisi;  similar,  but  much  smaller, 
projections  may  be  seen  on  the  lower  margin  of  the  pupil.  The  anterior  surface 
(Facies  anterior)  is  usually  dark  brown  in  color;  it  presents  fine  folds  (Plic»  iridis), 
some  of  which  are  concentric  with  the  pupil,  others  radial ;  they  fade  out  near  the 
pupil. 2  The  smooth,  narrow,  central  part  is  termed  the  annulus  iridis  minor,  while 
the  much  broader  plicated  part  is  the  annulus  iridis  major.  The  posterior  surface 
(Facies  posterior)  is  usually  black;  the  color  is  caused  by  a  layer  of  pigmented 
cells  which  is  regarded  as  part  of  the  retina.  It  presents  numerous  fine  radial  lines 
except  at  the  pupillary  margin.  Its  central  part  is  in  contact  with  the  anterior 
surface  of  the  lens,  but  peripherally  the  two  are  separated  by  a  narrow  space 
termed  the  posterior  chamber.  The  iris  consists  chiefly  of  the  stroma  iridis,  a 
delicate  framework  of  connective  tissue  which  supports  numerous  blood-vessels, 
and  contains  branched  pigmented  cells.  The  muscular  tissue  is  unstriped  and 
consists  of  a  sphincter  and  a  dilator  of  the  pupil.  The  sphincter  pupillae  lies  in 
the  posterior  part  around  the  pupil,  with  which  the  fibers  are  largely  concentric. 
The  dilatator  pupillae  consists  of  fibers  which  radiate  from  the  sphincter  to  the 
ciliary  border.  The  anterior  surface  of  the  iris  is  covered  by  a  continuation  of  the 
endothelium  of  the  cornea.  Beneath  this  is  a  condensation  of  the  stroma,  in  which 
the  cells  are  close  together  and  are  full  of  pigmented  granules.^  There  appear  to 
be  minute  clefts  here  by  which  the  lymph-spaces  of  the  stroma  communicate  with 
the  anterior  chamber. 

The  arteries  of  the  vascular  tunic  come  from  the  ciliary  branches  of  the  oph- 
thalmic artery.  The  arteries  of  the  chorioidea  are  derived  chiefly  from  the  short 
posterior  ciliary  arteries.  These  (four  to  six  in  numljer)  perforate  the  sclera  around 
the  posterior  pole,  run  forward  in  the  lamina  vasculosa,  ami  form  the  rich  capillary 
network  of  the  choriocapillaris.  The  two  long  (aliary  arteries  perforate  the  ^■clera 
obliquely  near  the  optic  nerve;  they  run  forward  in  the  lamina  suprachorioidea  in 
the  horizontal  meridian,  one  on  the  medial,  the  other  on  the  lateral  side  of  the 
eyeball.  On  reaching  the  ciliary  body  each  divides  into  two  diverging  branches; 
the  subdivisions  of  these  unite  with  each  other  and  with  twigs  of  the  anterior  ciliary 
arteries,  thus  forming  near  the  periphery  of  the  iris  the  circulus  arteriosus  major. 
From  this  branches  go  to  the  ciliary  muscle  and  processes  and  to  the  iris.  The 
branches  in  the  iris  run  toward  the  pupillary  margin,  and  by  anastomotic  branches 
form  an  incomplete  circulus  arteriosus  minor.  The  two  anterior  ciliary  arteries, 
dorsal  and  ventral,  form  an  episcleral  plexus  around  the  corneo-scleral  junction, 
and  give  off  branches  which  perforate  the  sclera.  These  supply  twigs  to  the  ciliary 
muscle  and  recurrent  branches  to  the  chorioid,  and  assist  in  forming  the  circulus 
arteriosus  major.  The  l^lood  is  carried  away  from  the  vascular  tunic  chiefly  by  four 
or  five  venous  trunks,  the  venae  vorticosae,  which  are  formed  by  the  convergence  in 
whorls  of  numerous  veins  from  the  chorioid,  the  ciliary  body,  and  the  iris.  The 
vense  vorticosae  perforate  the  sclera  about  at  the  equator  and  join  the  veins  of  the 
ocular  muscles. 

The  nerves  come  from  the  long  and  short  ciliary  nerves.  They  form  a  plexus 
in  the  lamina  suprachorioidea,  which  contains  ganglion  cells,  and  sends  numerous 
non-medullated  fibers  chiefly  to  the  ])lood-vessels  of  the  chorioid.  At  the  ciliary 
muscle  a  second  plexus  (P.  gangliosus  ciliaris)  is  formed,  which  supplies  the  muscle 
and  sends  fibers  to  the  iris.  The  sphincter  pupillae  is  supplied  by  fibers  derived 
from  the  oculomotor  nerve,  while  the  dilatator  pupillae  is  innervated  by  the  sym- 
pathetic. 

1  Also  known  as  corpora  nigra. 

2  Some  of  these  folds  are  permanent,  while  others  are  temporary,  i.  e.,  produced  by  contrac- 
tion of  the  iris. 

3  In  albinos  the  pigment  is  absent  here,  as  elsewhere,  and  the  iris  is  pink  in  color. 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 


THE  RETINA 
The  retina  or  nervous  tunic  of  the  eyeball  is  a  delicate  membrane  which  extends 
from  the  entrance  of  the  optic  nerve  to  the  margin  of  the  pupil.  It  consists  of 
three  parts.  The  large  posterior  part,  which  alone  contains  the  nervous  elements, 
including  the  special  neuro-epithelium  and  the  optic  nerve-fibers,  is  termed  the 
pars  optica  retinae.  It  extends  forward  to  the  ciliary  body,  where  it  terminates  at 
an  almost  regular  circular  line  called  the  era  ciliaris  retinae.^  Here  the  retina 
rapidly  loses  its  nervous  elements,  becomes  much  thinner,  and  is  continued  over  the 
ciliary  body  and  the  posterior  surface  of  the  iris  by  two  layers  of  epithelial  cells  as 
the  pars  ciliaris  retinae ;  the  inner  stratum  is  non-pigmented,  while  the  outer  layer 
is  a  direct  continuation  of  the  stratum  pigmenti  of  the  pars  optica.  The  pars 
iridica  retinae  is  a  layer  of  pigmented  cells  which  covers  the  posterior  surface  of  the 
iris.     In  the  dead  subject  the  pars  optica  is  an  opaque,  gray,  soft  membrane  which 


6. 


I    5. 


Fig.  697. — Ixner  Surface  of  Anterior  Part  of 
Eyeball  of  Horse  (Equ.^torial  Section). 
1,  Sclera;  2,  chorioidea;  3,  retina  (drawn  away 
from  chorioidea);  4,  ciliary  processes;  o,  crystalline 
lens,  through  which  the  pupil  (ff)  is  seen.  (After 
Ellenberger,  in  Leisering's  Atlas.) 


Fig.  698. — Fundus  Oculi,  Seen  on  Equatorial  Sec- 
tion of  Eyeball  of  Horse. 
1,    Sclera;     3,    chorioidea;     3,    retina    (loosened); 
4,  tapetum;    o,  optic  papilla;    6,  optic  nerve.      (After 
Ellenberger,  in  Leisering's  Atlas.) 


can  be  stripped  off  the  chorioid,  leaving  most  of  its  outer  pigmented  layer  on  the 
latter.  During  life  it  is  transparent,  except  as  to  its  pigmented  epithelium,  and  the 
reddish  appearance  of  the  fundus  as  viewed  by  the  ophthalmoscope  is  caused  by 
the  blood  in  the  network  of  the  choriocapillaris.  The  entrance  of  the  optic  nerve 
forms  a  sharply  defined,  oval,  light  area,  the  optic  papilla  (Papilla  nervi  optici), 
situated  about  15  mm.  ventral  to  the  horizontal  meridian  and  3  to  4  mm.  lateral 
to  the  vertical  meridian.  The  central  part  of  the  papilla  is  slightly  depressed 
(Excavatio  papillae  n.  optici). 

The  transverse  diameter  of  the  papilla  is  about  6  to  7  mm.,  and  the  vertical  about  4  to  .5  mm. 
It  is  commonly  situated  a  little  below  the  margin  of  the  tapetum,  but  the  latter  may  extend  down 
somewhat  on  either  side  of  the  papilla.  The  lower  margin  is  often  indented  a  little.  In  inspec- 
tion of  the  fundus  with  the  ophthalmoscope  numerous  fine  branches  of  the  arteria  centralis  retinae 
are  seen  radiating  from  the  periphery  of  the  papilla. 

The  optic  nerve  fibers  converge  from  all  parts  of  the  pars  optica  to  the  papilla, 
where  they  collect  into  bundles  which  traverse  the  lamina  cribrosa  of  the  chorioidea 
and  sclera,  and  constitute  the  optic  nerve.  The  area  centralis  retinae  is  a  round 
spot,  2  to  3  mm.  in  diameter,  situated  dorso-lateral  to  the  optic  papilla;   it  corre- 

1  In  man  the  line  is  finely  serrated  and  is  termed  the  ora  serrata. 


REFRACTIVE  MEDIA  OF  THE  EYEBALL  869 

sponds  to  the  macula  lutea  of  man,  which  is  histologically  more  highly  differen- 
tiated than  the  rest  of  the  retina  and  is  the  area  of  most  acute  vision. 

The  structure  of  the  retina  is  very  complex.  It  consists  of  nervous  elements 
which  are  supported  in  a  peculiar  sustentacular  tissue,  and  are  covered  externally 
by  a  layer  of  pigmented  epithelium  (Stratum  pigmenti  retinae).  The  nervous  ele- 
ments comprise  a  highly  specialized  neuro-epithelium,  the  rods  and  cones;  ganglion- 
cells,  the  axones  of  which  form  the  optic  nerve;  and  intermediate  neurones.  Ten 
layers  may  be  recognized  in  sections  microscopically.^ 

The  arteries  of  the  retina  are  derived  from  the  arteria  centralis  retinae  and 
anastomotic  branches  from  the  short  ciliary  arteries.  The  arteria  centralis  enters 
the  optic  nerve  a  short  distance  behind  the  eyeball  and  runs  in  the  axis  of  the  nerve. 
It  divides  two  or  three  millimeters  before  reaching  the  papilla,  and  gives  off  thirty  to 
forty  branches  which  radiate  in  the  posterior  part  of  the  retina  and  divide  dichoto- 
mously  into  end-arteries  in  the  layer  of  nerve  fibers.  The  veins  accompany  the 
arteries  except  in  the  capillary  plexuses;  their  walls  consist  merely  of  a  layer  of 
endothelial  cells,  around  which  are  a  lymph-channel  and  sheath. ^ 


CHAMBERS  OF  THE  EYE  AND  AQUEOUS  HUMOR 
The  anterior  chamber  of  the  eye  (Camera  oculi  anterior)  is  enclosed  in  front  by 
the  cornea  and  behind  by  the  iris  and  lens  (Figs.  689,  692,  694).  It  communicates 
through  the  pupil  with  the  posterior  chamber  of  the  eye  (Camera  oculi  posterior) ; 
this  is  a  small  annular  space,  triangular  in  cross-section,  which  is  bounded  in  front 
by  the  iris,  behind  by  the  peripheral  part  of  the  lens  and  its  ligaments,  and  externally 
by  the  ciliary  processes.  The  chambers  are  filled  by  the  aqueous  humor  (Humor 
aqueus),  a  clear  fluid  which  consists  of  about  98  per  cent,  of  water,  with  a  little 
sodium  chlorid  and  traces  of  albumin  and  extractives.  It  is  carried  off  chiefly 
through  the  spaces  in  the  zonula  ciliaris  (or  suspensory  ligament  of  the  lens)  into 
the  plexus  venosus  sclerae. 


REFRACTIVE  MEDIA  OF  THE  EYEBALL 

The  vitreous  body  (Corpus  vitreum)  is  a  semifluid,  transparent  substance 
situated  between  the  crystalline  lens  and  the  retina.  In  front  it  presents  a  deep 
cavity,  the  fossa  hyaloidea,  which  fits  the  posterior  surface  of  the  lens.  It 
consists  of  a  framework  of  delicate  fibrils,  the  vitreous  stroma  (Stroma  vitreum), 
the  meshes  of  which  are  filled  by  the  fluid  vitreous  hirnior  (Humor  vitreus).  The 
surface  is  covered  by  a  condensation  of  the  stroma  known  as  the  hyaloid  membrane 
(Membrana  hyaloidea) . 

The  crystalline  lens  (Lens  crystallina)  is  a  biconvex,  transparent  body  which 
is  situated  in  front  of  the  vitreous  body  and  in  partial  contact  with  the  posterior 
surface  of  the  iris.  Its  periphery,  the  equator  of  the  lens  (^Equator  lentis),  is 
almost  circular  and  is  closely  surrounded  by  the  ciliary  processes.  The  anterior 
surface  (Facies  anterior)  is  convex;  it  is  bathed  by  the  aqueous  humor  and  is  in 
contact  with  the  iris  to  an  extent  which  varies  with  the  state  of  the  pupil.  The 
posterior  surface  (Facies  posterior)  is  much  more  strongly  curved  than  the  anterior. 
It  rests  in  the  fossa  of  the  vitreous  body  (Fossa  hyaloidea).  The  central  points  of 
the  surfaces  are  the  anterior  and  posterior  poles  (Polus  anterior  et  posterior  lentis), 
and  the  line  which  connects  them  is  the  axis  of  the  lens  (Axis  lentis). 

The  transverse  diameter  of  the  lens  is  about  2  cm.,  the  vertical  diameter  is  slightly  smaller, 
and  the  axis  measures  about  13  mm.     The  radius  of  curvature  of  the  anterior  surface  is  13.5  mm., 

1  For  the  minute  structure  of  the  retina  reference  must  be  made  to  histological  works. 

2  Martin  states  that  in  the  horse  a  capillary  plexus  does  not  exist,  but  that  the  arteries  com- 
municate with  the  veins  by  closely  wound  loops. 


870  THE    SENSE    ORGANS   AND    SKIN    OF   THE   HORSE 

and  of  the  posterior  surface,  9.5  to  10  mm.     But  the  curvatures  of  its  surfaces — especially  that  of 
the  anterior — varj'  during  Ufe  according  as  the  eye  is  accommodated  for  near  or  far  vision. 

The  zonula  ciliaris  or  suspensory  ligament  of  the  lens  (Fig.  689)  consists  of 
delicate  fibers  (Fibrae  zonulares)  which  pass  in  a  meridional  direction  from  the 
ciliary  processes  to  the  capsule  of  the  equator  of  the  lens.  Many  fibers  cross  each 
other,  and  the  spaces  between  the  fibers  (Spatia  zonularia)  are  filled  with  aqueous 
humor;  they  communicate  with  each  other  and  with  the  posterior  chamber. 

The  substance  of  the  lens  (Substantia  lentis)  is  enclosed  by  a  structureless, 
highly  elastic  memlDrane,  the  capsule  of  the  lens  (Capsula  lentis),  and  consists  of  a 
softer  cortical  substance  (Substantia  corticalis),  and  a  dense  central  part,  the 
nucleus  of  the  lens  (Nucleus  lentis).  The  capsule  is  thickest  on  the  anterior  surface, 
and  here  it  is  lined  by  a  layer  of  flat  polygonal  cells,  the  epithelium  of  the  lens 
(Epithelium  lentis).  The  lens  substance,  when  hardened,  is  seen  to  consist  of  con- 
centric laminae  arranged  somewhat  like  the  layers  of  an  onion,  and  united  by  an 
amorphous  cement  substance.  The  laminae  consists  of  lens  fibers  (Fibrae  lentis), 
hexagonal  in  section,  and  of  very  different  lengths.  Faint  lines  radiate  from  the 
poles  and  indicate  the  edges  of  layers  of  cement  substance  which  unite  the  groups 
of  lens  fibers.  These  lines,  the  radii  lentis,  are  three  in  number  in  the  foetus  and 
new-born,  and  form  with  each  other  angles  of  120  degrees.  On  the  anterior  surface 
one  is  directed  upward  from  the  pole  and  the  other  two  diverge  downward ;  on  the 
posterior  surface  one  is  directed  doAvnward  and  the  others  diverge  upward.  The 
developed  lens  has  neither  vessels  nor  nerves. 

In  the  foetus  the  lens  is  nearly  globular,  and  is  soft  and  pink  in  color.  During  part  of  foetal 
life  it  is  surrounded  by  a  vascular  network,  the  tunica  vasculosa  lentis.  This  is  derived  chiefly 
from  a  temporary  vessel,  the  Iwaloid  artery,  which  is  a  continuation  forward  of  the  arteria  cen- 
trahs  retina}  through  the  hyaloid  canal  that  traverses  the  vitreous  bodj'.  In  old  age  the  lens  tends 
to  lose  its  elasticity  and  transparency;  it  also  becomes  flatter  and  the  nucleus  especially  grows 
denser. 


The  Ear 

The  ear  or  organ  of  hearing  (Organon  auditus)  consists  of  three  natural  divi- 
sions— external,  middle,  and  internal. 


THE  EXTERNAL  EAR 

The  external  ear  (Auris  externa)  comprises — (1)  the  auricula,  a  funnel-like 
organ  which  collects  the  sound  waves,  together  with  its  muscles;  and  (2)  the 
external  acoustic  meatus,  which  conveys  these  waves  to  the  tympanic  membrane, 
the  partition  which  separates  the  canal  from  the  cavity  of  the  middle  ear. 

The  auricula  or  pinna  is  attached  by  its  base  around  the  external  acoustic 
process  in  such  a  manner  as  to  be  freelj^  movable.  In  the  following  description  it 
will  be  assumed  that  the  opening  is  directed  outward  and  that  the  long  axis  is 
practically  vertical.  It  has  two  surfaces,  two  borders,  a  base,  and  an  apex.  The 
convex  surface  or  dorsum  (Dorsum  auriculae)  faces  medially  and  is  widest  in  its 
middle  part;  its  lower  part  is  almost  circular  in  curvature,  while  above  it  narrows 
and  flattens.  The  concave  surface  (Scapha)  is  the  reverse  of  the  dorsum;  it 
presents  several  ridges  which  subside  toward  the  apex.  The  anterior  border  is 
sinuous;  it  is  largely  convex,  but  becomes  concave  near  the  apex.  It  divides  below 
into  two  diverging  parts  (Crura  helicis).  The  posterior  border  is  convex.  The 
apex  is  flattened,  pointed,  and  curved  a  little  forward.  The  base  is  stronglj'-  convex. 
It  is  attached  to  the  external  acoustic  process  of  the  petrous  temporal  bone,  and 
around  this  there  is  a  quantity  of  fat.  The  parotid  gland  overlaps  it  below  and 
laterally.     The  structure  of  the  external  ear  comprises  a  framework  of  cartilages 


THE    EXTERNAL    EAR 


871 


(which  are  chiefly  elastic),  the  integument,  and  a  compHcated  arrangement  of 
muscles. 

The  conchal  or  auricular  cartilage  (Cartilago  auricula;)  determines  the  shape 
of  the  ear;  its  form  can  be  made  out  in  a  general  way  without  dissection,  except 
below,  where  it  is  concealed  by  the  muscles  and  the  parotid  gland.  The  basal  part 
is  coiled  so  as  to  form  a  tube,  which  encloses  the  cavity  of  the  concha  (Cavum  con- 
chse).  This  part  is  funnel-shaped  and  curves  outward  and  a  little  Imckward.  Its 
medial  surface  is  strongly  convex,  forming  a  prominence  termed  the  eminentia 
conchae.  The  lowest  part  of  the  medial  margin  bears  a  narrow,  pointed  prolongation, 
the  styloid  process.  This  process  is  about  an  inch  long  and  projects  downward 
over  the  annular  cartilage;  the  guttural  pouch  is  attached  to  its  free  end.  Behind 
its  base  there  is  a  foramen  through  which  the  auricular  branch  of  the  vagus  passes. 

The  basal  part  of  the  posterior  border  is  cut  into  by  a  notch,  which  separates  two  irregular 
quadrilateral  plates.  The  upper  plate  (Tragus)  is  overlapped  by  the  anterior  border,  and  is  sep- 
arated from  the  adjacent  part  of  the  posterior  border  (Antitragus)  by  a  notch  (Incisura  inter- 
tragica).  The  lower  plate  is  curved  to  form  a  half  ring  and  partly  overlaps  the  anterior  border  and 
the  annular  cartilage.  Behind  the  notch  there  is  a  foramen,  which  transmits  the  internal  auricular 
artery  and  internal  auricular  branch  of  the  facial  nerve. 


The  annular  cartilage  (Cartilago  annularis)  is  a  quadrilateral  plate,  curved  to 
form  about  three-fourths  of  a  ring;  its 
ends  are  a  little  less  than  half  an  inch  (ca. 
1  cm.)  apart  medially  and  are  united  by 
elastic  tissue.  It  embraces  the  external 
acoustic  process  and  forms  with  the  lower 
part  of  the  conchal  cartilage  the  carti- 
laginous part  of  the  external  acoustic 
meatus. 

The  scutiform  cartilage  (Cartilago 
scutiformis  s.  Scutulum)  is  an  irregular 
quadrilateral  plate  which  lies  on  the  tem- 
poral muscle  in  front  of  the  base  of  the 
conchal  cartilage.  Its  superficial  face  is 
slightly  convex  from  side  to  side  and 
its  deep  face  is  correspondingly  concave. 
The  anterior  end  is  thin  and  rounded ;  the 
posterior  part  or  base  is  wider  and  thicker, 
and  its  medial  angle  is  prolonged  by  a 
pointed  process  half  an  inch  or  more  in 
length.  The  cartilage  moves  very  freely 
over  the  underlying  parts. 

The  external  acoustic  meatus  leads 
from  the  cavum  conchse  to  the  tympanic 
membrane.  It  does  not  continue  the 
general  direction  of  the  cavity  of  the 
concha,  but  extends  medially,  downward, 

and  slightly  forward.  It  consists  of  a  cartilaginous  part  (Meatus  acusticus  ex- 
ternus  cartilagineus)  which  is  formed  by  the  lower  part  of  the  conchal  cartilage 
and  the  annular  cartilage,  and  an  osseous  part  formed  by  the  external  acoustic 
process  of  the  temporal  bone.  These  are  united  by  elastic  membranes  to  form  a 
complete  tube.  Its  caliber  diminishes  medially,  so  that  the  lumen  of  the  inner  end 
is  about  half  of  that  of  the  outer  end. 

The  skin  on  the  convex  surface  of  the  concha  presents  no  special  features;  it 
is  attached  to  the  cartilage  by  a  considerable  amount  of  subcutaneous  tissue  except 
at  the  apex.     The  integument  which  lines  the  concave  surface  is  intimately  ad- 


FiG.  699. — Conchal  and  Annular  Cartilages  of 
Ear  of  Horse,  External  View. 
/,  Base  of  concha;  2,  posterior  border,  3,  anterior 
border  of  concha;  4<  intertragic  notch;  5,  eminentia 
conchse;  6,  styloid  process;  7,  annular  cartilage;  9, 
zygomatic  arch.  (After  EUenberger-Baum,  Anat.  fiir 
Kiinstler.) 


872  THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 

herent  to  the  cartilage  and  is  relativelj^  dark  in  color.  There  are  three  or  four 
cutaneous  ridges  which  run  about  parallel  with  the  borders  of  the  conchal  cartilage, 
but  do  not  extend  to  the  apex  or  the  cavum  conchse.  The  upper  and  marginal 
parts  and  the  ridges  are  covered  ■v\'ith  long  hairs,  but  the  skin  between  the  ridges 
and  below  is  thin,  covered  sparsely  with  very  fine  hairs,  and  supplied  ^^^th  numerous 
sebaceous  glands.  In  the  external  acoustic  meatus  the  skin  becomes  thinner;  in 
the  cartilaginous  part  it  is  supplied  with  numerous  large,  coiled,  ceruminous  glands 
(Glandulse  ceruminosse) ,  and  is  sparsely  covered  ^\^th  very  fine  hairs;  in  the  osseous 
part  the  glands  are  small  and  few  or  absent  and  there  are  no  hairs. 

THE  AURICULAR  MUSCLES 

The  auricular  muscles  may  be  subdivided  into  two  sets,  viz.,  (a)  extrinsic 
muscles,  which  arise  on  the  head  and  adjacent  part  of  the  neck,  and  move  the  ex- 
ternal ear  as  a  whole,  and  (b)  intrinsic  muscles,  which  are  confined  to  the  auricula. 
In  this  connection  the  scutiform  cartilage  may  be  regarded  as  a  sesamoid  cartilage 
intercalated  in  the  course  of  some  of  the  muscles. 

The  extrinsic  muscles  are  as  follows: 

1.  The  scutularis  is  a  thin  muscular  sheet  situated  subcutaneously  over  the 
temporalis  muscle.  Its  fibers  arise  from  the  zygomatic  arch  and  the  frontal  and 
parietal  crests,  and  converge  to  the  scutiform  cartilage.     It  consists  of  three  parts: 

(a)  The  fronto-scutularis  comprises  temporal  and  frontal  parts,  which  arise 
from  the  zj'gomatic  arch  and  the  frontal  crest,  and  are  inserted  into  the  lateral  and 
anterior  borders  of  the  scutiform  cartilage  respectively. 

(h)  The  interscutularis  arises  from  the  parietal  crest,  over  which  it  is  in  part 
continuous  "svith  the  muscle  of  the  opposite  side.  Its  fibers  converge  to  the  medial 
border  of  the  scutiform  cartilage. 

(c)  The  cervico-scutularis  is  not  well  defined  from  the  preceding  muscle.  It 
arises  from  the  nuchal  crest  and  is  inserted  into  the  medial  border  of  the  scutiform 
cartilage. 

2.  The  anterior  auricular  muscles  (Mm.  auriculares  orales)  are  four  in  number: 
(a)  The  zygomatico-axiricularis  arises  from  the  zygomatic  arch  and  the  parotid 

fascia,  and  is  inserted  into  the  outer  face  of  the  base  of  the  conchal  cartilage  partly 
under,  partly  above,  the  insertion  of  the  parotido-auricularis. 

(h)  The  scutulo-auricularis  supedicialis  inferior  arises  on  the  lateral  part  of 
the  superficial  face  of  the  scutiform  cartilage  and  ends  on  the  base  of  the  conchal 
cartilage  with  the  preceding  muscle. 

(c)  The  scutulo-auricularis  superficialis  medius  arises  from  the  posterior  part 
of  the  deep  surface  of  the  scutiform  cartilage  and  is  inserted  into  the  dorsum  of  the 
conchal  cartilage,  close  to  the  lower  part  of  its  anterior  border,  and  above  and  behind 
the  preceding  muscle.     It  receives  a  slip  from  the  cervico-scutularis. 

(d)  The  scutulo-auricularis  superficialis  superior  is  a  thin  slip  which  is  de- 
tached from  the  interscutularis  over  the  medial  border  of  the  scutiform  cartilage. 
It  ends  on  the  anterior  aspect  of  the  lower  part  of  the  dorsum  of  the  conchal  car- 
tilage. 

3.  The  dorsal  auricular  muscles  (]\Im.  auriculares  dorsales)  are  two  in 
number. 

(a)  The  scutulo-auricularis  superficialis  accessorius  is  a  narrow  band  which  is 
largely  covered  by  the  preceding  muscle.  It  arises  from  the  posterior  prolongation 
and  the  adjacent  part  of  the  superficial  face  of  the  scutiform  cartilage,  and  is 
inserted  into  the  convex  surface  of  the  conchal  cartilage  medial  to  the  preceding 
muscle,  the  two  crossing  each  other  at  an  acute  angle. 

(6)  The  parieto-auricularis  is  flat  and  triangular;  it  arises  from  the  parietal 
crest  under  cover  of  the  cervico-scutularis,  runs  outward  and  a  little  backward, 


THE    AURICULAR   MUSCLES  873 

and  is  inserted  by  a  flat  tendon  into  the  lower  part  of  the  convex  surface  of  the 
concha  under  cover  of  the  cervico-auricularis  superficialis. 

4.  The  posterior  auricular  muscles  (Mm.  auriculares  aljorales)  are  three  in 
number : 

(a)  The  cervico-auricularis  superficialis  is  a  thin  triangular  sheet.  It  is  wide 
at  its  origin  from  the  nuchal  crest  and  the  adjacent  part  of  the  ligamentum  nuchse, 
and  becomes  narrower  as  it  passes  outward  to  be  inserted  into  the  medial  side  of 
the  convex  surface  of  the  concha. 

(b)  The  cervico-auricularis  profundus  major  arises  from  the  ligamentum 
nuchse,  partly  beneath  and  partly  liehind  the  preceding  muscle.  It  is  directed 
outward  and  is  inserted  into  the  postero-Iateral  aspect  of  the  base  of  the  ear,  partly 
under  cover  of  the  parotido-auricularis. 

(c)  The    cervico-auricularis    profimdus    minor    arises    under   the    preceding 


Fig.  700. — External  Ear  of  Horse  and  its  Muscles;  Lateral  View. 
The  cervico-auricularis  superficialis  has  been  removed.  2,  Posterior  border;  3,  anterior  border  of  auricula;  8, 
scutiform  cartilage;  9,  zygomatic  arch;  n,  parotido-auricularis;  o,  zygomatico-auricularis;  o',  scutulo-auricularis 
superficialis  inferior;  o",  scutulo-auricularis  superficialis  medius  et  superior;  p,  interscutularis;  p',  fronto-scutularis 
(pars  temporalis) ;  g,  cervico-auricularis  profundus  major;  s,  anterior  oblique  muscle  of  head;  «,  splenius;  y,  tendon  of 
brachiocephalicus;   x,  wing  of  atlas.     (After  Ellenberger-Baum,  Anat.  fiir  Kiinstler.) 

muscle  and  passes  downward  and  outward  to  be  inserted  into  the  lowest  part  of 
the  convex  surface  of  the  concha,  partly  under  cover  of  the  parotid  gland. 

5.  The  parotido-auricularis  (s.  M.  auricularis  inferior)  is  a  ribbon-like  muscle 
which  lies  on  the  parotid  gland.  It  is  thin  and  wide  at  its  origin  from  the  fascia  on 
the  lower  part  of  the  parotid  gland,  and  becomes  somewhat  narrower  and  thicker 
as  it  ascends.  It  is  inserted  into  the  conchal  cartilage  just  below  the  angle  of  junc- 
tion of  its  borders. 

6.  The  deep  auricular  or  rotator  muscles  (M.  auricularis  profundi  s.  rotatores 
auriculae),  two  in  number,  are  situated  under  the  scutiform  cartilage  and  the  base 
of  the  concha  and  cross  each  other. 

(a)  The  scutulo-aiuicularis  profimdus  major  is  the  strongest  of  the  auricular 
muscles.     It  is  flat  and  is  about  an  inch  wide.     It  arises  from  the  deep  face  of  the 


874 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 


scutiform  cartilage  and  passes  backward  to  end  on  and  below  the  most  prominent 
part  of  the  base  of  the  concha  (eminentia  conchae). 

(6)  The  scutulo-auricularis  profundus  minor  lies  between  the  base  of  the  con- 
cha and  the  preceding  muscle,  and  is  best  seen  when  the  latter  is  cut  and  reflected. 
It  is  flat  and  about  an  inch  in  length.  It  arises  from  the  posterior  part  of  the  deep 
face  of  the  scutiform  cartilage  and  from  the  cervico-scutularis,  and  passes  down- 
ward, backward,  and  outward  to  be  inserted  into  the  base  of  the  concha  under 
cover  of  the  preceding  muscle. 

7.  The  tragicus  (or  mastoido-auricularis)  is  a  very  small  muscle  which  arises 
from  the  temporal  bone  just  behind  the  external  acoustic  process  and  from  the  an- 


FiG.  701. — Muscles  of  External  Ear  of  Horse;  Dorsal  View. 
On  the  right  side  parts  of  the  superficial  muscles  have  been  removed  and  the  scutiform  cartilage  turned  back  to 
•display  the  deeper  muscles,  n.  Frontal  part;  a',  temporal  part  of  f ronto-scutularis ;  b,  interscutularis;  c,  cervico- 
scutularis;  (I,  e,  scutulo-auricularis  superficialis  superior  and  medius;  /,  zygomatico-auricularis;  g,  scutulo-auricularis 
superficialis  accessorius;  o,  cervico-auricularis  superficiahs;  q,  scutulo-auricularis  superficialis  inferior;  t,  scutiform 
cartilage;  u,  parieto-auricularis ;  v,  cervico-auricularis  profundus  major;  w,  cervico-auricularis  prof,  minor;  x,  x\ 
scutulo-auricularis  prof,  major  et  minor;   y,  temporalis.      (EUenberger-Baum,  Anat.  d.  Haustiere.) 


nular  cartilage;  it  passes  upward  to  be  inserted  into  the  lower  part  of  the  anterior 
border  of  the  conchal  cartilage. 

The  intrinsic  muscles  are  very  small  and  of  little  importance.  The}^  are  as 
follows : 

1.  The  antitragicus  consists  of  a  few  bundles  which  are  attached  to  the  conchal 
cartilage  behind  the  junction  of  its  two  borders,  and  are  partially  blended  with  the 
insertion  of  the  parotido-auricularis. 

2.  The  helicis  is  a  small  muscle  attached  in  a  position  opposite  to  the  preceding 
on  the  anterior  border  of  the  conchal  cartilage ;  it  extends  also  into  the  depression 
between  the  two  divisions  of  the  border.  It  is  in  part  continuous  with  the  insertion 
of  the  parotido-auricularis. 


THE    MIDDLE    EAR  875 

3.  The  verticalis  auriculae^  is  a  thin  stratum  of  muscular  and  tendinous  fibers 
which  extends  upward  on  the  convex  surface  of  the  concha  from  the  eminentia 
conchse. 

Actions. — The  base  of  the  concha  is  rounded  and  rests  in  a  pad  of  fat  (Corpus 
adiposum  auriculae),  so  that  the  movements  of  the  external  ear  resemble  those  of 
a  ball-and-socket  joint.  It  is  noticeable  that  movements  about  the  longitudinal 
and  transverse  axes  are  accompanied  by  rotation.  When  the  ear  is  vertical  or 
drawn  forward  ("pricked  up"),  the  opening  is  usually  directed  forward ;  conversely, 
when  the  ears  are  "laid  back,"  the  opening  faces  backward.  These  movements 
evidently  result  from  the  coordinated  actions  of  several  muscles  which  are  very 
complex  and  cannot  be  discussed  in  detail  here.  The  scutularis  acting  as  a  whole 
fixes  the  scutiform  cartilage,  so  that  the  muscles  which  arise  on  the  latter  act 
efficiently  on  the  concha.  The  anterior  auricular  muscles  in  general  erect  the  ear 
and  turn  the  opening  forward.  The  interscutularis  concurs  in  this  action,  causing 
adduction  and  a  symmetrical  position  of  the  ears;  it  also  acts  directly  on  the 
conchal  cartilage,  since  the  scutulo-auricularis  superficialis  superior  is  in  reality  a 
conchal  insertion  of  the  interscutularis.  The  scutulo-auricularis  superficialis 
accessorius  draws  the  concha  forward  and  turns  the  opening  outward.  The  parieto- 
auricularis  adducts  the  concha  and  inclines  it  forward.  The  cervico-auricularis 
superficialis  is  chiefly  an  adductor  of  the  conchal  cartilage,  and  directs  the  opening 
outward.  The  cervico-auricularis  profundus  major  turns  the  opening  outward  and, 
acting  with  the  parotido-auricularis,  inclines  the  ear  toward  the  poll.  The  cervico- 
auricularis  profundus  minor  tends  to  direct  the  opening  downward  and  outward. 
The  parotido-auricularis  draws  the  ear  downward  and  backward,  and  acts  with  the 
cervico-auricularis  profundus  major  in  "laying  back  the  ears."  The  scutulo- 
auricularis  profundus  major  chiefly  rotates  the  concha  so  that  the  opening  is  turned 
backward.  The  scutulo-auricularis  profundus  minor  assists  in  rotating  the  ear 
so  that  the  opening  is  directed  forward.  The  tragicus  shortens  the  external  acoustic 
meatus.     The  actions  of  the  intrinsic  muscles  are  inappreciable. 

Vessels  and  Nerves. — The  arteries  of  the  external  ear  are  derived  from  the 
anterior  auricular  branch  of  the  superficial  temporal,  the  posterior  or  great  auricular 
branch  of  the  internal  maxillary,  and  the  anterior  branch  of  the  occipital  artery. 
The  veins  go  chiefly  to  the  jugular  and  superficial  temporal  veins.  The  nerves 
to  the  muscles  come  from  the  auricular  and  auriculo-palpebral  branches  of  the 
facial  nerve  and  from  the  first  and  second  cervical  nerves.  The  sensory  nerves  are 
supplied  by  the  superficial  temporal  branch  of  the  mandibular  nerve  and  the 
auricular  branch  of  the  vagus. 

THE  MIDDLE  EAR 

The  middle  ear  (Auris  media)  comprises  the  tympanic  cavity  and  its  contents, 
the  auditive  or  Eustachian  tubes,  and  two  remarkable  diverticula  of  the  latter, 
which  are  termed  the  guttural  pouches. 

The  t3mipanic  cavity  (Cavum  tympani)  is  a  space  in  the  tympanic  and  petrous 
parts  of  the  temporal  bone  situated  between  the  membrana  tympani  and  the  in- 
ternal ear.  It  is  an  air-cavity,  which  is  lined  by  mucous  membrane,  and  communi- 
cates with  the  pharynx  and  the  guttural  pouches  by  the  auditive  or  Eustachian 
tubes.  It  contains  a  chain  of  auditory  ossicles  by  which  the  vibrations  of  the 
membrana  tympani  are  transmitted  to  the  internal  ear. 

The  cavity  consists  of:  (1)  A  main  part  or  atrium,  which  lies  immediately  to 
the  medial  side  of  the  membrana  tympani;  (2)  the  recessus  epitympanicus,  situated 
above  the  level  of  the  membrane  and  containing  the  upper  part  of  the  malleus 

1  Ellenberger  and  Baum  regard  this  aa  the  homologue  of  the  transversus  and  obliquus 
auriculae  of  man. 


876 


THE    SENSE    ORGANS    AND    SKIN    OF   THE    HORSE 


and  the  greater  part  of  the  incus;    (3)  a  relatively  large  ventral  recess  in  the  bulla 


The  lateral,  membranous  wall  (Paries  membranacea)  is  formed  largely  by  the 
thin  membrana  tympani,  which  closes  the  medial  end  of  the  external  acoustic 
meatus,  and  thus  forms  the  septum  between  the  external  and  middle  parts  of  the  ear. 
The  membrane  is  an  oval  disc,  which  slopes  ventro-medially  at  an  angle  of  about 
30  degrees  A\ath  the  lower  wall  of  the  external  acoustic  meatus.  The  circumference 
is  attached  in  a  groove  (Sulcus  tympanicus)  in  the  thin  ring  of  bone  (Annulus 
tjTnpanicus)  which  almost  completely  surrounds  it.  The  handle  of  the  malleus 
(the  outermost  of  the  auditory  ossicles)  is  attached  to  the  inner  surface  of  the 
membrane  and  draws  the  central  part  inward,  producing  a  slight  concavity  of  the 
outer  surface.  The  periphery  is  thickened,  forming  the  annulus  fibrosus.  The 
membrana  tympani  consists  of  three  layers.  The  external  cutaneous  layer  (Stratinn 
cutaneum)  is  a  prolongation  of  the  lining  of  the  external  acoustic  meatus.     The 


Fig.  702. — Right  Petrous  Temporal  Bone  of  Horse; 
Antero-medial  View. 
1,  External  acoustic  meatus;  2,  annulus  tym- 
panicus; S,  laminse  radiating  from  $;  4,  membrana 
tympani;  5,  malleus;  6,  incus;  7,  stapes;  S,  fenestra 
cochlese  (s.  rotundum);  9,  facial  canal;  11,  11",  semi- 
circular canals;  11',  vestibule;  12,  cochlea.  (After 
Ellenberger,  in  Leisering's  Atlas.) 


Fig.  703. — Right  Auditory  Ossicles  and  Mem- 
brana Tympani,  Enlarged  a.vd  Viewed  from 
Inner  Side  and  Below. 

1,  Malleus;  2,  incus;  2',  2" ,  short  and  long  proc- 
esses of  2;  3,  stapes;  4,  tensor  tympani;  3,  ligament 
attaching  long  process  of  malleus;  6,  stapedius  muscle; 
7,  fenestra  cochleae  (s.  rotundum).  (After  Ellenberger,. 
in  Leisering's  .\tlas.) 


middle  fibrous  layer  or  membrana  propria  includes  two  chief  sets  of  fibers;  the 
external  layer  (Stratum  radiatum)  consists  of  fibers  which  radiate  from  the  handle 
of  the  malleus,  while  the  internal  layer  (Stratum  circulare)  is  composed  of  circular 
fibers  which  are  best  developed  peripherally.  There  are  also  branched  or  dendritic 
fibers  in  part  of  the  membrane.  The  internal  mucous  layer  (Stratum  mucosum) 
is  a  part  of  the  general  mucous  membrane  wdiich  lines  the  tympanic  cavity. 

The  medial,  labyrinthine  wall  of  the  tympanic  cavity  (Paries  labyrinthica) 
separates  it  from  the  internal  ear;  it  presents  a  numl^er  of  special  features.  The 
promontory  (Promontorium)  is  a  distinct  eminence  near  the  center  which  corre- 
sponds to  the  first  coil  of  the  cochlea,  and  is  marked  by  a  faint  groove  for  the  super- 
ficial petrosal  nerve.  Above  this  is  the  fenestra  vestibuli,  a  reniform  opening  which 
is  closed  by  the  foot-plate  of  the  stapes  and  its  annular  ligament.  The  fenestra 
cochleae  is  situated  below  and  behind  the  preceding;  it  is  an  irregularly  oval 
opening  and  is  closed  by  a  thin  membrane  (Membrana  tympani  secundaria), 
which  separates  the  tympanic  cavity  from  the  scala  tympani   of  the  cochlea. 

The  anterior,  tubal  wall  (Paries  tubaria)  is  narrow,  and  is  pierf'ed  by  the  slit- 


THE    MIDDLE    EAR 


877 


like  tympanic  opening  of  the  auditive  tube.  Above  this  and  incompletely  separated 
from  it  by  a  thin  plate  of  bone  is  the  semicanal  for  the  tensor  tympani  muscle. 

The  tegmental  wall  or  roof  (Paries  tegmentalis)  is  crossed  in  its  medial  part  by 
the  facial  nerve;  here  the  facial  canal  is  more  or  less  deficient  ventrally,  and  the 
nerve  is  covered  by  the  mucous  membrane  of  the  tympanum. 

The  posterior,  mastoid  wall  (Paries  mastoidea)  presents  nothing  of  importance; 
a  tympanic  antrum  and  mastoid  cells,  such  as  are  found  behind  the  tympanic 
cavity  proper  in  man  and  many  animals,  are  not  present  in  the  horse. 

The  t3mipanic  wall  or  floor  (Paries  tympanica)  is  concave  and  thin.  It  is 
crossed  by  delicate  curved  ridges,  which  radiate  from  the  greater  part  of  the  annulus 
tympanicus. 

The  auditory  ossicles  (Ossicula  auditus)  form  a  chain  which  extends  from  the 
outer  to  the  inner  wall  of  the  cavity.  They  are  named,  from  without  inward,  the 
malleus,  the  incus,  the  os  lenticulare,  and  the  stapes.  The  first  is  attached  to  the 
inner  surface  of  the  tympanic  membrane  and  the  last  is  fixed  in  the  fenestra  ves- 
tibuli. 

The  malleus  or  hammer,  the  largest  of  the  ossicles,  consists  of  a  head,  neck, 
handle,  and  two  processes.     The  bead  (Capitulum  mallei)  is  situated  in  the  epi- 


Fio.    704. — Auditory    Ossicles    and    Membrana 
Tympani;  Medial  View,  Enlarged. 
1,   Annulus  tympanicus;     S,    membrana   tym- 
pani;    J,    malleus;     4,    incus;     5,    stapes.     (After 
Ellenberger,  in  Leisering's  Atlas.) 


Fig.  70o. — Right  Auditory  Ossicles,  Enlarged  as  In- 
dicated BY  Lines  Giving  their  Actual  Length. 
a.  Malleus:  1,  head;  3,  neck;  S,  handle;  4.  long  proc- 
ess; o,  muscular  process,  b.  Incus:  1,  body;  S,  short 
branch;  3,  long  branch;  c,  os  lenticulare.  c.  Stapes;  1, 
head;  2,  crus;  ,3,  base;  .{,  attachment  of  stapedius.  (After 
Ellenberger,  in  Leisering's  Atlas.) 


tympanic  recess.  It  is  smooth  and  convex  above  and  in  front,  and  presents  on 
its  postero-medial  aspect  a  concave  facet  for  articulation  with  the  body  of  the 
incus.  The  neck  (Collum  mallei)  is  the  constricted  part  below  the  head;  its  medial 
surface  is  crossed  by  the  chorda  tympani  nerve.  The  handle  (Manubrium  mallei) 
is  directed  downward,  inward,  and  a  little  forward  from  the  neck,  and  is  attached 
along  its  entire  length  to  the  membrana  tympani.  On  its  medial  surface,  near  the 
upper  end,  there  is  a  slight  projection  to  which  the  tendon  of  the  tensor  tympani 
muscle  is  attached.  The  long  process  (Processus  longus)  is  a  pointed  spicule  which 
projects  forward  from  the  neck  toward  the  petro-tympanic  fissure.  The  short 
process  (Processus  brevis)  is  a  slight  projection  of  the  lateral  side  of  the  neck,  and 
is  attached  to  the  upper  part  of  the  membrana  tympani. 

The  incus  or  anvil  is  situated  chiefly  in  the  epitympanic  recess.  It  may  be 
said  to  resemble  in  miniature  a  human  bicuspid  tooth  with  two  divergent  roots,  and 
consists  of  a  body  and  two  processes.  The  body  (Corpus  incudis)  articulates  with 
the  head  of  the  hammer.  The  long  process  (Crus  longum)  projects  downward 
from  the  body  and  then  curves  inward;  its  extremity  has  attached  to  it  a  small 
nodule  of  bone,  the  os  lenticulare,  which  articulates  with  the  head  of  the  stapes. 
The  short  process  (Crus  breve)  projects  chiefly  backward,  and  is  attached  to  the 
wall  of  the  recess  by  a  small  ligament. 


878  THE   SENSE    ORGANS   AND    SKIN    OF   THE    HORSE 

The  stapes  or  stirrup  consists  of  a  head,  two  crura,  and  a  base.  The  head 
(Capitulum  stapedis)  is  directed  outward  and  articulates  with  the  os  lenticulare. 
The  crura,  anterior  and  posterior  (Crus  anterius,  posterius),  are  directed  inward 
from  the  head,  and  join  the  ends  of  the  base.  The  base  or  foot-plate  (Basis  stapedis) 
occupies  the  fenestra  vestibuli,  to  which  it  is  attached.  The  space  between  the 
crura  and  the  base  is  closed  by  a  membrane. 

The  articulations  and  ligaments  of  the  auditory  ossicles  comprise:  (1)  A 
diarthrodial  joint  between  the  head  of  the  malleus  and  the  body  of  the  incus  (Articu- 
latio  incudomalleolaris),  enclosed  by  a  capsule.  (2)  An  enarthrosis  between  the  os 
lenticulare  and  the  head  of  the  stapes  (Articulatio  incudostapedia),  also  surrounded 
by  a  capsule.  (3)  The  base  of  the  stapes  is  attached  to  the  margin  of  the  fenestra 
vestibuli  by  a  ring  of  elastic  fibers  (Lig.  annulare  baseos  stapedis).  (4)  Small 
ligaments  attach  the  head  of  the  malleus  and  the  short  crus  of  the  incus  to  the  roof 
of  the  epitympanic  recess.  (5)  The  axial  ligament  (of  Helmholtz)  attaches  the 
neck  of  the  malleus  to  a  small  projection  (Spina  tympanica  anterior)  above  and  in 
front  of  the  annulus  tympanicus. 

The  muscles  of  the  auditory  ossicles  are  two  in  number,  viz.,  the  tensor  tj^m- 
pani  and  the  stapedius.  The  tensor  tympani  arises  from  the  upper  wall  of  the 
osseous  Eustachian  tube,  and  ends  in  a  delicate  tendon  which  bends  outward  and 
is  inserted  into  the  handle  of  the  malleus  near  its  upper  end.  When  it  contracts, 
it  draws  the  handle  of  the  malleus  inward  and  tenses  the  membrana  tympani;  it 
probably  also  rotates  the  malleus  around  its  long  axis.  It  is  innervated  by  the 
motor  part  of  the  trigeminus  through  the  otic  ganglion.  The  stapedius  arises  from 
a  small  prominence  (Eminentia  pyramidalis)  of  the  posterior  wall  of  the  tympanum, 
runs  forward  on  the  facial  nerve,  and  is  inserted  into  the  neck  of  the  stapes.  Its 
action  is  to  draw  the  head  of  the  stapes  backward  and  rotate  the  anterior  end  of  the 
base  outward,  thus  tensing  the  aimular  ligament.  It  is  innervated  by  the  facial 
nerve. 

The  tjnnpanic  mucous  membrane  (Tunica  mucosa  tympanica)  is  continuous 
with  that  of  the  pharynx  and  the  guttural  pouch  through  the  auditive  or  Eustachian 
tube.  It  is  thin,  closely  united  with  the  underlying  periosteum,  and  is  reflected 
over  the  ossicles,  ligaments,  and  muscles,  the  chorda  tympani,  and  the  facial  nerve 
in  the  open  part  of  the  facial  canal.  It  contains  minute  lymph  nodules  and  small 
mucous  glands  (Glandulse  tympanicae).  The  epithelium  is  in  general  columnar 
ciliated,  but  over  the  meml^rana  tympani,  ossicles,  and  promontory  it  is  flattened. 

The  artery  of  the  tympanum  is  the  stylo-mastoid,  a  small  vessel  which  arises 
from  the  posterior  auricular  branch  of  the  internal  maxillary  artery.  It  enters  the 
tympanum  through  the  stylo-mastoid  foramen,  and  forms  a  circle  around  the  tym- 
panic membrane.  The  nerves  of  the  mucous  membrane  come  from  the  tympanic 
plexus. 

The  Auditive  or  Eustachian  Tube 
The  auditive  or  Eustachian  tube  (Tul)a  auditiva)  extends  from  the  tympanic 
cavity  to  the  pharynx;  it  transmits  air  to  the  former  and  equalizes  the  pressure 
on  the  two  surfaces  of  the  membrana  tympani.  It  is  directed  forward,  downward, 
and  slightly  inward,  and  is  four  to  five  inches  (ca.  10  to  12  cm.)  in  length.  Its 
posterior  extremity  lies  at  the  medial  side  of  the  root  of  the  muscular  process  of 
the  petrous  temporal,  and  communicates  with  the  anterior  part  of  the  tympanic 
cavity  by  the  small,  slit-like  tympanic  opening  (Ostium  tympanicum  tubae  auditiva?). 
For  a  distance  of  about  a  quarter  of  an  inch  (ca.  6-7  mm.)  in  front  of  this  opening 
it  is  a  complete  tube,  with  a  curved  lumen  which  is  little  more  than  a  capillary  space. 
Further  forward  it  has  the  form  of  a  plate  which  widens  anteriorly  and  is  curved  to 
enclose  a  narrow  groove  that  opens  ventrally  into  an  extensive  diverticulum  termed 
the  guttural  pouch.     The  pharyngeal  opening  (Ostium  pharyngeum  tuba?  audit- 


THE  GUTTURAL  POUCHES  879 

tivse)  is  situated  on  the  postero-superior  part  of  the  lateral  wall  of  the  pharynx,  just 
below  the  level  of  the  posterior  nares  (Fig.  349).  It  is  a  slit,  about  two  inches 
(ca.  5  cm.)  in  length,  which  slopes  downward  and  backward.  It  is  bounded  medi- 
ally by  the  thin  free  edge  of  the  tube,  from  the  lower  part  of  which  a  fold  of  mucous 
membrane  (Plica  salpingo-pharyngea)  extends  in  the  same  direction  on  the  lateral 
wall  of  the  pharynx  for  a  distance  of  a  little  more  than  an  inch  usually.  The  outer 
boundary  of  the  opening  is  the  lateral  wall  of  the  pharynx.  The  basis  of  the  tube 
is  a  plate  of  fibro-cartilage  (Cartilago  tubse  auditivae)  which  is  firmly  attached 
dorsally  to  the  fibrous  tissue  which  closes  the  foramen  lacerum,  the  temporal  wing 
of  the  sphenoid,  and  the  pterygoid  bone.^  On  cross-section  the  cartilage  is  seen 
to  consist — except  at  its  ends — of  two  laminse  which  are  continuous  with  each 
other  above  (Fig.  348).  The  medial  lamina  (Lamina  medialis)  gradually  widens 
toward  the  pharyngeal  end,  where  it  forms  a  broad  valvular  flap;  this  is  convex 
medially,  and  its  thin  anterior  edge  forms  the  basis  of  the  inner  margin  of  the  pharyn- 
geal opening.  Behind  this  the  lamina  has  a  thick  free  edge  which  projects  ventrally 
from  the  roof  of  the  guttural  pouch.  The  lateral  lamina  (Lamina  lateralis)  is 
narrow  and  thin,  and  is  related  laterally  to  the  levator  and  tensor  palati  muscles, 
which  are  in  part  attached  to  it;  it  does  not  extend  to  the  pharyngeal  end  of  the 
tube.  The  mucous  membrane  of  the  tube  is  continuous  behind  with  that  of  the 
tympanum  and  in  front  with  that  of  the  pharynx.  On  either  side  it  is  reflected  to 
form  a  large  diverticulum,  the  guttural  pouch.  It  is  covered  with  ciliated  epi- 
thelium, and  contains  mucous  glands  and  lymph  nodules. 

The  pharyngeal  opening  appears  to  be  closed  ordinarily.  Vermeulen  states  that  it  opens 
during  deglutition,  and  that  tliis  action  is  apparently  produced  by  the  part  of  the  palato-pharyn- 
geus  muscle  which  is  attached  to  the  flap-hke  expanded  part  of  the  tube. 

The  Guttural  Pouches 
The  guttural  pouches,  right  and  left  (Figs.  349,  706),  are  large  mucous  sacs, 
each  cf  which  is  a  ventral  diverticulum  of  the  Eustachian  tube  (Diverticulum 
tubse  auditivse) ;  they  are  not  present  in  the  domesticated  animals  other  than  the 
equidse.  They  are  situated  between  the  base  of  the  cranium  and  the  atlas  dorsally 
and  the  pharynx  ventrally.  Medially  they  are  in  apposition  in  part,  but  are  to 
some  extent  separated  by  the  intervening  ventral  straight  muscles  of  the  head. 
The  anterior  end  is  a  small  cul-de-sac  which  lies  below  the  body  of  the  presphenoid, 
between  the  Eustachian  tube  and  the  median  recess  of  the  pharynx.  The  posterior 
end  lies  near  or  below  the  atlantal  attachment  of  the  longus  colli.  The  pouch 
is  related  dorsally  to  the  base  of  the  cranium,  the  atlanto-occipital  joint  capsule, 
and  the  ventral  straight  muscles.  Ventrally  it  lies  on  the  pharynx  and  the  origin 
of  the  oesophagus.  Laterally  the  relations  are  numerous  and  complex.  They 
comprise  the  pterygoid,  levator  palati,  tensor  palati,  stylo-hyoideus,  occipito- 
hyoideus,  occipito-mandibularis,  and  digastricus  muscles;  the  parotid  and  mandib- 
ular salivary  glands;  the  external  carotid,  internal  maxillary,  and  external  maxil- 
lary arteries;  the  internal  maxillary  and  jugular  veins;  the  pharyngeal  lymph 
glands;  the  glosso-pharyngeal,  hypoglossal,  and  anterior  laryngeal  nerves.  The 
vagus,  accessory,  and  sympathetic  nerves,  the  anterior  cervical  ganglion,  the  in- 
ternal carotid  artery,  and  the  ventral  cerebral  vein  are  situated  in  a  fold  of  the 
dorsal  part  of  the  pouch.  The  pouch  is  reflected  around  the  dorsal  border  of  the 
great  cornu  of  the  hyoid  bone  so  as  to  clothe  both  surfaces  of  the  dorsal  part  of  the 
latter.  It  thus  forms  an  outer  compartment,  which  extends  backward  lateral  to 
the  great  cornu  and  the  occipito-hyoideus  muscle;  this  compartment  is  related 
laterally  to  the  parotid  gland,  the  articulation  of  the  jaw,  the  ascending  part  of  the 
internal  maxillary  artery,  the  superficial  temporal  artery,  and  the  facial  nerve;  dor- 

1  There  is,  strictly  speaking,  no  osseous  part  of  the  tube  3uch  as  occurs  in  man.  In  the  horse 
the  cartilage  extends  to  the  tympanic  orifice. 


880 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 


sally  it  covers  the  mandibular  nerve  and  its  chief  branches,  and  is  attached  to  the 
styloid  process  of  the  conchal  cartilage. 

Each  pouch  communicates  with  the  pharynx  through  the  pharyngeal  orifice 
of  the  Eustachian  tube,  and  is  in  direct  continuity  with  the  mucous  membrane  of 
the  latter. 

The  average  capacity  of  each  pouch  is  about  ten  fluidounces  (ca.  300  c.c);  of 
this,  the  lateral  compartment  is  about  one-third. 


Temporal  muscle 


Scutiform  cartilage, 
posterior  process 


Conchal  cartilage 

Brachiocephalicus 
tendon 


Nerves  IX,  X,  XI 

^  'entral  cerebral  vein 
Internal  carotid  artery 
(luttural  pouch 
Occipito-hyoideus 
muscle 

Jugular  vein 

Int.  maxillary  artery 
Ext.  maxillary  artery 

Parapharyngeal  lymph 
glands 

Occipito-mandibularis 
muscle 

Sterno-cephalicus  tendon 
Mandibular  gland 
Thyroid  cartilage 
Ext.  maxillary  vein 


Omo-hyoidei  +  sterno-hyoidei 
Fig.  706. — Cross-section  of  Head  of  Horse. 
The  section  passes  through  the  base  of  the  external  ear  and  just  behind  the  posterior  border  of  the  mandible.  1, 
Rectus  capitis  ventrahs  minor;  2,  rectus  capitis  ventralis  major;  3,  medial  walls  of  guttural  pouches  in  apposition; 
4,  4.  arytenoid  cartilage,  upper  piece  being  apex;  5,  posterior  pillar  of  soft  palate;  6,  false  vocal  cord;  7,  lateral  ventricle 
of  larynx;  S,  true  vocal  cord;  S,  vocal  muscle;  70,  thyro-hyoideus  muscle.  The  cavity  in  which  the  number  .5  is  placed 
is  the  pharynx,  which  was  left  unmarked  by  an  oversight. 


The  pouch  is  a  delicate  mucous  membrane  which  is  in  general  rather  loosely 
attached  to  the  surrounding  structures.  It  is  lined  with  ciliated  epithelium  and  is 
supplied  with  glands  which  are  chiefly  mucous  in  type. 

It_  is  worthy  of  note  that  the  pharyngeal  orifice  of  the  Eustachian  tube  is  at  such  a  level  as 
to  provide  (in  the  ordinary  position  of  the  head)  only  an  overflow  outlet  for  the  escape  of  fluid 
which  may  accumulate  in  the  pouch.  The  expanded  part  of  the  tube  forms  with  the  wall  of  the 
pharynx  a  sort  of  vestibule,  at  the  posterior  part  of  which  is  the  opening  of  the  guttural  pouch. 


THE    INTERNAL    EAR THE    OSSEOUS    LABYRINTH  881 

This  opening  is  only  about  an  inch  (ca.  2.5  cm.)  long.  The  two  pouches  are  often  unequal  in  size, 
and  variations  in  regard  to  the  distance  which  they  extend  backward  are  not  uncommon.  In  one 
case,  for  instance,  a  small  aged  horse,  the  right  pouch  extended  along  the  oesophagus  about  five 
inches  (ca.  12  cm.)  behind  the  ventral  tubercle  of  the  atlas,  and  the  left  one  a  little  more  than  two 
inches  (ca.  6  cm.) .  No  pathological  changes  were  apparent,  and  the  condition  was  not  recognizable 
externally.  Cases  of  extreme  size — so-called  tympanites —  of  the  pouches  occur,  and  are  apparently 
congenital  defects.  In  a  case  in  a  yearling  cok,  the  head  of  which  was  24  inches  long,  the  left 
pouch  extended  about  12  inches  (ca.  30  cm.)  behind  the  tubercle  of  the  atlas,  and  had  a  capacity 
of  six  quarts.  The  anterior  end  formed  a  cul-de-sac  about  two  inches  (ca.  5  cm.)  long  between  the 
Eustachian  tube  and  levator  palati  medially  and  the  lateral  pterygoid  muscle  laterally. 

THE  INTERNAL  EAR 
The  internal  ear  or  labyrinth  (Auris  interna  s.  Labyrinthus)  consists  of  two 
parts,  viz.:  (1)  A  complex  membranous  sac,  which  supports  the  auditory  cells  and 
the  peripheral  ramifications  of  the  auditory  nerve;  (2)  a  series  of  cavities  in  the 
petrous  temporal  bone,  which  encloses  the  membranous  part.  The  first  is  called 
the  membranous  labyrinth,  and  contains  a  fluid,  the  endolymph.  The  second  is 
the  osseous  labyrinth.  The  two  are  separated  by  the  perilymphatic  space,  which  is 
occupied  by  a  fluid  termed  the  perilymph. 

The  Osseous  Labyrinth 
The  osseous  labyrinth  (Labyrinthus  osseus)  (Fig.  702)  is  excavated  in  the 
petrous  temporal  bone  medial  to  the  tympanic  cavity.     It  consists  of  three  divisions': 
(1)  a  middle  part,  the   vestibule;    (2)  an  anterior  one,  the  cochlea ;   and  (3)  a  pos- 
terior one,  the  semicircular  canals. 

1.  The  vestibule  (Vestibulum)  is  the  central  part  of  the  osseous  labyrinth, 
and  communicates  in  front  with  the  cochlea,  behind  with  the  semicircular  canals. 
It  is  a  small,  irregularly  ovoid  cavity,  which  is  about  5  to  6  mm.  in  length.  Its 
lateral  wall  separates  it  from  the  tympanic  cavity,  and  in  it  is  the  fenestra  vestibuli, 
which  is  occupied  by  the  base  of  the  stapes.  The  medial  wall  corresponds  to  the 
fundus  of  the  internal  acoustic  meatus.  It  is  crossed  by  an  oblique  ridge,  the 
crista  vestibuli,  which  separates  two  recesses.  The  anterior  and  smaller  of  these  is 
the  recessus  sphdericus,  which  lodges  the  saccule  of  the  membranous  labyrinth. 
In  its  lower  part  there  are  about  a  dozen  minute  foramina  which  transmit  filaments 
of  the  vestibular  nerve  to  the  saccule.  The  posterior  and  larger  depression  is  the 
recessus  ellipticus,  which  lodges  the  utricle  of  the  membranous  labyrinth.  The 
crista  vestibuh  divides  below  into  two  divergent  branches,  which  include  between 
them  the  small  recessus  cochlearis ;  this  is  perforated  by  small  foramina,  through 
which  nerve-bundles  reach  the  ductus  cochlearis.  Similar  foramina  in  the  recessus 
elhpticus  and  the  crista  vestibuli  transmit  nerve  filaments  to  the  utricle  and  the 
ampullae  of  the  dorsal  and  lateral  semicircular  ducts.  The  anterior  wall  is  pierced 
by  an  opening  which  leads  into  the  scala  vestibuli  of  the  cochlea.  The  posterior  part 
of  the  vestibule  presents  the  four  openings  of  the  semicircular  canals.  The  inner 
opening  of  the  aquaeductus  vestibuh  is  a  small  slit  behind  the  lower  part  of  the 
crista  vestibuli.  The  aquaeductus  passes  backward  in  the  petrous  temporal  bone, 
and  opens  on  the  medial  surface  of  the  latter  near  the  middle  of  its  posterior  border; 
it  contains  the  ductus  endolymphaticus. 

2.  The  osseous  semicircular  canals  (Canales  semicirculares  ossei),  three  in 
number,  are  situated  behind  and  above  the  vestibule.  They  are  at  right  angles  to 
each  other,  and  are  designated  according  to  their  positions  as  dorsal,  posterior, 
and  lateral.  They  communicate  with  the  vestibule  by  four  openings  only,  since 
the  inner  end  of  the  dorsal  and  the  upper  end  of  the  posterior  canal  unite  to  form  a 
common  canal  (Crus  commune),  and  the  ampuUate  ends  of  the  dorsal  and  lateral 
canals  have  a  common  orifice.  Each  canal  forms  about  two-thirds  of  a  circle, 
one  end  of  which  is  enlarged  and  termed  the  ampulla.  The  dorsal  canal  (Canalis 
semicircularis  dorsalis)  is  nearly  vertical  and  is  placed  obliquely  with  regard  to  a 

56 


gS2  THE    SENSE    ORGANS    AND    SKIN    OF    THE    HORSE 

sagittal  plane,  so  that  its  outer  liml)  is  further  forward  then  than  the  inner  one.  The 
antero-lateral  end  is  the  ampulla  and  opens  into  the  vestibule  with  that  of  the  lateral 
canal.  The  opposite  non-dilated  end  joins  the  adjacent  end  of  the  posterior  canal 
to  form  the  crus  commune,  which  opens  into  the  dorso-medial  part  of  the  vestibule. 
The  posterior  canal  (Canalis  semicircularis  posterior)  is  also  nearly'  vertical.  Its 
ampulla  is  ventral,  and  opens  into  the  vestibule  directly,  while  the  non-dilated 
end  joins  that  of  the  dorsal  canal.  The  lateral  canal  (Canalis  semicircularis  lateralis) 
is  nearly  horizontal.  Its  ampulla  is  external  and  opens  into  the  vestibule  with  that 
of  the  dorsal  canal. 

3.  The  cochlea  is  the  anterior  part  of  the  bony  labyrinth.  It  has  the  form  of  a 
short  blunt  cone,  the  base  of  which  (Basis  cochleae)  corresponds  to  the  anterior 
part  of  the  fundus  of  the  internal  acoustic  meatus,  while  the  apex  or  cupola  (Cupola) 
is  directed  outward,  forward,  and  downward.  It  measures  about  7  mm.  across  the 
base  and  about  4  mm.  from  base  to  apex.  It  consists  of  a  spiral  canal  (Canalis 
spiralis  cochleae) ,  which  forms  two  and  a  half  turns  around  a  central  column  termed 
the  modiolus.  The  modiolus  diminishes  rapidly  in  diameter  from  base  to  apex. 
Its  base  (Basis  modioli)  corresponds  to  the  area  cochleae  of  the  fundus  of  the  internal 
acoustic  meatus,  and  its  apex  extends  nearly  to  the  cupola.  Projecting  from  the 
modiolus  like  the  thread  of  a  screw  is  a  thin  plate  of  bone,  the  lamina  spiralis  ossea. 
This  begins  between  the  two  fenestras  and  ends  near  the  cupola  as  a  hook-like 
process  (Hamulus  laminae  spiralis).  The  lamina  extends  about  half-way  to  the 
periphery  of  the  cochlea  and  partly  divides  the  cavity  into  two  passages;  of  these, 
the  upper  one  is  termed  the  scala  vestibuli,  and  the  lower  the  scala  tympani.  The 
membrana  basilaris  extends  from  the  free  margin  of  the  lamina  to  the  lateral  wall 
of  the  cochlea  and  completes  the  septum  between  the  two  scalae,  but  they  com- 
municate through  the  opening  at  the  cupola  (Helicotrema).  The  modiolus  is 
traversed  by  an  axial  canal  which  transmits  the  nerves  to  the  apical  coil,  and  by  a 
spiral  canal  (Canalis  spiralis  modioli),  which  follows  the  attached  border  of  the 
lamina  spiralis,  and  contains  the  spiral  ganglion  and  vein.  Close  to  the  beginning 
of  the  scala  tympani  is  the  inner  orifice  of  the  aquaeductus  cochleae,  a  small  canal 
which  opens  behind  the  internal  acoustic  meatus,  and  establishes  a  communication 
between  the  scala  tympani  and  the  subarachnoid  space. 

The  internal  acoustic  meatus  has  been  described  in  part  {vide  Osteology). 
The  fundus  of  the  meatus  is  divided  by  a  ridge  (Crista  transversa)  into  upper  and 
lower  parts.  The  anterior  part  of  the  upper  depression  (Area  n.  facialis)  presents 
the  internal  opening  of  the  facial  canal;  and  the  posterior  part  (Area  vestibularis 
superior)  is  perforated  by  foramina  for  the  passage  of  nerves  to  the  utricle  and 
the  ampullae  of  the  dorsal  and  lateral  semicircular  ducts.  The  anterior  part  of 
the  inferior  depression  (Area  cochleae)  presents  a  central  foramen  and  a  spiral  tract 
of  minute  foramina  (Tractus  spiralis  foraminosus)  for  the  passage  of  nerves  to  the 
cochlea.  Behind  these  is  an  area  of  small  openings  which  transmit  nerves  to  the 
saccule  (Area  vestibularis  inferior),  and  the  foramen  singulare  for  the  passage  of  a 
nerve  to  the  ampulla  of  the  posterior  semicircular  duct. 

The  Membranous  Labyrinth 

The  membranous  labyrinth  (Labyrinthus  membranaceus)  lies  within,  but 
does  not  fill,  the  osseous  labyrinth.  It  is  attached  to  the  latter  by  delicate  tra- 
beculae  which  traverse  the  perilymphatic  space.  It  conforms  more  or  less  closely 
to  the  bony  labyrinth,  but  consists  of  four  divisions,  since  the  vestibule  contains 
two  membranous  sacs — the  utricle  and  saccule. 

1.  The  utricle  (Utriculus),  the  larger  of  the  two  sacs,  lies  in  the  postero- 
superior  part  of  the  vestibule,  largely  in  the  recessus  ellipticus.  It  receives  the 
openings  of  the  semicircular  ducts,  and  the  small  ductus  utriculo-saccularis  leads 
from  its  lower  part  to  the  ductus  endolymphaticus. 


THE    MEMBRANOUS   LABYRINTH 


883 


2.  The  saccule  (Sacculus)  is  situated  in  the  recessus  sphaericus  of  the  vestibule. 
From  its  lower  part  the  ductus  reuniens  proceeds  to  open  into  the  ductus  cochlearis, 
a  little  in  front  of  the  blind  end  of  the  latter.  A  second  narrow  tube,  the  ductus 
endolymphaticus,  passes  from  the  posterior  part  of  the  saccule,  and  is  joined  by  the 
ductus  utriculo-saccularis;  it  then  traverses  the  aquaeductus  vestibuli,  and  ter- 
minates under  the  dura  mater  on  the  posterior  part  of  the  medial  surface  of  the 
petrous  temporal  bone  in  a  dilated  blind  end,  the  saccus  endolymphaticus. 

3.  The  semicircular  ducts  (Ductus  semicirculares)^  correspond  in  general  to 
the  osseous  canals  already  described,  but  it  may  be  noted  that  while  the  ampullae  of 
the  ducts  nearly  fill  those  of  the  osseous  canals,  the  other  parts  of  the  ducts  only 
occupy  about  one-fourth  of  the  bony  cavities. 

4.  The  cochlear  duct  (Ductus  cochlearis)  is  a  spiral  tube  situated  within  the 
cochlea.  It  begins  by  a  blind  end  (Caecum  vestibulare)  in  the  cochlear  recess  of 
the  vestibule,  and  ends  by  a  second  blind  end  (Caecum  cupulare) ,  which  is  attached 
to  the  cupola  of  the  cochlea.  The  vestibular  part  is  connected  with  the  saccule 
by  the  ductus  reuniens.  The  duct  is  triangular  in  cross-section,  and  it  is  usual  to 
regard  it  as  having  three  walls.  The  vestibular  wall  or  roof,  which  separates  the 
cochlear  duct  from  the  scala  vestibuli,  is  formed  by  the  very  delicate  membrana 
vestibularis  (of  Reissner),  which  extends  obliquely  from  the  lamina  spiralis  ossea 


Fig.  707. — Left  Membranous  Labyrinth  (En- 
larged). 
i.  Cochlea;  ;2,  fenestra  vestibuli;  3,  fenestra  coch- 
leae; 4.  ductus  endolymphaticus;  5,  dorsal,  6,  lateral,  7, 
ventral,  duct.  (After  EUenberger,  in  Leisering's  At- 
las.) 


Fig.  708.— Schematic  Sectional  View  of  Labyrinth 
(Enlarged). 
1,    2,    3,    Dorsal,    lateral,    and   ventral   ducts;     4. 
utricle;     5,    saccule;     6,    cochlea;      7,    acoustic    nerve. 
(After  EUenberger,  in  Leisering's  Atlas.) 


to  the  outer  wall  of  the  cochlea.  The  tympanic  wall  or  floor  intervenes  between 
the  cochlear  duct  and  the  scala  tympani;  it  is  formed  by  the  periosteum  of  the  mar- 
ginal part  of  the  lamina  spiralis  and  the  membrana  basilaris,  which  stretches  be- 
tween the  free  edge  of  the  lamina  and  the  outer  wall  of  the  cochlea.  The  outer 
wall  consists  of  the  fibrous  lining  of  the  cochlea,  which  is  greatly  thickened  to  formi 
the  ligamentum  spirale  cochleae. 

Structure.^ — The  membranous  labyrinth  consists  in  general  of  an  outer  thin 
fibrous  layer,  a  middle  transparent  tunic,  and  an  internal  epithelium,  composed  of 
flattened  cells.  But  in  certain  situations  special  and  remarkable  structures  occur, 
among  which  are  the  following:  (1)  The  maculae  acousticae  appear  as  small  whitish 
thickenings  of  the  inner  walls  of  the  saccule  and  utricle.  The  epithelium  here 
consists  of  two  kinds  of  cells,  viz.,  supporting  cells  and  hair  cells.  The  latter  are 
flask-shaped  and  are  surrounded  by  the  fusiform  supporting  cells.  The  free  end 
of  each  hair  cell  bears  a  stiff,  hair-like  process  composed  of  a  bundle  of  cilia.  Fibers 
of  the  saccular  and  utricular  branches  of  the  vestibular  nerve  form  arborizations 
about  the  basal  parts  of  the  hair  cells.     Adherent  to  the  surface  of  the  maculae 

1  Also  termed  the  membranous  semicircular  canals. 

2  For  the  finer  structure  reference  is  to  be  made  to  the  histological  Uterature. 


884  THE    SENSE    ORGANS   AND    SKIN    OF   THE    HORSE 

are  fine  crystals  of  lime  salts,  embedded  in  a  mucoid  substance,  and  termed  otoconia. 
(2)  The  cristae  acusticae  are  linear  thickenings  of  the  wall  of  each  ampulla  of  the 
semicircular  ducts.  Their  structure  is  similar  to  that  of  the  maculae.  (3)  The 
spiral  organ  of  Corti  (Organon  spirale)  is  an  epithelial  elevation  which  is  situated 
upon  the  inner  part  of  the  membrana  basilaris,  and  extends  the  entire  length  of  the 
ductus  cochlearis.  It  is  very  complicated  in  structure,  but  consists  essentially  of 
remarkable  supporting  cells  and  hair  cells.  Fibers  of  the  cochlear  nerve  ramify 
about  the  basal  parts  of  the  hair  cells. 

Vessels  and  Nerves. — The  artery  of  the  internal  ear  is  the  internal  auditory 
artery,  a  very  small  vessel  which  usually  arises  from  the  posterior  cerebellar  artery, 
and  enters  the  internal  acoustic  meatus.  The  veins  go  to  the  ventral  petrosal 
sinus.  The  vestibular  nerve  is  distributed  to  the  utricle,  saccule,  and  semi- 
circular ducts,  and  mediates  equilibration.  The  cochlear  nerve  gives  a  branch 
to  the  saccule  and  enters  the  central  canal  of  the  modiolus.  Along  its  course  it 
gives  off  fibers  which  radiate  outward  between  the  two  plates  of  the  lamina  spiralis 
ossea,  and  ramify  about  the  hair  cells  of  the  organ  of  Corti.  The  ganglion  spirale 
is  situated  in  the  spiral  canal  of  the  modiolus  near  the  fixed  border  of  the  lamina 
spiralis.     The  cochlear  nerve  mediates  the  sense  of  hearing. 


The  Common  Integument 

The  common  integument  (Integumentum  commune)  is  the  protective  covering 
of  the  body,  and  is  continuous  at  the  natural  openings  with  the  mucous  membranes 
of  the  digestive,  respiratory,  and  urogenital  tracts.  It  consists  of  the  skin  (Cutis), 
together  with  certain  appendages  or  modifications  thereof,  as  hair,  horn,  feathers,  etc. 
It  contains  peripheral  ramifications  of  the  sensory  nerves,  and  is  thus  an  important 
sense  organ.  It  is  the  principal  factor  in  the  regulation  of  the  temperature  of  the 
body,  and  by  means  of  its  glands  it  plays  an  important  part  in  secretion  and  ex- 
cretion. Some  of  its  special  horny  modifications  or  appendages  are  used  as  organs 
of  prehension  or  as  weapons. 

The  thickness  of  the  skin  varies  in  the  different  species,  on  different  parts  of 
the  body  of  the  same  animal,  and  also  with  the  breed,  sex,  and  age.  The  color 
also  varies  greatly,  but  this  is  masked  in  most  places  by  the  covering  of  hair  or  wool. 
The  skin  is  in  general  highly  elastic  and  resistant. 

Permanent  folds  of  the  skin  (Plicse  cutis)  occur  in  certain  situations,  and  in 
some  places  there  are  cutaneous  pouches  or  diverticula  (Sinus  cutis) . 

The  skin  is  attached  to  the  underlying  parts  by  the  subcutaneous  tissue  or 
subcutis  (Tela  subcutanea).  This  consists  of  connective  tissue  containing  elastic 
fibers  and  fat.  When  the  fat  forms  a  layer  of  considerable  thickness,  it  is  termed 
the  panniculus  adiposus.  Over  a  considerable  part  of  the  body  the  subcutis  con- 
tains striped  muscle,  the  m.  cutaneus  or  panniculus  camosus ;  in  some  regions  the 
fibers  of  the  muscle  are  inserted  into  the  skin,  and  their  contraction  tAvitches  the 
skin  or  produces  temporary  folds.^  The  amount  of  subcutaneous  tissue  varies 
widely;  in  some  places  it  is  abundant,  so  that  the  skin  can  be  raised  considerably; 
in  other  situations  it  is  practically  absent  and  the  skin  is  closely  adherent  to  the 
subjacent  structures.  Subcutaneous  bursas  often  develop  over  prominent  parts 
of  the  skeleton  where  there  is  much  pressure  or  friction,  e.  g.,  at  the  olecranon, 
tuber  coxae,  tuber  calcis. 

Structure. — The  skin  consists  of  two  distinct  strata,  viz.,  a  superficial  epithelial 
layer,  the  epidermis,  and  a  deep  connective-tissue  layer,  the  coritmi.  The  epi- 
dermis is  a  non-vascular,  stratified  epithelium  of  varying  thickness.     It  presents 

^  This  muscle  has  been  described  in  the  Myology. 


THE    COMMON    INTEGUMENT  885 

the  openings  of  the  cutaneous  glands  and  the  hair-folhcles,  and  its  deep  surface  is 
adapted  to  the  corium.^  It  is  divisible  into  a  superficial,  harder,  drier  part,  the 
stratum  comeum,  and  a  deeper,  softer,  moister  part,  the  stratum  germinativum. 
The  cells  of  the  latter  contain  pigment,  and  by  their  proliferation  compensate  the 
loss  by  desquamation  of  the  superficial  part  of  the  stratmn  corneum.  In  many 
places  further  subdivision  into  strata  is  evident  on  properly  prepared  cross-sections. 
The  cerium  consists  essentially  of  a  feltwork  of  white  and  elastic  fibers.  It  is  well 
supplied  with  vessels  and  nerves,  and  contain  the  cutaneous  glands,  the  hair-fol- 
licles, and  unstriped  muscle.  The  deeper  part  of  the  corium,  the  tunica  propria, 
consists  of  a  relatively  loose  network  of  coarse  bundles  of  fibers,  and  in  most  places 
there  is  no  clear  line  of  demarcation  between  it  and  the  subcutis.  The  superficial 
part,  the  corpus  papillare,  is  of  finer  texture  and  is  free  from  fat.  Its  superficial 
face  is  thickly  beset  with  blunt  conical  prominences,  the  papillae,  which  are  received 
into  corresponding  depressions  of  the  epidermis.  They  contain  vascular  loops  and 
nerves,  or,  in  certain  situations,  special  nerve-endings.^ 

The  glands  of  the  skin  (Glandulse  cutis)  are  chiefly  of  two  kinds,  sudoriferous 
and  sebaceous.  The  sudoriferous  or  sweat  glands  (Glandulae  sudoriferse)  consist 
of  a  tube,  the  lower,  secretory  part  of  which  is  coiled  in  the  deep  part  of  the  corium 
or  in  the  subcutis  to  form  a  round  or  oval  ball  (Corpus  glandulae  sutloriferse).  The 
excretory  duct  (Ductus  sudoriferus)  passes  almost  straight  up  through  the  corium, 
but  pursues  a  more  or  less  flexuous  course  through  the  epidermis,  and  opens  into  a 
hair-follicle  or  by  a  funnel-shaped  pore  (Porus  sudoriferus)  on  the  surface  of  the 
skin.  The  sebaceous  glands  (Glandulae  sebaceae)  are  in  great  part  associated  with 
the  hairs,  into  the  follicles  of  which  they  open.  Their  size  varies  widely,  and  is 
in  general  in  inverse  ratio  to  that  of  the  hair.  The  larger  ones  are  easily  seen  with 
the  naked  eye,  and  appear  as  small,  pale  yellow  or  brownish  bodies.  In  certain 
situations  (e.  g.,  the  labia,  vulvae,  anus,  prepuce)  they  are  independent  of  the  hairs 
and  are  well  developed.  In  form  they  may  be  branched  alveolar,  simple  alveolar, 
or  even  tubular  in  type.  They  secrete  a  fatty  substance,  the  sebum  cutaneum, 
which  serves  as  a  protective  against  moisture,  and  may  also  (by  its  aromatic  con- 
stituents) play  an  important  part  in  the  sexual  life  of  animals. 

The  two  kinds  of  glands  described  above  are  those  which  are  most  widely  distributed,  but 
many  special  types  occur.  Some  of  these  are  to  be  regarded  as  modified  sweat  glands,  e.  g.,  the 
naso-labial  glands  of  the  ox,  the  glands  of  the  snout  of  the  pig,  and  the  glands  of  the  digital 
cusliion  of  the  horse.  Others,  e.  g.,  the  tarsal  glands  of  the  eyelids,  are  modified  sebaceous.  Still 
others  are  not  yet  classified  satisfactorily.  Some  of  these  special  types  have  been  referred  to  in 
previous  chapters,  and  others  will  receive  attention  in  the  special  descriptions  which  follow.  The 
mammary  glands  are  highly  modified  cutaneous  glands,  which  are  intimately  associated  in  func- 
tion with  the  genital  organs,  and  have  been  described  with  the  latter. 

Vessels  and  Nerves. — The  arteries  of  the  skin  enter  from  the  subcutis,  where 
they  communicate  freely.  In  the  deeper  part  of  the  corium  they  form  a  plexus, 
and  another  network  is  formed  under  the  papillae.  Small  vessels  from  the  deep 
plexus  go  to  the  fat  and  sweat  glands,  and  the  subpapillary  plexus  sends  fine 
branches  to  the  papillae,  hair-follicles,  and  sebaceous  glands.  The  veins  form  two 
plexuses,  one  beneath  the  papillae,  and  another  at  the  junction  of  the  corium  and 
subcutis.     The  lymph  vessels  form  subpapillary  and  subcutaneous  plexuses. 

The  nerves  vary  widely  in  number  in  different  parts  of  the  skin.  The  terminal 
fibers  either  end  free  in  the  epidermis  and  in  certain  parts  of  the  corium,  or  form 
special  microscopic  corpuscles  of  several  kinds. 

1  To  prevent  a  possible  misapprehension,  it  may  be  stated  that  the  epidermis  primarily 
molds  the  corium,  and  that  the  glands  and  hair-follicles  are  invaginations  of  the  epidermis. 

2  The  papiUiE  are  best  developed  where  the  epidermis  is  thick  and  hairs  are  small  or  absent. 
On  tliickly  haired  regions  they  are  small  or  even  absent.  On  certain  parts  of  the  body  (anus, 
vulva,  prepuce,  scrotum,  eyelids,  etc.)  the  corium  contains  pigment  in  its  connective-tissue  cells. 


886  THE   SENSE    ORGANS   AND    SKIN    OF   THE   HORSE 

THE  APPENDAGES  OF  THE  SKIN 

The  appendages  of  the  skin  are  modifications  of  the  epidermis,  and  comprise 
the  hairs,  hoofs,  claws,  horns,  etc. 

The  hairs  (Pih)  cover  almost  the  entire  surface  of  the  bod}^  in  the  domesticated 
mammals,  and  some  parts  which  appear  at  first  sight  to  be  bare  are  found  on  close 
inspection  to  be  provided  with  sparse  and  very  fine  hair.  The  hairs  are  constantly 
being  shed  and  replaced,  but  at  certain  periods  in  the  horse,  for  example,  they  fall 
out  in  great  numbers,  constituting  the  shedding  of  the  coat.  It  is  customary  to 
distinguish  the  ordinary  hairs  (the  coat),  which  determine  the  color  of  the  animal, 
from  the  special  varieties  found  in  certain  places.     Among  the  latter  are  the  long 


i^\v. 


l^\ 


-Lateral  View  of  Horse  to  Show  Hair-streams  and  Vortices. 
Kiinstler.) 


(After  KIIenberger-B;nim,  Anat.  fiir 


tactile  hairs  about  the  lips,  nostrils,  and  eyes;  the  eyelashes  or  cilia;  the  tragi  of 
the  external  ear;  and  the  vibrissae  of  the  nostrils.  Other  special  features  will  be 
noted  in  the  discussion  of  the  skin  of  the  various  species.  The  hairs  are  directed 
in  such  a  way  as  to  form  more  or  less  definite  hair-streams  (Flumina  pilorum), 
and  at  certain  points  these  converge  to  form  vortices  (Vortices  pilorum). 

The  part  of  the  hair  above  the  surface  of  the  skin  is  the  shaft  (Scapus  pili), 
while  the  root  (Radix  pili)  is  embedded  in  a  depression  termed  the  hair-follicle 
(Folliculus  pili).  A  vascular  papilla  (Papilla  pili)  projects  up  in  the  fundus  of  the 
follicle  and  is  capped  by  the  expanded  end  of  the  root,  the  bulb  of  the  hair  (Bulbus 
pili).  The  hair-follicles  extend  obliquely  into  the  corium  to  a  varying  depth;  in 
the  case  of  the  long  tactile  hairs  they  reach  to  the  underlying  muscle.  Most  of  the 
follicles  have  attached  to  them  small  unstriped  muscles  known  as  the  arrectores 
pilorum;   these  are  attached  at  an  acute  angle  to  the  under  side  of  the  deep  part 


THE    SKIN    OF   THE    HORSE THE    HOOF  887 

of  the  follicle,  and  their  contraction  causes  erection  of  the  hair  and  compression  of 
the  sebaceous  glands,  one  or  more  of  which  open  into  the  follicle. 

The  hairs  are  composed  of  epidermal  cells,  and  consist  from  without  inward  of 
three  parts.  The  cuticle  is  composed  of  horny,  scale-like  cells  which  overlap  like 
slates  on  a  roof.  The  cortex  consists  of  horny  fusiform  cells  which  are  packed  close 
together  and  contain  pigment.  The  medulla  is  the  central  core  of  softer,  cubical 
or  polyhedral  cells;   it  contains  some  pigment  and  air-spaces. 

The  hair-follicles,  being  invaginations  of  the  skin,  are  composed  of  a  central 
epidermal  part  and  a  peripheral  layer  which  corresponds  in  structure  to  the  corium. 
The  follicles  of  the  tactile  hairs  have  remarkably  thick  walls  which  contain  blood- 
sinuses  between  their  outer  and  inner  layers;  in  ungulates  the  sinuses  are  crossed 
by  trabecules  and  assume  the  character  of  cavernous  or  erectile  tissue. 

The  hoofs,  claws,  horns,  and  other  horny  structures  consist  of  closely  packed 
epidermal  cells  which  have  undergone  cornification.  In  structure  they  might  be 
compared  to  hairs  matted  together  by  intervening  epidermal  cells.  They  cover  a 
specialized  corium  from  which  the  stratum  germinativum  derives  its  nutrition. 


THE  SKIN  OF  THE  HORSE 

The  thickness  of  the  skin  of  the  horse  varies  from  one  to  five  millimeters  in 
different  regions,  and  is  greatest  at  the  attachment  of  the  mane  and  on  the  tail. 

The  glands  are  numerous  and  are  larger  than  those  of  the  other  domesticated 
animals.  The  sebaceous  glands  are  specially  developed  on  the  lips,  the  prepuce, 
mammary  glands,  perineum,  and  labia  of  the  vulva.  The  sweat  glands  are  yellow 
or  brown  in  color.  They  occur  in  almost  all  parts  of  the  skin,  but  are  largest  and 
most  numerous  in  that  of  the  lateral  wing  of  the  nostril,  the  flank,  mammary  glands, 
and  free  part  of  the  penis. 

In  addition  to  the  ordinary  and  tactile  hairs  certain  regions  present  coarse 
hairs  of  great  length.  The  mane  (Juba)  springs  from  the  dorsal  border  of  the  neck 
and  the  adjacent  part  of  the  withers;  its  anterior  part,  which  covers  the  forehead 
to  a  variable  extent,  is  termed  the  foretop  (Cirrus  capitis).  The  tail,  with  the 
exception  of  its  ventral  surface,  bears  very  large  and  long  hairs  (Cirrus  caudse). 
The  tuft  of  long  hairs  on  the  flexion  surface  of  the  fetlock  (Cirrus  pedis)  gave  rise  to 
the  popular  name  of  this  region. 

The  development  of  these  special  hairs  varies  widely,  and  is  in  general  much  greater  in  the 
draft  breeds  than  in  others.  In  Shire  and  Clydesdale  horses,  for  instance,  the  hair  on  the  poste- 
rior aspect  of  the  metacarpus  and  metatarsus  and  fetlock  is  often  so  long  and  abundant  as  to  ac- 
count for  the  term  "feather,  "  which  is  commonly  appUed  to  it  by  horsemen. 

Subcutaneous  bursas  (Bursse  subcutaneae)  may  be  present  at  various  prominent 
points,  e.  g.,  the  olecranon,  the  tuber  coxae,  the  tuber  calcis,  the  withers,  etc.  They 
are  not  present  in  the  young  subject  and  appear  to  be  the  result  of  traumatism. 

THE  HOOF 
The  hoof  (Ungula)  is  the  horny  covering  of  the  distal  end  of  the  digit.     It  is 
.  convenient  to  divide  it  for  description  into  three  parts,  termed  the  wall,  sole,  and 
frog. 

1.  The  wall  (Paries  ungulse)  is  defined  as  the  part  of  the  hoof  which  is  visible 
vvhen  the  foot  is  placed  on  the  ground.^  It  covers  the  front  and  sides  of  the  foot, 
and  is  reflected  posteriorly  at  an  acute  angle  to  form  the  bars.  The  latter  (Pars 
inflexa  medialis,  lateralis)  ^  appear  on  the  ground  surface  of  the  hoof  as  convergent 

1  The  term  foot  is  used  here  in  the  popular  sense,  i.  e.,  to  designate  the  hoof  and  the  structures 
enclosed  witliin  it. 

2  The  term  "pila  ungulae"  has  been  suggested  by  Schmaltz  for  the  part  popularly  known  as 
the  "bar." 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 


t 


ridges,  which  subside  in  front  and  are  fused  with  the  sole;  they  are  united  with  each 
other  by  the  frog.  For  topographic  purposes  the  wall  may  be  divided  into  an  an- 
terior part  or  "  toe  "  (Paries  unguis?  dorsahs),  medial  and  lateral  parts  or  "  quar- 
ters "  (Paries  ungulse  medialis,  lateralis),  and  the  angles  or  "  heels  "  (Anguli  parie- 
tales).  It  presents  two  surfaces  and  two  borders.  The  external  surface  is  con- 
vex from  side  to  side  and  slopes  obliquely  from  edge  to  edge.  In  front  the  angle  of 
inclination  on  the  ground  plane  is  about  50°  for  the  f orelimb,  55°  for  the  hind  limb ; 
on  the  sides  the  angle  gradually  increases  and  is  about  100°  at  the  heels.  The  curve 
of  the  wall  is  wider  on  the  lateral  than  on  the  medial  side,  and  the  slope  of  the  medial 
quarter  is  steeper  than  that  of  the  lateral  one.^  The  surface  is  smooth  and  is  crossed 
by  more  or  less  distinct  ridges,  which  are  parallel  with  the  coronary  border  and 
indicate  variations  in  the  activity  of  the  growth  of  the  hoof.     It  is  also  marked  by 

fine  parallel  strise,  which  extend  from  border  to 
border  in  an  almost  rectilinear  manner  and  in- 
dicate the  direction  of  the  horn  tubes. 

The  internal  surface  is  concave  from  side  to 
side,  and  bears  about  six  hundred  thin  primary 
laminae,  which  extend  from  the  coronar^^  groove 
to  the  basal  border  of  the  wall.  Each  bears  a 
hundred  or  more  secondary  laminae  on  its  sur- 
faces, so  that  the  arrangement  is  pennate  on 
cross-section.  These  horny  laminae  are  continued 
on  the  inner  surface  of  the  bars,  and  dovetail  with 
corresponding  laminae  of  the  the  corium.  The  cor- 
onary border  (Margo  coronarius)  is  thin.  Its  outer 
aspect  is  covered  by  a  layer  of  soft  horn  known 
as  the  periople  (Limbus  corneus) ;  this  appears  as 
a  ring-like  prominence  above  and  gradually  fades 
out  below;  at  the  angle  it  forms  a  wide  cap  or 
bulb  and  blends  centrally  with  the  frog.  The 
inner  aspect  of  the  border  is  excavated  to  form 
the  coronary  groove  (Sulcus  coronarius  ungulae), 
which  contains  the  thick  coronary  corium.  The 
groove  is  deepest  in  front,  narrows  on  the  sides, 
and  is  wide  and  shallow  at  the  heels.-  It  is  per- 
forated by  innumerable  small,  funnel-like  openings 
which  are  occupied  by  the  papillae  of  the  coronary 
corium  in  the  natural  state.  Between  the  border 
of  the  wall  proper  and  the  periople  there  is  a  small 
groove  which  contains  the  corium  of  the  periople. 
At  the  heel  this  groove  is  merged  with  the  coronary 
groove.  The  basal  or  ground  border  (Margo  l)asi- 
laris)  of  the  unshod  hoof  comes  in  contact  with  the  ground.  Its  thickness  is  greatest 
in  front  and  decreases  considerably  from  before  backward  on  the  sides,  l)ut  there  is 
a  slight  increase  at  the  angles.     Its  inner  face  is  united  with  the  periphery  of  the 


Fig.  710. — Digit  of  Horse,  Showing 
Surface  Relations  of  Bones  and 
Joints.  The  Cartilage  is  Largely 
Exposed. 

o,  First  phalanx;  b,  second  phalanx; 
c,  third  phalanx;  d,  cartilage;  e,  distal  sesa- 
moid or  navicular  bone;  /,  pastern  joint; 
g,  cofSn  joint;  h',  cut  edge  of  wall  of  hoof 
(h) ;  i,  laminar  corium.  (After  Ellenberger, 
in  Leisering's  Atlas.) 


1  The  slope  of  the  wall  varies  considerably  in  apparently  normal  hoofs.  Lungwitz  found 
by  careful  measurements  of  56  fore  and  36  hind  feet  the  following  average  angles: 

Fore  Foot  Hind  Foot 

Toe 47.26°  54.1° 

Medial  angle 101.57°  96.5° 

Lateral  angle 101.37°  96.1° 

The  wall  of  the  fore  foot  may  even  be  more  upright  than  that  of  the  hind,  and  may  have  an 
angle  of  60°.  The  length  of  the  wall  at  the  toe,  quarters,  and  heels  is  in  the  ratio  of  about  3:2:1 
m  the  fore  foot  and  about  2  :  1 J^ :  1  in  the  hind  hoof. 

2  The  wide  groove  at  the  heels,  however,  contains  chiefly  the  corium  of  the  periople. 


THE    HOOF 


889 


sole  by  horn  of  lighter  color  and  softer  texture,  which  appears  on  the  ground  surface 
of  the  hoof  as  the  so-called  white  line  (Zona  lamellata) . 


Wall 
Lamince  of  wall 

Laminar  corium 
Third  phalanx 
Digital  cushm: 

Bar 

Frog 

Space  between 
bar  and  frog 

Angle  of  wall 
Periople  of  heel 


Fig.  711. — Cross-section  of  Foot  of  Horse,  Cut  Parallel  with  the  Coronary  Border. 
The  wall  appears  much  thicker  at  the  angles  than  it  actually  i.s,  because  it  is  cut  very  obliquely. 

In  the  case  of  unshod  horses  at  liberty  the  wall  is  usually  worn  off  to  the  level  of  the  adjacent 
sole,  but  if  the  ground  is  too  soft  the  wall  is  likely  to  become  unduly  long  and  spht  or  break  or 
undergo  deformation.     On  very  hard  or  rough  ground,  on  the  other  hand,  the  wear  may  be  in  ex- 


Periople 

Coronary 

groove 


Laminoe 


Periople  of  heel 


White  line 


Ridge  formed 
by  bar  and  frog 

Half  of  Hoof  of  Horse;  Internal  Surface. 


cess  of  the  growth.  In  the  case  of  shod  horses  it  is  necessary  to  remove  the  excess  of  growth  of  the 
wall  at  each  shoeing.  The  thickness  of  the  wall  at  the  toe,  quarters,  and  heels  is  about  in  the 
ratio  of  4  :  3  :  2  for  the  fore  foot  and  about  3  :  23^  :  2  for  the  hind  foot. 

2.  The  sole  (Basis  s.  solea  unguis)  forms  the  greater  part  of  the  ground  sur- 


890 


THE    SENSE    ORGANS   AND    SKIN    OF   THE    HORSE 


^^ace  of  the  hoof.  It  is  somewhat  crescentic  in  outhne,  and  presents  two  surfaces 
and  two  borders.  The  internal  surface  is  convex,  and  slopes  vnth  a  varying 
degree  of  obhquity  doA\Tiward  to  the  convex  border.  It  presents  numerous  small 
funnel-like  openings  Avhich  contain  the  papillae  of  the  sole  corium  in  the  natural 
state.  The  external  or  ground  surface  is  the  converse  of  the  preceding.  It  is  nor- 
mally arched— and  more  strongly  in  the  hind  than  in  the  fore  foot— but  the  curvature 
is  subject  to  wide  variation;  in  heavy  draft  horses  the  sole  is  commonly  less  curved 
than  in  the  lighter  breeds  and  may  even  be  flat.  The  surface  is  usually  rough,  since 
the  horn  exfoliates  here  in  irregular  flakes.  The  convex  border  is  joined  to  the  wall  by 
relatively  soft  horn,  previously  referred  to  as  forming  the  white  line  on  the  ground 
surface  of  the  hoof.     The  angle  of  junction  is  rounded  internally  and  presents  a 


Fig.  713. — Right  Fore  Hoof  of  Horse;  Ground  Sttrface. 
1,  Basal  or  ground  border  of  wall;   2,  laminae  of  wall;   3,  angle  of  wall;   4,  bar;   5,  sole;  5',  angle  of  sole;  6,  white 
line  (junction  of  wall  and  sole);   7,  apex  of  frog;   8,  central  sulcus  of  frog;  9,  9,  collateral  sulci  between  frog  and  bars; 
10,  10,  bulbs  of  hoof. 


number  of  low  ridges  and  specially  large  openings  for  the  papillte  of  the  corium. 
There  is  frequently  a  ridge  of  larger  size  at  the  toe.  The  concave  border  has  the 
form  of  a  deep  angle  which  is  occupied  by  the  bars  and  frog.  It  concurs  in  part 
with  these  in  forming  two  pronounced  ridges  in  the  interior  of  the  foot.  The  parts 
of  the  sole  between  the  wall  and  bars  are  termed  its  angles  (Anguli  solese). 

3.  The  frog  (Cuneus  ungulae)  is  a  wedge-shaped  mass  which  occupies  the  angle 
bounded  l)y  the  bars  and  sole,  and  extends  considerably  below  these  on  the  ground 
surface  of  the  foot.  It  may  be  described  as  having  four  surfaces,  a  base,  and  an 
apex.  The  internal  surface  bears  a  central  ridge,  the  spine  or  "frog-stay"  (Spina 
cunei  ungulse),  which  is  high  posteriorly  and  subsides  abruptly  in  front.  On  either 
side  of  this  there  is  a  deep  depression,  which  is  bounded  outwardly  by  the  rounded 


THE    HOOF 


891 


ridge  formed  by  the  junction  of  the  frog  with  the  bar  and  sole.  This  surface 
presents  fine  striae  and  openings  for  the  papillae  of  the  corium.  The  external  or 
ground  surface  presents  a  central 
sulcus  (Sulcus  cunei),  which  is 
bounded  by  two  ridges  or  crura 
(Crura  cunei).  The  medial  and  lat- 
eral surfaces  (Facies  medialis  et  lat- 
eralis) are  united  at  the  upper  part 
with  the  bars  and  sole,  but  are  free 
below  and  form  the  central  wall  of 
the  deep  collateral  sulci  (Sulci  para- 
cuneati),  which  are  bounded  out- 
wardly by  the  bars.  The  base  (Basis 
cunei)  is  depressed  centrally  and 
prominent  at  the  sides,  where  it 
unites  with  the  angles  of  the  wall; 
the  junction  here  is  covered  by  the 
expanded  periople  and  constitutes 
the  bulb  of  the  hoof  (Pulvinus  digi- 
talis). The  apex  (Apex  cunei)  oc- 
cupies the  central  angle  of  the  con- 
cave border  of  the  sole,  and  forms  a 
blunt,  round  prominence  a  little  in 
front  of  the  middle  of  the  ground  sur- 
face of  the  hoof. 

Structure  of  the  Hoof. — The  hoof 
is  composed  of  epithelial  cells  which 
are  more  or  less  completely  keratin- 
ized except  in  its  deepest  part,  the 
stratum  germinativum ;  here  the  cells 
have  not  undergone  cornification,  and 

by  their  proliferation  maintain  the  growth  of  the  hoof.  The  cells  are  in  part 
arranged  to  form  tubes  (Cylindri  cornei)  which  are  united  by  intertubular  epi- 
thelium, and  enclose  medullary 
cells  and  air-spaces.  The  wall 
may  be  regarded  as  consisting  of 
three  layers.  The  external  layer 
consists  of  the  periople  and  the 
stratum  tectorium.  The  periople 
is  composed  of  soft,  non-pig- 
mented,  tubular  horn,  and  be- 
comes white  w^hen  the  hoof  is 
soaked  in  water.  It  is  contin- 
uous with  the  epidermis  of  the 
skin  above,  and  extends  down- 
ward a  variable  distance.  Usually 
it  forms  a  distinct  band  somewhat 
less  than  an  inch  wide,  except  at 
the  heels,  where  it  is  much  wider, 
and  caps  the  angle  of  inflection  of 
the  wall.  The  stratum  tectorium 
is  a  thin  layer  of  horny  scales 
which  gives  the  outer  surface  of  the  wall  below  the  periople  its  smooth,  glossy  ap- 
pearance.    The  middle  layer  (Stratum  medium)  forms  the  bulk  of  the  wall,  and 


Fig.  714. — SErriON  of  Hoof  of  Horse. 
The  section  is  cut  just  above  the  ridges  of  the  frog  and 
bars  and  parallel  with  the  ground  surface.  1,  Wall;  2,  sole; 
S,  spine  of  frog  or  "frog-stay";  .4,  ridge  formed  by  junction 
of  frog  and  bar;  5,  central  furrow  over  apex  of  frog;  6, 
huninEe  of  wall;    7,  laminae  of  bar. 


Fig.  715. — Frontal  Section   of   Hoof  of  Horse,  Posterior 

Part  Viewed  from  in  Front. 

;,  Wall;  2,  sole;   3,  bar;  4,  frog;    5,  central  ridge  of  frog;  6, 

lateral  ridge   formed   by  junction  of   frog   and  bar;    7,  laminae  of 

bar;    S,  laminae  of  wall;  9,  coronary  groove;   10,  periople  of  heel. 


892  THE    SENSE    ORGANS   AND    SKIN    OF   THE    HORSE 

is  the  densest  part  of  the  hoof.  Its  horn  tubes  run  in  a  straight  direction  from  the 
coronary  to  the  basal  border.  In  dark  hoofs  it  is  pigmented  except  in  its  deep  part. 
The  laminar  layer  (Stratum  lamellatum)  is  internal;  it  consists  of  the  homy 
laminae  (Lamellae  cornese),  and  is  non-pigmented.  The  primary  laminae  are  narrow 
and  thin  at  their  origin  at  the  lower  margin  of  the  coronary  groove,  but  become  %\'ider 
and  thicker  distally.  At  the  junction  of  the  wall  and  sole  they  are  united  by  inter- 
laminar  horn  to  form  the  white  line.  Only  the  central  part  of  the  laminae  becomes 
fully  keratinized.     They  are  composed  of  non-tubular  horn  in  the  normal  state. 

The  sole  consists  of  tubular  and  intertubular  horn.  The  tubes  run  parallel 
with  those  of  the  wall  and  vary  much  in  size. 

The  frog  is  composed  of  relatively  soft  horn,  which  is  much  more  elastic  than 
that  of  the  wall  or  sole,  and  is  not  fully  keratinized.  The  horn  tubes  in  it  are  slightly 
flexuous. 

The  hoof  is  non-vascular  and  receives  its  nutrition  from  the  corium.  It  is 
also  destitute  of  nerves. 

THE  CORIUM  OF  THE  HOOF 

The  corium  of  the  hoof  or  pododerm  (Corium  ungulae)  is  the  specially  modified 
and  highly  vascular  part  of  the  corium  of  the  common  integument  which  furnishes 
nutrition  to  the  hoof.  It  is  convenient  to  divide  it  into  five  parts  which  nourish 
corresponding  parts  of  the  hoof.^ 

1.  The  perioplic  corium  or  ring  (Corium  limitans)  is  a  band  5  to  6  mm.  in 
width  which  lies  in  a  groove  between  the  periople  and  the  coronary  border  of 
the  wall.  It  is  continuous  above  with  the  corium  of  the  skin,  and  is  marked  off  by 
a  groove  from  the  coronary  corium.  At  the  heels  it  widens  and  blends  with  the 
corium  of  the  frog.  It  bears  very  fine,  short  papillae  which  curve  downward  and 
are  received  in  depressions  of  the  periople,  to  which  it  supplies  nutrition. 

2.  The  coronary  corium  (Corium  coronarium)  is  the  thick  part  of  the  corium 
which  occupies  the  coronary  groove,  and  furnishes  nutrition  to  the  bulk  of  the  wall. 
It  diminishes  in  width  and  thickness  posteriorly,  and  along  the  upper  border  of  the 
bar  it  is  not  clearly  defined  from  the  corium  of  the  frog.  The  convex  superficial 
surface  is  thickly  covered  with  filiform  papillae  4  to  6  mm.  in  length,  which  are  re- 
ceived into  the  funnel-like  openings  of  the  coronary  groove.  At  the  heels  and  along 
the  bars  the  papillae  are  arranged  in  rows,  separated  by  fine  furrows.  The  deep 
surface  is  attached  to  the  extensor  tendon  and  the  cartilages  of  the  third  phalanx 
by  an  abundant  subcutis  which  contains  many  elastic  fibers  and  a  rich  venous 
plexus. 

3.  The  laminar  corium  (Corium  lamellatum)  bears  primary  and  secondary 
laminae  which  are  interleaved  with  the  horny  laminae  of  the  wall  and  bars  in  the 
natural  state.^  It  is  attached  to  the  dorsal  surface  of  the  third  phalanx  by  a  modi- 
fied periosteum  (Stratum  periosteale)  which  contains  a  close-meshed  network  of 
vessels,  and  to  the  lower  part  of  the  cartilages  by  a  subcutis  which  contains  a  rich 
venous  plexus.  The  laminae  are  small  at  their  origin  above,  become  wider  below, 
and  end  in  several  papillae  4  to  5  mm.  in  length.  They  supply  nutrition  to  the  horny 
laminae  and  to  the  interlaminar  horn  of  the  white  line. 

4.  The  coriimi  of  the  sole  (Corium  soleare) — also  termed  the  sensitive  sole — 
corresponds  to  the  horny  sole,  to  which  it  supplies  nutrition.  It  is  often  more  or 
less  pigmented  and  bears  long  papillae,  which  are  specially  large  along  the  convex 

1  In  some  veterinary  works  the  statement  is  made  that  the  various  parts  of  the  corium  "se- 
crete" corresponding  parts  of  the  hoof.  The  statement  is,  of  course,  hidicrous,  as  the  relationship 
here,  both  anatomically  and  physiologically,  is  the  same  as  in  the  case  of  the  corium  and  epidermis 
of  the  skin.     Hence  the  terms  " keratogenous  membrane"  and  "matrix"  should  be  dropped. 

'^The  laminae  of  the  corium  are  commonly  termed  "sensitive"  laminae  to  distinguish  them 
from  the  "horny"  laminae,  which  are,  of  course,  insensitive. 


THE    CORIUM    OF   THE    HOOF 


893 


border  and  at  the  angles.  Centrally  it  is  continuous  with  the  corium  of  the  frog 
and  bars.  The  deep  surface  is  attached  to  the  sole  surface  of  the  third  phalanx 
by  a  modified  and  highly  vascular  periosteum. 


Cut  edge  of  skin 
Corium  of  periople 
Coronary  corium 
Laminar  corium     ■' 


Cartilage  of  third 
phalanx 
Position  of 
navicular  bursa 
Position  of 
navicular  bone 


*■ — '  Outline  of  hoof 


Fig.  716. — Later.^l  View  of  Foot  of  Horse  After  Removal  of  Hoof  and  Part  of  Skin.     (After  Schmaltz,  Atlas 

d.  Anat.  d.  Pferdes.) 
Dotted  lines  in  front  of  navicular  bone  indicate  position  of  coffin  joint. 

5.  The  corium  of  the  frog  (Corium  cuneatum) — also  called  the  sensitive  frog — 
is  moulded  on  the  deep  surface  of  the  frog  and  bears  small  papilljE.     Its  deep  face  is 


Periople  of  heel  or  bulb 


Angle  of  wall 
Angle  of  sole 


Perioplic  corium 
Coronary  corium 

Laminar  corium 

Corium  of  frog 
Position  of  navicular  bone 

Corium  of  sole 


Position  of  insertion  of 
deep  flexor  tendon 


White  line 

Basal  border  of  wall 

Fig.  717. — Ground  Surface  of  Foot  of  Horse  After  Removal  of  Half  of  Hoof  to  Show  Corium.     (After 
Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


blended  with  the  digital  cushion.     The  germinal  cells  of  the  frog  derive  their 
nutrition  from  this  part  of  the  corium. 


894 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 


The  digital  cushion  (Torus  digitahs)  is  a  wedge-shaped  mass  whicn  overlies  the 
frog.  It  presents  for  description  four  surfaces,  a  base,  and  an  apex.^  Its  deep 
surface  faces  upward  and  forward  and  is  connected  with  the  distal  fibrous  sheath  of 
the  deep  flexor  tendon.  The  superficial  surface,  covered  by  the  corium  of  the  frog, 
is  moulded  on  the  upper  face  of  the  frog.  The  sides  are  related  chiefly  to  the 
cartilages  of  the  third  phalanx;  distally  the  cushion  is  closely  attached  to  the 
cartilages,  but  higher  up  a  rich  venous  plexus  intervenes.  The  base,  situated 
posteriorly,  is  partly  subcutaneous,  and  is  divided  by  a  central  depression  into  two 
rounded  prominences  termed  the  bulbs  of  the  cushion.  The  apex  lies  below  and 
is  adherent  to  the  terminal  part  of  the  deep  flexor  tendon.  The  cushion  is  poorly 
supplied  with  vessels.  It  consists  of  a  feltwork  of  fibrous  trabeculse  and  elastic 
fibers,  in  the  meshes  of  which  are  masses  of  fat.     The  bulbs  are  soft  and  loose  in 


Coronary 
Wall        corium 


Extensor  tendon 


Collateral  ligament 


Fig.  718. — Section  op  Digit  of  Horse  at  Coronary  Border  op  Hoof. 
1,  Extenso?  process  of  third  phalanx;  2,  distal  end  of  second  phalanx;  3,  distal  sesamoid  or  navicular  bone;  4, 
deep  flexor  tendon;  5,  digital  cushion;  6,  cartilage  ©f  third  phalanx;  7,  7,  cavity  of  coffin  joint;  8,  podotrochlear  or 
navicular  bursa;  9,  digital  vessels;  10,  digital  nerve. 


texture  and  contain  a  relatively  large  amount  of  fat,  but  toward  the  apex  the  cushion 
becomes  denser  and  more  purely  white  fibrous  in  structure.  Branched  coil  glands 
occur  chiefly  in  the  part  of  the  cushion  which  overlies  the  central  ridge  of  the  frog. 
Their  ducts  pursue  a  slightly  flexuous  course  through  the  corium  and  pass  in  a  spiral 
manner  through  the  frog.     Their  secretion  contains  fat. 

Vessels  and  Nerves.^ — The  corium  is  richly  supplied  with  blood  by  the  digital 
arteries.  The  veins  are  valveless,  and  form  remarkable  plexuses  which  communi- 
cate freely  with  each  other  and  are  drained  by  the  digital  veins.  The  lymph  vessels 
form  subpapillary  plexuses  in  the  corium  of  the  sole  and  frog,  and  a  wider-meshed 
plexus  at  the  base  of  the  digital  cushion.  A  lymph  vessel  lies  in  the  attached  edge 
of  each  of  the  laminae.  The  nerves  are  branches  of  the  digital  nerves;  some  fibers 
end  in  lamellar  corpuscles  and  end-bulbs. 

*  Ths  cushion  is  to  be  regarded  as  a  special  modification  of  the  subcutaneous  tissue,  bearing 
on  its  superficial  face  the  corium  of  the  frog.     It  is  an  important  factor  in  diminishing  concussion. 


THE    ERGOT   AND    CHESTNUT THE    ORGAN    OF   TASTE  895 

The  Ergot  and  Chestnut 

The  ergot  is  a  small  mass  of  horn  which  is  situated  in  the  tuft  of  hair  at  the 
flexion  surface  of  the  fetlock.  It  is  commonly  regarded  as  the  vestige  of  the  second 
and  fourth  digits  of  extinct  equidse,  since  it  is  absent  in  cases  in  which  these 
digits  are  developed.  A  small  fibrous  band,  3  to  5  mm.  in  width,  extends  downward 
and  slightly  forward  from  the  fibrous  basis  of  the  ergot  on  each  side,  crosses  over  the 
digital  vessels  and  nerves  very  obliquely,  and  blends  below  with  the  digital  fascia 
and  the  digital  cushion.  It  is  known  as  the  ligament  or  tendon  of  the  ergot  (Fig. 
572). 

The  term  chestnut  is  applied  to  the  masses  of  horn  which  occur  on  the  medial 
surface  of  the  forearm,  about  a  handbreadth  above  the  carpus,  and  on  the  distal 
part  of  the  medial  face  of  the  tarsus.  They  have  an  elongated  oval  form  and  are 
flattened.  They  are  regarded  usually  as  vestiges  of  the  first  digit.  That  of  the 
hind  limb  is  absent  in  the  donkey  and  very  small  in  the  mule. 

These  horny  excrescences  are  quite  variable  in  form  and  size  and  are  correlated  with  the  fine- 
ness or  coarseness  of  the  integument  in  general.  The  supracarpal  chestnut  is  about  l}<2  to  2}^ 
inches  long,  oval  in  outline,  the  proximal  end  being  pointed;  it  overlies  the  flexor  carpi  radialis  at 
a  quite  variable  distance  above  the  carpus,  and  hence  should  not  be  used  as  a  surgical  landmark. 
The  tarsal  chestnut  lies  at  a  point  behind  the  lower  part  of  the  medial  Ugament  of  the  hock.  When 
well  developed  it  is  about  2  to  2}^  inches  long,  broad  below  and  produced  above  to  form  a  long 
pointed  end,  with  a  short  blunt  anterior  process.  They  are  composed  of  horn  somewhat  like  that 
of  the  frog. 


Organ  of  Smell 

The  peripheral  part  of  the  olfactory  apparatus  or  organ  of  smell  (Organon 
olfactus)  is  that  part  of  the  nasal  mucous  membrane  which  was  referred  to  in  the 
description  of  the  nasal  cavity  as  the  olfactory  region;  this  (Regio  olfactoria)  is 
limited  to  the  ethmoturbinates  and  the  adjacent  part  of  the  dorsal  turbinate  and 
the  septum  nasi,  in  which  the  fibers  of  the  olfactory  nerve  ramify.  It  is  distin- 
guished by  its  yellow-brown  color,  thickness,  and  softness.  It  contains  character- 
istic tubular  olfactory  glands,  which  are  lined  by  a  single  layer  of  pigmented  cells, 
and  a  neuro-epithelium,  the  olfactory  cells,  the  central  processes  of  which  extend 
as  non-meduUated  fibers  to  the  olfactory  bulb. 

The  epithelium  is  non-ciliated  and  is  covered  by  a  structureless  hmiting  layer.  It  consists 
essentially  of  three  kinds  of  cells,  supporting,  basal,  and  olfactory.  The  supporting  cells  are  of 
long  columnar  form  above  and  contain  pigment  granules;  below  they  taper  and  often  branch, 
and  their  central  processes  unite  with  those  of  adjacent  cells  to  form  a  protoplasmic  network. 
The  basal  cells  are  branched  and  lie  on  a  basement  membrane.  The  olfactory  cells  are  situated 
between  the  supporting  cells;  they  have  the  form  of  long  narrow  rods,  with  an  enlarged  lower 
part  which  is  occupied  by  the  nucleus.  The  peripheral  end  pierces  the  limiting  membrane  and 
bears  a  tuft  of  fine,  hair-Uke  ciUa  (olfactory  hairs).  A  central  process  extends  from  the  nucleated 
pole  of  the  cell  to  the  olfactory  bulb  as  a  non-medullated  oKactory  nerve-fiber. 

The  vomero-nasal  organ  (Fig.  452)  lies  along  each  side  of  the  anterior  part 
of  the  lower  border  of  the  septum  nasi.  It  communicates  with  the  nasal  cavity 
through  the  naso-palatine  canal.  It  consists  of  a  tube  of  hyaline  cartilage  lined 
with  mucous  membrane;  a  small  part  of  the  latter  along  the  medial  side  is  olfactory 
in  character. 


The  Organ  of  Taste 

The  peripheral  part  of  the  gustatory  apparatus  (Organon  gustus)  is  formed  by 
the  microscopic  taste  buds  (Calyculi  gustatorii),  which  occur  especially  in  the  foliate, 
fungiform,  and  vallate  papillae,  in  the  free  edge  and  anterior  pillars  of  the  soft 
palate,  and  the  oral  surface  of  the  epiglottis.     The  taste  buds  are  ovoid  masses. 


896        THE  SENSE  ORGANS  AND  COMMON  INTEGUMENT  OF  THE  OX 

which  occupy  corresponding  recesses  in  the  ordinary  epithehum;  each  presents  a 
minute  opening,  the  gustatory  pore.  The  buds  consist  of  fusiform  supporting  cells 
grouped  around  central  gustatory  cells.  The  latter  are  long  and  narrow;  the 
peripheral  end  of  each  bears  a  small  filament,  the  gustatory  hair,  which  projects  at 
the  gustatory  pore;  the  central  end  is  produced  to  form  a  fine  process  which  is  often 
branched.  The  taste  buds  are  innervated  by  fibers  of  the  glosso-pharyngeal  nerve 
and  the  lingual  branch  of  the  trigeminus. 


Upper  eyelid 


THE  SENSE  ORGANS  AND  COMMON  INTEGUMENT  OF  THE  OX 

THE  EYE 
The  eyelids  are  thick,  prominent,  and  less  pliable  than  those  of  the  horse. 

The  lower  lid  bears  a  considerable  number  of  cilia,  which  are,  however,  finer  than 

those  of  the  upper  lid.  The  tarsal 
glands  are  more  deeply  embedded 
./  -;«.#ipiv.  and  therefore  not  so  evident.     The 

conjunctiva  of  the  lower  lid  presents 
folds  or  ridges,  and  one  or  two  promi- 
nences which  contain  numerous  leuko- 
cytes; the  conjunctival  epithelium  is 
transitional  in  type.  The  superficial 
part  of  the  cartilage  of  the  third  eye- 
lid is  leaf  or  shovel-shaped  and  thicker 
than  in  the  horse;  the  edge  bears  a 
narrower  process,  on  which  there  is  a 
transverse  bar,  giving  the  arrange- 
ment some  resemblance  to  an  anchor. 
The  gland  of  the  third  eyelid  is  very 
large — an  inch  or  more  in  length — 
and  may  be  divided  into  two  parts. 
The  deep  part  is  pink  and  consists  of 
loose  lobules,  but  the  much  larger 
superficial  part  is  more  compact. 
There    are    two    large    and    several 

smaller  excretory  ducts.     The  subconjunctival  tissue  of  the  third  eyelid  contains 

lymph    nodules,    which    are    specially 

numerous  on  the  bulbar  side. 

The  lacrimal  gland  is  thick  and 

distinctly  lobulated.     It  is  more  or  less 

clearly  divided  into  a  thick  upper  and 

a  thinner  lower  part  (Glandula  lacri- 

malis  dorsalis,  ventralis).     There  are 

six  to  eight  larger  excretory  ducts  and 

several  smaller  ones.     The  naso-lacri- 

mal  duct  is  shorter  than  in  the  horse, 

and  is  almost  straight.     Its  terminal 

part   is  enclosed   between  two   plates 

of    cartilage,  and   it   opens   near   the 

nostril  on  the  lateral  wall  of  the  vesti- 
bule of  the  nasal  cavity;   the  orifice  is 

placed  on  the  medial  side  of  the  alar  fold  of  the  ventral  turbinate,  and  is  therefore 

not  easily  found. 


Fig.  719.— Eye  of  Ox. 


Lower  eyelid 

(After  Ellenberger-Baum,  Anat.  fiir 
Kiinstler.) 


Conjunctiva 

biilbi 

\ 

Sclera 

Third  eyelid 

r^"/ 

/ 

Caruncula     \^ 

^«"^\ 

lacrimalis 

\»J' 

^K^^^wBk_\ 

^no 

Cornea 

/ 

/ 

^^^ 

\- 

Pupil 

Fig.  720.- 

■Left 

Eyeball  of  Ox 

in  situ. 

19,    Orbital    fat. 

(After 

Ellenberger-Baum,     Anat.    fur 

Kunstler.) 

THE   EAR  897 

The  eyeball  resembles  that  of  the  horse  in  shape,  but  is  considerably  smaller.^ 
The  sclera  is  often  more  or  less  pigmented;  where  non-pigmented,  it  may  have 
a  bluish  tinge.  The  point  of  entrance  of  the  optic  nerve  is  about  2  mm.  lateral 
to  the  vertical  meridian,  and  about  7  mm.  below  the  horizontal  meridian.^  The 
cornea  is  thicker  than  that  of  the  horse.  The  tapetum  of  the  chorioid  is  extensive 
at  the  outer  side,  but  is  a  narrow  strip  medially.  It  has  a  metallic  luster,  shading 
from  a  brilliant  green  to  a  deep  blue;  centrally  it  has  a  reddish  sheen.  The  iris  is 
usually  very  dark  colored.  The  granula  form  a  continuous  series  of  small  nodules 
along  the  upper  margin  of  the  pupil  and  are  most  prominent  centrally;  they  are 
very  small  on  the  lower  margin.  The  optic  papilla  is  much  smaller  and  is  not  so 
sharply  defined  on  ophthalmoscopic  examination  as  that  of  the  horse.  Several 
relatively  large  retinal  arteries  radiate  from  the  center  of  the  papilla  to  the  periphery 
of  the  retina.  They  may  be  seen  to  wind  spirally  around  the  veins,  which  are  very 
large.     The  vitreous  body  is  less  fluid  than  that  of  the  horse. 

The  arteria  centralis  retinae  arises  from  a  posterior  ciliary  artery  and  divides  close  to  the 
optic  papilla  into  three  branches  usually;  the  upper  one  is  larger  than  the  two  lateral  branches. 
The  retina  is  more  vascular  than  that  of  the  horse;  it  has  a  round  area  centraUs  at  the  medial  side, 
which  is  continued  outward  by  a  narrow  strip  of  a  similar  histological  structure. 

THE  EAR 
The  external  ear  is  inclined  outward.  The  middle  part  is  much  wider  and  less 
curved  than  in  the  horse.  The  apex  is  also  wide  and  does  not  curve  forward. 
The  lower  part  of  the  anterior  border  is  bent  backward  and  bears  long  hairs.  The 
posterior  border  is  thin  and  is  regularly  convex,  except  below,  where  it  is  indented. 
The  opening  is  wide  and  the  concave  surface  presents  four  ridges;  the  convex 
surface  presents  corresponding  depressions.  The  styloid  process  of  the  conchal 
cartilage  is  short  and  blunt.  The  edges  of  the  annular  cartilage  are  in  contact  at 
the  medial  side  and  the  upper  border  is  notched  laterally.  The  scutiform  cartilage 
is  a  very  irregular  quadrilateral  plate;  it  is  situated  on  the  lateral  aspect  of  the 
cranium,  with  its  concave  surface  in  contact  with  the  fat  and  temporalis  muscle. 
The  osseous  external  acoustic  meatus  is  directed  practically  straight  inward;  it  is 
about  twice  as  long  as  that  of  the  horse,  and  tapers  very  gradually  from  without 
inward.  The  chief  special  characters  of  the  auricular  muscles  are  as  follows: 
(1)  The  scutularis  blends  with  the  frontalis  muscle.  The  interscutularis  arises 
from  the  base  of  the  processus  cornus  (or  the  corresponding  area  in  polled  cattle) 
and  from  the  frontal  crest.  (2)  The  cervico-scutularis  arises  from  the  posterior 
surface  of  the  cranium  below  the  frontal  eminence,  and  receives  slips  from  the 
parieto-auricularis  and  cervico-auricularis  superficialis.  (3)  The  zygomatico- 
auricularis  and  scutulo-auricularis  superficialis  ventralis  are  fused.  (4)  The  scutulo- 
auricularis  superficialis  dorsalis  is  distinct  from  the  interscutularis;  it  arises  from 
the  superficial  face  of  the  scutiform  cartilage.  (5)  The  cervico-auricularis  super- 
ficialis arises  from  the  ligamentum  nuchas  and  ends  on  the  convex  surface  of  the 
conchal  cartilage.  (6)  The  parieto-auricularis  arises  from  the  nuchal  surface  of 
the  frontal  bone,  the  adjacent  part  of  the  parietal  bone,  and  the  ligamentum  nuchse; 
it  is  inserted  below  the  preceding  muscle.  (7)  The  scutulo-auricularis  superficialis 
accessorius  arises  from  the  superficial  face  of  the  scutiform  cartilage  and  is  inserted 
by  a  round  tendon  into  the  anterior  part  of  the  convex  surface  of  the  conchal  car- 
tilage. (8)  The  cervico-auricularis  profundus  minor  consists  of  two  fasciculi:  the 
medial,  narrow  part  is  deep  red  in  color,  and  arises  from  the  fascia  of  the  cervical 
muscles  lateral  to  the  occipital  attachment  of  the  ligament  nuchse;    the  lateral 

1  The  average  transverse  diameter  is  about  42  mm.,  the  vertical  diameter,  41  mm.,  and  the 
axis,  36  mm.     The  angle  between  the  optic  axes  is  about  119°. 

2  The  thickness  of  the  sclera  is  about  2  mm.  at  the  Dosterior  pole,  1  mm.  at  the  equator,  and 
1.2  to  1.5  mm.  near  the  cornea. 

57 


898 


THE  SENSE  ORGANS  AND  COMMON  INTEGUMENT  OF  THE  OX 


wider  part  is  pale,  and  arises  beneath  the  cervico-auricularis  superficiahs  indirectly 
from  the  scutiform  cartilage.  The  two  unite  and  are  inserted  into  the  lower  aspect 
of  the  base  of  the  conchal  cartilage.  (9)  The  scutulo-auricularis  profundus  minor 
arises  from  the  temporal  crest  above  the  external  acoustic  meatus  and  is  inserted 
into  the  anterior  part  of  the  deep  face  of  the  scutiform  cartilage. 

The  cavum  t3anpani  is  small;  it  communicates  ventrally  with  the  air-cells  of 
the  bulla  ossea.  The  tympanic  membrane  is  nearly  circular  and  is  not  so  oblique 
as  in  the  horse.  The  auditory  ossicles  are  smaller  than  those  of  the  horse;  the 
malleus  is  more  curved,  the  body  of  the  incus  is  longer,  and  there  is  a  small  promi- 
nence on  the  front  of  the  head  of  the  stapes  for  the  attachment  of  the  stapedius 
muscle. 

The  auditive  or  Eustachian  tube  is  small  and  is  only  about  two  inches  long. 

The  pharyngeal  opening  is  small  and  is  situated  on  the  side  of  the  fornix  of  the 

pharynx  close  to  the  base  of  the  cranium.     There  is  no  flap-like  expansion  of  the 

cartilage,  but  the  medial  border  of  the  orifice  is  formed  l^y 

a  fold  of  mucous  membrane  (Fig.  476). 

The  internal  ear  has  essentially  the  same  arrangement 
as  in  the  horse. 


COMMON  INTEGUMENT 

The  thickness  of  the  skin  of  the  ox  is  greater  than 
that  of  any  of  the  other  domesticated  animals;  in  general 
it  is  about  three  or  four  millimeters,  but  at  the  root  of 
the  tail  and  the  point  of  the  hock  it  is  about  five  milli- 
meters and  on  the  brisket  six  or  seven  millimeters.  The 
variably  developed  prominence  at  the  anterior  part  of  the 
pectoral  region  known  as  the  brisket  consists  of  a  fold  of 
skin  (Plica  colli  ventralis  longitudinalis),  which  contains 
posteriorly  a  mass  composed  of  coarse  fibrous  trabeculse 
and  fat. 

The  cutaneous  glands  are  fewer  and  less  developed 
than  in  the  horse.  Except  about  the  natural  openings,  at 
the  point  of  the  hock,  and  the  flexion  surface  of  the  fet- 
lock, the  sweat  glands  do  not  form  a  coil,  but  are  enlarged 
at  the  deep  end  and  are  variably  flexuous.  The  sebaceous 
glands  are  best  developed  about  the  natural  openings  and  on  the  udder,  l)ut  there 
are  none  on  the  teats.  The  naso-labial  glands  form  a  thick  layer  under  the  bare 
skin  of  the  muzzle.  They  are  compound  tubular  glands  and  are  lined  with  cubical 
epithelium.     The  openings  of  their  excretory  ducts  are  easily  seen. 

The  hairs  are  extremely  variable  in  color  and  size  in  the  different  breeds  and 
in  different  individuals.  The  hair  of  the  frontal  region  is  often  curly,  especially 
in  the  bull.  There  is  no  mane,  and  the  long  hairs  of  the  tail  occur  only  at  the  end, 
where  they  form  the  ''brush"  (Cirrus  caudse). 

The  claws,  four  in  number  on  each  limb,  cover  the  ends  of  the  digits.  Those 
of  the  chief  digits  conform  in  a  general  way  to  the  shape  of  the  third  phalanges, 
and  each  may  be  regarded  as  having  three  surfaces.  The  abaxial  surface  is  convex 
from  side  to  side,  and  is  marked  l^y  ridges  parallel  with  the  coronary  border.  Its 
anterior  part  is  concave  from  edge  to  edge,  and  the  angle  which  it  forms  with  the 
ground  is  about  30°.  The  interdigital  surface  is  concave  and  grooved;  it  touches 
the  opposite  claw  only  at  its  ends.  The  basal  or  ground  surface  consists  of  two 
parts,  viz.,  a  slightly  concave  sole,  which  is  pointed  in  front  and  widens  behind,  and 
a  prominent  bulb  of  soft  thin  horn,  which  is  continuous  al)ove  with  the  skin.  The 
claw  may  be  regarded  as  consisting  of  three  parts — periople,  wall,  and  sole.     The 


Fig.      721. — Claws     ( 
Volar  Aspect. 
Ellenberger-Baum 
fiir  Kiinstler.) 


•     Ox; 

(After 
Anat. 


COMMON   INTEGUMENT 


899 


periople  surrounds  the  coronary  border  in  the  form  of  a  flat  band,  which  is  about 
half  an  inch  wide,  except  at  the  heels,  where  it  widens  to  cover  the  entire  surface. 
The  wall  forms  most  of  the  abaxial  part  of  the  claw  and  is  reflected  in  front  upon  the 
interdigital  surface.  It  thins  out  toward  the  bulb  or  heel,  which  appears,  as  stated 
above,  to  consist  of  the  thin  expansion  of  the  periople.  The  sole  occupies  the  angle 
of  inflection  of  the  wall;  it  is  continuous  Avithout  demarcation  with  the  periople  of 
the  bulb.  The  perioplic  corium  bears  relatively  long  papillae.  The  coronary  corium 
is  much  less  developed  than  in  the  horse  and  its  papilla;  are  short.  The  laminae  are 
much  narrower  and  are  more  numerous  than  in  the  horse;  secondary  laminae  are 
not  present.  The  corium  of  the  sole  is  not  marked  off  behind  from  that  of  the 
periople;    its  papillae  are  very  small  and  close  together.     The  corium  of  the  bulbs 


Lateral  extensor  tendon 
Metacarpal  bone 


Metacar po-phalangeal  articulation 
First  phalanx 
Lateral  extensor  tendon 
Common  extensor  tendon 
Proximal  inter  phalangeal  joint 
Second  phalanx  _ 
Periople 


Coronary  corium 

Third  phalanx 

Wall  of  hoof 


Upper  pouch 
of  metacarpo- 
phalangeal 
joint  capsule 
Superficial 
[flexor  tendon 
Sitspinsory 
liijinnent 
peep  flexor 
tendon 
Superficial 
flexor  tendon 
Annular 
ligament 
Proximal 
Sesamoid 
Cruciate 
ligament 
Small  claw 
Annular  ligament 
Digital  cushion 
Upper  pouch  of  capsule 
of  distal  inter  phalangeal 
joint 
Distal  sesamoid  bone 

Bursa 


Fig.  722. — Sagittal  Sectiox  of  Distal  Part  of  Forelimb  of  Ox. 


is  separated  from  the  flexor  tendon  by  a  mass  of  elastic,  fatty  tissue,  which  is 
analogous  with  the  digital  cushion  of  the  horse.  The  papillae  here  are  long  and 
often  compound. 

The  accessory  digits  bear  short  conical  horn  capsules  which  resemble  in  a 
general  way  those  of  the  chief  digits,  and  have  a  similar  corium,  which  covers  one 
or  two  nodular  vestigial  phalanges.  From  these  a  fibrous  band  descends  obliquely 
on  the  volar  aspect  of  each  chief  digit  and  is  attached  below  to  the  distal  phalanx 
and  sesamoid  bones,  sending  fibers  also  to  the  elastic  pad  of  the  heel. 

The  horns  (Cornua)  enclose  the  horn  processes  of  the  frontal  bones  (except  in 
the  polled  breeds).  They  vary  very  greatly  in  size,  form,  and  curvature.  The  root 
or  base  of  the  horn  (Radix  cornus)  has  a  thin  edge  which  is  continuous  with  the 


900  THE    SENSE    ORGANS   AND    COMMON    INTEGUMENT   OF   THE    PIG 

ordinary  epidermis.  It  is  covered  bj^  a  thin  layer  of  soft  horn  similar  to  the  periople 
of  the  hoof  of  the  horse.  Near  the  root  the  horn  is  encircled  by  variable  rings. 
Toward  the  apex  (Apex  cornus)  the  thickness  of  the  horn  increases  till  it  becomes 
practically  a  solid  mass.  The  horn  consists  mainly  of  tubes  which  are  very  close 
together,  except  at  the  rings,  where  there  is  more  intertubular  horn.  The  corium 
of  the  horn  (Corium  cornus)  is  united  to  the  horn  process  by  periosteum  which  is 
traversed  by  numerous  blood-vessels.  The  corium  at  the  root  of  the  horn  is  thick 
and  bears  long,  slender  papillae;  in  the  body  of  the  horn  it  becomes  thin  and  the 
papillae  are  smaller,  but  increase  in  size  apically.  Rudimentary  papillated  laminae 
also  occur. 

The  skin  of  the  sheep  varies  in  thickness  from  0.5  to  3  mm.,  but  differs  greatly 
in  fineness  and  in  other  respects  in  various  breeds.  In  Merinos  large  folds 
occur  on  the  neck.  Cutaneous  pouches  (Sinus  cutis)  are  constantly  present 
in  certain  situations.  The  infraorbital  or  lacrimal  pouch  (Sinus  cutaneus  infra- 
orbitalis)  is  an  invagination  about  half  an  inch  in  depth,  which  is  situated  in  front 
of  the  medial  angle  of  the  eye.  It  bears  scattered  fine  hairs,  into  the  follicles  of 
which  large  compound  sebaceous  glands  open;  coil  glands  are  also  present.  The 
secretion  of  the  glands  is  fatty  and  forms  a  yellow,  sticky  covering  on  the  skin  when 
dry.  The  inguinal  (or  mammary)  pouch  (Sinus  cutaneus  inguinalis)  is  much  more 
extensive,  and  is  situated  in  the  inguinal  region  in  both  sexes.  The  skin  of  the 
pouch  bears  scattered  fine  hairs  and  contains  well-developed  sebaceous  glands  and 
exceedingly  large  coil  glands.  The  interdigital  pouch  (Sinus  cutaneus  interdigi- 
talis)  is  a  peculiar  tubular  invagination  of  the  integument  which  opens  at  the 
anterior  part  of  the  interdigital  cleft.  On  sagittal  section  it  appears  as  a  bent  tube, 
an  inch  or  more  (ca.  2.5-3  cm.)  in  length,  and  about  a  fourth  of  an  inch  (ca.  6- 
7  mm.)  in  diameter.  The  pouch  extends  downward  and  backward,  and  then 
curves  sharply  upward  between  the  distal  ends  of  the  first  phalanges.  Its 
deep  blind  end  is  somewhat  ampullate.  The  subcutis  forms  a  capsule  around  it. 
The  skin  of  the  pouch  is  thin  and  pale;  it  bears  fine  colorless  hairs,  the  follicles  of 
which  receive  the  secretion  of  several  sebaceous  glands.  The  coil  glands  here  are 
compound  and  very  large;  they  open  into  the  hair-follicles  or  directly  into  the  pouch. 
The  secretion  of  the  glands  is  a  colorless  fatty  substance.  The  skin  is  covered  in 
great  part  by  wool,  which  is  similar  in  structure  to  hair,  but  is  finer,  curly,  and 
usually  contains  no  medullary  cells.  The  follicles  of  the  wool  are  curved,  and  are 
arranged  more  or  less  distinctly  in  groups  of  ten  or  a  dozen,  several  of  which  open 
in  common  on  the  surface.  A  considerable  part  of  the  face  and  the  limbs  is  covered 
with  short,  stiff  hair,  and  long  hairs  occur  more  or  less  interspersed  among  the  wool. 
The  claws  resemble  those  of  the  ox.  The  horns,  when  present,  are  more  or  less 
prismatic,  distinctly  ringed,  and  vary  in  length  and  curvature  in  different  breeds. 
Their  structure  is  similar  to  those  of  the  ox. 

The  olfactory  and  gustatory  organs  resemble  in  general  those  of  the  horse. 


THE  SENSE  ORGANS  AND  COMMON  INTEGUMENT  OF  THE  PIG 

THE  EYE 

The  posterior  part  of  the  orbital  margin  is  formed  chiefly  by  the  orbital  liga- 
ment, which  extends  from  the  extremely  short  supraorbital  process  to  the  small 
eminence  at  the  junction  of  the  malar  and  the  zygomatic  process  of  the  temporal. 

Cilia  occur  only  on  the  upper  eyelid.  The  medial  canthus  is  prolonged  by  a 
groove  on  the  infraorbital  region.  The  tarsal  glands  are  very  short  and  curved. 
The  conjunctival  epithelium  is  of  the  transitional  type,  with  many  goblet  cells. 


THE  EAR THE  SKIN  AND  APPENDAGES  901 

The  deep  part  of  the  cartilage  of  the  third  eyelid  is  broad  and  spoon-like,  the 
superficial  part  somewhat  anchor-shaped.  In  addition  to  the  gland  which  sur- 
rounds the  deep  part  of  the  cartilage,  there  is  a  deeper  one,  often  termed  the  gland 
of  Harder  (Glandula  palpebrae  tertise  profunda),  which  is  surrounded  by  a  distinct 
capsule  and  a  blood-sinus.  This  gland  is  brownish  or  yellowish-gray  in  color, 
elliptical  in  outline,  and  about  an  inch  (2-3  cm.)  in  length.  It  is  situated  deeply 
below  the  attachment  of  the  ventral  oblique  muscle. 

The  caruncula  lacrimalis  has  the  form  of  a  ridge;  it  divides  into  two  branches 
which  join  the  skin  at  the  medial  commissure.  It  is  red  in  color  and  contains 
numerous  large  coil  glands. 

The  lacrimal  gland  is  mucous  in  type.  There  is  no  lacrimal  sac,  and  the  two 
lacrimal  ducts  pass  through  separate  openings  at  the  infraorbital  margin.  The 
naso-lacrimal  duct  is  usually  short  and  opens  into  the  ventral  nasal  meatus  at  the 
posterior  end  of  the  ventral  turbinate.^  The  eyeball  appears  small,  partly  on 
account  of  the  narrowness  of  the  palpebral  opening;  it  closely  approaches  the  spheri- 
cal form.  The  cornea,  although  in  reality  almost  circular,  appears  oval  when  viewed 
from  the  front,  the  medial  end  being  much  the  broader.  The  chorioid  has  no 
tapetum.  The  iris  is  usually  dark  grayish-brown  or  yellowish-brown,  but  sometimes 
has  a  blue  tinge.  The  pupil  is  a  transverse  oval  in  ordinary  light,  l)ut  almost 
circular  when  dilated;  granula  are  not  present.  The  optic  papilla  is  nearer  the 
posterior  pole  than  in  the  horse  and  ox,  and  has  a  distinct  central  artery  and  vein. 


THE  EAR 
The  external  ear  differs  considerably  in  size,  thickness,  and  position.  It  may 
be  carried  vertically,  inclined  inward,  or  hang  downward.  It  is  relatively  wide  and 
is  little  curved  except  at  the  base.  The  concave  surface  presents  several  cutaneous 
ridges  which  correspond  approximately  with  the  long  axis  of  the  ear.  The  anterior 
border  of  the  concha  is  strongly  recurved  in  its  lower  part,  and  divides  into  two 
branches,  one  of  which  passes  almost  horizontally  backward  in  the  cavum  conchse, 
while  the  other  continues  the  general  direction  of  the  border.  The  posterior  border 
is  slightly  concave  above,  strongly  convex  below,  forming  a  prominence  somewhat 
analogous  to  the  lobule  of  the  human  ear.  The  osseous  external  acoustic  meatus 
is  very  long  and  is  directed  ventro-medially.  The  tympanic  membrane  is  almost 
circular.  The  tympanic  cavity  proper  is  small,  but  it  is  continuous  with  the  numer- 
ous cells  of  the  large  bulla  ossea.  The  auditive  or  Eustachian  tube  is  short;  its 
pharyngeal  opening  is  situated  in  the  upper  part  of  the  wall  of  the  pharynx,  imme- 
diately behind  the  posterior  nares.  It  is  somewhat  infundibular,  and  is  bounded 
medially  by  a  thick  fold  of  mucous  membrane  (Torus  tubarius). 


THE  SKIN  AND  APPENDAGES 

The  thickness  of  the  skin  in  improved  breeds  is  1  to  2  mm.  Fat  usually  accu- 
mulates in  the  subcutis  and  forms  a  distinct  and  often  extremely  thick  panniculus 
adiposus  over  the  greater  part  of  the  body.  The  sebaceous  glands  are  in  general 
small  and  much  fewer  than  in  the  other  animals.  The  sweat  glands,  on  the  other 
hand,  are  large,  yellow  or  brownish  in  color,  and  are  in  many  places  visible  to  the 
naked  eye.  At  the  medial  side  of  the  carpus  there  are  small  cutaneous  diverticula, 
the  so-called  carpal  glands,  into  which  numerous  compound  coil  glands  open.  Large 
glands  also  occur  in  the  skin  of  the  digits  and  interdigital  space.  Compound 
tubular  glands  are  present  in  the  skin  of  the  snout.     Large  sebaceous  and  sweat 

1  The  lower  punctum  lacrimale  is  frequently  absent  and  the  corresponding  duct  therefore 
blind.  There  is  often  a  duct  or  its  remnant  which  opens  below  the  ventral  turbinate  fold,  but  is 
not  connected  behind  with  the  functional  duct. 


902  THE   SENSE    ORGANS   AND    COMMON   INTEGUMENT   OF   THE    DOG 

glands  are  found  at  the  entrance  to  the  preputial  diverticulum.  The  hairs  are 
sparsely  scattered  in  improved  breeds — indeed,  in  some  cases  the  skin  is  almost 
bare.  The  long  hairs  or  bristles  are  arranged  usually  in  groups  of  three.  They 
are  most  developed  on  the  neck  and  back.  The  bristles  about  the  snout  and  the 
chin  are  sinus  hairs. 

The  claws  and  their  corium  resemble  those  of  the  ox,  but  the  bulbs  are  more 
prominent  and  form  a  greater  part  of  the  ground  surface;  they  are  also  better 
defined  from  the  sole,  which  is  small.  The  claws  of  the  accessory  digits  are  more 
developed  and  their  parts  better  differentiated  than  those  of  the  ox. 

The  olfactory  region  is  extensive  in  correlation  with  the  large  size  of  the 
olfactory  bulbs;   the  mucous  membrane  here  is  brown  in  color. 


THE  SENSE  ORGANS  AND  COMMON  INTEGUMENT  OF  THE  DOG 

THE  EYE 

The  posterior  margin  of  the  orbit  is  formed  by  the  orbital  ligament,  as  in  the 
pig.  The  orbital  axes  if  produced  backward  would  include  an  angle  of  about  79", 
the  optic  axes  an  angle  of  about  92.5°  (Koschel).  The  lower  eyelid  has  no  distinct 
cilia.  The  medial  angle  is  wide,  the  lacus  lacrimalis  shallow,  and  the  caruncula 
lacrimalis  small  and  yellowish-brown.  The  conjunctival  epithelium  is  cylindrical, 
with  many  goblet  cells.  The  gland  which  surrounds  the  deep  end  of  the  cartilage 
of  the  third  eyelid  is  large  and  pink;   it  is  a  mixed  gland. 

The  lacrimal  gland  is  flat  and  lies  chiefly  under  the  orbital  ligament.  It  is 
pink  in  color  and  mixed  in  structure.  The  naso-lacrimal  duct  is  variable  in  arrange- 
ment and  may  differ  on  the  two  sides.  It  may  open  into  the  ventral  meatus  im- 
mediately after  its  emergence  from  the  osseous  lacrimal  canal;  thence  it  continues 
forward  and  opens  on  the  lateral  wall  of  the  nostril  below  the  ventral  turbinate  fold. 

The  eyeball  is  almost  spherical  and  is  relatively  large,  especially  in  the  small 
breeds.  The  sclera  is  thick  in  the  ciliary  region,  where  it  contains  a  well-developed 
venous  plexus;  in  the  vicinity  of  the  equator  it  is  thin,  and  the  chorioid  shows 
through  it.  The  cornea  is  almost  circular.  The  chorioid  is  richly  pigmented, 
and  presents  a  well-defined  tapetum  cellulosum;  this  is  somewhat  triangular  in 
outline  and  has  a  metallic  luster.  Its  color  is  often  golden  green,  shading  to  blue 
peripherally,  but  the  blue  tone  may  predominate,  and  in  other  cases  it  is  mainly 
golden  yellow  or  reddish-yellow.  The  appearance  is  due  to  several  layers  of  peculiar 
flattened  polygonal  cells.  The  ciliary  muscle  is  more  developed  than  in  the  other 
species.  The  iris  is  commonly  light  or  yellow  brown,  but  not  rarely  has  a  blue 
tinge;  the  color  often  differs  in  the  two  eyes.  The  pupil  is  round;  its  edge  is 
either  smooth  or  bears  minute  round  prominences.  The  retina  presents  a  round 
area  centralis  lateral  to  the  optic  papilla.  The  latter  is  variable  in  outline;  com- 
monly it  has  the  form  of  a  triangle  with  the  angles  rounded  off,  but  is  often  round 
or  oval.  Branches  of  the  central  vessels  of  the  retina  radiate  from  the  middle  of 
the  papilla.  The  surfaces  of  the  lens  are  not  so  strongly  curved  as  in  the  other 
domestic  animals,  and  there  is  little  difference  in  the  radius  of  curvature  of  the  two 
surfaces. 

THE  EAR 

The  external  ear  differs  greatly  in  size  and  form  in  the  various  breeds;  in  most 
it  is  relatively  wide  and  thin  and  the  greater  part  of  it  hangs  down  over  the  opening. 


THE   SKIN   AND    APPENDAGES  903 

The  anterior  border  has  a  prominence  (Spina  helicis)  at  its  lower  part,  and  below 
this  it  divides  into  two  branches  (Crura  helicis).  One  of  these  continues  down  to  a 
blunt  point,  while  the  other  turns  into  the  cavity  of  the  concha.  The  posterior 
border  forms  a  pouch  below  its  middle,  and  is  thick  and  rounded  in  its  basal  pan. 
Here  the  conchal  cartilage  bears  a  pointed  process  (Processus  uncinatus),  which  pro- 
jects upward  and  backward.  The  outer  wall  of  the  cavum  conchae  is  supported 
by  a  quadrilateral  plate  (Tragus)  above  and  a  semi-annular  cartilage  below.  The 
concave  surface  presents  several  cutaneous  folds,  and  in  the  cavum  conchae  there 
are  ridges  and  irregular  prominences.  There  are  long  hairs  on  the  borders,  apex, 
and  the  folds  of  the  concave  surface,  but  the  skin  of  the  cavum  conchae  is  bare. 
The  annular  cartilage  is  a  complete  ring.  The  osseous  external  acoustic  meatus 
is  wide  and  extremely  short. 

The  auricular  muscles  are  thin.  The  scutularis  is  extensive  and  is  divisible 
into  interscutularis  and  fronto-scutularis.  It  partly  covers  the  occipitalis  muscle, 
which  is  oval  and  unpaired  and  ends  in  the  fascia  of  the  frontal  region.  The 
scutulo-auriculares  superficiales,  ventralis  et  accessorius,  and  the  cervico-scutularis 
are  not  differentiated  as  separate  muscles.  The  cervico-auricularis  superficialis 
and  the  parieto-auricularis  both  bifurcate  and  are  inserted  into  the  base  of  the 
concha  and  the  scutiform  cartilage.  The  parotido-auricularis  is  narrow  and  almost 
long  enough  to  meet  the  opposite  muscle.  The  tragicus  consists  of  two  parts;  of 
these,  the  lateral  one  is  long  and  arises  fron  the  border  of  the  mandible  above  the 
angular  process.     The  helicis  and  the  verticalis  auriculae  are  well  developed. 

The  tympanic  cavity  is  very  roomy,  extending  ventrally  into  the  large  but 
simple  cavity  of  the  bulla  ossea.  The  tympanic  membrane  is  extensive  and  oval. 
The  promontory  is  very  pronounced.  The  auditory  ossicles  are  large.  The 
auditive  or  Eustachian  tube  is  short,  and  has  a  fibrous  lateral  lamina.  Its  pharyngeal 
opening  is  an  oblique  slit  situated  on  the  lateral  wall  of  the  naso-pharyngeal  meatus, 
and  is  margined  medially  by  a  thick  mucous  fold.  The  cochlea  has  three  and  a 
half  turns  and  is  more  sharply  pointed  than  in  the  ungulates. 


THE  SKIN  AND  APPENDAGES 

The  skin  varies  greatly  in  thickness  in  different  breeds.  It  is  remarkably 
loose  on  the  dorsal  aspect  of  the  neck  and  trunk,  where  it  can  be  raised  in  extensive 
folds.  The  coat  is  also  subject  to  extreme  variation  in  length,  thickness,  color,  etc. 
The  hairs  are  arranged  in  groups  of  three  to  a  large  extent.  The  sebaceous  glands 
are  best  developed  in  the  short  and  rough  haired  breeds.  They  are  largest  and 
most  numerous  at  the  lips,  anus,  dorsal  surface  of  the  trunk,  and  sternal  region. 
The  sweat  glands  are  relatively  better  developed  in  the  long  and  fine  haired  breeds. 
The  largest  are  found  in  the  digital  pads.  Coil  glands  occur  in  the  skin  of  the 
perineum  and  the  paranal  pouches.  In  the  muzzle  glands  are  absent  or  very 
scanty.^ 

On  the  flexion  surface  of  the  carpus  and  digit  there  are  hairless,  cushion-like 
pads.  The  carpal  pad  (Torus  carpalis)  is  situated  medial  and  distal  to  the  accessory 
carpal  bone.  The  metacarpal  and  metatarsal  pads  (Torus  metacarpalis,  meta- 
tarsalis)  are  the  largest  and  are  situated  behind  the  distal  ends  of  the  metacarpal 
or  metatarsal  bones  and  the  greater  part  of  the  first  phalanges.  They  are  somewhat 
heart-shaped,  with  two  unequal  lateral  lobes,  and  the  apex  distal.  The  metapodio- 
phalangeal  joints  rest  on  them  when  the  paw  supports  the  weight.  The  digital 
pads  (Toruli  digitales)  are  oval  and  are  much  smaller;  they  similarly  support  the 
second  digital  joints.  That  of  the  first  digit  is  small  on  the  forelimb,  and  usually 
absent  from  the  hind  limb.     Each  receives  two  suspensory  bands  from  the  tubercles 

'  Trautmann  has  shown  that  the  secretion  which  appears  on  the  muzzle  comes  from  the 
lateral  nasal  gland,  which  is  well  developed. 


904 


THE  SENSE  ORGANS  AND  COMMON  INTEGUMENT  OF  THE  DOG 


at  the  distal  end  of  the  corresponding  second  phalanx.  The  pads  have  a  basis  of 
fibro-elastic  tissue  and  fat,  which  is  intimately  adherent  to  the  skin  and  is  connected 
by  trabeculae  with  the  bones  and  tendons.  The  epidermis  is  thick  and  largely 
keratinized,  and  is  studded  with  numerous  rounded  papillae  which  are  readily  seen 


Fig.  723. — Pads  of  Right  Fore  Paw  of  Dog.  Fig.  724. — Pads  of  Right  Hind  Paw  of  Dog. 

1-5,  Digital  pads;   6,  6,  metacarpal  and  metatarsal  pads;   7,  carpal  pad. 

with  the  naked  eye.     The  corium  has  large  papillae,  and  contains  sweat  glands  and 
lamellar  corpuscles. 

The  claws  (Ungues)  correspond  in  form  to  the  ungual  part  of  the  distal  pha- 
langes, which  they  enclose.  The  horn  of  the  claw  consists  of  a  body  or  wall  and  a 
sole.     The  former  is  strongly  curved  in  both  directions,  and  is  compressed  laterally. 


Fig.  725. — Half  op  Claw  of  Dog;  Inner  Surface. 
Coronary  part;   6,   volar  part  of  wall;  c,  sole;  d,  section  of  c;  e,  section  of  wall;  i,  coronary  border; 
3,  dorsal  surface.      (From  Leisering's  Atlas.) 


Its  coronary  border  fits  into  the  depression  under  the  bony  collar  or  ungual  crest 
of  the  third  phalanx  and  is  covered  by  skin.  The  lateral  borders  converge  and 
enclose  the  sole  anteriorly.  The  corium  presents  a  coronary  part  which  bears 
papillae  only  near  the  coronary  border.  On  the  dorsal  surface  it  is  thickened  to 
form  a  ridge,  and  the  corresponding  part  of  the  horny  covering  is  thick  and  main- 


OLFACTORY  AND  GUSTATORY  ORGANS  905 

tains  the  pointed  character  of  the  claw.  The  coriiim  of  the  sides  of  the  wall  bears 
small  laminae  which  converge  to  the  corium  of  the  sole.  The  latter  is  papillated. 
When  the  flexor  muscles  are  inactive,  the  distal  phalanges  and  the  claws  are  main- 
tained in  dorsal  flexion  by  two  elastic  ligaments.  These  arise  from  the  tubercles 
at  the  proximal  end  of  the  second  phalanx  and  converge  to  the  dorsal  aspect  of  the 
ungual  crest  of  the  third  phalanx. 


OLFACTORY  AND  GUSTATORY  ORGANS 

The  olfactory  region  lies  above  the  lamina  transversa,  which  separates  it  from 
the  naso-pharyngeal  meatus.  The  mucous  membrane  is  distinguished  by  its 
thickness  and  yellow  color,  and  is  very  extensive.  It  covers  about  half  of  the  large 
ethmoturbinates,  and  one-third  to  one-half  of  the  septum  nasi.  The  ethmotur- 
binate  which  projects  into  the  frontal  sinus  and  the  adjacent  inner  wall  of  the  sinus 
are  olfactory  in  character.  Olfactory  nerve-fibers  ramify  in  the  vomero-nasal 
organ. 

The  gustatory  apparatus  presents  no  special  features  of  importance. 


INDEX 


Abdomen,    lymph   vessels   of, 

701 
Abdominal  aortic  plexus,  833 

cavity,  410,  452 

inguinal  ring,  290,  292 

part  of  sympathetic  system, 
832 

plexuses,  832 

tunic,  288,  361 
Abomasum,  453,  456,  474 
Accessory  organs,  385 

pancreatic  duct,  434 

parotid  glands,  482 

spleens,  441 

thyroids,  536,  553 
Acetabular  angle,  106,  109 

fossa,  109 
Acoustic     meatus,      external, 
61,  870,  871 
internal,  62,  882 

process,  external,  61,  74 
Aditus  laryngis,  406,  407,  521 

oesophagi,  407 
Adrenal  bodies,  563,  566,  567, 
569,  570 

plexuses,  834 
Adventitia  of  ductus  deferens, 
575 

of  Fallopian  tubes,  599 

of  seminal  vesicles,  578 
^sthesiology,  857 
Aggregated   nodules   of   large 
intestine,  431 
of    small    intestine,    442, 
487,  501 
Ahd  nasi,  508 
Alar  canal,  54,  75,  78 

cartilages,  509,  537 

fold,  509 

notch,  184 
Alimentary  canal,  385 
Alveolar  border  of  premaxillaj, 
65 

ducts  of  lungs,  534 

periosteum  of  teeth,  395 

tuberosity,  64,  78 
Alveoli,  71 

dental,  64 

of  mammary  glands,  605 

of  thyroid  gland,  536 
Alveus,  787 

Amphiarthroses,  210,  211 
Ampulla     ductus     deferentis, 
575 

of  semicircular  canals,  881 

of  uterus,  613 

recti,  429 
Amygdaloid  nucleus,  792 
Anal  sacs,  502 
Anastomosis  of  arteries,  614 
Anatomy,  17 

comparative,  17 


Anatomy,  gross,  17 

macroscopic,  17 

microscopic,  17 

philosophical,  17 

special,  17 

systematic,  17,  18 

topographic,  17,  18 

veterinary,  17 
Angiology,  614 
Angle,  acetabular,  106,  109 

duodenal,  433 

of  mandible,  70,  71 

of  rib,  27 

splenic,  433 
Angular  process  of  mandible, 

195 
Annular  cartilage  of  ear,  871 
Ansate  fissure,  849 
Antrum  pyloricum,  416 
Anus,  432 

Aortic  plexus,  abdominal,  833 
thoracic,  831 

orifice  of  heart,  626 

valve,  626 
Aperture,  posterior,  of  pelvis, 

111 
Apex  of  hoof,  891 
Apical  lobe  of  lung,  540,  547, 

548,  551,  553 
Aponeurosis,  253 

of   obliquus   abdominis   ex- 
temus  muscle,  288 

of     transversus     abdominis 
muscle,  291 

pharyngeal,  407 
Appendages  of  skin,  886,  901, 

903 
Appendix  epididymidis,  573 

testis,  571 

ventriculi  laryngis,  522 
Aquaeductus  cochleae,  882 

vestibuli,  881 
Aqueduct  of  cerebrum,  780 
Aqueous  humor,  869 
Arachnoid  granulations,  763 
Arachnoidea,  762 

cerebral,  762 

spinal,  763 
Arbor  meduUaris,  777 
Arch,  distal  volar,  657 

hemal,  188 

lumbo-costal,  287 

of  aorta,  629 

of  cricoid  cartilage,  515 

plantar,  deep,  697,  721 
distal,  678,  697,  719 
proximal,  678,  679,  719 

subcarpal,  657 

venous,  692 

zygomatic,  60,  73 
Arcuate  fibers,  external,  773, 

774 

907 


Arcuate  fibers,  internal,  774 

of  cerebellum,  777 
Area  acustica,  779 
centralis  retinae,  868 
cribrosa,  558 
parolfactoria,  788 
Arteria  profunda  penis,  673 
Arteries  or  artery,   614,   629, 

706,  736,  744 
abdominal,  anterior,  635 

posterior,  675,  752 

subcutaneous,  675 
adrenal,  563,  666 
adventitia  of,  615 
alveolar,  inferior,  647,  737, 

747 
anastomosis  of,  614 
angular,  709 

of  eye,  644,  710 
antibrachial,  volar,  749 
aorta,  629,  736,  744 

abdominal,  630,  661,  713, 
750 

ascending,  629 

brachiocephalic,       trunk, 
631 

thoracic,  630, 660, 713, 750 
asternal,  635 

auricular,  anterior,  646,  709, 
747 

great,  747 

posterior,  644,  709,  736 
basilar,  640 
bicipital,  749 

brachial,  650,  707,  710,  736, 
738,  744,  747 

deep,  651,  710,  749 

left,  632 

right,  631 
brachiocephalic,    631,    736, 

744 
bronchial,  534,  535, 660,  713, 

737 
broncho-cesophageal,      535, 

660,  750 
buccinator,  649,  710,  737 
cajcal,  737,  751 

lateral,  665 

medial,  665 
carotid,  common,  635,  707, 
736,  744,  746 
left,  637 
right,  636 

external,    641,    709,    736, 
747 

internal,  640,  736,  747 
central,  of  retina,  649 
cerebral,  anterior,  641,   747 

deep,  641 

middle,  641 

posterior,  640 
cerebrospinal,  640,  747 


908 


INDEX 


Arteries,    cervical,  deep,  633, 
707,  736,  745 
dorsal,  745 

inferior,  635,  707,  736,  746 
chorioid,  anterior,  641 
ciliary,  649 

circulus  arteriosus,  641 
major,  867 
minor,  867 
circumflex,     anterior,     748, 
749 
of  humerus,  651 
external,  718 
lateral,  752 

of  thigh,  673 
of  coronary  cushion,  660 
of  scapula,  651 
posterior,  710,  749 
of  humerus,  651 
clitoridis,  717 
coats  of,  615 

coccygeal,  lateral,  672,  717 
middle,  672,  717 
superficial  lateral,  754 
ccEhac,  662,  713,  737,  750 
colic,  751 
dorsal,  666 

middle,  666,  715,  737,  751 
right,  737,  751 
ventral,  665 
commimicating,      posterior, 

640 
condyloid,  639,  708,  747 
coronary,  628,  630,  631,  707, 

744 
costo-cervical.  632 
cremasteric,  674 
digital,  659,  681,  739,  740, 
894 
common,  659,  739,  749 
dorsal,  712,  719 
plantar,  719 
volar,  712 
lateral,  719 
volar,  712 
medial,  719 
volar,  712 
plantar,  754 
proper,  739,  749 
volar,  712 
dorsal,  632,  707,  736,  745 
dorsalis  penis,  717 
end,  614 
ethmoidal,  649 
external  coat,  615 
facial,  642 

transverse,  646,  673,  674, 
709,  747 
femoral,  717,  740,  752 
anterior,  675,  718,  752 
deep,  675,  718,  739,  752 
posterior,  676,  754 
first,  of  small  colon,  666 
frontal,  710 
gastric,  535,  662,  750 
gastro-duodenal,  662,  750 
gastro-epiploic,  750,  751 
left,  663 
right,  662 
gastro-hepatic,  737 
gastro-splenic,  751 
gluteal,  anterior,  672,  717, 
754 
posterior,  672,  717 


Arteries,  haemorrhoidal,  ante- 
rior, 666 

middle,  670,  754 
hepatic,  438,  662,  713,  750 
hypogastric,  669 
ileal,  665,  737,  751 
ileo-ca^co-colic,  716,  737 
iliac,  circumflex,  673,  752 

external,  673,  717,  752 

internal,  669,  717^754 
iliaco-femoral,  673,  717 
ilio-lumbar,   672,   717,   739, 

754 
incisor,  647 
infraorbital,  649,  710,  737, 

747 
intercarotid,  640 
intercostal,  ■  660,   713,    737, 
750 

aortic,  660 
internal  coat,  615 
interosseous,  common,  654, 
711,  749 

dorsal,  656,  711 

recurrent,  656,  711 

volar,  655,  749 
intima  of,  615 
labial,  inferior,  643,  709 

superior,  643,  709 
lacrimal,  649 
laryngeal,  637,  707,  746 
lingual,  642,  708,  736,  747 
lumbar,  668,  669,  717,  738, 

750 
malar,  650,  710 
mammary,  675,  718 
masseteric,  641,  709 
maxillary,  external,  642, 708, 
736,  747 

mtemal,  646, 710,  736, 747 
median,  654,  711,  738,  748 
medullary,  22 
meningeal,  anterior,  641 

middle,  648,  710,  737,  747 

posterior,  639,  709,  747 
mental,  647 

mesenteric,    anterior,     665, 
715,  737,  751 

posterior,   666,  716,  737, 
752 
metacarpal,  711,  712,  739, 
749 

dorsal,  657,  712 

lateral  volar,  657 

medial  volar,  657 
metatarsal,    678,    719,   740, 
753,  754 

dorsal,  680 

great,  681 

plantar,  deep,  753 
superficial,  753 
middle  coat,  615 
musculo-phrenic,  635 
nasal,  709 

dorsal,  644,  710 

lateral,  643,  710 
nutrient,  of  femur,  676 

of  humerus,  654 

of  tibia,  676 
obturator,  673,  717,  718 
occipital,  660,  662,  713,  737, 

750 
oesophageal,  660,  662,  713, 

737,  750 


Arteries  of  bladder,  562 
of  bone,  22 
of  brain,  792 
of  bulb,  670,  754 
of  clitoris,  670 
of  corpus  callosum,  641 
of  digital  cushion,  659 
of  ductus  deferens,  575 
of  external  ear,  875 
of  eye,  859 

of  Fallopian  tubes,  599 
of  first  phalanx,  65,9 
of  internal  ear,  884 
of  pelvic  limb,  673,  717 
of  penis,  582,  754 . 

anterior  dorsal,  675 

deep,  754 

dorsal,  754 
of  rete  carpi  volare,  657 
of  retma,  869 

central,  649 
of  second  phalanx,  659,  660 
of  skin,  885 
of  small  intestine,  665 
of  third  phalanx,  660 
of  thoracic  limb,  650,  710 
of  tympanum,  878 
of  uterus,  601 
of  vagina,  602 
of  vascular  tunic  of  eye,  867 
omaso-abomasal,  713 
ophthalmic,  710 

external,  649,  747 

internal,  747 
ovarian,  598,  668 
palatine,  737 

greater,  650,  710 

lesser,  650 
pancreatic,  662 
pancreatico-duodenal,    662, 

750 
parotid,  637,  736 

inferior,  707 

superior,  709 
pericardiaco-phrenic,  635 
perineal,  670,  754 
periosteal,  22 
peroneal,  678 
pharyngeal,  642,  708,   709, 

746 
phrenic,  661,  713 
phrenico-abdominal,       737, 

751 
plantar,  678,  753 

lateral,  719 

medial,  719 
popliteal,  673,  676,  717,  740^ 

754 
prepubic,  675 
profunda  penis,  717 
pterygoid,  647 
pudic,    external,    575,    675, 
717,  740,  752 

internal,  669,  717,  754 
pulmonary,    534,    614,   629, 

736 
pyloric,  662 
radial,  712,  738,  749 

anterior,  654 

collateral,  710 

distal  collateral,  749 

posterior,  654 

proximal  collateral,  749 
ramus  collateralis,  716 


INDEX 


909 


Arteries,  renal,  560,  666,  717, 
737,  751 
ruminal,  713 
sacral,  lateral,  670,  717 
middle,  629,  717,  750 
saphenous,    675,    718,    740, 

753 
spermatic,    573,    575,    717, 
737,  751 
external,  674 
internal,  666 
spinal,  ventral,  640 
splenic,  662,  715,  737,  751 
structure  of,  615 
stylomastoid,  645 
subcostal,  633,  707,  736,  745 
sublingual,  642,  709 
submental,  642 
subscapular,  651,  710,  748 
supraorbital,  649 
suprascapular,  651 
systemic,  614,  629 
tarsal,  lateral,  677,  718,  753 
medial,  678,  718 
perforating,  678,  719,  740 
recurrent,  677 
temporal,  deep,  747 
anterior,  648,  710 
posterior,  648 
superficial,  646,  709,  737, 
747 
terminal,  614 

thoracic,  external,  635,  707, 
736,  746 
internal,    634,    707,    736, 
746 
thoracico-dorsal,  651,  710 
thoraco-acromial,  746 
thymic,  635 
thyroid,  707 

anterior,  637,  746 
posterior,  638,  736,  746 
thyro-laryngeal,  637 
tibial,    anterior,    678,    719, 
740,  754 
posterior,  676,    719,   740, 

754 
recurrent,  678 
tracheal,  746 
tympanic,  648 
ulnar,  654,  712,  738,  749 
proximal   collateral,    710, 
749 
umbilical,    670,    704,    717, 

754 
uterine,  754 
anterior,  668 
middle,  674,  717 
posterior,  670,  717 
utero-ovarian,  668,  717,  751 
vena  cava,  anterior,  755 
vertebral,    634,    707,     736, 

745 
vesical,  670 
vesico-prostatic,  670 
Arthrodia,  210 
Arthrology,  207 

comparative,  244 
Articular  cartilages,  208 
Articulations,    207.     See   also 

Joints. 
Arvtenoid  cartilages  of  larynx, 

517,  538,  546,  550 
Atlantal  bursa,  213 


Atlanto-occipital     membrane, 
dorsal,  215 
ventral,  215 
Atrio-ventricular  bundle,  628 
orifice,  left,  625,  626 
right,  621,  623 
Atrium  of  heart,  left,  625 
right,  620 

openings  in,  620 
ventriculi,  453,  458 
Auditive  tube,  878,  898 
Auditory  ossicles,  877 

tube,  osseous,  63 
Auricle,  620,  870 
Auricular  cartilage,  871 
plexus,  anterior,  803 
Axis  of  lens,  869 
of  orbit,  74 
of  pelvis.  111 
optic,  external,  863 


Bands,  longitudinal,  of  caecum, 
424 
of  great  colon,  428 
of  small  colon,  429 
moderator,  of  right  ventri- 
cle, 625 
recto-coccygeus,  431 
Bars  of  hoof,  887 
Basal  border  of  hoof,  888 
Basilar  plexus,  689 

tubercles  of  occipital  bone, 
51 
Basis  pedunculi,  780 
Bicipital  groove  of  humerus,  89 
Bicuspid  valve,  626 
Bifurcation  of  trachea,  525 
Bile  duct,  463,  468,  487,  490, 
501 
common,  476 
Bladder,   415,   554,   561,   566, 
569,  570 
fixation  of,  561 
lateral  ligament  of,  414 
middle  ligament  of,  414 
structure  of,  562 
Blind  sacs  of  rumen,  454 
Blood-vascular    system,    614, 

617,  705 
Blood-vessels,  614 
Body,  ciliary,  865 

geniculate,  medial,  781,  835, 

847 
mammillary,  769,  782,  847 
pineal,  781,  835 
pituitary,  769,  780,  782,  835, 

847 
restiform,  773 
vitreous,  869,  897 
Bone   or   bones,    acetabulum, 
109,  152,  181,  202 
acromion,  146,  197 
arteries,  22 
atlas,  35,  162,  184 
auditory,  877 
axis,  36,  163,  184 
basihyoid,  72 
breast-,  28 

carpal,  29,  93,  98,  148,  160, 
179,  200 
accessory,  94 
first,  95 


Bone,  carpal,  fourth,  96 

intermediate,  94 

radial,  94 

second,  95 

third,  96 

ulnar,  94 
carpus,  29 
cartilage,  23 

chemical  composition,  24 
chevron,  188 
clavicle,  29,  197 
collar-,  29 

compact  substance,  21 
condyle,  of  mandible,  71 
coracoid,  29 

cranial,  28,  49,  131,  166,  188 
descriptive  terms,  25 
development  and  growth,  23 
digital,  29,  30,  31,  161 
digits,  29,  30,  31,  149,  180, 

201 
diploe,  21 
endosteum,  22 
endoturbinates,  56 
epihyoids,  73 
ethmoid,  54,  134,  157,  170, 

191 
ethmo-turbinates,  55 
facial,  28,  63,  170,  191 
femur,    31,    112,    152,    160 

182,  203 
fibula,31, 117, 154, 160, 183, 

204 
fibular  tarsal,  120,  155 
flat,  20 
frontal,   59,   135,   157,   168, 

189 
gelatinous  marrow,  22 
hip,  31 
hock,  118 
humerus,  29,  88,  146,  176, 

198 
hyoid.  72,  140,  173,  195 
ilium,  31,  105,151,  160,180, 

200 
incus,  877 
innominate,    30,    105,    160, 

180 
interparietal,  56,   134,   167, 

189 
irregular,  20 
ischium,  31,  107,  151,  160, 

181,  202 
keratohyoid,  72 
knee,  29 
knee-cap,  31 
lacrimal,  68,  139,  159,  172, 

194 
lenticulare,  877 
long,  20 

lymph-vessels,  22 
malar,  68,  139,  194,  159,  172 
malleus,  877 
mandible,  70,  139,  159,  172, 

194 
marrow,  21,  22 

spaces,  21 
maxilla,  63,   137,   158,  170, 
191 

inferior,  70 
maxillo-turbinal,  69 
medullary  arteries,  22 

cavity,  20,  21 
membrane,  23 


910 

INDEX 

Bone,  mesosternum,  28 

Bone,  ribs,  floating,  27 

Bone,  vertebrae,  joints  of,  244 

metacarpal,  29,  30,  98, 

149, 

head,  27 

hgaments  of,  211,  244 

180,  200 

intercostal  spaces,  27 

lumbar,  25,  39,  128,  156, 

large,  98,  160 

lateral  surface,  27 

164,  187 

small,  99,  160 

medial  surface,  27 

mammillary  processes,  26 

third,  98 

neck,  27 

movable,  25 

metasternum,  28 

posterior  borders,  27 

notches,  26 

metatarsal,    31,    123, 

161, 

shaft,  27 

ossification  of,  26 

184,  205 

sternal,  27,  45 

sacral,  25,  41,  156 

fom-th,  124 

extremity,  27 

spinous  process,  26 

large,  123,  155 

tubercle,  27 

thoracic,  25.  37-39,   127, 

lateral,  124 

vertebral  extremity,  27 

156,  163,  186 

medial,  124 

sacrum,  41,   129,   156,   164, 

transverse  processes,  26 

second,  124 

187 

true,  25 

small,  124,  155 

scapula,    29,    86,    145,    176, 

ventral  spine,  26 

third,  123 

160,  197 

vessels,  21,  22 

nasal,  67,  139,  171,  194 

sesamoid,  30,  104,  125,  151, 

vomer,    70,    139,    159,    172, 

naso-turbinal,  69 

156,  160,  180,  201,  203, 

194 

navicular,  105 

204 

yellow  marrow,  22 

nerves,  21,  22 

distal,  30 

zygomatic,  68 

number,  20 

proximal,  30 

Brachial  plexus,  814,  840,  846, 

occipital,  49,  131,  157, 

166, 

short,  20 

853 

188 

shoulder-blade,  29 

Brachycephalic  skull,  195 

condyle,  50,  78,  79 
development,  52 

sinuses,  21 

Brain,  768,  834,  843,  847 

sphenoid,  52,  132,  157,  170, 

blood-vessels  of,  792 

of  arm,  29 

190 

Bronchi,   525,   534,   540,   546, 

of  cranium,  131 

spongy  substance,  21 

550 

of  forearm,  29,  63,  137 

158 

stapes,  877,  878 

interlobular,  534 

of  leg,  31 

sternum,  28,  48,   131,   157, 

structure  of,  534 

of  manus,  29 

166,  188 

Bronchial  branches  of  lungs, 

of  pelvic  limb,  30,  105, 

151, 

structure,  21 

534 

160,  180,  202 

stylohyoids,  73 

Bronchioles,  lobular,  534 

of  skull,  28,  49,  73,  173, 

188, 

tarsal,31,  118,  155,  161,183, 

respiratory,  534 

195 

205 

Buds,  taste,  895 

of  thoracic  limb,  29,  86, 

145, 

central,  121,  155 

Bulb  of  hair,  886 

160,  176,  197 

fibular,  120,  155 

of  urethra,   581,    585,   593, 

of  thorax,  28,  49 

first,  122,  155 

595 

ossa  cordis,  705 

fourth,  123,  155 

olfactory,  769,  771,  787,  838, 

palatine,  66,  138,  159, 

171, 

second,  122,  155 

844,  850 

193 

third,  122,  155 

Bulbar  conjunctiva,  859 

parietal,  57,  134,  157, 

167, 

tibial,  120,  155 

Bulbus  aorta?,  629 

189 

temporal,  60,  137,  158,  169, 

glandis  of  penis,  594 

patella,  31,   118,   155, 

161, 

189 

vestibuli,  603 

183,  204 

condyle  of,  60 

Bulla,  lacrimal,  139 

pelvis,  110 

thigh,  31 

ossea,  63 

periosteal  arteries,  22 

thorax,  49,  131,  166,  188 

Bundle,  atrio-ventricular,  628 

periosteum,  21 

thyrohyoids,  72 

Bursa,  atlantal,  213 

phalanges,  30,  100,  125, 

149, 

tibia,  31,  114,  153,  160,  182, 

bicipital,  302 

150,  156,  160,  180, 

184, 

203 

intertuberal,  of  biceps  bra- 

200 

condyles  of,  116 

chii,  302 

first,  100 

tibial  tarsal,  120,  155 

navicular,    of    deep    digital 

second,  30,  102 

tissue,  21 

flexor,  316 

third,  30,  102 

turbinate,  68,  139,  159,  172, 

of  biceps  femoris,  323 

physical  properties,  24 

545 

.    of  common  digital  extensor, 

pneumatic,  21 

dorsal,  194 

307 

premaxilla,    65,    138, 

159, 

ventral,  194 

of  gastrocnemius,  338 

170,  193 

ulna,  29,  92,  148,  177,  199 

of  lateral   digital  extensor, 

prenasal,  172 

veias  of,  22 

309 

presternum,  28 

vertebra?,  25,  33,  125,  156, 

of  obturator  internus,  329 

pterygoid,  67,  139,  159, 

171, 

161,  184 

of  rectus  femoris,  329 

193 

accessory  processes,  26 

of  semimembranosus  muscle, 

pubic,  31,  109,  151,  160, 

181, 

anticlinal,  44 

325 

202 

arch,  26 

of    semitendmosus    muscle, 

radius,  29,  90,  147,  160, 

177, 

articular  processes,  26 

323 

198 

body,  26 

of  tibialis  anterior,  337 

red  marrow,  22 

cervical,  25,  34,  156,  161, 

of    triceps    brachii    muscle, 

ribs,  27,  45,  130,  156, 

165, 

184                  ' 

303 

188 

coccygeal,  25,  43, 129, 156, 

ovarica,  599 

angle,  27 

164,  187 

ovarii,  612 

anterior  borders,  27 

diaphragmatic,  44 

podotrochlearis,  316 

asternal,  27,  45 

false,  25 

subcutaneous,  254,  884,  887 

costal  groove,  27 

fixed,  25 

of  superficial  digital  flexor, 

development,  27 

foramen,  26 

339 

extremities,  27 

hsemal  arch  of,  26 

subfascial,  254 

INDEX 


911 


Bursa,  supraspinous,  213 
synovial,  253 

of   infraspinatus   muscle, 

299 
of  superficial  digital  flexor, 

339 
of  teres  minor  muscle,  299 
trochanteric,  322 


C^CAL  impression  of  liver,  435 
Ca;co-colic  fold,  424,  428 

orifice,  424 
Caecum,  422,  465,  475,  487,  502 
Calcarine  fissure,  850 
Caliber  of  great  colon,  427 
Callosal  sulcus,  786 
Calloso-marginal  fissure,  785, 

837,  844,  850 
Calyces  ma j ores,  565 

minores,  565 
Canal,  alar,  54,  75,  78 

alimentary,  385 

carotid,  190 

carpal,  306 

central,  of  spinal  cord,  766 

cervical,  607 

condyloid,  131 

dental,  superior,  65 

facial,  62 

femoral,  326 

infraorbital,  65 

inguinal,  292 

lacrimal,  82 
osseous,  68 

mandibular,  71 

of  Gartner,  607 

of  tarsus,  123 

palatine,  64 

parieto-temporal,  63 

petro-basilar,  190 

pterygoid,  54,  67 

sacral,  43 

semicircular,  osseous,  881 

semilunar,  of  third  phalanx, 
103 

spiral,  of  cochlea,  882 

subsphenoidal,  54 

supraorbital,  137 

temporal,  63,  81 

vertebral,  44 

vidian,  54 
Canine  teeth,  394,  398,  448, 
479,  493 
deciduous,  403 
Canthi  of  eye,  857 
Capillaries,  614 
Capsula  adiposa,  557 
Capsule,  external,  792 

fibrous,   of  adrenal  bodies, 
563 
of  kidney,  558 
of  liver,  438 

internal,  781,  792 

of  kidney,  559 

of  lens,  870 

of  lymph  nodule,  616 

of  prostate,  579 

of  spleen,  441 
Cardia  of  rumen,  458 

of  stomach,  472,  498 
Cardiac    impression    of    lung, 

531 


Cardiac  lobe  of  lung,  540,  547, 
548,  551,  553 

notch  of  lung,  533 

opening  of  stomach,  416 

plexus,  831 

sphincter,  417 
Cariniform  cartilage,  48 
Carnassial  teeth,  494 
Carotid  canal,  190 

foramen,  190 

notch,  54 

plexus,  804 
external,  830 
internal,  830 
Carpal  articular  surface,  92 

canal,  306 

sheath  of  deep  digital  flexor, 
315 
of  superficial  digital  flexor, 
313 
Carpo-metacarpal  sac,  222 
Cartilage,  alar,  509,  537,  538 

annular,  of  ear,  871 

articular,  208 

arytenoid,    of   larynx,    517, 
538,  546,  550 

auricular,  871 

bones,  23 

cariniform,  48 

conchal,  871 

costal,  27,  47 

cricoid,  515,  550 
of  larynx,  538,  546 

cuneiform,  of  larynx,  550 

epiglottic,  516 

epiphyseal,  24 

interarytenoid,     of    larynx, 
546,  550 

marginal,  209 

of  larynx,  515 

of  septum  nasi,  510 

of  third  phalanx,  104 

parietal,     of    nasal    cavity, 
510,  537 

scutiform,  871 

thyroid,  515,  538,  546,  550 

xiphoid,  28,  49 
Caruncle,  lacrimal,  858 
Caruncula    sublingualis,    390, 

405 
Cauda  equina,  764 
Caudal   part   of   sympathetic 

system,  832,  856 
Caudate  lobe  of  liver,  434,  468, 
488,  503 

nucleus,  792 

process  of  liver,  434 
Cavernous  plexus,  830,  834 

sinuses,  688 
Cavity,  abdominal,  410,  452 

articular,  209 

costal,  of  sternum,  48 

cranial,   81,   142,   159,   175, 
197 

glenoid,  60,  73,  78,  87 

nasal,  82,  143,  159,  175,  197, 
508,  537,  545,  548 

of  larynx,  521 

of  mouth,  385,  444 

of  rumen,  456 

of  tunica  vaginalis,  576 

of  uterus,  601 

omental,  442 

pelvic,  152,  412,  453 


Cavity,  peritoneal,  411 

pleural,  526 

pulp,  of  teeth,  395 

thoracic,  525,  540 

tympanic,  875 
Cavum  tympani,  898 
Cecum,  422,  465,  475,  487,  502 
Cell,  nerve-,  760 

ethmoid,  55 

gustatory,  896 

olfactory,  895 
Cement  of  teeth,  395 
Center,     tendinous,     of     dia- 
phragm, 287 
Central  canal  of  spinal  cord, 

766 
Cephalic  part  of  sympathetic 

system,  829 
Cerebellar  peduncles,  777 
anterior,  776 
middle,  776 

tract,  direct,  777 
Cerebello-olivary      fasciculus, 

774 
Cerebellospinal  fasciculus,  775, 
777 
descending,  777 
Cerebellum,  771,  776,  835,  843, 

847 
Cerebral  arachnoidea,  762 

dura  mater,  761 

hemispheres,  771,  783,  836, 
843,  849 

peduncles,  769,  780,  835,  843 

pia  mater,  763 
Cerebrospinal   fasciculus,   776 
Cerebrum,  843 
Cervical  canal,  607 

enlargement,  764 

ganglion,  anterior,  830,  842, 
846,  856 
middle,  847 
posterior,  830,  842 

part  of  sympathetic  system, 
830,  842,  847,  858 

plexus,  dorsal,  812 

ventral,  812 
Cervix  uteri,  601,  606 
Chambers  of  eye,  869 
Cheek   teeth,    394,   399,    400, 

401,  448,  471,  480,  494 
Cheeks,  444,  471,  477,  492 
Chemical  composition  of  bone, 

24 
Chestnut,  895 
Chiasm,  optic,  769,  783 
Choans,  78,  512 

posterior,  406 
Chordae  tendineae,  624 
Chorioid,  865 

plexuses,  763,  780,  783,  787, 
792 
of  fourth  ventricle,  773 
Chyle,  615 

vessels,  615 
Cilia,  858,  886 
Ciliary  body,  865 

border  of  iris,  866 

ganglia,  829 

ganglion,  796,  838 

processes,  866 

ring,  866 
Circle,  coronary,  660 
Circulation,  foetal,  704 


912 


INDEX 


Circulation,  pulmonary,  704 
Circulatory  system,  734,  742 
Circulus  arteriosus,  641 
Cistema  chyli,  697,  722,  756 
Cisterns,  subarachnoid,  762 
Claustrum,  792 
Claws,  902,  904 
Cleft,  \'ulvar,  603 
Clinoid     processes,     anterior, 
190 
posterior,  170,  190 
Clitoris,  604,  608,  610,  611,  613 

prepuce  of,  604 
Coccygeal  ganglia,  832 

ganglion,  832 
Cochlea,  881,  882 
Cochlear    duct,  883 
Cceliac  ganglia,  856 

ganglion,  842 

plexus,  832,  843,  856 
CcEhaco-mesenteric      ganglia, 

833 
Colic  impression  of  liver,  435 

mesentery,  412,  429 

plexus,  856 
Collateral  fissure,  849 

sulci  of  hoof,  891 

vessel,  614 
CoUiculus  facialis,  779 

seminalis,  585,  590 
Collum  glandis  of  penis,  581 
Colon,  465.  475,  488,  502 

great,  425 

small,  429 
Color  of  skin,  884 
Columns,  gray,  of  spinal  cord, 
767 

of  fornix,  790 

renal,  558 

white,  of  spinal  cord,  767, 
768 
Commissure,  anterior,  of  cere- 
brum, 783 

gray,  of  spinal  cord,  766 

hippocampal,  787 

of  nostrils,  508 

of  vulva,  603 

optic,  769 

posterior,  of  cerebrum,  782, 
783 

white,  of  spinal  cord,  766 
Compact  substance  of  bone, 

21 
Comparative  anatomy,  17 
Concave  border  of  hoof,  890 
Conchal  cartilage,  871 
Condyloid  canal,  131 

crest,  90 

fossa,  50,  78 
Conical  papillae  of  mouth,  444 

of  tongue,  447 
Conjugate  diameter  of  pelvis, 

110,  112,  152 
Conjunctiva,  859,  896 

bulbar,  859 

palpebral,  859 
Conjunctival  sac,  859 
Conus  arteriosus,  623 

medullaris,  764,  765 
Convex  border  of  hoof,  890 
Coracoid  process,  88 
Core,  horn,  136 
Corium,  884,  885 

coronary,  892 


Corium,  laminar,  892 

of  hoof,  892 

of  sole,  892 

perioplic,  892 
Cornea,  864,  897 
Comu,    anterior,    of    thyroid 
cartilage,  515 

of  nostrils,  509 

posterior,   of  thyroid   carti- 
lage, 516 
Comua,  great,  of  horse,  73 

middle,  73 

of  uterus,  600,  606 

small,  72 

thyroid,  72 
Corona  glandis  of  penis,  580 

radiata,  792 
Coronal  fissure,  837,  844,  849 
Coronary  border  of  hoof,  888 

circle,  660 

corium,  892 

groove  of  heart,  619 
of  hoof,  888 

pillars  of  rumen,  457 

plexus,  692,  831 

sinus,  681,  754 
opening  of,  621 
Coronoid  fossa  of  humerus,  90 

process  of  mandible,  71 
Corpora    quadrigemina,    780, 

847 
Corpus  albicans  s.   fibrosum, 
598 

callosum,  784,  785,  789,  836 

cavemosum,  615 
of  penis,  581 
urethrse,  581 

clitoridis,  604 

luteum,  598 

papillare,  885 

rubrum,  598 

striatum,  792 

trapezoideum,  773,  847 
Corpuscle,  renal,  558,  559 
Cortex  of  thymus  gland,  536 
Cortical  substance,  777 

of  lymph  nodule,  616 
Corticopontile  fibers,  776 
Costal  arch,  28 

cartilages,  27,  47 

cavities  of  sternum,  48 

facets  of  thoracic  vertebrae, 
37,  38 

groove,  27 

pleura,  526 
Cotyledons,  uterine,  607 
Cranial  cavity,  81,   142,   159, 
175,  197 

region,  73,  78 

sutures,  217 
Crest,  condyloid,  90 

facial,  64,  68,  77 

frontal,  73 
external,  59 

intervenous,  622 

nasal,  65,  66,  82 

nuchal,  51,  79 

occipital,  51 

parietal,  135 

external,  51,  57,  73 
internal,  58,  81 

petrosal,  62,  81 

pterygoid,  54 

renal,  558,  559 


Crest,  sacral,  lateral,  129 
median,  129 
semilunar,  of  third  phalanx, 

103 
spheno-occipital,  53 
supracondj'loid,    lateral,    of 
femur,  112 
medial,  of  femur,  112 
temporal,  137 
tibial,  116 
turbinate,  dorsal,  67 

ventral,  64 
urethral,  585 
Cribriform  plate  of  ethmoid, 

54 
Cricoid  cartilage,  515,  550 

of  larynx,  538,  546 
Crico-thyroid  membrane,  518 
Crico-tracheal  membrane,  518 
Crista  acustica,  884 
gaUi,  55,  56,  82 
terminahs,  622 
vestibuh,  881 
Crown  of  tooth,  395 
Cruciate  fissure,  837,  844,  850 
Crura  fomicis,  790 

of  chtoris,  604 
Crus  laterale  dextrum,  287 
sinistrum,  287 
mediale  dextrum,  287 

sinistrum,  287 
of  fornix,  792 
penis,  581 
Cryptorchism,  577 
Crystalline  lens,  869 
Cuneiform  cartilages  of  larynx, 
550 
processes,  517 
Cupola,  882 
Cushion,  digital,  894 
Cuticle,  887 
Cystic  duct,  468 


Dartos  of  scrotum,  574 
Deciduous  teeth,  394,  403 
Decussation    of    anterior    pe- 
duncles, 778 

of  fillet,  774 

pyramidal,  773,  774 
Deferential   fold   of   testicles, 

577 
Deltoid  tuberosity,  88 
Dental  alveoli,  64 

canal,  superior,  65 

plexus,  maxillary,  798 
Dentine,  395 
Descent  of  testicles,  577 
Descriptive  terms,  18 
Diagonal  fissure,  837,  844 
Diameter,    conjugate,   of  pel- 
vis, 110,  112,  152 

transverse,    of   pelvis,    110, 
112,  152 
Diaphragma  sellae,  762 
Diaphragmatic  flexure,  425 

line  of  pleural  reflection,  530 

lobe  of  lung,  540,  547,  551, 
553 

pleura,  526 
Diarthroses,  208 
Diencephalon,  781 
Digestive    system     385,    444, 

470,  477,  491 


INDEX 


913 


Digital  cushion,  894 

synovial     sheath    of    deep 
digital  flexor,  316 
of     superficial     digital 
flexor,  314 
Dilatator  pupillse,  867 
Diploe,  21 

Diverticulum,  cutaneous,  884 
duodeni,  421 
nasi,  508 
pharyngeum,  482 
preputial,  593 
suburethral,  607 
ventriculi  of  stomach,  483 
Dolichocephalic  skull,  195 
Dorsum  linguae,  390 
Duct    or    ducts,    alveolar,    of 
lungs,  534 
bile,  463,  468,  487,  490,  501 

common,  476 
cochlear,  883 
cystic,  468 
excretory,  383,  578 

of  bulijo-urethral  glands, 
580 
hepatic,  438 
lacrimal,  860 
lactiferous,  605,  609 
lymphatic,  725 
right,  615,  698 
tracheal,  725,  756 
mandibular,  405,  496 
naso-lacrimal,  509,  860,  896 
of     bulbo-urethral     glands, 

585  _ 
of  epididymis,  573 
of  mammary  glands,  605 
of  testicles,  573 
pancreatic,    434,    463,    487, 
491,  501,  506 
accessory,  434 
parotid,  404,  477,  482,  492, 

495 
prostatic,  579,  585,  589 
semicircular,    membranous, 

883 
sublingual,  405,  496 
submaxillary,  405 
thoracic,  615,  697,  722,  740, 

756 
tracheal,  700 
Ductuli  aberrantes,  573 
Ductus  arteriosus,  629,  704 
deferens,  575,  587 
deferentes,  571 
endolymphaticus,  883 
incisivus,  387,  445,  514 
reuniens,  883 
sublinguales  minores,  482 
sublingualis  major,  482 
utriculo-saccularis,  882 
venosus,  468,  704 
Duodenal  angle,  433 

impression  of  liver,  435 
Duodeno-colic  fold,  429 
Duodenum,  4^9,  463,  486,  500 
Dura  mater,  761 
cerebral,  761 
sinuses  of,  687 
spinal,  762 


Ear,  870,  901,  902 
external,  870,  897 

58 


Ear,  internal,  881,  898 

middle,  875 
Ectolateral  fissure,  849 
Ectomarginal  fissure,  785,  837, 

844,  849 
Ectosylvian  fissure,  849 
Ejaculatory  orifice,  575 
Elastic  membrane  of  trachea, 

525 
Embryology,  17 
Eminence,  frontal,  136 

ilio-pectineal,  109 

intercondyloid,  of  tibia,  116 
Eminentia  conchae,  871 

medialis,  779 
Enamel  of  teeth,  395 
Enarthrosis,  210 
Encephalon,  768 
End-brain,  783 
Endocardium,  621,  628 
Endolymph,  881 
Endoskeleton,  20 
Endosteum,  22 
Endothelium  of  eye,  865 
Entomarginal  fissure,  785,  837, 

844,  849 
Epicardium,  617,  627 
Epicondvle,  lateral,  of  femur, 
114 
of  humerus,  90 

medial,  of  femur,  114 
of  humerus,  90 
Epidermis,  884 
Epididymis,  571,  573,  586 

structure  of,  572 
Epidural  space,  762 
Epigastric  zone,  411 
Epiglottic  cartilage,  516 
Epiglottis,  538,  546,  550 
Epiphyseal  cartilage,  24 
Epiphysis  cerebri,  781 
Epiploic  foramen,  442,  461 
Epithelium,  383 

corneae,  864 

of  lens,  870 
Equator  of  eye,  863 

of  lens,  869 
Erectile     tissue    of     urethra, 

585 
Ergot,  895 

tendon  of,  306 
Eruption  of   teeth,   403,   450, 

471,  481,  495 
Esophagus,  409,  451,  472,  483, 

497 
Ethmoid  cell,  55 
Ethmoidal  foramen,  53,  55,  75, 
82 

fossa,  55,  82 

meatuses,  55,  512 

sinus,  86 
Eustachian  tube,  878,  898 
osseous,  63 

pharyngeal      orifices     of, 
406 
Excretory  duct,  383,  578 

of  bulbo-urethral  glands, 
580 
Extensor  fossa  of  femur,  114 
Eve,  857,  896.  900,  902 
Eyeball,  862,  897 
Eyelashes.  886 
Eyelids,  857,  896 

'third,  859,  896 


Facet,  anterior,  of  larynx,  515 
costal,  of  thoracic  vertebrae, 

37,  38 
of  tibia,  116 
posterior,  of  larynx,  515 
Facial  canal.  62 
crest,  64,  68,  77 
nucleus,  801 
tuberosity,  137 
Fallopian  tubes,  596,  599,  606, 

609,  610,  612 
False  nostril,  260,  508 

vocal  cords,  522,  550 
Falx  cerebri,  761 
Fascia,  254 

abdominal,  287 
buccal,  255 
bulbi,  861 
carpal,  305 
coccygeal,  279 
common,  of  leg,  318 
cruris,  318 
deep,  254 

of  abdomen,  288 

of  forearm,  305 

of  head,  255 

of  neck,  266 

of  shoulder  and  arm,  298 

of  metacarpus  and  digit, 
306 

of  thigh,  317 
digital,  318 
endothoracic,  530 
femoral,  medial,  318 
gluteal,  317 
iliac,  317 
lata,  318 

lumbo-dorsal,  276 
metatarsal,  318 
of  back,  276 
of  forearm,  305 
of  head,  255 
of  loins,  276 

of  mammary  glands,  604 
of  manus,  305 
of  neck,  266 
of  pelvic  limb,  317 
of  tail,  279 
orbital,  861 
pectoral,  295 
pelvic,  317,  413 
perineal.  413 
pharJ^lgeal,  255 
propria  of  neck,  266 
scrotal,  574 
superficial,  254 

of  abdomen.  287 

of  forearm.  305 

of  gluteal  region,  317 

of  head,  255 

of  metacarpus  and  digit, 
306 

of  neck,  266 

of  shoulder  and  arm,  298 

of  thigh,  317 
tarsal,  318 
temporal,  255 
transversalis  of  transversus 

abdominis  muscle,  291 
Fasciculus,     cerebello-olivary, 

774 
cerebellospinal.  775,  777 

descending,  777 
cerebrospinal,  776 


914 


Fasciculus  cuneatus,  768 
dorsal  longitudinal,  776 
nucleo-cerebellar,    777 
pyramidal,  776 
Femoral  canal,  326 

lamina  of  external  oblique 

abdominal  muscle,  290 
Fenestra  cochleae,  876 

vestibuli,  876,  881 
Fibers,  corticopontile,  776 
of  heart,  628 
of  stomach,  417 
Fibro-cartilap;es,       interverte- 
bral, 211 
of  patella,  118 
Fibrous    capsule    of    adrenal 
bodies,  563 

of  kidney,  558 

of  liver,  438 
coat  of  kidney,  559 

of  ureters,  561 

of  viscera.  384 
layer  of  pericardium,  617 
membranes,  384 
rings  of  heart,  628 

of     intervertebral     fibro- 
cartilage,  211 
sheath  of  tendon,  254 
tunic  of  eye,  863 
Filiform  papilla  of  tongue,  391 
Fillet,  774 
lateral,  776 
medial,  776 
Filum  terminate,  764,  765 
Fimbria  of  brain,  787,  791,  792 
of  Fallopian  tubes,  599 
of  ovary,  599 
Fissure,  837 
ansate,  849 
calcarine,  850 
calloso-marginal,    785,    837, 

844,  850 
collateral,  849 
coronal,  837,  844,  849 
cruciate,  837,  844,  850 
diagonal,  837,  844 
ectolateral,  849 
ectomarginal,  785,  837,  844, 

849 
ectosylvian,  849 
entomarginal,  785,  837,  844, 

849 
genual,  837,  844,  850 
hippocampal,  850 
interlobar,  of  lung,  540 
lateral,  785,  837,  843,  849 

of  cerebrum,  478 
longitudinal,  of  brain,  769, 
771 

of  cerebrum,  784 
marginal,  785,  837,  844 
medilateral,  849 
naso-maxillary,  85 
occipito-tempora],  850 
palatine,  66,  78,  82 
palpebral,  857 
petrotympanic,  63 
portal^  434,  468 
presylvian,  785,  844,  849 
splenial,  844,  850 
sublimbic,  786 
suprasplenial,  850 
suprasylvian,  785,  837,  844, 

849 


Fissure,  transverse,  786.  837 

of  brain,  771 

of  cerebrum,  784 
umbilical,  435 
ventral  median,  765,  766 
Flexure,  diaphragmatic,  425 
sigmoid,  589 
sternal,  425 
Floccular  fossa,  190 
Floor  of  mouth,  390 
Fa'tal  circulation,  704 

lung.  531 
Fold,  alar,  509 

CcTco-colic,  424,  428 

deferential,  of  testicles,  577 

duodeno-colic,  429 

gastro-pancreatic,  417 

genital,  414 

glosso-epiglottic,  391 

ileo-csecal,  421 

of  mucous  membrane,  383 

of  skin,  884 

of  vena  cava,  526 

rumino-reticular,  457 

serous,  384 

spiral,  of  abomasum,  460 

sublingual,  390 

turbinate,  dorsal,  513 

ventral,  513 
umbilical,  lateral,  414 

median,  414 
valvular,  of  ca?cum,  424 
Foliate  papilla  of  tongue,  391 
Follicle,  hair-,  886 
lingual,  392 
lymph,  616 
of  thyroid  gland,  536 
Folliculi  oophori,  598 
Foramen  alare  parvum,  54,  75 
caecum,  847 
carotid,  190 
epiploic,  442,  461 
ethmoidal,  53,  55,  75,  82 
hypoglossal,  50,  78^,  82 
incisivum,  65,  73,  78 
infraorbital,  64,  77 
intervertebral,  26,  125,  128, 

703,  791 
lacerum,  51,  63,  78,  82 
lacrimal,  172 
magnum,  50,  78,  79 
mandibular,  71 
mastoid,  62 
maxillary,  65,  76 
mental,  70 
nutrient,  22 

of  femur,  112 

of  humerus,  88 

of  ilium,  106 

of  metacarpus,  99 

of  tibia,  116 
obturator,  109,  112,  152,  202 
optic,  53,  75,  82 
orbital,  53,  75 
orbito-rotundum,  134 
ovale,  134,  622,  704 
palatine,  76 

anterior,  66 

posterior,  65 
postglenoid,  60 
pterygoid,  54 
rotunclum,  53,  75 
sacral,  41 

ventral,  129 


Foramen,  sciatic,  greater,  231 
lesser,  231 

spheno-palatine,  65,  67,  76, 
82 

stylo-mast  oid,  62 

supraorbital,  59,  73 

supratrochlear,  198 

temporal,  54 

trochlear,  54,  75 

vense  cavae,  287 

vertebral,  26 

volar,  of  third  phalanx,  103 
Fore-fo9t,  29 
Formatio  reticularis,  767 
Fornix,  785,  790 

conjunctiva*,  859 

vaginae,  602 
Fossa,  acetabular,  109 

anterior,  of  skull,  82 

cUtoridis,  603 

condyloid,  .50,  78 

coronoid,  of  humerus,  90 

ethmoidal,  55,  82 

extensor,  of  femur,  114 

floccular,  190 

glandis  of  penis,  581 

hyaloidea,  869 

hypophyseal,  53 

infratemporal,  78 

intercondvloid,     of     femur,. 
114   ' 
of  tibia,  116 

interpeduncular,  769,  780 

lacrimal,  external,  159 

lateral,  769 

of  cerebrum,  784 

masseteric,  19.5 

middle,  of  skull,  82 

olecranon,  90 

ovalis,  622,  704 

ovulation,  597 

pituitarj^,  53 

posterior,  of  skull,  82 

pterygoid,  170 

pterygo-palatine,  67,  76 

rhomboidea,  778 

supracondyloid,    of    femur, 
112 

synovial,  208 

temporal,  73 

trochanteric,  of  femur,  113 
Fourth  ventricle,  778 
Fovea,  anterior,  of  fourth  ven- 
tricle, 779 

capitis  of  femur,  113 

dentis,  36 
Fraenula  labii,  387 
Frenum  hnguae,  390,  391 

preputial,  583 
Frog  of  hoof,  890,  892 
Frog-stay,  890 
Frontal  crest,  73 
external,  59 

eminence,  136 

process,  191 

region  of  skull,  73 

sinus,  59,  85,  143,  175,  197 

suture,  60 
Fronto-lacrimal  sutures,  60 
Fronto-maxillary  opening,  85 

suture,  60 
Fronto-palatine  suture,  60 
Front o-turbinate  sinus,  85 
Fundus  reticuh,  456 


INDEX 


915 


Fundus  uteri,  601 
Fungiform  papilla  of  tongue, 
391 


Gall-bladder,  468,  490,  505 
Ganglia,  760,  829 

ciliary,  829 

coccygeal,  832 

coeliac,  856 

coeliaco-mesenteric,  833 

lumbar,  832 

mesenteric,  anterior,  856 

of  sympathetic  trunk,  829 

otic,  829 

peripheral,  829 

sacral,  832 

sphenopalatine,  797,  829 

thoracic,  831,  842 
Ganglion,    cervical,    anterior, 
830,  842,  846,  856 
middle,  847 
posterior,  830,  842,  856 

ciUary,  796,  838 

coccygeal,  832 

coeliac,  842 

geniculate,  801 

intercaroticum,  804 

jugular,  805,  839,  845,  851 

mesenteric,  anterior,  842 
posterior,  833 

nodosum,  805,  839,  845,  851 

otic,  799,  838 

petrous,  804 

semilunar,  795 

spinal,  811 

spirale,  884 

splanchnic,  832 

stellatum,  830 

vestibular,  803 
Gartner,  canals. of,  607 
Gastric  impression  of  hver,  434 

plexus,  833 
anterior,  852 
posterior,  852 
Gastro-pancreatic  fold,  417 
Gastro-splenic  omentum,  412, 

417,  441 
Gelatinous  marrow  of  bone,  22 
Geniculate  body,  medial,  781, 
835,  847 

ganglion,  801 
Genital  fold,  414 

organs,  554 

female,  596,  605,  609,  610, 

612 
male,  571,  586,  591,  593 
Genu  of  corpus  callosum,  789 
Genual  fissm-e,  837,  844,  850 
Ginglymus,  210 
Girdle,  pelvic,  30,  105 

shoulder,  29 
Glands  or  gland,  382 

adrenal,  563,  566,  567,  569, 
570 

alveolar,  383 

alveolo-tubular,  383 

anal,  502 

buccal,  387,  445,  477 

bulbo-urethral,     571,     579, 
589,  592,  594 
ducts  of,  585 

cardiac,  of  stomach,  419 

ceruminous,  872 


Glands,  circumanal,  502 
coil,  of  digital  cushion,  894 
compound,  383 
cutaneous,  898 
duct  of,  383 
ductless,  439 
duodenal,  501 
fundus,  383 

of  stomach,  419 
gastric,  418 
haemolymph,  616 
labial,  387,  444 
lacrimal,  860,  896 
laryngeal,  523 
lingual,  392 
liver,  434,  465,  475,  488,  503 

structure  of,  438 
lobules  of,  385 
lymph,  616,  722,  733 
abomasal,  731 
anal,  703,  742 
atlantal,  724,  733 
atrial,  730 

axillarv,  703,  728, 741, 757 
broncliial,  700,  727,  741, 

757 
CcTcal,  702,  731,  742 
cervical,     anterior,     699, 
724,  756 
middle,   699,   724,   741, 

756 
posterior,  699,  724,  725, 

741,  756 
superficial,  699,  756 
coeliac,  728 

coHc,  702,  731,  742,  759 
costo-cervical,  725 
coxal,  733 
cubital,  703,  757 
duodenal,  731 
epigastric,  729 
gastric,  702,  730,  742 
hepatic,  702,  732,  742 
hyoid,  724 
iliac,   external,   701,   729, 

742,  758 
infraspinatus,  728 
inguinal  deep,  703 
iliac,   internal,   701,    728, 

742,  758 
inguinal,  superficial,  701, 

729,  734,  742,  759 
intercostal,  700,  725,  757 
ischiatic,  701,  730,  742 
jejuno-ileal,  731 
lumbar,  701,  728,  742,  758 
mammarv,  701,  734 
mandibular,  698,  722,733, 

740,  756 
mediastinal,  741,  757 
anterior,  700,  726 
diaphragmatic,  726 
dorsal,  726 
posterior,  700,  726 
ventral,  726 
mesenteric,  702,  731,  733, 

742,  759 
of  abdomen,  701 
of  head,  698 
of  pelvic  limb,  703 
of  pelvis,  701 
of  thoracic  limb,  703 
of  thorax,  700 
of  neck,  698 


Glands,  Ijonph,  omasal,  731 

pancreatic,  702 

pancreatico-intestinal,  732 

paralumbar,  729 

parapharyngeal,  699,  724 

parietal,  701 

parotid,  723,  733,  740,  756 

pericardiac,  727 

pharyngeal,  699 

popliteal,   703,   733,  742, 
759 

portal,  758 

prefemoral,  703,  732,  733, 
742 

prepectoral,  699,  741 

prescapular,  699,  725,  741, 
756 

pterygoid,  724 

pulmonary,  727,  757 

rectal,  702,  732 

renal,  701,  728,  759 

reticular,  731 

rhomboid,  728 

ruminal,  730,  731 

sacral,  701,  730,  758 
external,  730 
internal,  730 

splenic,  702,  742 

sternal,  727,  733,  741,  757 
anterior,  727 

subiliac,  703,  732 

submaxillary,  698 

supramammary,  729,  759 

supraphar\Tigeal,699, 722, 
733,  740,  756 

tarsal,  742 

thoracic,  741 

visceral,  701,  702 
mammary,    596,    604,    609, 

610,  611,  613 
mandibular,  404,  451,  482, 

496 
mucous,  of  pharynx,  408 
nasal,  514 
naso-labial,  444,  898 

of  duodenum,  421 
of  kidneys,  559 
of  large  intestine,  431 
of  skin,  885,  887 
of  small  intestine,  421 
of  third  eyelid,  896 
olfactory,  514,  895 
palatine,  389 
pancreas,  432,  468,  470,  476, 

491,  505 
parathyroids,  536,  544,  553 
parotid,  404,  451,  482,  495 

accessory,  482 
preputial,  583 
prostate,  571,  578,  589,  592, 

593 
pyloric,  of  stomach,  419 
renal,  742 

salivary,  404,  451,  471,  495 
sebaceous,  885,  898 
simple,  383 

spleen,  439,  476,  491,  506 
sublingual.  405, 451, 482, 496 
submaxillary,  404,  482 
sudoriferous,  885 
sweat,  885,  898 
tarsal.  859 
thvroid,  535,  536,  544,  548, 

553 


916 


INDEX 


Glands,     th>Toid,     accessory, 
536,  544,  553 
tracheal,  525 
tubular,  383 

tubulo-alveolar,  383 

urethral,  585 
lateral,  585 

uterine,  607 

zygomatic,  496 
Gland  ulaj     vestibulares     ma- 
jores,  603,  608 
minores,  603,  608 
Glans  clitoridis,  603,  604 

penis,  580,  589,  594 
Glenoid  cavity,  60,  73,  78,  87 

notch,  87 
Glomerulus  of  kidney,  559 
Glosso-epiglottic  fold,  391 
Glottis,  522 
Gluteal  Ime,  105 
Gomphosis.  208 
Granula  iridis,  867 
Granulations,  arachnoid,  763 
Gray  columns  of  spinal  cord, 
'767 

commissure  of  spinal  cord, 
766 

matter  of  nervous  system, 
760 
of  spinal  cord,  766 

rami,  829 
Great  colon,  425 
Greater   omentum,    442,   461, 

499 
Groove,  bicipital,  of  humerus, 
89 

coronary,  of  heart,  619 
of  hoof,  888 

dorsal  intermediate,  766 
median,  765 

dorso-lateral,  765 

intertuberal,  of  humerus,  89 

lacrimal,  64 

longitudinal,  of  heart,  619 

musculo-spiral,  88 

oesophageal,  458,  473 

of  rumen,  454,  455 

of  tibia,  116 

optic,  53 

rumino-reticular,  454 

supraorbital,  137 

palatine,  65,  78 

pubic,  109 
Gross  anatomy,  17 
Ground  border  of  hoof,  888 
Gubernaculum  testis,  577 
Gums,  387 
Gustatory  cells,  896 

organs,  905 
Guttural  pouches,  879 

region,  78 
Gyri,  837 

cerebellar,  777 

cerebri,  771,  785 
Gyrus  dentatus,  786 

subcallosal,  788 


HEMORRHOIDAL  plexus,  834 

anterior,  856 
Hair-follicle,  886 
Hairs,  886,  887,  898 

tactile,  886 
Hair-streams,  886 


Hamulus  pterygoideus,  67 
Hard  palate,  78,  387,  445,  470, 

477,  492 
Head,  lymph  vessels  of,  698 
Heart,  614,  617,  705,  734,  735, 
742,  743 

structure  of,  627 
Hemal  arches,  188 
Hemispheres,     cerebral,     771, 
783,  836,  843,^849 

of  cerebellum,  771,  776 

of  lu-ethra,  595 
Hepatic  duct,  438 

plexus,  439,  833 
Hiatus  aorticus,  287 

ocsophageus.  287 
Hilus  of  lung,  531 

of  ovary,  597 

of  spleen,  440,  470,  477 

renal,  555 
Hippocampal  commissure,  787 

fissure,  850 
Hippocampus,  786,  792 
Histology,  17 
Hock,  31 
Hoof,  887 
Horns,  899 

core,  136 

of  female  uterus,  610 

of  lateral  ventricle,  791 

of  spinal  cord,  767 

of  uterus,  600 
Horny  lamina  of  hoof,  892 
Humeral  articular  surface,  92 
Humor,  aqueous,  869 

vitreous,  869 
Hyaloid  membrane,  869 
Hydatides  terminales,  599 
Hymen,  602 
Hyoid  process,  62 
Hypogastric  zone,  411 
Hypoglossal  foramen,   50,   78, 

82 
Hypophyseal  fossa,  53 
Hypophysis,    769,    780,    782, 

835,  847 
Hypothalamic  nucleus,  781 

tegmental  region,  781 


Ileo-cecal  fold,  421 

orifice,  424 

valve,  421 
Ileo-colic  orifice,  501 

valve,  501 
Ileum,  420 

Iliac   lamina   of   external   ob- 
lique abdominal  muscle,  290 
Ilio-pectineal  eminence,  109 

line,  105 
Impression,  caecal,  of  liver,  435 

cardiac,  of  lung,  531 

colic,  of  liver,  435 

duodenal,  of  liver,  435 

gastric,  of  liver,  434 
Incisive  foramen,  65,  73,  78 
Incisor  teeth,   394,   397,   448, 
471,  479,  493 
deciduous,  403,  448 
Infraorbital  canal,  65 

foramen,  64,  77 

pouch,  900 
Infratemporal  fossa,  78 
Infundibular  recess,  783 


Infundibulum,  769,  780,  782, 
836 
of  incisor  teeth,  397 
tubse  uterina^,  599 
Inguinal  canal,  292 
pouch,  900 

ring,  abdominal,  290,  292 
external,  288,  292 
internal,  290,  292 
subcutaneous,  288,  292 
Inlet  of  orbital  cavity,  76 
of  thoracic  cavity,  525 
pelvic,  152,  160,  181,  202 
Inscriptiones  tendineae  of  rec- 
tus abdominis  muscle,  291 
Interalveolar  septa,  64 
space,  64,  65,  71,  78 
Interarytenoid     cartilage     of 

larjTix,  546,  550 
Inter-brain,  781 
Intercarpal  sac,  222 
Intercavernous  sinus,  688 
Intercondjdoid     eminence     of 
tibia,  116 
fossa  of  femur,  1 14 

of  tibia,  116 
spaces,  27 
Interdental  space,  64 
Interdigital  pouch,  900 
Interlobar  fissures  of  lung,  540 
Interlobular  bronchi,  534 

tissue,  383 
Intermediate  zone  of  kidney, 

550 
Intermuscular  septa,  254 
of  forearm,  305 
of  gluteal  region,  317,  318 
of  leg,  318 
of  shoulder,  298 
Interosseous      membrane      of 
til)io-fibular    articulation, 
239 
space  of  leg,  31,  116 

of  radius,  91 
tendon,  225 
Interpeduncular     fossa,     769, 

780 
Intertarsal  sac,  240 
Intertuberal   groo\'e   of   hum- 
erus, 89 
Interventricular  foramen,  783, 
791 
septum,  627 
Intervertebral  fibro-car t  ilages, 
211 

foramen,  26,  125,  128 
Intestine,  463,  475,  486,  500 
large,  422,  465,  487,  502 

structure  of,  430 
small,   419,   463,   475,   486, 
500 
Intraosseous  plexus,  692 
Iris,  866,  897 
Ischiatic  spine,  106,  107 
Isthmus  faucium,  390, 406, 446 
oesophagi,  497 
of  male  urethra,  585 
of  prostate,  579 
of  thyroid  gland,  535,  553 
pharyngeal,  408 


Je.iuno-ilbum,  420,  486 
Joints,  207,  211 


INDEX 


917 


Joints,  abduction  of,  210 
adduction  of,  210 
angular  movements,  209 
antibrachio-carpal,  221 
arteries  of,  209 
atlanto-axial,  214 
atlanto-occipital,  214 
basi-comual,  218 
capsule  of,  208 
carpal,  221,  246 
carpo-metacarpal,  221 
cartilages  of,  208 
cavity,  209 
chondro-sternal,  216 
circumduction  of,  210 
coccygeal,  213 
coffin,  228 
costo-central,  215 
costo-chondral,  216 
costo-trans verse,  216 
cost o- vertebral,  215 
crico-arytenoid,  517 
crico-thyroid,  517 
discs  of,  209 
elbow,  219,  246 
extension  of,  209 
femoro-patellar,  232 
femoro-tibial,  235 
fetlock,  224 
fibrous  layer,  208 
flexion  of,  209,  210 
folds  of,  20S 
gliding  movements,  209 
hip,  231,  250 
hock,  239,  251 
hyoidean,  218 
intercarpal,  221 
intercentral,  211 
intercomual,  218 
intermetacarpal,  223,  247 
intemeural,  212 
interphalangeal,  248 

distal,  228 

proximal,  228 
interstemal,  245 
intertransverse.  213 
knee,  221 

lymph-vessels  of,  209 
mandibular,  217 
metacarpo-phalangeal,   224, 

247 
movements  of,  209 
nerves  of,  209 
of  auditory  ossicles,  878 
of  larynx,  517 
of  pelvic  limb,  229,  250 
of  skull,  217 

of  thoracic  limb,  218,  245 
of  thorax,  215,  245 
of  vertebrae,  244 
pastern,  228 
radio-carpal,  221 
radio-ulnar,  221,  246 
rotation  of,  210 
sacral,  213 
sacro-iliac,  229,  250 
shoulder,  218,  245 
sternal,  217 
stifle,  232,  250 
surfaces  of,  208 
synovial  layer,  208 
temporo-hyoid,  218 
temporo-mandibular,  245 
thyro-hyoid,  518 


Joints,  tibio-fibular,  239,  251 

tibio-tarsal,  239 

veins  of,  209 

villi  of,  208 
Jugular    ganglion,    805,    839, 

845,  851 


Kidneys,  554,  564,  566,  567, 
569 
capsule  of,  559 
cortical  substance  of,  558 
fibrous  capsule  of,  558 

coat  of,  559 
fixation  of,  557 
glomerulus  of,  559 
intermediate  zone  of,  558 
left,  555,  565,  569 
lobules  of,  559 
lymph-vessels  of,  560 
medullary  substance,  558 
mucous  coat  of,  559 
muscular  coat  of.  559 
right,  554.  564,  569 
stroma  of,  559 
structure  of,  558 
vessels  and  nerves,  560 
weight  and  size  of,  557 

Ivnee,  29 


Labia  vulvae,  603 
Labyrinth,  membranous,  881, 
882 

of  ethmoid  bone,  55 

osseous,  881 
Labyrinthine  wall,  876 
Lacrimal  apparatus,  860 

bulla,  139 

canal,  82 
osseous,  68 

caruncle,  858 

ducts,  860  ^ 

foramen,  172 

fossa,  external,  159 

groove,  64 

lake,  858 

pouch,  900 

process,  194 

sac,  860 

tubercle,  68 
I^acteals,  615 
Lactiferous  ducts,  605,  609 

sinus,  605,  609 
Lake,  lacrimal,  858 
Lamina  basalis,  865 

choriocapillaris,  865 

cribrosa  sclerse,  863 

elastica  posterior,  864 

externa,  21 

fusca,  863 

homy,  of  hoof,  892 

interna,  21 

lateralis    of   ethmoid    bone, 
55 

layer  of  hoof,  892 

limitans  anterior,  864 

medullary,  777 

of  cricoid  cartilage,  515 

of  hoof,  888 

of  nostrils,  509 

of  thyroid  cartilage,  515 

omasi,  460 

propria,  383 


Lamina  spiralis  ossea,  882 
suprachorioidea,  865 
terminalis,  783 
transversalis      of      ethmoid 
bone,  170,  191 

of  palatine  bone,  171 
vasculosa,  865 
Laminar  corium,  892 
Laryngeal  saccule,  522,  550 
Larynx,  514,  538,  546,  550 
arytenoid    cartilages,     517, 

538,  546,  550 
cartilages  of,  515 
cavity  of,  521 
cricoid  cartilage  of,  515,  538, 

546,  550 
cuneiform  cartilages,  550 
facets,  515 
interarytenoid  cartilage  of, 

546,  550 
lateral  ventricle,   522,   539, 

550 
membranes  of,  517 
middle  ventricle,  522 
mucous  membrane,  523 
posterior  compartment,  523 
vessels  and  nerves,  523 
vestilnile  of,  522 
Layer,  fibrous,  of  pericardium, 

617 
laminar,  of  hoof,  892 
parietal,  384,  412 
serous,  of  pericardium,  617 
visceral,  384,  412 

of  pericardium,  617 
Lemniscus,  774 
Lens,  crystalline,  869 

fibers,  870 
Lenticular  nucleus,  792 

papillae  of  tongue,  447 
Ligament  or  ligaments,  209 
accessory,  of  hip  joint,  232 

of  prepubic  tendon,  292 
alar,  244 
annular,  254 

digital,  distal,  306 
proximal,  306 

dorsal,  of  carpus,  305 

of  leg,  318 

of  radius,  246 

volar,  of  carpus,  306 
of  fetlock,  306 
arytenoid,  transverse,  518 
atiantal,  lateral,  215 
atlanto-axial,  dorsal,  214 

ventral,  214 
l)road,  of  uterus,  415,  601, 

607,  612 
carpal,  dorsal,  222 

volar.  222 
caudate,  of  liver,  437 
check,  240 

inferior,  222,  315 

of  deep  digital  flexor,  341 

subcarpal,  315 

superior,  313 
collateral,  209 

of  coffin  joint,  228 

of  fetlock  joint,  224 

of    meiacarpo-phalangeal 
joints,  247 

of  pastern  joint,  228 
conjugal,  215 
coronary,  437,  488 


918 


INDEX 


Ligament,  costo-sternal,   radi- 
ate, 216 
costo-transverse,  dorsal,  216 
cruciate,  of  stifle  joint,  238 
dorsal,  of  hock  joint,  241 

of  interphalangeal  joints, 
250 
dorso-scapular,  276 
falciform,  437,  488 
lemoro-patellar,  233 
gastro-phrenic,  416 
hepato-renal,  437 
ilio-lumbar,  231 
inferior  check,  315 
inguinal,  288 
interchondral,  216 
interdigital,  248 

cruciate,  249 

distal,  249 
interosseous,  209 

of  forearm,  221 

of  tibial  and  fibular  tar- 
sal bones,  242 
intersesamoidean,  224 
interspinous,  214 
intra-articular,  209 
lateral,  left,  of  liver,  437 

of  bladder,  414,  562 

of  carpal  joints,  222 

of  elbow  joint,  221 

of  hock  joint,  240 

of  stifle  joint,  238 

right,  of  liver,  437 
longitudinal,  dorsal,  211 

ventral,  211 
medial,  of  carpal  joints,  222 

of  ell)ow  joint,  221 

of  hock  joint,  241 

of  stifle  joint,  237 
metacarpal,       interosseous, 

223 
middle,  of  bladder,  414,  562 
navicular,  distal,  229 

suspensory,  229 
odontoid,  214 
of  auditory  ossicles,  878 
of  cartilages  of  third  pha- 
lanx, 229 
of  coffin  joint,  228 
of  dens,  214 
of  ergot,  306 

of  fibular  tarsal  bone,  242 
of  hock  joint,  240,  242 
of  larynx,  517 
of  liver,  437,  488 
of  neck,  215 
of  ovary,  597,  612 
of  pelvic  girdle,  230 
of  peritoneum,  412 
of  stifle  joint,  233,  237 
of  tibial  tarsal  bone,  242 
of  vertebrae,  211,  244 
palpebral,  858 
patellar,  233,  234 
periarticular,  209 
pericardiaco-phrenic,  742 
phalango-sesamoidean,  229 
plantar,  of  hock  joint,  241 
pulmonary,  526 
radial,  313 
radiate,  215 

costo-sternal,  216 
round,  of  bladder,  414,  562 

of  hip  joint,  231 


Ligament,  round,  of  liver,  437, 
490 

of  uterus,  601,  607,  612 
sacro-iliac,  dorsal,  230 

lateral,  230 

ventral,  230 
sacro-sciatic,  230 
scrotal,  574 
serous,  384 
sesamoidean,  224 

collateral,  224,  229 

cruciate,  227 

deep,  227 

distal,  226 

middle,  226 

short,  227 

straight,  226 

superficial,  226 

suspensory,  317 
sternal,  internal,  217 
sterno-pericardiac,  705 
subcarpal,  222 

check,  315 
subtarsal,  240 
superior  check,  313 
supraspinous,  212 
suspensory,  225 

navicular,  229 
■   of  anus,  432 

of  penis,  580 

of  spleen,  441 

sesamoidean,  317 
thyro-epiglottic,  518 
tracheal  annular,  525 
transverse,  of  atlas,  245 

of  carpus,  306 

of    radio-ulnar    articula- 
tion, 221 
vaginal,  254 
ventricular,  518 
vocal,  518 

volar,  of  pastern  joint,  228 
Ligamenta  flava,  212 
Ligamentum  arteriosum,  629, 

704 
denticulatum,  764 
nuchee,  213 

pectinatum  iridis,  865,  866 
spirale  cochleae,  883 
Line,  diaphragmatic,  of  pleu- 
ral reflection,  530 
gluteal,  105 
ilio-pectineal,  105 
mylo-hyoid,  70 
of  pleural  reflection,  530 
popliteal,  of  tibia,  115 
sternal,  of  pleural  reflection, 

530 
terminal,  110,  410 
vertebral,  of  pleural  reflec- 
tion, 530 
white,  of  hoof,  889 
Linea  alba,  288 
Lingual  follicles,  392 

process,  72 
Lingula,  776 

Lips,  385,  444,  470,  477,  491 
Liquor  folliculi,  598 
pericardii,  617 
pleurae,  530 
Lobe  or  lobes,  apical,  of  lung, 

540,  547,  548,  551,  553 
cardiac,  of  lung,  540,  547, 

548,  551,  553 


Lobe,  caudate,  of  liver,  434, 

468,  488,  503 
cerebellar,  777 
diaphragmatic,  of  lung,  540, 

547,  551,  553 
intermediate,  of  lung,  540, 

534,  547,  551 
of  liver,  438,  488,  490,  503 
of  lung,  540,  547,  551 
of  mammary  glands,  605 
of  prostate,  579 
of  thymus  gland,  536 
of  thyroid  gland,  535,  536, 

553 
of  urethra,  595 
piriform,  784,  788,  850 

of  brain,  769 
Lobular  bronchioles,  534 
Lobulation  of  lungs,  534,  544 
Lobules  of  kidney,  559 
of  liver,  438 
pulmonary,  534 
Lumbar  enlargement,  765 
ganglia,  832 
part  of  sympathetic  system, 

856 
Lum))o-costal  arch,  287 
Lumbo-sacral  plexus,  824,  841, 

846,  855 
Lung,    530,     540,     544,    547, 

551 
alveolar  ducts  of,  534 
apex  of,  533,  534 
apical  lobe  of,  540,  547,  548, 

551,  553 
basal  border  of,  533 
base  of,  533 
body  of,  534 

bronchial  branches  of,  534 
cardiac  impression  of,  531 

lobe  of,  540,  547,  548,  551, 
553 

notch  of,  533 
color  of,  531 
costal  surface  of,  531 
diaphragmatic  lobe  of,  540, 

547,  551,  553 
dorsal  border  of,  532 
foetal,  531 
form  of,  531 
hilus  of,  531 

interlobar  fissures  of,  540 
intermediate   lobe   of,    534, 

540,  547,  551 
lobes  of,  540,  547,  551 
lobulation  of,  534,  544 
lymph-vessels  of,  534,  535 
mediastinal  surface  of,  531 
root  of,  534 
ventral  border  of,  533 
vessels  and  nerves  of,  534 
Lymph,  616 

ducts,  tracheal,  725,  756 
follicles,  616 
nodes,  616 
nodules,  616 
sinus,  central,  616 

peripheral,  616 
spaces,  616 
vessels,  615 

of  abdomen,  701 

of  adrenal  bodies,  564 

of  bladder,  562 

of  bone,  22 


INDEX 


919 


Lymph  vessels  of   corium   of 
hoof,  894 

of  Fallopian  tubes,  599 

of  head  and  neck,  698 

of  heart,  828 

of  kidneys,  560 

of  lung,  534,  535 

of  ovary,  599 

of  pelvic  limb,  703 

of  pelvis,  701 

of  penis,  582 

of  skin,  885 

of  spermatic  cord,  576 

of  testicles,  574 

of  thoracic  limb,  703 

of  thorax,  700 

of  uterus,  602 

of  vagina,  602 
Lymphatic  duct,  725 

right,  615,  698 
system,  615,  697,  722,  740, 

756 
Lymphocytes,  616 
Lyssa,  493 


Macroscopic  anatomy,  17 
Maculae  acusticae,  883 
Malleolus,  lateral,  of  tibia,  117 
medial,  of  tibia,  117 
of  tibia,  117 
Mammillary  body,  769,  782, 
847 
processes,  26,  45,  163 
Mandibular  canal,  71 
duct,  405,  496 
foramen,  71 
notch,  71 
space,  70 
teeth,  401 
Manubrium  stemi,  28,  48 
Marginal  cartilage,  209 
fissure,  785,  837,  844 
pole,  836 
Margo  plicatus,  418 
Marrow  of  bone,  21,  22 

spaces,  21 
Masseteric  fossa  of  mandible, 

195 
Mastoid   border  of    occipital 
bone,  52 
foramen,  62 
process,  61,  74 
Maxillary  dental  plexus,  798 
foramen,  65,  76 
process,  194 
region,  76 

sinus,  84,  144,  175,  197 
inferior,  84 
superior,  85 
teeth,  400 
tuberosity,  65 
Meatus,  acoustic,  external,  61, 
870,  871 
internal,  62,  882 
common,  of  nose,  69 
dorsal,  of  nasal  cavity,  545 

of  nose,  69,  83 
ethmoidal,  55,  512 
middle,  of  nasal  cavity,  545, 

550 
nasal,  common,  511 
dorsal,  511 
middle,  69,  83,  511 


Meatus,  nasal,  ventral,  69,  83, 
511 
ventral,  of  nasal  cavity,  546, 
550 
Medial  epicondyle  of    femur, 
114 
malleohis  of  tibia,  117 
supracondyloid  crest  of  fe- 
mur, 112 
Mediastinal  pleura,  526 
Mediastinum  thoracis,  525 
Medilateral  fissure,  849 
Medulla  oblongata,  769,  771, 
773,  834,  843,  847 
of  thymus  gland,  536 
cavity,  20,  21 
Medullary  cords,  616 
lamina,  777 
substance,  777 

of  adrenal  bodies,  563 
velum,  776 
anterior,  779 
posterior,  779 
Membrana  basilaris,  883 
nictitans,  859 
propria  of  middle  ear,  876 
tympani,  876 
vestibularis,  883 
Membrane,    atlanto-occipital, 
dorsal,  215 
atlanto-occipital,       ventral, 

215 
crico-thyroid,  518 
crico-tracheal,  518 
elastic,  of  trachea,  525 
fibrous,  384 
hyaloid,  869 
interosseous,  of  tibio-fibular 

articulation,  239 
obturator,  231 
of  larynx,  517 
serous,  384 

s\Tiovial,    of    carpal  joints, 
222 
of  elbow  joint,  219 
of  hip  joint,  232 
thyro-hyoid,  518 
Membranous   labvrinth,    881, 

882 
Meninges,  761 
Meniscus,  209,  235 
Mental  foramen,  70 
Meridians  of  eye,  863 
Mesaticephalic  skull,  195 
Mesencephalon,  780 
Mesenteric  ganglion,  anterior, 
842,  856 
posterior,  833,  843 
plexus,  anterior,  833,  856 
posterior,  833,  856 
Mesentery,  412 
colic,  412,  429 
great,  412,  420 
Mesocolon,  502 
Mesoduodenum,  419,  500 
Mesogastric  zone,  411 
Mesorchium,  576,  577 
Mesorectum,  413,  429 
Mesosalpinx,  599,  612 
Mesotendon,  253 
Mesothelium,  384 
Mesovarium,  597 
Microscopic  anatomy,  17 
Mid-brain,  780 


Moderator     bands     of     right 

ventricle,  625 
Modiolus,  882 
Molar  teeth,  394,  399 
Morphology,  17 
Motor  fibers,  808 
nucleus,  dorsal,  808 
of  fifth  nerve,  776 
ventral,  808 
root  of  fifth  nerve,  776 
Mouth,  385,  444,  477,  491 
cavity  of,  385,  444 
floor  of,  390 

mucous  membrane  of,  385 
Mucous  coat  of  bladder,  562 
of  Fallopian  tubes,  599 
of  kidney,  559 
of  small  intestine,  421 
of  stomach,  418 
of  vagina,  602 
membranes,  383 
of  abomasum,  462 
of  ductus  deferens,  575 
of  large  intestine,  431 
of  larynx,  523 
of  mouth,  385 
of  nose,  512 
of  oesophagus,  410 
of  omasum,  462 
of  pharjmx,  407 
of  reticulum  of  stomach, 

462 
of  rumen,  458 
of  seminal  vesicles,  578 
of  small  intestine,  421 
of  tongue,  390 
of  trachea,  525 
of  ureters,  561 
of  urethra,  585,  604 
of  uterus,  601,  607 
of  vulva,  603 
tympanic,  878 
Mucus,  383 

Muscle  or  muscles,  252,  264 
abdominal,    287,    349,   361, 

377 
abductor    cruris    posterior, 
378 
digiti  quinti,  381 
hallucis,  382 

pollicis  brevis  et  opponene 
pollicis,  375 
longus,  373 
accessory  structures,  253 
action  of,  253 
adductor,  326,  356,  365 
digiti  quinti,  375 

secundi,  375 
femoris,  380 
hallucis,  382 
of  second  and  fifth  digits, 

381 
pollicis,  375 
anconeus,  304,  363 
antitragicus,  874 
arrectores  pilorum,  886 
articularis  genu,  355 
ar\'tenoideus       transversus, 

520 
attachments  of,  252 
auricular,  872,  897 
anterior,  872 
deep,  873 
dorsal,  872 


920 


INDEX 


Muscle,    auricular,    posterior, 
873 
belly  of,  253 
biceps,  351 

brachii,  302,  363,  372 
femoris,  322,  355,  365,  378 
bipennate,  253 
biventcr  cervicis,  376 
blood  supply  of,  253 
brachialis,  302,  363,  373  _ 
brachiocephalicus,  294,  351, 

360,  362,  371 
brachioradialis,  308,  373 
buccinator,  258,  345,  368 
bulbo-cavemosus,  586,  589, 

595 
capsularis,    301,    333,    351, 

355,  363,  365,  380 
cervical  cutaneous,  347,  376 
cervicalis  ascendens,  269 
cervico-auricularis     profun- 
dus major,  873 
minor,  873 
superficialis,  873 
cervico-scutularis,  872 
chondro-pharyngeus,  407 
ciliary,  866 
cleido-cervicalis,  371 
cleido-mastoideus,  351,  362, 

371 
cleido-occipitalis,  351,  362 
coccygeus,  279,  377 
complexus,  273,  361,  376 

major,  376 
constrictor  vestibuli,  603 

vulvae,  603 
coraco-brachialis,  300,  351, 

363,  371 
corrugator  supercilii,  260 
cremaster,     external,     291, 

381,  576,  587,  591 
crico-arytenoideus    dorsalis, 
519 
lateralis,  519 
crico-pharyngeus,  407 
crico-thyroideus,  519 
cutaneous,    252,    254,    343, 
350,  368,  884 
colli,  254 
faciei,  254 
labiorum,  254 
omo-brachialis,  254 
trunci,  254 
deltoid,  351,  362,  371 

deltoideus,  298 

depressor     labii     inferioris, 
258,  344,  359,  368 
superioris,  344 
rostri,  359 
diaphragm,  285,  349,  361 
digastric,  253 
digastricus,   264,   346,   359, 

370 
digital    extensor,    common, 
307,  352.  363,  373 
lateral,   308,   335,   352, 
356,    363,    367,    373, 
380 
,  long,  333,  356,  366,  380 
medial,  352,  356 
of  second  digit,  363 
short,  356 
flexor,  deep,  315,  339,  354, 
364,  367,  374,  381 


Muscle,  digital  flexor,  long,  340 
superficial,     313,     339, 
353, 364, 367, 374, 381 
dilatator  naris  apicalis,  345 
lateralis,  258,  345,  359 
extensor  carpi  obliquus,  310, 
352,  363,  373 
radialis,  306,  352,  363, 
373 
brevis,  373 
longus,  373 
ulnaris,  374 
digitalis  brevis,  343,  367, 

380 
hallucis  longus,  367,  380 
of  fifth  digit,  374 
of  first  and  second  digits, 

373 
of  third  and  fourth  digits, 
373 
facial  cutaneous,  359 
flexor    carpi    radialis,    310, 
364,  374 
ubiaris,  310,  364,  374 
deep,  359 

digitahs  longus,  368 
pedis  longus,  381 
hallucis,  341,  368 
brevis,  382 
longus,  381 
polhcis  brevis,  375 
superficial,  359 
front  aUs,  343 
fronto-scutularis,  872 
gastrocnemius,     338,     359, 

367,  381 

gemeUus,  329,  356,  365,  378 
genio-glossus,  394 
genio-hyoideus,  265,  347 
gluteus  accessorius,  322 

medius,  321,  355,  365,  378 

profundus,  322,  355,  365, 
378 

superficialis,  321,  365,  378 
graciUs,  325,  356,  365,  380 
head  of,  253 
heUcis,  874 
hyo-epiglotticus,  519 
hyo-glossus,  392 
hyoid,  264,  347,  359,  370 
hyoideus   transversus,    265, 

347,  359 
hyo-pharyngeus,  407 
iUacus,  320,  354,  378 
ilio-psoas,  319,  378 
incisivus  inferior,  257,  344 

superior,  257 
infraspinatus,  299,  351,  362, 

371 
insertion  of,  252 
intercostal,     external,     283, 
349,  361,  376 

internal,  283,  349,  361 
interosseous,  317,  343,  365, 

368,  375,  381 
interosseus  medius,  354 
interscutularis,  872 
interspinals,  349,  362,  376, 

377 
intertransversales,  347,  349, 
361,  362,  376,  377 
caudse,  281 
coUi,  270 
lumborum,  279 


Muscle,  ischio-cavernosus,  582, 
589,  604 
ischio-urethral,  586,  595 
kerato-hyoideus,    265,    347, 

359 
kerato-pharyngeus,  407 
lateralis  nasi,  259 
dorsal  part,  345 
ventral  part,  345 
latissimus   dorsi,   295,   351, 

362 
levator  labii  superioris  pro- 
prius,  256,  344,  359,  368 
nasolabialis,      255,      258, 

343,  359,  368 
palati,  389 
palpebrse  superioris,  260, 

861 
rostri,  359 
levatores     costarum,      281, 

349,  361,  376 
Ungual,  392 

longissimus  atlantis,  o76 
capitis,  376 

et    atlantis,    271,    361, 
376 
costarum,  277,  349,  362, 

377 
dorsi,  278,  349,  371,  377 
longus  colU,  270,  347,  360, 

376 
lumbricales,  317,  343,  354, 

365,  368,  375,  381 
malaris,  260,  345 
mandibular,  260,  346,  359, 

370 
masseter,  261,  346,  359,  370 
mentahs,  258 
multifidus,  362 
cer\acis,  273 
dorsi,  279 
multipennate,  253 
mylo-hvoideus,     264,     347, 

359,  370 
nasal,  368 

nerve  supply  of,  253 
non-striated,  252 
obliquus    abdominis    exter- 
nus,    288,    349,    361, 
377 
internus,  290,  350,  361, 
377 
capitis  anterior,  275 
posterior,  273,  361 
dorsalis  s.  superior,  861 
ventraUs  s.  inferior,  861 
obturator,  378 

externus,  328,  356,  365 

internus,  328,  356,  365 

occipito-hyoideus,  265,  347, 

359 
occipito-mandibularis,    262, 

346,  370 
ocular,  861 
of  abdomen,  287,  349,  361, 

377 
of  anus,  432 
of  arm,  302,  351,  363 
of  auditory  ossicles,  878 
of  back,  349,  361,  376,  377 
of  cheeks,  255 
of  digit,  343 
of  eveball,  861 
of  eyelids,  260 


INDEX 


921 


Muscle  of  face,  343,  359,  368 
of  foot,  333,  356 
of  forearm,  305,  352,  363 
of  head,  255 

ventral,  360 
of  hip,  365 

lateral,  320,  355 
of  larynx,  518 

extrinsic,  518 

intrinsic,  519 
of  leg,  333,  356,  366 
of  lips,  255 

of  loins,  276,  349,  361,  377 
of  manus,  305,  352,  363 
of  metatarsus,  343 
of  neck,  266,  347,  360,  376 

lateral,  271 

ventral,  266 
of  nostrils,  258 
of  pelvic  limb,  319,  354,  365, 

378 
of  penis,  582 
of  pharynx,  407 
of  shoulder,  298,  351,  362 

girdle,  293,  350,  362 
of  soft  palate,  389 
of  tail,  279,  349,  362,  377 
of  thigh,  365 

anterior,  329,  355 

lateral,  320,  355,  356 

medial,  325 
of  thoracic  limb,  293,  350, 

362,  370 
of  thorax,  281,  349,  361,  376 
of  tongue,  392 
omo-hyoideus,  268,  347,  359, 

360 
omo-transversarius,  360,351, 

362,  370 
orbicularis  oculi,  260,  345 

oris,  255,  343,  359,  368 
origin  of,  252 
palatinus,  389 
palato-pharyngeus,  407 
palmaris  brevis,  375 

longus,  374 
palpebral,  368 
panniculus    carnosus,     254, 

884 
parieto-auricularis,  872 
parotido-auricularis,  873 
pectineus,  326,  356,  365,  380 
pectoral,  295 

deep,  296,  351,  371 
anterior,  296,  362 
posterior.  296,  362 

superficial,  295,  351,  371 
anterior,  295,  362 
posterior,  296,  362 
peroneus  brevis,  380 

longus,  356,  366,  380 

tertius,  335,  356,  366,  386 
piriformis,  378 
popUteus,  343,  367,  381 
preputial,  anterior,  590 

posterior,  590 
pronator  quadratus,  375 

teres,  354,  364,  374 
protractors,  590 
psoas  major,  319,  354,  365, 
378 

minor,  319,  354,  365,  378 
pterygoideus  lateralis,   262, 

346,  359,  370 


Muscle,    pterygoideus     medi- 
alis,  261,  346,  359 
pterygo-pharyngeus,  407 
quadratus  femoris,  328,  356, 
365,  378 
lumborum,  320,  354,  365, 

378 
plantiP,  381 
quadriceps  femoris,  329, 355, 

365,  379 
recti  capitis  dorsales,  361 
rectus  abdominis,  290,  350, 
361,  379 
capitis  dorsalis  major,  275 
minor,  276 
lateralis,  270,  347,  376 
ventralis    major,     269, 
347,  376 
minor,  269,  347,  376 
dorsalis  s.  superior,  861 
femoris,  329,  379 
lateralis,  861 
medialis,  861 
thoracis,  283,  361 
ventrahs  s.  inferior,  861 
relations,  253 
retractor,  590 
ani,  432,  502 
costfp,  283,  361 
oculi,  861 
penis,  582,  589 
rhomboideus,  293,  351,  371, 
362 
cervicalis,  293,  371 
thoracalis,  293,  371 
rotator,  873 

sacro-coccygeus,  362,  377 
accessory,  377 
dorsalis,  280 
lateralis,  280 
ventralis,  281 
sartorius,  325,  356,  365,  380 
scalenus,  268 

dorsalis,  347,  360,  376 
ventralis,  347,  360,  376 
scutularis,  872 
scutulo-auricidaris        pro- 
fundus major,  873 
minor,  874 
superficialis     accessorius, 
872 
inferior,  872 
medius,  872 
superior,  872 
semimembranosus,  324,  365, 

355,  379 
semitendinosus,     323,     355, 

365,  379 
serratus  cervicis,  297 

dorsalis  anterior,  277,  349, 
361,  377 
posterior,  277,  349,  361, 
377 
thoracis,  297 

ventrahs,   297,   351,   362, 
371 
shape  of,  252 
skeletal,  252 
soleus,  359,  339,  367 
sphincter,  252 
ani  exiernus,  432 

internus,  432 
vesicae,  562 
spinalis,  273 


Muscle,    spinalis   et    semispi- 

nalis,  362 
splenius,  271,  347,  361,  376 
stapedius,  878 
sterno-cephalicus,  266,  347, 

360,  376 
sterno-hyoideus,  359,  370 
sterno-mandibularis,  347 
sterno-mastoideus,  347 
sterno-thyro-hyoideus,   268, 

347,  360,  370 
sterno-thyi'oideus,  370 
striated,  252 
structure  of,  253 
stylo-glossus,  392 
stylo-hyoideus,     265,     347, 

370 
stylo-pharyngeus,  407 
sublumbar,  319,  354,  365 
submultifidus,  376 
subscapularis,  300,  351,  363, 

371 
supinator,  364,  374 
supraspinatus,  298,  351,  362, 

371 
synovial  membranes  of,  253 
temporahs,  261,  346,  370 
tendinous  inscriptions,  253 

intersections,  253 
tensor     fascial     antibrachii, 
303,  352,  363,  373 
latff,  320,  355,  365,  378 

palati,  390 

tympani,  878 
teres  major,  300,  351,  363, 
371 

minor,  299,  351,  362,  371 
thyro-arytenoideus       exter- 

nus,  521 
th>TO-hyoideus,  518 
thyr()-i)iuu>ngeus,  407 
tibialis   ant(>rior,    336,    357, 
366,  380 

posterior,  340,  367,  381 
trachealis,  525 
tragicus,  874 

transversus  abdominis,  291, 
350,  361,  378 

nasi,  259,  359 

thoracis,  285,  361 
trapezius,  293,  350,  362,  370 

cervicalis,  293 

thoracaUs,  293 
triceps,  352,  363,  373 

brachii,  303,  304 
ulnaris   laterahs,    313,    364, 

374 
unipennate,  253 
urethral,  586,  590,  593,  595, 

604 
vastus  intermedins,  333,  379 

lateralis,  330,  379 

medialis,  331,  379 
ventricularis,  520 
verticalis  auricula^,  875 
visceral,  252 
vocalis,  520 

zygomatico-auricularis,   872 
zygomaticus,  257,  344,  359, 

368 
Muscular  coat  of  abomasum, 
462 

of  bladder,  562 

of  ductus  deferens,  575 


922 


INDEX 


Muscular    coat  of    Fallopian 
tubes,  599 

of  kidney,  559 

of  large  intestine,  430 

of  a'sophagus,  409 

of  omasum,  462 

of  reticulum  of  stomach, 
462 

of  rumen,  461 

of  seminal  vesicles,  578 

of  small  intestine,  421 

of  stomach,  417 

of  ureters,  561 

of  m-ethra,  604 

of  uterus,  601,  607 

of  vagina,  602 

of  viscera,  384 
process   of   temporal  bone, 

63 
tissue,  384 
Muscularis  mucosa?,  383 

of  small  intestine,  421 
IVIusculi  papillares  of  left  ven- 
tricle, 627 

of  right  ventricle,  624,  625 
pectinati    of   right    atrium, 

621 
Musculo-spiral  groove,  88 
Myenteric  plexus,  833 
Mylo-hyoid  hne,  70 
Myocardium,  628 
Myology,  252 


Nares,  posterior,  78,  406,  512 
Nasal  cavity,  82, 143, 159, 175, 
197,  508,  537,  538,  545, 
548 
common  meatus,  511 
dorsal  meatus,  511,  545 
ethmoidal  meatuses,  512 
meatuses,  511 
middle  meatus,  511,  545, 

550 
parietal  cartilage,  510 
ventral  meatus,  511,  546, 

550 
vessels  and  nerves,  510 
crest,  65,  66,  82 
process,  65 
region,  73 
septum,  82,  84 
spine,  posterior,  193 
Naso-frontal  suture,  60,  67 
Naso-lacrimal  duct,  509,  860, 
896 
groove  for,  82 
orifice,  508 
suture,  67 
Naso-maxillary  fissure,  85 
notch,  67 
opening,  511 
suture,  67 
Neck,  lymph  vessels  of,  698 

of  tooth,  395 
Nerve  or  nerves,  760 
abducent,  770,  801 
acoustic,  770,  803 
alveolar,  inferior,  851 
mandibular,  800 
maxillarv,  798 
middle,  798 
posterior,  798 
articular,  761 


Nerve,  am-icular,  805 

anterior,  803 

internal,  802 

posterior,  802,  812 
auriculo-palpebral,  802,  839, 

851 
axillary,  815,  816 
broncliial,  80S 
buccal,  803,  839,  845,  851 
buccinator,  799 
cardiac,  808,  831,  856 
cerebral,  793 
cervical,  803,  812,  851 

eighth,  813 

fifth,  813 

first,  812 

fourth,  813 

second,  812 

seventh,  813 

six-th,  813 

third,  813 
chorda  tympani,  801,  802 
ciliary,  long,  850 

short,  796 
coccj'geal,  829 
cochlear,  803,  884 
cranial,  793,  838,  844,  850 
cutaneous,    lateral,   of    leg, 
826 

of  neck,  813 

of  thigh,  823 

posterior,  of  leg,  826 
of  thigh,  825 
dental,  798 
depressor,  807,  853 
digastric,  802 

digital,  819,  841,  846,  853, 
854,  855,  856 

lateral  volar,  of  fifth  digit, 
854 
dorsalis  penis,  828 
eighth,  770 
eleventh,  771 
ethmoidal,  796,  850 
facial,  770,  801,  839,  850 
femoral,  824 
fifth,  770 
fourth,  770 

frontal,  796,  838,  845,  850 
glosso-pharyngeal,  771,  773, 

804 
gluteal,  anterior,  824 

posterior,  824 
hsemorrhoidal,        posterior, 

828 
hypoglossal,  771,  773,  810, 

840,  845,  853 
ilio-hypogastric,  822 
lio-inguinal,  822 
infraorbital,  798,  845,  850 
nfratrochlear,  796,  850 
ntercostal,  820 
nterosseous,  819 
abial,  850 

superior,  798 
acrimal,  795,  838,  845,  850 
aryngeal,  852 

anterior,  807 
Ungual,  800,  805,  851 
lumbar,  822 

fifth,  823 

first,  822 

fourth,  823 

second,  822 


Nerve,  lumbar,  sixth,  823 

third,  823 
mandibular,  798,  800,  838, 

845,  850 
masseteric,  799 
maxillary,  796,  845,  850 

incisor,  798 
median,  814,  818,  841,  846, 

854 
metacarpal,  819 

volar,  854 
metatarsal,  dorsal,  856 
musculo-cutaneous,  814,815, 

819,  853 
mylo-hyoid,  800,  850 
nasal,  anterior,  798 

external,  798,  850 

posterior,  797,  850 
naso-ciliary,  796,  838,  845 
ninth,  771 
obturator,  824 
oculomotor,  769,   773,  780, 

794,  806,  808,  838 
ttsophageal,  dorsal,  839 

ventral,  840 
of  adrenal  bodies,  564 
of  corium  of  hoof,  894 
of  cornea,  865 
of  ductus  deferens,  575 
of  external  ear,  875 
of  eye,  859,  860 
of  Fallopian  tubes,  599 
of  heart,  629 
of  kidneys,  560 
of  penis,  582 
of  pterygoid  canal,  798 
of  skin,  885 
of  spermatic  cord,  576 
of  testicles,  574 
of  uterus,  602 
of  vagina,  602 
of  vascular  tunic  of  eye,  867 
of  veins,  615 
olfactory,  793 
ophthalmic,  795,  850 
optic,  769,  793 
palatine,  850 

anterior,  798 

greater,  798 


posterior,  798 
pectoral,  814,  815 
peroneal,  826 

common,  855 

deep,  826,  841,  846,  855 

superficial,  826,  841,  846, 
855 
petrosal,  802 
pharyngeal,  804,   807,  839, 

852 
phrenic,  813 
plantar,  828,  846 

digital,  841 

lateral,  841,  856 

medial,  841,  856 

metatarsal,  856 
pterygoid,  799 
pudic,  828 
pulmonary,  534,  535 
radial,  815,  816,  841,  846, 

853 
recurrent,  807,  853 
sacral,  828 
saphenous,  824,  855 


INDEX 


923 


Nerve,  sciatic,  great,  825 
second,  769 
seventh,  770 
sixth,  770 
spermatic,  external,  823 

internal,  833 
sphenopalatine,  797,  850 
spinal,  810,  840,  845,  853 
accessory,  771.  808,  840 
splanchnic,  great,  831,  842 
gi-eater,  856 
lesser,  856 
smaU,  832,  842 
stapedial,  802 
subscapular,  814 
suprascapular,  814,  815 
sympathetic,  629 
temporal,  803 
deep,  799 

superficial,  800,  838,  845, 
850 
tenth,  771 
third,  769 
thoracic,  820 
anterior,  814 
external,  815 
long,  815 
posterior,  815 
thoraco-dorsal,  815 
tibial,  827,  841,  846,  856 
tracheal,  808 
fefigeminal,  770,  795,  838 
trochlear,  777,  780,  794 
twelfth,  771 
tympanic,  804 
uhiar,   814,   817,   841,   846, 

853 
vagus,  629,  771,  773,  805, 
839,  845,  851 
left,  806 
right,  805 
vestibular,  803,  884 
volar,  819,  841 
lateral,  819 
medial,  819 
zygomatic,  796,  850 
Nerve-cell,  760 
Nerve-fibers,  olfactory,  769 
Nerve-plexus,  761 
Nervous  system,  760,  764,  834, 
843,  847 
sympathetic,     829,     842, 
846,  856 
Nervus  dorsalis  penis,  828 

transversarius,  830 
Neuroglia,  760 
Neurology,  760 
Neurone,  760,  829 
Nippers,  395 
Nodes,  lymph,  616 
Nodules,  aggregated,  of  large 
intestine,  43 
of    small    intestine,    422, 
487,  501 
lymph,  616 
of  thyroid  tissue,  536 
soUtary,  of  large  intestine, 
431 
of    small    intestine,    422, 
487 
splenic,  441 
Nodulus,  776 

Nostrils,  508,  537,  545,  548 
false,  260,  508 


Nostrils,  true,  508 
Notch,  alar,  184 

cardiac,  of  lung,  533 
carotid,  54 
mandibular,  71 
naso-maxillary,  67 
oesophageal,  435 
oval,  54 

popliteal,  of  tibia,  116 
sciatic,  greater,  106 

lesser,  108 
semilunar,  of  ulna,  93 
sphenoidal,  60 
spinous,  54 
Nuchal  crest,  79 

of  skull,  51 
Nucleo-cerebellar     fasciculus, 

777 
Nucleus  ambiguus,  808 
amygdaloid,  792 
caudate,  792 
cuneatus,  774 
dorsaUs,  767 
facial,  801 
gracilis,  774 
hypothalamic,  781 
lenticular,  792 
motor,  dorsal,  808 

of  fifth  nerve,  776 

ventral,  808 
of  lens,  870 

of  origin  of  nerves,  760,  774 
of  soUtary  tract,  808 
olivary,  anterior,  776 

posterior,  774 
pulpy,      of      intervertebral 

fibro-cartilage,  211 
red,  781 

sensory,  dorsal,  808 
terminal,  of  nerves,  760,  774 
Nutrient  foramen,  22 

of  femur,  112 

of  humerus,  88 

of  iUum,  106 

of  metacarpus,  99 

of  tibia.  116 


Obex,  779 

Obturator  foramen,  109,  112, 
152,  202 

membrane,  231 
Occipital  condyles,  50 

crest,  51 

protuberance,  external,   51, 
79 
internal,  57 

sinuses,  688 
Occipito-mastoid  suture,  52 
Occipito-temporal  fissure,  850 
Esophageal  groove,  458,  473 

notch,  435 

plexus,  808,  831,  853 
(Esophagus,  409,  451,  472,  483, 

497 
Olecranon  fossa,  90 
Olfactory  bulb,  769,  771,  787, 
838,  844,  850 

cells,  895 

nerve-fibers,  769 

organs,  905 

stria-,  769,  788 

tract,  769,  788,  844 


Olivary  nucleus,  anterior,  776 

posterior,  774 
Olivo-cerebellar  fibers,  777 
Omaso-abomasal  orifice,  460 
Omasum,  453,  456,  474 
Omental  cavity,  442 
Omentum,  412 

gastro-splenic,  412,  417,  441 

greater,  412,  417,  442,  461, 
499 

lesser,   412,   417,   456,  460, 
499 
Ontogeny,  17 
Optic  axis,  external,  863 

chiasm,  769,  783 

commissure,  769 

foramen,  53,  75,  82 

groove,  53 

papilla,  868 

recess,  783 

tract,  769,  780,  783,  835 
Ora  ciliaris  retinae,  868 
Orbit,  74 

Orbital  foramen,  53,  75 
internal,  53 

region,  74 

wings,  53 
Organ,  spiral,  of  Corti,  884 

vomero-nasal,  514,  895 
Organs  of  senses,  857, 896,  900, 

902 
Orifice,  aortic,  of  horse,  626 

atrio-ventricular,   left,   625, 
626 
right,  621,  623 

ca?co-cohc,  424 

ejaculatory,  575 

ileo-caecal,  424 

ileo-coHc,  501 

naso-lacrimal,  508 

omaso-abomasal,  460 

preputial,  583 

pulmonary,  of  right  ventri- 
cle, 624 

reticulo-omasal,  459 

rumino-reticular,  458 

ureteral,  562 
internal,  562 

urethral,    external,    female, 
603,  607 
male,  585,  589 
internal,  male,  585 
Orificium  externum  uteri,  601 

internum  uteri,  601 
Os  acetabuli,  110 

penis,  594 

rostri,  545 
Osseous  labyrinth,  881 
Ossicles,  auditory,  877 
Ossification,  23 

center  of,  23 

endochondral,  23 

intramembranous,  23 
Osteoblasts,  23 
Osteoclasts,  23 
Osteogenesis,  23 
Osteology,  20 
Ostium  abdominale  tubae,  599 

uterinum  tubs,  599 
Otic  ganglia,  829 

ganglion,  799,  838 

papilla,  897 
Outlet  of  pelvis.  111,  112,  413 
Ova,  598 


924 


INDEX 


Oval  notch,  54 

Ovaries,   596,   605,    609,    610, 

612 
Ovisacs,  598 
Ovulation,  598 

fossa,  597 


Palate,   hard,   78,   387,   445, 
470,  477,  492 

soft,  388,  446,  477,  492 
Palatine  canal,  64 

fissure,  66,  78,  82 

foramen,  anterior,  66 
posterior,  65,  76 

groove,  65,  78 

process  of  maxilla,  64,  65 
of  premaxilla,  66 

region,  78 

sinus,  137,  145 

suture,  median,  78 
transverse,  79 
Pallium,  785 
Palpebral  conjunctiva,  859 

fissure,  857 

sebum,  859 
Pampiniform  plexus,  693 

of  testicles,  574 
Pancreatic  duct,  434,  463,  487, 
491,  501,  506 
accessory,  434 
Panniculus  adiposus,  884 
Papilla,  383 

filiform,  of  tongue,  391 

foliate,  of  tongue,  391 

fungiform,  of  tongue,  391 

hair,  886 

incisiva,  387 

of  hard  palate,  445 

of  cheeks,  445 

of  hps,  444 

of  mammary  gland,  604 

of  skin,  885 

of  tongue,  391,  447 

optic,  868 

otic,  897 

renal,  565 

vallate,  of  tongue,  391 
Paradidymis,  573 
Paramastoid   process,   50,   78, 

79 
Paranasal  sinuses,  84 
Parenchyma  of  adrenal  bodies, 
563 

of  Uver,  438 

of  mammary  glands,  604 

testis,  572 
Pai'letal    border    of    occipital 
bono,  52 

cartilage    of    nasal    cavity, 
510,  537 

crest,  135 

external,  51,  57,  73 
internal,  58,  81 

layer,  384,  412 

pleura,  526 

radicles,  693 

region  of  skull,  73 

suture,  57 
Parieto-frontal  suture,  57,  60 
Parieto-occipital  suture,  52,  57 
Parieto-temporal  canal,  63 
Paroophoron,  599 


Parotid  duct,   404,   477,  482, 
492,  495 

plexus,  803 
Pars  ciliaris  retinse,  868 

disseminata,  589,  592 

iridica  retinte,  868 

longa  glandis,  594 

optica  retina?,  868 
Patches,  Peyer's,  422,  487,  501 
Pecten  ossis  pubis,  109 
Peduncles,   anterior,   decussa- 
tion of,  778 

cerebellar,  777 
anterior,  776 
middle,  776 

cerebral,  769,  780,  835,  843 

middle  cerebellar,  776 
Pelvic  cavity,  152,  412,  453 

girdle,  30,  105 

inlet,  152,  160,  181,  202 

limb,  lymph  vessels  of,  703 

outlet,  413 

part  of  sympathetic  system, 
832 

peritoneum,  413 

plexus,  832,  834,  856 
Pelvis,  lymph  vessels  of,  701 

renal,  559 

symphysis,  231 
Penis,  580,  589,  592,  594 

collum  glandis  of,  581 

corona  glandis,  580 

corpus  cavernosum,  581 

fossa  glandis  of,  581 

glans,  580,  589,  594 

structure  of,  581 

suspensory  ligaments,  580 

trabecular  of,  581 

tunica  albuginea,  581 

vessels  and  nerves  of,  582 
Pericardiac  pleura,  526 
Pericardium,    617,    705,    734, 

742 
Perilymph,  881 
Perilymphatic  space,  881 
Perimysium,  252 
Periople,  888,  891 
Periophc  corium,  892 
Periorbita,  860 
Periosteum,  21 

alveolar,  of  teeth,  395 
Peripheral  gangha,  829 
Peritoneal  cavity,  411 
Peritoneum,  411,  441 

pelvic,  413 
Permanent  teeth,  394,  396 
Petro-basilar  canal,  190 
Petrosal  crest,  62,  81 

sinuses,  dorsal,  688 
ventral,  688 
Petrotympanic  fissure,  63 
Petrous  ganghon,  804 
Peyer's  patches,  422,  487,  501 
Pharyngeal  aponeurosis,  407 

isthmus,  408 

opening  of  Eustachian  tube, 
878 

orifices  of  Eustachian  tubes, 
406 

plexus,  807,  852 

recess,  407 
Pharynx,  405,   451,  472,  482, 

497 
Philosophical  anatomy,  17 


Phrenico-costal  sinus,  530 
Phylogeny,  17 
Pia  mater,  763 
cerebral,  763 
spinal,  763 
Pillar,  posterior,  of  soft  palate, 

408 
Pillars  of  rumen,  457 
Pilomotor  fibers,  829 
Pinchers,  395 
Pineal  body,  781,  835 

recess,  783 
Piriform  lobe,  784,  788,  850 
of  brain,  769 
recess,  408 
Pituitary  body,  769,  780,  782, 
835,  847 
fossa,  53 
Plantar  arch,  deep,  697,  721 
distal,  678,  697,  719 
proximal,  678,  679,  719 
Plate,  cribriform,  of  ethmoid, 

54 
Pleura,  526,  540,  547 
costal,  526 
diaphragmatic,  526 
mediastinal,  526 
parietal,  526 
pericardiac,  526 
pulmonary,  526 
visceral,  526 
Pleural  cavity,  526 

reflection,        diaphragmatic 
line  of,  530 
lines  of,  530 

sternal  reflection  of,  530 
vertebral  fine  of,  530 
Plexus,  abdominal,  832 
adrenal,  834 
aortic,  abdominal,  833 

thoracic,  831 
auricular,  anterior,  803 
basilar,  689 

brachial,  814,  840,  846,  853 
cardiac,  831 
carotid,  804 
external,  830 
internal,  830 
cavernous,  830,  834 
cervical,  dorsal,  812 

ventral,  812 
chorioid,  763,  780,  783,  787, 
792 
of  fourth  ventricle,  773 
ca>Uac,  832,  843,  856 
colic,  856 
coronary,  692,  831 
dental,  maxillary,  798 
dorsal,  692 
gastric,  833 
anterior,  852 
posterior,  852 
ha^morrhoidal,  834 

anterior,  856 
hepatic,  439,  833 
intraosseous,  692 
lumbosacral,  824,  S41,  846, 

855 
mesenteric,     anterior,     833, 
856 
posterior,  833,  856 
myenteric,  833 
nerve-,  761 
oesophageal,  808,  831,  853 


INDEX 


925 


Plexus,  pampiniform,  693 
of  testicles,  574 

parotid,  803 

pelvic,  832,  834,  856 

pharyngeal,  807,  852 

prostatic,  834 

pulmonary,  808,  831,  853 

renal,  834 

s.  sinus  venosus  sclerse,  863 

spermatic,  574,  834,  856 

splenic,  833 

submucous,  833 

subsidiary,  856 

tracheal,  808 

tympanic,  804 

utero-ovarian,  834 

utero-vaginal,  834 

vascular,  614 

venous,  614 

vesical,  834 

volar,  692 
Plica        pterygomandibularis, 

390 
Pododerm,  892 
Pons,  769,  775,  835,  843,  847 
Pophteal  line  of  tibia,  115 

notch  of  tibia,  116 
Portal  fissure,  434,  468 

ring,  433 

system,  614 
Post  glenoid  foramen,  60 

process,  60,  73 
Pouch,  cutaneous,  884 

guttural,  879 

infraorbital,  900 

inguinal,  900 

interdigital,  900 

lacrimal,  900 

recto-genital,  415 

recto-vesical,  414 

vesi co-genital,  415 
Premaxillary  region,  73 
Premolar  teeth,  394,  399 

deciduous,  403 
Preorbital  region  of  horse,  76 
Prepubic  tendon,  292 
Prepuce,  582,  590,  593,  595 

of  clitoris,  604 
Preputial  di v^erticulum,  593 

frenum,  583 

orifice,  583 

ring,  583 
Presylvian   fissure,    785,    844, 

849 
Process,  acoustic,  external,  61, 
74 

angular,  of  mandible,  195 

caudate,  of  Uver,  434 

cihary,  866 

clinoid,  anterior,  190 
posterior,  170,  190 

coronoid,  of  mandible,  71 

cuneiform,  517 

frontal,  191 

hyoid,  62 

lacrimal,  194 

hngual,  72 

mammillary,  45,  163 

mastoid,  61,  74 

maxillary,  194 

muscular,  of  temporal  bone, 
63 

nasal,  65 

palatine,  of  maxillae,  64,  65 


Process,     palatine,     of     pre- 
maxillae,  66 
paramastoid,  50,  78,  79 
postglenoid,  60,  73 
pterygoid,  54,  171 
spinous,  of  lumbar  vertebrae, 
129 
of  thoracic  vertebrae,  128 
of  vertebrae,  44 
styloid,  63,  871 
of  radius,  199 
of  ulna,  148 
supraorbital,  59,  73 
urethral,  581 
vocal,  517 

zygomatic,  of  frontal  bone, 
59 
of  malar  bone,  68 
of  maxillary  bone,  65 
of  temporal  bone,  60 
Processus  anconaeus,  93 
cornus,  136 
urethrae,  585 
vaginalis,  577 
Projection  fibers,  792 
Promontory,  876 
Prostatic  ducts,  579,  585,  589 

plexus,  834 
Protuberance,     occipital,     ex- 
ternal, 51,  79 
internal,  57 
Proventriculi  of  stomach,  453 
Psoas  tubercle,  106 
Pterygoid  canal,  54,  67 
crest,  54 
foramen,  54 
fossa,  170 
process,  54,  171 
Pterygo-palatine  fossa,  67,  76 
Pubic  groove,  109 
Pulmonary  circulation,  704 
lobule,  534 

orifice  of  right  ventricle,  624 
pleura,  526 
plexuses,  808,  831,  853 
valve,  625 
Pulp  cavity  of  teeth,  395 
of  tooth,  395 
spleen,  441 
Pulpy   nucleus   of   interverte- 
bral fibro-cartilage,  211 
Puncta  lacrimaha,  860 
Punctum  lacrimale,  858 
Pupil,  866 

Pupillary  border  of  iris,  866 
Pyloric   opening   of   stomach, 
416 

sphincter,  417 
valve  of  stomach,  419 
Pyramid  of  medulla  oblongata, 
773 
renal,  558,  565 
Pyramidal    decussation,    773, 
774 
fasciculus,  776 
tracts  of  oblongata,  774 


Radiation  of  corpus  callosum, 

790 
Radicles,  parietal,  693 

visceral,  693 
Radii  lentis,  870 
Radio-carpal  sac,  222 


Rami  communicantes,  829 

of  lower  jaw,  70 
Ramus  communicans,  811 

gray,  829 
Raphe  of  oblongata,  774 

pharyngis,  407 

praeputii,  583 

scroti,  574 
Recess,  infundibular,  783 

optic,  783 

pharyngeal,  407 

pineal,  783 

piriform,  408 
Recessus  cochlearis,  881 

elUpticus,  881 

sphaericus,  881 
Recto-coccygeus  band,  431 
Recto-genital  pouch,  415 
Recto-vesical  pouch,  414 
Rectum,  429,  488,  465,  502 
Red  nucleus,  781 
Refractive  media  of  eyeball, 

869 
Region,  cranial,  73,  78 

frontal,  of  skull,  73 

guttural,  78 

maxillary,  of  horse,  76 

nasal,  73 

orbital,  74 

palatine,  78 

parietal,  of  skull,  73 

premaxillary,  73 

preorbital,  76 
Renal  columns,  558 

corpuscles,  558,  559 

crest,  558,  559 

hilus,  555 

papilla,  565 

pelvis,  559 

plexuses,  834 

pyramids,  558,  565 

sinus,  555 

tubules,  559 
Respiratory  bronchioles,  534 

system,  508,  537,  545,  548 
Restiform  bodies,  773 
Rete  carpi  dorsale,  657 

mirabile,  614,  707 
cerebrale,  710 

testis,  586 
Retia  vasculosa,  614 
Reticulo-omasal  orifice,  459 
Reticulum   of  lymph   nodule, 
616 

of  stomach,  453,  455,  473 
Retina,  868 
Retractor  ani,  432 
Rhombencephalon,    773,    785, 

787 
Rhomboideus  capitis,  371 
Ridgp,  trochanteric,  of  femur, 

113 
Rima  glottidis,  522,  539,  546 

oris,  477,  491 
Ring,  cihary,  866 

fibrous,  of  heart,  628 

of     intervertebral     fibro- 
cartilage,  211 

inguinal,     abdominal,     290, 
292 
external,  288,  292 
internal,  290,  292 
subcutaneous,  288,  292 

portal,  433 


926 


INDEX 


Ring,  preputial,  583 

of  trachea,  525 

vaginal,  290,  576,  587 
Root  of  hair,  886 

of  tongue,  390 

of  tooth,  395 
Rostrum  of  corpus  callosum, 
789 

suis,  545 
Rubro-spinal  tract,  778 
Rumen,  453,  472 

blind  sacs  of,  454 

cardia  of,  458 

ca\aty  of,  456 

dorsal  curvature  of,  454 

grooves  of,  454,  455 

longitudinal  grooves  of,  454 

mucous  membrane  of,  458 

muscular  coat  of,  461 

pillars  of,  457 

serous  coat  of,  460 

ventral  curvature  of,  454 
Rumino-reticular  fold,  457 

groove,  454 

orifice,  458 


Sac,  anal,  502 

blind,  of  rumen,  454 

carpo-metacarpal,  222 

conjunctival,  859 

intercarpal,  222 

intertarsal,  240 

lacrimal,  860 

radio-carpal,  222 

synovial,  of  hock-joint,  240 

tarso-metatarsal,  240 

tibio-tarsal,  240 
Sacculations  of  caecum,  424 
Saccule,  883 

laryngeal,  522,  550 
Saccus  csecus,  416 
Sacral  canal,  43 

crest,  lateral,  129 
median,  129 

foramen,  41 
ventral,  129 

ganglia,  832 

part  of  sympathetic  system, 
856 
Sagittal  pole,  836 

sinus,  687,  688 
Scala  tympani,  882 

yestibuli,  882 
Sciatic  foramen,  greater,  231 
lesser,  231 

notch,  greater,  106 
lesser,  108 
Sclera,  863,  897 
Scrotum,  574,  586,  591,  593 
Scutiform  cartilage,  871 
Sebum  outaneum,  885 

palpebral,  859 
Secretory  fibers,  829 
Sectorial  teeth,  494 
Semicircular    canals,    osseous, 
881 

ducts,  membranous,  883 
Semilunar  canal  of  third  pha- 
lanx, 103 

crest  of  third  phalanx,  103 

ganglion,  795 

notch  of  uhia,  93 


Seminal  vesicles,  571,  578,  587, 

591,  593 
Seminiferous  tubules  of  testi- 
cles, 572 
Sense  organs,   857,   896,   900, 

902 
Sensory  fibers,  808 
nucleus,  dorsal,  808 
root  of  fifth  nerve,  776 
Septum,  dorsal,  median,  766 
interalveolar,  64 
intermuscular,  254 
of  forearm,  305 
of  gluteal  region,  317,  318 
of  leg,  318 
of  shoulder,  298 
interventricular,  627 
nasi,  82,  84,  510 

cartilage  of,  510 
pellucidum,  791 
penis,  589,  594 
scroti,  574 
Serous  coat  of  bladder,  562 
of  Fallopian  tubes,  599 
of  large  intestine,  430,  465 
of  liver,  438 
of  rumen,  460 
of  small  intestine,  421 
of  spleen,  441 
of  stomach,  417,  499 
of  uterus,  601 
folds,  384 

layer  of  pericardium,  617 
membranes,  384 
Shaft  of  hair,  886 
Sheath,  carpal,  of  deep  digital 
flexor,  315 
of       superficial       digital 
flexor,  313 
fibrous,  of  tendon,  254 
synovial,  253 

digital,    of    deep    digital 
flexor,  316 
of     superficial     digital 
flexor,  314 
of    common    digital    ex- 
tensor, 307 
of  coraco-brachialis  mus- 
cle, 300 
of     extensor     carpi     ob- 
liquus,  310 
radialis,  306 
of  flexor  carpi  radialis,  310 
of  lateral  digital  extensor, 

309,  335 
of  long  digital  extensor, 
335 
flexor,  340 
of  tibialis  anterior,  337 
of  ulnaris  lateralis,  313 
tarsal,  of  deep  digital  flexor, 
342 
Shoulder  girdle,  29 
Sidebone,  104 
Sigmoid  flexure,  589 
Sinus,  cavernous,  688 
communicans,  688 
coronary,  681,  754 
opening  of,  621 
ethmoidal,  86 

frontal,  59,  85,  143,  175,  197 
fronto-turbinate,  85 
intercavernous,  688 
lactiferous,  605,  609 


Sinus,  longitudinal,  dorsal,  687 
ventral,  688 

lymph,  central,  616 
peripheral,  616 

maxillary,  84,  144,  175,  197 
inferior,  84 
superior,  85 

occipital,  688 

of  aorta,  630 

of  bone,  21 

of  dura  mater,  687 

of  lymph  nodule,  616 

of  pulmonary  artery,  629 

palatine,  137,  145 

paranasal,  84 

petrosal,  dorsal,  688 
ventral,  688 

phrenico-costal,  530 

renal,  555 

sagittal,  687,  688 

sphenoidal,  53,  145,  175 

sphenopalatine,  53,  67,  86 

straight,  688 

tarsi,  120 

tonsillar,  446 

transverse,  688 

of  pericardium,  617 

urethral,  581 

urogenital,  603 

venarum  of  right  atrium  of 
heart,  620 

venous,  615 

vertebral,  longitudinal,  689 
Skeleton,  20,  32,  125,  156,  161, 
184 

appendicular,  20 

axial,  20 

flat  bones,  20 

irregular  bones,  20 

long  bones,  20 

medullary  cavity,  20 

number  of  bones,  20 

short  bones,  20 

splanchnic,  20 

visceral,  20 
Skin,  884,  887,  898,  900,  901, 
903 

appendages  of,  886,  901,  903 

of  concha,  871 

of  eyelids,  858 

of  mammary  glands,  604 

of  nostrils,  509 
Skull,  brachycephalic,  195 

dolichocephalic,  195 

mesaticephalic,  195 

synarthroses  of,  217 

synchondroses  of,  218 
Smegma  prsputii,  583 
Smell,  organ  of,  895 
Snout,  545 

Soft  palate,  387,  446,  477,  492 
Sole,  889,  892 

Sohtary  nodules  of  large   in- 
testine, 431 
of    small    intestine,    422, 
487 
Space,  epidural,  762 

interalveolar,  64,  65,  71,  78 

interdental,  64 

interosseous,  of  leg,  116 
of  radius,  91 

mandibular,  70 

perilymphatic,  881 

subarachnoid,  762 


INDEX 


927 


Space,  subdural,  762 

submaxillai-y,  70 
Special  anatomy,  17 
Spermatic  cord,  575,  586,  591, 
593 

plexus,  574,  834,  856 
Spheno-frontal  suture,  60 
Sphenoidal  notch,  60 

sinus,  53,  145,  175 
Spheno-occipital  crest,  53 
Sphenopalatine    foramen,    65, 
67,  76,  82 

gangUa,  797,  829 

sinus,  53,  67,  86 
Spheno-squamous  suture,  61 
Sphincter  ani  externus,  432 
internus,  432 

cardiac,  417 

ilei,  424 

of  mammary  gland,  605 

pupillse,  867 

pyloric,  416,  417 

vesica;,  562 
Spinal  arachnoidea,  763 

cord,  764,  834,  843,  847 

dura  mater,  762 

gangUon,  811 

pia  mater,  763 

root  of  fifth  nerve,  775 
Spine,  ischiatic,  106,  107 

nasal,  posterior,  193 

of  hoof,  890 

of  tibia,  116 

ventral,  26 

of  cervical  vertebrse,  125 
Spinous  notch,  54 

process  of  cervical  vertebrse, 
125 
of  lumbar  vertebrae,  129 
of  thoracic  vertebrse,  128 
of  vertebrse,  44 
Spiral  canal  of  cochlea,  882 

folds  of  abomasum,  460 

organ  of  Corti,  884 
Splanchnic  fibers,  afferent,  829 
efferent,  829 

ganglion,  832 
Splenial  fissure,  844,  850 
Splenic  angle,  433 

nodules,  441 

plexus,  833 
Splenium,  789 

Spongy  substance  of  bone,  21 
Squamous  suture,  58,  60,  61 

temporal  bone,  60 
Sternal  flexure,  425 

line  of  pleural  reflection,  530 
Stomach,  415,  453,  472,  483, 
497 

cardiac  opening  of,  416,  472, 
498 

fibers  of,  417 

greater  curvature  of,  416 

lesser  curvature  of,  416 

mucous  coat  of,  418 

pyloric  extremity,  416 
opening,  416 

serous  coat  of,  417,  499 

structure  of,  417 
Stop  of  face,  196 
Straight  sinus,  688 
Stratum  corneum,  885 

germinativum,  885 
of  hoof,  891 


Stratum  granulosum,  598 

tectorium  of  hoof,  891 
Stria,  lateral,  769,  788 

medial,  769,  788 

medullaris,  781 

olfactory,  769,  788 
^  terminahs,  781,  792 
Stroma  iridis,  867 

of  kidney,  559 

of  ovary,  598 

of  thyroid  gland,  536 

vitreous,  869 
Styloid  process,  63,  871 
of  radius,  19tf 
of  uhia,  148 
Stylo-mastoid  foramen,  62 
Subarachnoid  cisterns,  762 

space,  762 
Subcallosal  gyrus,  788 
Subcarpal  arch,  65.7 
Subcutaneous    inguinal    ring, 
288,  292 

tissue,  884 
Subcutis,  884 
Subdural  space,  762 
Sublimbic  fissure,  786 
Sublingual  duct,  405,  496 

fold,  390 
Submaxillary  duct,  405 

space,  70 
Submucous  plexus,  833 

tissue,  383 
Subserous  tissue,  384 
Subsidiary  plexus,  856 
Subsphenoidal  canal,  54 
Substantia  gelatinosa  of  spinal 
cord,  767 

perforata  posterior,  769,  780 

nigra,  780 

propria,  864 
Suburethral  diverticulum,  607 
Succus  entericus,  421 
Sulcus,  callosal,  786 

central,  of  hoof,  891 

cerebellar,  777 

collateral,  of  hoof,  891 

intertubercularis,  89 

limiting,  of  fourth  ventricle, 
779 

median,  of  fourth  ventricle, 
779 

muscularis  of  tibia,  117 

of  brain,  771 

omasi,  460 

rhinahs,  785,  837,  844,  850 

sclerae,  863 
Supracondyloid  crest,  lateral, 
of  femur,  112 
medial,  of  femur,  112 

fossa  of  femur,  112 
Supraoccipital  part  of  skull,  51 
Supraorbital  canal,  137 

foramen,  59,  73 

groove,  137 

process,  59,  73 
Supraspinous  bursa,  213 
Suprasplenial  fissure,  850 
Suprasylvian  fissure,  785,  837, 

844,  849 
Supratrochlear  foramen,  198 
Suspensory  ligaments  of  penis, 

580 
Sustentaculum  tali  of  fibular 

tarsal  bone,  121 


Sutura  harmonia,  207 
serrata,  207 
squamosa,  207 
Suture,  207 
cranial,  217 
frontal,  60 
fronto-lacrimal,  60 
fronto-maxillary,  60 
fronto-palatine,  60 
naso-frontal,  60,  67 
naso-lacrimal,  67 
naso-maxillary,  67 
occipito- mastoid,  52 
palatine,  median,  78 

transverse,  79 
parietal,  57 
parieto-frontal,  57,  60 
parieto-occipital,  52,  57 
spheno-frontal,  60 
spheno-squamous,  61 
squamous,  58,  60,  61 
Sympathetic  nervous  system, 
829,  842,  846,  856 
trunk,  829 
Symphysis,  207 

mandibulsp,  72,  218 
pelvis,  231 
Synarthroses,  207 

of  skull,  217 
Synchondrosis,  207 

'of  skull,  218 
Syndesmosis,  207 
Synovial  bursa,  253 
'  fossa?,  208 

membrane  of  carpal  joints, 
222 
of  elbow  joint,  219 
of  hip  joint,  232 
sacs  of  hock  joint,  240 
sheath,  253 

digital,    of    deep    digital 
flexor,  316 
of     superficial     digital 
flexor,  314 
of    common    digital    ex- 
tensor, 307 
of  coraco-brachialis  mus- 
cle, 300 
of     extensor     carpi     ob- 
liquus,  310 
radialis,  306 
of   flexor    carpi    radialis, 

310 
of  lateral  digital  extensor, 

309,  335 
of   long  digital   extensor, 
335 
flexor,  340 
of  tibialis  anterior,  337 
of  ulnaris  lateralis,  313 
Systematic  anatomy,  17,  18 


Tabttla  vitrea,  21 
Tactile  hairs,  886 
Taenia  thalami,  783 
Tapetum,  897 

cellulosum,  902 

fibrosum,  865 

of  chorioid,  865 
Tarsal  sheath  of  deep  digital 

flexor,  342 
Tarso-metatarsal  sac,  240 


928 


INDEX 


Tarsus  of  eye,  859 
Taste  buds,  895 

organ  of,  895 
Teat  of  mammary  glands,  604, 

609,  613 
Teeth,  394,  396,  448,  471,  478, 
479,  493 

alveolar  periosteum  of,  395 

canine,  394,  398,  448,  479, 
493 
deciduous,  403 
,    carnassial,  494 

cement  of,  395 

cheek,   394,  399,  448,  471, 
480,  494 
lower,  401 
upper,  400 

crown  of,  395 

deciduous,  394,  403 

enamel  of,  395 

eruption  of,  403,  450,  471, 
481,  495 

incisor,  394,  397,  448,  471, 
479,  493 
deciduous,  403,  448 

mandibular,  401 

maxillary,  400 

molar,  394,  399 

neck  of,  395 

nippers,  395 

permanent,  394,  396 

pinchers,  395 

premolar,  394,  399 
deciduous,  403 

pulp  of,  395 
cavity  of,  395 

root  of,  395 

sectorial,  494 

structure  of,  395 

temporary,  394 

wolf,  64,  71,  395,  400 
Tegmentum,  780 
Tela  chorioidea,  763,  773,  779, 

783,  787 
Telencephalon,  783 
Temporal  canal,  63,  81 

crest,  137 

foramen,  54 

fossa,  73 

wings  of  horse,  53 
Temporary  teeth,  394 
Tendinous      center     of      dia- 
phragm, 287 
Tendo  AchiUis,  338 

calcaneus,  338 
Tendon,  252 

interosseous,  225 

of  ergot,  306 

prepubic,  292 
Tentorium  cerebelli,  762 

osscum,  81 
Teres  tuberosity,  88 
Terminal  line,  110,  410 

nuclei  of  nerves,  760,  775 
Testicles,  571,  586,  591,  593 

deferential  fold  of,  577 

descent  of,  577 

ducts  of,  573 

lymph-vessels  of,  574 

pampiniform  plexus  of,  574 

parenchyma  of,  572 

seminiferous  tubules,  572 

structure  of,  572 

tunica  albuginea  of,  572 


Testicles,      tunica      vaginalis 
propria  of,  572 

vessels  of,  573 
Thalamo-cortical  fibers,  778 
Thalamus,  781 
Theca  folliculi,  598 
Thickness  of  skin,  887 
Third  eyeUd,  859,  896 

ventricle,  783 
Thoracic  aortic  plexus,  831 

cavity,  28,  525,  540 

duct,  615,  697,  722,  740,  756 

ganglia,  831,  842 

limb,  lymph  vessels  of,  703 

part  of  sympathetic  system, 
831 
Thorax,  547 

lymph  vessels  of,  700 
Thyro-hyoid  membrane,  518 
Thyroid    cartilage,    538,    546, 
515,  550 

cornua,  72 
Tibial  crest,  116 
Tibio-tarsal  sac,  240 
Tissue,  interlobular,  383 

muscular,  384 

subserous,  384 
Tongue,   390,   447,   471,    478, 

493 
Tonsil,  388,  471,  478,  493 
Tonsillar  sinus,  446 
Topographic  anatomy,  17,  18 
Torus  pyloricus,  485 
Trabecular    carnese    of    right 
ventricle,  625 

of  lymph  nodule,  616 

of  penis,  581 

splenic,  441 
Trachea,  523,  540,  546,  550 
Tracheal  ducts,  700 

lymph  ducts,  725,  756 

plexus,  808 
Tract,  oKactory,  769,  78S,  844 

optic,  780,  783,  835 

pyramidal,  774 

rubro-spinal,  778 
Tractus   centralis   of   thymus 

gland,  536 
Tragus,  886 
Tricuspid  valve,  624 
Trigonum    olfactorium,    769, 
784,  788 

vesicae,  562 
Trochanter   major    of    femur, 
113 

minor  of  femur,  112 

tertius,  112 
Trochanteric  fossa  of  femur, 
113 

ridge  of  femur,  113 
Trochlea  of  femur,  113 

of  tibial  tarsal  bone,  120 
Trochlear  foramen,  54,  75 
Trochoid,  210 
True  nostril,  508 

vocal  cords,  522,  550 
Truncus  bicaroticus,  635 

intestinaUs,  737 

of  corpus  callosum,  789 
Tuber   calcis  of  fibular  tarsal 
bone,  121 

cinereum,  769,  782,  847 

coxse,  106 

ischii,  108 


Tuber  sacrale,  106 
scapulae,  87 
spina?,  86 
Tubercle,     anterior,    of     tha- 
lamus, 781 
lacrimal,  68 
psoas,  106 
Tuberculum  cinereum,  773 
faciale,  773 
olfactorium,  844 
pubicum,  109 
Tuberosity,  alveolar,  64,  78 
deltoid,  88 
facial,  137 
maxillary,  65 
of  tibia,  116 
Tubules  of  mammary  glands, 
605 
renal,  559 
seminiferous,     of     testicles, 

572 
uriniferous,  559 
Tunic,  abdominal,  288,  361 
fibrous,  of  eye,  863 
vascular,  of  eye,  865 
Tunica  albuginea,  572,  589 
of  penis,  581 
propria  of  skin,  885 
vaginaUs,  576,  586,  593 
communis,  576 
parietal  layer  of,  574,  576 
propria,  572 
visceral  layer  of,  576 
Turbinate  crest,  dorsal,  67 
ventral,  64 
fold,  dorsal,  513 
ventral,  513 
Tusks,  479 

Tympanic  cavity,  875 
mucous  membrane,  878 
opening  of  Eustachian  tube, 

878 
plexus,  804 


Umbilical  fissure,  435 
fold,  lateral,  414 
median,  414 
Ureteral  orifice,  562 

internal,  562 
Ureters,  554,  561,  566,  569,  570 
Urethra,  554 
bulb  of,  581 
female,  604,  609,  611 
male,  571,  584,  590,  593,  595 
Urethral  crest,  585 

orifice,  external,  female,  603, 
607 
male,  585,  589 
internal,  male,  585 
process,  581 
sinus,  581 
Urinary  bladder.     See  Bladder 

organs,  554,  564,  567,  569 
Uriniferous  tubules,  559 
Urogenital  sinus,  603 

system,  554 
Uterine  cotyledons,  607 

tubes,    596,   599,   606,   609, 
610,  612 
Utero-ovarian  plexuses,  834 
Utero-vaginal  plexus,  834 
Uterus,  broad  ligament  of,  415 


INDEX 


929 


Uterus,  female.  596,  599,  606, 

609,  610,  612 
masculinus,   579,   589,   592, 

593,  594 
Utricle,  882 
Uvula,  478 


Vagina,   596,   602,   607,   610, 

613 
Vaginal  ring,  290,  576,  587 
Vallate  papilla  of  tongue,  391 
Valve,  aortic,  626 
bicuspid,  626 
ileo-csecal,  421 
ileo-colic,  501 
pulmonary,  625 
pyloric,  of  stomach,  419 
tricuspid,  624 
Valvular  fold  of  caecum,  424 
Vas  deferens,  575,  576,  591 
Vasa  vasorum,  615 
Vascular  plexus,  614 

tunic  of  eye,  865 
Vasomotor  fibers,  829 
Vein  or  veins,  614,  681,  719, 

740,  754 
abdominal,  posterior,  696 

subcutaneous,  696,  721 
adrenal,  563,  693 
alveolar,  inferior,  684 
auricular,  great,  685 
brachiocephalic,  755 
bronchial,  683,  690,  755 
buccinator,  686,  740 
cardiac,  681 

great,  681,  755 

lesser,  755 

middle,  681 

small,  682 
central,   of  adrenal  bodies, 

563 
cephalic,  687,  690,  755 

accessory,  690,  720,  755 
cerebellar,  dorsal,  689 

ventral,  689 
cerebral,  687,  689 

ascending,  689 

basal,  689 

deep,  689 

descending,  689 

dorsal,  685 

great,  689 

internal,  689 

ventral,  685,  720 
cervical,  deep,  682 

inferior,  687 
circumflex,  lateral,  695 
coats  of,  615 
condyloid,  685 
coronary,  628 

left,  681 

right,  681 
dental,  684 
digital,  692,  721,  756 

common,  692 

dorsal,  720,  755 

lateral,  720 

medial,  720 

volar,  720,  755 
common,  720 
diploic,  687,  689 
dorsal,  682 
59 


Vein  or  veins,  emissarium,  615 
emissary,  687 

facial,     anterior     auricular, 
684 

transverse,  685,  686 
femoral,  695,  756 

anterior,  696 

deep,  695 

posterior,  696 
frontal,  720 
gastric,  anterior,  695 

posterior,  695 
gastro-duodenal,  695 
gastro-epiploic,  right,  695 
hepatic,  439,  693 
hypogastric,  695 
iliac,  circumflex,  695 

common,  695 

external,  695,  756 

internal,  695,  756 
iliaco-femoral,  695 
ilio-lumbai',  695 
infraorbital,  686 
intercostal,  dorsal,  683 

ventral,  682 
internal  coat,  615 
interosseous,  common,  692 
jugular,  683,  719,  755 

external,  720,  755 

internal,  719,  755 
labial,  685 

common,  685 

superior,  720 
lingual,  686 

dorsal,  683 
lumbar,  693,  695 
masseteric,  685 
maxillary,  external,  685,  740 

internal,  683,  755 
median,  691 
meningeal,  687,  689 

middle,  684 
mesenteric,  693 

anterior,  694 

posterior,  694 
metacarpal,  692,J20,  755 
metatarsal,  697,  721,  756 
middle  coat,  615 
nasal,  dorsal,  720,  740 
obturator,  695 
occipital,  685 
oesophageal,  683,  687 
of  bladder,  562 
of  bone,  22 
of  brain,  793 
of  corium  of  hoof,  894 
of  cranium,  689 
of  ductus  deferens,  575 
of  external  ear,  875 
of  Fallopian  tubes,  599 
of  head,  683 
of  internal  ear,  884 
of  mammary  glands,  721 
of  neck,  683 
of  ovary,  598 
of  pehnc  limb,  695 
of  penis,  582 
of  retina,  869 
of  skin,  885 

of  thoracic  limb,  690,  720 
of  uterus,  602 
of  vaginn,  602 
of  vascular  tumc  of  eye,  867 
ophthalmic,  686 


Vein  or  veins,  orbital,  720 
palatine,  gi'eat,  686 
pancreatic,  695     ' 
pancreatico-duodenal,  695 
parotid,  687 
perineal,  721 
phrenic,  693 
plantar,  697 
popliteal,  696,  756 
portal,  438,  693,  722,  755 
pterygoid,  684 
pudic,  external,  696,  721 

internal,  575 
puhnonary,   534,   535,   614, 

625,  681 
radial,  755 

anterior,  692 
renal,  560,  693 
sacral,  middle,  721 
saphenous.  696,  721,  756 
satellite,  614 
spermatic,  574,  576 

internal,  693 
sphenopalatine,  686 
spinal,  689 
splenic,  693,  694 
structure  of,  615 
sublingual,  687,  720 
submental,  685 
tarsal,  perforating,  697,  721 

recurrent,  696,  721,  756 
temporal,    posterior,    deep, 
684 

superficial,  684 
thoracic,  external,  690 

internal,  682 
thoraco-dorsal,  690 
thyroid,  687 
tibial,  anterior,  696,  756 

posterior,  697,  756 

recmrent,  696 
tracheal,  687 
ulnar,  692,  755 
umbilical,  704 
utero-ovarian,  693 
valves  of,  615 
vena  azygos,  621,  682,  755 

cava,  614 
anterior,  682 

opening  of,  620 
posterior,  692,  720,  755 
opening  of,  620 

hemiazygos,  683,  719,  755 

reflexa,  686,  720,  740 

rhinalis  posterior,  689 
vertebral,  682,  689 
Velum,  medullary,  776 

anterior,  779 

posterior,  779 
Vena  comitans,  614 
Venae  vorticosje,  867 
Venous  arch,  692 
plexuses,  614 
sinuses,  615 
Ventricle,  fourth,  778 
lateral,  785,  791 

of  larynx,  522,  539,  550 
middle,  of  larvnx.  522 
of  heart,  left,  625 

right,  623 
of  olfactory  bulb,  787 
third,  783 
Vermis  cerebelli,  771,  776 
Vertebral  canal,  26,  44 


930 


INDEX 


Vertebral    column,    25,    125, 
156,  161,  184 

curves,  129,  165 

foramen,  26 

formula,  25 

line  of  pleural  reflection,  530 

notches,  26 

sinuses,  longitudinal,  689 
Vertex  corneje,  864 
Verticalis  auriculae,  875 
Vesical  plexus,  834 
Vesicles,    seminal,    571,    578, 

587,  591,  593 
Vesico-genital  pouch,  415 
Vesicular  seminales,  571,  578, 

587,  591,  593 
Vestibular  ganglion,  803 
Vestibule  of  ear,  881 

of  larynx,  522 

of  omental  cavity,  442 
Veterinary  anatomy,  17 
Vibrissae,  886 


Vidian  canal  of  horse,  54 
Visceral  layer,  384,  412 
of  pericardium,  617 

pleura,  526 

radicles,  693 
Vitreous  body,  869,  897 

humor,  869 

stroma,  869 
Vocal  cords.  521,  539,  546,  550 
false,  522,  550 
true,  522 

process,  517 
Vomero-nasal  organ,  514,  895 
Vortex  cordis,  628 
Vulva,  596,  603,  607,  610,  611, 

613 
Vulvar  cleft,  603 


Wall  of  hoof,  887,  891 
White  columns  of  spinal  cord, 

767,  768 


White    commissure   of   spinal 
cord,  766 
line  of  hoof,  889 
matter  of  nervous  system, 
760 
of  spinal  cord,  767 
Wolf  tooth,  64,  71,  395,  400 


Xiphoid  cartilage,  28,  49 


ZoisTE,  epigastric,  411 
hypogastric,  411 
intermediate,  of  kidney,  558 
mesogastric,  411 
Zonula  ciliaris,  870 
Zygomatic  arch,  60,  73 
process  of  frontal  bone,  59 
of  malar  bones,  68 
of  maxillary  bone,  65 
of  temporal  bone,  60 


